Neutral Leaching Residue Research Articles

Reductive leaching of indium and zinc from zinc neutral leach residue with sulphuric acid and sulphur dioxide

ABSTRACT Indium and zinc extractions from zinc neutral leach residue were investigated with sulphuric acid and sulphur dioxide. Sulphur dioxide maintained a low concentration of Fe3+ in the solution and promoted the decomposition of zinc ferrite. More zinc, indium, and iron dissolve into the solution, while copper co-precipitates with arsenic and sulphur into the residue. The optimal reductive leaching conditions were determined as 120 g/L H2SO4, 200 kPa sulphur dioxide partial pressure, a liquid-to-solid ratio of 8 mL/g and a stirring speed of 500 r/min at 105°C for 4 h. Extractions of 95.24% of zinc, 98.66% of iron, 95.04% of indium and 0.036% of copper were achieved. Copper in final residue exist as sulphides and can be recovered by subsequent oxygen pressure leaching. Selective recovery of valuable metals from zinc neutral leach residue is realised.

Reductive leaching of indium from the neutral leaching residue using oxalic acid in sulfuric acid solution

The present study evaluates the reductive leaching of indium from indium-bearing zinc ferrite using oxalic acid as a reducer in sulfuric acid solution. The effect of main factors affecting the process rate, including the oxalic-acid-to-sulfuric-acid ratio, stirring rate, grain size, temperature, and the initial concentration of synergic acid, was precisely evaluated. The results confirmed the acceptable efficiency of dissolving indium in the presence of oxalic acid. The shrinking-core model with a chemical-reaction-controlled step can correctly describe the kinetics of indium dissolution. On the basis of an apparent activation energy of 44.55 kJ/mol and a reaction order with respect to the acid concentration of 1.14, the presence of oxalic acid was found to reduce the sensitivity to temperature changes and to increase the effect of changes in acid concentration. Finally, the equation of the kinetic model based on the factors under study is presented.

Dielectric properties and microwave heating behavior of neutral leaching residues from zinc metallurgy in the microwave field

AbstractThe method of microwave strengthens roasting neutral leaching slag contained germanium is put forward. The dielectric properties and temperature rising behavior of neutral leaching slag in the microwave field are analyzed via experimental and theoretical analysis. The experiment used the dielectric constant test device, the microwave roasting device and the temperature measuring device. The neutral leaching slag can absorb microwave energy and transform into heat energy. The specific surface area of the calcined slag containing the neutral leaching slag is increased by microwave roasting, and the microwave energy can reduce the particle size of the mineral particles to some extent. At the same time, cracks can be seen on the surface of the calcined sand after microwave roasting. The surface of neutral leaching slag roasted by microwave reformed cracks which help to open reaction channels making the oxygen to inside takes part in oxidizing reaction significantly improving germanium oxide reaction conditions, besides increasing the leaching process of the reaction area and increasing the leaching rate. The research on the dielectric constants and temperature characteristics of neutral leaching residue can provide the theoretical and experimental basis for microwave strengthen roasting.

Magnetic Seed-Assisted Iron Recovery from the Reductive Leaching Solution in Hydrometallurgical Process

The recovery of iron is the key step for zinc recycling by electrolysis in zinc hydrometallurgy industry. Iron exists mainly as ferrites in the zinc neutral leaching residue and is difficult to decompose. In this paper, the reductive leaching process using sulfur dioxide was adopted to replace the traditional hot-acid leaching method, and the magnetic seed-assisted iron precipitation was developed. Under the optimum reductive leaching conditions, the initial concentration of sulfuric acid, the temperature and the partial pressure were determined as: 80 g/L H2SO4, 90 °C, 200 kPa at the fixed liquid/solid ratio of 10:1 and the stirring speed of 400 rpm. The most suitable iron precipitation reaction conditions were as follows: the pH: 3.0–3.5; the temperature: 95 °C. The recovery of iron mainly depended on the oxydrolysis of the ferrous. The ferrous precipitated as goethite and its crystallinity noticeably decreased with decreasing pH. The addition of the magnetic seeds shortened the reaction time from 4.5 to 3.0 h when the iron precipitation rate reached more than 99%. Simultaneously, the loss rates of zinc and cadmium in the iron process were also reduced from 10.96% and 9.27% to 4.23% and 3.73%, respectively. Besides, the sedimentation and filtration performance were greatly improved after the addition of magnetic seeds. The adsorption and inclusion were the main reasons for better sedimentation and filtration performance and higher metal loss rate.

Extraction of Valuable Metals from High-Iron Zinc Sulfide Concentrate by Reductive Leaching

This study was conducted as part of the development of a new process to recover valuable metals of zinc, copper and indium from high-iron zinc sulfide concentrate (HIZSC) by the reductive leaching of high-iron zinc neutral leaching residue (HIZNLR) with zinc concentrate precipitation of copper with iron powder, neutralization of free sulfuric acid with zinc calcine, precipitation of indium with zinc powder and hematite precipitation to reject iron. Among these stages, reductive leaching is the crucial step, which makes that valuable metals in the materials can be effectively leached and ferric iron in the solution is reduced to ferrous iron. The reductive leachate enables copper, indium and iron separation from the solution in the subsequent process. The results show that by increasing the sulfuric acid concentration, HIZSC addition and prolonging the reaction time, the leaching efficiency of zinc, copper, indium and iron in the sample materials was significantly increased. The maximum metal-leaching efficiency was obtained; 84.3% of the iron was in its soluble ferrous state, and zinc ferrite in the HIZNLR was almost entirely dissolved under the experimental conditions of an H2SO4-to-HIZNLR mass ratio of 1.6, a liquid-to-solid ratio of 11.34 mL/g, a temperature of 90°C, an HIZSC addition of 1.05 times of the stoichiometric amount and a reaction time of 5 h.

The effect of CaO and MgO addition and cooling rate on stability of slag obtained after jarosite and neutral leaching residue treatment in the Waelz process

The effect of CaO and MgO addition and cooling rate on stability of slag obtained after jarosite and neutral leaching residue treatment in the Waelz process

Reductive leaching of zinc and indium from industrial zinc ferrite particulates in sulphuric acid media

Zinc ferrite is the principal constituent in zinc neutral-leach residue (NLR) which is commonly treated by hot-acid leaching in electrolytic zinc plants. Reductive leaching of zinc ferrite with sphalerite concentrate as a reducing agent was performed. It was found that leaching of zinc ferrite in the presence of sphalerit concentrate was a viable process that effectively extracted zinc and indium and converted Fe3+ into Fe2+ at the same time. Reflux leaching tests by two stages were performed to achieve extractions of 98.1% for zinc and 97.5% for indium, and a Fe2+/Fe3+ molar ratio of 9.6 in leach solution was also obtained. The leaching behaviors of other elements, such as iron, copper and tin were also studied. The results showed that iron and copper were completely leached, whereas tin presented lower extraction values.

Reductive acid leaching of cadmium from zinc neutral leaching residue using hydrazine sulfate

Zinc neutral leaching residue (ZNLR) from hydrometallurgical zinc smelting processing can be determined as hazardous intermediate containing considerable amounts of Cd and Zn which have great threats to the environment. The ZNLR contained approximately 35.99% Zn, 15.93% Fe and 0.26% Cd, and Cd mainly existed as ferrites in the ZNLR in this research. Reductive acid leaching of ZNLR was investigated. The effects of hydrazine sulfate concentration, initial sulfuric acid concentration, temperature, duration and liquid-to-solid ratio on the extraction of Cd, Zn and Fe were examined. The extraction efficiencies of Cd, Zn and Fe reached 90.81%, 95.83% and 94.19%, respectively when the leaching parameters were fixed as follows: hydrazine sulfate concentration, 33.3 g/L; sulfuric acid concentration, 80 g/L; temperature, 95 °C; duration of leaching, 120 min; liquid-to-solid ratio, 10 mL/g and agitation, 400 r/min. XRD and SEM-EDS analyses of the leaching residue confirmed that lead sulfate (PbSO4) and hydrazinium zinc sulfate((N2H5)2Zn(SO4)2) were the main phases remaining in the reductive leaching residue.

Reductive clean leaching process of cadmium from hydrometallurgical zinc neutral leaching residue using sulfur dioxide

Large quantities of cadmium-containing zinc neutral leaching residues (ZNLR) are produced constantly in the electrolytic production of zinc, creating serious cadmium pollution. In order to solve the problem and realize a clean zinc production process, a new reductive cleaning leaching process using sulfur dioxide as reducing agent has been developed, in which the beneficiation of cadmium pollution factor is solved. The cadmium leaching mechanisms were briefly analyzed and the effects of temperature, initial sulfuric acid and partial pressure of sulfur dioxide on the kinetics of cadmium dissolution in the mixed SO2+H2SO4 system was investigated. The order of reaction with respect to particle size, initial sulfuric acid concentration and partial pressure of sulfur dioxide at the fixed liquid/solid ratio and stirring speed were determined as −0.98, 1.49 and 0.51, respectively. Diffraction peak of zinc ferrite or cadmium-bearing zinc ferrite disappeared and the main compositions of the reductive leaching residue were lead sulfate (PbSO4), zinc sulfide (ZnS) according to the XRD analysis.

Enhanced Cadmium Extraction from Zinc Neutral Leaching Residue Using Sulfur Dioxide

Enhanced reductive leaching of cadmium from zinc neutral leaching residue, along with zinc and iron, was conducted using sulfur dioxide as reductant. Cadmium mainly exists as cadmium-bearing zinc ferrite (CdxZn(1-x)Fe2O4) (x = 0~1). The influence of variables on the extraction rates of cadmium, zinc, and iron was studied. The results showed the maximum extraction of cadmium, zinc, and iron reached 99.11%, 93.43%, and 93.38% under the optimum conditions. The raw and the reductive leaching residue were characterized by XRD, ICP, and SEM-EDX analysis. Lead sulfate, zinc, and cadmium sulfide are the main phases contained in the reductive leaching residue.

Mechanical Activation-Assisted Reductive Leaching of Cadmium from Zinc Neutral Leaching Residue Using Sulfur Dioxide

In this work, zinc neutral leaching residue was mechanically activated by ball-milling. The subsequent leaching behavior and kinetics of cadmium extraction in a mixed SO2-H2SO4 system were studied. Changes in the crystalline phase, lattice distortion, particle size and morphology, which were induced by mechanical activation, were also investigated. The activated samples showed different physicochemical characteristics, and cadmium extraction was found to be easier than for the un-activated samples. Under the same conditions, mechanical activation contributed to higher cadmium leaching. The cadmium extraction kinetics at 75–95°C was found to fit the shrinking core model. The raw neutral leaching residue, and the samples activated for 60 min and 120 min had a calculated activation energy of 65.02 kJ/mol, 59.45 kJ/mol and 53.46 kJ/mol, respectively. The leaching residue was characterized by ICP, XRD and SEM analysis. According to XRD analysis, the main phases in the residue were lead sulfate (PbSO4), zinc sulfide (ZnS) and cadmium sulfide (CdS).

Kinetic–Statistical Approach in a Detailed Study of the Mechanism of Thermal Decomposition of Zinc–Iron-Intermetallic Phase

Kinetic–statistical approach was applied to investigate the mechanism of thermal decomposition of Zinc–Iron-intermetallic phase, as by product from neutral leach residues. In present paper, in order to characterize the tested material, the following experimental techniques were used: Rietveld analysis, scanning electron micrograph and tube furnace sample heating procedure. Based on dependence of Avrami constant in function of effective activation energy, it was found that at T > 950 °C, the process of crystal growth takes place in autocatalytic stage, under the conditions, where rate of nucleation rapidly increases. It was established that high nucleation rate can be attributed to formation of both Zn and Fe rich regions which provide a high number of heterogeneous nucleation sites. It has been proposed that emergence of line defects under ZnO branched crystals can serve as pin-points for secondary nucleation to occur. It was confirmed that increase in temperature in Zn vapor did not result in a decrease of existing in Zn constitutional vacancies.

Kinetic modeling of thermal decomposition of zinc ferrite from neutral leach residues based on stochastic geometric model

The stochastic geometric model was applied to kinetic modeling the complex process of thermal decomposition of zinc ferrite from neutral leach residues, at different operating temperatures (600°C, 750°C, 950°C and 1150°C). Based on functional dependence of Avrami׳s constant (n) in a function of the effective activation energy (Ea), it was found that at T>950°C, the crystallization process takes place in autocatalytic stage, under the conditions where the rate of nucleation rapidly increases. It was established that the high nucleation rate can be attributed to formation of both Zn and Fe rich regions which provide a high number of heterogeneous nucleation sites. Based on the obtained final shape of the particles, it was found a strong presence of zinc, iron (present only in the form of Fe3O4 (magnetite)), magnesium (in the form of Mg2Si2O6), and also lead oxides. Thermodynamic analysis showed that the decomposition depends on the introduction of heat, and exerts a positive value of the Gibbs free energy of activation. Such a feature was expected since the ferrite system has been submitted to a forced decomposition and volatilization reactions.

Effect of mechanical activation on dissolution kinetics of neutral leach residue of zinc calcine in sulphuric acid

Neutral leach residue of zinc calcine (NLRZC) was mechanically activated by a stirring ball mill. Subsequently, the changes in physicochemical properties and dissolution kinetics in sulphuric acid were studied. The crystalline structure, morphology, particle size and specific surface area of the non-activated and mechanically activated NLRZC were characterized by X-ray diffraction, scanning electron microscope, particle size analyzer and volumetric adsorption analyzer, respectively. The characterization results indicate that mechanical activation (MA) induced remarkable changes in the physicochemical properties of NLRZC. The leaching experiments show that MA significantly enhances the leaching reactivity of NLRZC using the zinc extraction as evaluating index. After NLRZC is mechanically activated for 30 min and 60 min, the activation energy decreases from 56.6 kJ/mol of non-activated NLRZC to 36.1 kJ/mol and 29.9 kJ/mol, respectively. The reaction orders of the non-activated, 30 and 60 min activated NLRZC dissolution with respect to H2SO4 concentration were found to be 0.34, 0.30, and 0.29, respectively.

Influence of the Mechanical Activation on the Reactivity of Germanium-Containing Zinc Neutral Leaching Residue

Zinc neutral leaching residue from conventional roast-leach-electrowin often contains a considerable content of germanium. In two-stage leaching process (weak acid leaching and hot acid leaching), dissolution yield of germanium as well as zinc is low due to the compact structure of the residue. In the paper, an attempt of increasing their dissolution yield was made by pretreatment of mechanical activation. The experimental results obtained show that the activated residue has much faster leaching kinetics, and that according to current technical standard operating in Yunnan Chihong Zinc & Germanium Co., Ltd, dissolution of germanium and zinc is increased by 18.12% and 22.93%, respectively. The increase may mainly be due to the structure deformation of the residue by further investigation.

Effect of Mechanical Activation on Extracting Indium from Neutral Leach Residue of Zinc Calcine

This study was concerned with the effects of mechanical activation (MA) on structural characterization for neutral leach residue of zinc calcine (NLR) and kinetics of indium extraction from NLR in sulphuric acid. The X-ray diffraction (XRD) analysis showed that MA caused the decrease in crystalline phase and increase in lattice distortion. The activation time, reaction temperature and H2SO4concentration had positive effect on indium extraction from NLR. The activation energies of the unactivated, milled for 30 and 60 min NLR samples calculated for indium extraction were 39.3, 32.1, and 30.4 kJ/mol, respectively, which indicated that MA increased the leaching kinetics of indium extraction from NLR. The empirical orders of the unactivated, activated for 30 and 60 min samples for extracting indium with respect to H2SO4concentration were 0.52, 0.51, and 0.51, respectively.

The recycling of heavy-metalcontaining wastes: Mass balances and economical estimations

As environmental legislation has become stricter in recent decades, efforts for treating residues have also increased. The existing pyrometallurgical reprocessing methods for metal-containing wastes recover mainly only one valuable metal or produce low-grade byproducts. The aim of developing an economic process has to be the simultaneous recovery of more than one valuable metal and increased product quality. In the case of zinccontaining residues the goal has to be a high-quality zinc product. Moreover, the target is a nearly zero waste process and, accordingly, small amounts of generated residues. In this paper four possible secondary raw materials are compared regarding their mass and energy balance for a treatment in a carbon-containing metal bath. Furthermore, an evaluation of the economy is given for a neutral leaching residue, Waelz kiln slag, dust from secondary copper industry as well as an electro arc furnace dust from carbon steel production.

Recovery of enriched lead–silver residue from silver-rich concentrate of hydrometallurgical zinc smelter

During the conventional zinc hydrometallurgical process operated in olden days prior to jarosite process, lead and silver reported in the neutral leach residue along with zinc ferrite. Lead and silver values from the zinc plant leach residue were recovered by a froth flotation process to obtain a silver-rich concentrate. This work deals with an alternative and innovative process to treat this silver-rich concentrate to produce an enriched lead–silver residue which can be consumed in lead smelter. The process involves the treatment of silver concentrate generated in the flotation circuit by acid-roasting followed by moderate temperature-water leach to solubilize zinc and iron completely thereby enriching lead and silver values in the leach residue. This residue contained high levels of silica which was removed by alkali roasting with caustic followed by water wash. Silica content dissolves into solution phase thereby generating a residue rich in lead and silver values. This residue was suitable for treatment in lead smelter to produce lead and silver metal. Based on the experimental results, a conceptual flowsheet was developed.

Fundamentals of zinc recovery from metallurgical wastes in the Enviroplas process

The Enviroplas process was developed at Mintek to treat certain metallurgical wastes, such as lead blast furnace slag, electric arc furnace dust, and neutral leach residues from the zinc industry. The process relies on a DC arc furnace and an ISP lead splash condenser for the direct recovery of the contained zinc as prime western grade metal, with the simultaneous production of a disposable slag. This paper outlines certain fundamental issues of the process, including feed preparation and specifications, operating temperatures, coke (coal) requirements, flux addition, and recycling of the fumes and the condenser dross. In addition, the chemical reactions involved and the associated kinetics are presented and discussed, as well as the major factors that influence the condensation process. Selected test results are also included to highlight the significance of the most important factors that affect the process.

Innovative processing technique to produce zinc concentrate from zinc leach residue with simultaneous recovery of lead and silver

During the conventional zinc hydrometallurgical roast-leach-electrowin process lead and silver report in the neutral leach residue along with zinc ferrite. Lead and silver from the zinc plant leach residue are recovered by a froth flotation process followed by roast-leach-precipitation-reduction to obtain a highly pure silver. Inherent process constraints of water balance and build-up of problem impurities from the silver recovery plant to the main zinc circuit, low recovery of metal values (especially lead and silver), loss of sulphur values and high cost of flotation reagents make the Mitsubishi Materials Corporation's (MMC) silver recovery process through roast-leach-precipitation-reduction technique uneconomical. Attempts have been made to make the process more effective and attractive by removing the above process constraints. An alternative and innovative approach has been developed to achieve high recovery of lead and silver, effective utilization of sulphur values and better control of impurities. The process involves the treatment of silver concentrate generated in the flotation circuit at moderate temperature-sulfuric acid leach to partially solubilise the zinc and iron and enrich lead and silver in the leach residue. The residue is treated with brine solution to solubilise most of the lead and silver which are cemented out from the leach solution with the help of aluminium to obtain a high purity lead–silver sponge which will be fed to the silver circuit to recover the metal values through a pyro-refining route. The brine leach residue which is equivalent to high quality zinc concentrate containing high levels of zinc and sulphur and minimum levels of impurities finds application as a feed to the fluo-solid roaster. This approach is different from conventional practice. The paper describes the results of moderate temperature-sulfuric acid leaching, brine leaching, quality of zinc concentrate and lead–silver sponge obtained by this proposed route with other advantages. Based on the experimental results a conceptual flow sheet has been developed. The process is simple, eco-friendly and economically viable with excellent recoveries of lead, silver, zinc and sulphur values and can be easily implemented in the existing zinc hydrometallurgical plant.