Zinc and silver recoveries from zinc–lead–iron complex sulphides by pressure oxidation

Acid pressure oxidation followed by cyanide leaching of the residue is a promising process for the treatment of complex sulphides and the recovery of precious metals along with the base metals will improve the economy of the process. However, silver is incorporated into the jarosite specie during the pressure oxidation and cyanide leaching of the residue yields very low silver extraction.In this work, iodide was added to the pressure oxidation of zinc–lead–iron complex sulphides to prevent the deportment of silver ions into the jarosite phase. At low temperature range (110–130 °C), the silver ions were completely sequenced into the silver iodide phase because of the fast precipitation kinetics of silver iodide and its stability at low temperatures. The leaching of the residue in cyanide solution yielded high silver extraction (above 90%).Silver extraction from the residue decreased when the pressure oxidation was conducted at high temperatures (140–150 °C). At this temperature range, the enhanced stability and the precipitation kinetics of the jarosite specie posed a challenge by competing (with iodide) for silver ions. This competition was minimised by using moderately high initial acid for the pressure oxidation.High zinc extraction was achieved during the pressure oxidation. Also, there were appreciable iron precipitation and acid neutralisation of the slurry. The resulting pregnant solution is suitable for zinc recovery by electrowinning and the residue can be leached for silver and gold extraction.     

A QEM*SEM study of a suite of pressure leach products from a gold circuit

High lime consumption during the neutralisation of oxidised solids at the Lihir gold operation can be related to both ore mineralogy and conditions within the autoclaves. During the pressure oxidation process, basic iron sulphate and potassium jarosite precipitated and silicate clay minerals were dissolved. Illite in the plant feed was identified as a source of potassium for potassium jarosite precipitation — a greater extraction of which was obtained during a period of ‘low’ lime consumption. By contrast potassium feldspar was found to be largely un-reactive.The dissolution of basic iron sulphate under alkali conditions resulted in the consumption of lime. The difference between the conversion of 4% and 8% of the total solid, by weight, from basic iron sulphate to ferric hydroxide can account for either ‘low’ or ‘high’ lime consumption. Potassium jarosite was largely non-reactive during neutralisation.The quantity of basic iron sulphate present in the autoclave discharge is likely to be a function of both ore mineralogy and autoclave conditions. These mineralogical changes occur mostly in the ultrafine, −10 μm size fraction.In order to control the consumption of lime in the plant, it is clear that during pressure oxidation the formation of basic iron sulphates needs to be minimised and that of potassium jarosite promoted.     

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。     

湿法炼锌赤铁矿法沉铁渣水热除杂

湿法炼锌过程赤铁矿法沉铁渣可通过高温水热反应制备高附加值的氧化铁红.为揭示赤铁矿沉铁渣在高温水热转化过程中氧化铁、碱式硫酸铁、铁矾等的行为特点,采用热力学计算与试验研究相结合的方式,对高温水热反应过程中各物质的热稳定性进行研究.结果表明,在温度180～260℃下,铁矾和碱式硫酸铁的热稳定性差,氧化铁的热稳定性强,高温水...     

Investigating heap bioleaching: Effect of feed iron concentration on bioleaching performance

This paper describes an investigation into the effect of iron concentration in the leach solution on the bioleaching of a low grade copper ore, where chalcopyrite was the dominant copper sulphide. The concentration of dissolved iron is primarily controlled by pH and the relative proportion of ferric to ferrous iron, with significant jarosite precipitation occurring above pH ≈ 1.8 in a highly oxidised system. The solution pH may be increased by the dissolution of acid soluble gangue and when iron oxidation is significantly higher than sulphur oxidation. The study was approached using two experimental systems. In the former, the leach solution was recycled through an ore bed of low aspect (reactor height divided by diameter) ratio for a portion of the experiment. During the recycle phase, no acid was added to the system and acid consumption by gangue material led to a pH increase (1.6–2.2). The resulting jarosite precipitation reduced soluble iron from 2.5 g/l to less than 250 mg/l. Copper recovery decreased, but not in proportion to the decrease in iron. This was partly attributed to adsorption on, or entrainment within, the jarosites. To study the effect of reduced iron concentration on leach performance under more controlled conditions, bioleaching was performed in packed bed column reactors with feed iron concentrations ranging from 5 g/l to 200 mg/l. Observations indicated an initial decreased rate of copper liberation with reduced iron concentration in the feed. The relationship between available Fe³⁺ concentration and copper liberation was not proportional. However, with time, the liberation of copper became independent of iron concentration in the percolation liquor. Further, the specific rate of copper liberation was consistently below the theoretical value on a basis of ferric iron concentration. The highest values of copper liberation were reported at the lowest iron concentrations. In summary, while increased iron concentration in solution may enhance the initial rate of leaching, mineral availability appears to dominate CuFeS₂ leach kinetics through the majority of the leach. Furthermore, high iron concentrations in solution aggravate jarosite formation with concomitant retention of copper in the ore bed.     

Acidic sulphate leaching of chalcopyrite concentrates in presence of pyrite

Copper concentrates with mineralogy dominated by chalcopyrite have slow leaching kinetics at atmospheric pressure in sulphate media because of the formation of passivation layer on its surface during the leaching. To enhance the leaching rate of the copper concentrate, pyrite was added to act as a catalyst. Pyrite and copper sulphide minerals then form a galvanic cell which increases both the copper leaching rate and yield. Effect of parameters such as solution redox potential, temperature, initial acid concentration, solids content, total initial iron concentration and pyrite to copper sulphide minerals mass ratio were investigated. Mineralogical analyses by XRD were performed on selected leach residues and the feed materials. A copper recovery higher than 80% in 24 h was achieved at a redox potential of 410 mV vs Ag, AgCl, a temperature of 85 °C, 15 g/L of initial acid concentration, a solid content of 7.8% (w/v), a total initial iron concentration 5 g/L and pyrite to copper sulphide minerals mass ratio 2:1. XRD patterns on leach residues showed that candidates for surface passivation, i.e. jarosite and elemental sulphur, were formed at high total initial iron concentrations.     

The role of metal-cyanide species in leaching gold from a copper concentrate

The cyanidation of copper-gold ores is a difficult issue owing to the ready formation of copper cyanide complexes during gold leaching. Moreover, the speciation of other metal cyanides in leach slurries and the interaction between them have not been researched extensively, and are of fundamental importance to gold mills.In this paper the role of the cyanide complexes of copper, silver, nickel, iron and zinc in gold leaching was investigated by examining the leaching of a copper concentrate. It was found that copper-cyanide and other metal cyanide species, including Ag, Fe, Ni and Zn, all play an important role in gold cyanidation under conditions of zero free cyanide. These species dissociate, and the cyanide made available by the dissociation leaches gold. These metals species then precipitate, usually as a hydroxide under typical leaching conditions. Silver is an exception, which may precipitate as a metal or AgCN species. When cyanide is present, the mechanism of copper-cyanide assisted gold leaching is the dissociation of the weakly bound fourth ligand of Cu(CN)₄³⁻. The cyanide made available can then be used to leach gold and other metals.     

提高黄钾铁矾法炼锌中银回收率的探讨

本文分析了银在焙烧、浸出和沉矾过程中的行为。铁矶渣中95%的银来自沉矾中和剂焙烧料。采用低污染黄钾铁矾法是提高银回收率的有效途径。     

二氧化氯氧化法处理含氰废水试验研究

针对某含氰含铜废液,采用二氧化氯氧化法脱除废液中氰,再用硫化法沉淀回收溶液中铜。结果表明,二氧化氯氧化法除氰合理工艺条件为: 反应温度25 ℃、溶液初始pH=9.5、反应时间60 min、二氧化氯气体流速60 mL/min,此时除氰率达到96%以上; 硫化沉淀法回收除氰后液中的铜,合理工艺条件为: 反应温度25 ℃、反应时间60 min、溶液初始pH=3、搅拌速度300 r/min、硫化钠用量为理论量3倍,此时沉铜率达到93%以上。     

Formation of jarosite during Fe2+ oxidation by Acidithiobacillus ferrooxidans

Jarosite precipitation is a very important phenomenon that is observed in many bacterial cultures. In many applications involving Acidithiobacillus ferrooxidans, like coal desulphurization and bioleaching, it is crucial to minimize jarosite formation in order to increase efficiency. The formation of jarosite during the oxidation of ferrous iron by free suspended cells of A. ferrooxidans was studied. The process was studied as a function of time, pH and temperature. The main parameter affecting the jarosite formation was pH. Several experiments yielded results showing oxidation rates as high as 0.181–0.194 g/L h, with low jarosite precipitation of 0.0125–0.0209 g at conditions of pH 1.6–1.7 with an operating temperature of 35 °C.     

Enhanced leachability of gold and silver in cyanide media: Effect of alkaline pre-treatment of jarosite minerals

Composite samples of tailings containing gold (1.35 g/t) and significant amounts of silver (155 g/t) were subjected to batchwise cyanide leaching to assess the feasibility of extracting gold and silver. The tailings are waste solids arising from flotation and leaching operations whereby the flotation product (sphalerite concentrate) is calcined and then solubilised into dilute sulphuric acid solution and eventually sequestered from the electrolyte by electrowinning. Silver and gold are part of the zinc refinery residue, flotation tailings and to a limited extent the calcine leach tailings. Mineralogical results showed that composite tailings are refractory in nature (44% quartz, 17% silico aluminates and 12% jarosites).The concept of enhancing gold and silver recovery from the tailings focused on firstly decomposing the jarosite minerals by alkaline pre-treatment and then secondly leaching with cyanide solution. These two steps ensured that free gold and silver found in the zinc refinery residue and in the jarosite minerals could be leached simultaneously. The composite tailings were treated with Ca(OH)₂ solutions and then heated to 90 °C for 2 h to decompose the silver-bearing mineral (Ag,PbFe₃(SO₄)₂(OH)₆). The alkaline pre-treated tailings were then subjected to cyanide leach tests at different NaCN dosages (2.5–10 kg/t) and particle size (96–200 μm). Without an alkaline pre-treatment stage, leach efficiencies achieved were 41% and 25% for gold and silver, respectively at 40 °C and 8 h mixing time. But, better leach efficiencies (55% for Au, 81% for Ag) were achieved after the feed was pre-treated with Ca(OH)₂. The leaching mechanism of gold was explained by the shrinking sphere model denoted by surface chemical reaction.     

Mineralogical characteristics and treatment of refractory gold ores

Refractory gold ores and concentrates are characterised by low gold recoveries and high cyanide consumptions when subjected to direct cyanide leaching. Therefore an oxidation pretreatment step is required before cyanidation that will break up the sulphide lattice and render gold particles accessible to cyanide ions. The main three options for the treatment of refractory ores and concentrates include the traditional oxidation roasting, the modern pressure oxidation and the bacterial oxidation which is still at an advanced experimental stage. The present work focuses on the mineralogical factors influencing the refractoriness of gold, the main characteristics and developments of each process and provides economic comparative data from various operations worldwide. Environmental considerations are also briefly discussed.     

Bioprocessing of pyrite concentrate from coal tailings for the production of the coagulant ferric sulphate

The aim of this work was to produce a high concentration ferric sulphate solution from coal pyrite tailings that could be used as coagulant for water and wastewater treatment. At laboratory scale it was performed the oxidation of pyrite in an aqueous medium in a packed bed leaching column in an oxidizing environment with the presence of acidophilic bacteria (Acidithiobacillus ferrooxidans) as well as nutrients for bacterial growth. It was indicated that an aqueous solution rich in ferric sulphate can be produced which was found suitable for application in water treatment plants.     

铅锌精矿中游离自然银和游离硫化银的测定

拟定了分离测定铅锌精矿中游离硫化银和游离自然银的方法。用硫酸-硫脲-硫代乙醇酸溶液选择溶解硫化银;用硫酸-硫脲-硫酸高铁铵溶液选择溶解自然银。方铅矿、闪锌矿和一定量的黄铜矿、黄铁矿和毒砂存在不影响浸取率。     

Electrochemical passivation of sphalerite during bacterial oxidation in the presence of galena

Sphalerite (ZnS), a mineral of particular hydrometallurgical interest, is generally found associated with galena (PbS). As such, the effect of galena on the leaching of sphalerite is of importance, and has been studied here for bacterial and ferric sulphate leaching. During both leaching processes galena was selectively oxidised to anglesite in favour of the dissolution of sphalerite. It is believed that this selective behaviour is due to galvanic interactions between the two minerals, whereby galena is sacrificed and sphalerite is passivated. This theory is consistent with the order of measured rest potential values of both minerals in solution, being 325 mV for galena and 375 mV for sphalerite (versus a standard hydrogen electrode). During bacterial oxidation, sphalerite passivation was observed across a range of mixed sphalerite/galena samples, including a mineral species and four ore specimens of varying grades. From the bacterial oxidation of a mixed mineral species, sphalerite was found to leach in the presence of lead sulphate precipitate, though the presence of this precipitate is believed to have caused diffusion limitation.     

难处理金矿热压氧化工艺研究

本试验以国内某超细微难处理金矿为研究对象,开展酸性热压氧化工艺研究;分析了温度因素对硫化矿物氧化、元素迁移和金氰化浸出等的影响。试验结果表明,通过温度变化可影响黄铁矿和砷黄铁矿氧化反应速率,进而对S、Fe和As元素的迁移状态产生影响。反应温度越高黄铁矿和砷黄铁矿氧化越彻底,有利于金的氰化浸出;完全氧化后金的浸出率约为94%。浮选金精矿中的黄铁矿、砷黄铁矿逐渐氧化转变为砷酸铁盐、铁砷硫硅等多元素共沉物质,未发现有碱式硫酸铁或铁矾物相,反应生成的各种沉淀产物对浸出率无显著影响。      

Studies on the mechanism and kinetics of bioleaching

The use of off gas analysis and redox potential measurement has shown that bioleaching involves at least three important sub-processes. The primary attack of the sulphide mineral is a chemical ferric leach. The role of the bacteria is to convert the iron from the ferrous to the ferric form, thereby maintaining a high redox potential.The kinetics of bacterial ferrous iron oxidation by Thiobacillus ferrooxidans and a Leptospirillum-like bacterium, and the chemical ferric leach kinetics of pyrite have both been described as functions of the ferric/ferrous-iron ratio. Thus, the chemical ferric leach of the mineral and the bacterial oxidation of the ferrous iron are linked by the redox potential, and are in equilibrium when the rate of iron turnover between the mineral and the bacteria is balanced.These rate equations have been used to predict the steady state redox potential and sulfide mineral conversion in a continuous bioleach reactor. The model successfully predicts laboratory data and is being tested against data from pilot-plant and full-scale bioleach systems. Furthermore, the model predicts which bacterial species will predominate and which mineral will be preferentially leached under specific operating conditions. Enzyme restriction analysis has shown that in pyrite-arsenopyrite bioleach reactors the dominant iron oxidizer is L. ferrooxidans, which is in agreement with the predictions of the model.     

Bioleaching of a Spanish complex sulphide ore bulk concentrate

In the present work the applicability of bioleaching using a mixed culture of mesophilic microorganisms (Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirilum ferrooxidans) on a bulk concentrate of a Spanish complex sulphide ore was studied. The bulk concentrate mainly consisted of by chalcopyrite, sphalerite and pyrite. Effects of nutrient medium, stirring, pulp density, temperature and the addition of CO₂ (1% v/v) to the air flow were also studied. The highest leaching rates and recoveries were obtained with mechanically stirred reactors at 5% pulp density and 9K medium. However, by using 9K medium higher jarosite precipitation was observed. Results showed that the optimum temperature for copper bioleaching was 30°C, whereas zinc dissolution increased with a rise in the temperature.     

硫酸亚铁和氰化钠在铅锌硫化矿分离中的作用

为了用重选法回收锡石,大厂锡矿需先用粗粒优先浮出硫化矿石,但分选比较困难。本研究采用硫酸亚铁与氰化钠作为铁闪锌矿的组合抑制剂,适宜的药剂条件抑制活性黄铁矿。优先分离出了脆性硫锑铅矿,研究了该组合抑制剂的作用机理。     

Removal of cyanide in aqueous solution by oxidation with hydrogen peroxide in presence of activated carbon prepared from olive stones

This work is dedicated to the removal of the very toxic free cyanide from aqueous solution by oxidation with hydrogen peroxide H₂O₂ in the presence of activated carbon prepared from olive stones. Effects of the initial molar ratio [H₂O₂]₀/[CN^?]₀, the initial cyanide concentration, the activated carbon concentration and the temperature on cyanide removal have been examined. The removal of free cyanide in absence of activated carbon showed very slow kinetics. The presence of activated carbon has increased the reaction rate showing thus a catalytic activity. The kinetics of cyanide removal has been found to be of pseudo-first-order with respect to cyanide and the rate constants have been determined for different values of the aforementioned parameters. The apparent activation energy has been determined from tests carried out at three different temperatures. It was found equal to 46.2 kJ/mol in the presence of activated carbon, which is about half of the 82.7 kJ/mol found for the oxidation in absence of the activated carbon.This process can be interesting for the cyanide removal from processed solutions because it does not use soluble metal catalyst and it consumes only hydrogen peroxide as chemical product.