Sustainable reuse of nickel converter slag as a heterogeneous electro-fenton catalyst for treating textile dyeing wastewater: Activity, mechanism and stability assessment

Abstract

The high production and improper disposal of nickel converter slag (NCS) are raising serious concerns about its environmental impact, owing to the waste of resources and the foregone contribution to air, soil and groundwater pollution. This work uncovered that NCS could be reused as a superior catalyst for the treatment of textile dyeing wastewater by the heterogeneous electro-Fenton (hetero-EF) process. The NCS-laterite porous ceramsite (NLPC) catalyst showed the highest activity when the ratio of NCS to laterite was 3:2 and calcined at 900 °C. The methylene blue (MB) removal rate and chemical oxygen demand (COD) removal rate were 98.64% and 87.84%, respectively, after 30 min reaction under optimal operating parameters (100 g L−1 NLPC, 4 V of cell voltage and initial pH 3.0). Compared with the electro-Fenton (EF) system without NLPC catalyst, the degradation rate constant was increased by 223.9% (0.0452–1.464 min−1) and the energy consumption was reduced by 65.84% (2.02–0.69 kWh m−3). After six cycles, the MB removal rate only decreased by 5.35%, and the NLPC mass loss rate was 2.04%. Synergies between Co, Ni, Fe and Cu species to promote reactive oxygen species (ROS) generation were the predominant catalytic mechanism. Two possible pathways of MB degradation were deduced. In addition, the NLPC catalyst also showed excellent effects in different wastewater treatments. This work demonstrated an upgrade strategy for cleaner production of non-ferrous metallurgical by-products.