Cyanogenic Plants to Extract Gold: an Alternative for Artisanal MIners

在全球范围内，70多个国家的手工金矿开采（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初级汞齐化技术，每年消耗1，400吨元素汞，而且还在不断增加。这是世界上最大的人为汞污染源。汞齐化的主要替代方法是氰化法，但许多矿工没有足够的管理技能或资本，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。技术本身并不是应对贫困和污染这一严峻局面的唯一对策，但替代汞和改善黄金回收的负担得起的简单技术已列入所有国际机构、各国政府、非政府组织和学术界的议程。如果矿工们学会了简单而又负担得起的方法，以比混汞法（通常提取<30%的Au）更有效的方式提取黄金，他们肯定会采用这些技术。超过2000种蔬菜含有可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生氰植物。木薯是全世界5亿多人的主食，而意外食用氯化萘含量超过2，000毫克/千克的苦木薯，每年导致约2，000人死亡，数十万人因食用这种生氰根而遭受被称为“kopnzo”的毁灭性运动神经损伤。 利用苦木薯和其他生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一种潜在选择。UBC的初步研究在植物学系和土地与食品系统系的协助下进行，并与巴西EMBRAPA密切合作，从黄金浮选精矿中提取了30%的黄金。在我们的知识中有许多空白使用甘氨氰化物的黄金提取过程。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，以产生提取金的简单方法。其想法是在实验室测试使用生氰植物从精矿中提取黄金的最佳条件，然后将其应用于哥伦比亚（或其他面临AGM汞问题的国家）的实地试点研究。初步可行性研究将完成一个简单工厂的工程设计，利用当地蔬菜清洁生产黄金。

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.