Simultaneous extraction of gold and zinc from refractory carbonaceous gold ore by chlorination roasting process

A novel process based on chlorination roasting was proposed to simultaneously recover gold and zinc from refractory carbonaceous gold ore by using NaCl as chlorination agent.The effects of roasting temperature,roasting time and NaCl content on the volatilization rates of gold and zinc were investigated.The reaction mechanism and the phase transition process were also analyzed by means of SEM,EDS and XRD.The results demonstrated that under the optimal conditions of NaCl content of 10%,roasting temperature of 800℃,roasting time of 4 h and gas flow rate of 1 L/min,the rates of gold and zinc were 92%and 92.56%,respectively.During low-temperature chlorination roasting stage,a certain content of sulfur was beneficial to the chlorination reactions of gold and zinc;and during high-temperature chlorination roasting stage,the crystal structure of vanadium-bearing mica was destroyed,and the vanadium-containing oxides were beneficial to the chlorinating volatilization of gold and zinc.Eventually,the chlorinated volatiles of gold and zinc could be recovered by alkaline solution.

An Application of Microwave Pre-oxidation in Improving Gold Recovery of a Refractory Gold Ore

Microwave radiation was employed as a pretreating technology to oxidise a refractory gold ore. Heating characteristics showed that, in an identical microwave field, the bulk temperature of the sample increased with microwave power, microwave radiation time and particle size. The rate of sulphur removal increased with microwave radiation time. Particle size also had a significant effect on the oxidation rate. Pyrite and marcasite could be oxidised into Fe 2O 3 with a high porous structure. When microwave radiation was carried out in a rotary bed, the oxidation was more uniformly developed, in comparison with in a fixed bed. Gold extraction by cyanidation could be remarkably improved after the ore was subjected to microwave radiation. The results showed that gold recovery could be improved from 37% to 69%～ 81.2 %.

Characterization of an iron oxy/hydroxide(gossan type) bearing refractory gold and silver ore by diagnostic leaching

A detailed characterization of an iron oxy/hydroxide(gossan type) bearing refractory gold/silver ore was performed with a new diagnostic approach for the development of a pretreatment process prior to cyanide leaching. Gold was observed to be present as native and electrum(6-24 μm in size) and associated with limonite, goethite and lepidocrocite within calcite and quartz matrix. Mineral liberation analysis(MLA) showed that electrum is found as free grains and in association with beudantite, limonite/goethite and quartz. Silver was mainly present as acanthite(Ag2S) and electrum and as inclusions within beudantite phase in the ore. The cyanide leaching tests showed that the extractions of gold and silver from the ore(d80: 50 μm) were limited to 76% and 23%, respectively, over a leaching period of 24 h. Diagnostic leaching tests coupled with the detailed mineralogical analysis of the ore suggest that the refractory gold and silver are mainly associated within iron oxide mineral phases such as limonite/goethite and jarosite-beudantite, which can be decomposed in alkaline solutions. Based on these characterizations, alkaline pretreatment of ore in potassium hydroxide solution was performed prior to cyanidation, which improved significantly the extraction of silver and gold up to 87% Ag and 90% Au. These findings suggest that alkaline leaching can be used as a new diagnostic approach to characterize the refractoriness of iron oxy/hydroxide bearing gold/silver ore and as a pretreatment method to overcome the refractoriness.

Mineralogical characterization and pretreatment for antimony extraction by ozone of antimony-bearing refractory gold concentrates

The mineralogical characterization of antimony-bearing refractory gold concentrates and the antimony extraction by ozonein HCl solution were investigated.The mineralogical study shows that there exist stibnite(Sb2S3),arsenopyrite(FeAsS),pyrite(FeS2)and quartz in the concentrates,and the gold is mainly(67.42%)encapsulated in sulfides.The antimony extraction by ozone inhydrochloric acid was employed and the influences of temperature,liquid/solid ratio,HCl concentration and stirring speed on theextraction of antimony were investigated.High antimony extraction(93.75%)is achieved under the optimized conditions.After thepretreatment by ozone,the antimony is recovered efficiently and the gold is enriched in the leaching residue.

Acid leaching decarbonization and following pressure oxidation of carbonic refractory gold ore

Carbonate decomposition of carbonic refractory gold ore and the following pressure oxidation were studied.In the carbonate decomposition procedure,the effects of liquid-to-solid ratio and reaction time on decomposition ratio of carbonate were investigated.The experimental result shows that the decomposition ratio of carbonate is 98.24%under the conditions of liquid-to-solid ratio of 5:1,Fe^(3+)concentration of 20 g/L,sulfuric acid concentration of 20 g/L,reaction temperature of 80 ℃ and reaction time of 2 h.Then,the slurry obtained from carbonate decomposition was put into the titanium autoclave for pressure oxidation leaching.Effects of liquid-to-solid ratio,temperature,time and oxygen partial pressure on sulfur oxidation ratio were studied during pressure oxidation.With the prolonged time,pyrite and arsenopyrite are oxidized to ferric subsulfate,hydrated ferric sulfate and jarosite,resulting in the increasing residue ratio.The residue ratio and the sulfur content in the residue can be decreased by ferric subsulfate dissolution.The oxidation ratio of the sulfur is 99.35% under the conditions of oxidation time of 4 h,temperature of 210 ℃,oxygen partial pressure of 0.8 MPa and stirring speed of 600 r/min.

Improved recovery of a low-grade refractory gold ore using flotation–preoxidation–cyanidation methods

In this work, different flotation–preoxidation–cyanidation methods are considered for treating a lowgrade refractory gold ore. On the one hand, the results of selective flotation show that 22% and 31.1%of total Sb and As, respectively, remained in the final tailings and only about 28% of the total Au remained for further cyanidation processes. On the other hand, in bulk method of flotation the maximum Au recovery of 90.6% achieved after 60 min of flotation at the grind size with K80 of 146 micron. In addition, the bulk flotation method resulted in the concentrate with low concentrations of Sb and As elements. To improve the recovery of low-grade refractory gold ores, flotation should be followed by roasting, biological, or pressure oxidation processes so that the gold could be liberated prior to cyanidation processes. It is also found that the pressure oxidation pre-treatment of the concentrates prior to cyanidation may yield high gold recoveries of over than 83%. In these processes, recoveries are controlled by the temperature and the oxygen partial pressure in the solvent. However, by utilizing the bio-oxidation technique, the oxidation of sulfur to sulfate cannot be completed and, consequently, the gold recovery may be limited to only 72.2%.

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 concen- trate leaching-lead and zinc flotation from the gold concentrate leaching residue. Closed-circuit trials of gold flotation yielded a gold concen- trate 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.

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.

Research on Technology of Pressure Pretreatment with Oxygen for Refractory Gold Ores

An combined technology of pressure pretreatment with oxygen on refractory gold ores is pointed out and discussed on this paper, according to the experiments included the test in 1 kg grade batch pressure pretreatment with oxygen of the concentrate from the refractory gold ores of Dongbeizhai in Sichuan province, which is called the most refractory gold ores in China. It is shown that gold recovery reach 91.73% in the combined process which is described as follows: The flotation of the sulphide gold ores is under controlled conditions, producing the concentrate for pressure pretreatment with oxygen in acidic medium and the middling for the pressure pretreatment with oxygen in alkaline medium. The thickening and washing process substitute the pressure filtration process of the pulp after pressure pretreatment. The thick slimes of the two kinds of pressure pretreatment were mixed and then enter the CIL process for simplifying the flowsheet. The possible superabundance of acid of pressure pretreatment with oxygen in acidic medium was neutralized by the tailings of flotation and the cost of neutralization will be lower. The combined technology of pressure pretreatment with oxygen has the same advantages as the normal technology of pressure pretreatment and both is helpful for environment protection.

Roasting and chlorine leaching of gold-bearing refractory concentrate:Experimental and process analysis

This paper deals with gold extraction from a refractory concentrate by chlorine leaching.The process considers a pre-treatment of refractory materials by low temperature oxidation carried out with low oxygen concentration.The oxidized material is treated by leaching with brine.After gold adsorption/reduction onto activated carbon,iron and base metals can be precipitated by NaOH.Roasting tests show the necessity to carry out a thermal pre-treatment at least at 550°C to obtain a reduction of sulfur and mercury in the material(50%and 90%,respectively).Highest gold extraction yield(around 93%)is obtained in the leaching test performed with material sample treated at 650°C.This result confrms the necessity to optimize the thermal pre-treatment to improve Au recovery and to reduce chlorine consumption.A comparison with conventional cyanidation confrms that chlorination could be an useful alternative:in fact,gold extraction yield is quite low:57%in non-pre-treated material and 25%in pre-treatment material.

Thermodynamics and technology of extracting gold from low-grade gold ore in system of NH_4Cl-NH_3-H_2O

According to the principles of simultaneous chemical equilibrium and electronic charge neutrality, the thermodynamics of Au-NH4Cl-NH3-H2O system was studied by using the exponential computation method and through MATLAB programming, and the solid figure of potential-c(NH4Cl)-c(NH4OH) was drawn. The results show that when the sum concentration of Au+ and Au3+ is equal to 5×10-5 mol/L, φ(Au+/Au) is about -0.2 V; when the sum comes up to 0.5 mol/L, the value of φ(Au+/Au) increases to 0.2 V. In this case, φ(O2/OH - ) is as high as 0.7 V. This means that it is feasible to extract gold in this system. In addition, to predict the feasibility of reducing gold from the Au(I)-NH4Cl-NH3-H2O system with copper or zinc powder, the solid figures of potential-c(NH4Cl)-c(NH4OH) for both systems of Cu-NH4Cl-NH3-H2O and Zn-NH4Cl-NH3-H2O were also drawn. The results indicate that both copper and zinc powders can reduce Au+ into metal gold, and zinc powder can also reduce H2O into H2, while copper powder can not. The leaching results of a cuprous gold ore show that the extraction of gold can reach 80% in this system. The preliminary results of reduction with copper and zinc powders show that with deoxygenizing, the reduction effects are relatively good.

BIOOXIDATION OF TWO ARSENICAL REFRACTORY GOLD CONCENTRATES AND GOLD CYANIDATION

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Effect of mechanical activation on thiosulfate leaching of gold from complex sulfide concentrate

The use of mechanical activation to enhance gold recovery from a CuPbZn complex sulfide concentrate was investigated. The effects of milling time, ball size, sample to ball ratio and milling speed on thiosulfate leaching were studied. Under optimum conditions of milling time 1 h, ball size 20 mm, sample to ball ratio 1/15 and mill speed 600 r/min, nearly 78% of sample is amorphized, particle size decreases from d100=30 μm to d100=8 μm, specific surface area increases from 1.3 m2/g to 4.6 m2/g and gold recovery enhances from 17.4 % in non-activated sample to 73.26 %.

LEACHING GOLD BY LOW CONCENTRATION THIOSULFATE SOLUTION

The effects of the concentrations of thiosulfate,copper and ammonia on the extraction of gold from sulfide gold concentrate have been studied.The results show that it is possible to reduce thiosulfate concentration.More than 95%of the gold could be extracted by a 0.2 mol/L thiosulfate leaching solution in two hours under suitable conditions.Therefore,the process of washing the residue was simplified,and the consumption and loss of thiosulfate carried by the washing residue were reduced.

Pool bio-oxidation and fitting analysis of low-grade arsenic-containing refractory gold ore

To overcome the limitations of geography,climate,and ore characteristics on the ore beneficiation process,biooxidation studies on low-grade arsenic-bearing refractory gold ore by pool leaching were carried out,as well as process fitting analysis.The gold particles are encapsulated by pyrite and arsenopyrite.After 60 days of biooxidation,the oxidation rates of arsenic,sulfur,and gold were 39%~69%,24%~41%,and 49%~83%,respectively.The inoculated Acidithiobacillus ferrooxidans,Ferroplasma acidiphilum,and Leptospirillum ferrodiazotrophum could all mediate the initial pyrite/arsenopyrite oxidation and the Fe^(2+)oxidation reaction,but only the former could mediate the subsequent sulfur compound oxidation.When compared to daily bacterial circulation and bacterial replacement every ten days,aeration improved the gold leaching rate by 14%~22%.The Boltzmann model could fit both the arsenic and sulfur bio-oxidation,with model fit variances greater than 0.98.Based on the experimental and fitting results,the bio-oxidation cycle was determined to be 60 days,and the bio-oxidation mechanisms are summarized.This study has significant practical implications for the rational utilization of gold resources and provides theoretical and practical guidance for similar gold ores.

河南某微细粒复杂难选金矿回收金试验研究

河南某金矿石含金1.91 g/t,为主要有价元素,现场经浮选处理后尾矿中仍含金0.43 g/t,有较多损失,为进一步降低尾矿中金的含量,提高金的回收率,对原矿进行了详细的工艺矿物学分析。结果显示,矿石中含金矿物主要为银金矿,载体矿物主要为黄铁矿,脉石矿物主要为石英、长石、云母、白云石等,金的嵌布粒度整体较细,绝大部分在10μm以下,选别难度较大。针对矿石性质,进行了磨矿细度、矿浆pH值、分散剂用量、活化剂用量、捕收剂种类及用量、起泡剂用量等条件试验和金回收的闭路试验。结果表明,在磨矿细度为-0.074 mm占85%、矿浆pH自然状态、分散剂六偏磷酸钠用量为300 g/t、活化剂组合硫酸铜和KDH01用量分别为100 g/t和50 g/t、捕收剂丁基黄药用量为200 g/t、起泡剂MIBC用量为40 g/t的条件下,原矿采用“一次粗选—两次扫选—两次精选”流程,中矿采用循序返回方式,扫选药剂用量依次按粗选药剂用量减半添加,精选不加药,全流程闭路试验最终可获得金品位30.63 g/t、回收率86.28%的金精矿产品,尾矿中金品位降至0.28 g/t,显著提高了金的回收率,回收效果较好,同时,自研活化剂KDH01对该金矿有较好的适用性,增加了矿物表面活性位点,增强了浮选效能,有效指导了实际生产。

难处理高砷金矿的细菌氧化-提金研究

采用经过驯化的HQ0211菌对高砷金矿进行氧化预处理-氰化提金实验研究。该矿石含金128.5 g/t,含砷16.84%(质量分数,余同),含硫21.72%,含铁26.62%,氰化浸出率只有29.35%,是典型的高砷难处理矿。经过细菌氧化预处理,金矿脱砷率达到96.2%,失重率达到43.9%。矿石的金氰化浸出率由原来的29.35%提高到92.57%,效果十分显著。

难处理复杂金矿循环流态化焙烧提金技术

300 t/d循环流态化焙烧提金示范工程投产运行状况及提金结果表明,采用循环流态化焙烧含金物料时,气固混合剧烈,物料温度分布均匀、停留时间长,碳燃烧充分完全。对含金平均品位在4-8 g/t的复杂含砷低硫精矿尾渣,通过循环流态化焙烧——氰化浸出后,渣金品位下降至平均1.5-2.5 g/t,金回收率75%-85%,焙烧温度750℃,煤耗3.5%左右。

难处理金精矿生物氧化——氰化炭浸法提金试验

针对某难处理金精矿含砷、高碳的特点,采用生物氧化-氰化炭浸提金工艺,考察了矿浆浓度、氧化时间、溶氧量、搅拌速度、培养基用量等因素对Fe、As、S脱除率、硫化物氧化率及金浸出率的影响。氰化炭浸试验结果表明,金的浸出率由直接氰化炭浸时的15.53%提高到95.82%,同时分析了氧化过程Eh、pH变化及Fe的行为。

从难处理含砷金矿中湿法回收砷

测定了As2O3在稀硫酸中的溶解度和湿法收砷结晶出的As2O3粒度,考察了影响Na2S沉淀稀酸中As2O3的因素。结果表明,As2O3在60%稀硫酸中的溶解度最低;湿法收砷的As2O3平均粒度为25.13μm;在S/As=3.75、反应时间120min、常温和两步加料的条件下,Na2S沉淀As2O3效果最佳。并提出一种全新安全环保的湿法收砷工艺,以回收含砷难处理金矿中的砷。