Zinc Hydrometallurgy Research Articles

Physicochemical Properties and Leaching Toxicity Assessment of Jarosite Residue

The safe disposal of hazardous waste from zinc hydrometallurgy, such as jarosite residue, is crucial for the sustainable development of the industry. The chemical, structural and morphological properties of jarosite residue from zinc smelting were studied by a combination of various characterizations, and environmental stability was evaluated using the toxicity characteristic leaching procedure (TCLP), Chinese standard leaching tests (CSLT) and long-term leaching experiments (LTLE). Phase composition analysis revealed that zinc ferrite and sodium jarosite were the main phases present in the jarosite residue. TCLP and CSLT analyses indicated that the Zn and Pb contents exceeded their respective toxicity identification standards by more than 30 times and 8 times, respectively, exceeding the threshold values of the standard. The LTLE results demonstrated that Pb concentrations continued to exceed the standard limits, even after long contact times. This study has paramount significance in the prediction of jarosite residue stability and the evaluation of its potential for secondary environmental pollution.

Mechanism of removal of toxic arsenic (As) from zinc sulfate solution by ultrasonic enhanced neutralization with zinc roasting dust

Arsenic in zinc sulfate solution greatly hinders the zinc hydrometallurgy process, and the treatment of arsenic residue with lime also generates large cost due to the large amount of residue. Herein, a new process of neutralization by zinc roasting dust (ZRD) and ultrasound (US) field enhancement of arsenic removal was proposed. The process includes the following steps:one-stage neutralization, KMnO4 oxidation and two-stage neutralization to remove arsenic. The process has the advantages of a good arsenic removal effect, no introduction of new impurities, and less residue. The effects of the ZRD dosage, temperature and US power on arsenic removal were investigated. The optimal conditions were 12 g/L, 70 ℃ and 300 W, respectively, and the arsenic removal rate reached 99.3%. The X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FE-SEM-EDS) were utilized to analyze the raw materials and residue. The results showed that, compared with conventional conditions, US strengthening treatment led to more complete reaction of ZRD. The arsenic removal residue after US treatment mainly existed in the form of ZnFe2O4, Fe3O4 and ZnS, which exhibited low reactivity. Ultrasound could effectively destroy the wrapper on the surface of ZRD, and enhance the liquid–solid reaction, which reduced the amount of residue and improved the arsenic removal efficiency. Interestingly, we found that ultrasound could enhance arsenic removal by increasing the ligand exchange between arsenate and sulfate. Compared with the lime and conventional ZRD neutralization, the wet residue weight after US treatment was reduced by 46.8% and 16.3%, respectively.

A Fuzzy Control Method Based on Rule Extraction for Zinc Leaching Process of Zinc Hydrometallurgy

A Fuzzy Control Method Based on Rule Extraction for Zinc Leaching Process of Zinc Hydrometallurgy

In Situ Synthesis of NiFeLDH/A-CBp from Pyrolytic Carbon as High-Performance Oxygen Evolution Reaction Catalyst for Water Splitting and Zinc Hydrometallurgy.

Nickel-iron-layered double hydroxide (NiFeLDH) is one of the promising catalysts for the oxygen evolution reaction (OER) in alkaline electrolytes, but its conductivity limits its large-scale application. The focus of current work is to explore low-cost, conductive substrates for large-scale production and combine them with NiFeLDH to improve its conductivity. In this work, purified and activated pyrolytic carbon black (CBp) is combined with NiFeLDH to form an NiFeLDH/A-CBp catalyst for OER. CBp not only improves the conductivity of the catalyst but also greatly reduces the size of NiFeLDH nanosheets to increase the activated surface area. In addition, ascorbic acid (AA) is introduced to enhance the coupling between NiFeLDH and A-CBp, which can be evidenced by the increase of Fe-O-Ni peak intensity in FTIR measurement. Thus, a lower overvoltage of 227 mV and larger active surface area of 43.26 mF·cm-2 are achieved in 1 M KOH solution for NiFeLDH/A-CBp. In addition, NiFeLDH/A-CBp shows good catalytic performance and stability as the anode catalyst for water splitting and Zn electrowinning in alkaline electrolytes. In Zn electrowinning with NiFeLDH/A-CBp, the low cell voltage of 2.08 V at 1000 A·m-2 results in lower energy consumption of 1.78 kW h/KgZn, which is nearly half of the 3.40 kW h/KgZn of industrial electrowinning. This work demonstrates the new application of high-value-added CBp in hydrogen production from electrolytic water and zinc hydrometallurgy to realize the recycling of waste carbon resources and reduce the consumption of fossil resources.

Study of cadmium ions cementation with zinc powder from high-cadmium-concentration zinc sulphate solutions

ABSTRACT The recovery of metals from industrial and metallurgical effluents is crucial to minimise the environmental and economic impacts associated with the generation and disposal of these solutions. Therefore, this study uses zinc powder for the cementation of cadmium from a high-cadmium-concentration zinc sulphate solution. This study investigates the dependence of cadmium removal efficiency on the initial copper concentration, solution pH, stoichiometric ratio of added zinc, temperature, particle size, zinc powder activation and mode of zinc addition. The results show the possibility of achieving a cadmium removal efficiency 90–95% under optimal conditions. The reaction kinetics calculations revealed an activation energy of 11.89 kJ mol–1, indicating a diffusion-controlled reaction mechanism and the possibility to reduce the limitations of the controlling step by increasing the stirring rate during the cementation process. These observations provide further understanding and guidance toward the efficient utilisation of cadmium cementation to prepare sponge cadmium in zinc hydrometallurgy.

Enhanced removal of organic matter from oxygen-pressure leaching solution by modified anode slime

Organic matter has become a typical harmful impurity, posing a serious problem and catastrophic effects in the hydrometallurgical extraction of zinc. The highly efficient and inexpensive method for the removal of organics from the leaching solution is of great practical significance for the efficient operation of zinc hydrometallurgy. For this reason, the removal of organic matter from oxygen-pressure leaching solution using modified anode slime was investigated by TOC analysis, FTIR spectroscopy, XRD, GCMS, and other characterization methods, and its mechanism was also discussed. The results show that the removal of organic matter using anode slime modified with sulfuric acid was significantly improved, and the removal of TOC reached 57.83% for anode slime modified at a temperature of 80 °C with a ratio of sulfuric acid to anode slime of 14 mL/100 g, which was more than 2.7 times that of untreated anode slime. The good removal effect of organic matter using the modified anode slime could be attributed to the transformation of inert α-MnO2 to active MnOOH by concentrated sulfuric acid-mediated modification. It was also found that the acid–solid ratio and temperature exhibited a significant effect on the modification of anode slime. The XPS analysis results of Mn 2p, Mn 3s, and O 1s, combined with the XRD patterns of the modified products indicated that the modification of anode slime led to the conversion of MnO2 in anode slime to MnOOH in the presence of H2SO4. However, MnO2 was further converted into high crystallinity MnOOH, even MnSO4 when the temperature exceeded 80 °C or the acid–solid ratio exceeded 18 mL/100 g, resulting in the decreased degradation performance for organic matter. The characterization results of FTIR spectroscopy and GCMS show that modified anode slime does not exhibit a degradation effect on all types of organic substances in leaching solution; however, it is very effective for some alcohols, olefins, and esters.

Application of PLC-Based Spectrophotometric System Nitrogen Protection Device to Automated Direct Measurement of Target Substances in Zinc Hydrometallurgy

Due to the fast material reaction in zinc hydrometallurgy, the traditional national standard photometric method cannot capture the characteristic information of target substances in real time. Herein, a nitrogen protection device is built based on ultraviolet spectrophotometry, supplemented by a programmable logic controller (PLC), to form an automatic control system for the direct detection of target substances (SO42−, Pb2+ and S2−) in zinc hydrometallurgy. The baseline straightness comparison results show that the nitrogen atmosphere can effectively improve the stability of the instrument. Furthermore, the detection sensitivity of SO42−, Pb2+ and S2− under the nitrogen atmosphere is higher than that of the air atmosphere, manifesting in sensitivity increases of 16.23%, 18.05% and 17.91%, respectively. Additionally, devices based on PLC systems show advantages over manual control both in states feedback and information backtrack. Moreover, the regulation time and nitrogen consumption during the regulation process are reduced by 80% and 75%, respectively, which effectively reduces the test cost and improves the equipment utilization rate (from four cycles per day to six cycles per day). The device can meet the requirements of different target substances and different process conditions by changing the electronic control parts and air source, so it has great application potential in the automatic direct measurement of target substances in zinc hydrometallurgy.

Enhancing the dechlorination of CuCl residue using a microwave sulfation-roasting method: Process optimization and mechanism investigation

Spent CuCl residue produced from zinc hydrometallurgy is a typical toxic and hazardous solid waste as well as a secondary resource owing to its high contents of chlorine and valuable metals (Pb, Cu, Zn). The removal of chlorine from the CuCl residue and recycling of valuable metals are critical issues for the copper slag resource treatment process. In this study, a novel method of microwave sulfation-roasting under an oxygen atmosphere is used to improve the dechlorination process, and various parameters, such as roasting temperature, duration, sulfuric acid concentration, and liquid/solid ratio, are optimized. First, according to thermodynamic calculations, the addition of H2SO4 can significantly decrease both the roasting temperature and time needed for microwave oxidation-roasting. The dechlorination experimental results reveal that the dechlorination rate of the CuCl residue is as high as 91.91% under a temperature of 250 °C, holding time of 120 min, sulfuric acid concentration of 70%, and liquid-solid ratio of 1.42. The microstructure, chemical composition, and phase changes of the CuCl residue before and after roasting are characterized using scanning electron microscopy coupled with energy-dispersive spectroscopy, X-ray fluorescence and X-ray diffraction; further, the mass contents of the main elements in the roasting product and tail gas absorption solution are determined by chemical analysis, Evidently, the selective heating property of microwaves produces more holes and cracks in the copper slag, which can provide a new reaction channel for H2SO4 and CuCl slag reactions, and almost all CuCl in the copper slag is completely removed by transformation into CuO, CuSO4 and Cu2O(SO4). Simultaneously, a large number of gas by-products produced in the dechlorination process, such as SO2 and Cl2, can be absorbed by the NaOH solution. Therefore, no pollution is generated in the environment. These findings illustrate that microwave sulfation-roasting is an effective method for promoting the treatment and recycling of CuCl waste residues.

Dynamic synergistic modelling for cobalt removal process in zinc hydrometallurgy and the research of parameter estimation based on unscented Kalman filter

AbstractThe cobalt removal process with arsenic salt of zinc hydrometallurgy has serious non‐linearity, uncertainty, and mutual coupling. Its accurate dynamic modelling has always been a challenging problem. On the basis of in‐depth analysis of cobalt removal process and reaction mechanism, considering the cascade relationship between the reactors, a dynamic synergistic continuously stirred tank reactor (SCSTR) mechanism model of the cobalt removal process was constructed. Aiming at the unknown parameters in the SCSTR model, the idea of the Kalman filter was introduced, and the unknown parameters were characterized as unknown states; a method of estimating the unknown model parameters was developed using the augmented state equation and the unscented Kalman filter (UKF) algorithm. Simulation results with industrial data of a zinc smeltery showed that the parameter estimation model has high accuracy, and the estimated parameters can be used in the SCSTR model. An intensive simulation analysis of the dynamic characteristics of the complete SCSTR model was carried out to verify the influence of different input disturbances on the output ion concentration of each reactor, which demonstrated the excellent dynamic performance and potential of the model. Ultimately, according to the industrial calculation analysis, the SCSTR model has a guiding effect on the addition of zinc powder in the reactors, overcomes the blindness in the production process, and provides a momentous basis for the optimization control of the cobalt removal process.

Hybrid modeling and distributed optimization control method for the iron removal process

<p style='text-indent:20px;'>Iron removal by goethite is a key procedure in zinc hydrometallurgy. Due to its complex chemical reaction mechanism, multiple reactors cascade, and high uncertainty, it is difficult to optimize and control in industrial process. In this paper, a distributed optimization control method which is based on a novel hybrid model of the iron removal process is proposed. By combining the mechanism model and a data-driven oxygen mass transfer coefficient model, a hybrid model is first established. Then, to overcome the influence of the former reactor on the latter reactor, the ratio of the status in each subsystem to the set point is taken as a new status, and a distributed optimization control problem is constructed. Considering the high dimensionality of this problem, it is necessary to reconstruct it by Virtual Motion Camouflage (VMC), so that the optimal control problem is transformed into a nonlinear constrained optimal trajectory planning problem. And a Legendre pseudo-spectral method is used to solve the problem accurately to obtain the optimal trajectory of the ion concentration. Finally, simulation results show that the proposed method can effectively reflect the industrial process, and track the fluctuation of inlet ion concentrations with a nice real-time performance.</p>

Enhanced mechanical stirring by eccentric impeller stirring system in zinc hydrometallurgy process for cadmium removal

Abstract The fluid in the reactor can be poorly mixed, so an eccentric impeller is proposed to improve the fluid mixing efficiency. In this investigation, numerical simulations and cadmium removal experiments for the purification of zinc sulfate solution were conducted. The effect of eccentric impellers on the purification efficiency was discussed. The mechanism of the effect of concentric and eccentric arrangement of stirring impellers on mixing in the stirred tank was elucidated. The results showed that the average axial velocity of the eccentric impeller stirring system (EIS) was 131.52% of that of the concentric stirring system (CS) and 134.23% of that of the eccentric stirring system (ES). In the purification and removal of cadmium in the zinc hydrometallurgy experiment, unit ion purification energy was introduced to quantify the energy consumed for each 1% of Cd2+ removed. The eccentric impeller shortens the reaction time by 40% and reduces the reaction energy consumption by 31.8% compared to the non-eccentric impeller. Compared to CS and ES, EIS disrupts the periodicity of fluid flow and facilitates the destruction of isolated mixing regions. EIS can enhance mechanical stirring to improve purification efficiency.

Green and efficient recovery of valuable metals from by-products of zinc hydrometallurgy and reducing toxicity

Germanium-containing dust as an intermediate by-product in the process of zinc hydrometallurgy, which often contains a large number of heavy metal substances. Due to the constraints of economic benefits and process technology, green and efficient treatment of germanium-containing dust is always a great challenge. In this work, XRD, ICP-OES, XPS, SEM and other characterization methods were used to analyze the existing state and quantity of main substances in germanium-containing dust. It was found that the occurrence state of germanium was closely related to sphalerite. At the same time, longer reaction time would lead to continuous hydrolysis of silicate, which would eventually affect the recovery of zinc, germanium and lead and the fixation of toxic substances. Therefore, the ultrasonic enhanced ammonium persulfate oxidation process was proposed to control the waste of resources and environmental pollution caused by the accumulation of germanium-containing dust. The final results showed that more than 95% of zinc and 89% of germanium were efficiently recovered, and heavy metals such as arsenic and cadmium were fixed in the liquid, and then concentrated in the purification and impurity removal stage. The residue after reaction is high-grade lead sulfate residue, which can be returned to the lead smelting system for recycling. In summary, the ultrasonic-enhanced ammonium persulfate process eventually makes all substances in germanium-containing dust harmless and resource treatment.

Research on microstructure of membrane-slime layer on lead-based anode surface in zinc hydrometallurgy by combining μ-XRF with mm-XRF

In this paper, the synchrotron radiation μ-XRF and the mm-XRF method were used to emphatically study the composition, content and distribution of lead and manganese in anode slime on lead-based surface. The paper mainly explored the chemical features and the content evolution law of lead and manganese in the anode micro-zone of the anode surface, analyzed the corresponding relationship between the variation trend of lead and manganese contents and the thickness of micro-zone of the anode surface, scientifically determined the parameters of membrane preservation and slime removal by studying the quantitative layered structure of membrane-slime layer on the lead-based anode surface, and further verified the accuracy of the layered structure of membrane-slime layer through field slime removal experiment. The research results show that: (1) By using the respective advantages of μ-XRF and mm-XRF, and through in-situ study on the microstructure of anode slime by combining the two methods, it is revealed that there exists quantitative and fine layered structure of membrane-slime layer on the lead-based anode surface.(2) Through the research and analysis based on synchrotron radiation μ-XRF microprobe, the anode slime from the lead-based interface can be divided into membrane layer (high lead and dense), membrane-slime layer (intertwined high lead and low manganese and intertwined medium lead and high manganese) and slime layer (low lead and high manganese.(3) Further mm-XRF analysis of a large amount of data shows that the change rates of lead and manganese contents in anode slime from the lead-based interface vary significantly within the range of unit thickness; when the thickness is ＜1.0 mm, the lead content decreases most rapidly from 99% to 35%, and the lead content change value ΔPb is 64%/1 mm; when the thickness is 1.0–2.6 mm, the lead content change tends to be gentle, with a decrease from 35% to 10%, and ΔPb is 16%/1 mm; when the thickness is ＞2.6 mm, the lead content has no obvious change and fluctuates in a small range of about 10%. (4) Based on the above research, 2.6 mm on the lead-based surface can be determined as the limit thickness of anode membrane preservation and slime removal; the results of the membrane preservation and slime removal equipment developed on this basis show that compared with the manual slime removal results, the lead content of the anode surface after removing the slime by using membrane preservation and slime removal equipment drops from 80% to less than 10%.

Effect of in-situ oxidation on the phase composition and magnetic properties of Fe3O4: Implications for zinc hydrometallurgy

• Iron precipitates at different oxidation degrees are obtained by H 2 O 2 . • Ms value of Fe 3 O 4 shows a decrease and then recovery with oxidation. • Magnetic properties are affected via a Fe-O bond length-related mechanism. • The “magnetic iron oxides” method is promoted for industrial iron precipitation. Large quantities of hazardous waste are generated in the removal process of iron in zinc hydrometallurgy, which poses a severely permanent threat to the environment. Recently, an innovative magnetite (Fe 3 O 4 ) method for iron precipitation has been proposed. Whereas, the magnetic separation performance and phase composition of Fe 3 O 4 are sensitively disturbed by the oxidizing conditions in the pregnant leach solution from zinc hydrometallurgy. In this work, a series of Fe 3 O 4 samples with different oxidation degrees were in-situ formed. We found that oxidation did not worsen the Fe removal and that all samples have a relatively high iron content (>42.3%). Meanwhile, although the magnetic properties of the samples showed a decrease (from 32.31 to 6.56 emu/g), it could be recovered (10.60 emu/g) by controlling the oxidation to a certain degree. This is correlated with the phase transition of iron oxides as the oxidation degree increase. Furthermore, it is clarified that the mechanism by which the oxidation affects the magnetic properties was the change of Fe-O bond length, as revealed by Raman and Fourier transform infrared spectrometer measurement. This work provides a new strategy for the practical implication of the “magnetic iron” instead of the magnetite precipitation method in zinc hydrometallurgy.

Dynamic multi-objective optimization and fuzzy AHP for copper removal process of zinc hydrometallurgy

In order to improve the production efficiency and reduce the production cost of copper removal process (CRP), it is necessary to control the addition rate of zinc powder in CRP. In this study, the control of zinc powder addition rate is modeled as a dynamic multi-objective optimization problem (DMOP). A Pareto set which contains multiple control schemes is obtained by using multi-objective state transition algorithm based on decomposition, and then a new fuzzy multi-criteria decision-making (MCDM) is proposed to select the best control scheme. In the MCDM, according to the real-world requirements of CRP, four criteria are adopted to evaluate these schemes, and the fuzzy analytic hierarchy process (AHP) is adopted to determine the criteria weights according to a fuzzy comparison matrix. Furthermore, the nonlinear mixed integer programming model is established to guarantee consistency of the fuzzy comparison matrix. Experimental results of an industrial plant in China have demonstrated the effectiveness and superiority of the proposed method in terms of the cost, reaction rate, stability of outlet copper ion concentration, etc.

Removal of chlorine from zinc sulfate solution: a review.

During zinc hydrometallurgy process, the chloride ions in the materials go into the leaching solution, which have abominable effects on equipment, electrowinning, and environment. So, it is necessary to remove chloride ions from zinc sulfate solution. The present review outlines the current research of removal methods of chlorine by holistically highlighting the advantages and mechanisms. The main techniques used to remove chloride ions from zinc sulfate solution are also discussed in detail. Among the methods, the precipitation method using copper slag to remove chlorine is widely used and the chlorine removal rate is up to 98%. In addition, the combination of electrochemistry and nanofiltration technology can form a closed-loop production process with less waste output and near-zero emissions. In addition, the challenges and possible future directions of chlorine removal from zinc sulfate solutions are also delineated.

Minimizing Fe-Bearing Waste Guided by Modulating the Precipitation Pathway: A Novel Magnetite Precipitation Approach for Zinc Hydrometallurgy

Minimizing Fe-Bearing Waste Guided by Modulating the Precipitation Pathway: A Novel Magnetite Precipitation Approach for Zinc Hydrometallurgy

Jarosites: Formation, Structure, Reactivity and Environmental

Jarosite, beudantite and alunite are members of the alunite supergroup. Minerals like those have been detected in different environments on Earth. These jarosite-type compounds are common in acid rock drainage environments and acid sulfate soils, resulting from the weathering of sulfide ores; they are also present in bioleaching systems because they are found in cultures of iron-oxidizing microorganisms. Jarosite is also generated in hydrometallurgical circuits, mainly in zinc hydrometallurgy. These minerals can be used to immobilize different elements such as arsenic and lead, among others. Jarosite and alunite have also been detected on the surface of Mars; the presence of jarosite and alunite and other sulfates provides evidence for the existence of water on Mars. In this work, an exhaustive review of the natural formation, synthesis, structure, thermodynamics, and reactivity of jarosite, beudantite and alunite are included. The capacity of jarosites for the immobilization of the elements, such as lead and arsenic, and information about studies related to jarosite formation on Mars are also included.

Ozonation precipitation for iron removal in zinc hydrometallurgy

ABSTRACT Iron is an undesirable constituent and should be removed before zinc electrowinning. Oxidative precipitation using ozone for iron removal from ZnSO4 solution was investigated. Meanwhile, using air as an oxidant was compared at parallel tests. The results indicated that the per centage of iron removal is above two times higher using O3 than using air. With ozone, the effects of important process parameters, such as ZnO mass, temperature, O3 mass flow rate, time, and stirring speed, were systematically investigated. Under optimised conditions, i.e. MZnO/Fe of 1.45, temperature of 90°C, ozone mass flow rate of 3.12 g/h, 30 min, and stirring speed of 300 rev min−1, 99.98% of iron can be removed, causing 0.15% of Zn loss. The precipitate existed as good crystalline phases of FeOOH, MnO2 and ZnSO4·H2O, and composed of rough and dense particles with different size, which is beneficial for solid–liquid separation.

A Review: Modeling of pH Probability Density Distribution in Zinc Hydrometallurgy Based on Gaussian Mixture Model

A Review: Modeling of pH Probability Density Distribution in Zinc Hydrometallurgy Based on Gaussian Mixture Model