A new mechanism and kinetic analysis for the efficient conversion of inorganic bromide in waste printed circuit board smelting ash via traditional sulfated roasting

The waste printed circuit board smelting ash (WPCB-SA) produced in the waste printed circuit board smelting process is a hazardous material that not only contains valuable metals, but also contains a large amount of toxic and harmful inorganic bromides. The utilization of metals has received considerable attention in previous studies, but the recovery of hazardous bromides requires further study. In this article, a new idea of converting inorganic bromine in WPCB-SA by traditional sulfated roasting is proposed. Debromination kinetics under simulated experimental conditions are discussed, and kinetic equations are established. The kinetic results show that during low-temperature sulfated roasting, the conversion of Br in CuBr and PbBr2 conforms to the chemical reaction diffusion model and diffusion control the product layer model, respectively. A possible reaction mechanism is also proposed. Our research shows that the conversion of Br in CuBr is divided into three processes: covalent bond decomposition, hydrogen ion form acid, copper ion form salt, and HBr oxidation conversion, whereas the conversion of Br in PbBr2 is divided into two processes: sulfuric acid ionization, lead ion form salt and HBr oxidation conversion. This work provides the theoretical basis for the improvement and application of inorganic bromide recovery technology in WPCB-SA

A Unified Elastoplastic Model of Unsaturated Soils Considering Capillary Hysteresis

Unlike its saturated counterparts, the mechanical behavior of an unsaturated soil depends not only upon its stress history but also upon its hydraulic history. In this paper, a soil-water characteristic relationship which is capable of describing the effect of capillary hysteresis is introduced to characterize the influence of hydraulic history on the skeletal deformation. The capillary hysteresis is viewed as a phenomenon associated with the internal structural rearrangements in unsaturated soils, which can be characterized by using a set of internal state variables. It is shown that both capillary hysteresis and plastic deformation can be consistently addressed in a unified theoretical framework. Within this context, a constitutive model of unsaturated soils is developed by generalizing the modified Cam-Clay model. A hardening function is introduced, in which both the matric suction and the degree of saturation are explicitly included as hardening variables, so that the effect of hydraulic history on the mechanical response can be properly addressed. The proposed model is capable of capturing the main features of the unsaturated soil behavior. The new model has a hierarchical structure, and, depending upon application, it can describe the stress-strain relation and the soil-water characteristics in a coupled or uncoupled manner

An integrated and sustainable hydrometallurgical process for enrichment of precious metals and selective separation of copper, zinc, and lead from a roasted sand

This study developed an efficient and sustainable hydrometallurgical process for the enrichment of gold and silver and the stepwise separation of copper, zinc, and lead from sulfated roasted sand of waste printed circuit board smelting ash. Selective separation of copper and zinc was achieved by water leaching, and silver dispersion was reduced by controlling the amount of NaCl added during the leaching process. The results of the water leaching showed that the copper and zinc leaching rates were 99.85% and 99.47%, respectively, whereas the loss rate of silver was 2.1% with optimal leaching parameters. The high-chloride-complex method was used to study the efficient conversion and separation of lead from the leached residue, and the leaching kinetics and conversion mechanism of lead were discussed. The results showed that under the optimal conditions, the leaching rate of lead was 99.79%. Leaching kinetics analysis showed that lead leaching in the high - chlorine system was controlled by a chemical reaction; the apparent activation energy was 53.63 kJ/mol. After the leaching of copper, zinc, and lead, 1.66% Ag and 213 g/t Au were enriched in the leached residue; and the precious metal enrichment goal was reached. The chlorinated leachate showed good recycling performance, and a lead leaching rate of 97.93% was obtained after three circulations. After cooling, crystallization, and purification, lead chloride with a purity of 99.89% and high economic and industrial value was obtained from the lead-rich leachate. This process has favorable and sustainable industrial application prospects