Molecular characterization of microbial populations in a low-grade copper ore bioleaching test heap

A culture-independent approach based on PCR amplification and denaturing gradient gel electrophoresis (DGGE) and sequencing of 16S rRNA gene fragments from both Bacteria and Archaea were used to analyze the microbial community inhabiting a low-grade copper sulfide run-of-mine (ROM) test heap of a project in Chile. In this paper, we summarize results of a 1-year monitoring study. Phylogenetic analyses of 16S rRNA fragments revealed that the retrieved sequences clustered together with Acidithiobacillus ferrooxidans, Leptospirillum ferriphilum, Ferroplasma acidiphilum and environmental clones related to them. In addition, some sequences were distantly related (< 95% similarity in the 16S rRNA gene fragment analyzed) to cultured microorganisms from the Sulfurisphaera and Sulfobacillus genera. Thus, the prokaryotic assemblage might be mainly composed of sulfur- and iron-oxidizing microorganisms. The remaining sequences were related to uncultured chrenarchaeota clones or had only partial homology with known microorganisms. Attempts were made to estimate the dynamic of phylogenetic microbial groups in different stages of the leaching cycle and to correlate them with chemical and physical parameters in the heap. The temporal distribution of microbial 16S rRNA gene sequences could be divided in three periods. In the bioleaching cycle, first stage A. ferrooxidans and Sulfurisphaera-like archaea were dominant within each respective phylogenetic domain. In the second stage (from days 255 to 338), Leptospirillum and Ferroplasma groups were mainly detected, respectively. Finally (the third period from operation days 598 to 749), Sulfobacillus-like microorganisms became predominant, while Ferroplasma was the only Archaea detected. These data are now being used to obtain more detailed and quantitative information on prokaryotic community structure over time and to explore the nature of the community metabolic pathways. These results extend our knowledge on microbial dynamics in bioheaps, a key issue required to improve commercial applications.     

难浸金矿生物堆浸存在问题与对策

综述了难浸金矿生物堆浸的历史及现状,比较了国内外在该技术领域的差距,分析了其中存在的问题。认为我国通过近20 年的开发研究,目前仍处于室内与现场交替试验时期。通过室内试验和现场实践,从矿石性质角度分析认为酸耗量、渗透性差、硫含量低和金矿物受机械包裹的难浸矿石在目前条件下仍难以用生物堆浸的手段予以处理。另外,还从试验周期、室内外试验结果的差异、自然条件和氧化菌种等方面探讨了生物堆浸技术发展所需的环境和条件,提出了相应的对策。最后,通过对我国现有的资源优势、目前的市场条件、近年来我国在该技术领域的开发经验及该技术延伸领域(难浸金精粉的堆式生物氧化、难浸金矿的堆式生物氧化+ 炭浸提金) 应用探讨,认为生物堆浸技术在难浸金矿资源的开发利用领域有着广阔的应用前景。     

某铀矿石微生物柱浸翻柱对比试验

以某铀矿堆浸生产线的矿石为原料,考察微生物柱浸翻柱方式对铀浸出率的影响。结果表明,经过113天试验,两柱液计累计铀浸出率分别为80.62%和76.49%,渣计铀浸出率分别为88.67%和85.24%,耗酸率分别为9.17%和9.04%。在酸化阶段提前翻柱可有效减轻泥化、板结现象,促进铀的浸出。     

Bioleaching model of a copper-sulfide ore bed in heap and dump configurations

A two-dimensional (2-D) model for a heap or dump bioleaching of a copper ore containing mainly chalcocite and pyrite has been developed. The rate of the mineral sulfide dissolution was related to the rate of oxidation by bacteria attached onto the ore surface. The latter was calculated using the model of Michaelis-Menten, where both temperature and dissolved oxygen in the leach solution were taken into account by the kinetic equation. Oxygen transport through the ore bed was associated with natural air convection originating from the decrease in gas density inside the ore bed, which was attributable not only to heating, but also to humidification and decrease in the oxygen concentration. The model was used to estimate air-velocity fields and profiles of temperature and oxygen concentrations as well as mineral conversions during the bioleaching operation for ore beds with different pyrite contents, bacterial populations, widths, heights, and permeabilities. The model provides a useful tool for the design, improvement, and optimization of industrial operating conditions.     

Bacterial succession in bioheap leaching

Bioheap leaching of secondary copper ores is applied commercially at operations in Chile, Australia, and Myanmar. Bioheap leaching of sulfidic refractory gold ores has been demonstrated at large scale. There is limited comprehension of what actually occurs microbiologically in full-scale bioheap operations, despite the commercial achievement of copper ore bioheap leaching and the anticipated technical and commercial success of gold ore bioheap leaching. Copper bioheaps are typically inoculated with the bacteria contained in the raffinate or intermediate leach solution, whereas, sulfidic refractory gold ore bioheaps can be inoculated with bacteria developed in a separate reactor. Chemical and physical conditions within bioheaps change radically from the time the bioheap is stacked and inoculated until bioleaching is completed. Redox, acidity, temperature, oxygen and solution chemistry conditions vary widely during the oxidation period. Such conditions likely select for microorganisms or may, in fact, effect a succession of organisms in portions of the bioheap. Bioheap solutions are recycled and constituent build-up over time also affects the microbiology. Organic entrapment in the raffinate from the solvent extraction circuit may influence microbial activity. Heterotrophic microorganisms may also play some role in bioheap leaching. Understanding the microbiology of bioheaps is key to advancing commercial bioheap applications. Such knowledge will increase the ore types as well as the diversity of mineral deposits that can be processed by bioheap technology. It will also enable better control of conditions to improve leach rates, metal recoveries and costs. This paper briefly explains commercial practices, describes chemical, physical and microbiological monitoring of bioheaps, considers conditions that control microbial populations in bioheaps, and examines the types of ore deposits that could be bioleached, if the microbiology was elucidated.     

紫金山铜矿生物堆浸过程酸铁平衡实践与优化方向

紫金山铜矿低品位矿石采用生物堆浸—萃取—电积工艺产出阴极铜。矿石中主要铜矿物为蓝辉铜矿及铜蓝,同时含有较高含量的黄铁矿,耗酸脉石含量低。铜矿物浸出过程中,伴随着黄铁矿的氧化产酸产铁,造成堆浸系统溶液中酸铁浓度的不断累积,影响到浸出、萃取及环保处理工序,需要通过不断地中和来降低酸铁浓度。介绍了紫金山铜矿生物堆浸的技术特点,对生物堆浸过程中高酸高铁和低酸低铁两种工艺实践中酸铁平衡实践进行总结;结合紫金山铜矿矿石矿物学信息,进行酸平衡计算,确定了堆浸过程中黄铁矿氧化过程对酸铁平衡的影响;分析工艺条件对酸铁平衡的影响,并提出未来解决酸铁过剩的工艺优化方向。     

低品位次生硫化铜矿生物堆浸工艺优化研究

针对低品位次生硫化铜矿生物堆浸生产中浸出周期长的问题,进行了不同矿石粒度、不同堆高对铜、铁浸出影响的实验室试验和现场柱浸工业试验,优化了生物堆浸工艺,缩短浸出周期,提高了铜浸出率。结果表明,矿石粒度的降低可显著提高铜的浸出率,且不提高铁的溶出。相同粒度条件下,堆高提高有利于堆内温度保持,铜浸出率随之升高。-40mm工业柱浸出194d,铜的浸出率为62.67%,比-80mm高出10个百分点。     

Rapid and specific detection of Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans by PCR

Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans are two of the most important bacteria in heap bioleaching processes of copper sulphide at common operating temperatures (18–24 °C). In this paper, both microorganisms were detected in solutions and ores coming from processes in 2 days, using specific amplification of 16S rDNA sequences by PCR. The technique was first validated using template DNA from pure cultures of the microorganisms. Then it was applied to samples of solutions and ores from bioleaching processes. Results were confirmed using tRFLP (terminal Restriction Fragment Length Polymorphism) with universal primers and by identification of isolated bacteria by means of culture. This methodology is more rapid and specific than the identification by tRFLP or by culture, which require from 1 to three weeks to positively detect the bacteria. The detection limit of this technique is 10⁵ cells per ml.     

The bioleaching of nickel-copper sulfides

Demand for nickel, largely driven by the Chinese stainless steel market, currently exceeds production, causing an unprecedented rise in the price of nickel and renewed interest in bioleaching technology for the processing of low grade nickel sulfide ores and concentrates. Although nickel inhibits bacterial physiological functions such as iron- and sulfur-oxidation, some bacteria adapt readily to high concentrations. In pilot‐scale continuous reactors, mixed microbial populations grew actively over many months in the presence of up to 400 mM nickel (23 g/L). The results of bench-scale test work have been sufficiently encouraging to prompt pilot- and demonstration-scale trials in heaps and agitated tanks in Australia, China, Finland and South Africa in recent years. The first commercial implementation of nickel sulfide heap leaching is likely to be the operation at Talvivaara, Finland.     

Use of mesophilic and thermophilic bacteria for the improvement of copper extraction from a low-grade ore

Bioleaching was examined for copper extraction from a low grade ore using mesophilic and moderate thermophilic bacteria. Five equal size columns were used for the leaching of the ore. Sulfuric acid solution with a flow rate of 3.12 L.m-2.h-1 and pH 1.5 passed through each column continuously for 90 d. In the first and the second column, bioleaching was performed without agglomeration of the ore and on the agglomerated ore, respectively. 28wt% of the copper was extracted in the first column after 40 d, while this figure was 38wt% in the second column. After 90 d, however, the overall extractions were almost the same for both of them. Bioleaching with mesophilic bacteria was performed in the third column without agglomeration of the ore and in the fourth column on the agglomerated ore. After 40 d, copper extractions in the third and the fourth columns were 62wt% and 70wt%, respectively. Copper extractions were 75wt% for both the columns after 90 d. For the last column, bioleaching was performed with moderate thermophilic bacteria and agglomerated ore. Copper extractions were 80wt% and 85wt% after 40 and 90 d, respectively. It was concluded that crushing and agglomeration of the ore using bacteria could enhance the copper extraction considerably.     

Silver-catalyzed bioleaching of low-grade copper ores.: Part I: Shake flasks tests

A study of the effect of different variables (inoculation, pulp density, [Ag], nutrient medium, pH and [Fe³⁺]) on the silver-catalyzed bioleaching of a low-grade copper sulfide ore has been carried out in shake flasks. Chalcopyrite was the dominant copper mineral in the ore. Preliminary tests showed that addition of other ions (Sb, Bi, Co, Mn, Ni and Sn) did not enhance the copper dissolution rate. Conversely, an inoculation with mesophilic microorganisms and the addition of silver had a markedly catalytic effect on the extraction of copper. The kinetics of the silver-catalyzed chalcopyritic ore bioleaching was greatly affected by pulp density and silver concentration. Small amounts of silver (14.7 g Ag/kg Cu) dramatically accelerated the copper dissolution process while large amounts (294.12 g Ag/kg Cu) had an inhibitory effect. The copper dissolution rate was slightly affected in the range of pH between 1.2 and 2.5 but was significantly slower at pH 3.0. The effect of [Fe³⁺] in the presence of silver was studied both in abiotic and biotic conditions. High ferric iron concentrations in abiotic tests recovered similar copper amounts (∼ 95%) to those obtained without or with low [Fe³⁺] in the presence of bacteria. The leaching of copper from the low-grade copper ore can be very effectively enhanced with silver and mesophilic microorganisms. For that system, the onset of oxidizing conditions starts at an Eh value slightly higher than 650 mV. Above that critical value of potential the copper dissolution rate slows down. This also corresponds with the completion of the leaching process. As the potential rises past 650 mV, the copper extraction reaches a plateau.     

非饱和矿堆溶液渗流迟滞与毛细扩散行为表征

为深入理解非饱和矿堆内溶浸液毛细渗流扩散以及渗流迟滞行为,本文构建适于非饱和矿堆的毛细渗流模型,利用COMSOL multiphysics有限元数值平台开展毛细渗流可视化模拟研究,并利用时域反射器（Time domain reflector,TDR）实时探测了非饱和堆内持液率变化,探索了基于Design Expert的毛细渗流过程多因素响应规律,讨论了非饱和矿堆持液率、毛细吸力、孔隙率与喷淋强度间的潜在关联机制.研究结果表明：孔隙率对矿堆持液率的影响高于喷淋强度,矿堆持液率随喷淋时间的增长收敛性增加,且孔隙率小的矿堆需要更长的时间才能达到稳态持液;不考虑溶液喷淋强度影响时,矿堆持液率与孔隙比、水力传导系数呈正相关;特别是在喷淋初期（0～20 s）,喷淋强度、水力传导系数和孔隙比对矿堆持液率的影响更为显著;初步构建了考虑气液两相运移的非饱和矿堆溶液毛细渗流模型;毛细吸力的变化对孔隙率较小的矿堆更敏感;喷淋强度较大、孔隙比越小时,矿堆底部的毛细吸力越大,更易达到稳态持液状态.     

硫化铜矿粒孔隙模型重构与溶液渗流模拟

以次生硫化铜矿粉为原料,添加黏结剂、氯化钠制备矿粒,并借助CT扫描技术、图像处理及三维重构方法,开展了单个矿粒浸出试验,探究了溶浸前后矿粒内部的孔隙变化;运用COMSOL Multiphysics模拟仿真软件,构建了溶液在孔隙通道中流动的仿真模型。结果表明:经过一周时间的溶浸,矿粒内部孔隙的数目、平均体积、平均表面积及孔隙平均等效直径分别增长了99%、151%、223%和90%,孔隙率增长了4倍,孔隙连通度增长了近2倍。在孔隙通道较狭窄的区域和底部区域,溶液的流速、压力急剧增加,对矿粒结构的稳定性产生较大影响。      

Biotechnology in minerals processing: Technological breakthroughs creating value

The maturation of biotechnology applied to the minerals industry has required some key breakthroughs. Commercial success started with the mesophilic oxidation of refractory gold ores via the now-well-established BIOX® process. This was followed by the development of the BioCOP™ process for extracting copper from concentrates. In its initial format, this was a mesophilic process with limited capabilities for recovery of copper from chalcopyrite. The key breakthrough was determining how to achieve good copper extraction from primary sulfides using thermophiles, coupled with acceptable residence times and solids loadings. This opened a potential route to heap leaching of chalcopyrite, which is now a major focus of research and development. Future developments will require the management of temperature, together with the progressive establishment of different microbial regimes.     

低品位铀矿石微生物柱浸试验

对某低品位铀矿石进行了不同喷淋条件的微生物柱浸试验。结果表明,试验用混合菌群对目标铀矿石具有较强适应性,浸出周期172d,菌浸期间5%和10%喷淋量条件下渣计平均浸出率分别为87.70%和88.53%,耗酸率分别为5.36%和5.37%。菌浸阶段采用较大喷淋量可提高浸出率,但液固比会显著增加,综合成本相应提高。因此,喷淋量的选择应综合考虑铀资源回收率与浸出成本。     

对加温及增强渗透提高浸堆金浸率的探讨

采用堆浸法提金工艺处理低品位金矿的技术在世界发达国家或地区已经日益趋于成熟,我国在研究应用低品位金矿堆浸技术方面也已经取得了较大成就, 但对低温地区的浸堆加温及含粉矿、粘土矿物较高的金矿石解决渗透性的堆浸技术方面, 我国矿业界仍需要加快研究,以利于我国黄金工业发展和金矿资源保护。     

Possibility of using chemical fertilizers instead of 9K medium in bioleaching process of low-grade sulfide copper ores

The possibility of applying chemical fertilizers as a source of nutrients for bacterial growth in bioleaching process was investigated. In the first part of the experiment the nutrient content of four sulfide copper ore samples was determined. The results confirmed that the amount of calcium, magnesium and sulfur were sufficient to support bacterial growth, whereas nitrogen, phosphorous and potassium were not sufficient. Therefore, N, P, and K from a chemical fertilizer source were applied to the sulfide copper ores to make a cost-effective bioleaching process. According to shake flask experiments by using mesophilic, iron-sulfur oxidizing bacteria, bacterial activity and copper recovery in some proposed media was satisfactory compared to 9K medium. Additionally, potassium had positive effect on the copper ore bioleaching while NO₃⁻ and Cl⁻ had inhibitory effect on the bacterial activity.     

Influence of microwave pretreatment on the bioleaching behaviour of low-grade complex sulphide ores

Mineralogical information on the mechanisms by which microwave pretreatment improves the bioleaching behaviour of low-grade complex sulphide ore, and an interpretation of the interrelationship between mineralogy, microwave processing, and bioleaching process are provided in this study. The influence of microwave irradiation on the bioleaching behaviour and mechanisms of a low-grade complex sulphide ore subjected to microwave heating in a kitchen type microwave oven at a power output 1100 W for 5 min was investigated in a mixed mesophilic bacterial culture through bioleaching experiments and electrochemical techniques. Results revealed that microwave treatment improved the bioleaching of behaviour of the ore, with more effect on copper and iron dissolutions than on zinc and lead. Both microwave treated and untreated samples showed similar electrochemical behaviour. However, microwaved samples displayed higher reactivity, dissolution rates, dissolution currents, current densities and a decreased polarization resistance. Increase in dissolution of the microwaved treated samples resulted from phase changes in the ore which promoted galvanic interaction within the system, decrease in the amounts of sulphur contents, and an increase in electrochemical sites resulting from an increase in the number of cracks induced by microwave heating.     

浸矿微生物与矿物相互作用的研究方法与技术

深入研究和理解浸矿微生物与矿物之间的相互作用机制对于提高金属浸出效率及控制酸性矿坑水的形成是必须的.研究浸矿微生物与矿物之间的相互作用过程中,各种理论方法和检测探测技术起到了决定性的作用.为了使各种方法技术更加深入地应用于研究中,文中概述了研究浸矿微生物-矿物相互作用的物理化学方法,表面成分检测方法以及微观形貌探测技术,并指出各种研究方法技术的结合是更好地探测浸矿微生物-矿物相互作用的发展方向.     

低品位金铜混合矿综合利用工业试验

针对紫金山低品位金铜混合矿,采用生物堆浸—介质转换—氰化提金工艺进行千吨级工业试验,考察了生物堆浸过程中铜和铁的浸出行为、酸碱介质转换和氰化提金技术指标,并进行经济效益分析。结果表明,在矿石粒度50mm、堆高5m条件下生物浸出周期80d,氰化浸出30d,渣计铜、金浸出率分别为55.2%、50%;吨矿生产成本72.24元,产值75.11元。