Cyanogenic Plants to Extract Gold: an Alternative for Artisanal MIners

在全球70多个国家，手工黄金开采（AGM）涉及约1600万人，每年生产380-450吨黄金。这些矿工使用的主要方法是基本的汞合并技术，每年消耗1400吨元素汞，而且还在增加。这是世界上最大的人为汞污染来源。汞化的主要替代方法是氰化，但许多矿工没有足够的管理技能或资金，甚至无法获得氰化物。手工采矿者使用的加工技术的改变意味着对采矿者的教育和组织的改变。技术本身并不是应对这种贫穷和污染的唯一办法，所有国际机构、各国政府、非政府组织和学术界的议程上都有可负担和简单的技术来取代汞和提高黄金的回收率。如果矿工们学会了简单和负担得起的方法来提取黄金，而且比汞合并（通常提取不到30%的金）效率更高，他们肯定会采用这些技术。超过2000种蔬菜含有可以通过水解转化为氰化物的糖苷。竹子、高粱和木薯是热带和亚热带地区广泛种植的主要产氰植物。木薯是世界上超过5亿人的主食，每年因误食苦木薯（含2000多毫克/公斤）而导致约2000人死亡，数十万人因食用这种发绀的根而遭受毁灭性的运动神经损伤，称为“kopnzo”。使用苦木薯和其他产氰植物作为黄金回收过程中的氰化物来源是替代手工金矿中汞的潜在选择。在植物系和土地与粮食系统学院的协助下，在UBC进行了初步研究，并与巴西EMBRAPA密切合作，结果从金浮选精矿中提取了30%的金。我们对用糖氰化物提金工艺的了解还存在许多空白。必须进一步研究pH值、温度、时间、溶解氧和其他催化剂的影响，以产生一种简单的提取金的方法。这个想法是在实验室中测试使用产氰植物从精矿中提取金的最佳条件，然后将其应用于哥伦比亚（或其他面临AGM中汞问题的国家）的实地试点研究。一项前期可行性研究将完成一个简单工厂的工程设计，利用当地蔬菜更清洁地生产黄金。

Worldwide, artisanal gold mining (AGM), in more than 70 countries, involves approximately 16 million people to produce 380-450 tonnes of gold annually. The main method used by these miners is the rudimentary amalgamation technique that consumes 1400 tonnes/a of elemental mercury and increasing. This is the world's largest source of man-made mercury pollution. The main alternative to amalgamation is cyanidation but many miners do not have adequate management skills or capital or even access to cyanide. A change in processing techniques used by artisanal miners implies in education and organization of the miners. Technology alone is not the only response to this dramatic picture of poverty and pollution, but affordable and simple techniques to replace mercury and Improve gold recovery is in the agenda of all International Agencies, Governments, NGOs and academics. If miners learn simple and affordable methods to extract gold with more efficiency than amalgamation (which usually extracts <30% of Au ), definitely they will adopt these techniques. More than 2000 vegetables contain glucosides that can be converted to cyanide by hydrolysis. Bamboo, sorghum and cassava are the main cyanogenic plants extensively cultivated in tropical and subtropical regions. Cassava is the stipple food of more than 0.5 billion people in the world and the accidental consumption of bitter cassava, with more than 2000 mg CN/kg, takes the lives of approximately 2000 people annually and hundreds of thousands suffer a devastating motor neurological damage called "kopnzo" due to the consumption of this cyanogenic root. Using bitter cassava and other cyanogenic plants as a source of cyanide for gold recovery process is a potential option to replace mercury in artisanal gold mines. The preliminary studies at UBC, being conducted with assistance of the Dept of Botany and Faculty of Land and Food Systems, as well as in close collaboration with the EMBRAPA, Brazil, resulted in extractions of 30% of gold from a gold flotation concentrate. There are many gaps in our knowledge about the gold extraction process using glycocyanide. The effect of pH, temperature, time, dissolved oxygen, and other catalysts must be further investigated generating a simple method to extract gold. The idea is to test in the lab the best conditions to extract gold from concentrates using cyanogenic plants and then apply this in a pilot study in the field in Colombia (or other country facing problems with Hg from AGM). A pre-feasibility study will complete the engineer design of a simple plant for cleaner production of gold using local vegetables.