Separation and recovery of valuable metals from real mix electroplating wastewater by solvent extraction

• Solvent extraction was used for valuable metal recovery from a real complex electroplating wastewater.
• Zn, Cu, Fe, Ni and Cr were recovered in pure form by using Aliquat, LIX 984N-C, DEHPA, LIX 984N-C and Cyanex 272 respectively.
• Equilibrium pHs were determined for them 1.45, 1.20, 1.0, 5.25 and 6.00, respectively.
• Formation of huge amount of heavy metal sludge or slime will be circumvented.

Recycling of electroplating wastewater is very important because of the large amounts of wastewater generated, the enormous economic value and large environmental concerns when conventional neutralization–precipitation processes are used to dispose of the wastewater. This work describes the recovery of valuable metals from industrial wastewater collected at a galvanizing industrial site using a solvent extraction process. Several extractants such as DEHPA, TBP, LIX 984N-C, Cyanex 272 and Aliquat 336 were tried for the separation and recovery of valuable metals from the wastewater. Optimum extraction parameters for zinc, copper, iron, nickel and chromium were determined as 10% Aliquat 336, 5% LIX 984N-C, 10% DEHPA, 15% LIX 984N-C and 10% Cyanex 272 in kerosene at equilibrium pH 1.45, 1.20, 1.00, 5.25 and 6.00 with 99.6%, 100%, 100%, 99.9% and 100% extraction efficiencies at almost 100% selectivity, respectively. These extraction efficiencies were attained at two extraction stages for zinc, copper and chromium and at one extraction stage for iron and nickel. Copper-loaded LIX 984N-C, iron-loaded DEHPA, nickel-loaded LIX 984N-C and chromium-loaded Cyanex 272 were stripped with 450 g/L, 2 M, 150 g/L and 1 M H2SO4 respective strip solutions with relative 100% stripping efficiencies. A two-stage process stripped the zinc-loaded Aliquat 336 with a 2 M NaOH solution with 100% efficiency. Based on the data, a flow sheet for the separation of the five metal ions is provided.