Baozhong Ma

Recovery of iron from copper tailings via low-temperature direct reduction and magnetic separation: process optimization and mineralogical study

Currently, the majority of copper tailings are not effectively developed. Worldwide, large amounts of copper tailings generated from copper production are continuously dumped, posing a potential environmental threat. Herein, the recovery of iron from copper tailings via low-temperature direct reduction and magnetic separation was conducted; process optimization was carried out, and the corresponding mineralogy was investigated. The reduction time, reduction temperature, reducing agent (coal), calcium chloride additive, grinding time, and magnetic field intensity were examined for process optimization. Mineralogical analyses of the sample, reduced pellets, and magnetic concentrate under various conditions were performed by X-ray diffraction, optical microscopy, and scanning electron microscopy–energy-dispersive X-ray spectrometry to elucidate the iron reduction and growth mechanisms. The results indicated that the optimum parameters of iron recovery include a reduction temperature of 1150°C, a reduction time of 120 min, a coal dosage of 25%, a calcium chloride dosage of 2.5%, a magnetic field intensity of 100 mT, and a grinding time of 1 min. Under these conditions, the iron grade in the magnetic concentrate was greater than 90%, with an iron recovery ratio greater than 95%.

A simple and effective process for recycling zinc-rich paint residue

Continuous growth of the shipping industry and infrastructure has consumed large amounts of zinc-rich paint (ZP) for the protection of steel structures against corrosion. Consequently, a growing amount of waste zinc-rich paint residue (ZPR) is being generated from anticorrosion spraying. ZPR is classified as hazardous waste in most industrialized countries, but it contains considerable amounts of organic compounds with high calorific value and zinc species that can potentially be recycled. Most of the ZPR generated is not properly treated, and this study presents a simple and efficient process for recycling ZPR. The zinc in ZPR was recovered via a hydrometallurgical route through oxidative alkaline leaching and electrowinning. The results show that the leaching ratio of zinc was greater than 98% at 95 °C, NaOH concentration of 250 g/L, liquid/solid ratio of 10:1, air flow rate of 0.6 L/min, and leaching time of 1.5 h. The appropriate minimum concentration of zinc for electrowinning was determined to be 10 g/L. Adding 50 mg/L of gelatin to the electrolyte significantly refined the grain and the optimum current density was determined to be 200 A/m2. Fern shaped cathode zinc powders with a purity of 99.8% were obtained. A high current efficiency (92.7%) was also obtained with energy consumption of 2330.3 kWh per ton of zinc produced. The composition and thermal analysis of the leaching residue suggest that co-processing in cement kiln may be suitable for disposing the leaching residue of ZPR. The experimental results show that the proposed process is promising for ZPR recycling.

An Innovative Oxygen-Enriched Flash Smelting Technology for Lead Smelting and Its Industrial Application

This paper introduces an oxygen-enriched flash smelting (OFS) process for lead smelting. Compared with the bath smelting, OFS has many advantages, including wide adaptability, high yield, low energy consumption, little uncontrolled emission, and considerable metals recoveries. Test results showed that increasing CaO could effectively reduce lead content in the slag, and the appropriate mass ratios of FeO-to-SiO2 and CaO-to-SiO2 were 1.15 and 0.6, respectively. The testing and commissioning indicated when OFS was used to treat material containing 30% of lead, the residual lead in slag could decrease to 4–10%. Furthermore, after zinc volatilization using an ore-smelting electric furnace, contents of lead, zinc, silver, gold and copper in the final slag were below 2%, 2%, 6 g/L, 0.1 g/L and 1%, respectively. The total recoveries of lead, zinc, silver, gold, copper and sulfur were above 98, 90, 99.5, 99.5, 85 and 98%, respectively.

Deep cleaning of a metallurgical zinc leaching residue and recovery of valuable metals

Huge quantities of zinc leaching residues (ZLRs) generated from zinc production are dumped continuously around the world and pose a potential environmental threat because of their considerable amounts of entrained heavy metals (mainly lead). Most ZLRs have not been properly treated and the valuable metals in them have not yet been effectively recovered. Herein, the deep cleaning of a ZLR and recovery of valuable metals via a hydrometallurgical route were investigated. The cleaning process consists of two essential stages: acid leaching followed by calcium chloride leaching. The optimum conditions for extracting zinc, copper, and indium by acid leaching were a sulfuric acid concentration of 200 g·L−1, a liquid/solid ratio of 4:1 (mL/g), a leaching time of 2 h, and a temperature of 90°C. For lead and silver extractions, the optimum conditions were a calcium chloride concentration of 400 g·L−1, a pH value of 1.0, a leaching time of 1 h, and a temperature of 30°C. After calcium chloride leaching, silver and lead were extracted out and the lead was finally recovered as electrolytic lead by electrowinning. The anglesite phase, which poses the greatest potential environmental hazard, was removed from the ZLR after deep cleaning, thus reducing the cost of environmental management of ZLRs. The treatment of chlorine and spent electrolyte generated in the process was discussed.