THE ACID GENERATED IN THE TANKHOUSE IS RETURNED IN COPPER=Different Types of Extractant

THE ACID GENERATED IN THE TANKHOUSE IS RETURNED IN COPPER-DEPLETED ELECTROLYTE TO STRIP MORE COPPER FROM THE CIRCULATING LOADED ORGANIC SOLUTION THE ORGANIC REAGENT IS REGENERATED DURING THE STRIPPING PROCESS AND IS RETURNED TO THE EXTRACTION SECTION TO EXTRACT MORE COPPER

Extraction CuSO4(aq) + 2LH(org) 10487741048774CuL2(org) + 2H+(aq)

Stripping CuL2(org) + 2H+(aq) 10487741048774CuSO4(aq) + 2LH(org)

Equilibrium constant (K) = [CuL 2 ] [H + ] 2

[CuSO4] [LH]2

Distribution (D) = Cu(org) is given

Cu(aq) by Log D = Log K = 2 Log [LH] + 2pH

Mode of Operation

Cross-Current Operation

Crosscurrent mode is mostly used in batch operation Batch extractors have traditionally

been used in low capacity multi-product plants such as are typical in the pharmaceutical

and agrochemical industries For washing and neutralization operations that require very

few stages crosscurrent operation is particularly practical and economical and offers a

great deal of flexibility The extraction equipment is usually an agitated tank that may

also be used for the reaction steps

In these tanks solvent is first added to the feed the contents are mixed settled and then

separated Single stage extraction is used when the extraction is fairly simple and can be

achieved without a high amount of solvent If more than one stage is required multiple

solvent-washes are given

Though operation in crosscurrent mode offers more flexibility it is not very desirable due

to the high solvent requirements and low extraction yields

Counter-Current Operation

For larger volume operation and more efficient use of solvent countercurrent mixersettlers

or columns are employed Countercurrent operation conserves the mass transfer

driving force and hence gives optimal performance

The dimensionless term mSF included in all the above equations is called the extraction

factor (E) and is an important parameter in the design of extraction processes For a

given number of stages the higher the E factor the higher is the reduction ratio and

easier is the extraction Systems with E of less than 13 are not likely to be commercially

feasible

Different Types of Extractant

Different Types of Extractants determine how well the extraction yield It affect the time taken the solubility pH values and selectivity(product purity) Below are 5 main extractants and its advantages and uses Extractants are used because it is necessary to form a chemical compound (= complex) with the solute and thus make it soluble in the organic phase

Chelating Agents

bull Main commercial extractants for copper

bull Operate on hydrogen ion cycle

bull Function with acid and ammoniacal leach solutions

bull More selective than other extractant classes

bull Kinetically slower than ion pair extractants

bull Have good physical properties in terms of phase separation low aqueous solubility

chemical stability

Ions-Pair Extractants

bull Commercial extractants for uranium thorium vanadium gold cobalt and other metals

bull Kinetics both extraction and stripping are fast

bull Extraction is usually of a metal anion complex

bull Selectivity is not high Other anions can compete with the metal being extracted

bull Selectivity can be pH dependent

Neutral Solvating Extractants

bull Kinetically fast

bull Extract neutral metal complexes

bull Selectivity is low

bull Organometallic complex must be organic soluble

Organic Acid Extractants

bull Operate on a hydrogen ion cycle but do not display hydrogen ion stoichiometry

bull Selectivity is poor and careful pH control may be required to achieve reasonable

selectivity

Ligand Subtitution Extractants

bull Extraction is not pH sensitive

bull Stripping(transfer of the metal back into a second pure aqueous phase for winning or

further processing) is by decomposition of the metal ligand chloride complex at relatively

low chloride ion

concentration

bull Selectivity can be very high and is based to an extent on extraction kinetics

separated Single stage extraction is used when the extraction is fairly simple and can be

achieved without a high amount of solvent If more than one stage is required multiple

solvent-washes are given

Though operation in crosscurrent mode offers more flexibility it is not very desirable due

to the high solvent requirements and low extraction yields

Counter-Current Operation

For larger volume operation and more efficient use of solvent countercurrent mixersettlers

or columns are employed Countercurrent operation conserves the mass transfer

driving force and hence gives optimal performance

The dimensionless term mSF included in all the above equations is called the extraction

factor (E) and is an important parameter in the design of extraction processes For a

given number of stages the higher the E factor the higher is the reduction ratio and

easier is the extraction Systems with E of less than 13 are not likely to be commercially

feasible

Different Types of Extractant

Different Types of Extractants determine how well the extraction yield It affect the time taken the solubility pH values and selectivity(product purity) Below are 5 main extractants and its advantages and uses Extractants are used because it is necessary to form a chemical compound (= complex) with the solute and thus make it soluble in the organic phase

Chelating Agents







chemical stability















selectivity





low chloride ion

concentration


Chelating Agents







chemical stability















selectivity





low chloride ion

concentration




low chloride ion

concentration


THE ACID GENERATED IN THE TANKHOUSE IS RETURNED IN COPPER=Different Types of Extractant

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