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

黄金加工业通过在氰化物溶液中浸提矿石，然后在活性炭上吸附和电解来提取黄金。然而，氰化和碳吸附都存在一些主要问题。由于氰化物毒性很大，黄金厂被迫破坏废水中的氰化物，这导致昂贵的氰化物损失和总运营成本的增加。另一方面，在600-1200摄氏度下生产的活性炭价格昂贵，并且仅对金没有选择性，因此需要进一步精炼以生产纯金。此外，在吸附过程中，金被捕获在活性炭的微孔内，需要高温洗脱以重新活化活性炭。因此，活性炭的制造和再生是采矿作业中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发现研究计划，以开发一种创新的和可持续的黄金回收技术。在我们的过程中，从水溶液中回收金的生物吸附在我们的吸附剂具有新的功能基团。这些吸附剂是在一个非常简单的过程中制备的，通过在100 ℃下用硫酸交联不同的生物质废物。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的进步，在高质量的期刊和世界级的会议论文集中发表了67篇论文。从这项研究中，我们发现了一些显着的结果，如：1）与活性炭不同，只有金被吸附在我们的新型生物吸附剂上，因此不需要进一步的处理来去除杂质; 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黄金回收变得更加简单，更具成本效益和能源效率，因为不需要剥离，高温洗脱和电解。然而，我们观察到，同时吸附还原金对我们的新型生物吸附剂只发生在酸性氯化物介质中，而不是在碱性氰化物溶液。 考虑到迫切需要改进金氰化工艺，在拟议的研究中，我计划在碱性-酸性混合系统中使用我们的新型生物吸附剂回收金，其中金将在碱性氰化物溶液中浸出，然后酸化将氰化物回收到浸出厂，在酸性氯化物介质中留下金，同时进行生物吸附-生物还原以生产纯金。我们提出的回收有毒氰化物的生物吸附工艺将确保对环境的零排放。这将消除目前在废水中销毁昂贵氰化物的做法，为工业节省大量成本，并最大限度地减少温室气体排放。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.