Evaluation of pyrolysis residue derived by oily sludge on removing heavy metals from artificial flotation wastewater

Abstract

Pyrolysis residue, with the porous structure similar to activated carbon, was proposed as a material to remove heavy metals with low levels from synthetic flotation wastewater in the work. The effects of the dosage on removal efficiency, adsorption kinetics and isotherms were studied. The adsorption mechanism was also discussed. The results showed that pyrolysis residue could remove effectively Cd2+, Pb2+ and Cu2+ from the flotation solution and increase simultaneously its effluent pH. The removal efficiency of Cd2+, Pb2+ and Cu2+ was 99.3, 98.9 and 99.4%, and the corresponding solution pH was 9.79, 9.12 and 8.45 when pyrolysis residue dosages was 1, 0.8 and 0.8 g/L with same 20 mg/L concentrations of Cd2+, Pb2+ and Cu2+ and natural synthetic solution pH, respectively. The pseudo-second-order rate constant (k2) and the qmax of Cd2+, Pb2+and Cu2+ were 0.05, 0.03, 0.04 g/(mg·min) and 106.16, 140.65, 128.04 mg/g. Heavy metals was mainly removed by formation of stable metal sulfides and hydroxides on the surface. The above results have uncovered that pyrolysis residue was viable for removal of heavy metals with low levels from flotation wastewater for the first time.