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

Original scientific paper

Abstract

The nickel removal 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 °C 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 content of 37.2 % and a true density of 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 °C. 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.