Transformation of copper sulfate and catalytic effects of copper sulfur compounds during sludge wet air oxidation

Abstract

Catalytic wet air oxidation (CWAO) is a promising sludge treatment technology, and Cu ions were commonly used as homogeneous catalysts. However, the transformation of Cu ions in CWAO has not been investigated. This study conducted CWAO experiments using CuSO₄ as the catalyst to reveal the change in Cu forms and catalytic performance. The results showed that Cu ions increased the mineralization rate of organic matter by at least 12 % and notably enhanced the degradation of humic acids. During the reactions, Cu ions were first complexed with organic substances and finally became stable CuS/Cu₂S slag with a ratio close to 90 %. However, all the forms of Cu exhibited similar catalytic effects. To check the result further, chalcopyrite, which has an identical mineral composition to the CuS/Cu₂S slag, was used in CWAO to replace CuSO₄. The result verified that chalcopyrite had the same catalytic ability, and at most 88 % of organic matter was mineralized. Therefore, this study revealed the essential characteristics of homogeneous CWAO and found an effective and cheap catalyst without a heavy burden of copper recovery from the effluent. The finding provides a more cost-effective solution for sludge treatment.