Columnists Features

Bio mining: Unique method of extraction of metal

BIO MINING uses micro-organism such as bacteria rather than using traditional methods of extreme heat or chemicals. This uses bioleaching in which leaches the mineral from the ore, which is then further with chemical reagents and the bacteria which liberate the metal from the ores. This provides a high efficiency and low-cost extraction process.

Some of the advantages that bio mining offers over other conventional methods include:
• Improved rates of metal recovery;
• Reduced capital cost;
• Robust technology;
• A ‘self-managing’ process;
• Ideally suited for use in remote locations;
• Environmentally friendly;
• Easier to get permits;
• Requires low operator skills (just the know-how) to operate;
• Applicable over wide concentrate feed range;
• Appropriate to recovering a wide spectrum of metals and stabilising toxic elements;
• Works well at a variety of scales with easy ‘add-on capacity’;
• Short lead time from design to construction to operation; and
• Low maintenance requirements compared with alternative processing methods.
Bio-mining is more environmentally friendly than other processing methods such as smelting or roasting, which is one of the key advantages. Smelting and roasting produces a lot of pollutants such as sulphur dioxide and carbon dioxide. But bio-based approaches are getting popularity due to their low energy consumption and reduced pollutants emission. The bioleaching technology is implemented in closed-circuit, so water usage is well controlled. The micro-organism used are native from nature, so that they don’t cause any biological danger.
One of the main advantages is that the arsenic, which is used in gold extraction, is precipitated as a stable ferric arsenate using limestone. Of course, bio-mining process has some bad environmental impact. For instance, where base metals such as cobalt, zinc, nickel or copper are extracted by use of acidiphilic bacteria, water containing sulphuric acid needs to be properly disposed of. In contrast, biotech mining process produces disposable waste where no additional chemicals are required and it can be reused.
There are several factors that a mine should consider listed as below:
• Financial factors, such as the best net present value (NPV), predicted metal recovery, capital and operating cost, and implementation time;
• Technical factors, such as cost and recovery risk, flexibility, ease of expansion, water consumption and quality requirements.
• Operational factors, such as operability, maintainability, level of operator skill required, instrumentation and process-control requirements; and
• Regulatory factors, such as environmental acceptance, safety considerations, footprint, use of local personnel and closure requirements.
A good opportunity to use bioleaching is when the operation site is close to a community as it has less environmental impact (than chemical leaching).
Bio mining could have a bright future in the mining industry. For example, the need for the treatment of refractory gold concentrates is increasing, as the easy-to-treat oxides ores are being depleted.
For this reason, it is believed that bio-oxidation will continue to be one of the most important technologies for the treatment of refractory gold ores and will only improve over time.
Meanwhile, the technology has already been well accepted for treating arsenical gold concentrates. It is expected that there will be a greater acceptance for application in base metal extraction and complex polymetallics, which are difficult to treat using alternative methods.
The technology lends itself to treat lower-grade materials and will find acceptance as a treatment method in environmental remediation of mine wastes metal recovery and stabilisation of acid mine drainage and toxic elements.
The future of bio-mining could be ‘in situ’ mining involves; injecting micro-organisms to dissolve copper with no necessity of moving minerals or waste, dramatically reducing the need for tailings dams or waste dumps.
While bio mining techniques such as autotrophic bioleaching have been well established on an industrial scale in mining operations for a few decades, we see a major potential for our second generation bio mining processes in the field of recycling.
In order to fulfil the scope of a circular economy in the coming years, bio-based approaches will have to play a crucial role by providing sustainable processes that are economically viable and socially accepted.
The authors are lecturers in the School of Mines at the University of Zambia.


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