The use of ion exchange resins for the treatment of cyanidation tailings part 1––process development of selective base metal elution

This work investigates the use of oxidative acid eluents for the elution of base metals from strong base ion exchange resins. Eluents composed of a mixture of H₂O₂ and H₂SO₄ were tested for eluting base metals from resins loaded with mixtures of base and precious metal cyanides. This process removed 100% of Cu and Zn loaded on the resin, without affecting the precious metal loading. It was found that copper could be removed separately from the other base metals. The elution technique was not effective for removing iron from the resin. Cyanide associated with base metals was recovered as NaCN. Some oxidation of cyanide was noticed, subject to the elution conditions.This oxidative acid elution process could be used in commercial operations for the selective elution of base metals from a strong base ion exchange resin bed operating in alternative adsorption/base metal elution cycles. Thus, virtually all metal cyanide species could be recovered from cyanide leached solutions or slurries to give relatively clean tailings without compromising precious metal recovery efficiency. The process also caters for cyanide recovery and recycling.     

The effect of salinity on the capacity and selectivity of ion exchange resins for gold cyanide

Despite the success of several resin-in-pulp pilot plant operations in the Western World and large scale plants in the former Soviet Union the process of extracting gold from slurries using ion exchange resins is yet to gain recognition as a viable alternative to the carbon-in-pulp process. An experimental research program has investigated the potential use of anion exchange resins containing a variety of quaternary ammonium functional groups in highly saline process water such as that found in Western Australia. The effect of univalent and bivalent ions on gold adsorption has been studied. It was shown that the selectivity of the resin for gold cyanide was enhanced with increasing ionic strength. It has been proposed that the degree of hydration, polarisation and size of the adsorbing species are factors that contribute to the observed change in selectivity of the ion exchange resin at different salinity. It was observed that in highly saline solutions copper cyanide did not load significantly on any of the experimental resins studied. Furthermore, it has been shown that an existing commercial non-selective resin loads no significant amount of copper cyanide under saline conditions. It is proposed that the apparent change in selectivity of resins for gold cyanide is caused by anions that have a stronger affinity for the resin in these highly non-ideal solutions as well as a possible change in the distribution of copper cyanide complexes in solution. The results of this study demonstrate that the selectivity of ion exchange resins in highly saline water is significantly improved and as a consequence the resin-in-pulp process may be more efficient than carbon-in-pulp in process streams of high salinity.     

用离子交换树脂从氰化物溶液中回收金的技术及其展望

树脂提金是一种先进的无过滤提金技术,金在树脂上的吸附容量很高,有机物质对树脂的吸附过程影响不大,树脂提金工艺成熟,回收率高,对矿石的适应性强。本文将探讨离子交换技术浸金的化学原理,浸金树脂类型研究的最新进展及其前景以及在生产中的工艺特点。     

D296R树脂对氰化物的吸附和解吸性能研究

为研究D296R大孔阴离子交换树脂对氰化物的吸附和解吸性能,分别考察了溶液浓度、流速对D296R树脂吸附和解吸氰化物的影响,测定了动态吸附曲线,并确定了解吸条件。结果表明,D296R树脂对氰化物的动态饱和吸附容量为28.02 mg/mL;用氯化钠作为代替酸解吸的中性解吸剂,解吸率可达96%以上。10批次的吸附—解吸—再生稳定性试验表明,D296R树脂用于处理自配氰化液,吸附、解吸、再生循环性能稳定。用D296R树脂回收氰化物具有吸附速率快、易解吸、操作简单、无潜在二次污染、试剂消耗少、成本低等优点,是很有工业应用前景的回收氰化物的树脂。     

Selective elution of the gold cyanide complex from anion exchange resin using mixed solvents

This study is concerned with the use of mixed solvents for the elution of the cyanide complexes of copper and gold from Purolite A500, a strong-base anion exchange resin. The mixed solvents investigated include acetone + water, dimethylsulfoxide + water and N-methyl-2-pyrrolidone + water. Three types of counterions are employed in each of the mixed solvents: CN⁻, Cl⁻ and OH⁻. The effects of counterion concentration and mixed solvent composition on the elution of the complexes are examined. High recoveries of the gold cyanide complex are achieved in the mixed solvents at relatively low counterion concentrations. In contrast, the recoveries of the copper cyanide complexes are 1–3 orders of magnitude lower for the given initial loading of the metals on the resin. The selectivity of the elution process for gold is discussed in terms of the degree of solvation of the various anions in the mixed solvents. The results of this study point to the possibility of using mixed solvents to develop an elution process that is selective for gold over multivalent cyanide complexes.     

A review of copper cyanide recovery technologies for the cyanidation of copper containing gold ores

Many gold producers are today processing gold ores containing significant amount of cyanide soluble copper. Typically, cyanide destruction is used to prevent the discharge of copper cyanide into tailings storage facilities. This imposes a significant financial cost to producers from the additional cyanide used to solubilize the copper and the cost of cyanide destruction reagents. Therefore, the recovery of copper as a valuable by-product and the recycle of cyanide to the leach circuit have the potential for significant economic and environmental benefits. This includes enabling the treatment of gold ores with even higher soluble copper. Over the years, a variety of processes have been developed or proposed to recover the copper and/or cyanide including acidification based technologies such as AVR and SART, direct electrowinning, activated carbon, ion exchange resins, solvent extraction, polychelating polymers, and membrane technologies. In this paper, these processes are critically reviewed and compared, with particular focus on the advantages and limitations, and the separation of copper from cyanide. Ultimately, there is no universal process solution and the choice is highly dependent on the nature of the stream to be treated and integration with the whole processing plant.     

Cyanide regeneration by AVR process using ion exchange polymeric resins

This work presents laboratory bench scale results for cyanide regeneration from pure alkaline aqueous solutions of gold, copper and iron cyanocomplexes using an innovative option of the AVR process associated to the ion exchange polymeric resins Imac HP555s^® ((Room&Haas––USA) and Amberlite IRA-420^® (Room&Haas Brasil Ltda.) in columns. The resin Imac HP555s^® adsorbed 64.5% CN from the alkaline solution containing metal cyanocomplexes. Meanwhile, the elution stage with H₂SO₄ and thiourea reached 31.2% CN, 86.2% Au, 86.4% Cu and 41.5% Fe. The resin IRA-420^® adsorbed 53.4% CN under the same experimental conditions adopted for the resin Imac HP555s^®. The resin Amberlite IRA-420^® eluted 48% CN, 96.8% Au, 9.1% Cu and 76% Fe.     

某金矿氰化浸出液的树脂和活性炭吸附试验研究

采用强碱性阴离子树脂从云南某金矿氰化浸出液中吸附金、银和铜离子络合物,不仅金的吸附率高,而且银和铜离子的吸附率分别达到98.52%和99.88%。铜离子不仅严重地影响活性炭吸附银和金的络合物、银的吸附率很低,而且还显著地增加氰化物用量、影响尾液的循环利用,在缺水的地方,这种不利的影响更加明显。因此,树脂吸附工艺对于提高银的吸附率、降低氰化物用量、综合利用尾液中的有价组分(氰化物、碱金属铜、石灰和水等)具有重要的实际价值。     

The adsorption of precious metals and base metals on a quaternary ammonium group ion exchange resin

Adsorption tests were conducted with a quaternary ammonium group ion exchange resin to determine the equilibrium adsorption of precious- and base metals. The resin used is a macroreticular polystyrene type 1 strong base anion exchange resin. The adsorption was determined for synthetic single metal solutions as well as for multi-component solutions. The effect of the Cl⁻ concentration on the equilibrium adsorption was determined for three different HCl concentrations, i. e. 6, 8 and 10%. The effect of chloride strength in the solution was also determined for mixed and base metal solutions. Pure metals, i.e. platinum, palladium and gold, were dissolved in aqua-regia and diluted to 2000 ppm (as metal) in 4M HCl. Ruthenium, rhodium and iridium were dissolved from pure salts in HCl. A 2000 ppm base-metal solution was prepared by dissolving all the required components, including precious metals, to match an in-plant industrial base-metals solution composition. For each precious metal the equilibrium adsorption was determined for typically two solution concentrations. Data points were established by varying the amount of resin added to the solution. The equilibrium concentrations were determined by ICP analysis after 24 hours exposure using the bottle-roll technique.     

Legacy of Cyanide and ARD at a Low-Scale Gold Mine (Furtei, Italy)

A gold deposit was exploited from 1997 to 2003 at Furtei, Sardinia (Italy). Gold and silver were recovered from oxidized ores by cyanidation; copper concentrates were separated from the sulfide ores by flotation. Following unplanned closure, sulfide-rich materials derived from mining and processing residues were left on site. During operation, cyanide solutions were disposed of in a tailings impoundment. The cyanide underwent natural degradation so that by 2011, cyanide concentrations in the tailings impoundment and seeps were below the Italian limit for industrial effluents. However, during the rainy season, sulfide-rich materials in the waste rock dumps produce extreme acidic solutions and concentrations of some dissolved contaminants, especially ammonium, aluminum, arsenic, copper, iron and manganese, still exceed discharge criteria in the tailings impoundment and seeps. Highly contaminated drainage flows downstream from the mine and poses a hazard to agricultural areas.     

Dynamic modelling of competitive elution of activated carbon in columns using neural networks

In previous papers the mechanism and dynamics of the elution of gold cyanide from activated carbon have been investigated in detail. Sub processes such as the pre-soaking step, the degradation of cyanide, the elution of the spectator cations, the associated shift in the equilibrium of adsorption or desorption as a result of the removal of cations, the reactivation of the carbon surface, and the elution of gold cyanide have been explained quantitatively to some extent, although further work is evidently required Previous work has also shown that equilibrium conditions may be' assumed when adsorption is weak, hence when aggressive pre-soaking conditions have been used. However, these studies have not taken the competitive effect of base metals into account, although this is known to have an adverse effect on the efficiency of gold elution.The present study has shown quantitatively that copper has a significant effect on the recovery of gold. Nickel and silver also have a detrimental effect, but only if they are present as high loadings. In contrast, the elution of the base metals is to a large degree unaffected by the elution of gold. It is shown in this paper that the multi-component equilibrium relationship between the spectator cations and the various metal cyanides can be very complex, and perhaps ill-defined. In such circumstances it is preferable to use a non-parametric technique such as a back-propagation neural network to represent such an equilibrium relationship. Owing to the difficulty of estimating the final conditions of the pre-soaking step, it is not always possible to predict the exact level of equilibrium. Therefore, it could be necessary in practice to adjust the equilibrium predicted by a neural net by a factor which is dependent on the conditions of pre-soaking.     

Separation of copper and zinc from waste acidic mine effluents of Rio Tinto area

A study of removal of Copper and Zinc from acidic mine effluents by means of chelating ion exchange resins has been carried out. The effluents having pH ranging from 1.7 to 1.9, contain mainly iron, copper and zinc and some other elements at much lower concentrations. The study includes chemical characterisation of effluents samples, the assessment of chelating resins and their selectivity for the separation of copper and zinc. Chelating resins containing either carboxylic, phosphoric or/and amine groups have been employed. The results obtained are correlated to the specific metal-complexing group attached to the polymer matrix. Resins containing carboxylate groups were found to provide most selective copper/zinc separations. A conceptual flowsheet of the separation process based on the data obtained for treating the effluents with different resins is presented.     

用离子交换树脂法从金堆城钼冶炼废酸中回收铼的工业应用

从钼冶炼废酸中高效回收铼一直是研究的热点,本文结合金堆城钼矿中铼回收相关研究,分析了用强碱性阴离子交换树脂和弱碱性阴离子交换树脂吸附回收铼的工艺流程、技术指标和优缺点。目前采用弱碱性阴离子交换树脂直接吸附法,从钼精矿焙烧废酸中回收铼,粗铼酸铵产品经2~3次溶解结晶,制备出合格铼酸铵产品,废酸中铼含量平均为17.86 mg/L,离子交换过程铼吸附率为97.5%,解吸附率为99.7%,总回收率为91.6%,高铼酸铵产品纯度可达99.99%。该生产工艺具有流程简单、生产稳定、技术指标好的特点,具有较好的推广应用前景。      

Copper–gold ore processing with ion exchange and SART technology

Anglo Asian Mining has developed a 50,000 oz Au/yr open pit gold mine at Gedabek in Western Azerbaijan. The deposit at Gedabek is a copper–gold porphyry, comprising both oxide and sulphide ore mineralisation, which is being mined at the rate of about 1 million tons of ore per year. Ore processing is by conventional cyanide heap leaching, which produces a pregnant leach solution (PLS) containing 1–2 ppm of gold, together with 1000 ppm or more of copper. The PLS is treated by column ion exchange, using Dow’s gold-selective MINIX resin. Loaded resin is stripped with an acidic thiourea solution, from which gold and silver are electrowon on to stainless steel mesh cathodes. Copper concentrations in the leach solutions are controlled by passing part of the PLS flow through a SART process, where the acronym stands for “Sulphidisation, Acidification, Recycling and Thickening”. The product from the SART process is a copper/silver sulphide precipitate, which is thickened, filtered and dried and then sold for copper smelting.     

Potential use of carbon felt in gold hydrometallurgy

The use of carbon felt as a three-dimensional electrode appears to be very promising for the recovery of heavy metals, and toxic compounds removal from dilute solutions, considering its favourable physico-chemical properties: high specific surface area, good fluid permeability and compressibility, chemical inertness and good electrical conductivity.This work presents the contribution of the carbon felt electrode in two different steps of the gold cyanidation recovery process

• •- firstly as a cathode for the electrowinning of gold solution obtained after the elution of loaded carbon;
• •- secondly as an anode for the electro-oxidation of cyanide ions present at low concentration (200–300mg/l) in waste streams.

In the first case, more than 10 kg of gold per m² of felt (2000 kg of gold per m³ of felt) can be loaded at 400 A/m² from dilute gold solutions (30 mg/l Au) with classic Faradic yields (6–12 %) and high overall extraction efficiency (>90 %). The felt homogeneously loaded with adhesive gold deposit can be smelted in an electric furnace without addition of fluxes since the carbon felt decomposes in gaseous products without formation of ashes.In the second case, the cyanide ion concentration can be lowered to as low as 10 mg/l by electro-oxidation to cyanate form (CNO⁻) at 400 A/m² in the anodic compartment of a divided cell. The presence of copper ion significantly improves the current efficiency of this electro-oxidation and sharply reduces the oxidation of the carbon felt. Copper ions accelerate the oxidation rate of free cyanide ions through the formation of easily oxidizable complexes owing to a mechanism in which the Cull Cu^ll redox couple acts as an electron transfer mediator.     

Copper cyanide removal by precipitation with quaternary ammonium salts

Cyanide is widely used in the mining industry to extract gold from ores. Some of the minerals processed for precious metals extraction contain copper species which may react with cyanide to form cuprocyanide complexes. The presence of these copper species affects adversely the process and causes high cyanide consumption. In order to overcome these limitations this laboratory work explores the feasibility of removing the copper–cyanide complexes by precipitation with quaternary ammonium salts, allowing the remaining solution, free of copper and containing free cyanide, to be recycled to the cyanidation process. The first part of the experimental work was performed with synthetic copper–cyanide solution simulating a high copper–cyanide solution (2700 mg/L cyanide, 730 mg/L copper and pH adjusted to 12 with CaO) and three quaternary ammonium salts: hexadecyl trimethyl ammonium chloride (HTA), octadecyl trimethyl ammonium chloride (OTA) and dioctadecyl dimethyl ammonium chloride (DDA). The results showed that it is possible to remove up to 90% of the copper in the precipitate when adding 12.32 g OTA/g copper at pH 12. The free cyanide remains unreacted in the solution and could be recycled to the process. Results of tests performed at different pH values suggest that regardless the initial species distribution in the solution, the solid formed will contain mainly copper tricyanide and some of copper tetracyanide. The molar ratio CN/Cu in the solid is around 3 while the molar ratio OTA/Cu is around 2. This implies that some amount of copper tetracyanide is transformed into copper tricyanide while reacting with the amine and forming the precipitate. When zinc is also present in the cyanide solution, the ammonium salt will react first with the zinc–cyanide complexes before precipitating the copper cyanides. Tests performed with an industrial solution corroborated the results obtained with synthetic solutions: quaternary ammonium salts (e.g. OTA) react with copper and zinc cyanides (but not with free cyanide) to form a precipitated that can be separated from the solution by filtration. An analytic technique for measuring quaternary ammonium salts HTA and OTA in solution was developed.     

硫代硫酸盐浸金及回收过程中氨的作用研究现状

硫代硫盐法是最有希望取代氰化法的提金方法,氨及铜氨络离子在浸金以及从贵液中回收金的过程中发挥着重要作用。综合评述了硫代硫酸盐浸金及金回收过程中氨、铜氨络离子的作用机理和影响。     

A kinetic and electrochemical study of the ammonia cyanide process for leaching gold in solutions containing copper

One of the biggest challenges for the gold industry in the 21st century is the presence of copper in gold containing ore bodies. This is because copper consumes large quantities of cyanide. In addition, copper cyanide species are more stable than free cyanide, and hence are problematic in events of tailings spillage. One of the methods which has been suggested for treating copper containing ores is to leach with an ammonia cyanide solution. The effect of copper and ammonia addition on gold leaching kinetics was studied in the present paper. It will be shown that when the solutions do not contain copper, the addition of ammonia decreases the rate of gold leaching. When copper is added to solution, the leach rate does decrease due to the formation of the copper cyanide complexes. However it will be shown that under conditions of zero free cyanide, gold does leach readily via the Cu(CN)₃²⁻ complex. It was found that the addition of ammonia had little effect on the leaching of gold by Cu(CN)₃²⁻, but did increase the leaching kinetics when the major cyanide species present is Cu(CN)₂⁻. Under these conditions, leaching in the absence of ammonia is very slow. The effect of copper(II) addition was also studied, and it was found that in the absence of free cyanide the presence of copper(II) increases the leach rate, provided there is enough ammonia to stabilise it against reaction with the copper(I) cyanide complexes.     

萃取-电沉积处理含铜氰化废水回收铜和氰化物

以季铵盐N263为萃取剂,采用萃取—电沉积工艺对铜氰废液中的铜和氰化物进行回收。结果表明,N263对含氰溶液中的铜氰配合离子有良好的萃取能力,在高碱性条件下其对铜的单级萃取率仍超过90%;饱和负载有机相经反萃可为后续电沉积提供高浓度含铜溶液;提高电沉积温度有利于铜的回收与氰化物的保护;处理后尾液可直接用于氰化浸出。通过萃取—电沉积工艺实现了废水中铜和氰化物的综合回收利用。     

Copper removal from cyanide solutions by acidification

Cyanidation is the most used method to recover gold and silver from their ores. In this process, other metals besides gold and silver may dissolve under certain circumstances and interfere with the efficiency of extraction. Copper is one of these metals, being able to reach concentrations as high as 1000 mg/L. When the cyanide solution contains a high copper concentration, the extraction of precious metals decreases and the operating costs increase. In addition, the control of the process is more complicated because the free cyanide analysis performed by the operators by titration does not represent the actual cyanide available to dissolve gold and silver. This experimental work has two objectives: to evaluate the amount of copper–cyanide complexes that are measured when titration is used for free cyanide analysis, and to develop and propose a method for copper removal from cyanidation solutions. The method consists in the acidification of the solution with sulfuric acid, and the separation of the precipitated solid (CuCN) by filtration. The thermodynamics of the copper–cyanide system is discussed, and the hydrogen cyanide evolution (HCN) at pH acid is evaluated.One of the main operating variables in cyanidation plants is the “free cyanide” concentration, that is, the amount of cyanide available to dissolve the precious metals. The usual method to estimate free cyanide is titration. When copper is present in the cyanide solution, the titration method not only measures the free cyanide but also part of the cyanide that is forming complexes with copper. It was demonstrated from the tests performed in this work, that for cyanide/copper ratios of 1–10, typically found in cyanidation solutions, around 10% of the free cyanide measured by titration corresponds to copper–cyanide complexes and is not available for gold and silver dissolution.In order to recycle the solution to the process, it is necessary to remove part of the copper. A method of copper removal is proposed, based on the precipitation of CuCN when the copper–cyanide solution is acidified. The precipitated solid is separated from the solution by filtration and finally the clear solution is neutralized. The acidification/filtration/alkalinization of cyanidation solutions containing copper permits the removal of most of the copper present in the solution, thus allowing the recycling of the solution. For synthetic solutions containing 200–730 mg/L Cu at different cyanide/copper ratios, it was found that 93–98% of the copper can be removed as CuCN at pH 2.5, releasing free cyanide to the solution. If a flotation stage is considered to remove the solid formed, the HCN formed by acidification should not represent a problem: the amount of HCN gas stripped at pH 2.5 when using the usual flotation gas flow rates (0.17 cm/s, 0.28 L/min, 1 h for our experimental design) was only 6%, which can be easily controlled with conventional equipment.