Extraction behavior and mechanism of nickel in chloride solution using a cleaner extractant

A large amount of nickel discharge from Ni-plating wastewater, inevitably causes serious water pollution and resources waste issue, which has attracted extensive attentions worldwide. Solvent extraction is one of the most effective methods for the removal and recovery of nickel from Ni-plating wastewater. However, conventional extraction with acidic extractants brought secondary pollutant (acid wastewater). To eliminate the initial and secondary pollution caused by Ni-plating wastewater treatment, an acid-free and alkali-free extraction process for nickel by using a cleaner extractantePEPD was proposed. The effects of Cl- concentration, PEPD concentration, equilibrium pH, O/A ratio and reaction time on the nickel extraction efficiency were evaluated employing single variable method. The results demonstrated that PEPD showed a high extraction capacity (single-stage extraction: 94%) and selectivity (beta(Ni/Ca): 284, beta(Ni/Mg): 306) to nickel at room temperature. The extraction mechanism was further studied by means of FT-IR, UV-VIS, NMR and ESI-MS spectra and the structure of coordinated complex between Ni and PEPD was determined to be NiCl4(PEPD)(2). Remarkably, PEPD exhibited a good stability after going through five extraction and stripping cycles. In conclusion, using PEPD to substitute the conventional acidic extractants is of great potential application value due to the merits of pollution reducing and utilization effectiveness improvement of resources. (c) 2019 Published by Elsevier Ltd.