Application of copper tailings combined with persulfate for better removing methyl orange from wastewater

In this paper, wasted copper tailings (CT) were used to activate persulfate (PS) to degrade azo dye methyl orange (MO). The results show that a large amount of FeS₂ contained in CT can slowly release Fe²⁺ in the aqueous solution to activate PS to generate reactive oxygen species to degrade MO. When the dosage of CT and PS was 2 g/L and 3 mM respectively, the MO degradation efficiency of 20 mg/L in the CT/PS system was 96.52% within 60 min. At the same time, it is found that CT has a certain adsorption capacity for MO, and the intra-particle diffusion model can well describe the adsorption process of MO by CT. The effects of related reaction parameters (CT dosage, PS dosage, initial MO concentration and solution pH) on MO degradation in CT/PS system were investigated. Compared with the direct addition of an equal amount of Fe²⁺ as in the CT/PS system, for homogeneous activated PS to degrade MO (Fe²⁺/PS), the results showed that the degradation efficiency of Fe²⁺/PS system for MO was lower than that of CT/PS system due to excessive Fe²⁺ consumption of SO₄ ^·-. By comparing the Fe²⁺ and Fe³⁺ concentrations in the two systems, it was found that the CT/PS system could maintain a low Fe²⁺ concentration during the reaction process, and the Fe²⁺ released by CT could be used by PS to degrade MO more efficiently. The free radical scavenging experiments showed that the reactive oxygen species in the CT/PS system was mainly SO₄ ^·-. This study not only proposed a new CT utilization approach, but also solved the problem of reduced degradation efficiency of organic pollutants caused by excessive Fe²⁺ in the Fenton-like reaction.