The effects of salinity and temperature on phase transformation of copper-laden sludge

To stabilize the copper and aluminum ions in simulated sludge, a series of sintering processes were conducted to transform Cu/Al precipitation into spinel structure, CuAl2O4. The results indicated that the large amount of salt content in the simulated sludge would hinder the formation of crystalline CuAl2O4 generated from the incorporation of CuO and Al2O3, even after the sintering process at 1200 degrees C. Opposite to the amorphous CuAl2O4, the crystalline CuAl2O4 can be formed in the sintering process at 700-1100 degrees C for 3 h with the desalinating procedure. According to the theory of free energy, the experimental data and references, the best formation temperature of CuAl2O4 was determined at 900-1000 degrees C. As the temperature rose to 1200 degrees C, CuAlO2 was formed with the dissociation of CuAl2O4. The XPS analysis also showed that the binding energy of copper species in the simulated sludge was switched from 933.8 eV for Cu(II) to 932.8 eV for Cu(I) with the variation of temperature. In this system, the leaching concentration of copper and aluminum ions from sintered simulated sludge was decreased with ascending temperature and reached the lowest level at 1000 degrees C. Furthermore, the descending tendency coincided with the formation tendency of spinel structure and the diminishing of copper oxide. (c) 2012 Elsevier B.V. All rights reserved.