Stabilization of nickel-laden sludge by a high-temperature NiCr2O4 synthesis process

The feasibility of stabilizing nickel-laden sludge by a high-temperature NiCr2O4 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 NiCr2O4 was formed at around 800 degrees C by transforming NiO and Cr2O3 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. NiCr2O4 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. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.