Sustainable mining

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Courtesy of EcoLog Environmental Resources Group

It's imperative that natural resource industries adopt a proactive (even aggressive) approach to the disposal and management of their wastes. Operators must challenge themselves to raise the bar in terms of environmental performance not only to meet the expectations of regulators today (and investors and the general public), but in the future, when requirements will no doubt be even more stringent. Environmental performance concerns cleanup if contamination at dormant sites as well as the implementation of systems that ensure sustainability in new or revitalized operations.

Such activities are in part motivated by the industry's commitment to social responsibility, but there are important financial factors. A critical issue for mining firms, for example, is the treatment of contaminated water from mining operations -- an issue that has been very much in the news lately. Contaminated water can represent the single greatest long-term environmental liability for mining operators, and can extend well beyond the lifespan of the mine. In fact, regulators require mining firms to post substantial bonds to cover the long-term costs of environmental remediation, and much of this is for the treatment of metal-contaminated wastewater.

Naturally, mining firms are looking for sustainable ways to reduce their environmental liabilities, and the subsequent impact on their finances.

ACID MINE DRAINAGE

Wastewater is produced as the by-product of mining and mineral processing activities and also appears naturally at about 70 percent of the world's mine sites as 'acid mine drainage.' This occurs when rainwater and oxygen react with residual minerals to form a weak acid solution that dissolves metals exposed in open rock faces, waste piles and underground workings. The resulting metal-contaminated solution is toxic to the environment, and mining companies are required by regulation to treat it.

For years, mining operations have used lime treatment technology to remove metals and acidity from contaminated water. The drawback of lime treatment is that it moves the metal contaminant from one form (water) to another (sludge), without removing the toxins from the environment. The resulting sludge creates a long-term environmental liability that must be managed and monitored, often for decades. This is precisely the type of liability that mining firms wish to eliminate.

Lime treatment has been widely used because it's eas- ily engineered and relatively simple to operate; plus, it's been successful in meeting water quality discharge standards in most jurisdictions. But this will not be the case for much longer. A growing number of regulatory bodies are adopting stricter regulations for water treatment and are more closely scrutinizing sludge management. Furthermore, the newly introduced regulatory requirements for the reduction of sulphate concentrations (that are always present in acid mine drainage) demand performance well beyond the capabilities of existing lime plants.

SOLUTIONS

Fortunately, a new water treatment technology has emerged that can remove toxins and produce clean water, using sustainable processes that reduce long-term liabilities and even produce saleable by-products to offset water treatment costs. This technology has been successfully used at mine sites in Canada and the U. S. since 2001, and is now being deployed at mining operations in China, Australia, and Mexico.

This process is unique because it removes metals from the contaminated water to produce a saleable metal product along with clean water. The water is, in fact, clean enough to meet strict criteria and to be discharged safely into the environment. Again, the approach is a sustainable business model, since the metals recovered from the water can be sold to offset cleanup costs and, in some cases, generate further revenues.

SULPHATE REMOVAL

In addition to metal-contaminated water, tightening regulations for sulphate discharges have been a particular concern for the industry, as regulators respond to rising concerns about the effect of sulphate on water quality, human health, and agriculture. Lime treatment can remove sulphate, but only down to concentrations that still exceed regulated values. Other methods that meet regulatory requirements are prohibitively expensive.

The prevailing technology typically considered for sulphate removal is reverse osmosis (R/O) membrane technology. While R/O is very effective in removing sulphate, it's expensive both in terms of capital and operating costs. Reverse osmosis requires large amounts of electrical power -- a real drawback in an age when energy costs are rising and consumption is under constant scrutiny. The membranes are also costly to replace. In
addition, the process produces a residual byproduct that can require special handling and disposal.

From a long-term perspective, using R/O to remove sulphate is not the most sustainable practice.

An alternative solution for sulphate removal is newly developed ion exchange technology. This process produces clean water and a saleable gypsum product that can be used in fertilizer manufacturing and building products. The process has significantly lower capital and operating costs than R/O, and also uses less power, further reducing the environmental footprint. Ion exchange technology is currently being installed to remove sulphate at mining and metal processing operations in the U. S. and Chile.

Leading mining operations know that sustainable practices pay dividends in multiple ways. In addition to enhancing environmental performance and stewardship, environmental liabilities and costs are reduced. Companies like Xstrata, Jiangxi Copper, Aditya Birla, and Molymet are working with these technology advancements to sustainably treat water and leave a positive legacy for future generations, as should all mining companies. These technologies also have application for certain other industries and for the treatment of contaminated groundwater.

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