The separation technique in which a solution (usually aqueous) is brought in contact with a second solvent (usually organic) immiscible with the first in order to bring about a transfer of the solute into the second solvent. This occurs through the partitioning process, which involves the distribution of a solute between two immiscible liquid phases. This technique is called solvent extraction and also known as liquid-liquid extraction.
Principle of solvent extraction:
When the solute (liquid or solid) is add to a heterogeneous system of two immiscible liquids (in both of which the solute is soluble), the solute distributes between the two liquids.
This distribution governed by Nernst distribution law.
Factors affecting on the solvent extr-action:
1: Salting out agents:
The extraction of metals may enhance by adding high concentrations of inorganic salts to the aqueous phase. This process known as salting out effect.
2: pH Value:
The process of the liquid extraction is largely influence by the pH. The two metals may be extract at the difference pH value.
3: Oxidation state;
The selectivity of the extraction maybe sometimes increased by modifying the oxidation state of metal.
For example, extraction of Fe from chloride solution can be prevent by reducing Fe(III) to Fe(II) which does not extract.
4: Masking agents;
These agents which are metal complexing agents, prevent particular metals from taking part in their usual reactions and in this way they remove their interference without requiring an actual separation.
For example, Aluminium can be extract in the presence of iron with 8-quinolinol by masking the iron with an alkali cyanide to form stable ferrocyanide ion. Cyanide, tartrate and EDTA are commonly use as masking agents.
Modifiers are the additives to the organic phase to increase the solubility of the extractant in diluent. Example of modifiers is alcohol with high molecular weight.
6: Synergistic agents:
The Synergistic agents are add to the organic phase, in order to enhance the extraction. They form complexes, which taken up by the extract-ant. Neutral organophosphorous compounds added to acidic organophosphours compound exert synergistic effect.
organic phase, in order to enhance the extraction. They form complexes, which are taken up by the extract-ant. Neutral organophosphorous compounds added to acidic organophosphours compound exert synergistic effect.