Process For Recovery Of Zinc Research Articles

The Circular Economy in Terms of Zinc Recovery from Industrial Waste – Directions for the Development and Profitability of Recycling

The article reviews the current state of the art in the field of zinc recycling. The results of model studies of the profitability (profitability) of the process of zinc recovery in precipitation in the form of dusts and sludges are presented. The cost of purchasing waste and the necessary energy and material expenditures were taken into account. It has been shown that access to a cheap source of waste is essential for the profitability of the zinc recovery process.

Leaching Kinetics of Secondary Zinc Oxide in a NH3–NH4HCO3–H2O System

Secondary zinc oxide (SZO), which comes from the zinc industry, is an important secondary resource of zinc and other valuable metals. In this study, the production feasibility and rationality of a cleaner zinc recovery process using SZO and a hydrometallurgical method were described. Zinc extraction is promoted by the addition of ammonium bicarbonate to a NH3–H2O system, and the maximum recovery of zinc could be close to 80% at the optimum leaching conditions of a stirring rate of 400 rpm, an ammonia/ammonium ratio of 7:3, a total ammonia concentration of 4 mol/L, and a liquid/solid ratio of 7 mL/g for 30 min at 35 °C. The kinetics of leaching were modeled using the shrinking core model of constant-size particles, and the rate-controlling step was determined to be the diffusion through the product layer. The apparent activation energy of the reaction was estimated to be 11.04 KJ·mol−1, while the order of reaction with respect to total ammonia concentration was 1.53 and the liquid/solid ratio was 2.26. The analysis results of the initial residue and the leached residue indicated that lead was transferred from PbCl2 to PbCO3 and that ZnFe2O4 was not leached in the NH3-NH4HCO3-H2O system.

Manganese Biomining from Manganese-Bearing Industrial Wastes of Georgia

In Georgia, the amount of manganese-bearing industrial wastes is estimated at 15 million tons, of which over 10 million tons are mine wastes of Chiatura deposit. The resource potential of these technogenic formations makes 1.5 million tons of pure manganese. Every year the volume of these wastes increases by one mln t on average. An economic loss from non-utilization of this valuable manganese stock is great. Also great is an environmental damage. Analysis of a possibility of recycling manganese-bearing waste indicates the prospects of using environmentally safe and profitable biotechnological processes of utilizing this technogenic raw material. For intensifying the known methods of manganese biomining, the authors have developed a new technological leaching scheme, which, at the first stage, for processing the stock provides for its desilicalization by silicate bacteria B.mucilaginosus. The result of this stage is an increase in the content of manganese in the raw material by 25–30%, with an increase in the cumulative response surface for applying bacteria A.ferrooxidans at the next stage. One of the main distinctive features of the proposed scheme is also integration of the manganese leaching process with the copper and zinc recovery process. The advantage of this combined process consists in the application of the afterproduct of leaching of these nonferrous metals—a ferrous (II) sulfate compound for speeding up the manganese extraction, and, vice versa, in the application of ferric (III) sulfate produced upon manganese leaching to activate copper and zinc extraction. The advantage of the use of the bicultural solution A.ferrooxidans-R.phaseoli in manganese leaching instead of the monoculture one (A.ferrooxidans) is also substantiated. As a result of practical realization of the proposed technical novelties, the manganese extracting degree can be increased to 98–99%, while the length of leaching can be reduced to 14–21 days. The commercial exploitation of the proposed combined technological scheme of manganese biomining will increase the resource base of Georgian manganese, for it will create a new possibility for recycling environmentally harmful wastes and cut-off grade ores of Chiatura deposit.

Hydrometallurgical Process for Zinc Recovery from C.Z.O. Generated by the Steelmaking Industry with Ammonia–Ammonium Chloride Solution

In this research, some experimental steps were investigated to recover zinc contained in crude zinc oxide (C.Z.O.). In the first stage, the C.Z.O. was treated in NH3–NH4Cl–H2O solution to dissolve the metals. The optimized leaching conditions in batch experiments were obtained: agitation speed 250 rpm, concentration of ammonia and ammonium chloride 2.5 mol/L and 5 mol/L, respectively, time 30min, temperature 40 °C, and L/S = 6 mL/g. The extraction percentage of zinc was over 81% under the optimized leaching conditions. The kinetic study indicates that zinc extraction from the C.Z.O particles was very rapid. In the second stage, the solution from the leaching process was purified by adding zinc dust to the solution. The Cu, Cd, Pb, Sb, and As could be reduced to levels of 0.03, 0.09, 0.87, 0.22, and 0.12 mg/L after the purification process. Finally, the electrowinning process was used to recover dissolved Zn from the final solution. The zinc content in the electrowon zinc was more than 99.99%.

Development of Zinc-separating Process of Blast Furnace Dust using Hydrometallurgical System

Blast furnace (BF) dust is recycled as iron source in sintering process. However, dust-recycling rate is limited due to the zinc in dust. Thus, it is necessary to remove zinc from dust in order to improve dust-recycling rate. In this study, zinc-separating process of BF dust using hydrometallurgical (wet-type) system is proposed with a zinc purification process. Laboratory-scale experiments using BF dust were conducted to investigate zinc and iron behavior. This process is composed of (1) acid leaching treatment, (2) leachate-purification process and (3) zinc-recovery process as alkali precipitation. By acid leaching treatment, 68 wt% of zinc was selectively leached into the solution under the pH value of 2.0 with sulfuric acid, while only 6.4 wt% of iron was leached. Leachate-purification process is the key process. The iron leached by acid leaching treatment was completely separated from leachate as iron hydroxide under the pH value of 5.0, added with hydrogen peroxide as oxidizing agent. On the other hand, zinc in leachate was maintained at the same level and well-purified successfully. Zinc was finally recovered as sludge of zinc hydroxide precipitation at alkali condition such as the pH value of 9.0. Zinc concentration in the sludge was concentrated to 42.6 wt%. With this new process, zinc in dust was successfully separated and the sludge containing high concentrations of zinc was obtained. Thus, dust can be potentially used as zinc source as well as iron source.

Zinc recovery from metallurgical slag and dust by coordination leaching in NH3-CH3COONH4-H2O system.

Metallurgical slag and dust (MSD) from lead and zinc smelting, steel dust and galvanized steel scrap are important secondary sources of zinc and other valuable metals. This paper describes the production feasibility and rationality of a cleaner zinc recovery process using MSD and a hydrometallurgical method. It was found that the addition of CH3COONH4 to a NH3–H2O system promotes zinc extraction, and 83.76% of zinc could be dissolved and recovered from the MSD under the following conditions: total ammonia concentration of 5 mol l−1, stirring speed of 300 r.p.m., ammonia/ammonium ratio of 1 : 1, solid/liquid ratio of 1 : 5, leaching temperature of 25°C and a leaching time of 60 min. A leaching kinetic study indicates that the leaching process is controlled by the diffusion and interface transfer and that the reaction apparent activation energy is 22.66 kJ mol−1. Fourier transform infrared spectroscopy and electrospray ionization mass spectrometry analysis showed that zinc can combine with the carboxylate anion to form Zn complexes such as [Zn2(Ac)3(NH3)2]+. Zn2SiO4, ZnS and ZnFe2O4 in NH3–CH3COONH4–H2O system did not disappear according to X-ray diffraction analysis for leaching residue.

Microwave drying of CuCl residue from hydrometallurgical zinc recovery process

ABSTRACTCuCl residue is a hazardous waste from the hydrometallurgical zinc recovery plant. It is very difficult to recycle due to complicated composition, highly corrosive nature, and refractory characteristics. Recently, a new process of microwave drying and roasting was successfully developed to produce both CuO solid and HCl gas products from the CuCl residue. In this paper, the dielectric property of the CuCl residue was measured under different moisture contents. The microwave absorption characteristics of the CuCl residue improved considerably as its moisture content increased. Laboratory-scale drying tests were conducted to evaluate the kinetics of microwave drying and to optimize the operation parameters. The efficiency of microwave drying was further demonstrated in industrial-scale level by microwave dryer developed in in-house. Finally, the drying mechanism of microwave heating of the sticky material was discussed and several measurements were optimized/implemented to intensify the drying process.

Microwave roasting and leaching of an oxide-sulphide zinc ore

In this paper, a novel combination of phase transformation and leaching is proposed to recover zinc from an oxide–sulphide zinc ore. Accordingly, various analytical technologies, such as X-ray diffraction, chemical analysis, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, are employed. The phase transformation of a raw ore and the effects of microwave heating and Na2O2 addition on zinc leaching are investigated. The results show that the addition of a strong oxide Na2O2 can directly transform the refractory phases, particularly zinc sulphide, into zinc sulphate. As a result, SO2 emissions are avoided and an environmentally friendly zinc recovery process is realised. Both microwave heating and the Na2O2 level have significant effects on phase transformation and zinc leaching. The zinc leaching rate can reach 82.06% under the following conditions of microwave heating: adding Na2O2 at a mass ratio of 25%, leaching in an ammonium chloride solution with a total ammonium concentration of 7.5mol/L and an ammonia/ammonium chloride molar ratio of 1:1, adding NaClO as an aid-leaching reagent and leaching for 1h. By contrast, the zinc leaching degree for the ore samples roasted in a traditional electric resistant furnace is only 30.62%. Moreover, at the same oxidation degree, the total energy consumption by the proposed process is 0.78kWh/(kg·ore), which is lower than that by traditional heating (same power). Thus, the combination technology of microwave-heated phase transformation and leaching is effective in treating oxide–sulphide zinc ore.

The Study of Hydrometallurgical Process for Recovery of Zinc from Electric Arc Furnace Dust

In this study the optimum conditions for recovery of valuable metal in Electric Arc Furnace Dusts were investigated. 2M of H2SO4, 1~5 of solid/liquid ratio, 0~180 min of leaching time has been established for leaching condition, and for electrowinning, each of Pt, C, Zn, Pb anode and Zn, Cu cathode was compared respectively at pH 2, 4 and 6. The result of elemental analysis of Zn crystal, a lagre quantity of Fe and H has been observed with Zn and other heavy metal, therefore, impurities removing process would be requir for enhancing purity of Zn. As the result, about 60% of Zn has been recovered under condition of 2 M of H2SO4, 1:2 of S/L ratio at 120 min, and Pt or Pb for anode, Zn for cathode has been shown the highest efficiency of electrowinning at pH 6.

Selective recovery of zinc from spent pickling baths by the combination of membrane-based solvent extraction and electrowinning technologies

This work deals with the analysis of an integrated zinc recovery process by means of electrowinning of the stripping solutions coming from the treatment of spent pickling baths (SPB) by a membrane-based solvent extraction (MBSX) process able of increasing the initial Zn/Fe molar ratio. Several stripping solutions containing different concentrations of zinc and iron in acid media obtained previously by the treatment of SPB by MBSX, were subjected to electrowinning to assess the efficiency and selectivity of zinc electrodeposition over iron under different operation conditions.At similar values of the zinc concentration in the stripping solution, the influence of the Zn/Fe molar ratio on the zinc electrodeposition process was negligible. On the other hand, although the variation of the initial concentration of zinc in the stripping solution neither affected the efficiency of zinc electrowinning, it increased the minimum value of zinc concentration in solution beyond which iron co-deposition started. Finally, the increase in the applied current, promoted the increase in zinc fractional conversion and in the zinc space–time yield, while the zinc current efficiency was reduced due to the stronger effect of secondary reactions.Although the change in the stripping characteristics seems not to strongly affect the zinc electrodeposition process, the use of a pretreatment step based on MBSX technology improved the results in terms of zinc percentage recovered and the rest of figures of merit, in comparison with those obtained by the direct electrowinning of SPB.

Selective process of zinc extraction from spent Zn–MnO2 batteries by ammonium chloride leaching

Recycling of spent Zn–MnO2 batteries by hydrometallurgy is usually carried out by leaching in acid media, mainly with sulphuric acid solutions. Another type of leachant was used in this work, specifically solutions of concentrated ammonium chloride. The development of this study has relied on the prediction of the chemical behavior of the constituting phases based on data obtained from theoretical and experimental equilibrium values. The assessment of the effects of factors on leaching efficiency was also done.It was concluded that about 70% of zinc, as ZnO, can be selectively extracted using this media, under optimized conditions such as 4–5M NH4Cl, 90–100°C and 4h, the remaining zinc namely that corresponding to the spinel form ZnO·Mn2O3 being insoluble. All other manganese species were also almost insoluble, besides iron, holding up that ammonium chloride leaching is a very selective process for zinc recovery from batteries. The factors temperature, leachant concentration and time are indicate to be very significant in leaching, while stirring velocity was less relevant. The apparent activation energy was calculated based on the initial velocity differential method and the value achieved (5.7±0.7kcalmol−1) showed a mixed control process. This indicates that, although the surface chemical reaction is still playing an important role in the leaching mechanism, the contribution of diffusion phenomena shall not be disregarded at all.

Recovery of Metallic Values from Brass Waste Using Brønsted Acidic Ionic Liquid as Leachate

The waste formed during industrial brass manufacturing is rich in copper and zinc metals. Therefore, treatment of this waste is a necessity from economic and environmental aspects. This study presents a process for recovery of zinc and copper through Bronsted ionic liquid (1-butyl-3-methyl-imidazolium hydrogen sulfate; [Bmim]HSO4), as leachate. It was found that all zinc content could be dissolved from the waste under two optimum conditions: (1) in ionic liquid (IL) concentration of 70% (v/v) at 60°C in 30 min or (2) in IL concentration of 50% (v/v) at 100°C in 60 min. On the other hand, ionic liquid leaching gave poor copper solubility under the conditions of the study. Zinc dissolution in the range 5–75 min by [Bmim]HSO4 can be explained with the shrinking core model controlled by diffusion through a product layer, and the apparent activation energy was calculated as 4.36 kJ/mol. The leach liquor was treated to obtain metallic zinc by the electrowinning method without a purification step. Scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDX) investigations showed that the layer of metallic zinc was plated successfully on the cathode.

Synthesis of hydrometallurgical processes for valorization of secondary raw materials using ant colony optimization and key performance indicators

An algorithm-based method for synthesis of hydrometallurgical processes using limited amounts of experimental data is presented. The method enables simultaneous selection and sequencing of unit operations and optimization of operating parameters. An ant colony optimization (ACO) based algorithm is used to identify the most economic process alternative in an iterative manner. Key performance indicators are used for comparison of candidate processes: a purification performance index measures purity improvement and a separation cost indicator is used as an objective function in process optimization. Computational times were reduced significantly with the suggested method compared to an algorithm which evaluates all the possible process options. The practical applicability of the method to hydrometallurgy is demonstrated by investigating zinc recovery from argon oxygen decarburization dust with two alternative leaching methods and recovery of lanthanides from nickel metal hydride (NiMH) batteries. In the first zinc recovery process, 150min normal batch leaching with 0.5M H2SO4 is used, and in the other one 270min batch leaching with H2SO4 is done by controlling the pH (>3.0). In both cases the leachate is extracted with D2EHPA at pH4.27, and stripped with circulating solution from zinc electrolysis. For lanthanides recovery the algorithm suggested a process in which the raw material is leached with 1.3M HCl, the leachate is extracted with D2EHPA at pH2.2, organic phase is stripped with 2.0M HCl and 99% pure Ln-oxalates are precipitated with oxalic acid at pH0.6. Compared to previously suggested process for the same raw material, the algorithm suggests operating the leaching step such that higher selectivity is achieved by sacrificing some yield.

Hydrometallurgical process for zinc recovery from electric arc furnace dust (EAFD). Part II: Downstream processing and zinc recovery by electrowinning

The characterization and the agitation leaching of electric arc furnace dust (EAFD) by diluted sulphuric acid have been studied in Part I, as a separate article. The aim of the present research work (Part II) is the development of a purification process of the leach liquor for the recovery of high-purity zinc by electrowinning. The proposed hydrometallurgical process consists of the following four (4) unit operations: (1) Removal of iron as easily filterable crystalline basic sulphate salt of the jarosite type, at atmospheric pressure, by chemical precipitation at pH: 3.5 and 95 °C. (2) Zinc solvent extraction by Cyanex 272 at pH: 3.5, T: 40 °C, with 25% extractant concentration. (3) Stripping of the loaded organic phase by zinc spent electrolyte (62.5 g/L Zn 2+) at T: 40 °C with diluted H 2SO 4 (3 mol/L). (4) Zinc electrowinning from sulphate solutions (at 38 °C) using Al as cathode and Pb as anode. The acidity of the electrolyte was fixed at 180 g/L H 2SO 4, while the current density was kept constant at 500 A/m 2.

Hydrometallurgical process development for the production of a zinc sulphate liquor suitable for electrowinning

This study deals with the development of an innovative hydrometallurgical process for zinc recovery from Waelz Oxide, a concentrate of zinc and lead oxides obtained pyrometallurgically from the treatment of EAF dusts. Its main objective is the production of a zinc sulphate liquor to be used as feedstock in electrolytic processes. The process requires different stages to achieve this goal. The first stage consists of a double-sulphuric-acid-leaching, achieving a 88% lixiviation of the zinc present in the Waelz Oxide. After the leaching, to fulfil the strict requirements of an electrolysis feed, some purifying stages, such as oxidation, removing more than the 99% of the iron present in the leach liquor, and cementation to remove cadmium, lead and copper were investigated. Finally, if the concentration of some metallic impurity is above the accepted level for electrolytic processes, an additional purification stage could be considered. Through this process, sulphate zinc liquors with a zinc purity of around 99.75%, containing less than 135 ppm of metallic impurities, could be obtained.

Hydrometallurgical process for zinc recovery from electric arc furnace dust (EAFD): Part I: Characterization and leaching by diluted sulphuric acid

The present paper is the first of a series of two articles dealing with the development of an integrated process for the recovery of zinc from electric arc furnace dust (EAFD), a hazardous industrial waste generated in the collection of particulate material during steelmaking process via electric arc furnace. Part I presents the EAFD characterization and its leaching process by diluted sulphuric acid, whereas Part II deals with the purification of the leach liquor and the recovery of zinc by solvent extraction/electrowinning. The characterization of the examined electric arc furnace dust was carried out by using granulometry analysis, chemical analysis, X-ray diffraction (XRD), thermogravimetric/differential thermal analysis (TG/DTA) and scanning electron microscopy (SEM). The leaching process was based on the Zn extraction with diluted sulphuric acid from EAFD under atmospheric conditions and without using any preliminary treatment. Statistical design and analysis of experiments were used, in order to determine the main effects and interactions of the leaching process factors, which were: acid normality, temperature and solid to liquid ratio. The zinc recovery efficiency on the basis of EAFD weight reached 80%. X-ray diffraction and scanning electron microscopy were used for the characterization of the leached residues.

Leaching Behaviour of Industrial Oxidic By-Products: Possibilities to Use as Neutralisation Agent in Bioleaching

In this study chemical leaching with sulphuric acid has been performed on 10 selected oxidic by-products in order to determine their neutralising capacity. The ultimate aim with this work is to replace the lime or limestone normally used in bioleaching operations to maintain pH at 1.5, the optimum pH-level for bioleaching microorganisms, with oxidic by-products. The investigated by-products includes three ashes from combustion for energy production, five slag samples from ore and scrap based steelmaking, an EAF dust and mesa lime from a paper and pulp industry, slaked lime (Ca(OH)2) was used as reference material. The neutralising potential of the by-products were evaluated by leaching them with sulphuric acid and comparing the amount of acid needed to that of the reference. Most of the by-products examined had good neutralisation potential and some had even higher capacities than Ca(OH)2. Neutralisation kinetics were lower for some slag products due to slow dissolution of some of the silicates present, but kinetics are considered good enough since stirred tank bioleaching is a relatively slow process. Zinc recoveries from the zinc containing materials were high, which thus is an additional benefit if these materials were to be used for neutralisation in a bioleaching process for zinc recovery.

Separation of Zinc by a Non‐dispersion Solvent Extraction Process in a Hollow Fiber Contactor

A process for recovery of zinc from acid solution with di(2‐ethyl hexyl phosphoric acid) (D2EHPA) dissolved in iso‐dodecane was carried out at 20°C in a countercurrent tubular membrane extractor using a hollow fiber as solid support. Experiments were performed at different aqueous metal concentrations (0.1–1.0 g/L), pH 0.1–2.1, and D2EHPA concentrations (2–8 v%). It was found that both the flux of metal and the extraction extent was highly influenced by the extractant concentration and the pH of the feed solution. Overall mass transfer coefficients were determined and related to the tube side, the membrane, and the shell side mass transfer by varying the aqueous flow rate (0.38–0.80 L/min) and organic flow rate (0.22–0.57 L/min) in countercurrent flow. The overall mass transfer coefficient for zinc extraction ranged from 6.2×10−6 m/s to 25.3×10−6 m/s. It was concluded that extraction kinetics were a major contributor to the overall resistance to mass transfer.

Investigation of optimal conditions for zinc electrowinning from aqueous sulfuric acid electrolytes

Results are reported of an experimental investigation of the effects of aqueous zinc(II) and sulfuric acid concentrations on current efficiencies and deposit morphologies of metallic zinc, aimed at designing a process for zinc recovery from solid industrial wastes by leaching and electrodeposition. Voltammetry and chronopotentiometry of additive-free solutions of zinc(II) sulfate and sulfuric acid were used to determine the zinc(II) reduction kinetics, prior to investigating the deposition in a Hull cell to observe the effects of the current density and the bath composition on current efficiencies and deposit morphologies. For a current density of 45 mA cm−2, best performance was obtained with zinc(II) concentrations of the same order of magnitude as the H+ concentration; too acidic solutions resulted in lower current yields and pronounced 3-D growth of the deposit.

Precipitation of iron from concentrated chloride solutions: Literature observations, challenges and preliminary experimental results

The removal of iron is necessary during the purification of leachates from zinc bearing ores prior to electrowinning due to its negative impact on both product quality and current efficiency. Whilst precipitation down to acceptable levels is readily achieved, the challenge lies in producing an easily filterable precipitate which is relatively pure (for resale and/or reuse). Crystalline hematite is an iron precipitate which potentially fulfils these requirements. Some work has been presented in literature on precipitation of hematite from sulphate solutions and dilute chloride solutions, however no work has been found on the selective precipitation of hematite from concentrated halide solutions. This technical note presents some preliminary observations on the selective formation of hematite from a leachate which originated from the zinc recovery process developed by Intec Ltd. The process is novel in the use of a mixed halide leachant over the traditional sulphide leachant, with the advantages of operation at low temperatures and atmospheric pressure, and that the leachant may be regenerated and recycled. The solution contains relatively high chloride/bromide concentrations which makes direct extrapolation from literature reports difficult.