Dear Regulators, we’re in a quandary, aren’t we?
For the longest time, everything was simple. Acid drainage was treated by lime-based treatment plants, except for small flows at abandoned coal mines in Appalachia, where limestone-based passive systems did the trick. For non-acidic streams, there was a variety of reliable approaches, such as ferric chloride addition for arsenic, stripping towers for ammonia, various sulphide reagents for trace metals, and occasionally, ion-exchange or other technologies for odd streams. Passive wetlands or bioreactors worked at abandoned mines where there wasn’t enough money to build a proper treatment plant, but this was an iffy proposition.
But then, a number of developments started to complicate things. First, we learned what it means to operate lime-based treatment plants for many years and discovered that they generate a lot of sludge. A well-run High-Density Sludge (HDS) plant produces fantastically clean water, but managing this sludge is onerous after more than 20 years (never mind in perpetuity).
Second, we started to handle potentially acid-generating (PAG) waste more carefully. Reactive tailings are deposited deep in impoundments, with little likelihood of generating acidic, metal-laden drainage. Other PAG waste is either backfilled underground or segregated and piled next to the open pit, where it will be backfilled at closure to avoid generating acidic, metal-laden drainage.
Third, we started to reclaim reactive waste rock much better than before. We have developed sophisticated soil covers that prevent 95% of potential contaminant release. They aren’t quite perfect – they will never reach 100% prevention – but it’s a hell of an improvement.
Finally, we started regulating a different class of contaminants like selenium or sulphate. These compounds are not nasty like cadmium or mercury, but they can potentially exert ecotoxic effects. The trouble is that these compounds are regulated to very low levels, while we have not yet developed methods to treat them to these levels.
Suddenly, we discover that we are in a very different regulatory landscape. Contaminated streams at new mines are rarely acidic or metal-laden. Under these conditions, lime-based treatment plants are far less effective. This tried and true technology, which has proven itself many times in the past, does not make sense in this case. Nowadays, mine drainage at closure will be voluminous, but with low levels of contaminants.
There is a strong temptation to turn to reverse osmosis or ion-exchange because these technologies are widely used in other applications, such as desalination or treatment for drinking water. The trouble is, the economics of making a product you can sell do not compare with those of treating in perpetuity large volume of mine drainage, with no compensating revenue stream.
Passive treatment systems are appealing because they can handle high volumes/low contaminant drainage. The trouble is: we have no experience with them because we used to rely on lime-based treatment plants. Regulators are skittish about approving these systems because they’re unproven and insist on the above, costly technologies. This is a losing proposition for the mining industry.
Something has to give. We have to recognize that we operate in a different environment and that we will need to rely on different approaches. Maybe it’s time for industry and regulators to start talking and look at other possible solutions. Until then, project approval will slow down to a crawl and we will all lose.
Early career hydrologist
6yRefreshing to hear someone speak to this difficult problem. My research site is a reclaimed coal mine in eastern KY where the “contaminant” of interest is total dissolved solids, or elevated salinity. And yes, RO is prohibitively expensive to control alkaline mine drainage. Instead, prevention is the method of choice but to date it’s not clear to me how effective this has been in controlling highly saline discharges. My initial thoughts based on experience are that fill simply cannot be placed in valleys where it’s essentially impossible to keep the water out. It becomes necessary to keep all the fill on the mine area and not in excess spoil fills.
CoFounder at The KNEW Company
8yhave a look at www.miningfracking.com
Environmental management with minerals
8yMaybe, adapting environmental regulation to local circumstances, allows for other possible solutions that industry and regulators can come up with. However, we should not forget that a lot of public funding is nowadays needed for remediation of the pollution of the mining facilities that private companies and their shareholders carelessly abandoned in the past. Nothing wrong with investing a substantial part of profit in high treatment costs of mining influenced water due to strict regulation, because it is also an incentive to invest in research and development for more cost-effective treatment technologies. Maybe that public funds, financed by consumer tax on the use of commodities, can not only pay for remediation of existing pollution, but also support the mining industry in cleaner production and prevention of future pollution, while simultaneously stimulate the research for alternatives.
Project Director at SCS Engineers - Water and Wastewater Process Design
8yIn looking to desalination plants who have done RO for decades, they may now be wishing their membranes had been co-located with power generation to help with cost and concentrate management. Something to learn there if membranes are in the future for mines?
Principal Geochemist at Geochimica, Inc.
8yAt least in arid and semi-arid lands, and in other environments, too, where clean water is not available to meet demand, the treated water from membrane systems might well have value, even substantial value as product. Even if the revenue streams do not break even or better, there may be substantial value in terms of cash flow against total costs. Obviously, the life-cycle costs (including the costs of brine disposal and plant replacement) need to be addressed, but clean water will have increasing value in the future.