In this work, a numerical simulation study on the mixing characteristics of multiphase flow in an autoclave was carried out using CFD technology. The Eulerian–Eulerian model and discrete phase model (DPM) were employed to investigate the solid holdup, critical suspension speed, nonuniformity of solid suspension, gas holdup distribution, bubble tracks, and residence time during stirring leaching in the autoclave. Experiments validate the accuracy of the numerical model, and the experimental values correspond well with the simulation results. The numerical simulation results show that the solid–liquid mixing is mainly affected by the axial flow, the best agitation speed is 400 rpm, and increasing the speed further cannot make the mixture more homogenous and buildup occurred above the autoclave. The calculated critical suspension speed is 406 rpm, which is slightly lower than that obtained from the empirical formula. The gas phase is mainly concentrated in the vortex area above the blade. When the gas phase is in a completely dispersed state (N = 300 rpm), the average residence time of the bubbles is 5.66 s.

This paper proposes a combined microwave and ultrasonic technique that aims to extract the refractory mineralogical properties of complex zinc ore. This technique consists of two steps: microwave-assisted phase transformation and ultrasonic-assisted complexation leaching. During the microwave-assisted phase transformation step, the refractory zinc phases transform into manageable phases using doping oxidation agents. In the ultrasonic-assisted complexation leaching step, the effect of NTA³ on Zn²⁺ species distribution is explored. The results show that microwave roasting with 20% Na₂O₂ at 600 °C for 15 min adequately transforms ZnS, ZnCO₃ and Zn₂SiO₄ into ZnO and avoids the generation of Zn₂SiO₄. Further, 0.5 mol/L NTA³⁻ (nitrilotriacetic acid) is especially effective as a complex additive for complexes with Zn²⁺ as Zn (NTA)₂⁴⁻. The ultrasonic technique can reduce the diffusion resistance and open the products in the leaching process, improving zinc leaching by 4.7%. The degree of zinc recovered from zinc ore can reach 91.4% when leach is assisted with 225 W ultrasonic force at 80 °C for 75 min. This paper shows great potential for the green extraction of non-traditional zinc-containing resources.

In the process of zinc smelting, when the chloride ion concentration exceeds 100 mg/L, it continuously corrodes the electrode plate and affects the stability of the electrodeposition process. Therefore, the chloride concentration must be reduced below 100 mg/L. Compared with other methods used to control the reactions of Cu(II), the use of the copper slag produced in zinc smelting without other additives does not cause reverse dissolution; to reduce the cost, turn the waste into treasure, and protect the environment, research was carried out on chloride removal by the copper slag via a synergistic valence control process. In this study, the influencing factors, such as the amount of copper slag, the reaction time, and reaction temperature, were systematically investigated. The results showed that the optimum dechlorination conditions were as follows: the copper: copper(II): chloride molar ratio was 6:5:1, the reaction time was 60 min, and the reaction temperature was 20 °C. The chloride ion concentration was decreased from 1.6 g/L to 0.05 g/L, the dechlorination efficiency was 96.875%, and the residual chloride ion concentration was less than 100 mg/L, which provides a basis for industrial use.

The gas-liquid flow and oxygen content in a pressurized leaching stirred tank significantly influence the chemical reaction rates, while the specific dynamics of gas-liquid flow in the sulfuric acid system remain largely unexplored. In this study, a mathematical model of gas-liquid flow within a stirred tank is developed using the Euler-Euler approach, with the turbulence and drag force models being validated against experimental data. Utilizing this validated and reliable model, this study investigates the impacts of the sulfuric acid concentration, baffles, air inlet velocity, and bubble diameter on the flow field and gas holdup in a two-phase system consisting of a sulfuric acid solution and oxygen. The findings indicate that introducing a specific concentration of sulfuric acid decreases the solution velocity and increases the gas holdup within the tank. However, once the sulfuric acid concentration reaches a certain threshold, further increases have a diminished effect on the gas-liquid phases. The installation of baffles enhances the turbulent kinetic energy and increases the gas holdup while only resulting in a minimal 1.2% increase in power consumption. Additionally, the inlet velocity and bubble diameter have a relatively minor impact on the tank’s flow field. However, increasing the inlet velocity significantly boosts the gas holdup, whereas an increase in the bubble diameter marginally reduces it. Furthermore, introducing a sulfuric acid solution into the tank can enhance the gas holdup when the gas inlet velocity is low. Conversely, when the gas inlet velocity is high, the addition of sulfuric acid results in a decrease in the gas holdup. The conclusions from this study contribute to enhancing the mixing effectiveness and oxygen content within the tank, providing a substantial theoretical basis for optimizing the design and operating conditions of pressurized leaching stirred tanks.

The generation of Ge-containing dust (GCD) during Zn hydrometallurgy raises considerable toxicity concerns; however, GCD contains useful metals, such as Zn, Ge, and Pb. The unique characteristics of Ge often result in the formation of specific Ge compounds within GCD, which manifest as either independent insoluble phases or inclusions, which complicates their separation and recovery. To address the challenges associated with the traditional recovery methods, this study proposes a novel process that utilizes SO₂ reduction in conjunction with H₂SO₄ to extract Zn and Ge from GCD. The introduction of SO₂ facilitates the conversion of insoluble materials through reduction reactions. A high SO₂ flow rate enhances its interaction with the solid surface, thereby promoting continuous peeling and improving the reaction efficiency. The key parameters influencing the leaching rate of Zn and Ge, and the toxicity of the resulting reaction residue, include the initial acidity, liquid–solid ratio, duration of SO₂ exposure, reaction temperature, and reaction time. Experimental findings indicate that SO₂-promoted H₂SO₄ leaching outperforms the conventional methods, achieving increases of 3% and 12% in the leaching rates of Zn and Ge, respectively. Furthermore, the concentration of toxic metals in the residue is reduced to suitable levels post-reaction. The resultant Pb residue can be reintegrated into the Pb-recovery process for further utilization. In conclusion, the SO₂-promoted H₂SO₄-leaching method represents a promising and environmentally sustainable approach for the recovery of useful metals from GCD.