Zinc Leaching Residue Research Articles

Multi-objective optimization of clean utilization for zinc leaching residues by rotary kiln using neural network coupled modeling

Aiming at the complicated problems of green and high efficiency recovery for metal zinc in the process of resource utilization for zinc leaching residues by rotary kiln，it is crucial to optimize the zinc volatilization efficiency (VEZn) with minimizing the emission intensity of CO2 (EICO2) and kiln slag (EIks). A quantitative regulation approach of key parameters coupled with neural network simulations and multi-objective optimization algorithm is proposed in this study. The index prediction models of VEZn, EICO2 and EIks have been established through the back propagation neural network (BP-NNP) and its two improved algorithm, respectively. Through training by long time series of actual operating data, the results showed that the BP-NNP model improved by particle swarm optimization (PSO) could more accurately describe the complex nonlinear mapping relationship between wide fluctuating parameters and VEZn, EICO2 and EIks, and the mean absolute percentage errors (MAPE) could be reduced to 6.00 × 10−3, 8.52 × 10−3 and 6.08 × 10−2, respectively. Furthermore, the developed index prediction model was incorporated into cuckoo search (CS) and non-dominated sorting genetic algorithm-II (NSGA-Ⅱ) that performed Pareto dominance-based multi-objective optimization. In experiments conducted, the significant advantages of NSGA-Ⅱ were revealed that the corresponding Pareto-optimal solutions with VEZn distribution between 93.32% and 94.52% were obtained. Meanwhile, EICO2 and EIks could be reduced to 1.525 t/t and 0.317 t/t, respectively. And comprehensive benefits by Pareto-optimal solutions were analyzed to provide various representative countermeasures to assist decision-makers. New insights gained herein could enable clean, efficient and low-carbon process regulations for recycling of solid waste in zinc hydrometallurgy industry.

Efficient and clean treatment of indium-bearing zinc ferrite: A new approach using a water-regulated deep eutectic solvent

Indium, a strategic key metal, is mainly recovered from zinc leaching residue. However, a challenging problem in the treatment of zinc leaching residue is how to efficiently and cleanly treat the poorly soluble phase, the indium-bearing zinc ferrite (IBZF). Here, we propose a novel strategy for the selective extraction of indium, zinc and iron from IBZF. By introducing water to regulate the coordination environment of a choline chloride-anhydrous oxalic acid based deep eutectic solvent (ChCl-Oxa based DES), efficient leaching and deep separation of indium, zinc and iron were achieved. Water, acting as both co-solvent and diluent, played a critical role in the whole process. The addition of a little water reduces the viscosity of the DES, thereby improving the leaching of indium, zinc and iron. Under specific leaching conditions (leaching temperature of 90 °C, liquid/solid ratio of 20:1 ml/g, molar ratio of ChCl:Oxa = 1:1, molar ratio of DES:H2O = 1:3 and reaction time of 3.5 h), the leaching efficiencies of indium, zinc and iron were 96.27 %, 95.55 % and 96.33 %, respectively. The subsequent addition of large amounts of water dilutes and dissociates the structure of the DES, facilitating the stepwise precipitation and deep separation of metal ions. The precipitation efficiency of zinc and iron reached 93.06 % and 98.07 %, respectively. Residual indium ions in the solution were effectively adsorbed by activated carbon, with a recovery efficiency of 75.7 % after five cycles of adsorption. The solution separated from the metal ions was well regenerated by evaporation and addition of Oxa. Our work represents a novel approach for the recycling and clean utilization of zinc leaching residue. And the regulation of the coordination environment of metal ions in DES is proved to have great potential in metal recycling.

Ultrasound enhanced in-situ chemical oxidation for leaching Ag from zinc leaching residue and response surface optimization

Zinc leaching residue is the important source of silver due to its high silver content. The traditional leaching process of silver from zinc leaching residue has shortcomings such as higher acid or ammonium concentration, resulting in strong corrosion and serious pollution. Here developed an acid-free in-situ chemical oxidation technology using ultrasound enhanced persulfate to leach Ag from zinc leaching residue. The effects of leaching temperature, leaching time, sodium persulfate concentration, liquid–solid ratio, and ultrasonic power on the leaching efficiency of Ag were investigated. Under the optimal conditions, the maximum leaching efficiency of silver reaches 91.09 %. The leaching efficiency is higher than that without ultrasound. Kinetic analysis revealed that the activation energy of ultrasound enhanced leaching process is 65.23 kJ/mol, and the leaching process is controlled by chemical reactions. The ultrasound enhanced leaching process can reduce the activation energy of the reaction. Response surface methodology was employed to identify significant factors influencing the efficiency of Ag, which were found that sodium persulfate concentration and ultrasonic power were the most important factors. In addition, the developed method has a certain leaching effect on transition metals and is a potential solution to recover transition metals from secondary resources.

A novel leaching process of zinc ferrite and its application in the treatment of zinc leaching residue

Zinc ferrite is a refractory phase generated in the pyrometallurgical process of zinc and steel production. Much energy is invested in the decomposition of zinc ferrite to recycle zinc since zinc ferrite is difficult to leach. In this work, a novel leaching process targeted at decomposition of zinc ferrite was proposed to save energy and improve metal recovery efficiency. The key of this novel leaching process was the use of copper powder as the reductant. Leaching of zinc ferrite in the presence of copper powder was investigated. The extraction of zinc was 100% when molar ratio of copper to zinc ferrite was 1.5 while the extraction of zinc was only 19.3% without copper. Effects of leaching temperature, acid concentration, the ratio of liquid to solid and reaction time were studied. Under the conditions: 60 °C, ≥ 70 g·L1 H2SO4, the ratio of liquid to solid ≥ 25 mL/g and the molar ratio of copper to zinc ferrite ≥ 1.5 at the open system, the synthetic zinc ferrite was dissolved completely within 60 min. Besides, the zinc ferrite-bearing zinc leaching residue from a roast-leach-electrowin plant was analyzed and leached under the optimal conditions. It was found that most of zinc ferrite in the zinc leaching residue was removed, remaining unreacted lead sulphate in the leached residue. The leaching efficiency of zinc in zinc leaching residue reached 94.2%. The results suggest that copper powder enhanced facile and efficient zinc extraction from zinc ferrite without concentrated acid, high temperature, long reaction time and specific investment. The recyclability of copper and its intrinsic commodity value showed the potential application in industrial zinc and iron containing wastes.

Application of Oxygen-enriched Side-blowing Technology in Treating Zinc Leaching Residue in China

Zinc hydrometallurgy is the main process of zinc smelting in the world. The leaching residue produced by different hydrometallurgical processes have different components, but they contain valuable metals such as zinc, silver, gold, indium and germanium, and heavy metals such as lead, cadmium and arsenic. In China, leaching residue is defined as hazardous waste, which requires harmless treatment and recovery of valuable metals. At present, China’s main zinc leaching residue treatment technologies include Welz kiln, fuming furnace and Top-submerged lance Smelting furnace. These technologies have been applied for many years and are mature and reliable, but they need further improvement in energy conservation and environmental protection. In recent years, with the continuous progress of China’s smelting technology, the oxygen-enriched side-blowing technology has been successfully applied to the treatment of zinc leaching residue, mainly including the Side-submerged combustion smelting technology of China ENFI and the Vanukov side-blowing technology. At present, the above two side blowing technologies have been put into industrial practice in many zinc smelters in China, which are characterized by low energy consumption, high recovery rate of valuable metals and high sulfur recovery rate. This paper introduces the application of the above two side blowing technologies in China’s zinc smelters, and compares them from furnace structure, production operation, and technical indicators. Oxygen-enriched side-blowing technology will become the mainstream treatment process of zinc residue in China and even in the world in the future.

Synthesis of polyacrylate-divinylbenzene hydroxamic resins and its gallium adsorption performance in sulfuric acid solution

In this study, the adsorption behavior of gallium ions on a synthesized hydroxamic acid resin from sulfuric acid solution was investigated, aiming to recover Ga directly from pressure leaching solution in zinc hydrometallurgical plant. Hydroxamic acid chelating resin (HA-PDR) was prepared by introducing hydroxamic acid groups into the pre-made polyacrylate resin (PDR) with methyl ester group through hydroxylamine reaction. Polyacrylate-divinylbenzene hydroxamic resins with a nitrogen content of up to 3.85 % were obtained at a divinylbenzene (DVB) content of 13 % and an optimal raw material ratio of NH2OH·HCl: NaOH: −CH3 = 4:4.5:1 (molar ratio). The obtained materials was characterized using FTIR, XPS and SEM to verify the successful introduction of hydroxamic acid groups. The results of adsorption experiments showed that the adsorption capacity of 27.65 mg/g could be obtained with a chemical, multilayered, and heterogeneous adsorption process, and film diffusion and intra-particle diffusion rate controlled mainly the adsorption efficiency. It has been proven that polyacrylate-divinylbenzene hydroxamic resins has extremely high adsorption selectivity for gallium in sulfuric acid solution, and the desorption effect is obvious, which can be applied promisingly in the industrial development of gallium extraction technology from zinc leaching residue in sulfuric acid system.

A decade’s Production Practice of JCC Kivcet Technique

This article provides an overview of the Kivcet technique in Jiangxi Copper Corporation, reviews the production status and problems encountered in the past decade, introduces its technological advantages and prospect. It is believed that the Kivcet process has advantages such as strong adaptability to raw materials, stable operation, high metal recovery rate, and low cost of zinc leaching residue treatment, which is the vitality of lead-zinc smelting enterprises in the future.

Parameter relationship and product characteristics analysis of heavy-metal hazardous wastes vitrification under the combination of data science and experiment

Heavy-metal hazardous wastes (HMHW) have a large emission, high toxicity and strong resource properties. Its proper disposal and resource utilization is a key challenge. High-temperature melt vitrification technology is an effective solution to realize the detoxification and resource utilization of HMHW. This paper summarizes and analyzes the control parameters of the existing vitrification treatment of HMHW. The phase transformation process of temperature, slag content, and CAS ratio (CaO-Al2O3-SiO2) in the vitrification treatment of zinc leaching residue (ZLR) was investigated around the vitreous content. The common evolution characteristics of the formed vitrification products in infrared spectrum, UV–vis diffuse reflection spectrum, and microstructures were revealed. The idea of using the maximum UV–vis absorption intensity to qualitatively determine the vitreous content of the products is proposed. Moreover, the correlation between experimental parameters and vitreous content was quantified by combining the data science method, and the mapping of the whole process of ZLR vitrification treatment was constructed. This work provides reliable parameter guidance and method induction for the vitrification treatment of HMHW, especially for wastes with less glassy matrix such as Ca and Si.

Characterization of glass-ceramics developed from zinc leaching residue by sintering method

Zinc leaching residue is the waste residue produced by the wet zinc extraction process, which cannot be effectively utilized due to its complex composition and the presence of toxic heavy metals. At this stage, a large amount of residue is piled up in the tailing storage, there is a waste of resources and the risk of environmental pollution. This paper introduced a study on the preparation of glass-ceramic in building materials from zinc leaching residue by the sintering method, using silica sand and albite as additives. It was found that the glass-ceramics prepared with zinc leaching residue incorporation of 70–75 % and sintering temperature in the range of 900–1000 °C exhibited excellent mechanical properties and stable chemical properties. The zinc leaching residue content and the sintering temperature together controlled the crystallization process and influenced the properties of the glass-ceramic. Increasing the zinc leaching residue content caused an increase in the content of non-bridging oxygen bonds in the glass-ceramic, which led to an increase in the degree of polymerization of the matrix and a decrease in the activation energy of the crystallization, which promoted the crystallization process. Higher temperatures provided more energy for the crystal crystallization reaction and facilitated the process. The glass-ceramics showed good solidification of heavy metals and compliance with the requirements for various heavy metals in the toxicity leaching test. The glass-ceramic made from zinc leaching residue eliminated the risk of heavy metals contamination and was a green, harmless, high-performance material that can be used in a wide range of fields.

Biomass as a clean reductant for recovery of zinc from zinc leaching residue

Detoxification and utilization of zinc leaching residue (ZLR) is a critical urgent problem for the zinc metallurgical industry. Traditional roasting methods relying on fossil fuels as reducing agents not only increase the operating cost but also contribute to environmental pollution. This work investigates the effectiveness of using biomass as the reducing agent for decomposing zinc ferrite in the process of ZLR roasting. Analysis methods including XRD, TG-DTG-DSC, and SEM-EDS are used to analyze the pyrolysis of biomass and the phase transformation and microstructural evolution of ZLR. The mechanism that biomass pyrolysis gas promotes the reduction of zinc ferrite in ZLR also is elucidated. The reduction rate of zinc ferrite can reach 43.87% under optimal reduction conditions when pine powder is used as the reducing agent. These optimal conditions include a reduction temperature of 750 °C, a biomass addition ratio of 0.75, and a reduction time of 90 min. It's believed that the reduction process mainly proceeds in the path of ZnFe2O4→Fe3O4→FeO→Fe. By using acid leaching, the extraction of zinc and iron from the reduction roast achieved 89.62% and 58.90%, respectively. During the biomass reduction process, loosely structured with abundant microcracks are obtained probably due to the reaction between the reducing gas and zinc ferrite particles. This study offers precious insights into the utilization of biomass for reductive roasting of ZLR with potential energy conservation and emission reduction.

Migration behavior of germanium and its related elements in zinc hydrometallurgy process

Lead-zinc sulfide ore is one of the raw materials for the recovery of strategic germanium resources. Due to the complexity of its mineralization and the diversity of elements, the occurrence and migration of germanium and its related elements in the process of zinc hydrometallurgy is still a mystery. This leads to the recovery efficiency of germanium is always in a disappointing state, which seriously reduces the economic benefits and resource recovery rate in the process of germanium recovery, and limits the development of some cutting-edge industries. Therefore, in view of the above problems, based on the properties of germanium compounds in lead–zinc sulfide minerals, this study analyzed the occurrence state and quantity of germanium in the products of each stage in the process of zinc hydrometallurgy by ICP, XRD, FT-IR, SEM, XPS, Raman spectrum and TG, so as to reveal the reaction behavior and migration law of germanium compounds in the process of zinc hydrometallurgy. The results indicate show that the two roasting will lead to the mutual transformation of GeO2 crystal form between soluble and insoluble, especially in the process of reduction and volatilization of zinc leaching residue. The phenomenon of soluble GeO2 to insoluble GeO2 is particularly significant, and the germanium-containing silicate cannot be reacted in the whole process. In addition, zinc blende, zinc ferrite, tin dioxide and other substances that exhibit isomorphism with germanium compounds will carry germanium into lead slag due to their low solubility. Finally, in view of the problems existing in the current germanium recovery process, positive solutions are proposed to introduce green additives in the two roasting stages to improve the phase of germanium, and to add oxidants or reducing agents in the leaching stage.

Study on glass-ceramic prepared by zinc leaching residue and solidification mechanism of heavy metals

Zinc leaching residue is a hazardous solid waste with difficult treatment, high hazard and high yield, and it is a great challenge to treat it efficiently, harmlessly and economically among the various methods available. This paper introduced a micro-crystallization method to process zinc leaching residue into glass-ceramics with excellent performance and high value. The heavy metals in the raw material were well solidified in the glass-ceramics, eliminating the high hazard of heavy metals and other components. The bending strength, compressive strength, and Vickers hardness of the glass-ceramics prepared at the sintering temperature of 950 °C were 69.2 MPa, 434.3 MPa, and 6.66 GPa, respectively, while the water absorption, density, and acid and alkali corrosion resistance were excellent. The relationship between the microstructure and properties of glass-ceramics was investigated using traditional analytical techniques such as XRD, Raman, and SEM, and the mechanism of solidification of heavy metals Pb, Zn and Mn in glass ceramics were innovatively researched by the modified BCR sequential leaching test and XPS analysis. Anorthite and diopside ferrian were the two main crystalline phases in glass-ceramics. The sintering temperature affected the formation and growth of crystals, and determined the crystal size and crystallization rate, thus affecting the properties of glass-ceramics. Part of the heavy metal was solidified in the amorphous phase in the glass-ceramic, and the other major part entered the crystal as an impurity substitution to form a solid solution at a specific location. The zinc leaching residue based glass-ceramic had been studied, which was pioneering and with excellent performance and environmental safety. Thus, the safe and economical treatment of these hazardous wastes promotes the clean, green and efficient development of related industries.

Microwave drying method investigation for the process and kinetics of drying characteristics of zinc-leaching residue.

Due to the high moisture content in the zinc-leaching residue, it is easy to cause safety problems when directly entering the kiln. Microwave drying can minimize particle agglomeration and promote cracks on the mineral surface, which benefits the subsequent recovery and smelting of zinc-leaching residue. The results showed that increasing microwave power and particle size range could improve the maximum drying rate and reduce the drying time. The maximum drying rate of 20g zinc-leaching slag with a microwave power of 700 W, a particle size of 1-10mm, and a moisture content of 20% can be higher than 0.365%/s and reach complete drying within 120s. The drying results were fitted and statistically analyzed using nine common kinetic models of drying, the surface diffusion coefficient changes were further analyzed at four levels, and the reaction activation energy (Ea) was calculated. According to Fick's second law, when the average particle size increased from 0.044 to 5.5mm, the surface diffusion coefficient increased from 6.2559 × 10-9 to 3.8604 × 10-6 m2/s, which showed that the effect of particle size change on microwave drying process was significant. The Ea of the drying reaction was 18.1169kJ/mol. This method provides an idea for efficiently treating secondary resources containing valuable metals.

Processing of a Zinc Leach Residue by a Non-Fossil Reductant.

The suitability of a non-fossil reductant in high-temperature treatment of a zinc leach residue was studied in laboratory-scale experiments. The pyrometallurgical experiments carried out at temperatures of 1200-1350 °C consisted of melting the residue under an oxidizing atmosphere to produce an intermediate, desulfurized slag, which was further cleaned of metals such as Zn, Pb, Cu, and Ag, using renewable biochar as a reductant. The aim was to recover valuable metals and produce a clean, stable slag for use as construction material, for example. The first experiments indicated that biochar is a viable alternative to fossil-based metallurgical coke. The capabilities of biochar as a reductant were studied in more detail after optimizing the processing temperature at 1300 °C and modifying the experimental arrangement by adding rapid quenching of the sample (to a solid state in less than 5 s) to the procedure. Modifying the slag viscosity by adding 5-10 wt % MgO was found to enhance the slag cleaning significantly. With an addition of 10 wt % MgO, the target Zn concentration in slag (Zn < 1 wt %) was reached after as little as 10 min of reduction, and the Pb concentration was also decreased relatively close to the target value (Pb < 0.03 wt %). With an addition of 0-5 wt % MgO, the target Zn and Pb levels were not reached within 10 min, but with longer treatment times of 30-60 min, 5 wt % of MgO was enough to decrease the Zn content in slag sufficiently. The lowest Pb concentration achieved with an addition of 5 wt % MgO was 0.09 wt % after a 60 min reduction time.

Reductive leaching kinetics of indium and further selective separation by fraction precipitation

Reductive leaching of high-iron bearing zinc leaching residue (HIZLR) by zinc sulfide concentrate to extract indium and its further selective separation from the leachate were studied. The results indicated that over 95% of indium extraction was achieved at particle sizes of 74−105 μm, reaction temperature of 90 °C, leaching time of 300 min and sulfuric acid concentration of 1.4 mol/L. The leaching kinetics was analyzed by the shrinking core model, and the leaching data from various experimental conditions indicated that the reactions were controlled by the diffusion through the solid product layer with an activation energy of 17.96 kJ/mol. The order of the reaction with respect to the sulfuric acid concentration was determined to be 2.41. Over 99% of copper and arsenic were coprecipitated in the cementation of copper with iron powder. More than 98% of indium was selectively separated from zinc sulfate solution with high ferrous ion content, and the indium-rich precipitate, which had an indium content of approximately 2.4%, could be further treated by the acid leaching−solvent extraction−electrowinning process to produce pure indium.

An innovation technology for recovering silver and valuable metals from hazardous zinc leaching residue through direct reduction

Zinc leaching residue (ZLR) is a hazardous solid waste with complex phase composition, comprising high content of valuable metals, and sulfur. The extraction of silver is the key to harmless utilization of ZLR. In this paper, a short-flowsheet comprehensive recycling valuable metals method by direct reduction was proposed. During reduction, lead and zinc compounds were reduced to metallic state, which were volatilized and recovered in gas phase. Moreover, metallic iron in reduction product was recovered by magnetic separation. Silver was enriched in FeS phase, and it was beneficiated by flotation with hydrophobic FeS as carrier. Under the optimized conditions, silver concentrate with silver content and recovery of 601.43 g/t and 83.41 %, respectively; iron powder with iron content of 96.39 %; and lead and zinc volatilization rate of 78.65 % and 97.64 %, respectively, were obtained. Toxicity characteristic leaching procedure (TCLP) results indicated that tailings were harmless. The mechanisms were subsequently investigated by combining thermodynamics analyses and systematic characterizations. Especially, a one-step containing two-stage capture silver mechanism was ascertained in reduction with sulfur: formation of silver-lead alloys, and encapsulation of silver-lead alloys by FeS phase to decrease symbiotic relationship between valuable metals and slag. This entire recycling process can provide ideas for harmless recovering precious metals from hazardous waste.

Enhanced recovery of zinc and lead by slag composition optimization in rotary kiln

High-efficiency recovery of Zn and Pb from silicon-rich zinc leaching residues is realized in a rotary kiln. Characterizations by means of XRD, SEM, EDS and ICP reveal that the leaching residue contains 12.4 wt.% SiO2, 16.1 wt.% Zn, and 7.4 wt.% Pb. Thermodynamic analysis shows that metallic vapor of Zn and Pb can be easily generated from the zinc leaching residue at 1150−1250 °C inside the rotary kiln. Viscosities and melting points of 13 slag compositions were analyzed and three slag compositions (47wt.%SiO2−23wt.%CaO−30wt.%FeO, 40wt.%SiO2− 28wt.%CaO−32wt.%FeO, and 40wt.%SiO2−30wt.%CaO−30wt.%FeO) possessed the desirable physical properties, with the melting point and viscosity in the range of 1150−1280 °C and 0.2−0.5 Pa·s, respectively. The industrial tests show that adopting the optimized slag composition can contribute to very high recovery rates of Zn and Pb (97.3% for Zn and 94.5% for Pb), corresponding to slags with very low average contents of Zn and Pb (0.51 wt.% Zn and 0.45 wt.% Pb). The National-Standard leaching tests of the water-quenched slags result in 1.82 mg/L Zn, ~0.01 mg/L Cu, 0.0004 mg/L As, ~0.01 mg/L Cd, 0.08 mg/L Pb, and ~0.02 mg/L Hg in the leachate, verifying the detoxification of the zinc leaching residue at the same time.

Phase Transformation and Zinc Extraction from Zinc Ferrite by Calcium Roasting and Ammonia Leaching Process

Zinc ferrite (ZnFe2O4), one of the major forms of zinc in electric arc furnace dust and zinc leaching residue, is very difficult to chemically dissolve in either acidic or alkaline solutions. It is therefore necessary to study the extraction of zinc from zinc ferrite to achieve the full recovery of the zinc resources. In this paper, CaO was used to degrade the structure of zinc ferrite and then the ammonia leaching method was applied to recover zinc. The thermodynamic analysis indicated that the zinc ferrite could react with CaO to form zinc oxide and dicalcium ferrite. The CaO–Fe2O3–ZnO phase diagram shows that Ca2Fe2O5 can be in equilibrium with ZnO rather than ZnFe2O4 at a higher CaO area. The experimental results indicated that the phase transformation of zinc ferrite, reacted with CaO, to zinc oxide and dicalcium ferrite could be completely achieved with a CaO addition of 2.4:1 (mole ratio). The peaks of zinc ferrite in the X-ray diffraction (XRD) patterns cannot be clearly observed after calcium roasting at 1220 °C for 2 h. The ammonia leaching tests showed that the zinc leaching rate was about 90% under optimal roasting conditions.

Impacts of Surface Water on Windborne Lead Dispersion from the Zinc Plant Leach Residue in Kabwe, Zambia

Effects of the water content of ground surface on windborne lead (Pb) dispersion from the zinc (Zn) leach residue site at the Kabwe mine, Zambia, were simulated. The Pb-bearing Zn plant leach residue site was selected as the source of the dispersion, and water conditions of the surface of the source were evaluated by the modified normalized difference water index (MNDWI) under the actual weather conditions in the year 2019. The MNDWI was calculated based on Sentinel-2 datasets, which were acquired in the year 2019. The index was used for monitoring the surface condition of the source necessary for simulating Pb dispersion, because the higher surface water content reduces the intensity of windborne source. The results showed that the wind speeds and directions had huge impacts on Pb dispersion when the MNDWI had negative values, and that the dispersion was inhibited when the MNDWI had positive values. These indicate that the water content of the surface is sensitive to dispersion, and that MNDWI is an effective parameter that expresses the source strength.

One-stage ultrasonic-assisted calcium chloride leaching of lead from zinc leaching residue

To efficiently leach Pb from Zn leaching residue, an ultrasonic-assisted one-stage leaching process was developed and compared with a two-stage leaching process under conventional conditions. The results showed that Pb leaching efficiency reached up to 83.8% under the optimized one-stage ultrasonic leaching conditions (including 480 W of ultrasonic power, 100 min duration, 350 g/L of CaCl2, 5:1 of liquid-solid ratio, 35°C, and pH of 3), higher than that under conventional process with same conditions (65.7%). A diffusion model controlled the ultrasonic-assisted leaching process at 7.57 kJ/mol activation energy. X-ray diffraction and scanning electron microscopy showed that the mineral phase of Pb-containing anglesite disappeared during the leaching. By contrast, the Zn-containing franklinite minerals and Zn orthosilicate remained in the leached residue. The possible leaching mechanism of the ultrasonic-assisted effect was related to that the Pb released from Zn leaching residue by forming PbCl42− in the leachate, avoiding PbCl2 precipitation under the conventional method. Moreover, introducing could lower the leaching temperature and reduce the amount of leaching agent, which could potentially be a sustainable technique for increasing the leaching efficiency of Pb from Zn leaching residue.