Thiosulphate leaching of gold in the presence of carboxymethyl cellulose (CMC)

Carboxymethyl cellulose (CMC) was introduced as a surfactant in the leaching of pure gold as well as a sulphide ore using ammoniacal thiosulphate medium. Competing with thiosulphate anions to complex with the cupric ion at the axial coordinate sites, CMC in small quantities reduced the consumption of thiosulphate in the ammoniacal thiosulphate leaching system. The dissolution of pure gold in thiosulphate solution was enhanced in the presence of CMC, and this beneficial effect became more pronounced with an increase in the CMC concentration up to a certain level. Extraction rates of gold and silver from the sulphide ore were improved greatly, while the consumption of thiosulphate was reduced in the presence of CMC especially at a higher CMC concentration. The enhanced leaching performance was attributed to the stabilisation of thiosulphate, likely reduced leaching passivation and the dispersion of mineral particles in the slurry system. Addition of CMC facilitates satisfactory gold extraction at low reagent consumption in thiosulphate leaching.     

Prospects for underground leaching in gold mines

The authors describe experiments on pretreatment of ore by injection of explosive gases before underground leaching of gold in mine conditions. It is shown that injection of explosive gases into opening micro-fractures enhances efficiency of underground leaching owing to microstructural transformation of ore containing dispersed gold.     

The role of amino acids in the thiosulphate leaching of gold

Amino acids L-valine, glycine, DL-α-alanine and L-histidine were applied in the ammoniacal thiosulphate leaching of a pyrite concentrate. Amino acids formed more stable complexes with cupric ions than does ammonia, resulting in lower thiosulphate consumption due to reduced interaction between thiosulphate and the copper complexes. Overall gold extraction was largely improved by the addition of amino acids, despite lower initial kinetics. Thiosulphate consumption decreased with an increase in the amino acid concentration. Among the amino acids, L-histidine improved overall gold extraction and reduced the thiosulphate consumption to the greatest extent.     

Productivity of chemical-electrochemical gold leaching from rebellious ore

The authors describe experimental research findings on chemical-electrochemical leaching of gold from rebellious minerals. A laboratory-scale plant has been designed for studying the leaching kinetics. Rational parameters of chemical-electrochemical leaching are specified (duration of the process, electrode current density, NaCl concentration). The researchers analyze the changed microstructure and phase composition of arsenopyrite surface after the leaching and substantiate the leaching improving practices.     

某铀精矿酸法搅拌浸出氧化剂的选择

对比了二氧化锰、二氧化锰加硫酸亚铁以及硫酸铁3种氧化剂处理某铀精矿的酸法搅拌浸出结果.结果表明,采用硫酸铁作氧化剂后酸耗明显减少、浸出所需温度低、浸出速率快、浸出液中磷和锰含量少.     

The mechanism of leaching of gold from refractory ores

Refractory gold ores commonly contain free gold, submicroscopic gold, base metal sulphides, pyrite, pyrrhorite, labile sulphides and carbonaceous material. The analysis of gold deportment with the diagnostic leaching technique has opened a research field to gain more insight into the fundamentals of the kinetic behaviour of gold dissolution from refractory ores. Hence, more detailed studies on the kinetics of the reactions that occur during leaching with cyanide are now possible.Previous research work has indicated that the dissolution rate of gold during cyanidation becomes depressed after a certain time with no further increase in the rate. However, a second noticeable increase in the gold dissolution rate has been observed after a leaching time of 5 to 12 hours during some of the cyanidations, following the destruction of a mineral with the diagnostic leaching technique. If such a second increase in dissolution rate does not occur, the re-leaching of the filtered solids with a fresh cyanide solution yields an additional gold extraction of 4 to 8 %.Various experimental results have indicated that a passivative film forms on the surface of some of the liberated gold. The selective destruction of the various minerals with oxidative acid leaches destroys and/or decomposes certain minerals which may form films on the gold surface by precipitation. The chemical composition of these films and precipitates depends on the mineralogy of the sample. These films may be oxides, sulphides, carbonates and cyanide complexes.The complexes can be destroyed, depending on the nature of the film, by interstage dilute acid and/or cyanide washes in an agitated vessel. The destruction of the films exposes the gold surface for cyanidation. Whereas most of the previous studies on the leaching of gold have focused on the whole ore, the emphasis in this study was on the leaching behaviour of gold from various ore constituents. This approach of studying the leaching behaviour of different gold bearing minerals has provided reasons why some ores leach better than others.     

从焙烧氰化尾渣中回收金、银

对于含铜、砷金精矿,国内外黄金冶炼厂通常采用焙烧氰化法提取金、银,但所产的氰渣中金、银的含量较高,其品位分别为Au1.5～2.5g/t、Ag150～250g/t.如何从焙烧氰化尾渣中回收Au、Ag,合理地利用矿产资源,提高企业的经济效益,是目前黄金选冶工艺中急待解决的难题.为此,我们以山东招远黄金冶炼厂焙烧氰化尾渣为原料进行了试验研究.结果表明,采用添加剂进行尾渣焙烧-氰化浸出的工艺,金、银的回收率分别达到61.54%和76.81%.该方法投资少、成本低、简单易行,具有较好的经济效益和社会效益,值得推广应用.     

某氧化金矿堆浸提金试验研究

贵州某氧化金矿金以极微细粒形态包裹于石英、褐铁矿、阳起石、角闪石、绢云母等矿物中;本研究通过正交堆浸试验,得出影响金浸出效果的因素依次为:矿石粒度＞浸出时间＞NaCN用量＞石灰用量.按照最佳条件组合,获得金浸出率为90%以上的较佳指标.     

Simulation study of the optimal distribution of cyanide in a gold leaching circuit

The mineral industry has been using cyanidation to recover gold from ores for more than a century; however, a systematic study of the best reactant addition strategy in a cascade of agitated leaching tanks is not available in the open literature. A phenomenological mathematical model of the gold cyanidation process, calibrated with a set of industrial data from an Australian plant, together with an economic performance index is used to analyze this problem. The simulated results show that the best compromise between the two antagonistic effects, cyanide consumption and gold recovery, which are both function of cyanide concentrations, leads to a reagent distribution that depends on the leaching and cyanide consumption kinetics, pulp feed characteristics, and economic factors such as the gold market value. For the specific studied plant, in the operating range of low cyanide consumption and fast gold dissolution, all the cyanide must be added in the first tank; however, in the operating conditions of high cyanide consumption, cyanide has to be distributed in the first, second and third tanks.     

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 effect of iron contaminants on thiosulphate leaching of gold

Metallic iron and ferric ions were subjected to wet grinding with a sulphide ore in a ceramic ball mill to simulate the fine grinding process using mild steel, in an attempt to investigate the effect of iron species on the ammoniacal thiosulphate leaching of gold. Metallic iron and ferric ions decreased gold leaching in both kinetics and overall extraction when they were added in the wet grinding of a sulphide ore. This detrimental effect became more pronounced with the addition of metallic iron and ferric ions at higher concentrations. Metallic iron retarded the gold leaching more than ferric ions at the same dosage. The decomposition of thiosulphate in the leaching of the sulphide ore increased with the addition of metallic iron and ferric ions in the wet grinding. Thermodynamic analysis indicated that the predominant species for iron was ferric hydroxide under the leaching conditions. Wet grinding at a higher pH of 9 and use of ethylenediaminetetraacetic acid (EDTA) were ineffective in improving the gold leaching with the addition of metallic ions and ferric ions in the wet grinding. Iron oxide and hydroxide slime coatings at the surfaces of pyrite and pyrrhotite were reduced using carboxymethyl cellulose (CMC) to render the sulphide and slime particle surfaces highly negatively charged. Precipitation of iron oxide species at the surfaces of pyrite and pyrrhotite was observed in the morphological study of the leach residues with the addition of metallic iron in the wet grinding. The addition of CMC effectively reduced iron oxide slime coating at the sulphide surfaces and the aggregation of fine particles.     

The effect of sulphur species on thiosulphate leaching of gold

Thiosulphate is a metastable anion that tends to readily undergo chemical decomposition in aqueous solutions. The presence of tetrathionate, trithionate and sulphide is unavoidable in the ammoniacal thiosulphate system, as they are products of thiosulphate decomposition. Thiosulphate decomposition is of great importance in the thiosulphate leaching of gold. The effect of three typical sulphur species tetrathionate, trithionate and sulphide on thiosulphate leaching has been investigated in both pure gold and ore systems. The gold dissolution increased at low concentrations of the sulphur species, but decreased at high concentrations. The presence of these sulphur species significantly reduced thiosulphate decomposition, and this beneficial effect became more prominent at high levels of the species. The Eh–pH diagram for the Au–N–S–H₂O system indicated that the sulphide ion could form HS⁻ to complex gold, enhancing gold leaching. Tetrathionate, trithionate and sulphide would convert to thiosulphate with some elemental sulphur being formed via oxidation or reduction routes. The presence of the sulphur species shifted the thiosulphate decomposition reactions, and hence stabilised thiosulphate. Raman spectra demonstrated that the gold surfaces were readily passivated in the presence of the sulphur species, and the passivation tended to be more severe at higher levels of the species.     

加压氧化-氰化浸出法从氰化尾渣中回收金

山东某金矿为高硫多金属矿床,矿石中的伴生元素为Ag、Fe、Cu、Pb、Zn、S等元素,该矿采用浮选法将矿石中的金富集,生产的金精矿再磨后直接氰化浸出。生产实践表明,在氰化尾渣中金的品位高达3～4g／t,这不但浪费了国家资源,还影响了企业经济效益的提高。本文运用加压氧化-氰化浸金的原理,采用一种加压氧化-氰化浸金设备,对氰化尾渣进行了加压氧化-氰化浸金工艺试验。     

Interactions between sulphides and manganese dioxide in thiosulphate leaching of gold ores

The interactions between manganese dioxide and pyrite or chalcopyrite were investigated in both the ammoniacal and ammoniacal thiosulphate leaching systems. Pyrite and chalcopyrite dissolved at enhanced rates in the presence of manganese dioxide in both ammoniacal and ammoniacal thiosulphate solutions. The interactions between manganese dioxide and sulphides were also applied in the thiosulphate leaching of gold from a pyrite concentrate and a sulphide ore. The addition of a small amount of manganese dioxide in the thiosulphate leaching of the sulphide bearing gold ores improved both the kinetics and the overall gold extractions without much impact on thiosulphate consumption.A pre-treatment process with copper ammoniacal solutions enhanced gold extractions from the sulphide bearing ores and reduced thiosulphate consumption to a large extent. The sulphides partially degraded in the pre-treatment process likely exposing gold to leach solutions. SEM images of the surface corrosion of pyrite and chalcopyrite in contact with manganese dioxide showed that the pre-treatment with manganese dioxide enhanced the degradation of the sulphide matrices, thus achieved a better gold leaching from the sulphide bearing ores.     

On the use of lignin-based biopolymer in improving gold and silver recoveries during cyanidation leaching

In the present paper, influence of a lignin-based biopolymer in improving gold and silver recoveries during cyanidation leaching is discussed. Series of laboratory cyanidation leaching testworks at the absences and the presences of the biopolymer were performed under variations of the biopolymer concentration, NaCN concentration, slurry density and particle size distribution. The ore samples used were from Pongkor Gold Mine of PT. Antam, Tbk. in Indonesia. The biopolymer additive was found to reduce slurry viscosity that leads to a higher dissolved oxygen concentration in the leach solution. The testwork results show that the use of biopolymer improves gold and silver recoveries as well as leaching kinetics. At biopolymer dosage of 800 mg/L, the increases of gold and silver recoveries were 4.5% and 6.4%, respectively. The lignin-based biopolymer is able to disperse fine solid particles and stabilizes the ore suspension in the leach-slurry that results in a better contact between the ore and the leaching agents. The effect of biopolymer on the gold and silver recoveries was found to be more significant at lower cyanide dosages. The addition of biopolymer resulted in the increase of cyanide consumption, lowering final pH and higher dissolved iron which is associated with gold-bearing pyrite dissolution. Enhanced dissolution of gold-bearing pyrite at higher dissolved oxygen concentration was found as the major factor that improves gold recovery at the presences of the biopolymer in addition to lowering slurry viscosity that leads to higher dissolved oxygen concentration and effect of fine particles dispersion.     

Study of cryogenic disintegration of gold-quartz ores to intensify the heap leaching of gold

It is shown how the airy and nival conditions of cryogenic eolation affect the structural changes and weakening of gold-qnartz sulfide ores under cyclic exposure to frost-penetration and thaw. It is revealed that leaching of ores after cryogenic eolation in the nival conditions and additional pretreatment is more intensive, by 25%, than leaching of ores that were not prepared by cryogenic eolation. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 1, pp. 102–110, January–February, 2006.     

Chloride assisted leaching of chalcocite by oxygenated sulphuric acid via Cu(II)–OH–Cl

The beneficial effect of the addition of sodium chloride upon the leaching kinetics of complex iron–nickel–copper sulphides at elevated temperatures and oxygen pressures has been widely reported since the late 1970s, but the role of chloride is still being investigated or debated. Previous researchers have considered chloride as: (i) a complexing agent for cuprous ions; (ii) a surfactant that disperses the molten sulphur and thus removes passivation of the mineral surface by elemental sulphur during pressure leaching; and (iii) a reagent which increases the surface area and the porosity of the insoluble product layer on the surface. A proper understanding of the role of chloride based on the leaching of individual sulphides of known composition in the absence of host minerals at low pulp densities would be useful for the development of chloride assisted sulphate leaching processes for complex sulphide ores, concentrates, and mattes. In the present study evidence for the formation of basic salts of Cu(II) and Fe(III) during leaching are presented. The published rate data are analysed for the leaching of copper from mono-sized chalcocite particles in oxygenated sulphuric acid solutions maintained at 85 °C, a temperature lower than the melting point of sulphur. The initial leaching follows a shrinking particle (sphere) model, and the apparent rate constants are first order with respect to the concentration of dissolved oxygen and chloride. The intrinsic rate constant for the surface reaction (0.2 m s⁻¹) is two orders of magnitude larger than the calculated mass transfer coefficient of oxygen (3 × 10⁻³ m s⁻¹). The proposed reaction mechanism considers the formation of an interim Cu(II)(OH)Cl⁰ species which facilitates the leaching process.     

加压碱浸——常压酸浸提纯隐晶质石墨工艺

针对现有石墨提纯技术的不足,提出加压碱浸—常压酸浸工艺,考察了加压碱浸和常压酸浸各因素对提纯效果的影响。结果表明,在加压碱浸温度200℃、碱浓度250g/L、液固比3、反应时间1h、矿石粒度P90=-45μm,常压酸浸温度80℃、酸浓度2.16%条件下,提纯后石墨产品固定碳含量可达96%以上。     

处理地(堆)浸铀浸出液离子交换装置类型的选择

地(堆)浸浸出液一般为清液,用离子交换法从地(堆)浸浸出液中提取铀,其装置均属于适宜处理清液中铀的离子交换效率高的密实床.对于同属于密实床的固定床吸附装置与密实移动床吸附塔作了简单的比较;对于多种型式的密实床解吸设备,从操作运行到其适用场合等方面作了介绍和分析对比;固定床及密实移动床均适合于地(堆)浸提铀厂使用,它们各有其特点.如何具体地选择这类装置,这与工厂规模、建厂方式(整体式提铀厂还是卫星厂和中心厂的分体式)、甚至还可能与各国的使用习惯等均有关,是一个较复杂的问题.