Pretreatment of copper-bearing refractory gold ores by bio-heap leaching

The refractory gold ores associated with rich copper and trapped in pyrite and quartz were studied. With conventional technique (all-sliming cyanidation), the gold recovery rate is only 51.78%. To eliminate the negative effects of copper and pyrite on cyanidation and increase the gold recovery rate, the investigation on bio-heap leaching pretreatment was made, by which Cu would be dissolved and gold would be liberated from pyrite. The experiment adopted mixed bacteria, mainly Thiobacillus ferrooxidan (named T. f1), as the bacterial catalyst for bio-preconditioning and was carried out in a PVC column with a diameter of 20 cm and a height of 1.3 m loaded with gold ores. The temperature was controlled between 28 and 30℃, the pH value was kept between 2.0-2.5,and the flux of sprinkling bacterial liquid was maintained 0.80 L/h. After 45-day's bio-oxidization, among the samples sizing from 0to 5 mm, the oxidation rates of Cu, Fe and S were respectively 44.62%, 28.16% and 25.46%, and the gold recovery rate by cyaniding increased to 80.35%. The bio-heap leaching pretreatment can therefore effectively dissolve Cu and liberate gold from pyrite and lead to the increase of gold extraction.     

难浸金精矿的生物氧化?硫代硫酸盐浸出

A process of biooxidation followed by thiosulfate leaching of gold from refractory gold concentrate was investigated. Mineralogical studies on the concentrate showed that very fine gold grains (<10 μm) were encapsulated in pyrite and arsenopyrite, while the proportion of monomer gold was only 21%. The gold-bearing sample was identified as a high-sulfur fine-sized wrapped-type refractory gold concentrate. The gold leaching efficiency obtained by direct cyanidation was only 59.86%. After biooxidation pretreatment, the sulfide minerals were almost completely decomposed, 92wt% of the mineral particles of the biooxidation residue were decreased to <38 μm, and the proportion of monomer gold in the biooxidation residue was over 86%. Meanwhile, the gold content in the biooxidation residue was enriched to 55.60 g/t, and the S, Fe, and As contents were reduced to approximately 19.8wt%, 6.97wt%, and 0.13wt%, respectively. Ammoniacal thiosulfate was used for gold extraction from the biooxidation residue of the refractory gold concentrate. The results showed that the optimal reagent conditions were 0.18 M thiosulfate, 0.02 M copper(II), 1.0 M ammonia, and 0.24 M sulfite. Under these conditions, a maximum gold leaching efficiency of 85.05% was obtained.     

Biooxidation-thiosulfate leaching of refractory gold concentrate

A process of biooxidation followed by thiosulfate leaching of gold from refractory gold concentrate was investigated. Mineralogical studies on the concentrate showed that very fine gold grains(10 μm) were encapsulated in pyrite and arsenopyrite, while the proportion of monomer gold was only 21%. The gold-bearing sample was identified as a high-sulfur fine-sized wrapped-type refractory gold concentrate.The gold leaching efficiency obtained by direct cyanidation was only 59.86%. After biooxidation pretreatment, the sulfide minerals were almost completely decomposed, 92 wt% of the mineral particles of the biooxidation residue were decreased to 38 μm, and the proportion of monomer gold in the biooxidation residue was over 86%. Meanwhile, the gold content in the biooxidation residue was enriched to 55.60 g/t,and the S, Fe, and As contents were reduced to approximately 19.8 wt%, 6.97 wt%, and 0.13 wt%, respectively. Ammoniacal thiosulfate was used for gold extraction from the biooxidation residue of the refractory gold concentrate. The results showed that the optimal reagent conditions were 0.18 M thiosulfate, 0.02 M copper(II), 1.0 M ammonia, and 0.24 M sulfite. Under these conditions, a maximum gold leaching efficiency of 85.05% was obtained.     

New insights into the extraction of invisible gold in a low-grade high-sulfur Carlin-type gold concentrate by bio-pretreatment

To extract gold from a low-grade (13.43 g/t) and high-sulfur (39.94wt% sulfide sulfur) Carlin-type gold concentrate from the Nibao deposit, Guizhou, a bio-pretreatment followed by carbon-in-pulp (CIP) cyanide leaching process was used. Various methods were used to detect the low-grade gold in the concentrate; however, only time-of-flight secondary-ion mass spectrometry (TOF-SIMS) was successful. With bio-pretreatment, the gold recovery rate increased by approximately 70.16% compared with that obtained by direct cyanide leaching of the concentrate. Various attempts were made to increase the final gold recovery rate. However, approximately 20wt% of the gold was non-extractable. To determine the nature of this non-extractable gold, mineralogy liberation analysis (MLA), formation of secondary product during the bio-pretreatment, and the preg-robbing capacity of the carbonaceous matter in the ore were investigated. The results indicated that at least four factors affected the gold recovery rate:gold occurrence, tight junctions of gold-bearing pyrite with gangue minerals, jarosite coating of the ore, and the carbonaceous matter content.     

Pretreatment and thiosulfate leaching of refractory gold-bearing arsenosulfide concentrates

A hydrometallurgical process for refractory gold-bearing arsenosulfide concentrates at ambient temperature and pressure was presented, including fine grinding with intensified alkali-leaching (FGLAL), enhanced agitation alkali-leaching (EAAL), thiosulfate leaching and displacement. Experimental results on a refractory gold concentrate showed that the total consumption of NaOH in alkaline leaching is only 41% of those theoretically calculated under the conditions of full oxidization for the same amount of arsenides and sulfides transformed into arsenates and sulfates, and 72.3% of gold is synchro-dissoluted by thiosulfate self-generated during alkaline leaching. After alkaline leaching, thiosulfate leaching was carried out for 24 h. The dissolution of gold is increased to 91.9% from 4.6% by cyanide without the pretreatment. The displacement of gold by zinc powder in the solution gets to 99.2%. Due to an amount of thiosulfate self-generated during alkaline leaching, the reagent addition in thiosulfate leaching afterwards is lower than the normal.     

Processing technologies for gold-telluride ores

Gold telluride ores are important gold refractory ores due to the presence of sulfides and other gangue materials. The classification and main physical properties of gold telluride ores were described, and possible treatment methods including flotation, leaching, and oxidation were reviewed. The results show that flotation procedures are much easier for gold tellurides compared to other refractory gold-bearing ores. For the conventional cyanide leaching process, pretreatment such as oxidation is required to achieve high gold recovery. Roasting is a relatively simple but not environment-friendly method; bio-oxidation technology seems to be more suitable for the oxidation of flotation concentrate. Other treatment methods involve cyanide leaching, thiourea leaching, ammoniacal thiosulfate leaching, carbon-in-pulp, and resin-in-pulp, all of which are less commonly utilized.     

双氰胺钠浸金性能与机理研究

In this work, sodium dicyanamide (SD) was used as a leaching reagent for gold recovery, and the effects of the SD dosage and solution pH on the gold-leaching performance were investigated. A gold recovery of 34.8% was obtained when SD was used as the sole leaching reagent at a dosage of 15 kg/t. In the presence of a certain amount of potassium ferrocyanide (PF) in the SD solution, the gold recovery was found to increase from 34.8% to 57.08%. Using the quartz crystal microbalance with dissipation (QCM-D) technique, the leaching kinetics of SD with and without PF were studied. The QCM-D results indicate that the gold-leaching rate increased from 4.03 to 39.99 ng·cm–2·min–1 when the SD concentration was increased from 0 to 0.17 mol/L, and increased from 39.99 to 272.62 ng·cm–2·min–1 when 0.1 mol/L of PF was used in combination with SD. The pregnant solution in the leaching tests was characterized by X-ray photoelectron spectroscopy and electrospray mass spectrometry, which indicated that Au and (N(CN)₂)– in the SD solution formed a series of metal complex ions, [AuNa_x(N(CN)₂)_x+2]– (x = 1, 2, 3, or 4).     

A review of gold extraction using noncyanide lixiviants: Fundamentals,advancements, and challenges toward alkaline sulfur-containing leaching agents

Alkaline sulfur-containing lixiviants,including thiosulfate,polysulfides,and alkaline sulfide solutions,stand out as a promising class of alternatives to cyanide because of their low toxicity,high efficiency,and strong adaptability.In this paper,we summarized the research progress and remaining challenges in gold extraction using these noncyanide reagents.After a brief introduction to the preparation method,the transformation process of various sulfur-containing species in alkaline solutions was discussed.Thereafter,some insights into the mechanism of gold leaching in alkaline sulfur-containing solutions were presented from different aspects,including thermodynamics analysis,electrochemical dissolution,and leaching kinetics.Moreover,recent progress in in-situ generation of sulfur-containing anions from gold-bearing sulfide minerals was outlined as well.Gold passivation caused by sulfur species was discussed in particular because it is considered the greatest challenge facing sulfur-containing leaching systems.Alkaline sulfur-containing lixiviants are expected to serve as alternatives in industrial applications of gold extraction,particularly for refractory gold ores containing copper and carbonaceous matter.     

Investigation on microwave heating for direct leaching of chalcopyrite ores and concentrates

The use of microwave energy in materials processing is a relatively new development presenting numerous advantages because of the rapid heating feature. Microwave technology has great potential to improve the extraction efficiency of metals in terms of both a reduction in required leaching time and an increase in the recovery of valuable metals. This method is especially pertinent in view of the increased demand for environment-friendly processes. In the present study, the influence of microwave heating on the direct leaching of chalcopyrite ores and concentrates were investigated. The results of microwave leaching experiments were compared with those obtained under conventional conditions. During these processes, parameters such as leaching media, temperature, and time have been worked to determine the optimum conditions for proper copper dissolution. Experimental results show that microwave leaching is more efficient than conventional leaching. The optimum leaching conditions for microwave leaching are the solid-to-liquid ratio of 1:100 g/mL, the temperature of 140℃, the solution of 0.5 M H₂SO₄ + 0.05 M Fe₂(SO₄)₃, and the time of 1 h.     

Leaching of a copper flotation concentrate with ammonium persulfate in an autoclave system

The leaching behavior of a copper flotation concentrate was investigated using ammonium persulfate (APS) in an autoclave system. The decomposition products of APS, active oxygen, and acidic medium were used to extract metals from the concentrate. Leaching experiments were performed to compare the availability of APS as an oxidizing agent for leaching of the concentrate under atmospheric conditions and in an autoclave system. Leaching temperature and APS concentration were found to be important parameters in both leaching systems. Atmospheric leaching studies showed that the metal extractions increased with the increase in APS concentration and temperature (up to 333 K). A similar tendency was determined in the autoclave studies up to 423 K. It was also determined that the metal extractions decreased at temperatures above 423 K due to the passivation of the particle surface by molten elemental sulfur. The results showed that higher copper extractions could be achieved using an autoclave system.     

Recovery of gold from refractory gold ores: Effect of pyrite on the stability of the thiourea leaching system

The extraction of gold from refractory gold ores(RGOs) without side reactions is an extremely promising endeavor. However, most RGOs contain large amounts of sulfide, such as pyrite. Thus, investigation of the influence of sulfide on the gold leaching process is important to maximize the utilization of RGOs. In this work, the effects of pyrite on the stability of the thiourea system were systematically investigated under different conditions. Results showed that the decomposition rate of thiourea was accelerated sharply in the presence of pyrite. The effect of pyrite on gold recovery in thiourea leaching systems was then confirmed via a series of experiments. The decomposition efficiency of thiourea decreased by 40% and the recovery efficiency of gold increased by 56% after the removal of sulfide by roasting. Under optimal conditions, the efficiency of the gold recovery system increased to 83.69% and only 57.92% of thiourea decomposition was observed. The high consumption of thiourea by the leaching system may be attributed to not only adsorption by mineral particles but also catalytic decomposition by some impurities in the ores, such as pyrite and soluble ferric oxide.     

含钴矿石摇瓶生物浸出比较试验的研究

对含钴矿石进行了工艺矿物学研究,明确了该含钴矿石的主要化学成分、粒度分布、矿物组成与嵌布特征.研究表明,硫化矿物主要为硫铜钴矿、黄铜矿、斑铜矿、辉铜矿、铜蓝、黄铁矿等.硫铜钴矿大多数以单体形式赋存,还有一部分为连生体.该含钴矿石含钴163%,铜105%,铁124%,硫1500%.用实验室驯化培养的具有良好抗钴性能的ZY101菌种对此含钴矿石进行摇瓶浸出实验研究,浸出结果表明:利用优良菌种浸出,钴浸出率达8571%.对比生物法与非生物的高铁溶液浸出,生物法钴浸出率提高6326%,耐钴ZY101浸矿菌浸钴效果显著.     

硫脲法浸取硫化金矿的工艺改进研究

本文研究了硫脲法浸取硫化金矿的最佳条件、回收方法和硫脲的循环使用等问题。原矿经磨细,焙烧,用稀酸预浸出铜后,在常温,硫脲浓度１０克／斤,硫酸铁浓度３．３克／升,ｐＨ值为１－２条件下,浸取两小时可以得到接近１００％的浸取率。选用钢屑回收浸取液中的金,回收率大于９６％,且硫脲不受损失。实验发现,硫脲可以多次循环使用,这样可以部分解决硫脲法浸金过程中硫脲消耗量大的问题。     

金银铜多金属黄铁矿烧渣综合回收试验研究

根据黄铁矿烧渣的物理、化学性质特征,完成了多金属综合回收试验.结果表明:烧渣组成以氧化铁为主,并含有贵金属及有色金属,部分金、银、铜包裹于黄铁矿等硫化物中,而锌主要以铁酸锌形式存在.对烧渣进行氰化浸出,在试样未磨情况下,采用石灰调节矿浆pH=10～11、矿浆浓度35%、浸出时间24 h、氰化钠耗量6 kg.t-1的试验条件,可以获得金、银浸出率分别为67.25%、60.08%;采用浮选法处理烧渣可获得金品位8.66 g.t-1、回收率为37.82%的浮选产品,其中银品位和回收率分别为100.3 g.t-1、20.26%;对浮选尾矿直接进行氰化浸出,可获得金、银浸出率分别为96.85%、70.08%.     

A review of gold extraction using noncyanide lixiviants: Fundamentals,advancements, and challenges toward alkaline sulfur-containing leaching agents

Alkaline sulfur-containing lixiviants, including thiosulfate, polysulfides, and alkaline sulfide solutions, stand out as a promising class of alternatives to cyanide because of their low toxicity, high efficiency, and strong adaptability. In this paper, we summarized the research progress and remaining challenges in gold extraction using these noncyanide reagents. After a brief introduction to the preparation method, the transformation process of various sulfur-containing species in alkaline solutions was discussed. Thereafter, some insights into the mechanism of gold leaching in alkaline sulfur-containing solutions were presented from different aspects, including thermodynamics analysis, electrochemical dissolution, and leaching kinetics. Moreover, recent progress in in-situ generation of sulfur-containing anions from gold-bearing sulfide minerals was outlined as well. Gold passivation caused by sulfur species was discussed in particular because it is considered the greatest challenge facing sulfur-containing leaching systems. Alkaline sulfur-containing lixiviants are expected to serve as alternatives in industrial applications of gold extraction, particularly for refractory gold ores containing copper and carbonaceous matter.     

Electrochemical behavior of gold and its associated minerals in alkaline thiourea solutions

Electrochemical measurements were conducted to study the electrochemical behavior of gold (Au) and its commonly associated minerals in alkaline thiourea solutions. The results indicated that without addition of any stabilizer, selective dissolution of Au from stibnite and pyrite was only possible at relatively low thiourea concentrations. As Na₂SiO₃ was added, pyrite started to become active and an oxidation peak appeared; the oxidation peaks of arsenopyrite and chalcocite appeared earlier than that of Au. The chalcocite peak shifted in the positive direction and the peak current increased. Stibnite did not show an oxidation peak and its current was nearly zero. Adding Na₂SiO₃ favored the selective dissolution of Au when its minerals were associated with chalcocite and stibnite. At pH 12, the Au anode dissolution peak current increased with stabilizer concentration. At 0.38 and 0.42 V and for Na₂SiO₃ concentration below 0.09 M, the current density continuously increased with Na₂SiO₃ concentration. The Na₂SiO₃ concentration had to be adequate to stabilize thiourea. When the potential was higher than 0.42 V, the surface of the Au electrode started to passivate. With an additional increase in potential, the presence of Na₂SiO₃ could not stop the inevitable decomposition of thiourea.     

丁二酮肟-氧化剂型无毒浸金剂的浸出性能研究

用分子设计理论提出了一类新型浸金剂 ,它由丁二酮肟和某种氧化剂构成 ,具有无毒害和化学稳定性好的特点 ,实验结果表明 :1)丁二酮肟能与许多氧化剂尤其是高锰酸钾组合成高效浸金剂 ;2 )在丁二酮肟 -高锰酸钾浸出体系中 ,适宜的Ox/Lig(氧化剂与金络剂分子比 )比值范围为 0 .2 5～ 0 .50 ,最佳范围为 0 .30～0 .4 0 ;3)丁二酮肟 -高锰酸钾浸出体系的操作pH范围为 8～ 10 ;4 )与氰化物相比 ,丁二酮肟的浸出率与它相当但浸出速度明显快很多 ;5)从含丁二酮肟的浸出贵液中回收金既可采用炭吸附法也可采用锌置换法 图1,表 5,参 9     

Comprehensive recovery of gold and base-metal sulfide minerals from a low-grade refractory ore

The comprehensive recovery of small amounts of valuable minerals such as gold and base-metal sulfide minerals from a low-grade refractory ore was investigated. The following treatment strategy was applied to a sample of this ore: gold flotation–gold concentrate leaching–lead and zinc flotation from the gold concentrate leaching residue. Closed-circuit trials of gold flotation yielded a gold concentrate that assayed at 40.23 g·t-1 Au with a recovery of 86.25%. The gold concentrate leaching rate was 98.76%. Two variants of lead-zinc flotation from the residue—preferential flotation of lead and zinc and bulk flotation of lead and zinc—were tested using the middling processing method. Foam from the reflotation was returned to the lead rougher flotation or lead–zinc bulk flotation, whereas middlings from reflotation were discarded. Sulfur concentrate was a byproduct. The combined strategy of flotation, leaching, and flotation is recommended for the treatment of this kind of ore.