Research Article Electrodialysis of Phosphates in ...downloads.hindawi.com/archive/2013/865727.pdf · ISRN Electrochemistry the studies of electrodialysis show that concentrated phos-phoric

Hindawi Publishing CorporationISRN ElectrochemistryVolume 2013 Article ID 865727 12 pageshttpdxdoiorg1011552013865727

Research ArticleElectrodialysis of Phosphates in Industrial-GradePhosphoric Acid

J J Machorro1 J C Olvera1 A Larios1 H M Hernaacutendez-Hernaacutendez2

M E Alcantara-Garduntildeo3 and G Orozco1

1 Centro de Investigacion y Desarrollo Tecnologico en Electroquımica SC Parque Tecnologico Queretaro76703 Sanfandila Pedro Escobedo QRO Mexico

2Universidad Tecnologica de Queretaro 76148 Queretaro QRO Mexico3 Universidad del Mar Ciudad Universitaria Puerto Angel 70902 Distrito de San Pedro Pochutla OAX Mexico

Correspondence should be addressed to G Orozco gorozcocideteqmx

Received 27 August 2013 Accepted 31 October 2013

Academic Editors M Barragan and H Zhao

Copyright copy 2013 J J Machorro et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The objective of this research was to study the purification of industrial-grade phosphoric acid (P2O5) by conventional electro-

dialysis The experiments were conducted using a three-compartment cell with anion and cation membranes and industrial acidsolutionwas introduced into the central compartmentThe elemental analysis of the diluted solution indicated that the compositionofmagnesium phosphates and sodiumwas reduced in the central compartmentThe ratios of the concentration of the ions and thephosphates were essentially unchanged by the process Consequently electrodialysis could not purify the acid in the central com-partment and the migration of phosphate ions to the anolyte produced a highly concentrated phosphoric acid solution containingsulfates and chlorides as impurities However the migration of the phosphate ions across the membrane consumed a large amountof energy Detailed speciation diagrams were constructed in this study These diagrams showed that metal-phosphate complexeswere predominant in the industrial phosphoric acid solution This result explains why the ratios of the concentrations of the ionmetals and the phosphates did not change in the purification processThe energy consumed in the electrodialysis indicated that themetal-phosphate complexes were less mobile than the free-phosphate ions The speciation diagrams explained the experimentalresults satisfactorily

1 Introduction

Theannual global phosphorus consumption is approximately20764 million metric tons [1] Phosphoric acid and phos-phate salts have several applications For example phosphoricacid fuel cells use liquid phosphoric acid as an electrolyte [23] Industrial-grade phosphoric acid is produced from phos-phate rock and consequently has a high content of mineralimpurities which lower the acid quality for commercial useThis industrial-grade phosphoric acid (52ndash54 P

2O5) is also

named as merchant-grade acid Phosphoric acid purificationis a major challenge and a variety of methods have been usedto eliminate the impurities in the industrial-grade phosphoricacid [4ndash18] These methods which are described in the

literature are enumerated in Table 1 In addition Table 2shows electrodialysis process for concentrating industrial-grade phosphoric acid [19ndash27] These studies in Table 2provided more comprehensive and consistent informationon the energy requirements for the process Comparingthese methods is very difficult for the following reasons (a)there is a wide variation in the types of the impurities inindustrial-grade acid because ores of similar grades canoriginate from different mines (b) consequently the studiesinvestigated different metal impurities (c) the studies wereneither consisted nor complete in their description of theacid purity and (d) the studies used dissimilar efficiencycriteria Therefore the methods described in Table 1 cannotbe ranked in terms of their relative efficacies Nonetheless

2 ISRN Electrochemistry

Table 1 Studies of industrial-grade phosphoric acid purification

Process Efficiencyenergy requirementspower consumption (kWhkg) ReferenceSelectiveprecipitation 63 of Pb and As was precipitated from the phosphate solution Purification was carried out at 49∘C [4]

Selectiveprecipitation

Mg was removed by mixing the crude acid with SiF62minus to form MgSiF6sdot6H2O Also 25Fe and

10Al were removed Filtrate had 037ndash051 of MgO in 72P2O5 The temperatures range was 20to 30∘C

[5]


Ammonia was added to crude acid Iron precipitates as Fe3(KNH4)H8(PO4)6sdotH2O Theconcentrations of Al Fe and Mg were decreased by ten times their initial values The process wascontinued for 8 h at 70∘C

[6]

Solvent extraction

The purified acid contained between 50 and 60 phosphate and approximately 1 SO4minus and

02Fminus The concentration of the cation impurities was approximately 02 Crude phosphoric acid(P2O5 52) was fed at rate of 191mLmin at temperature of 65∘CThe process produced 375phosphoric acid and the impurities were extracted by solvent extraction at 110∘C

[7]

Solvent extraction The process removed approximately 95 of Cd after 260 h of operation The method used threehydraulic pumps an extraction module (14m2) and a back-extraction module at pressure of 4 psi [8]

Flotation andselectiveprecipitation

95 of the Cd and metals impurities (119872119899+) were removed by neutralizing the solution to pH 14ndash20and cooling it to 5ndash40∘CThe metals were precipitated as metal xanthates (MXan) The xanthatehaving the longest and most branched organic part produced the best results

[9]

Nanofiltration bymembranes

The filtering process operated at a temperature of approximately minus1∘C to about 30∘C and at a pressurebetween 600 and 1000 psig The feed solution was filtered through a nanofiltration membrane toremove approximately 90 of the metal ion impurities

[10]

Solvent extraction

Resin impregnated with extractants was put into contact with phosphoric acid for 24 h using areciprocal shaker (150 rpm) at 25∘C Solvent extraction removed approximately 90 of the Cd fromconcentrated phosphoric acid solutions The presence of cations strongly decreased the Cd removalefficiency

[11]

Reverse osmosisand nanofiltration

Nanofiltration was more efficient than reverse osmosis The permeate flow was 135 Lm2h at1800 psi The acid permeation was 463 and 993 of the cationic impurities were globally rejectedThe concentration of the impurities was reduced by approximately 100 times the initial valueHowever the acid concentration was reduced to half its original value

[12]


This method produced an acid solution with an As concentration of less than 1 ppmThe purificationmethod produced P2O5 concentration of at least 724 The temperatures range was 130 to 150∘CExamples of the method produced concentrations of impurities in industrial 84-85 phosphoricacid were as follows Fe (02ndash16) Cr (01ndash08) Ni (01ndash06) Mo (lt05) and Na (01)

[13]


An 8M acid solution was filtrated at 1000 psi for different periods of time For periods longer than120 h the rejection of impurities decayed considerably The acid permeation at 25∘C wasapproximately 90 and the metal impuritiesrsquo retention was approximately 97

[14]

Solvent extraction

Phosphoric acid was purified using solvent mixtures at 30∘CThe most efficient P2O5 recovery wasobtained using 55 methyl isobutyl ketone and 45 tributyl phosphate A phase diagram wascreated for the ternary system of H3PO4-water-optimal phosphate solvent The concentration ofimpurities decreased 1000 times from their initial values Mg2+ purification was higher than that forthe other impurities

[15]

Complexformation andzeolites asadsorbents

Bentonite and potassium amyl xanthate were used to remove organic impurities and Fe from crudephosphoric acid The efficiency of potassium amyl xanthate in reducing the iron content was 7919and was accompanied by a small decrease in the P2O5 concentration Bentonite clay was used toremove the organic impurities Na2SiO3 and Na2CO3 reduced the Fminus content at 70∘C at adefluorination efficiency of 9056 The Fe content was reduced to 052 of its initial value at a P2O5loss of 3 Cd and Cu were removed at a P2O5 loss of 170 The Fe minimizing efficiency was1095ndash5238 at the temperatures of 25 to 70∘C

[16]


Precipitation occurred at 60∘CThe process produced 85 acid with 200 ppb of Sb The impuritieswere removed by adding H2S However the S2

minus content was 220 ppb [17]

Solvent extraction

The phosphoric acid was purified using n-butanol n-hexanol and n-octanol Octanol was the mostefficient alcohol The final concentration of H

3PO4was 92M 98 of Fminus was removed and the final

concentration of Fe was 10 ppm The Cu Cd Mn and Zn concentrations were too low to bedetermined The temperature (5∘C and 60∘C) had a small effect

[18]

ISRN Electrochemistry 3

Table 2 Electrodialysis (ED) studies of industrial phosphoric purification (54 P2O5 or 745 H3PO4)

ED process characteristics Energy ReferencePhosphoric acid was concentrated using a combination ofapatite Ca5(PO4)3(F Cl OH) digestion by sulfuric acid andaluminum production from alunite KAl3(SO4)2(OH)6 Thecatholyte (H3PO4) was separated from the middle compartment(K2SO4) by a CEM and the anolyte (water) was separated byAEMThe products were KH2PO4 (catholyte) a dilutedsolution of K2SO4 and H2SO4 (anolyte)

A cell voltage of 6V and a current of 45 A were usedThe current efficiency was approximately 96Electric power consumption was 127 KWhKg ofP2O5 at 25 weight P2O5

[19]

This method concentrated phosphoric acid by ED usingmembranes typically used to desalinate water The stackassembly consisted of 20 cell pairs sandwiched between twoelectrode compartments A CR-61 cation-transfer membraneand an AR-I03 anion-transfer membrane were used toconcentrate the acid from 01 to 10M by electrodialysis Thediluted compartment was fed with 010M 020M 029M and045M reagent-grade acid solutions and the compartmentconcentrate had 1M of industrial-grade acid

The total effective membrane area was 2300 cm2 Theelectrical currents applied were 8 10 12 and 14AThe voltages varied from 10 to 43V This methodconcentrated reagent-grade H3PO4 from 01 to 10MThe energy requirements ranged from 173 to250 kWhKg of P2O5

[20]

A cell (133 cm2) was divided into two compartments by anAEMThe cathode was graphite and the anode was platinizedtitanium The volume of the catholyte (411M industrial-gradeacid supplemented by ammonium ions) was 100 cm3 and thevolume of the anolyte (pure 1M H3PO4) was 1000 cm

3 Theimpurities were retained in the catholyte compartment In theanolyte compartment H3PO4 was formed with the anionscrossing through the AEM and protons produced at the anodeAEM ARA 1710 from Solvay (France) and RAI 5035 fromRaipore (USA) were used

A constant current of 60Amminus2 was applied for90min The acid concentration changed from 1M to411M with a 63 of yield A 4M acid solution wasobtained for a current efficiency of 74 in theanolyte compartment Mg Al and Fe were removedat 95ndash100 The efficiency was limited by themigration of protons across the anion membrane(proton leakage)

[21]

Cell with two compartments was divided by a membrane Thecatholyte was industrial phosphoric acid 10 to 55 percent P2O5and anolyte was 1 to 40 P2O5

The electrical current density ranges from 100 to3000 (Am2) [22]

An electrodeionization cell (36 cm2) with a centralcompartment (industrial 11 P2O5 or 152 H3PO4) wasdelimited by AEMtextile membrane and CEMtextilemembrane Catholyte and anolyte were 2M H3PO4 solutionsplaced in the other compartments

Very low current efficiencies for both cations andanions were observed after 5 h of treatment Thismethod produced 11 phosphoric acid with lowconcentrations of impurities Mg (14 gdmminus3) Fe(09 gdmminus3) Zn (04 gdmminus3) Cd (001 gdmminus3) andSO42minus (165 gdmminus3) The highest current efficiency

for cations was found for Mg2+

[23]

Cell with liquid membrane of amyl alcohol with the addition ofa trialkylamine The catholyte was H3PO4 10M and anolyte wasH2O The cathode was made of stainless steel and anode wasmade of platinum or titanium coated with ruthenium dioxide

Extraction of phosphate ions from the startingsolution was 95 [24]

The raw material was H3PO4 containing mainly calciumphosphate A low concentration of acid was fed into alternatepartition chambers formed cation transfer membranes H3PO4was introduced on the anode sides of the partition chambersProcess is carried out under acidic conditions avoidingprecipitates of the impurities such as iron and aluminum

No data [25]

Cells with a large number of anion and cation membranes werealternately arranged Industrial phosphoric acid and dilutedpure phosphoric acid (10ndash44 P2O5) were supplied to theanode and to the cathode compartments respectively

The current density was 100ndash2000Am2 The energyrequirement ranged from 395 to 1578 kWhKg ofP2O5

[26]

Electro-electrodialysis with laboratory-scale cell The cathodewas graphite and the anode was platinized titanium There werethree compartments divided by anionic and cationicmembranes The industrial H

3PO4was introduced into the

central compartment

The cell voltage was 4V and current of 10A A 28H3PO4 was removed from central compartment andimpurities decrease Also Food-grade H3PO4 at 25was produced in anolyte after 21 h at 3-4V and 11 A

[27]

AEM anion-exchange membranes CEM cation-exchange membranes


the studies of electrodialysis show that concentrated phos-phoric acid with a low concentration of metal impurities canbe obtained by electrodialysis see Table 2

Table 1 serves to display the great importance of the acidpurification Although a variety of problem-solving tech-niques have been identified there are a limited number ofstudies with acceptable resultsThe production of food-gradephosphoric acid is a difficult business

A significant factor for elucidating the purification pro-cess is the speciation of the metals in the concentrated acidsHowever the studies presented in Tables 1 and 2 do notaddress this issue Therefore in this study speciation dia-grams were constructed to more thoroughly analyze thepurification process

The goal of this work is to evaluate the viability of elec-trodialysis for the production of high-value chemicals fromraw materials that are abundant in the central region ofMexico and therefore these would be feasible resources formass production Other studies are also being conducted inour laboratory on a different highly pure raw material Thecurrent study will serve as an important benchmark for ourfuture research

2 Materials and Methods

21 Materials and Reagents Two samples of industrial-gradephosphoric acid (also called wet-industrial phosphoric acid)were obtained from Fertinal S A (Mexico) These raw mate-rials were produced by the acid digestion of phosphate rockPure phosphoric acid 86 was purchased from J T Baker(ACS Grade) All other reagents were of analytical grade andwere obtained from commercial sources and used withoutfurther purification The high ionic strength of industrialphosphoric acid can produce a layer of precipitates of metal-phosphates metal-sulfates and so forth on the membranesurfaceThus a dilution solution of industrial acid at 5 wwwas used to prevent membrane fouling

A trace element mineral analysis was performed byinductively coupled plasma mass spectrometry (PerkinElmer USA model Optima 3300 DV) and by flame atomicabsorption spectrophotometry (Perkin Elmer USA modelAAnalyst 200) The presence of sulfate fluoride and phos-phate was identified by UV-Vis spectrometry Samples takenfrom a phosphoric acid production site were analyzed bypotentiometric titration with a NaOH solution

The membranes were purchased from Ameridia (the USrepresentative of Tokuyama Corporation Japan) The maincharacteristic of these membranes is their excellent exchangecapacity (mequiv gminus1 of ion in the dry membrane form) AnAMX-Neosepta anion exchange membrane was used withan exchange capacity of 125mequiv gminus1 A CMX-Neoseptacation exchangemembranewas usedwith an exchange capac-ity 162mequiv gminus1 Neosepta-AMX contains quaternaryammonium groups as fixed charges and Neosepta-CMXcontains sulfonic acid groups as fixed charges [28] Thesemembranes were equilibrated with 1MKCl solution for 12 hbefore each experiment

22 Speciation Calculations The speciation diagrams predictthe value of120572 the fraction of ions that are free or associated ata given pH value The dissociation equilibrium for the phos-phate-containing species in the diagrams is given by

H3PO4

0larrrarr H+ +H

2PO4

minus

119870

1=

[H+] [H2PO4

minus]

[H3PO4

0]

(1)

H2PO4

minuslarrrarr H+ +HPO

4

2minus119870

2=

[H+] [HPO4

4minus]

[H2PO4

minus]

(2)

HPO4

2minuslarrrarr H+ + PO

4

3minus119870

3=

[H+] [PO4

3minus]

[HPO4

2minus]

(3)

The HA acids were HF HCl and H2SO4 and the respec-

tive anions were Fminus Clminus HSO4

minus and SO4

2minus The generaldissociation acid reaction is given by

HAlarrrarr H+ + Aminus 119870

4=

[H+] [Aminus][HA]

(4)

Note that the silicon concentration is related to the fluo-ride concentrationThat is during industrial phosphoric acidproduction fluoride is produced in the form of fluorosilicicacid However this acid and the SiF

6

2minus ion dissociate intoSi(HO)

4and HF The dissociation reactions are as follows

H2SiF6997888rarr 2H+ + SiF

6

2minus (5)

SiF6

2minus+ 4H2O 997888rarr 4H+ + Si(HO)

4+ 6Fminus (6)

Fminus +H+ 997888rarr HF (7)

Therefore Si(HO)4and SiF

6

2minus were also included in thespeciation diagrams In addition 18 metal-phosphate com-plexes or ion-pairs that is NaHPO

4

minus AlHPO4

+ and so forthwere included with their respective simple cations that isNa+ Al3+ and so forthThe general equation of the chemicalequilibrium for the metal-phosphate complexes is

MH119909PO4

119899+119909minus3larrrarr M119899 +H

119909PO4

119909minus3

119870

5=

[M119899] [H119909PO4

119909minus3]

[MH119909PO4

119899+119909minus3]

(8)

where 119909 equals 1 2 or 3 depending on the partial deprotona-tion of the phosphoric acid and 119899 can vary between 1 and 3Values derived from the literature [29ndash31] were used for theequilibrium constants 119870

1to 1198705 The quantity 120572 is defined by

the following equation

120572A =[A]119862

119905

(9)

where [A] is the concentration of species A and 119862119905is the

total concentration of all the species that contain A Material


balances must be formulated to determine the fraction 120572Thetotal quantities of themetal impurities (119872

119905) the acids (119862H

119899A)

and the phosphates (119875119905) are fixed in a closed system therefore

the following set of equations holds

119875

119905= [H3PO4

0] + [H

2PO4

minus] + [HPO

4

2minus] + [PO

4

3minus] (10)

119872

119905= [M+] + [MH

2PO4

0] + [MHPO

4

minus] + [MPO

4

2minus]

(11)

119862H119899A = [H119899A] + [H119899minus1A

minus] + sdot sdot sdot + [Aminus] (12)

Equations (10) (11) or (12) can be combinedwith the equi-librium constants (1)ndash(5) and (8) and (9) to obtain a set of120572-fractions as functions of [H+] The 120572-fraction for theH119909PO4

119909minus3 species is defined by the following equation

120572H119909PO4

119909minus3 =

[H119909PO4

119909minus3]

119875

119905

=

1

[H+]119899+[H+]119899minus11198701+[H+]119899minus2119870

1119870

2+sdot sdot sdot

(13)

where [H+] denotes the proton concentration which wasrelated to the pH and 119870

119899denotes the equilibrium constants

119870

1to 1198703 The 120572-fractions of the metal-phosphate complexes

were directly related to the 120572-fraction of H119909PO4

119909minus3 speciesand their equilibrium constants for example

120572Ca2+ =[Ca2+]119872

119905

= 1 times (1 +

120572PO4

3minus

10

minus65+

120572HPO4

2minus

10

minus27

+

120572H2PO4

minus

10

minus14)

minus1

(14)

The speciation diagrams were calculated for solutionsat 25∘C and zero ionic strength The ionic strength variedduring the experiments however the equilibrium constantshave been reported to depend weakly on the ionic strength(040value) [32] The temperature increased by 10∘C duringthe experiments However only a small variation with tem-perature has been reported for the equilibrium constants forcomplex formation (0045deg) [32] Thus the concentrationfractions in diagrams were representative of the actual values

23 Experimental Apparatus The system consisted of anelectrodialysis cell from Asahi Glass Co DS-0 (Japan) threestorage tanks three hydraulic pumps and aDC power sourceThe electrodes (each with an effective area of 002m2) weremade of titanium coated with platinum and stainless steelThe solution flowed through a plastic schedule 40 polyvinylchloride pipe Hydraulic pumps propelled the electrolytesolution from the storage tank to the electrodialysis cellthrough the pipe and back to the storage tanks A bypass wasintroduced to control the flow rate (at 5 Lmin) at each inlet

Table 3 Average composition of two industrial phosphoric acidsamples

Species Concentration Milliequivalents of solute per literP2O5 54ww mdashSO42minus 134480 gL (minus) 2740

CaO 84116 gL (+) 2999SiO2 180240 gL (SiO4

4minus) (minus) 11999Fe2O3 79843 gL (+) 1499Al2O3 81567 gL (+) 2399MgO 48364 gL (+) 2399Na2O 30989 gL (+) 999K2O 37678 gL (+) 799HF 34196 gL (minus) 1709HCl 01773 gL (minus) 937Thephosphoric acid concentration is typically expressed in terms of the P2O5concentration The conversion formula is as follows [H3PO4] = [P2O5] times196142Thus 54P2O5 concentration corresponds to an acid concentrationof 745

Figure 1 is a schematic of the experimental apparatus forphosphoric acid demineralization The two membranes wereseparated by 15mm and the gap in the anolyte and thecatholyte compartments was 225mm

Prior to each experiment the three compartments werefed with a 001M NaCl solution (for 30min) which wasreplaced a posteriori with the respective solutions (for30min) and finally with fresh solutions for demineralizationThe central compartment was filled with the solutions shownin Figure 1 Then the central compartment contained a01M NaCl solution in 5ww analytical-grade phosphoricacid Also solutions of 5ww industrial-grade acid wereintroduced into the central compartment and the behaviorof the solutions was compared

The current-voltage curves were obtained in a galvanody-namic mode and the limiting current density was obtainedfrom the electrical resistance (R) versus 1electrical current(I) plots as described by Sorensen [33] The temperaturethe conductivity the flow rate the electrical voltage and theelectrical current were measured during the experimentsMore details of the apparatus are provided in our previouswork [34] The Toroidal Conductivity Sensor (Model 226Rosemount Analytical USA) was calibrated with KCl solu-tions The experiments were performed in triplicate

3 Results

31 Speciation Diagrams The industrial-grade phosphoricacid was chemically analyzed for eleven components (seeTable 3) The concentration of the impurities was 7133 gLwhich was representative of the raw material produced byFertinal (Mexico) The pH of the industrial phosphoric acidwas approximately 1 consequently the speciation diagrams(Figure 2) were concentrated in the acidic region

During the manufacture of industrial-grade phosphoricacid by treating the rock with acids fluoride was volatilizedand lost in the residues and approximately 3 gL of fluorideremains in the phosphoric acid Figure 2(a) shows that


Anion-exchange membrane

Anode (+) Cathode (minus)

H3PO4 NaOHConc

AnionminusCation+

H+ OHminus

Diluted

001MSee Table 3

Cation-exchange membrane

H+

Cation+

Anionminus

H3PO4Conc

OHminus

001MH3PO4H3PO4 NaOH

PO4minus

(a)

Catholyte outlet

Concentrate outlet

Catholyte inlet

Concentrate inlet

ElectrodeSpacer

Cationicmembrane

Anionic

Na+

SpacerSpacer

Spacer

membrane

Electrode

SpacerSpacer

Spacer

Spacer

Catholyte outlet

Anolyte inletAnolyte outlet

Concentrate inlet

Clminus

(b)

Figure 1 (a) Schematic of phosphoric acid demineralization apparatus (b) classical electrodialysis cation-exchange and anion-exchangemembranes fed solutions and products

hydrogen fluoride (HF) and siliceous acid Si(OH)4were the

predominant species in the industrial acid The speciationdiagrams show that electrodialysis cannot be used to removefluoride and silicon because the Coulombic attraction waslowered considerably To be precise electrodialysis only canremove ionic impurities from industrial acid by using an elec-tric current to pull these ions across the membrane For HFand Si(OH)

4 there is no net driving Coulombic force to

produce a migration that is nonionic compounds did notmigrate when an electric field was imposed Figure 2(b)shows eight negatively charged species however only twoions (sulfates and chlorides) have high concentrationsThere-fore elevated migration can only be expected for these ionsFigure 2(c) shows the seven positively charged species in thepH region that was studied However only a few ionic species(K+ Na+ and Mg2+) have high concentrations and conse-quently will migrate abundantly Moreover only about 40of Ca2+ ions can migrate Figures 2(d) and 2(e) predict thatmetal-phosphate complexes or ion-pairs such as FeHPO

4

+can form for most metal impurities Although included inthe mathematical analysis the amounts of the ion-pairs of

sodium or potassium were always negligible in our solutionsfor example NaPO

4

2minus see Figure 2(f) Migneault and Force[35] and Pethybridge et al [36] found lower ion-pair associ-ation constants of sodium or potassium

These complexes or ion-pairs are essentially larger ionswith lower effective electric charge density The implicationof this lower charge is an increase in the electrical resistanceto be precise their positive charges allow the complexes tomigrate near to the membrane when electric field is appliedacross the cell However their large size prevents their passageabundantly through the membrane Consequently thesecharged molecules tend to accumulate on the dilute side ofmembrane and result in a buildup of membrane electricalresistance

The industrial-grade phosphate had high concentrationof phosphate and consequently the metal-phosphate com-plexes and ion-pairs were formed copiously However thestudies presented in Table 1 did not address this issue becausethe speciation diagrams were not consulted The implicationof this is that studies cannot comprehensively analyze theirpurification process On the other hand the construction of


Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

minus1 0 1 2 3 4

Si(HO)4

H3PO4

HCl H2SO4

HF

(a)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

minus1 0 1 2 3 4

C1minus

Fminus

HSO4minus

H2PO4minus

SO42minus

HPO42minusPO4

3minus SiF62minus

(b)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

K+

Mg2+Na+

Ca2+

Fe3+

Fe2+

Al3+

(c)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

FeHPO4+

AlHPO4+

AlH2PO42+

FeH2PO42+

(d)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

FeH2PO4+

CaH2PO4+

MgH2PO4+

CaPO4minus FePO4

minus MgPO4minusFeHPO4

0 CaHPO40

(e)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

KHPO4minus NaHPO4

minusKPO42minus NaPO4

2minus

KH2PO40

NaH2PO40

(f)

Figure 2 Speciation diagrams for (a) acids (b) anions (c) cations (d) phosphate-metal (III) complexes (e) phosphate-metal (II) complexesand (f) phosphate-metal (I) complexes


the speciation diagrams implied very time-consuming calcu-lationsHowever there are software can easily constructed thediagrams For example MEDUSA with its thermodynamicconstants database HYDRA [37] is able to draw the diagramsThe database HYDRA is incomplete for the metal-phosphatecomplexes and ion-pairs constant but it is possible addeddataThe diagrams constructed using the softwareMEDUSAand our diagrams were compared The results are not shownfor the sake of brevity The computational software can beapplied to create efficiently the speciation diagrams

Azaroual et al [38] recently show preliminary results forquantifying the undesirable mineral impurities from phos-phate ores using a computation tool (SCALE2000 software)However it is not possible yet to compare the estimateddiagrams of aqueous speciation of phosphoric acid

Figure 3 shows that the conductance of the industrialphosphoric acid was higher than that of the analytical-gradeacid The low conductivity of the pure acid was becausethe H

2PO4

minus ion comprised only 6 of the phosphate con-centration However the conductance of the industrial acidwas related to the high ion concentration The industrialphosphoric acid viscosity has also been reported to increasewith the phosphoric acid concentration [39] Note that pureH3PO4consists of tetragonal groups that are linked by hydro-

gen bonds [40] This structure results in a high viscosityfluid especially at high phosphoric acid concentrationsThe dimeric anion (H

5P2O8

minus) has been found at high acidconcentrations but has not been observed in dilute solutionsat room temperature [41 42] For solutions below 50 phos-phoric acid there are more bonds between the phosphateions and water than between the phosphate ions themselves[40] These larger anions pass scarcely through the positivelycharged anion exchange membrane Therefore electrodial-ysis was conducted in dilute acid solutions to prevent theformation of phosphate dimeric anions

32 Limiting CurrentDensities The limiting current densities(Table 4) were obtained from the current-potential curves(Figure 4) These limiting currents were obtained directlyfrom plots of the electrical resistance versus the reciprocalof the electrical current (which are not shown for brevity)using a method that has been described elsewhere [33 34]The inflexion point in the curve for the solution ofNaCl in theanalytical-grade acid was produced at steady state that is thenumbers of ions entering the membrane equaled the numberof ions entering the diffusion zone The limiting currents ofthe industrial-grade phosphoric acid were difficult to obtainwhereas the limiting currents of the analytical-grade acidsolutions were straightforward to determine In additionthe limiting current was also selected to avoid damage tothe membrane Therefore the limiting current values forthe solutions of NaCl in analytical-grade phosphoric acidwere selected for the electrodialysis of the industrial-gradephosphoric acid These current-potential behaviors wereaffected by the electrical resistance of the electrodialysis cellwhich was given by the sum of the solution and membraneresistances In addition the formation of the polarizationlayers adjacent to both sides of the membranes produced agreat contribution to the electrical resistance of the cell

Table 4 Limiting currents of the experimental three-compartmentelectrodialysis cells dilute central compartment experimental solu-tion anolyte 001M HCl catholyte 001M NaOH

Experimental solution Limiting current (A)Wet industrial phosphoric acid diluted at5 (ww) indeterminate

Wet industrial phosphoric acid diluted at1 (ww) indeterminate

Solution of 627 gL of NaCl and 54analytical-grade phosphoric acid dilutedat 5 (ww)

020

Solution of 1254 gL of NaCl andanalytical-grade phosphoric acid dilutedat 1 (ww)

015

lowast015 A was the average current level during the electrodialysis process

Con

duct

ance

(mS

cm)

Phosphoric acid ()

Visc

osity

(cen

tipoi

se)

25

20

15

10

5

00 10 20 30 40 50 60 70

200

180

160

140

120

100

80

60

40

20

0

Figure 3 Conductance values for industrial phosphoric acid (- - - -)and analytical-grade phosphoric acid (mdash) phosphoric acid viscositydata (998835) as reported by Lobo [39]

The electrical resistances of the solution are discussedfirst The solution of NaCl in the analytical-grade acid pro-duced the highest electrical current This behavior wasobserved because the sodium and chlorine ions were movingfaster than the metal-phosphate complexes More preciselythe motion of these ions was unimpeded by attachment tophosphates Metals such as aluminum would have to dragtheir phosphate ligands along resulting in a high electricalresistance for the complex Similar results were obtained byDiallo et al [43] who observed that the electrophoreticmobility of ions was proportional to the ion chargesize ratioDiallo et al [43] observed that ion mobility in an electricfield range could be ranked in descending order as followsClminus gt H

2PO4

minusgt H3PO4

0gt Fe(H

2PO4)

4

minus Therefore thecomplexes decreased the electrostatic interactions resultingin a low electrical current (Figure 4) The phosphate-freeions (see Figures 2(b) and 2(c)) had more mobility thanthe acids (Figure 2(a)) and the metal-phosphate complexes(Figure 2(d)) The membranes electrical resistances are dis-cussed next Pismenskaya et al [44 45] reported a lowelectrical conductivity for an anionic-exchange membranein contact with a phosphate solution Koter and Kultys [46]


Pure acid + NaC1

Industrial acid

Voltage (V)

Curr

ent (

A)

16

14

12

10

08

06

04

02

00

minus02

2 4 6 8 10 12

Figure 4 Current-potential curves for the electrodialysis cell at aflow rate of 5 Lmin for industrial phosphoric acid (- - - -) and ana-lytical-grade phosphoric acid with 627 gL NaCl (mdash)

observed a low efficiency for phosphoric acid removal byelectrodialysis with anionic membranes Koter and Kultys[46] theoretically calculated an association equilibrium con-stant between H

2PO4

minus and the fixed charges of the anionicmembrane This association diminished the efficacy of theseparation process because the H

2PO4

minus neutralized the fixedcharges in the anionic membrane In a previous study weobserved a similar association between nitrate ions and thefixed charges in an anionic membrane using Raman spec-troscopy and electrochemical impedance spectroscopy [34]The excessive potential drop across the cation exchangemembrane was because only the protons and the phosphate-free cations were able to migrate effectively The metal-phosphate complexes had large ionic radii and low chargedensities which decreased their electrostatic interactions andmobilities inside the membrane This increase of the elec-trical resistance was explained in Section 31 The speciationdiagrams clearly show that most positive ions migrated witha very low efficiency because of their reduced ionic chargeHowever proton transfer across the membrane increasedat the highest electrical currents depleting the proton con-centrations inside the membrane Therefore the internalmembrane resistance increased

33 Demineralization of Industrial- and Analytical-GradeAcids The conductance of the acids decreased during theelectrodialysis process as shown in Figure 5The pHdecreas-ed slightly during the demineralization while the temper-ature increased by 10∘C These changes did not alter thechemical composition of the solutions and the transport ofions was negligibly affected by the small temperature change

Hannachi et al [15] observed that the highest cationremoval occurred for theMg2+ species see Table 1This resultis supported by the speciation diagrams (Figure 2) whichclearly show that the Mg2+ and phosphate can migrate inde-pendently of each other It is known that Mg2+ and phos-phate do not form a covalent complex for example Raman

Table 5 Ion concentrations in the central compartment before andafter demineralization for 450min the cell potential was approxi-mately 74V and the average electric current was was 015 A

Initial concentration Final concentrationMgO H3PO4 MgO H3PO4

0 0192M 0707M 00072M 0206M

Pure acid + NaC1

Industrial acid

Con

duct

ance

(mS)

Time (min)

pHinitial 114 pHfinal 09

Tinitial 18∘C Tinitial 28

∘C48

44

40

36

32

28

24

0 100 200 300 400 500

Figure 5 Variation in the conductance of the central compartmentduring electrodialysis a constant electrical current of 015 A wasapplied to the conventional electrodialysis cell containing industrialphosphoric acid at 5 (mdash) and analytical-grade phosphoric acid at5 with 627 gL NaCl (- - - -) the initial and final temperatures andpH values are also reported

spectroscopy has been used to show that the intermolecularMgndashOndashP bonding in phosphate salts is more ionic than forother metalndashOndashP bonds [47] These ions were selected as arepresentative species to determine the electrodialysis effi-ciency The initial and final concentrations of these speciesare listed in Table 5 The Mg2+ concentration decreased byapproximately 63 on average of its initial value whereasapproximately 70 of the phosphates migrated which wasmore than expected However the ratio between the con-centration of the Mg2+ ions and that of the phosphoric acidwas the same before and after the demineralization process(see Figure 6) The same behavior was observed for the ratiobetween the concentration of the Na+ ions and that of theanalytical-grade phosphoric acid These results show thatelectrodialysis cannot be used to purify the acid in the centralcompartment The migration of phosphates could produce ahighly concentrated phosphoric acid solution in the anolytehowever the sulfates and chlorides would also migrate Con-sequently electrodialysis would produce an anolyte solutioncontaining anionic impurities The low migration of freecations could be used to produce a catholyte containingcationic impurities

The energy consumed in the migration of the Na+ andClminus species was compared with the energy consumption forthe electrodialysis of the industrial-grade acid (see Table 6)


Table 6 Energy consumption of the electrodialysis celllowast

Process characteristics EnergyThe central compartment contained a 01M NaClsolution in 5 analytical-grade phosphoric acidThe cell current was constant at 02 A and theaverage potential was 85 V The NaCl was dilutedfrom 627 g to 103 g and approximately 40 of theacid was removed

157 kWhkg

The central compartment containedindustrial-grade phosphoric acid The cell currentwas constant at 02 A and potential wasapproximately 88 VThe concentration changes are reported in Table 5

78 kWhkg

lowastThe volume of the feed tank was 10 LThe flow rate was at 5 Lminminus1 averagetemperature was 24 plusmn 2∘CThe duration of the experiment was 230min

Catio

n co

ncen

trat

ion

phos

phat

e con

cent

ratio

n

Timetotal time

001360

001355

001350

001345

001340

001335

001330

00 02 04 06 08 10

Figure 6The ratio between the concentration ofMg2+ ions and thatof H3PO4acid (-◼-◼-) and the ratio between the concentration of

Na+ ions and that ofH3PO4acid (-I-I-) during the demineralization

process

The energy consumption for the migration of the Na+ andClminus ions was ten times more effective than the industrial-grade acid demineralization That is the energy consumedin Clminus migration (157 kWhkg) was lower than the energyconsumed inH

2PO4

minusmigration (78 kWhkg)This result canbe explained by the mass transfer limitations at low H

2PO4

minus

concentrations The discussion on the electrical resistancesof the solution and the membrane which was previouslypresented in Section 32 can also explain this result

There is insufficient energy consumption data to comparethe studies in Table 1 with the present study On the otherhand the data in Table 6 show that electrodialysis producedphosphoric acid concentrations that were similar to thosereported by the studies in Table 2 Hanley et al [20] reportedlower energy consumption and this author also reporteda higher acid concentration than that was observed in thepresent study but did not report the final concentration ofimpurities see Table 2

The energy consumption for the Na+ and Clminus migra-tion showed that the membranes performed acceptably forelectrodialysis however the energy consumption for theindustrial-grade acid showed that phosphate ions could notmigrate efficiently across the membranes

4 Conclusions

Many methods have been evaluated in the literature for thepurification and concentration of merchant-grade phospho-ric acid (52 P

2O5) see Table 1 However these methods

cannot be ranked in terms of efficacy because speciationdiagrams have not been considered The speciation diagramsin this study showed that the formation of metal-phosphatecomplexes decreased electrostatic interactions because of thelower mobility of the complexes This observation was infair agreement with the electrodialysis results The speciationdiagrams predicted that the low resistance of sodium andchloride ions relative to the other ions can facilitate phospho-ric acid removal which was verified by the observed energyconsumption in the electrodialysis process The results of thestudies in Tables 1 and 2 must be reexamined in light ofthe speciation diagrams that were constructed in the presentwork For exampleMg2+ purificationwas higher than that forthe other metal impurities as speciation diagrams predicted

A dilute industrial phosphoric acid solution was used toprevent membrane foulingThe three-compartment cell pro-duced a highly concentrated phosphoric acid solution withionic impurities in the anolyte In the central compartmentthe acid concentration decreased without purifying the acidPrevious electrodialysis studies [20 21] have assumed thatphosphate ions can efficiently migrate across membraneshowever our results show that such a migration processconsumes a large amount of energy and would therefore beextremely costly In addition the voltages of the ED processwere sufficient to damage the membrane Our results showthat electrodialysis is not commercially viable for purifyingindustrial-grade phosphoric acid Nevertheless in futureresearch our group will test another phosphate raw materialNa3PO4 by the electrodialysis technique using this study as

a benchmark

Acknowledgment

The authors would like to acknowledge the financial sup-port provided by Project from CONACYT (FOSIHGO1999025008)

References

[1] G Villalba Y Liu H Schroder and R U Ayres ldquoGlobal phos-phorus flows in the industrial economy from a production per-spectiverdquo Journal of Industrial Ecology vol 12 no 4 pp 557ndash569 2008

[2] M Ghouse andH Abaoud ldquoMaterials used in the developmentof a 1 kW phospshoric acid fuel cell stackrdquo Journal of NewMaterials for Electrochemical Systems vol 2 no 3 pp 201ndash2061999


[3] H-Y Kwak H-S Lee J-Y Jung J-S Jeon and D-R ParkldquoExergetic and thermoeconomic analysis of a 200 kWphospho-ric acid fuel cell plantrdquo Fuel vol 83 no 14-15 pp 2087ndash20942004

[4] R J Kepfer and W R Devor ldquoPhosphoric acid purificationrdquoUS Patent 2174158 1939

[5] D Goldstein ldquoPhosphoric acid purificationrdquo US Patent3819810 1974

[6] D H Michalski and V Srinivasan ldquoProcess of removing cati-onic impurities from wet process phosphoric acidrdquo US Patent4639359 1987

[7] L W Bierman M L Lopez and J E Perkins ldquoPurification ofphosphoric acidrdquo US Patent 4877594 1989

[8] A I Alonso A M Urtiaga S Zamacona A Irabien and IOrtiz ldquoKinetic modelling of cadmium removal from phospho-ric acid by non-dispersive solvent extractionrdquo Journal of Mem-brane Science vol 130 no 1-2 pp 193ndash203 1997

[9] H F T Haraldsen ldquoMethod for removal of heavy metals fromphosphoric acid containing solutionsrdquo US Patent 49869701991

[10] H J Skidmore and K J Hutter ldquoMethods of purifying phos-phoric acidrdquo US Patent 5945000 1999

[11] L H Reyes I S Medina R N Mendoza J R Vazquez M ARodrıguez and E Guibal ldquoExtraction of cadmium from phos-phoric acid using resins impregnated with organophosphorusextractantsrdquo Industrial and Engineering Chemistry Research vol40 no 5 pp 1422ndash1433 2001

[12] M P Gonzalez R Navarro I Saucedo M Avila J Revilla andC Bouchard ldquoPurification of phosphoric acid solutions byreverse osmosis and nanofiltrationrdquo Desalination vol 147 no1ndash3 pp 315ndash320 2002

[13] K Hotta and F Kubota ldquoMethod for purification of phosphoricacid high purity polyphosphoric acidrdquo US Patent 68610392005

[14] M P Gonzalez Munoz R Navarro I Saucedo et al ldquoHydroflu-oric acid treatment for improved performance of a nanofiltra-tion membranerdquo Desalination vol 191 no 1ndash3 pp 273ndash2782006

[15] A Hannachi D Habaili C Chtara and A Ratel ldquoPurificationof wet process phosphoric acid by solvent extraction with TBPand MIBK mixturesrdquo Separation and Purification Technologyvol 55 no 2 pp 212ndash216 2007

[16] A A El-Asmy H M Serag M A Mahdy and M I AminldquoPurification of phosphoric acid by minimizing iron coppercadmium and fluoriderdquo Separation and Purification Technologyvol 61 no 3 pp 287ndash292 2008

[17] K Ishikawa K Yokoi K Takeuchi Y Kurita and H UchiyamaldquoHigh purity phosphoric acid and process of producing thesamerdquo US Patent 7470414B2 2008

[18] M I Amin M M Ali H M Kamal A M Youssef and M AAkl ldquoRecovery of high grade phosphoric acid from wet processacid by solvent extraction with aliphatic alcoholsrdquoHydrometal-lurgy vol 105 no 1-2 pp 115ndash119 2010

[19] K W Loest and J T Schaefer ldquoProduction of monobasicpotassium phosphate by electrodialysisrdquo US Patent 40338421977

[20] T R Hanley H-K Chiu and R J Urban ldquoPhosphoric acidconcentration by electrodialysisrdquo AIChE Symposium Series vol82 pp 121ndash132 1986

[21] D Touaibia H Kerdjoudj and A T Cherif ldquoConcentrationand purification of wet industrial phosphoric acid by electro-electrodialysisrdquo Journal of Applied Electrochemistry vol 26 no10 pp 1071ndash1073 1996

[22] S A Ueda ldquoMethod for purifying phosphoric acidrdquo JapanesePatent Kokai No Sho 48 [1973]-10312 1973

[23] M B C Elleuch M B Amor and G Pourcelly ldquoPhosphoricacid purification by a membrane process electrodeionizationon ion-exchange textilesrdquo Separation and Purification Technol-ogy vol 51 no 3 pp 285ndash290 2006

[24] Y K Litsis and B A Popov ldquoMethod of extraction of phospho-ric acidrdquo Russian Inventorrsquos Certification No443839 1974

[25] T Yamabe ldquoMethod for the manufacture of phosphoric acidrdquoJapanese Patent Kokai No Sho 48 [1976]-106696 1976

[26] T Yoshihara ldquoAmethod for refining phosphoric acidrdquo JapanesePatent Kokai No Sho 53 [1978]-96994 1978

[27] KMoeglich ldquoElectrochemical processes utilizing layeredmem-brane electrochemical processes utilizing layered membranerdquoUS Patent 4326935 1982

[28] P Długołecki K Nymeijer S Metz and M Wessling ldquoCurrentstatus of ion exchange membranes for power generation fromsalinity gradientsrdquo Journal of Membrane Science vol 319 no 1-2 pp 214ndash222 2008

[29] E Hogfeldt Stability Constants of Metal-Ion Complexes PartA Inorganic Ligands vol 21 of IUPAC Chemical Data SeriesPergamon Press 1982

[30] DD PerrinDissociation Constants of Inorganic Acids and Basesin Aqueous Solution IUPAC Butterworths London UK 1969

[31] A E Martell and R M Smith Critical Stability Constants vol4 of Inorganic Complexes Plenum Press New York NY USA1976

[32] J N Butler Ionic Equilibrium Solubility and PH CalculationsJohn Wiley amp Sons Toronto Canada 1998

[33] T S Sorensen Interfacial Electrodynamics of Membranes andPolymer Films in Surface Chemistry and Electrochemistry ofMembranes CRC Press New York NY USA 1999

[34] U Lopez-Garcıa R Antano-Lopez G Orozco T Chapmanand F Castaneda ldquoCharacterization of electrodialysis mem-branes by electrochemical impedance spectroscopy at lowpolarization and by Raman spectroscopyrdquo Separation andPurification Technology vol 68 no 3 pp 375ndash381 2009

[35] D R Migneault and R K Force ldquoDissociation constants ofphosphoric acid at 25∘C and the ion pairing of sodium withorthophosphate ligands at 25∘Crdquo Journal of Solution Chemistryvol 17 no 10 pp 987ndash997 1988

[36] A D Pethybridge J D R Talbot and W A House ldquoPreciseconductance measurements on dilute aqueous solutions ofsodium and potassium hydrogenphosphate and dihydrogen-phosphaterdquo Journal of Solution Chemistry vol 35 no 3 pp 381ndash393 2006

[37] I Puigdomenech Make Equilibrium Diagrams Using Sophisti-cated Algorithms (MEDUSA) Inorganic Chemistry Royal Insti-tute of Technology Stockholm Sweden 2004

[38] M Azaroual C Kervevan A Lassin et al ldquoThermo-kineticand physico-chemical modeling of processes generating scalingproblems in phosphoric acid and fertilizers production indus-triesrdquo Procedia Engineering vol 46 pp 68ndash675 2012

[39] V M M Lobo Handbook of Electrolyte Solutions Part A Phys-ical vol 41 of Sciences Data Elsevier Science New York NYUSA 1989


[40] F A Cotton and G Wilkinson Quımica Inorganica AvanzadaLimusa Cancun Mexico 1st edition 1993

[41] M Cherif A Mgaidi N Ammar G Vallee and W Furst ldquoAnew investigation of aqueous orthophosphoric acid speciationusing Raman spectroscopyrdquo Journal of Solution Chemistry vol29 no 3 pp 255ndash269 2000

[42] W W Rudolph ldquoRaman-spectroscopic measurements of thefirst dissociation constant of aqueous phosphoric acid solutionfrom 5 to 301∘Crdquo Journal of Solution Chemistry vol 41 no 4 pp630ndash645 2012

[43] H Diallo M Rabiller-Baudry K Khaless and B Chaufer ldquoOnthe electrostatic interactions in the transfer mechanisms of ironduring nanofiltration in high concentrated phosphoric acidrdquoJournal of Membrane Science vol 427 pp 37ndash47 2013

[44] N Pismenskaya E Laktionov V Nikonenko A El Attar BAuclair and G Pourcelly ldquoDependence of composition of ani-on-exchange membranes and their electrical conductivity onconcentration of sodium salts of carbonic and phosphoricacidsrdquo Journal of Membrane Science vol 181 no 2 pp 185ndash1972001

[45] N Pismenskaya V Nikonenko B Auclair and G PourcellyldquoTransport of weak-electrolyte anions through anion exchangemembranes Current-voltage characteristicsrdquo Journal of Mem-brane Science vol 189 no 1 pp 129ndash140 2001

[46] S Koter and M Kultys ldquoModeling the electric transport ofsulfuric and phosphoric acids through anion-exchange mem-branesrdquo Separation and Purification Technology vol 73 no 2pp 219ndash229 2010

[47] V Koleva and V Stefov ldquoPhosphate ion vibrations in dihydro-gen phosphate salts of the type M(H

2PO4)2sdot2H

2O (M = Mg

Mn Co Ni Zn Cd) Spectra-structure correlaterdquo VibrationalSpectroscopy vol 64 pp 89ndash100 2013

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


Table 1 Studies of industrial-grade phosphoric acid purification

Process Efficiencyenergy requirementspower consumption (kWhkg) ReferenceSelectiveprecipitation 63 of Pb and As was precipitated from the phosphate solution Purification was carried out at 49∘C [4]


Mg was removed by mixing the crude acid with SiF62minus to form MgSiF6sdot6H2O Also 25Fe and

10Al were removed Filtrate had 037ndash051 of MgO in 72P2O5 The temperatures range was 20to 30∘C

[5]


Ammonia was added to crude acid Iron precipitates as Fe3(KNH4)H8(PO4)6sdotH2O Theconcentrations of Al Fe and Mg were decreased by ten times their initial values The process wascontinued for 8 h at 70∘C

[6]

Solvent extraction

The purified acid contained between 50 and 60 phosphate and approximately 1 SO4minus and

02Fminus The concentration of the cation impurities was approximately 02 Crude phosphoric acid(P2O5 52) was fed at rate of 191mLmin at temperature of 65∘CThe process produced 375phosphoric acid and the impurities were extracted by solvent extraction at 110∘C

[7]

Solvent extraction The process removed approximately 95 of Cd after 260 h of operation The method used threehydraulic pumps an extraction module (14m2) and a back-extraction module at pressure of 4 psi [8]

Flotation andselectiveprecipitation

95 of the Cd and metals impurities (119872119899+) were removed by neutralizing the solution to pH 14ndash20and cooling it to 5ndash40∘CThe metals were precipitated as metal xanthates (MXan) The xanthatehaving the longest and most branched organic part produced the best results

[9]


The filtering process operated at a temperature of approximately minus1∘C to about 30∘C and at a pressurebetween 600 and 1000 psig The feed solution was filtered through a nanofiltration membrane toremove approximately 90 of the metal ion impurities

[10]

Solvent extraction

Resin impregnated with extractants was put into contact with phosphoric acid for 24 h using areciprocal shaker (150 rpm) at 25∘C Solvent extraction removed approximately 90 of the Cd fromconcentrated phosphoric acid solutions The presence of cations strongly decreased the Cd removalefficiency

[11]

Reverse osmosisand nanofiltration

Nanofiltration was more efficient than reverse osmosis The permeate flow was 135 Lm2h at1800 psi The acid permeation was 463 and 993 of the cationic impurities were globally rejectedThe concentration of the impurities was reduced by approximately 100 times the initial valueHowever the acid concentration was reduced to half its original value

[12]


This method produced an acid solution with an As concentration of less than 1 ppmThe purificationmethod produced P2O5 concentration of at least 724 The temperatures range was 130 to 150∘CExamples of the method produced concentrations of impurities in industrial 84-85 phosphoricacid were as follows Fe (02ndash16) Cr (01ndash08) Ni (01ndash06) Mo (lt05) and Na (01)

[13]


An 8M acid solution was filtrated at 1000 psi for different periods of time For periods longer than120 h the rejection of impurities decayed considerably The acid permeation at 25∘C wasapproximately 90 and the metal impuritiesrsquo retention was approximately 97

[14]

Solvent extraction

Phosphoric acid was purified using solvent mixtures at 30∘CThe most efficient P2O5 recovery wasobtained using 55 methyl isobutyl ketone and 45 tributyl phosphate A phase diagram wascreated for the ternary system of H3PO4-water-optimal phosphate solvent The concentration ofimpurities decreased 1000 times from their initial values Mg2+ purification was higher than that forthe other impurities

[15]

Complexformation andzeolites asadsorbents

Bentonite and potassium amyl xanthate were used to remove organic impurities and Fe from crudephosphoric acid The efficiency of potassium amyl xanthate in reducing the iron content was 7919and was accompanied by a small decrease in the P2O5 concentration Bentonite clay was used toremove the organic impurities Na2SiO3 and Na2CO3 reduced the Fminus content at 70∘C at adefluorination efficiency of 9056 The Fe content was reduced to 052 of its initial value at a P2O5loss of 3 Cd and Cu were removed at a P2O5 loss of 170 The Fe minimizing efficiency was1095ndash5238 at the temperatures of 25 to 70∘C

[16]


Precipitation occurred at 60∘CThe process produced 85 acid with 200 ppb of Sb The impuritieswere removed by adding H2S However the S2

minus content was 220 ppb [17]

Solvent extraction

The phosphoric acid was purified using n-butanol n-hexanol and n-octanol Octanol was the mostefficient alcohol The final concentration of H

3PO4was 92M 98 of Fminus was removed and the final

concentration of Fe was 10 ppm The Cu Cd Mn and Zn concentrations were too low to bedetermined The temperature (5∘C and 60∘C) had a small effect

[18]





[19]



[20]




[21]






[23]




No data [25]



[26]



central compartment


[27]












H3PO4

0larrrarr H+ +H

2PO4

minus

119870

1=

[H+] [H2PO4

minus]

[H3PO4

0]

(1)

H2PO4


4

2minus119870

2=

[H+] [HPO4

4minus]

[H2PO4

minus]

(2)

HPO4


4

3minus119870

3=

[H+] [PO4

3minus]

[HPO4

2minus]

(3)



minus and SO4



4=

[H+] [Aminus][HA]

(4)


6




6

2minus (5)

SiF6


4+ 6Fminus (6)



6


4

minus AlHPO4


MH119909PO4


119909PO4

119909minus3

119870

5=

[M119899] [H119909PO4

119909minus3]

[MH119909PO4

119899+119909minus3]

(8)




120572A =[A]119862

119905

(9)





119905) the acids (119862H

119899A)



119875

119905= [H3PO4

0] + [H

2PO4

minus] + [HPO

4

2minus] + [PO

4

3minus] (10)

119872

119905= [M+] + [MH

2PO4

0] + [MHPO

4

minus] + [MPO

4

2minus]

(11)

119862H119899A = [H119899A] + [H119899minus1A




120572H119909PO4

119909minus3 =

[H119909PO4

119909minus3]

119875

119905

=

1

[H+]119899+[H+]119899minus11198701+[H+]119899minus2119870

1119870

2+sdot sdot sdot

(13)



119870




120572Ca2+ =[Ca2+]119872

119905

= 1 times (1 +

120572PO4

3minus

10

minus65+

120572HPO4

2minus

10

minus27

+

120572H2PO4

minus

10

minus14)

minus1

(14)





CaO 84116 gL (+) 2999SiO2 180240 gL (SiO4





3 Results






H3PO4 NaOHConc

AnionminusCation+

H+ OHminus

Diluted

001MSee Table 3


H+

Cation+

Anionminus

H3PO4Conc

OHminus

001MH3PO4H3PO4 NaOH

PO4minus

(a)

Catholyte outlet

Concentrate outlet

Catholyte inlet

Concentrate inlet

ElectrodeSpacer

Cationicmembrane

Anionic

Na+

SpacerSpacer

Spacer

membrane

Electrode

SpacerSpacer

Spacer

Spacer

Catholyte outlet


Concentrate inlet

Clminus

(b)






4



4





Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

minus1 0 1 2 3 4

Si(HO)4

H3PO4

HCl H2SO4

HF

(a)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

minus1 0 1 2 3 4

C1minus

Fminus

HSO4minus

H2PO4minus

SO42minus

HPO42minusPO4

3minus SiF62minus

(b)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

K+

Mg2+Na+

Ca2+

Fe3+

Fe2+

Al3+

(c)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

FeHPO4+

AlHPO4+

AlH2PO42+

FeH2PO42+

(d)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

FeH2PO4+

CaH2PO4+

MgH2PO4+

CaPO4minus FePO4


0 CaHPO40

(e)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

KHPO4minus NaHPO4


2minus

KH2PO40

NaH2PO40

(f)






2PO4



5P2O8







020


015


Con

duct

ance

(mS

cm)

Phosphoric acid ()

Visc

osity

(cen

tipoi

se)

25

20

15

10

5

00 10 20 30 40 50 60 70

200

180

160

140

120

100

80

60

40

20

0



2PO4

minusgt H3PO4

0gt Fe(H

2PO4)

4



Pure acid + NaC1

Industrial acid

Voltage (V)

Curr

ent (

A)

16

14

12

10

08

06

04

02

00

minus02

2 4 6 8 10 12



2PO4


2PO4






0 0192M 0707M 00072M 0206M

Pure acid + NaC1

Industrial acid

Con

duct

ance

(mS)

Time (min)



∘C48

44

40

36

32

28

24

0 100 200 300 400 500







157 kWhkg


78 kWhkg


Catio

n co

ncen

trat

ion

phos

phat

e con

cent

ratio

n

Timetotal time

001360

001355

001350

001345

001340

001335

001330

00 02 04 06 08 10



process


2PO4


2PO4

minus




4 Conclusions





a benchmark

Acknowledgment


References


















































2PO4)2sdot2H

2O (M = Mg











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





[19]



[20]




[21]






[23]




No data [25]



[26]



central compartment


[27]












H3PO4

0larrrarr H+ +H

2PO4

minus

119870

1=

[H+] [H2PO4

minus]

[H3PO4

0]

(1)

H2PO4


4

2minus119870

2=

[H+] [HPO4

4minus]

[H2PO4

minus]

(2)

HPO4


4

3minus119870

3=

[H+] [PO4

3minus]

[HPO4

2minus]

(3)



minus and SO4



4=

[H+] [Aminus][HA]

(4)


6




6

2minus (5)

SiF6


4+ 6Fminus (6)



6


4

minus AlHPO4


MH119909PO4


119909PO4

119909minus3

119870

5=

[M119899] [H119909PO4

119909minus3]

[MH119909PO4

119899+119909minus3]

(8)




120572A =[A]119862

119905

(9)





119905) the acids (119862H

119899A)



119875

119905= [H3PO4

0] + [H

2PO4

minus] + [HPO

4

2minus] + [PO

4

3minus] (10)

119872

119905= [M+] + [MH

2PO4

0] + [MHPO

4

minus] + [MPO

4

2minus]

(11)

119862H119899A = [H119899A] + [H119899minus1A




120572H119909PO4

119909minus3 =

[H119909PO4

119909minus3]

119875

119905

=

1

[H+]119899+[H+]119899minus11198701+[H+]119899minus2119870

1119870

2+sdot sdot sdot

(13)



119870




120572Ca2+ =[Ca2+]119872

119905

= 1 times (1 +

120572PO4

3minus

10

minus65+

120572HPO4

2minus

10

minus27

+

120572H2PO4

minus

10

minus14)

minus1

(14)





CaO 84116 gL (+) 2999SiO2 180240 gL (SiO4





3 Results






H3PO4 NaOHConc

AnionminusCation+

H+ OHminus

Diluted

001MSee Table 3


H+

Cation+

Anionminus

H3PO4Conc

OHminus

001MH3PO4H3PO4 NaOH

PO4minus

(a)

Catholyte outlet

Concentrate outlet

Catholyte inlet

Concentrate inlet

ElectrodeSpacer

Cationicmembrane

Anionic

Na+

SpacerSpacer

Spacer

membrane

Electrode

SpacerSpacer

Spacer

Spacer

Catholyte outlet


Concentrate inlet

Clminus

(b)






4



4





Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

minus1 0 1 2 3 4

Si(HO)4

H3PO4

HCl H2SO4

HF

(a)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

minus1 0 1 2 3 4

C1minus

Fminus

HSO4minus

H2PO4minus

SO42minus

HPO42minusPO4

3minus SiF62minus

(b)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

K+

Mg2+Na+

Ca2+

Fe3+

Fe2+

Al3+

(c)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

FeHPO4+

AlHPO4+

AlH2PO42+

FeH2PO42+

(d)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

FeH2PO4+

CaH2PO4+

MgH2PO4+

CaPO4minus FePO4


0 CaHPO40

(e)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

KHPO4minus NaHPO4


2minus

KH2PO40

NaH2PO40

(f)






2PO4



5P2O8







020


015


Con

duct

ance

(mS

cm)

Phosphoric acid ()

Visc

osity

(cen

tipoi

se)

25

20

15

10

5

00 10 20 30 40 50 60 70

200

180

160

140

120

100

80

60

40

20

0



2PO4

minusgt H3PO4

0gt Fe(H

2PO4)

4



Pure acid + NaC1

Industrial acid

Voltage (V)

Curr

ent (

A)

16

14

12

10

08

06

04

02

00

minus02

2 4 6 8 10 12



2PO4


2PO4






0 0192M 0707M 00072M 0206M

Pure acid + NaC1

Industrial acid

Con

duct

ance

(mS)

Time (min)



∘C48

44

40

36

32

28

24

0 100 200 300 400 500







157 kWhkg


78 kWhkg


Catio

n co

ncen

trat

ion

phos

phat

e con

cent

ratio

n

Timetotal time

001360

001355

001350

001345

001340

001335

001330

00 02 04 06 08 10



process


2PO4


2PO4

minus




4 Conclusions





a benchmark

Acknowledgment


References


















































2PO4)2sdot2H

2O (M = Mg











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of











H3PO4

0larrrarr H+ +H

2PO4

minus

119870

1=

[H+] [H2PO4

minus]

[H3PO4

0]

(1)

H2PO4


4

2minus119870

2=

[H+] [HPO4

4minus]

[H2PO4

minus]

(2)

HPO4


4

3minus119870

3=

[H+] [PO4

3minus]

[HPO4

2minus]

(3)



minus and SO4



4=

[H+] [Aminus][HA]

(4)


6




6

2minus (5)

SiF6


4+ 6Fminus (6)



6


4

minus AlHPO4


MH119909PO4


119909PO4

119909minus3

119870

5=

[M119899] [H119909PO4

119909minus3]

[MH119909PO4

119899+119909minus3]

(8)




120572A =[A]119862

119905

(9)





119905) the acids (119862H

119899A)



119875

119905= [H3PO4

0] + [H

2PO4

minus] + [HPO

4

2minus] + [PO

4

3minus] (10)

119872

119905= [M+] + [MH

2PO4

0] + [MHPO

4

minus] + [MPO

4

2minus]

(11)

119862H119899A = [H119899A] + [H119899minus1A




120572H119909PO4

119909minus3 =

[H119909PO4

119909minus3]

119875

119905

=

1

[H+]119899+[H+]119899minus11198701+[H+]119899minus2119870

1119870

2+sdot sdot sdot

(13)



119870




120572Ca2+ =[Ca2+]119872

119905

= 1 times (1 +

120572PO4

3minus

10

minus65+

120572HPO4

2minus

10

minus27

+

120572H2PO4

minus

10

minus14)

minus1

(14)





CaO 84116 gL (+) 2999SiO2 180240 gL (SiO4





3 Results






H3PO4 NaOHConc

AnionminusCation+

H+ OHminus

Diluted

001MSee Table 3


H+

Cation+

Anionminus

H3PO4Conc

OHminus

001MH3PO4H3PO4 NaOH

PO4minus

(a)

Catholyte outlet

Concentrate outlet

Catholyte inlet

Concentrate inlet

ElectrodeSpacer

Cationicmembrane

Anionic

Na+

SpacerSpacer

Spacer

membrane

Electrode

SpacerSpacer

Spacer

Spacer

Catholyte outlet


Concentrate inlet

Clminus

(b)






4



4





Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

minus1 0 1 2 3 4

Si(HO)4

H3PO4

HCl H2SO4

HF

(a)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

minus1 0 1 2 3 4

C1minus

Fminus

HSO4minus

H2PO4minus

SO42minus

HPO42minusPO4

3minus SiF62minus

(b)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

K+

Mg2+Na+

Ca2+

Fe3+

Fe2+

Al3+

(c)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

FeHPO4+

AlHPO4+

AlH2PO42+

FeH2PO42+

(d)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

FeH2PO4+

CaH2PO4+

MgH2PO4+

CaPO4minus FePO4


0 CaHPO40

(e)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

KHPO4minus NaHPO4


2minus

KH2PO40

NaH2PO40

(f)






2PO4



5P2O8







020


015


Con

duct

ance

(mS

cm)

Phosphoric acid ()

Visc

osity

(cen

tipoi

se)

25

20

15

10

5

00 10 20 30 40 50 60 70

200

180

160

140

120

100

80

60

40

20

0



2PO4

minusgt H3PO4

0gt Fe(H

2PO4)

4



Pure acid + NaC1

Industrial acid

Voltage (V)

Curr

ent (

A)

16

14

12

10

08

06

04

02

00

minus02

2 4 6 8 10 12



2PO4


2PO4






0 0192M 0707M 00072M 0206M

Pure acid + NaC1

Industrial acid

Con

duct

ance

(mS)

Time (min)



∘C48

44

40

36

32

28

24

0 100 200 300 400 500







157 kWhkg


78 kWhkg


Catio

n co

ncen

trat

ion

phos

phat

e con

cent

ratio

n

Timetotal time

001360

001355

001350

001345

001340

001335

001330

00 02 04 06 08 10



process


2PO4


2PO4

minus




4 Conclusions





a benchmark

Acknowledgment


References


















































2PO4)2sdot2H

2O (M = Mg











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



119905) the acids (119862H

119899A)



119875

119905= [H3PO4

0] + [H

2PO4

minus] + [HPO

4

2minus] + [PO

4

3minus] (10)

119872

119905= [M+] + [MH

2PO4

0] + [MHPO

4

minus] + [MPO

4

2minus]

(11)

119862H119899A = [H119899A] + [H119899minus1A




120572H119909PO4

119909minus3 =

[H119909PO4

119909minus3]

119875

119905

=

1

[H+]119899+[H+]119899minus11198701+[H+]119899minus2119870

1119870

2+sdot sdot sdot

(13)



119870




120572Ca2+ =[Ca2+]119872

119905

= 1 times (1 +

120572PO4

3minus

10

minus65+

120572HPO4

2minus

10

minus27

+

120572H2PO4

minus

10

minus14)

minus1

(14)





CaO 84116 gL (+) 2999SiO2 180240 gL (SiO4





3 Results






H3PO4 NaOHConc

AnionminusCation+

H+ OHminus

Diluted

001MSee Table 3


H+

Cation+

Anionminus

H3PO4Conc

OHminus

001MH3PO4H3PO4 NaOH

PO4minus

(a)

Catholyte outlet

Concentrate outlet

Catholyte inlet

Concentrate inlet

ElectrodeSpacer

Cationicmembrane

Anionic

Na+

SpacerSpacer

Spacer

membrane

Electrode

SpacerSpacer

Spacer

Spacer

Catholyte outlet


Concentrate inlet

Clminus

(b)






4



4





Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

minus1 0 1 2 3 4

Si(HO)4

H3PO4

HCl H2SO4

HF

(a)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

minus1 0 1 2 3 4

C1minus

Fminus

HSO4minus

H2PO4minus

SO42minus

HPO42minusPO4

3minus SiF62minus

(b)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

K+

Mg2+Na+

Ca2+

Fe3+

Fe2+

Al3+

(c)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

FeHPO4+

AlHPO4+

AlH2PO42+

FeH2PO42+

(d)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

FeH2PO4+

CaH2PO4+

MgH2PO4+

CaPO4minus FePO4


0 CaHPO40

(e)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

KHPO4minus NaHPO4


2minus

KH2PO40

NaH2PO40

(f)






2PO4



5P2O8







020


015


Con

duct

ance

(mS

cm)

Phosphoric acid ()

Visc

osity

(cen

tipoi

se)

25

20

15

10

5

00 10 20 30 40 50 60 70

200

180

160

140

120

100

80

60

40

20

0



2PO4

minusgt H3PO4

0gt Fe(H

2PO4)

4



Pure acid + NaC1

Industrial acid

Voltage (V)

Curr

ent (

A)

16

14

12

10

08

06

04

02

00

minus02

2 4 6 8 10 12



2PO4


2PO4






0 0192M 0707M 00072M 0206M

Pure acid + NaC1

Industrial acid

Con

duct

ance

(mS)

Time (min)



∘C48

44

40

36

32

28

24

0 100 200 300 400 500







157 kWhkg


78 kWhkg


Catio

n co

ncen

trat

ion

phos

phat

e con

cent

ratio

n

Timetotal time

001360

001355

001350

001345

001340

001335

001330

00 02 04 06 08 10



process


2PO4


2PO4

minus




4 Conclusions





a benchmark

Acknowledgment


References


















































2PO4)2sdot2H

2O (M = Mg











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




H3PO4 NaOHConc

AnionminusCation+

H+ OHminus

Diluted

001MSee Table 3


H+

Cation+

Anionminus

H3PO4Conc

OHminus

001MH3PO4H3PO4 NaOH

PO4minus

(a)

Catholyte outlet

Concentrate outlet

Catholyte inlet

Concentrate inlet

ElectrodeSpacer

Cationicmembrane

Anionic

Na+

SpacerSpacer

Spacer

membrane

Electrode

SpacerSpacer

Spacer

Spacer

Catholyte outlet


Concentrate inlet

Clminus

(b)






4



4





Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

minus1 0 1 2 3 4

Si(HO)4

H3PO4

HCl H2SO4

HF

(a)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

minus1 0 1 2 3 4

C1minus

Fminus

HSO4minus

H2PO4minus

SO42minus

HPO42minusPO4

3minus SiF62minus

(b)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

K+

Mg2+Na+

Ca2+

Fe3+

Fe2+

Al3+

(c)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

FeHPO4+

AlHPO4+

AlH2PO42+

FeH2PO42+

(d)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

FeH2PO4+

CaH2PO4+

MgH2PO4+

CaPO4minus FePO4


0 CaHPO40

(e)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

KHPO4minus NaHPO4


2minus

KH2PO40

NaH2PO40

(f)






2PO4



5P2O8







020


015


Con

duct

ance

(mS

cm)

Phosphoric acid ()

Visc

osity

(cen

tipoi

se)

25

20

15

10

5

00 10 20 30 40 50 60 70

200

180

160

140

120

100

80

60

40

20

0



2PO4

minusgt H3PO4

0gt Fe(H

2PO4)

4



Pure acid + NaC1

Industrial acid

Voltage (V)

Curr

ent (

A)

16

14

12

10

08

06

04

02

00

minus02

2 4 6 8 10 12



2PO4


2PO4






0 0192M 0707M 00072M 0206M

Pure acid + NaC1

Industrial acid

Con

duct

ance

(mS)

Time (min)



∘C48

44

40

36

32

28

24

0 100 200 300 400 500







157 kWhkg


78 kWhkg


Catio

n co

ncen

trat

ion

phos

phat

e con

cent

ratio

n

Timetotal time

001360

001355

001350

001345

001340

001335

001330

00 02 04 06 08 10



process


2PO4


2PO4

minus




4 Conclusions





a benchmark

Acknowledgment


References


















































2PO4)2sdot2H

2O (M = Mg











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

minus1 0 1 2 3 4

Si(HO)4

H3PO4

HCl H2SO4

HF

(a)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

minus1 0 1 2 3 4

C1minus

Fminus

HSO4minus

H2PO4minus

SO42minus

HPO42minusPO4

3minus SiF62minus

(b)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

K+

Mg2+Na+

Ca2+

Fe3+

Fe2+

Al3+

(c)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

FeHPO4+

AlHPO4+

AlH2PO42+

FeH2PO42+

(d)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

FeH2PO4+

CaH2PO4+

MgH2PO4+

CaPO4minus FePO4


0 CaHPO40

(e)

Con

cent

ratio

n fr

actio

n

pH

10

08

06

04

02

00

0 1 2 3 4

KHPO4minus NaHPO4


2minus

KH2PO40

NaH2PO40

(f)






2PO4



5P2O8







020


015


Con

duct

ance

(mS

cm)

Phosphoric acid ()

Visc

osity

(cen

tipoi

se)

25

20

15

10

5

00 10 20 30 40 50 60 70

200

180

160

140

120

100

80

60

40

20

0



2PO4

minusgt H3PO4

0gt Fe(H

2PO4)

4



Pure acid + NaC1

Industrial acid

Voltage (V)

Curr

ent (

A)

16

14

12

10

08

06

04

02

00

minus02

2 4 6 8 10 12



2PO4


2PO4






0 0192M 0707M 00072M 0206M

Pure acid + NaC1

Industrial acid

Con

duct

ance

(mS)

Time (min)



∘C48

44

40

36

32

28

24

0 100 200 300 400 500







157 kWhkg


78 kWhkg


Catio

n co

ncen

trat

ion

phos

phat

e con

cent

ratio

n

Timetotal time

001360

001355

001350

001345

001340

001335

001330

00 02 04 06 08 10



process


2PO4


2PO4

minus




4 Conclusions





a benchmark

Acknowledgment


References


















































2PO4)2sdot2H

2O (M = Mg











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





2PO4



5P2O8







020


015


Con

duct

ance

(mS

cm)

Phosphoric acid ()

Visc

osity

(cen

tipoi

se)

25

20

15

10

5

00 10 20 30 40 50 60 70

200

180

160

140

120

100

80

60

40

20

0



2PO4

minusgt H3PO4

0gt Fe(H

2PO4)

4



Pure acid + NaC1

Industrial acid

Voltage (V)

Curr

ent (

A)

16

14

12

10

08

06

04

02

00

minus02

2 4 6 8 10 12



2PO4


2PO4






0 0192M 0707M 00072M 0206M

Pure acid + NaC1

Industrial acid

Con

duct

ance

(mS)

Time (min)



∘C48

44

40

36

32

28

24

0 100 200 300 400 500







157 kWhkg


78 kWhkg


Catio

n co

ncen

trat

ion

phos

phat

e con

cent

ratio

n

Timetotal time

001360

001355

001350

001345

001340

001335

001330

00 02 04 06 08 10



process


2PO4


2PO4

minus




4 Conclusions





a benchmark

Acknowledgment


References


















































2PO4)2sdot2H

2O (M = Mg











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Pure acid + NaC1

Industrial acid

Voltage (V)

Curr

ent (

A)

16

14

12

10

08

06

04

02

00

minus02

2 4 6 8 10 12



2PO4


2PO4






0 0192M 0707M 00072M 0206M

Pure acid + NaC1

Industrial acid

Con

duct

ance

(mS)

Time (min)



∘C48

44

40

36

32

28

24

0 100 200 300 400 500







157 kWhkg


78 kWhkg


Catio

n co

ncen

trat

ion

phos

phat

e con

cent

ratio

n

Timetotal time

001360

001355

001350

001345

001340

001335

001330

00 02 04 06 08 10



process


2PO4


2PO4

minus




4 Conclusions





a benchmark

Acknowledgment


References


















































2PO4)2sdot2H

2O (M = Mg











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




157 kWhkg


78 kWhkg


Catio

n co

ncen

trat

ion

phos

phat

e con

cent

ratio

n

Timetotal time

001360

001355

001350

001345

001340

001335

001330

00 02 04 06 08 10



process


2PO4


2PO4

minus




4 Conclusions





a benchmark

Acknowledgment


References


















































2PO4)2sdot2H

2O (M = Mg











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of
















































2PO4)2sdot2H

2O (M = Mg











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










2PO4)2sdot2H

2O (M = Mg











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

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