The effect of pH on cadmium extraction by Lix 34

The pH dependence of the extraction of cadmium from nitrate solution using LIX 34 diluted with Kermac 470B has been studied. The optimum pH for cadmium extraction in the system studied is in the neighborhood of 8.3. Below pH 7, the reagent forms a two-to-one ligand to cadmium ion chelate, whereas, at pH greater than 7, the extraction mechanism is extremely complicated due to the presence of NH₃, NH₄⁺ and some other unknown buffers. Moreover, the difference between the initial and equilibrated aqueous pH values, ΔpH, can be estimated by the following equation

$\text{Delta;}\text{pH}\text{=}\text{log}\text{1}\text{1 +(i?2)}\text{[}\text{cd}\text{]}{}_0\text{[}\text{NH}{}_3\text{]}{}^{\mathrm{<mtext>I</mtext>}}$

where i is the average co-ordination number of cadmium by ammonia in the aqueous phase. [Cd]₀ represents the equilibrium cadmium concentration in the organic phase and [NH₃]^I denotes the initial aqueous ammonia concentration.