Abstract
The solidified landfill disposal of hazardous solid waste such as electroplating sludge in arid/semi-arid areas has potential risks and hazards. In this study, the electrochemical method was used to destroy the structures of metal complexes in electroplating sludge and release metal ions so that the organics were removed by direct mineralization in the anode while the metal was recovered in the cathode. A SnO2/Ti electrode was used as the anode during the electrolysis process. The effect of different current densities (10, 20, 30, 40, 50, 60 A/m2), different pH values (2, 3, 4, 5, 6), and the presence of chloride (0.1 or 0.2 M NaCl) and sulfate (0.1 or 0.2 M Na2SO4) on treatment were investigated. Under the optimal treatment conditions (current density = 50 A/m2, pH = 3), the removal rates of CODCr, TOC, and Ni2+ reached 88.01%, 85.38%, and 97.57%, respectively, with a metal recovery of 97.01%. Further studies showed that active chlorine and active persulfate generated in the presence of chloride and sulfate had less effect on the removal of organics, while hydroxyl radicals played a major role. The dilution of the leachate would be detrimental to electrochemical treatment. The by-products of organic chlorination were produced in low amounts, mainly CHCl3. This method can be used to treat electroplating sludge in various areas to recover valuable metals while removing organic pollutants, complying with the concept of sustainable development. This method provides a new solution for the treatment of metal-containing hazardous solid waste such as electroplating sludge from the perspective of practical application.
Highlights
Electroplating sludge is listed in the National Hazardous Waste List (2021) in the HW17 and HW21 waste categories due to the presence of heavy metals such as Ni, Pb, Cu, and other toxic substances that are classified as hazardous solid wastes
Increasing the current density accelerated the production of the oxidant, and promoted the electron transfer between organic pollutants and the electrode, which improved the oxidation effect
Compared with 50 A/m2, the CODCr removal effect at 60 A/m2 was not significantly increased. This might be attributed to the fact that at higher current density, the anode underwent more side reactions of oxygen evolution with weak oxidation capacity, which competed with the main reaction, while the electrode surface generated various bubbles, reducing the electrode area involved in the reaction [40,41]
Summary
Electroplating sludge is listed in the National Hazardous Waste List (2021) in the HW17 and HW21 waste categories due to the presence of heavy metals such as Ni, Pb, Cu, and other toxic substances that are classified as hazardous solid wastes. Solidified landfill is an important final disposal method for solid wastes (including hazardous wastes). The infiltrating pollutants include a variety of contaminants such as heavy metals, aromatic hydrocarbons, and phenols, which seriously damage the fertility of soil and endanger human health through the food chain. Treating hazardous solid wastes such as electroplating sludge by solidified landfill is potentially harmful, and a method that can address such metal-containing hazardous solid wastes from the source is urgently needed
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