Jarosite pseudomorph formation from arsenopyrite oxidation using Acidithiobacillus ferrooxidans

In this work, the oxidizing action of a native strain type A. ferrooxidans on a sulphide containing a predominance of arsenopyrite and pyrite has been evaluated. Incubation of the A. ferrooxidans strain in flasks containing 200 mL of T&K medium with the ore (particle size of 106 μm) at pulp density 8% (w/v) at 35 °C on a rotary shaker at 200 rpm resulted in preferential oxidation of the arsenopyrite and the mobilization of 88% of the arsenic in 25 days. Mineralogical characterization of the residue after biooxidation was carried out with FTIR, XRD and SEM/XEDS techniques. An in situ oxidation of the arsenopyrite is suggested on the basis of the frequent appearance of jarosite pseudomorph replacing arsenopyrite, in which the transformations Fe²⁺ → Fe³⁺, S^− 2 → S^+ 6 and As^− 1 → As^+ 3 → As^+ 5 occur for the most part without formation of soluble intermediates, resulting in a type of jarosite that typically contains high concentrations of arsenic (type A-jarosite). However, during pyrite oxidation, dissolution of the constituent Fe and S predominates, which is evidenced by corrosion of pyrite particles with formation of pits, generating a type of jarosite with high quantities of K (type B-jarosite). Lastly, a third type of jarosite (type C-jarosite) also precipitated forming a thin film that covered the grains of pyrite principally.     

Removal of sulfate from high-strength wastewater by crystallisation

Sulfate causes considerable problems in anaerobic digesters, related to generation of sulfides, loss of electrons (and hence methane), and contamination of gas streams. Removal of sulfides is generally expensive, and still results in methane losses. In this paper, we evaluate the use of precipitation for low-cost sulfate removal, in highly contaminated streams (>1 gS L⁻¹). The main precipitate assessed is calcium sulfate (gypsum), though the formation of complex precipitates such as jarosite and ettringite to remove residual sulfate is also evaluated. The four main concerns in contaminated wastewater are:- high solubility, caused by high ion activity and ion pairing; slow kinetics; inhibition of nucleation; and poisoning of crystals by impurities, rendering product unsuitable for reuse as seed. These concerns were addressed through batch experiments on a landfill wastewater with a similar composition to other sulfate rich industrial wastewaters (high levels of organic and inorganic contaminants). Crystallisation rates were rapid and comparable to what is observed by others for pure solutions (2-5 h). The kinetics of crystallisation showed a 2nd order dependence on supersaturation, which have implications for crystalliser design, as discussed in the paper. No spontaneous nucleation was observed (seed was required). Seed poisoning did not occur, and product crystals were as effective as pure seed. Solubility was increased by an order of magnitude compared to a pure solution (2.6 × 10⁻³ M² vs. 0.22 × 10⁻³ M²). As evaluated using equilibrium modelling, this was caused equally by non-specific ion activity, and specific ion pairing. Jarosite and ettringite could not be formed at reasonable pH and temperature levels. Given the lack of complex precipitates, and relatively high solubility, gypsum crystallisation cannot practically be used to remove sulfate to very low levels, and gas-sulfide treatment will likely still be required. It can however, be used for low-cost bulk removal of sulfate.     

Hazardous jarosite use in developing non-hazardous product for engineering application

Jarosite released from zinc metal extraction process is hazardous in nature and its world wide disposal has become a major environmental concern. In this study, an attempt has been made to immobilise and recycle the jarosite released from Hindustan Zinc Limited, India, using CCRs, so called fly ash, and clay soil. Results revealed that the particle size of jarosite was finer than that of CCRs and had higher porosity and water holding capacity due to fine textured materials resulting in high surface area (10,496.18 +/- 30.90 cm(2)/g). Jarosite contain higher concentration of toxic elements (lead, zinc, sulphur, cadmium, chromium and copper) than that of CCRs. Concentrations of radionuclides such as (226)Ra, (40)K and (228)Ac in jarosite found less than in CCRs are similar to that of soil. Statistically designed experiments on solidified/stabilised (s/s) sintered jarosite--CCRs products confirmed that the compressive strength of jarosite bricks reached as high as 140 kg/cm2 with 14.5% water absorption capacity at the combination of 3:1 ratio of jarosite and clay, respectively, but, concentrations of all the toxic elements recommended by United States Environmental Protection Agency (USEPA)--Toxicity Leachate Characteristics Procedure (TCLP) standard are not within the permissible limits. However, it is confirmed that the toxic elements leaching potentials of s/s-sintered products developed using 2:1 jarosite clay ratio with 15% CCRs comply with the USEPA-TCLP limits and also meet the quality for engineering applications.     

基于背景多层次分离的遥感矿化蚀变信息提取模型及应用实例

基于背景多层次分离的遥感矿化蚀变信息提取模型,以地物的波谱特征和遥感技术的物理机制为基础,以"矿化蚀变岩波谱特征分析—视反射率图像计算—"背景"多层次分离—蚀变信息增强—蚀变信息提取"为技术流程,能快速、准确地提取矿化蚀变信息。以新疆焉耆县哈都虎拉山一带为研究区,以最新的Landsat8-OLI多光谱数据为数据源,将该模型用于提取研究区的黄钾铁矾蚀变岩石信息,共提取出80余处黄钾铁矾蚀变岩石出露点,其中有两处黄钾铁矾蚀变岩石集中分布区,为研究区的找矿工作提供了重要线索。     

镉熔炼含氯烧碱渣在黄钾铁矾法炼锌中的再利用研究

通过热水溶解、液固分离工艺从炼锌回收镉所产生的含氯烧碱渣中回收镉。含氯碱液在沉矾前进入锌湿法系统,沉矾时用Cl-替代OH-,铜镉渣的热酸浸出及铜渣的低酸洗涤生产CuCl等以消除Cl-的危害;沉矾时用Na+代替NH4+,锌、镉回收率达到99.90%。试生产证明经济效益、环保效益良好。     

废航天磁性材料浸出液黄钾铁矾法除铁工艺

采用黄钾铁矾法除去废航天磁性材料浸出液中的铁,探究除铁的最佳条件。结果表明,在pH=1.5、温度90℃、反应时间2h时除铁效率可以达到95%左右。在添加晶种、pH=1.5、温度90℃、反应1.5h的条件下,除铁率也可以达到95%。     

Effect of biooxidation conditions on cyanide consumption and gold recovery from a refractory gold concentrate

This study investigates the biooxidation of a refractory gold concentrate using a mixed culture of acidophilic mesophiles, moderate thermophiles and extreme thermophiles and their effect on the subsequent cyanidation and gold recovery. The experiments with high % solids using mixed mesophiles showed better oxidation potential compared to moderate thermophiles and extreme thermophiles. However, the extreme thermophiles performed better than mesophiles and moderate thermophiles during the biooxidation with < 5% solids (w/v). The biooxidized residues obtained from the experiments with extremophiles, gave a maximum gold recovery of 92% after cyanidation. The NaCN consumption during cyanidation of the biooxidized residues obtained from experiments with extremophiles was lower than bioresidues obtained from experiments with mesophiles and moderate thermophiles. The highest consumption of NaCN of 17.5 kg/ton was from the experiment with 10% solids (w/v) using mesophiles. X-ray diffraction studies and chemical analysis of the biooxidized residues confirms the precipitation of jarosites at high redox potential which produces some ferricyanide, thereby explaining the reason for high cyanide consumption during cyanidation.     

Recycling hazardous jarosite waste using coal combustion residues

Increase in environmental concern due to improper management of both hazardous and non hazardous wastes released from different industrial process prioritized the necessity for the innovation research. In this context, this paper deals with the immobilization of jarosite waste released from the zinc industry and converting it into a value added product using coal combustion residues (CCRs) through solidification/stabilization (s/s) and sintering process. Experiments were conducted using different ratio of jarosite waste and clay soil with varying concentration of CCRs. The optimized experimental results (using jarosite waste and clay soil ratio of one with 15% CCRs) showed that it is possible to make a composite having desirable mechanical properties such as compressive strength (50–81 kg/cm²); water absorption (13–17%); shrinkage (11–32%); and density (1.6–1.8 gm cm^?3) to use as a construction material. Under solid state sintering process, with the application of CCRs, the mineral phases such as X Fe₃ (SO₄)₂(OH)₆ [where X = K and NH₄], 2Fe₂O₃SO₃.5H₂O, PbSO₄, CaSO₄ in jarosite waste were transformed into a silicate matrices. The leachate studies confirmed that the toxic elements such as Cd, Pb, etc. were immobilized in the jarosite waste composite and meeting the USEPA TCLP toxicity norms for safe utility. The composite product thus developed has showed potential for recycling jarosite waste in construction sector leading to cross sector waste recycling.     

铁矾法炼锌工艺中回收银的研究

在铁矾法炼锌工艺中,溶解于溶液中的Ag~+吸附于锌焙烧料中残余的闪锌矿ZnS(0.3—0.5wt%S)表面,或生成银铁矾型化合物使银富集于酸浸渣。控制沉矾过程中焙砂的用量,保证沉矾前液清亮是降低铁矾渣中的银含量的有效措施。高酸浸出渣中的银铁矾型化合物须酸分解转化为可浮的银矿物。故从高酸浸出渣Ag(300g/t)中可用超酸浸出—硫化浮选法回收银,银的回收率76.54%,银精矿品位4456.0g/t。     

低污染钠、铵铁矾法除铁

本文在钠铁矾、铵铁矾沉淀除铁动力学研究的基础上,研究了含钠、铵等沉矾离子及三价铁离子的锌焙砂高酸浸出液的预中和、以及中和后溶液的钠铁矾、铵铁矾沉淀除铁,探讨了湿法炼锌低污染钠、铵铁矾法除铁的途径及有效性。