Sustainable Recovery of Gold using Biomass Wastes in an Alkaline-Acidic Hybrid System

黄金加工业采用氰化浸出矿石、活性炭吸附、电积法提取黄金。然而，氰化法和碳吸附法都存在一些主要问题。由于氰化物是剧毒的，黄金工厂被迫销毁废水中的氰化物，这导致了昂贵的氰化物的损失，并增加了总体运营成本。另一方面，活性炭在600-1200℃的温度下生产，价格昂贵，而且对金没有选择性，因此需要进一步精炼才能生产出纯金。此外，在吸附过程中，金被困在活性炭的微孔中，需要高温洗脱才能使活性炭重新活化。因此，活性炭的制造和再生占采矿作业运营成本的主要部分。此外，它还向环境释放温室气体。为了克服这些问题，2011年，我开始了我的NSERC发现研究项目，开发一种创新的、可持续的黄金回收技术。在我们的工艺中，金通过生物吸附在我们的新型官能团吸附剂上回收。这些吸附剂是通过在100℃下将不同的生物质废弃物与硫酸交联，以非常简单的方法制备的。生物吸附是湿法冶金研究的一个新领域，自2011年以来，我们在这一领域取得了巨大进展，在高质量期刊和世界级会议论文集上发表了67篇论文。研究结果表明：1)与活性炭不同，新型生物吸附剂只吸附金，无需进一步处理；2)当金被吸附在我们的新型生物吸附剂上时，它同时被还原为金属金。这些突破性的发现将使金的回收变得更加简单、更具成本效益和节能，因为不需要剥离、高温洗脱和电积。然而，我们观察到，金在我们的新型生物吸附剂上的同时吸附-还原只发生在酸性氯化物介质中，而不是在碱性氰化物溶液中。考虑到改进金氰化工艺的迫切需要，在本次研究中，我计划使用我们的新型生物吸附剂在碱-酸混合系统中回收金，金将在碱性氰化物溶液中浸出，然后酸化，将氰化物回收回浸出厂，将金留在酸性氯化物介质中，同时进行生物吸附-生物还原，以生产纯金。我们提出的生物吸附工艺与有毒氰化物的回收将确保零排放到环境中。这将消除目前在废水中销毁昂贵氰化物的做法，并为工业节省巨额成本，并尽量减少温室气体排放。加拿大矿业公司将从这项创新研究中受益。

The gold processing industry extracts gold by leaching ore in cyanide solution followed by adsorption on activated carbon and electrowinning. However, both cyanidation and carbon adsorption have some major problems. Since cyanide is very toxic, gold plants are forced to destroy the cyanide in effluent that results in loss of expensive cyanide and increase in the overall operating cost. On the other hand, activated carbon, which is manufactured at 600-1200 oC, is expensive and it is not selective to gold only, hence further refining is necessary to produce pure gold. Also, during adsorption, gold is trapped inside the micro-pore of activated carbon that requires high temperature elution to reactivate the carbon. As a result, manufacturing and regenerating of activated carbon represents a major portion of the operating cost in a mining operation. Also, it releases greenhouse gases to the environment. To overcome these problems, in 2011, I started my NSERC Discovery research program to develop an innovative and sustainable gold recovery technology. In our process, gold was recovered from aqueous solution by biosorption on our adsorbents having novel functional groups. These adsorbents were prepared in a very simple process by crosslinking different biomass wastes with sulphuric acid at 100 oC. Biosorption is a new field in hydrometallurgical research, and since 2011, we made tremendous advancement in this area, generating 67 publications in high quality journals and in world-class conference proceedings. From this research, we found some remarkable results, such as: 1) unlike activated carbon, only gold is adsorbed on our novel bioadsorbents, hence no further treatment is necessary for impurity removal; and 2) when gold is adsorbed on our novel bioadsorbent, it is simultaneously reduced to metallic gold. These ground-breaking findings will make gold recovery much simpler, more cost-effective and energy efficient because no stripping, high temperature elution, and electrowinning are necessary. However, we observed that simultaneous adsorption-reduction of gold on our novel bio-adsorbents only takes place in acidic chloride media but not in alkaline cyanide solutions. Considering the urgent need to improve the gold cyanidation process, in the proposed research, I plan to recover gold using our novel bioadsorbents in an alkaline-acidic hybrid system where gold will be leached in an alkaline cyanide solution followed by acidification to recycle cyanide back to the leaching plant leaving behind gold in an acidic chloride media for simultaneous biosorption-bioreduction to produce pure gold. Our proposed biosorption process with recycling of toxic cyanide will ensure zero emission to the environment. This will eliminate the current practice of destruction of expensive cyanide in the effluent and result in huge cost savings for the industry and minimization of greenhouse gas emissions. Canadian mining companies will benefit from this innovative research.