细菌氧化法处理金矿的工艺初步研究

1、细菌氧化法处理金矿的工艺初步研究摘要介绍了细菌氧化法处理金矿的工艺，细菌氧化冶金的原理、细菌氧化法金的回收、细菌氧化的影响因素、细菌氧化冶金的优缺点，以及目前工艺中存在的问题及对策。指出了细菌氧化法处理金矿工艺的发展方向以及在实际工业中重要作用。关键词：金矿；细菌氧化；金回收率1前言细菌氧化是二十世纪下半叶冶金学领域十分活跃的学科之一。从本世纪七十年代末始，黄金资源就成为矿业界最热门的开发领域。近二十年，世界范围内黄金资源勘探、开发程度的迅速提高直接促进了选冶技术的革新和发展，用于金矿开发的预处理技术也得到一定程度的利用。焙烧、加压氧化和细菌氧化法成为当今黄金选冶领域三大预处理技术。由于焙烧法

2、存在环保问题、加压氧化法投资高、技术难度大，人们便把更多的目光投向无污染、低成本的细菌氧化法，使之成为近几年开发速度最快的新兴技术。2细菌氧化冶金细菌氧化冶金技术，又称细菌浸出技术，通常指矿石的细菌氧化或生物氧化，由自然界存在的细菌进行。这些细菌被称作适温细菌，大约有0.5-2.0微米长、0.5微米宽，只能在显微镜下看到，靠无机物生存，对生命无害。这些细菌靠黄铁矿、砷黄铁矿和其他金属硫化物如黄铜矿和铜铀云母为生。在自然界，微生物在多种元素的循环当中起着重要作用，地球上许多矿物的迁移和矿床的形成都和微生物的活动有关。生物湿法冶金是一种很有前途的新工艺，它不产生二氧化硫，投资少，能耗低，试剂消耗少

3、，能经济地处理低品位、难处理的矿石。目前，这种方法仍处于发展之中，它还必须克服自身的一些局限性，如反应速度慢、细菌对环境的适应性差，超出了一定的温度范围细菌难以成活，经不起搅拌，等等。为此，一些科学家建议应从遗传工程方面开展工作，通过基因工程得到性能优良的菌种。2.1细菌氧化冶金原理2.1.1细菌浸矿的作用方式关于细菌浸矿机理主要有直接作用和间接作用两种。直接作用理论认为细菌通过直接附着在矿物特定位点上，直接氧化矿物中的亚铁和低价硫或砷。2FeS2+7O2+2H2O一2FeSO4+2H2SO42FeAs+7O2+H2SO4+2H202H3As04+Fe2(SO4)34FeSO4+O2+2H2S

4、O42Fe2(SO4)3+2H2O从而使金矿物的包裹层溶解。间接作用理论认为细菌以溶液中的Fe2+为能量和电子供体生长，形成的代谓产物Fe3+间接氧化矿物中的亚铁和低价硫，构成循环浸出。FeS2+7Fe2(SO4)3+8H2O一15FeSO4+8H2SO44FeSO4+O2+2H2SO42Fe2(SO4)3+2H2O但多数人认为这两种作用共同起作用，即常说的联合作用，具体到细菌催化的详细步骤，是一个复杂的涉及NAD，FAD，NADP，ATP等生物大分子的酶系统，是一个有高效催化能力的电子传递链(已知的酶催化效率为普通化学催化剂的几十至上千倍)。2.1.2反应机理矿物的细菌氧化是靠一种天然的棒状

5、(长0.5-2.0微米，宽0.5微米) 噬硫杆菌来完成的。噬硫杆菌的食物包括黄铁矿、砷黄铁矿、辉铜矿、黄铜矿、闪锌矿和其它贱金属硫化物。这些细菌需要从空气中获取氧气和二氧化碳，以及少量氮和磷。噬硫杆菌和其它有关类型的细菌(如小螺旋菌和硫化裂片菌属)，可以在酸性温泉及其附近地区、火山活动地区以及硫化物丰富地区找到。后两种细菌一般在45-90 的温度下繁殖。它们的生命力强，能在金属离子高浓度和pH值低于2.5的硫酸环境下迅速繁殖。这些以岩石为食物的细菌将坚硬的矿物分解成可溶于酸的硫、铁及其它金属，诸如砷、铜、锌、镍、钴等。可溶铁在氧化状态下(三价铁)是硫化矿物的强氧化荆。这些细菌能使铁维持在三价状

6、态下。因此，硫化矿物在化学和微生物的共同作用下进行分解，使显微和亚显微金颗粒裸露出来。与在不含细菌的水和空气中进行氧化的方法相比，矿物细菌氧化的速度要快50-100万倍。在适当条件下(酸性pH值和足够的空气)细菌的数量会急剧增长，一直到每克矿石或精矿，或是1毫升酸性水中多达1亿-100亿个的惊人数字。在充气搅拌槽及特殊构筑的浸堆中，矿物的细菌氧化不仅迅速而且高效，例如，在4-5天的时间内，可将难选的含金硫化矿精矿氧化，金回收率提高到90以上。但在此前，还不到3O。2.2细菌氧化法回收金2.2.1槽式细菌氧化法浮选精矿的细菌氧化过程，是把精矿同高浓度细菌悬浮液在较弱硫酸溶液中充气搅拌的连续过程，

7、即先将悬浮在酸液中的浮选精矿送往第一槽，待大部分细菌氧化后，送入第二槽再次充气搅拌。在通常情况下，细菌氧化装置按三段串联配置。第一段规格大，后两段规格小。在第二段精矿停留时间较短。这种配置不仅为硫化矿的细菌分解提供了充裕的时间，而且消除了可能造成金回收率降低的矿浆短路现象。以下两个参数对细菌氧化法回收金的经济效益有很大影响：（1）为获得满意的金回收率需用细菌分解的硫化矿数量。这一参数决定着所需的氧气量和搅拌工作量，影响基建投资和生产成本。（2）细菌分解硫化矿物的速度。这一参数决定着每一段的处理能力和需要的段数，也影响基建投资。槽式细菌氧化法大都用于处理价值高的硫化矿精矿。这是因为对细磨的矿物进

8、行充气搅拌需要消耗动力，另外，建造能耐硫酸和三价铁混合物腐蚀的浸出槽，费用高昂。2.2.2细菌堆浸法这一方法包括的作业有：破碎矿石，垫上筑堆、含菌(通常是噬硫杆菌和小螺旋菌)稀酸液喷淋。当大量的硫化矿物被氧化，金裸露出来后，要用水洗涤矿物，以除去酸和其它金属，再加石灰提高pH值，接着用氰化物溶液处理矿石。由于用堆浸法进行细菌氧化的矿石颗粒粗，通常大于6.5毫米，所以，堆浸法生产，金的回收率低于充气搅拌的浸出槽的回收率。鉴此，当矿石品位较低，用选矿法处理不经济，可考虑用细菌堆浸法。2.2.3贱金属回收有价贱金属(包括铜、镍、锌、钴、钼)常以硫化矿物(常夹有贵金属)的形式赋存，也可用细菌分解，溶入

9、稀酸溶液的贱金属可用传统的冶炼方法回收。2.3细菌氧化的影响因素用细菌氧化法处理金矿时，会有许多的因素影响到金的产率，主要有细菌方面的因素、矿物学方面的因素、工艺方面的因素等等。2.3.1细菌方面的因素（）浸矿菌种浸矿细菌一般直接从要处理矿石的周围环境中分离获得。这些好氧的中温菌大多生长在酸热环境中，从而形成以硫化矿为主要基质的独特的生理特征，具有对二价铁、还原态硫的独特的氧化能力。（）pH值对细菌生长的影响影响培养基中有机化合物的电离，引起微生物表面(细胞膜)电荷变化，从而改变有机物质渗入细胞的难易程度；pH有较大偏差时，由于氨基酸残基离子化的改变和非共价相互作用的破坏，可导致酶的变性；pH

10、值太小，降低CO2在水中的溶解度，结果使得细菌的碳源物质匮乏。只有在适宜的pH值下，细菌才能正常完成迟缓期内的生理过程，促进浸矿过程。2.3.2矿物学方面的因素矿石由矿物组成，矿物是细菌氧化的工作对象，它构成了细菌浸矿工艺的内因。在进行细菌氧化时，首先应查明矿石的化学成分和矿物成分。矿石的研究成为细菌氧化工艺研究的主体。（）矿石矿物组成矿石中金的赋存状态、载金矿物的类型、硫化物的镶嵌共生状态必然影响金精矿中的颗粒在浸液中的电化学性质，它们构成了不同电位差的伽伐尼电池，使细菌对硫化物的氧化产生差异。（）矿石中硫化物的化学成分硫化物化学成分的复杂性，给细菌浸出带来了一定的困难。世界上难浸金矿的分类

11、也主要根据矿石化学成分的差异来进行分类的，有高砷微细粒金矿石、含碳金矿石、含碲金矿石、含多金属金矿石。2.4细菌氧化冶金优缺点细菌浸出技术的主要优点有：（1）提高金的回收率；（2）从商业角度证实下游技术如溶剂萃取、电积法可用于经生物技术处理过的溶液现物生产金（3）生产过程的简单化降低了前期投入和运营费用，缩短了建设时间，维修简单方便；（4）生产在常压和室温（约为25摄氏度）条件下进行，不用冷却设备，节约了投资和运营资本；（5）细菌浸出的废弃物为环境所接受，节约了处理废弃物的成本，细菌浸出的废弃物的预防措施也很少；（6）细菌易于培养，可承受生产条件的变化，对水的要求也很低，每百万水溶液中可溶解固

12、体物2万份。细菌浸出技术的缺点是：（1）罐浸出的时间通常为46天，与焙烧和高压氧化的几小时相比，时间较长；（2）难以处理碱性矿床和碳酸盐型矿床。3存在问题与发展对策从我国目前细菌氧化技术的开发研究现状来看，工业化进程与理论研究、试验水平之间的差距较大，主要原因表现在技术本身存在某些障碍性因素，工程设计不完善，资金不足，科研力量无统一协调管理等，直接影响投资者信心与工业化实施。3.1技术问题氧化周期长是细菌氧化技术存在的最突出的恫题。一般金精粉氧化需要5lOd时间，原矿堆浸氧化则要60d以上，长周期氧化作业直接影响着生产成本和经济效益。另外一个问题就是处理难度很大的金精粉，矿浆浓度很低(小于l0

13、 )时，才能达到理想的氧化效果，这也是生产效率低的原因之一。因此，在细菌氧化技术应用过程中，尽可能创造适合细菌作用的环境是提高氧化效率的措施外，培养氧化能力强、适应范围广的高效菌种则可能是解决问题的主要途径。3.2设备问题细菌氧化技术应用于槽浸生产中，除遇到技术问题外，还存在设备和机械材料问题。为了要达到理想的氧化效果，一般都要采用降低矿浆浓度或延长氧化时间来实现这样则直接影响设备的设计规模及投资。另外，还有充气方式、充气量、叶轮结构、转速及散热方式等设计参数，都会影响设备效率。因此，在细菌氧化技术的工业化应用过程中，如何设计合理的设备规模与结构、选择合理的工程材料、降低工程造价都是提高技术实

14、用性与竞争力的关键因素。从这一角度上讲解决设备问题比解决工艺问题更重要。4细菌氧化冶金的应用细菌氧化治金在经济可行性上可有效地与焙烧竞争。故可以相信在不久的将来细菌氧化冶金技术可很好地应用。采矿项目中环境因素占很大比重，这又可以加速细菌氧化冶金技术的应用，因为该技术的产品或为沉淀物或为想获得的金属。细菌氧化浸出，充分利用了自然有机体在控制的条件下对硫化物的加速递降分解。除了电积法过程有部分氧气参与外，并无有害气体和废弃物直接进入环境。该技术的环境优势可节省审批的时间，减少项目商业化从设计到投产的时间。矿业中日益增加的有利于环境清洁的加工技术要求是细菌氧化冶金技术商业化的强大动力。长期半工业化实

15、验工厂的研究和独立的经济核算证明了该技术的技术可行性和经济可行性。大规模示范工厂的建立将证明这些发现，并将推动细菌氧化冶金技术提取贱金属精矿走向商业化。细菌氧化冶金技术在黄金领域中的主要应用是作为预处理工艺用于难处理金矿资源的开发上，细菌氧化提金技术。未来，细菌湿法冶金由于其利于环境保护、基建投资少、在某些情况下运作成本低等优越性，将获得进一步的发展。5结语细菌氧化技术不是处理金矿唯一可供选择的技术方法，但在今后一段时间内它是最具吸引力的，尤其是在处理难浸金矿石上。我国在此领域经过十几年的探索之后，已建立了较完整的试验体系，开发研究能力相对提高，并且在难浸金精粉的槽浸细菌氧化和低品位难浸矿石堆

16、浸细菌氧化方面都有一定的工业偿试。尽管在工业化进程方面与发达国家有一定的差距，但急待开发的难浸金矿资源与投资者日益高涨的投资兴趣，都加大了这一技术的产业化力度，为大规模工业化生产提供了必要条件。随着这一技术的广泛应用，将对我国黄金产业的健康稳定发展产生积极影响。附录BExtra-terrestrial Mineral Production: Multiple Aspects ofSustainabilityL. S. GertschRock Mechanics and Explosives Research Center, Missouri University of Science and

17、Technology, United StatesABSTRACT The production of minerals for human use at locations other than the Earth is expected to "advancehuman prosperity inways that do not compromise the potential prosperity and quality of life of future generations" (Brundtland, 1987); in other words, sustain

18、ably. This paper examines the interaction of extra-terrestrial mineral production (ETMP) with the following sustainability imperatives:·The sustainability of human activities on Earth;·The sustainability of human activities elsewhere;·Human survival in general, the ultimate sustainabi

19、lity goal Some of the consequences of mineral production on Earth are widely considered to decrease the future prosperity and quality of human life. Examples include noxious by-products or wastes andunsettling economic up- and downswings. Moving mineral production activities to extra-terrestrialloca

20、tions, where appropriate, will decrease many of its deleterious effects. Terrestrial mineral production presently is decreasing in some countries and increasing in others, moving from the cheaper and easier ores to more expensive, difficult materials. When the full costs of maintaining the terrestri

21、al environment in a sustainable manner are included, total mineral production costs must increase. The cost of extracting mineral products from extra-terrestrial sources will be substantially higher, especially in the initial phases, but as the full costs of terrestrial production increase, at some

22、point in the future (different points for different minerals), the curves will cross (Fig.1).This will occur at different points for different materials, a process whose prediction will be complicated by substitution of cheaper materials for some uses as prices of the original material rise. In summ

23、ary, mineral products from extra-terrestrial sources will tend to increase the sustainability of human civilization, once steady state has been reached.Keywords: Space mining; Moon; Mars; Asteroids; Comets; Extra-terrestrialINTRODUCTION The production of minerals for human use at locations other tha

24、n the Earth is expected to "advancehuman prosperity inways that do not compromise the potential prosperity and quality of life of future generations" (Brundtland, 1987); in other words, sustainably. This paper examines the interaction of extra-terrestrial mineral production (ETMP) with the

25、 following sustainability imperatives:·The sustainability of human activities on Earth;·The sustainability of human activities else- where;·Human survival in general, the ultimate sustainability goal.Some of the consequences of mineral production on Earth are widely considered to decr

26、ease the future prosperity and quality of human life. Examples include noxious by-products or wastes and unsettling economic up- and downswings. Moving mineral production activities to extra-terrestrial locations, where appropriate, will decrease many of its deleteriouseffects. Terrestrial mineral p

27、roduction presently is decreasing in some countries and increasing in others, moving from the cheaper and easier ores to more expensive, difficult materials. When the full costs of maintaining the terrestrial environment in a sustainable manner are included, total mineral production costs must incre

28、ase. The cost of extracting mineral products from extra-terrestrial sources will be substantially higher, especially in the initial phases, but as the full costs of terrestrial production increase, at some point in the future (different points for different minerals), the curves will cross. This wil

29、l occur at different points for different materials, a process whose prediction will be complicated by substitution of cheaper materials for some uses as prices of the original materialrise. This paper discusses the relationships between extra-terrestrial mineral production and the sustainability of

30、 human existence. This goes beyond the term "sustainable development, "which currently is taken to mean better integration of mineral production with local ecological and social issues. While the sustainability of human existence certainly must include these aspects, the full concept more

31、generally comprises the aggregate sustainability of all human activities. Furthermore, "human existence" is used here to mean a civilized quality of life beyond mere survival. Civilization fundamentally requires the extraction of mineral resources. To be sustainable,this extraction must sa

32、tisfy the equation:R-C=Bwhere R is revenue, C is cost, and B is benefit. Revenue is the immediate gain, usually economic, derived from the mineral extraction. Cost is all costs incurred thereby. Though commonly determined in economic units, both also contain aspects that are less easily quanti-fable

33、, such as maintainance of quality of life above a certain minimum threshold. Benefit is sometimes called profit, but just as revenue and cost cannot always be calculated in precise monetary units, benefit is not necessarily or immediately financial.SUSTAINABILITY ASPECTS OF MINERAL PRODUCTION The ot

34、her speakers in this Workshop have given far more comprehensive descriptions than are possible in this short space about current thought regarding the sustainability of modern mineral production practices on Earth. Instead, this section is devoted to the effects of mineral production on the survivab

35、ility of humans living and working in space, whether on other solar system bodies or in orbit. No space environment discovered to date or expected in future is inherently conducive to human existence in the manner that the Earth, our planetary home, is. Typical environmental hazards include no or no

36、xious atmospheres, micro-gravity, widely varying gravity fields, high-energy radiation, extreme temperatures, and extreme gradients of gravity, temperature, etc. The processes involved in creating usable commodities from natural geologic deposits also create waste materials, which can be in any stat

37、e. On Earth, many of these wastes create health and environmental hazards. This will also be true in space, especially in the engineered artificial environments in which humans must live. Extra-terrestrial humans will not have the large buffering effects of the planetary biosphere, geosphere, hydros

38、phere, and atmosphere to mitigate waste effects. Consequently, the life support systems will be much more sensitive to these effects than we are accustomed to. Some aspects of mineral production could serve to modify those environments, so they more nearly approximate human-survivable parameters. Ex

39、amples include soil compac-tion/excavation and the creation of greenhouse gases, heat, waste gases and other by-products. In addition, mineral exploration gathers data that is applicable also to environmental characterization and monitoring.EXTRA-TERRESTRIAL MINERAL PRODUCTIONSpace exploration Sever

40、al nations and groups of nations presently maintain access to space, and more nations are planning to join this group. The United States plans to re-establish human presence on the Moon by 2020, partly in preparation for sending humans onward to Mars a decade or two later, and partly for scientific

41、research. These activities will most likely be achieved by cooperation of the United States with the several other spacefaring nations. At present, the United States plans to launch a series of robotic missions to study the Moon beginning in October 2008, and the first crewed flight will occur befor

42、e 2020. Japan and China plan to send human explorers to the Moon at about the same time, followed by the European Union, Russia, and India. Going onward to Mars will happen after that time, possibly 20302045.Robotic and/or human excursions to asteroids or comets that might impact the Earth will proc

43、eed on a separate, though related, timeline from lunar and martian exploration, a timeline that is controlled by parameters external to the Earth and its politics. At present, most of the effort being expended in this area is devoted to detection, identification, and orbit determination of objects g

44、reater than 1 kilometer in diameter, whose orbits intersect the orbit of Earth around the Sun. Once an object has been confirmed to be on a collision course with the Earth, several different approaches have been proposed for averting the impact, depending on how much time will elapse prior, and on d

45、etails of the relative trajectories of the body and of Earth. One proposed approach would be to mine the body in such a manner that its orbit is sufficiently modified to avert the impact. Another is to fragment the body into pieces too small to survive passage through Earth's atmosphere. The fir

46、st approach could generate useful products from the material of the body, depending on its constituents; if it is an asteroid, those products might include metals or oxygen. If it is a comet, they might instead be spacecraft propellants or explosive compounds. All would be potentially useful directl

47、y during the mining/fragmentation process, or could be used elsewhere in space.The development of ETMP Mineral production from extra-terrestrial resources will likely proceed in two main phases, that each will supply two different types of markets:·Support for the exploration and eventual colon

48、ization of space; in other words, the extra-terrestrial market. This will, over the course of time spent in space, eventually divide into submarkets: Local supply. In-space supply, especially spacecraft propellant manufacture. Export to other nonterrestrial locations.·The terrestrial market. Th

49、is includes materials and products for export to Earth.These two phases will overlap each other, but the first one will supply the extra-terrestrial market from Earth's Moon. The major value of mineral production from this source is to reduce the mass of material that must be lifted, at very hig

50、h energy cost, from the deep well of Earth's gravity to supply the materials needed for the return to space. This phase will grow and remain important, though its size may eventually be eclipsed by exports to other extra-terrestrial locations, as well as to Earth itself. The first terrestrial ma

51、rket may be power generation from nuclear fusion reactors using 3 He as fuel (Kulcinski and Schmitt, 1991). There will also be a novelty market for lunar materials, perhaps as jewelry or simple samples.The techniques of ETMP The mining and processing of materials from the Moon, Mars, asteroids, come

52、ts, and other bodies of the solar system will begin by adapting techniques first developed on Earth. People have been extracting materials from the ground for at least 300 thousand years and possibly 2.5 million years (Verri et al., 2004; and Leakey, 1994; respectively). As humans gain experience in

53、 space operations, the equipment and the approaches used will undoubtedly evolve from this starting point; in the meantime, however, the approach will comprise variations on currentart. Mining methods can be categorized in various ways, including whether access to the deposit is from the surface or

54、from underground. These categories can be further modified by incorporating the mode of energy dissipation inherent in the mining process, modified with traditional approaches. Methods that rely on unique terrestrial properties are not included, such as hydraulicking, which uses large-volume water j

55、ets for fragmentation, excavation, and transportation.EFFECTS ON SUSTAINABILITY In this paper, sustainability effects are grouped into those associated with the continuation of quality human existence on the Earth, human activities on other bodies, and survival of the human species in general, regar

56、dless of the location of individual members or groups.Human activities on Earth Energy availability is an important limiter of the human quality-of-life. A large fraction of the human population spends most of their time obtaining the energy needed for survival, both directly (fuel) and indirectly (

57、food). In addition, many aspects of mineral processing are energy-intensive. Presently all energy must be obtained from the same sources: the sun, with lesser contributions from terrestrial radioactive isotopes. This is true throughout the solar system, and in fact only two planets receive amounts o

58、f solar energy comparable to the Earth's share'. However, the amount of solar energy available in near-Earth space is enormous. According to the U.S. National Security Administration (2007), "Every 1 km-wide insolation band at GEOZ receives nearly as much energy per annum as the content

59、 of the entire 1.28T BBLs of recoverable oil remaining on Earth." As mentioned previously, hazardous waste from mining and mineral processing has widely recognized deleterious effects. Generating and mitigating these effects elsewhere than the single planet where humanity is adapted to live will enhance our future. Natural resource-based economic aspects are both positive and neg