With the increasing depletion of mineral resources and growing environmental pressures, the resource utilization of industrial solid waste has become crucial for sustainable development. Aiming at copper slag, a typical metallurgical solid waste, a phase-controlled oxidation modification method using CaO-MgO as modifier under high temperature was proposed in this study, which realized the efficient separation and recovery of iron and silicon resources. Through the systematic investigation of key parameters including oxidation temperature, basicity, and holding time, combined with characterization techniques such as XRF, XRD, SEM-EDS, and XPS, the phase transformation mechanism during the oxidation modification process was elucidated. The results showed that the basicity determined the presence form of iron and silicon, the temperature regulated the ion diffusion conditions, and the holding time affected the crystalline integrity of (Mg,Fe 2+ )Fe 2 O 4 . Under optimal conditions (oxidation temperature: 1300 °C, basicity: 2.0, holding time: 60 min), the iron element was effectively enriched to (Mg,Fe 2+ )Fe 2 O 4 and silicon element was converted to Ca 2 SiO 4 , forming distinct phase boundaries favorable for separation. After magnetic separation, the iron recovery rate was 85.83%, the total iron of the concentrate was 46.18%, and the content of Si, P, and S was reduced. The concentrate is suitable for direct recycling as ironmaking raw material in steel plants, and the Ca 2 SiO 4 -rich tailings can be utilized as construction materials to achieve synergistic "waste reduction-resource recovery" treatment of copper slag. This study provides new insights for high value utilization of metallurgical wastes, while offering practical solutions to alleviate resource pressures and environmental risks.
With the rise in installed capacity of photovoltaic systems, the growing generation of waste crystalline silicon solar cells has become an important issue. Silicon is one of the most valuable materials in cells; recyclable treatments with green techniques must be developed for it. A new strategy for the recovery of silicon wafers has been proposed using choline chloride and oxalic acid-based deep eutectic solvent–hydrogen peroxide (DES–H2O2) aqueous solution systems. With the synergistic effect of DES and H2O2, the leaching efficiency of silver from cells reached 89.19%, along with complete aluminum leaching. Compared with only the DES control, the leaching efficiency of silver was enhanced by as high as 97.45%. Subsequently, reusable silicon wafers were obtained with 97.47 wt% surface purity, and 99.41% of silicon retention rate (169 μm) after removing Si3N4. Favorable results were mainly attributed to the higher concentration of H+ due to a boost by oxalic acid-based DES compared to concentrations in an oxalic acid aqueous solution, which could provide stronger oxidizing power, and besides, lower oxidation activation energy for silver in H2O2. In this work, high-purity silicon wafers were obtained with high leaching efficiency of metals in a short time (2 h) at a low temperature (80 °C) without using strong acids; among solvents, the DES showed great potential for reuse. It is concluded that the DES–H2O2 aqueous solution system provides an environmentally friendly process for green and nearly lossless recovery of silicon wafers from silicon solar cells.
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