Stabilization of nickel-laden sludge by a high-temperature NiCr 2O 4 synthesis process

Abstract

The feasibility of stabilizing nickel-laden sludge by a high-temperature NiCr 2O 4 synthesis process was investigated with different sintering temperatures, salt contents, molar ratios, and reaction atmospheres. The crystalline phases of species were investigated by using an X-ray diffraction, and the surface characteristics of particles were observed by scanning electron microscopy. The leaching behavior of the stabilized sludge was evaluated by Toxicity Characteristic Leaching Procedure (TCLP) test. The results indicated that NiCr 2O 4 was formed at around 800 °C by transforming NiO and Cr 2O 3 into a spinel structure. Leaching concentrations of both nickel and chromium decreased with an increase in the sintering temperature. The existence of salt in the sludge disturbed the formation of spinel, but a moderate salt content contributed to stabilization efficiency. A Cr/Ni molar ratio >2 also contributed to the stabilization efficiency of heavy metals after the thermal process. NiCr 2O 4 was transformed from simulated sludge under both an N 2 and air atmosphere. The sintering strategy designed for nickel-laden sludge was proven to be beneficial in stabilizing nickel and chromium.