Cloud point extraction studies on recovery of nickel(II) from highly saline sulfate medium using salicylideneaniline mono-Schiff base chelating extractant

Abstract

A novel cloud point extraction process (CPEP) has been developed for recovery of nickel(II) from saline sulfate medium via the use of the lipophilic chelating extractant, salicylideneaniline (SAN), and the nonionic surfactant, Triton X-100. Surfactant solutions are employed in conjunction with SAN to form nickel complexes, which are subsequently entrapped in the micelles of the surfactant-rich phase, upon increase the temperature above the cloud point temperature. The effects of the main experimental parameters such as pH, extractant concentration, non-ionic surfactant concentration and temperature on the cloud point extraction process of nickel(II) with SAN were studied and optimized. The use of the SAN/TritonX-100 system led to very good extraction efficiency and concentrating ability for Ni(II) pollutant. Indeed, nearly 90% extraction efficiency with a minimal volume fraction of surfactant-rich phase (ϕs=0.1), and a high concentration factor (CF≈35) was achieved at pH 8.8, in one step. The analysis of the extraction data revealed that the cloud point process of nickel proceeds via a cation exchange mechanism. The stoichiometry of the complex extracted into the surfactant-rich phase was ascertained by the slope analysis method to have a composition of 1:2 [Ni:SAN]. Under the similar conditions, a higher extraction constant was determined for CPE compared with classical solvent extraction, illustrating the feasibility and utility of CPE for Ni(II) recovery. The optimum conditions of the extraction-recovery have been established as the following: (1) 5.1×10−3mol/L ligand; (2) 5wt.% surfactant; (3) pH of 8.8 and (4) temperature of 65°C.