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.     

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.     

Review of rate constants for thiosulphate leaching of gold from ores,concentrates and flat surfaces: Effect of host minerals and pH

A review of literature data for different types of sulphide concentrates and gold ores has been carried out to examine the impact of host minerals and pH upon gold leaching. Analysis of initial rate data over the first 30–60 min of gold leaching from sulphide concentrates or silicate ores over a range of ammonia, thiosulphate, and copper(II) concentrations, pH (9–10.5) and temperatures up to 70 °C shows the applicability of a shrinking sphere kinetic model with an apparent rate constant of the order k_ss = 10⁻⁶–10⁻³ s⁻¹. The dependence of apparent rate constant on pH and initial concentrations of copper(II) and thiosulphate is used to determine a rate constant k_Au(ρr)⁻¹ of the order 1.0 × 10⁻⁴–7.4 × 10⁻⁴ s⁻¹ for the leaching of gold over the temperature range 25–50 °C (ρ = molar density of gold, r = particle radius). These values are in reasonable agreement with rate constants based on electrochemical and chemical dissolution of flat gold surfaces: k_Au = 1.7 × 10⁻⁴–4.2 × 10⁻⁴ mol m⁻² s⁻¹ over the temperature range 25–30 °C. The discrepancies reflect differences in surface roughness, particle size and the effect of host minerals.     

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.     

无氰工艺回收利用黄金尾矿试验研究

为了综合回收利用内蒙古某黄金矿山堆浸尾矿中的金、银,采用无氰浸出工艺,选用新型无氰环保药剂作浸出剂,在矿浆质量浓度33%、pH=11、浸出剂用量2.0 kg/t、浸出时间24 h的条件下,金浸出率达52%,银浸出率约59%,浸出指标稳定。该工艺简单易行,可实现尾矿资源的二次利用,并能取得较大的经济效益。     

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.     

Sorption properties of manganese ores

Sorption properties of manganese ores to arsenic compounds in aqueous media are examined on the ore samples extracted from three Siberian deposits. The relation between sorption activity of manganese ores and medium pH, sorbent consumption, manganese content in the ore, and a manganese ore preparation process is established. Sorption properties in combination with earlier found oxidizing properties substantially expand the scope of integrated application of manganese ores.     

黏土型钒矿分级富集浸出试验的研究

将黏土型钒矿进行分级富集,对直接分级得到的精矿及未经分级富集的原矿进行了对比浸出试验研究,考察了硫酸用量、助浸剂A及B对V2 O5浸出率的影响．结果表明,精矿较原矿难浸出,需适当增加硫酸、助浸剂A及B的用量以达到理想的浸出率;浸出1 t的V2 O5所用的硫酸量,精矿的用量比原矿的约节省1／5．     

Cyclic voltammetry responses of gold electrodes in thiosulphate electrolyte

The gold thiosulphate system has been studied for some time due its prospective favourable economics over the gold cyanide system when treating certain ore types. Despite the large amount of work which has been done with gold thiosulphate system, various questions (uncertainties) still remain. For example, the causes for slow gold dissolution kinetics in thiosulphate and the gold losses during leaching observed in some applications. In this study, cyclic voltammetry was used to investigate the oxidation and reduction of gold in magnesium thiosulphate electrolyte. The anodic dissolution of gold is discussed in terms of possible reactions and mechanisms involving catalysts such as thallium and thiourea. The abrupt increase in anodic current in the presence of these catalysts indicates that the passivation of gold anodic dissolution is related to surface phenomenon and not to the depletion of thiosulphate ion at the reaction interface. The Tafel-like plots identified the increase of exchange current for gold oxidation and reduction reactions for catalyst assisted systems. The large anodic to cathodic peak separation ranged between 0.25 V and 0.37 V allowed most of the leached gold to diffuse away from the electrode. This indicates the electrochemically quasi-reversible to irreversible character of this system even in the presence of catalysts. The relationship between reduction peak current and concentration of gold thiosulphate in the bulk electrolyte was estimated based on relevant equation for electrochemically irreversible reaction.     

浸出氧化锰矿泥制取碳酸锰的研究

本文研究了采用废糖蜜作还原剂对氧化锰矿泥进行酸浸试验。结果表明,采用废糖蜜作还原剂,在适宜浸出条件下,浸出率可达94.67%,浸出液采用针铁矿法除铁,硫化法除重金属后得到的净化液可制取碳酸锰,其产品质量达到企业标准合格品,锰回收率可达到82.04%。     

铜矿峪低品位矿石地下生物溶浸可行性研究

本文详细阐述了利用生物浸出技术回收铜矿峪矿崩落区、毛石台及5#E矿体上部存留的大量低品位氧化矿及表外矿的可行性。     

Fungal pretreatment of sulfides in refractory gold ores

This study assessed the capability of the fungus, Phanerochaete chrysosporium, to decompose pyrite, arsenopyrite and a sulfide-containing flotation concentrate in an effort to develop a microbial process for pretreating refractory gold ores. The extent of biotransformation was monitored by analyzing for iron, sulfur and arsenic in incubation solutions, and for sulfide sulfur in the residual solids. The results were then expressed as percentages of the initial weights. For arsenopyrite, 1.5 wt.%, 7.2 wt.% and 10.3 wt.% of iron, arsenic and sulfur respectively were present as soluble constituents in the incubation solution within 21 days of fungal treatment, whereas for pyrite, there was 1.2 wt.% iron and 6.0 wt.% sulfur. For the same processing period in the case of the flotation concentrate, 1.8 wt.%, 6.1 wt.% and 10.7 wt.% respectively of iron, arsenic and sulfur remained in solution. Overall, the decomposition of sulfide sulfur in the samples was 15 wt.%, 35 wt.% and 57 wt.% respectively for pyrite, arsenopyrite and the flotation concentrate. Changes in sulfide sulfur concentration and the formation of oxide phases during fungal treatment were confirmed using Raman spectroscopy and X-ray diffraction analysis. These results suggest that P. chrysosporium is a potential microorganism for oxidative decomposition of metal sulfides associated with refractory gold ores.     

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.     

A review of the selective leaching of gold from oxidised copper-gold ores with ammonia-cyanide and new insights for plant control and operation

The ammonia-cyanide leach system was first patented over 100 years ago and stands out as a unique method of selectively leaching up to 90% Au and <1% Cu from oxidised copper-gold ores using <10% NaCN used in conventional cyanidation processes. However, the system has proved to be difficult to control and predict performance with different ores due to a lack of understanding of the chemistry and mechanism and proper process control. Several laboratory studies have been carried out using various empirical concentrations of ammonia and cyanide with mixed success and only a few commercial operations have been successful.This paper reviews some of the recent applied and fundamental studies on the leaching of copper-gold ores with the ammonia-cyanide system and provides insights into the mechanism to give a better appreciation of the key parameters required for the optimum leaching of gold with minimum copper dissolution. Recommended leach compositions, Eh and pH are provided to enable process control measures to be adopted for a variety of ores. The selective recovery of gold from the leach solutions by cementation or adsorption onto activated carbon or ion-exchange resins is also discussed.     

铀矿堆浸工艺中助渗剂应用的研究

在某些铀矿堆浸工艺中,由于矿石的泥化、膨胀和细颗粒迁移等原因,经常出现通道堵塞、渗透率低的问题,为此,提出了添加助渗剂的方案。助渗剂以表面活性剂为主体,目的是提高溶浸剂的渗透性和浸出工艺的效率。经对多种硬岩矿和泥矿的试验,证明其效果明显。还对助渗剂的作用机理作了初步探讨。     

卡林金矿中腐殖酸的提取及测定

采用陕西卡林型金精矿,研究了提取液浓度、温度、搅拌浸出时间及固液比对腐殖酸提取和测定的影响。结果显示,提取剂浓度,浸出温度、时间及固液比对腐殖酸的提取及测定有明显的影响。增加碱浓度和提高浸出温度可促使黄铁矿的脱硫反应,使腐殖酸含量测定结果偏高;固液比增大,使腐殖酸提取量降低,使腐殖酸含量测定结果偏低;碱浓度的增加,可减少搅拌浸出时间。