Recovery of high value copper and zinc oxide powder from waste brass pickle liquor by solvent extraction

•High pure ZnO and Cu metal powders were recovered from spent brass pickle liquor.•Zn and Cu from spent brass pickle liquor were separated by SX with LIX 984N.•From stripped solutions high pure ZnO and Cu powders were produced by hydrothermal route.•Complete process flow sheet for recovery of acid and metal values has been proposed.

Solvent extraction of Cu and Zn from spent brass pickle liquor has been carried out using LIX 984N as an extractant. Very high difference in ΔpH1/2 value for the two metals during the extraction indicates the ease of separating them under the appropriate conditions. Based on the bench scale results, metals were separated in a continuous mode using a laboratory scale mixer settler unit from the spent brass pickling solution containing 35 kg/m3 Cu, 30 kg/m3 Zn, 1.5 kg/m3 Fe, 0.75 kg/m3 Cr, 0.03 kg/m3 Ni and 70 kg/m3 H2SO4 with 30% LIX 984N in kerosene. High copper extraction (99.9%) at the phase ratio (O/A) of 2/1 was obtained at the equilibrium pH of 2.5 in a two-stage counter-current extraction process, leaving behind Zn, Cr and Ni in the raffinate. Zinc from the chromium free solution was then quantitatively extracted in three counter-current extraction stages at pH 5.5 and O/A = 2/1 with negligible co-extraction of nickel. From the respective loaded organic phases, copper and zinc were completely stripped off using 150 kg/m3 H2SO4. The stripped solutions of Cu and Zn were utilized for the synthesis of high pure Cu metal powder and ZnO particles by the hydrothermal reduction/precipitation processes. Copper powder was synthesised in an autoclave at 20 bar H2 pressure and 423 K in 2 h. On the other hand ZnO powder (4 bar) was prepared from zinc striped solution at pH 12 in an autoclave under autogenous pressure at 423 K in 2 h. The purity and morphology of the as-prepared powders were determined by chemical analysis, XRD and SEM-EDS studies.

Graphical abstractZinc Oxide and Cu powders from waste brass pickle liquor.Download full-size image