5 Enrichment in Solution

7/25/2019 5 Enrichment in Solution

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EXTRACTIVE METALLURGY OFEXTRACTIVE METALLURGY OF GOLDGOLD

55. Enrichment in solution. Enrichment in solution

Fathi HabashiFathi Habashi

Laval University, Quebec City, CanadaLaval University, Quebec City, Canada

[email protected]@arul.ulaval.ca

ConcentrationConcentration -- PurificationPurification

Adsorption on activated charcoal

Ion exchange

Solvent extraction


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Adsorptionon activated

charcoalIon exchange Solvent extraction

Maximumefficiency

dilutesolution

dilute solution concentratedsolution

Speed slow slow rapid

Capacity low high high

Clarity ofsolution

clear orturbid

clear or turbid clear

Method ofoperation

batch orsemi-

continuous

batch,semi-

continuous, or

continuous

continuous

Cost low high moderate

Mechanism physical physico-chemical

chemical

Adsorption & Ion ExchangeAdsorption & Ion Exchange1.

Sorption

Feed or

influent

Effluent

to waste

Washing

Water

Loosely

sorbed

effluent

to waste

2.

Elution

Eluent

Eluate

for metal

recovery

Washing

Water

To wast e


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Solvent ExtractionSolvent Extraction

Leach

solution

Barrensolution

(raffinate)

Organic phase

(loaded)

Organic phaserecycle

(unloaded)

Strip

solution

Stripsolution

recycle

Pure metal salt for

reduction to metal

Precipitetingagent

Extraction Stripping Recovery


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Varieties of CarbonVarieties of Carbon

Carbon black

Prepared by the incomplete combustion of gaseous or liquidcarbonaceous material, e.g., natural gas, acetylene, oils, resins, tar,etc., in a limited supply of air. It is nonporous fine particles of carbon.Example: lamp black and acetylene black. Used as pigments, in therubber industry, and in ink manufacture.

Charcoals

Prepared by heating of solid carbonaceous material such as coal,wood, nut shells, sugar, and synthetic resins at about 600 C in theabsence of air, to volatilize the component elements other than carbon a process known as carbonization . Such charcoals have lowporosity

Act ivated charcoal

Prepared by heating charcoal at 400800C for a limited t ime with air,chlor ine, or steam. A highly porous material is produced. Used as anadsorbent in the chemical and the metallurgical industry, usually inthe form of pellets about 2 mm in diameter.


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Charcoal vs.

Graphite

Activated CharcoalActivated Charcoal

Surface OxidesSurface Oxides

OHC=O

HO O

O

OOH

OHC

C

O

O

=

O

C

=C

O

O

Carboxylic

acid

Phenolic

hydroxyl

Quinone

carbonyl

Carboxylic

anhydride

Cyclic

peroxide

Fluorescein

lactone

Normal

lactone


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Activated CharcoalActivated Charcoal

Effect of Oxygen on AdsorptionEffect of Oxygen on Adsorption100

80

60

40

20

020 60 100

Acidadsorption,

me

quiv./

g

Oxygen pressure, mm Hg

ADSORPTIONADSORPTION

MechanismMechanismSurface

Bulk of solid


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Adsorption Isotherm 1Adsorption Isotherm 1

EmpericalEmperical

FreundlichFreundlich IsothermIsotherm

GasesGases w = kp1/n

Aq. SolutionsAq. Solutions w = kC1/n

Adsorption Isotherm 2

Theoretical: LangmuirTheoretical: Langmuir

kp(1 ) = k


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Adsorption of Gold & SilverAdsorption of Gold & Silver

from cyanide solutionfrom cyanide solution1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0 1 2 3

Log concentration in solution

Logconcentrationincharcoal

[Au(CN)2]

[Ag(CN)2]

CN

AdsorptionAdsorption

Effect of TemperatureEffect of Temperature

400

300

200

100

02.5 5.0 7.5 10.0 12.50

Silveroncharcoal

mic

romolesAg/gcharcoal

Silver in solution, millimolesAg/L

25 C

40 C54 C

63.5 C

73.5 C


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AdsorptionAdsorption

effect of organic solventseffect of organic solvents10090

80

70

60

50

40

30

20

10

0 5 10 15 20

Number of bed volumes

of strip solution

Golddesorption%

With 20%

ethanol

Without

ethanol

DeDe

--sorptionsorption

Effect of TemperatureEffect of Temperature100

90

80

70

60

50

40

3030 40 50 60 70 80 90 100

G

olddesorption%

Temperature, C


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Engineering Aspects 1Engineering Aspects 1

Sorption of the gold cyanide complex on charcoal.

Washing with water to remove the entrained solution.

Desorption, usually with a solution of 0.2% NaCNand 1% NaOH at 90 C.

Acid washing to remove CaCO3precipitate.

Washing the depleted charcoal with water to removethe entrained solution.

Dewatering, activation by heating for 30 minutes at

700 C in absence of air, then quenching andrecycling.


Two factors contribute to the choice of the

adsorption process:

Filtration properties of the pulp

Presence of organic matter in the ore


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Column process

Clear solutions

Carbon-in-pulp process

Ores containing finely divided clay particles which are difficult to filter. In

this process, the cyanide leaching pulp is agitated in tanks with the charcoalpellets . When adsorption is complete, the pulp is screened to separate thegold-laden pellets for washing and de-sorption. The process has theadvantage of eliminating filtration.

Carbon-in-leach processOres containing organic matter

Adsorption on CharcoalAdsorption on Charcoal

SUMMARYSUMMARY

Activated charcoal is hydrophilic because of theorganic surface complexes formed during activation.It has a large surface area and a high porosity

Adsorption of gold or silver cyanide complexes is aphysical process

Oxygen is necessary for adsorption processes

Adsorption decreases when the solution contains an

organic solvent of lower polarity than water sinceunder these conditions the electrostatic forces ofattraction decrease

Adsorption decreases with increased temperature


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Ion ExchangeIon Exchange

Ion Exchange 2Ion Exchange 2

+

+++

++

+ +

++

+

+++

+

+

+ +

+

Matrix

Holes


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IonogenicIonogenic GroupsGroups

A matrix carries a positive or a negativeelectric charge

This is compensated by ions of oppositesign, called counter-ions

Ions of the same sign as that on theframework are called co-ions

The counter-ions are free to move withinthe framework and can be replaced by

other ions of the same sign, while thefixed ions are not mobile

Ion Exchange Equations


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Ion Exchange EquipmentIon Exchange Equipment

Columns.Columns. Clear solutionsClear solutions

ResinResin--ininPulp.Pulp. SlurrySlurry

Continuous system.Continuous system. Clear solutionsClear solutions

ResinResin--inin--PulpPulp

Top ofstroke

Bottom ofstroke

Reciprocating rod

Stainless steelangle frame

Stainless steel screen onfour sides and bottom

Binder stripbolted to frame


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Continuous Ion Exchange System

Mixer Settlers

Leach

Strip

Unloaded

Organic

Rafinate

EXTRACTION

STRIPPING

Strip

solution

solutionto metalrecovery

(recycle to

leaching)

solution

Leach

Wash

Unloaded

Organic

Loaded

EXTRACTION

Washsolution

Strip solution

STRIPPING

to metal recovery

solution

solution

Rafinate

(recycle toleaching)

Stripsolution

Aqueou s

Organic

Organic

Aqueou s

Mixer Settler


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Columns

Interface

Interface

Solventinlet

Solventinlet

Aqu eousinlet

Aqu eousinlet

Solventoutlet

Solventoutlet

Aqu eousoutlet

Aqu eousoutlet

Piston

platesPerforated

Loaded solvent

Raffinate

queous

feed

Solvent

feed

THANKS

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5 Enrichment in Solution