Ammoniacal thiosulphate leaching of gold in the presence of pyrite

The effect of pyrite on gold dissolution was investigated in the ammoniacal thiosulphate leaching system using pure gold foils. Special emphasis was placed on gold leaching in association with pyrite dissolution, thiosulphate decomposition and gold leaching passivation. The presence of pyrite retarded gold dissolution and this detrimental effect became more pronounced at higher pyrite contents. Pyrite catalysed the decomposition of thiosulphate to trithionate. The addition of sulphate enhanced gold leaching by retarding the dissolution of pyrite in ammoniacal thiosulphate solutions. XPS analysis indicated the presence of iron hydroxide species at the gold surfaces in the presence of pyrite, which was likely responsible for the reduced gold dissolution. SEM analysis indicated a lesser extent of gold dissolution occurring in the presence of pyrite.     

Effect of the composition of some sulphide minerals on cyanidation and use of lead nitrate and oxygen to alleviate their impact

An investigation was carried out on synthetic ores containing high purity pyrite, pyrrhotite and chalcopyrite and on two gold ores currently processed to evaluate the impact of cyanicides on cyanidation and to improve the leaching performance by using a pre-leaching, injecting oxygen and adding lead nitrate. With regard to the synthetic ores, it was found that pyrrhotite did not generate a high cyanide consumption while pyrite and chalcopyrite were detrimental. Pre-leaching was deleterious for the ore containing chalcopyrite while pre-leaching with lead nitrate was very efficient to decrease the reactivity of the ore containing pyrite. The two gold ores studied had very different compositions. The low sulphide ore had a low sulphide content (1.36% S), present as pyrrhotite while the second had a very high sulphide content (20.2% S), in the form of pyrite, pyrrhotite and chalcopyrite. The efficiency of the process conditions was peculiar to the ores. The high sulphide ore required a stronger, longer pre-leaching period (12 h) with greater amounts of lime (7.0 kg/t) and lead nitrate (600 g/t) than the low-sulphide ore. The ore with a low sulphide content required a pre-leaching of only 1 h with a small quantity of Pb(NO₃)₂ (50 g/t) and leaching can be performed at 360 ppm NaCN to allow a recovery of 96.4% Au and a low cyanide consumption at 0.18 kg/t. As for the high sulphide ore, cyanidation had to be conducted at 560 ppm NaCN to recover 88.4% Au with a cyanide consumption of 0.80 kg/t. An increase in the amount of lime enhanced oxidation of soluble sulphides. Lead nitrate stabilized copper and iron dissolution by forming a passivation layer at the surface of sulphide minerals. Lead nitrate also prevented the formation of a passive layer at the surface of gold.     

Heap Biooxidation - Bioleachingofa Refractory Gold-Bearing Ore

Abstract

A refractory pyrite/arsenopyrite ore containing 3.7 g/ton of gold finely disseminated in the sulphide matrix was subjected to microbial leaching in a heap containing 120 tons of ore crushed to minus 15 mm. The ore was initially leached by means of acidophilic chemolithotrophic bacteria to oxidize the sulphide minerals and to liberate the gold. About 50% of the sulphide sulphur was oxidized within 90 days. Previous laboratory experiments had shown that such degree of sulphide oxidation resulted in a high gold extraction during the subsequent leaching of the pretreated ore. After the bacterial pretreatment the ore was washed with water and was treated by alkaline solutions until the pH of the heap effluents was established in the range of 9- 10. Then the leaching of the gold was started with solutions containing amino acids of microbial origin and thiosulphate as gold-complexing agents as well as some ions participating in the oxidation and/or complexation of the gold. 70.7% of the gold was leached within 12 days in this way. Silver was leached together with gold. The pregnant solutions were treated by cementation with metallic zinc to precipitate the dissolved precious metals.     

氰化浸金优化工艺参数的试验研究

本文研究的金精矿中耗氰耗氧的矿物含量较高，有３０．７４％的细粒金赋存于黄铁矿内．试验研究结果显示，金的浸取不仅取决于超细磨矿，还必须经过强碱浸预处理，以改变硫化矿的基质，并使矿浆中总氰与铜的摩尔比高于３：１，才能实现降低氰耗及获取较高的金浸出率。     

浮选金精矿细菌氧化-氰化提金连续扩大试验研究

某金矿石金矿物粒度细小且大部分以次显微金的形式存在,属于高砷硫化矿难选金矿石。由于浮选金精矿含砷,常规氰化浸出率仅为11.84%。经细菌氧化—氰化提金连续扩大试验研究,磨矿细度-0.071 mm占96%,矿浆浓度20%,矿浆温度45 ℃,矿浆pH值1.5～1.8,细菌氧化采用二级氧化,氧化时间9 d,金浸出率达到93.24%,比常规氰化浸出率提高了81.40%,各项指标大幅提高,解决了销售难题,达产后年利润提高了5 000万元,为含砷硫化矿难选金矿石的开发利用提供了选冶新工艺。     

Cyanide and Other Lixiviant Leaching Systems for Gold with Some Practical Applications

Selection of a leaching system for gold involves consideration of ore texture and mineralogy, chemical requirements, leaching techniques, the development of flowsheets, and environmental management. Aqueous dissolution chemistry for alkaline, neutral, and acid systems is mainly considered here. All systems require an oxidant to oxidise gold and a ligand to complex with gold in solution. Adjustment of pH is usually necessary.

Alkaline lixiviant systems (pH > 10)include cyanide, ammonia-cyanide, ammonia, sulphide, nitriles, and a few other minor possibilities. Oxygen is the main oxidant. Cyanide, which is the main ligand in these systems, forms an anionic complex, “Au(CN)2”, with Au(I). Gold dissolution rates are controlled by oxygen solubility in solution.

Neutral lixiviant systems (pH 5-9)include thiosulphate, halogens, sulphurous acid, and bacteria plus natural organic acids as the ligand. Oxygen is the normal oxidant and either Au(I) or Au(III)complexes are formed.

Acid leaching systems (pH ? 3)may contain thiourea, thiocyanate, chlorine, aqua regia, or ferric chloride. Chloride is the ligand in the last three systems and the oxidants include chlorine, ferric chloride, hydrogen peroxide, and nitric acid which produce Au(III) anionic complexes, e.g. [AuClJ". Fast gold dissolution is possible but reagent consumptions are high. Thiourea is unusual in producing a cationic Au(I)complex, “Au(NH2CSNH2)2” and gold dissolution is slower.

For treating simple auriferous oxide-silicate-carbonate ores, and many otfier materials, cyanide remains the preferred lixiviant.

Most non-cyanide leaching systems appear to have little wide-spread practical application. Possible niche applications include the use of chlorine or aqua regia to dissolve coarse gold from gravity concentrates, oxidising acid chloride solutions for die treatment of auriferous base metal sulphide concentrates, thiosulphate for dissolving gold from gold-copper ores, and thiourea for auriferous hydrometallurgical intermediates.     

Selective dissolution of uranium from a copper flotation concentrate

The copper flotation concentrate produced from the Olympic Dam copper— uranium gold deposit in South Australia contains uranium associated with the copper sulphide and gangue minerals. Work with a copper concentrate in which the copper mineralization was of the chalcocite-bornite type has shown that 94–97% uranium can be dissolved with sulphuric acid (> 40 g/L) at 30–60°C in 24 h. The addition of an oxidant was not necessary. Copper was leached from the concentrate along with the uranium. In the first 15 min, 5–7% copper dissolved but thereafter virtually no further copper dissolved when the reaction was carried out under nitrogen or argon (i.e., in the absence of oxygen). In air and oxygen, copper dissolution continued over the 24 h of the reaction. The initial rapid dissolution of copper was associated with oxidation of djurleite to roxbyite and dissolution of surface oxidation products. In air and oxygen, oxidation of roxbyite and bornite to blaubleibender covellite was associated with further dissolution of copper. The redox potential of the suspensions was controlled by reactions of the copper sulphide minerals. For reactions under nitrogen the redox potential of the system was 225–250 mV vs. saturated calomel electrode (SCE), while in air or oxygen the potential gradually rose (to 350 mV vs. SCE) as successive copper sulphides were oxidized. These results, and work at the Olympic Dam metallurgical pilot plant, have shown that uranium can be removed selectively from copper flotation concentrates produced from the Olympic Dam deposit.     

GOLDOX湿法冶金工艺提高金回收率的试验研究

鑫汇金矿矿石为多金属硫化矿,同时含有一定的碳,采用浮选-金精矿氰化-锌粉置换-金泥湿法冶炼工艺流程,由于精矿中杂质含量较高,加上碳的“劫金效应”,金浸出较为困难。为提高矿石金回收率,在前期小型试验的基础上,经过充分论证,从2013年7月开始,在氰化生产流程中进行了历时6个月的GOLDOXTM纯氧浸出工业试验研究。从工业试验前后主要生产指标对比来看,氰渣中金品位降低了0.20×10^-6,每年可增加经济效益80.8万元。该项研究成果对同类性质的黄金矿山企业具有一定的借鉴意义,将对纯氧浸出工艺在我国黄金行业的应用起到良好的示范和推动作用。     

新疆那拉提成矿带某金矿选矿工艺试验研究

新疆那拉提成矿带某金矿矿石结构主要为半自形—他形粒状结构,矿石中主要硫化物为黄铁矿,金主要以显微自然金形式存在。针对矿石性质特征,开展了尼尔森重选、全泥浸出和浮选探索试验。结果表明:相比尼尔森重选、全泥浸出工艺,浮选工艺适于处理该矿石,其闭路流程可获得金精矿金品位50.44 g/t、金回收率92.90%的良好指标。     

哈西亚图金矿选矿综合回收利用研究

哈西亚图铁多金属矿床中共生的金矿规模已达中型,可大大提高该矿床的经济效益,对金矿综合回收利用方法的研究显得尤为重要。矿石工艺类型为中硫化物矽卡岩型金矿石,矿石自然类型属混合矿。矿石中主要金属矿物为磁铁矿、磁黄铁矿和黄铁矿,贵金属矿物为自然金和银金矿。通过试验研究,浮选工艺推荐“浮选金-尾矿磁选铁-铁精矿浮硫”方案,浸出工艺推荐“全泥氰化炭浸提金-尾渣磁选铁-铁精矿浮硫”方案。试验结果表明,采用全泥氰化炭浸-磁选铁（浮选除硫）工艺处理哈西亚图金矿石效果最佳。     

Hydrometallurgy of precious metals recovery

The hydrometallurgical process for the treatment of gold and silver ores remained unchanged for the first 70 years of this century, and consisted essentially of leaching in cyanide solution followed by solid-liquid separation, with the solid residues being washed as efficiently as possible, and the leach liquor being treated by zinc cementation to recover the precious metals. White this process is generally extremely efficient and fairly cheap, it does have limitations in the treatment of low-grade ores and certain complex ore types. For example, ores with a high content of clay or other soft, fine minerals are usually difficult to filter, and losses of soluble gold or silver in the residues can be unacceptably high. In other situations, where the precious metal host rock contains high concentrations of sulphides such as pyrite or arsenopyrite, for example, or base-metal oxides or carbonates, the traditional process often suffers from poor gold recovery (due to encapsulation of the precious metals in the sulphides) or high cyanide consumption, or both of these. Whereas these occurrences were fairly rare (or were avoided!) in the first half of this century, they are now assuming great importance, and each year a higher percentage of world gold production derives from sources such as these.A number of new hydrometallurgical processes have been developed and implemented in the gold industry in the last 20 years, and these have transformed gold processing into a chemical “high tech” industry, and have allowed increasingly complex ore types and progressively lower grades of ore to be treated economically. As a result, in a period when gold production might have been expected to decline, world-wide production has almost doubled over the two decades.This paper describes the traditional cyanidation and zinc cementation processes, but focuses on the new developments in the industry. In particular, new leaching technologies such as heap leaching for low-grade ores and pressure leaching for refractory sulphide ores are discussed, as well as the carbon-in-pulp and carbon-in-leach processes that have effectively replaced filtration and countercurrent decantation on almost every gold plant built since 1980. Some emerging technologies such as bacterial leaching and resin-in-pulp are also discussed briefly.     

选冶联合处理低品位含金尾矿的试验研究

为高效回收尾矿资源中的金矿物,对含金尾矿进行了选冶联合试验研究.化学分析结果表明,固体废弃物中的金含量为0.86 g/t.工艺矿物学研究表明,矿样宜采用浮选—浮选金精矿预处理—浸出的选冶联合工艺来回收金.浮选条件试验、开路试验和闭路试验研究结果表明:粗选在Na2CO3用量为500 g/t、(NaPO3)6(六偏磷酸钠)...     

某含金高硫铜矿石浮选试验研究

采用新药剂对某含金高硫铜矿石进行了系统浮选试验研究.通过对比试验,发现采用传统的捕收剂黄药和黑药选别含金高硫铜矿石,虽然能够有效地回收含金硫化物,但获得的精矿产率高,铜和金的品位低,很难售出.而采用新药剂选别该类型矿石,可以使问题得到有效解决.新药剂对硫化铜矿物具有非常好的选择性,在粗选阶段采用新药剂可以有效回收硫化铜矿物,获得合格的铜精矿;在扫选阶段,采用黄药和黑药可以有效回收黄铁矿和其他硫化矿物,保证铜和金的回收率;扫选中矿单独处理,中矿采用六偏磷酸钠分散剂来消除矿泥对精选作业的影响,精选获得的混合精矿可以直接销售.     

Electrochemical interactions between gold and its associated minerals during cyanidation

Gold occurs in the Witwatersrand gold mines in association with sulphide, oxide and gangue minerals. The leaching behaviour of gold in contact or in association with various minerals depends largely on the galvanic interaction between gold and the mineral, and partially on the formation of a passivating film on the gold surface. Gold in contact with conducting minerals will passivate as a result of the enhanced magnitude of the cathodic current, resulting in decreased gold dissolution rates.Chalcopyrite, pyrite and pyrrhotite cause the largest decrease in the rate of leaching when in contact with gold. Galena strongly enhances the dissolution rate owing to the action of dissolve Pb²⁺ ions on the surface of the gold. When these Pb²⁺ ions are prevented from coming into contact with the gold, galena inhibits the leaching rate. In all experiments the rotating disc of gold passivated so that the rate of dissolution was much slower than that predicted by a mass-transport limiting model.The various films that occur on the surface of the gold and associated minerals, as well as the galvanic interaction (related to electrical conductivity), depend largely on the pretreatment of the ore. Pre-elimination of host minerals from the gold-bearing ore has a marked positive effect on the dissolution rate of gold, and explains the kinetics of reaction on the gold surface to a large extent. From the results presented in this paper on passivation owing to both film formation and galvanic interaction, it can be seen that passivation is not merely a laboratory curiosity, but it can reduce the efficiency of industrial operations and is thus most relevant to practical leaching processes.     

提高金铜硫化矿矿石金铜回收率工艺研究

本文对湖北某大型金铜矿石的浮选进行了系统研究。并对其硫精矿中金的回收进行了详细试验。结果表明，对硫精矿采用再磨再选技术，可使硫精矿中金的品位降至１．３１ｇ／ｔ，金的回收率可提高８．６７％，而且铜的回收率提高３．８９％。     

广西某微细粒浸染型金矿石提金试验研究

对广西某微细粒浸染型难处理金矿石进行了提金试验研究。其结果表明：在原矿金品位12.00 g/t时,采用原矿浮选—浮选尾矿氰化工艺流程,获得浮选精矿金品位41.30 g/t,金回收率29.93%,浮选尾矿氰化金浸出率71.24%,金总回收率为79.85%的较好指标。     

微细粒浸染型金矿石选金试验研究

详细研究了矿石中金的赋存状态和载金矿物特征，进行了多方案选金试验研究。试验结果表明：对合金黄铁矿精矿进行压热氧化--氰化浸出，是处理该微细粒浸染型金矿石较有效的方法。     

提高含铜难处理金矿金浸出率的试验研究

江西东北部某金矿石主要金属矿物为黄铜矿、黄铁矿、砷黝铜矿,常规氰化难浸,金精矿浸出率仅40．34％,进行了滚瓶、引入磁场强化低氧细菌预处理及磁场强化氧化渣浸金等浸金试验研究,金精矿金浸出率获显著提高,达93.21％。     

从含铜金黄铁矿中综合回收金属铜与金的研究

针对某含有金、银、铜等多种有价元素的黄铁矿,在对其原矿物化性质分析的基础上,通过低温氧化焙烧,烟气制酸,焙砂硫酸浸铜,浸铜渣氰化浸金的工艺对该黄铁矿实现了综合利用.使用上述工艺对含硫45.85%(质量分数)、含铜1.92%(质量分数)、含金1.60 g/t的黄铁矿进行处理,得到铜的浸出率为90.09%,金的浸出率可达70%,氰化渣中铁的含量为63.46%,可作为铁精矿外售.金、铜、铁等有价组分实现了综合回收.