Removal of nickel from Ni(II)-NH3-SO2-CO2-H2O system by electrocoagulation, sedimentation, and filtration processes

Abstract

The nickel removing by electrocoagulation of Ni(II)-NH3-CO2-SO2-H2O system was studied in a batch reactor of 50 L useful volume, with stirring, and two pairs of aluminum electrodes. The operating parameters were nickel concentration between 255 and 342 mg L-1, current density of 11.0 and 16.6 mA cm-2, pH 8.34±0.06, mean temperature 58.4±3.9 oC and retention time of 50 min. The maximum nickel removal was 99.7 % at 11.0 mA cm-2, specific energy consumption 16.86 kWh kg-1 of Al3+, 2.438 kWh kg-1 of Ni and the adsorption capacity 5819 mg Ni g-1 of Al3+. The precipitate contained a nickel concentration of 37.2 % and true density 2720 kg m-3, hydro­talcite-like structure layered double hydroxides. The unit area of sedimentation was between 0.25 and 1.96 m2 t-1 day, at a density from 971 to 1019 kg m-1 and 53±4 oC. A model for pre­dicting the specific cake resistance was estimated as a function of pressure drop and sus­pension concentration at 44.45 kPa and 59.52 kg m-3, resulting in the value of 6.47±107 m kg-1. The average cake humidity was 88 % base humid.