5 enrichment in solution
TRANSCRIPT
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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.
Engineering Aspects 2Engineering Aspects 2
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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Engineering Aspects 3Engineering Aspects 3
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