Nickel removing by electrocoagulation of Ni(II)-NH3-CO2-SO2-H2O system. Kinetics, isothermal, mechanism and estimated cost of operation.

Abstract

This study reports nickel removing by electrocoagulation of Ni(II)-NH3-CO2-SO2-H2O system at laboratory scale. Experiments were done using Al/Al pair electrodes at initial nickel concentration between 293 and 1356 mg·L-1 and under operation parameters of pH 8.6, current density 9.8 mA·cm-2, electrolysis time 30 min, and temperature 60 ºC. The obtained results show removal efficiencies between 97.7 and 99.7 %. Kinetics modeling suggested combined effects of external diffusion and nucleation, and as controlling step the chemical reaction and a possible autocatalytic contribution. The process followed the Langmuir´s isotherm with a maximum adsorption capacity of 7519 mg·g-1. ICP-OES, XRD and FTIR characterization of the precipitates indicated a typical Ni-Al layered double hydroxide structures with 33.4-40.7 % nickel and 6.3-7.0 % aluminum depending on initial nickel concentration. The operation costs of energy and electrode consumption were 320 - 537 $·t-1 of removed nickel.