Optimization of elemental recovery from electronic wastes using a mild oxidizer

A combined and sustainable approach and a novel mechanism for recovering Bi, Au and Ag from high-chloride leachate of waste printed circuit board smelting ash

High-chloride leachate is a solution rich in precious metals that is produced in chloride hydrometallurgy. It has high levels of both rare and precious metals and hazardous chloride ions, and resource recovery from this solution and its safe disposal have become key objectives in the field of hydrometallurgy. In this study, a sustainable process involving "ultrasound-assisted precipitation-Pb powder cementation" was proposed for the stepwise separation and high-value utilization of Bi, Au and Ag obtained from high-chloride leachate. Targeted separation and conversion of Bi were achieved by precipitation-re-acid hydrolysis-ultrasonication-assisted coprecipitation-centrifugal purification. Under the optimal process conditions, the removal rate of Bi reached 99.52%, while the loss rates of Au and Ag were only 4.63% and 8.72%, respectively. Single-factor experiments of Au and Ag cementation by Pb powder showed that the recovery rates of precious metals could be improved by increasing the temperature, raising the solution pH, and applying mechanical force and ultrasonication. A possible reaction mechanism for Au and Ag cementation with Pb powder was proposed based on macroscopic kinetic analysis and microscopic mineral characterization. This work provides technical support and a theoretical basis for the separation and enrichment of rare and precious metals in chloride hydrometallurgy.

Geochemical characteristics and migration patterns of rare earth elements in coal mining subsidence lakes under the influence of multiple factors

Mining activities cause surface subsidence and the formation of subsidence lakes, which dynamically change with the continuous coal mining activities. Under the combined influence of various human activities such as agriculture, aquaculture, and floating photovoltaic (FPV), the lake environment undergoes continuous changes, thereby altering the geochemical characteristics of rare earth elements (REEs) in the sediment. This study focused on the subsidence lakes in the Huainan coalfield in eastern China to examine the REEs content in the sediment, elucidated the temporal variations and geochemical characteristics of REEs distribution, explored the main controlling factors of REEs in the sediment, and revealed the migration and transformation behavior of REEs during dynamic subsidence processes. The study revealed that the migration pattern of REEs in the sediment was closely related to the duration of subsidence. The average content of REEs in lake sediments with subsidence duration <5 years increased from 219 μg·g-1 to 248 μg·g-1 compared to the soil, showing an enrichment model primarily driven by rainwater runoff, groundwater input retention, and mineral dissolution. With further subsidence, the processes of reduction dissolution of Fe-Mn oxides/hydroxides, organic colloid adsorption, and hydraulic disturbance gradually replaced the aforementioned enrichment behavior as the main migration pathways, resulting in a decrease in the average REEs content in the sediment to 179 μg·g-1 for subsidence durations exceeding 10 years. There was no strong correlation between REEs fractionation and subsidence duration. Artificial activities, such as FPV, are important factors causing Cerium and Erbium anomalies in some subsidence lake sediments. This study was not only of significant importance for understanding the migration, distribution, and environmental behavior of pollutants in aquatic environments under the interference of human activities but also provided a solid theoretical foundation for the future management of coal mining subsidence lakes.