Chemical Analysis of Phosphate Rock Using Different Methods-Advantages and Disadvantages

8/11/2019 Chemical Analysis of Phosphate Rock Using Different Methods-Advantages and Disadvantages

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X-RAY SPECTROMETRYX-Ray Spectrom. 2006; 35 : 154158Published online 7 April 2006 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/xrs.886

Chemical analysis of phosphate rock using differentmethods advantages and disadvantages

Madian Jamil Sa,1

M. Bhagwanth Rao,1

K. Surya Prakash Rao2

and Pradip K. Govil3

1 University College of Technology, O.U., Hyderabad-500 007, A.P., India2 Applied Geochemistry (R&T), O.U., Hyderabad-500 007, A.P., India3 NGRI, Hyderabad-500 007, A.P., India

Received 30 May 2005; Revised 19 December 2005; Accepted 21 December 2005

Many analytical methods are considered for chemical analysis of phosphate rock because the accuracyof analysis is very important. In the present investigations, spectrophotometric and x-ray spectrometricmethods were used to determine P 2O 5 whereas SiO 2 , CaO, MgO, Al 2O 3 and Fe 2O 3 were determined bygravimetric and x-ray spectrometric methods. Volumetric and x-ray spectrometry methods are necessaryfor uorine determination. The investigations revealed that x-ray spectrometry is a precise and accurate

technique, which is cost effective and so better than other methods. Spectrophotometric, volumetric andgravimetric methods are expensive, time consuming and laborious. X-ray spectrometry is suggested forcommercial companies using regular analyses to save chemicals, time and labour and to maintain quality.Copyright 2006 John Wiley & Sons, Ltd.

INTRODUCTION

Several methods are used for the determination of P 2O5,CaO, SiO 2, Fe2O3, Al2O3, MgO and F contents in phosphaterocks. However, the most reliable method used in the pastis the spectrophotometric determination of P 2O5. Atomicabsorption spectrometry has been applied to the determina-

tion of MgO, CaO, SiO 2, Fe2O3 and Al 2O31

and gravimetricmethods for the determination of P 2O5, CaO, SiO2, R2O3(D Fe2O3 C Al2O3) and MgO. The potentiometric methodwith a uoride-selective electrode has long been used for thedetermination of uorine with high accuracy. Fluorine hasalso been determined by volumetric methods. 1 3 However,these analytical methods are old and outdated for criticalanalysis. Major and minor oxides such as SiO 2, Al2O3, TiO2,CaO, MgO, KiO 2, MnO, P 2O5 and Fe 2O3 and a few selectedtrace elements, Zr, Y, Sr, Rb, V, Ba, Cr, Ni, Co, Cu and Zn inIWG standards AN-G, BE-N and MA-N, were determinedrelative to USGS geological reference samples and syntheticstandards by using a PW1400 XRF analyser with a P851computer system in an attempt to obtain reliable values forthe standards. 4 Further, the technique is extremely usefulfor analyses in mining, mineralogy and geology and in envi-ronmental work and waste material analysis. XRF is a veryuseful analytical technique in research and pharmacy. 5 Amethod has been developed to determine the major, minorand trace elements in seamount phosphorite using a modernXRF spectrometric technique. For elements having an ana-lytical line lower in energy than the energy of the Fe K lineabsorption edge, the inter-element absorption-enhancementeffects were corrected using an inuence coefcient method.For the other elements, the matrix effects were corrected

Correspondence to: Madian Jamil Sa, University College of Technology, O.U., Hyderabad-500 007, A.P., India.E-mail: med [email protected]

using the ratio of the element peak to the Rh K Comptonpeak (for I, the Rh K Compton peak was used instead). Therelative standard deviationwas < 1.0% forthe major elements(except C, Naand Cl). The accuracy ofthismethodwas tested by evaluating analyses of three certied reference materials.The direct analysis of major and minor elements in geo-logical materials by the pressed pellet method without anychemical procedures makes XRF spectrometry a particularlyenvironmentally friendly analytical technique. 6 A detailedchemical characterisation of phosphatised basaltic hyalo-clastites assigned at Sal Island, Cape Verde archipelago, wasundertaken using synchrotron radiation x-ray uorescence. 7

Two different methods of microanalysis, energy-disper-sive spectrometry (EDS) and proton-induced x-ray emission(PIXE), were used to determine the appearance of traceelements (Zn, Sr and Fe) present in bone at the implantationsite containing the ceramic. Thespectra obtained by thePIXEmethod showed two regions for each element characterizingeither the bone tissue or the ceramic. The PIXE method was

apparently sufciently sensitive for monitoring the amountof trace element appearing in bone-implanted material. 8

Modern chemical laboratories use XRF spectrometry forthe analysis of phosphate rock samples. We used the latestXRF spectrometric and also older conventional methods tocompare the results.

EXPERIMENTALCollection and Preparation of Specimens forAnalysisThe standard specimen SRM 120c was designated S 1.

One specimen of soft phosphate collected from the lower

bed in the southeastern side in the Eastern B mines in Syriawas coned and quartered and dried. The fraction 0.015 toC 0.037 mm was selected for wet screening and subjected togrinding to 300 mesh and this specimen was designated S 2.

Copyright 2006 John Wiley & Sons, Ltd.


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Table 2. Chemical composition of the references provided by GECOPHAM

Number and identication Constituent Concentration (wt%) Constituent Concentration (wt%)

Concentrated Syrian phosphate (Khneiss-1SF) Al 2O3 0.2 0.03 Fe2O3 0.34 0.03CaO 49 .3 0.14 P2O5 30.8 0.08MgO 0 .52 0.01 SiO2 6.8 0.2

F 3.7 0.05Concentrated Syrian phosphate (Eastern A-2SF) Al 2O3 0.4 0.1 Fe2O3 0.28 0.05

CaO 46 .4 0.3 P2O5 28.4 0.1MgO 0 .63 0.02 SiO2 7.5 0.3

F 2.2 0.1Concentrated Syrian phosphate (Eastern A-3SF) Al 2O3 0.3 0.1 Fe2O3 0.47 0.03

CaO 51 .9 0.2 P2O5 29.7 0.07MgO 0 .55 0.02 SiO2 4.3 0.3

F 3.76 0.09High-grade Syrian phosphate (4SF) Al 2O3 0.26 0.04 Fe2O3 0.29 0.06

CaO 51 .89 0.13 P2O5 37.19 0.1MgO 0 .33 0.02 SiO2 5.38 0.4

F 4.03

0.1Low-grade Syrian phosphate (5SF) Al 2O3 0.70 0.02 Fe2O3 0.92 0.04CaO 52 .02 0.17 P2O5 15.42 0.05MgO 1 .25 0.02 SiO2 7.34 0.2

F 2.97 0.02Moderate-grade Syrian phosphate (6SF) Al 2O3 0.38 0.02 Fe2O3 0.31 0.03

CaO 56 .26 0.12 P2O5 23.21 0.05MgO 0 .35 0.02 SiO2 4.15 0.2

F 3.26 0.08Low-grade Syrian phosphate (7SF) Al 2O3 1.04 0.02 Fe2O3 0.90 0.02

CaO 49 .83 0.08 P2O5 19.15 0.04MgO 1 .56 0.02 SiO2 11.77 0.1

F 3.26 0.05Moderate-grade Syrian phosphate (8SF) Al 2O3 0.36 0.02 Fe2O3 0.26 0.02

CaO 49 .86 0.17 P2O5 26.12 0.05MgO 0 .87 0.02 SiO2 9.44 0.2

F 3.70 0.02

Table 3. XRF analysis and the parameters for the measurement of each element a

Channel X-tal Collimator ( m) Detector kV mA Angle ( 2 )

Offset BackgroundChannel 1 (Bg1)

(2 )

Si PE 002-C 550 Flow 40 60 108.9726 2.5206Al PE 002-C 550 Flow 40 60 144.8606 2.5584Fe PX9 150 Scint. 30 40 57.4932 0.9596Mn PX9 150 Scint. 40 80 62.9406 0.9760Mg PX1 150 Flow 40 60 23.1016 2.3114Ca PX9 150 Flow 40 70 113.1196 1.0718Na PX1 550 Flow 40 70 27.9086 2.3812K PX9 150 Flow 50 40 136.6522 2.0056Ti PX9 150 Flow 40 70 86.1484 0.9296F PX1 550 Flow 30 70 43.6202 2.1876P Ge 111-C 550 Flow 40 70 141.0412 1.9026

a The other conditions are same for all the elements: anode, rhodium; type, Goniometer; line, K ; tube lter, none; measuring

time, 20 s.

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Table 4. Chemical analyses of S 1 , S2 , S 3 , S 4a and S 4

Specimen Chemical analyses P 2O5 (%) CaO (%) MgO (%) Fe2O3 (%) Al2O3 (%) SiO2 (%) F (%)

S1 XRF method 33.29 48.08 0.32 1.09 1.29 5.59 3.78Other methods a 33.14 48.57 0.40 R2O3 D Al2O3 C Fe2O3 D 2.55 IR 4.87 2.60NIST analysis 33 .34 0.06 48.02 0.17 0.32 0.01 1.08 0.03 1.30 0.04 5.50 0.02 3.82 0.02

S2 XRF method 25.66 52.98 0.34 0.26 0.33 7.35 3.48Other methods a 25.25 49.59 0.49 R2O3 D Al2O3 C Fe2O3 D 0.49 IR 3.23 2.90

S3 XRF method 17.36 57.72 0.37 0.32 0.46 5.84 2.93Other methods a 19.52 51.69 0.49 R2O3 D Al2O3 C Fe2O3 D 0.49 IR 3.23 2.90

S4a XRF method 23.37 51.17 1.73 0.29 0.39 3.48 3.50S4 XRF method 26.63 50.23 1.26 0.59 0.81 4.49 3.61

Calculated b 26.66 50.13 1.26 0.55 0.69 4.15 3.61

a P2O5 content was determined by spectrophotometry, CaO, MgO, R 2O3 and SiO 2 contents by gravimetry and uorine by thevolumetric method. b The contents of S 4 were calculated by component balance using the mass fractions of the specimens.

gravimetric method became inaccurate and gave incorrectresults for the tailings (phosphate rejected in the mines). Thisis dolomitic phosphate with a high CaO content of about57.72% and a high CaO/P 2O5 ratio, i.e. 3.32, as found byXRF, but the gravimetric method gave a 51.69% CaO contentand the CaO/P 2O5 ratio of 2.65.

The specimen S 4 was prepared by taking 2 g of aspecimen (S 4a) analysed by XRF spectrometry and blendingit with 1 g of SRM 120c so that the mass fractions of thespecimens were 0.67 and 0.33, respectively. The specimenobtained was ground to 300 mesh particle size andanalysed by XRF spectrometry; the chemical analyses of the resultant specimen (S 4) are given in Table 4. Fromthe component material balance and comparison with theanalytical results for the specimen obtained (means betweentheexperimental and the theoretical results), thesame valuesfor the F and MgO contents were found for both thecalculated and analytical results. The absolute errors forP2O5, SiO2, Al2O3, Fe2O3 and CaO were 0.03, 0.34, 0.12, 0.04and 0.1 and the relative errors were 0.001, 0.08, 0.15, 0.07 and0.002, respectively.

From the above results, it is clear that the XRF spectro-metric method gave more accurate results and can be usedfor larger range of concentrations and for all major elementsin phosphate rock with a wide range of standards. In the XRF

method the standards used should have a similar chemicalcomposition to the specimen being analysed, e.g. phosphaterock with MgO contents > 3.00% can not be analysed usingthe given standards in this work and it may give wrongresults when dolomite pebbles with higher MgO contentsare analysed. Different standards may be required for spec-imens obtained from other mines. Table 5 shows the rangeof the analyte elements and the range of variations, and it isevident that XRF shows high accuracy for the major, minorand trace elements in phosphate rock.

In the volumetric method, several chemical processeshave to be carried out for preparation of chemicals,

calcination, digestion, boiling, distillation, agitation neutral-ization and titration. The volumetric method is not precisefor the determination of uorine content. The gravimetricmethod becomes inaccurate with low-grade phosphate rock

Table 5. Accuracy of XRF for the determined andundetermined elements

Analyte Range of content (%) Range of variation ( )

SiO2 4.111.2 0.20.4Al2O3 0.21.8 0.10.04Fe2O3 0.21.1 0.030.06MnO 0.010.03 0.0010.002MgO 0.31.6 0.010.02CaO 43.656.3 0.080.4Na 2O 0.80.5 0.0010.02K2O 0.10.5 0.0040.02TiO2 0.10.02 0.0040.006F 2.24.0 0.020.1P2O5 15.037.0 0.040.1

(i.e. tailings rejected in the mines) so it cannot be used fordolomitic phosphate where the P 2O5 content is low and thatof CaO is high. Even with high-grade rock (high P 2O5 con-tents) it gives inaccurate results for SiO 2. The gravimetricmethod cannot yield results for Al 2O3 and Fe 2O3 directly.However, it gives iron oxide and aluminium oxide together.For other major components, such as P 2O5, MgO and CaO, itcan be used to determine the concentrations of unknown ele-ments.The spectrophotometric methodcan beutilizedforthedetermination of P 2O5 only for low and high concentrations 9and is unsuitable for intermediate concentrations.

CONCLUSIONS

XRF spectrometry is a rapid, accurate and precise methodfor the elemental analysis of phosphate rock specimens andrequires simple and minimal preparation at low cost. Ithas the advantage of giving separate concentrations of eachelement not related to other contents. XRF spectrometry isa non-invasive method, which means that the specimensanalysed are not destroyed or changed by exposure to x-rays

and theycan besaved for further use as a reference orin othertypes of testing. XRF covers a wide range of concentrationusing a relatively inexpensive computer for calculations butit requires a large number of well-analysed samples for



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the initial determination of the coefcients and needs anexpert with a good knowledge of software to operate thespectrometer.

Commercial companies require XRF spectrometry inroutine analyses instead of the out-of-date methods becausethe daily checking of multiple specimens in a short time can

save chemicals, time and labour and can give precise results.

REFERENCES1. National Institute of Standards and Technology. Certicates of

Analysis of Standard Reference Materials 694 Western PhosphateRock and 120c Florida Phosphate Rock. SRM StandardReference Materials Program. NIST: Gaithersburg, MD; 2003;www.nist.gov/srm.

2. Association of Florida Phosphate Chemists. AFPC Analytical Methods, 6th edn, vol. 9. AFPC Publications: Bartow, FL: 1980;37.

3. Furman NH. Standard Methods of Chemical Analysis: the Elements,6th edn, vol. 1. Van Nostrand: New York, 1962.

4. Govil PK. J. Geol. Soc. India 1985; 26: 38.5. Brouwer P. Theory of XRF: Getting Acquainted with Principles, 1st

edn. PANanalytical: Almelo, 2003.6. Wang X, Li G, Zhang Q, Wang Y. Geostand. Geoanal. Res. 2004; 28:

81.

7. Figueiredo MO, da Silva TP, Veiga JP, Chevallier P. J. Phys. IV 2003; 104: 399.8. Frayssinet P, Braye F, Weber G. J. Scanning Microsc. 1997; 19:

253.9. EuropeanFertilizerManufacturers Association. Production of NPK

Fertilizers by the Mixed Acid Route. Booklet No. 8. EuropeanFertilizer Manufacturers: Brussels, 2000; 1.


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Chemical Analysis of Phosphate Rock Using Different Methods-Advantages and Disadvantages