Simultaneous removal of nickel and phosphorus from spent electroless nickel plating wastewater via calcined Mg–Al–CO3 hydroxides

Abstract

For electroless nickel plating wastewater, a novel approach for the simultaneous removal of nickel and phosphorus on calcined Mg–Al–CO₃ hydroxides (CLDHs) is proposed. The dependence of the adsorption efficiency on several parameters, including initial ions' concentration, temperature, contact time and pH, has been investigated with batch experiments. The adsorption kinetics data of nickel and phosphorus could be well depicted by a pseudo-second-order model. Adsorption isotherms studies showed that the uptake of nickel and phosphorus on CLDHs followed Langmuir and Freundlich models, respectively, and that the maximum removal of nickel or phosphorus was up to 22.87 or 761.5 mg g⁻¹. Thermodynamic analyses implied that the adsorption process of nickel or phosphorus on CLDHs was spontaneous and endothermic. Further, the possible mechanisms were explored in: low concentration solutions, CLDHs took part in reconstitution involving the isomorphous substitution of nickel at the magnesium sites in sheets and by the concomitant utilization of phosphorus by the generated superficial sheets; and in high concentration solutions, the CLDHs rebuilding hydrotalcite structures were influenced and formed mixed metal salts of phosphites, hydroxides, and hypophosphites, which were attributed to the presence of plentiful phosphorus and brought about the reduced uptake of nickel.