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°C. Opposite to the amorphous CuAl₂O₄, the crystalline CuAl₂O₄ can be formed in the sintering process at 700-1100°C for 3h 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°C. As the temperature rose to 1200°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 933.8eV for Cu(II) to 932.8eV 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°C. Furthermore, the descending tendency coincided with the formation tendency of spinel structure and the diminishing of copper oxide.