The most challenging issue associated with recycling the sludge generated from printed circuit boards (PCBs) is the separation of copper (Cu) from iron (Fe), using multi-stage leaching, or adding oxidizing and precipitating agents. Herein we investigated simple acid leaching to effectively extract copper and limit iron dissolution. Selective copper leaching was achieved with all the acids studied, including HCl, HNO₃, and H₂SO₄. The lower concentration of acid solutions resulted in a larger difference in leachabilities between Cu and Fe. Among three leachates, the H₂SO₄ solution performed effectively on the selective leaching of Cu and Fe. Adjusting the pulp density to 4% and the H₂SO₄ concentration at ~0.2 M, accomplished ~95% Cu leaching and reduced the Fe extraction to less than 5%. Kinetic studies revealed that Cu leaching followed the ash diffusion-controlled mechanism. Aactivation energy (E_a) of 9.8 kJ/mol was determined for the first 10 min of leaching. Further, leaching up to 60 min corresponded to a mixed control model, increasing the E_a to 20.9 kJ/mol. The change in the control model with regard to the two leaching stages can be attributed to the Cu hydroxide and metal phases present in the original sample. A simple, economically attractive H₂SO₄ acid leaching process was demonstrated, recovering Cu efficiently and selectively from PCBs waste sludge under moderate conditions.

It is important to estimate the energy required in ore processing to select the most affordable and efficient energy system for the integration of renewable resources into the mining industry. In the present work, the energy consumption for the concentrate of tungsten ore in Mongolia was theoretically predicted based on operational variations (particle size and the hardness of the tungsten ore) and different equipment. The energy was in the range from 0.48 to 1.32 kWh/t for the crushing stage, and a cone crusher was more suitable than a jaw crusher due to the particle size of feed material and product. The required energy in the grinding stage was from 6.22 to 11.88 kWh/t using a SAG mill or from 3.04 to 7.39 kWh/t using a ball mill. The further separation by a flotation consumed 4.83 kWh/t or by a shaking table consumed 1.29 kWh/t. The maximum energy consumption per hour for the whole process was estimated to be 2–3 MW, which was better to integrate with a hybrid renewable energy system. The sizing method Power Pinch Analysis was used to estimate the electric supply based on the combination of wind, biomass and solar resources, which was sufficient for the demand from the predicted range of energy.

The metal-containing sludge generated from the printed circuit boards (PCBs) manufacturing has been recycled as a secondary resource of copper (Cu) rather than being treated as a hazardous solid waste. However, it should consider the complexity of processing and using of oxidizing or precipitation agents to dissolve and separate Cu from other impurities, especially iron (Fe). This study has combined the dissolution and separation step in one stage by integrated acid leaching and electrodeposition to simplify the recovery process, while maintaining the high efficiency of separation. The chemistry of acid leaching and electrodeposition of the metals demonstrated that the metals (Cu and Fe) in the sludge sample were dissolved in the H₂SO₄ electrolyte, and Cu could be selectively deposited on the cathode based on the different potential conditions to reduce it on the cathode. The important factors affecting the deposition of Cu were investigated, finding the optimal conditions (current density 15 mA/cm², H₂SO₄ 100 g/L, Cu 20 g/L, at 45 °C, and for 6 h) which could completely recover Cu from the electrolyte in a selective manner. The obtained copper product possessed a high purity of >99% with adequately uniform morphology and an acceptable consumption of energy (1.7 kWh/kg). It is an effective and simple approach to reclaim the value metal copper from the industrial waste in one single stage of integrated extraction and refining.

The traditional roasting technique using sodium salts in vanadium production has been disadvantageous due to the large consumption of energy and the emission of harmful gases. A modified process using molten salt roasting and water leaching to extract vanadium and titanium from domestic titanomagnetite concentrate was investigated. The roasting process was performed under optimal conditions: the weight ratio between the sample and NaOH of 1:1, the temperature of 400 °C, and the experiment time 90 min, and the conversion of vanadium could be maximized to 90%. The optimization of water leaching (at 60 °C for 90 min with a pulp density of 0.05 g/mL) could extract 98% of the vanadium from the roasted products into the solution, leaving titanium and iron remaining in the residue. Further purification of vanadium and titanium using the precipitation/hydrolysis process followed by calcination obtained the final products V₂O₅ and TiO₂ with high purities of 90% and 96%, respectively. A potential approach with modification of the roasting stage using NaOH was proposed, which was not only efficient to selectively extract the value metals from the titanomagnetite but also eco-friendly based on the reduction in energy consumption and emission of harmful gases.