Formation of copper aluminate spinel and cuprous aluminate delafossite to thermally stabilize simulated copper-laden sludge.

The study reported herein indicated the stabilization mechanisms at work when copper-laden sludge is thermally treated with gamma-alumina and kaolinite precursors, and evaluated the prolonged leachability of their product phases. Four copper-containing phases - copper oxide (CuO), cuprous oxide (Cu(2)O), copper aluminate spinel (CuAl(2)O(4)), and cuprous aluminate delafossite (CuAlO(2)) - were found in the thermal reactions of the investigated systems. These phases were independently synthesized for leaching by 0.1M HCl aqueous solution, and the relative leachabilities were found to be CuAl(2)O(4)<CuAlO(2)<<Cu(2)O<CuO. The sintering condition and formation mechanism employed to stabilize copper into CuAl(2)O(4) and CuAlO(2) are extensively discussed here. With a 3h of short sintering, it was found that CuAl(2)O(4) could be effectively formed between 850 and 950 degrees C by the gamma-alumina precursor. Although kaolinite had a lower incorporation capability than gamma-alumina, it was found to transform a considerable amount of copper into CuAl(2)O(4) between 950 and 1000 degrees C. At higher temperatures, CuAlO(2) was produced only in the gamma-alumina system as the occurrence of Cu(2)O-cristobalite solution in the kaolinite system precluded the production of CuAlO(2). The hypothesis that the spinel formation mechanism has two stages was supported by the results of the changing Cu/Al mole ratio in the system, and the rate-limiting step was identified as the diffusion process in the second stage.