Engineered strains enhance gold biorecovery from electronic scrap

Gold bioleaching from electronic scrap materials (ESM) was examined using the bacterium Chromobacterium violaceum which produces and detoxifies cyanide, one of the few lixiviants capable of leaching gold. Gold recovery by the wild-type C. violaceum and two genetically engineered strains (pBAD and pTAC) with an additional cyanide-producing operon were investigated and compared. The ESM was pretreated to remove metals competing for metal cyanide complexation with gold. The effect of pulp density on leaching performance by the various strains was also investigated. The pBAD strain produced the highest cyanide concentration, and achieved the highest gold recovery of 30% at 0.5% w/v pulp density, compared to 11% recovery by the wild-type bacteria. Our results demonstrated the application of lixiviant metabolic engineering in the construction of enhanced bioleaching microbes for the bioleaching of precious metals from electronic waste.     

Bioleaching of gold and copper from waste mobile phone PCBs by using a cyanogenic bacterium

Chromobacterium violaceum (C. violaceum), a cyanide generating bacterium has been used to leach out gold and copper from the waste mobile phone printed circuit boards (PCBs) containing ∼34.5% Cu and 0.025% Au in YP (yeast extract and polypeptone with glycine) medium. The bioleaching was carried out in an incubator shaker (150 rpm) at 30 °C and 15 g/L pulp density in the pH range 8-11. Dissolution of gold and copper increased from 7.78% (0.225 ppm) to 10.8% (0.46 ppm) and 4.9% (419 ppm) to 11.4% (879 ppm) in 8 days with increase in pH from 8 to 11 and 8 to 10 respectively. Supplementing oxygen with 0.004% (v/v) H₂O₂ increased the copper leaching to 24.6% (1743 ppm) at pH 10 in 8 days whereas improvement in gold leaching was insignificant with the recovery of 11.31% Au at pH 11.0. The waste PCBs can thus be recycled in environmental friendly manner.     

生物氧化在内蒙某低品位原生金矿浸出研究中的应用

对内蒙某低品位原生金矿进行了生物氧化浸出实验研究,考查了配入硫磺以及硫精矿对降低酸耗,以及金浸出率的影响。结果表明,当磨矿细度-74 μm 80%,酸浸1 h,矿石酸耗为31 kg/t;全泥浸出24 h,金浸出率为51%~55%;生物搅拌浸出,氧化6 d,硫氧化率为80%,金的浸出率提高到91.4%;生物柱浸,矿石粒度 12 mm 80%,生物氧化170 d-转型-氰化浸出180 d较直接氰化浸出360 d,金浸出率提高3.72%~23.54%;柱内配入硫磺及硫精矿不利于金的氰化浸出;柱外生物氧化硫磺可以减少硫酸酸耗15.7 kg/t。      

微细粒浸染包裹含砷金矿石金的回收

提供了一种微细粒浸染包裹含砷金矿石的选冶联合工艺,包括浮选、碱性常温常压强化碱浸预氧化和氰化。先对含砷金矿石进行浮选,获得含金63.80 g/t、产率5.51%、金回收率92.08%的浮选金精矿,然后对金精矿进行超细磨和碱性常温常压强化碱浸预氧化,氧化渣金的浸出率88.56%,金的选冶总回收率81.55%。     

Respirometry studies of bioleaching of low-grade chalcopyrite ore using six acidophilic strains

Respirometry was used to study the growth and activity of six pure cultures of acidophilic bioleaching strains grown on a concentration series of low-grade chalcopyrite ores under various pH conditions. Sulfolobus metallicus, Acidithiobacillus ferrooxidans, Acidianus brierleyi and Leptospirillum ferriphilum were able to grow on a very low-grade ore (equivalent to 0.1% Cu content). However, the two sulphur-oxidising bacteria Acidithiobacillus caldus and Acidithiobacillus thiooxidans grew poorly on the low-grade ore. Growth rates of all strains, except for perhaps S. metallicus at highest ore grades, displayed growth that was limited by substrate availability on this low-grade ore (0.5% Cu content in the ore). The decrease in solution pH from 3.0 to 1.0 enhanced both the cell growth and Cu dissolution.     

Evaluation of leaching parameters for a refractory gold ore containing aurostibite and antimony minerals: Part I – Central zone

A cyanidation study was conducted on a mild refractory gold ore sample from the Central zone of Clarence Stream Property, owned by Freewest Resources Canada, to develop a leaching strategy to extract gold. Gold, at a grade of 8.00 g/t, is present as native gold, electrum and aurostibite. The ore also contains 2.8% pyrrhotite, together with several antimony minerals (0.8% berthierite and gudmundite, 0.18% native antimony and stibnite). It also exhibits weak preg-robbing properties with 0.16% organic carbon. Aurostibite, a gold antimony compound, is particularly known to be insoluble in cyanide solution. The antimony dissolves in cyanide solution to form antimonates, which retards gold dissolution. Industrial practice of extracting gold from aurostibite generally consists of producing a flotation concentrate, which is leached in a pipe reactor at low alkalinity and high oxygen pressure with about 20 g/L cyanide.The proposed new approach is efficient and allows the extraction of gold directly from an ore at atmospheric pressure and a low cyanide concentration at pH 10.5. The effects of grinding, pre-treatment, lead nitrate, kerosene and cyanide concentrations have been investigated. The maximum gold extraction obtained on the ore was 87.9% using 800 ppm NaCN, 500 g/t lead nitrate, 30 g/t kerosene, DO (dissolved oxygen) 10 ppm and pH 10.5 in 168 h. The associated cyanide consumption was 1.3 kg/t. The additions of lead nitrate and kerosene increased gold extraction. In comparison to a P₈₀ of 74 μm, a P₈₀ of 30 μm significantly increased gold extraction. Gold in solid solution in gudmundite and arsenopyrite was believed to be responsible for the un-leached fraction until mineralogical analysis of hydroseparation concentrates of leach residues showed that most of the un-leached gold occurs as aurostibite, either as locked grains in sulphides/sulpharsenides or as grains with passivation rims of an Au–Sb–O phase. Coarse gold was also found. Gold extraction was not sensitive to cyanide concentration from 250 to 1200 ppm NaCN and high pH was detrimental. Decreasing the cyanide concentration reduced the cyanide consumption from 1.39 to 0.85 kg/t. The removal of coarse gold using a Knelson concentrator and a Mosley table prior to leaching increased the gold extraction to 90.4% (leach residue at 0.77 g/t).     

新疆某围岩蚀变型含泥金矿选矿试验

新疆某国有大型黄金矿山矿石特点为矿体极度破碎、原生泥和次生泥含量高,载金硫化矿浮选分离精度低,部分载金黄铁矿嵌布粒度微细且结晶程度较差,金的高效回收技术难度大。基于矿石工艺矿物学特性,取消原泥砂分选工艺,开发应用“全粒级粗磨粗选-中矿再磨单独选别-再选产品梯级返回”选矿工艺流程,强化泥质脉石高效抑制和载金矿物有效活化,应用泥质脉石抑制剂XJ-12和微细粒载金黄铁矿浮选增效剂AXJ-1,在原矿Au品位2.19g/t条件下,实验室全流程闭路试验获得Au品位30.30g/t、Au回收率86.28%的金精矿,有效降低细泥对浮选的干扰,提高难选目的矿物可浮性,实现了金的高效回收。     

福建某低品位金铜混合矿石综合回收利用工艺研究

福建某低品位金铜混合矿石含Au 0.36 g/t、Cu 0.29%、Ag 7.4 g/t、S 4.02%,若直接氰化,铜进入金氰化浸出系统,不但得不到回收,还会恶化选金指标,增加生产成本。针对该低品位金铜混合矿,采用浮选+氰化联合工艺进行选别。浮选作业考察了磨矿细度、石灰用量、捕收剂种类、分散剂种类对浮选指标的影响,结果表明,在磨矿细度为-0.074 mm 60%、石灰用量为1500 g/t、Z-200作捕收剂、水玻璃作分散剂时,浮选效果最佳,闭路实验获得铜精矿含Au 16.74 g/t、Cu 20.21%,金、铜回收率分别为61.90%和87.09%。将浮选尾矿进行氰化浸出,考察了氰化钠浓度和氰化时间对金浸出率的影响,结果显示,在氰化钠初始浓度300 mg/L浸出24 h,金浸出率为71.26%。全流程Au回收率达到89.05%,Cu回收率达到87.09%,最终达到综合高效回收矿石中金铜的目的,为此类资源的开发提供了技术支撑。      

Treatment of pyritic matrix gold–silver refractory ores by ozonization–cyanidation

Most of the gold and silver produced worldwide are extracted by the cyanidation process. The recovery of the precious metals involves two distinct operations: the oxidative dissolution of gold and silver by an alkaline cyanide solution, and the reductive precipitation of metals from the solution. From the cyanidation point of view, gold and silver ores can be classified as free milling, and refractory ores. The term “refractory ore” defines those materials that when submitted to a conventional cyanidation process, show low recoveries (<80%) or high consumption of reactants [Weir, D., Berezowsky, M., 1984. Gold Extraction from Refractory Concentrates, Sherrit Research Centre, Alberta, Canada, pp. 1–26; Haque, K.E., 1992. The Role of Oxygen in Cyanide Leaching of Gold Ore, CIM Bulletin 85963, pp. 31–38]. These refractory ores are usually pretreated by some oxidizing process after which gold and silver can be recovered by standard cyanidation process. Since ozone gas (O₃) is a strong oxidizing, it may be regarded as a promising alternative in the treatment of refractory ores.The present work summarizes the results obtained when two pyritic refractory ores from Mexican sites (samples A and B), were pretreated with an oxygen/ozone stream in acid media before cyanidation. Two contacting methods were studied: the indirect method (contacting the ore three times with ozone saturated water), and the direct method (direct addition of ozone to the mineral slurry). Sample A did not show any difference in recoveries with indirect pretreatment, while the direct pretreatment reduced the cyanidation time for maximal gold and silver recovery from 40 to 24 h. Sample B, only tested with indirect contact method, increased the gold recovery from 53% to 88% and the silver recovery from 26% to 78%.     

An evaluation of pretreatments to increase gold recovery from a refractory ore containing arsenopyrite and pyrrhotite

The effect of three ore pretreatments on gold recoveries from an ore in which the gold existed in solid solution in an arsenopyrite matrix, as well as being encapsulated in a pyrrhotite phase, was examined. The three pretreatments evaluated included fine grinding, pyrolysis-roast (Pyrox), and an oxidative pressure acid leach (PAL). It was found that untreated ores did not yield high gold recoveries even when a fine grind (<45pin) was employed, while oxidative treatments led to a significant improvement of recoveries. The Pyrox pretreatment was found to decompose the sulfide matrix of the ore to a greater extent than a 3 hour PAL treatmemt. However, the PAL process produced a slightly better gold recovery of 79% compared to the Pyrox recovery of 75%, and both of these were greater than the 55–60% recoveries achieved with the untreated ore. Furthermore, the depletion of dissolved oxygen levels observed during cyanide leaching were significantly reduced by the two oxidative treatments, compared to the untreated ores. PAL was found to benefit over the Pyrox pretreatment by affording a solid product, which Pyrox pretreatment by affording a solid product, which effectively “locked” the arsenic component of the mineral from being recovered in solution. The PAL process required more lime for neutralization of acid produced from the decomposition reaction. rights reserved.     

地质聚合反应制团对低品位铜矿石高压辊破碎—生物浸出的影响

为使团聚体在酸性条件下保持稳定并提高浸出效率,对高压辊磨机破碎后的低品位铜矿石进行了地质聚合反应制团后的生物浸出研究。考察了地质聚合物凝胶对浸矿微生物氧化活性的影响,以及原料、团聚体和粗颗粒矿石在柱浸中的表现,并借助核磁共振波谱（NMR）和扫描电子显微镜（SEM）分析技术研究了团聚体的性质。结果表明：经高压辊磨机破碎的矿石制团后浸出,66 d浸出率为61%,而粗颗粒矿石在相同时间内浸出率仅为28%;地质聚合物凝胶不会减弱微生物的氧化活性;原料经制团后渗透性显著提高且团聚体在柱浸时能长时间保持稳定;地质聚合物凝胶的形成是团聚体在酸性条件下稳定的原因,且矿石颗粒以地质聚合反应团聚后,颗粒间仍存在有大量的孔隙和裂纹而利于浸出。高压辊磨机破碎后的低品位铜矿石经地质聚合反应制团后生物浸出可使得低品位铜矿石的提取更加高效,并被期望在堆浸中得到应用。     

安徽某高砷高硫难处理金矿选矿试验研究

对安徽某高砷高硫难处理金矿进行了详细的矿物学研究,在此基础上提出了磁重联合试验方案,并通过磁选入选细度、磁场强度、重选入选细度等条件试验,最终得到含硫36.11%,含砷0.03%,回收率为17.81%的合格硫精矿及含金16.84g/t,含砷13.63%,金回收率为47.63%的金精矿。     

Bioleaching of six nickel sulphide ores with differing mineralogies in stirred-tank reactors at 30 °C

A bioleaching study was conducted with six nickel sulphide ores from different geographical locations across Canada. Mineralogical and chemical examination revealed considerable variability between the samples, particularly in the silicate phases. The ores contain 0.3–1% nickel, primarily in pentlandite and secondarily in pyrrhotite. Copper is present primarily in chalcopyrite, and cobalt in pentlandite. The ores were subjected to the same crushing and grinding procedure, and bioleached under the same conditions for 3 weeks with a mixed culture of iron- and sulphur-oxidizing bacteria. Stirred-tank experiments with finely ground ore (−147 μm) at 30 °C were conducted to assess the effect of pH (2–5) and the impact of the bacteria. Nickel extraction from pentlandite and pyrrhotite during bioleaching at pH 2 and 3 was generally good (49–86% after 3 weeks), and cobalt extraction tracked nickel extraction over most conditions. All six ores showed a similar response to a change in pH; an increase in pH from 2 to 3 resulted in approximately the same nickel and cobalt extraction (within statistical error), and a statistically significant reduction in sulphuric acid consumption, dissolved iron, and magnesium extraction.     

广西某低品位金矿氰化浸出助浸剂实验研究

广西某低品位金矿石含金量为1.29 g/t,脉石矿物以石英为主,有色金属铜、铅、锌等及有害元素砷的含量极低。对该矿石进行氰化浸金实验研究,分别考查磨矿细度、溶液pH值、氰化物用量、搅拌转速、浸出时间对金浸出效果的影响;通过单矿物氰化助浸实验,确定多种助浸效果较好的助浸剂,并按同一比例混合,获得了三种新型助浸剂A、B、C;针对广西某低品位金矿石,进行氰化浸出助浸实验。结果表明,矿样细度-0.074 mm 93.27%,溶液pH值为10.5,氰化钾用量为4 kg/t,搅拌转速为1500 r/min,浸出时间为24 h的实验条件下,金的浸出率为92.58%;而氰化钾用量减少至3 kg/t,其余条件不变的情况下,加入新型助浸剂A浸出18 h后,金的浸出率可达93%。新型助浸剂的加入有效地提高了金的浸出率,同时将氰化物的损耗降低了25%,浸出时间缩短了6 h以上。     

Initial loss of cyanide, thiocyanate, and thiosulfate adjuvants following amendment to an oxidic gold ore

Gold extraction and gold phytomining involve the use of adjuvants such as cyanide, thiocyanate, or thiosulfate to facilitate the dissolution of gold and its subsequent recovery. The adjuvants can be applied at high rates, in excess of 1 kg t⁻¹ for some ores. At these concentrations, concerns have been expressed about adjuvant persistence and associated detrimental repercussions for the environment. The incubation study here examined the initial disappearance of these adjuvants in the dark following their amendment at 1 g kg⁻¹ gold ore. Over a 24 d period, nearly 75% of the initial thiocyanate was lost within 24 d while >50% of thiosulfate and cyanide was lost over the same time frame. Cyanide and thiosulfate loss showed an exponential loss while thiocyanate was observed to follow a biphasic relationship. For the oxidic ore used, the adjuvants were not inherently persistent, suggesting that natural attenuation may rapidly promote adjuvant loss under specific conditions.     

The effect of potential heap construction methods on column bioleaching of copper flotation tailings containing high levels of fines by mixed cultures

It is known that excess fines may reduce heap permeability and block channelings of leachate flow in heap bioleaching operation, and further cause low metal recovery. The purpose of this investigation was to compare the effects of three potential heap construction methods including layered heap construction method (Method A), agglomerate heap construction method (Method B) and pelletized sintering heap construction method (Method C) of copper flotation tailings on column bioleaching behaviors. In the three heap construction methods, the tailings copper extractions achieved 54.61%, 60.09% and 43.93%, respectively, in Method A, B and C on day 83. Copper extraction of Method B reached maximum. In addition, compositions and structures of microbial communities were examined using Illumina Miseq sequencing technology based on 16S rRNA amplification. Acidithiobacillus, Leptospirillum and Ferroplasma were main microorganisms in three heap construction methods. Detrended correspondence analysis showed that Method C had little effect on microbial communities. These studies revealed the influence of different heap construction methods on leaching behaviors and microbial dynamics, which will facilitate the bioleaching of fine-grained ores.     

某高硫高砷含碳金矿选矿试验

某高硫高砷含碳金矿石金品位为4.21 g/t,含砷0.82%、含碳0.85%,呈细粒、微细粒嵌布。硫化物包裹金和裸露金占总金的98.31%,金多分布于黄铁矿与石英、绢云母等脉石矿物连生体中。为回收利用矿石中的金,分别进行直接氰化浸出、预处理-氰化浸出、浮选-预处理-氰化浸出试验。结果表明,直接氰化浸出、预处理-氰化浸出金回收指标均较差;原矿经一段磨矿（-0.074 mm 90%）-1粗3精2扫浮选-二段磨矿（-0.038 mm 93%）-1粗3精2扫闭路浮选-尾矿预处理-氰化浸出选别,浮选可获得金品位23.36 g/t、含银96.00 g/t的金精矿,金精矿回收率为6722%,金浸出率23.36%,金总回收率达90.58%,指标较好,可作为该金矿石选矿工艺流程。     

碳酸盐型难选金矿石选矿工艺流程试验研究

碳酸盐型难选金矿石含碳较高,碳在生产流程中循环,造成现场生产指标较差。为了提供较好的流程改造方案,对复杂碳酸盐型难选金矿石开展了选矿工艺流程试验研究。根据矿石的特点,采用常规浮选工艺流程、分段精选流程、二段粗精矿返回一段球磨,一次精选尾矿和一段粗选尾矿给二段球磨流程、粗选一段磨矿中矿再磨再选流程四种试验方案和闭路试验指标进行对比分析,结合现场生产场地实际情况,最终推荐采用二段粗精矿返回一段球磨,一次精选尾矿和一段粗选尾矿给二段球磨流程,闭路试验获得金品位58.89g/t,金回收率为86.70%。     

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.     

广西某金矿石选矿工艺试验

广西某含砷金矿石金品位4.20 g/t,含砷1.76%,金主要呈超显微金、胶态金的形态包裹于黄铁矿、毒砂及其次生矿物褐铁矿中,嵌布粒度细,较难选别。为回收该矿石中的金,分别采用直接浸出工艺和浮选-焙烧-浸出工艺进行选矿试验。结果表明：①堆浸直接浸出工艺金浸出率低,在入浸矿石粒度-5 mm时浸出率仅28.48%;②全泥氰化浸出工艺在磨矿细度-0.074 mm 6.58%时,金浸出率34.03%,仍不理想;③浮选-焙烧-浸出工艺在磨矿细度-0.074 mm 5.74%、焙烧温度550 ℃、氰化钠用量1 500 g/t时,可获得金浸出率90.43%的良好指标,可作为确定该金矿石选矿工艺的技术依据。