by Jack Caldwell
Can you treat acid rock drainage? The answer generally depends on the chemistry of the acid drainage waters relative to the chemistry of the treatment media. It is the same old chemistry problem we faced in the first-year lab: what chemical has what effect on what other chemical? The specifics of the many papers on this topic may give you some chemical insight to your problem. More important for the non-chemist is the question: Are there case histories of successful, cost-effective treatment that represent a precedent for future success at your property? The answer is a partial yes if you are poor and a definitive yes if you have money.
The estimated longevity of typical plants for alkali-based water treatment plants is twenty years. The cost of treating acid drainage, based on North American case histories is high: an average unit volume treatment cost of 27c/m3 for acidity less than 800mg/l and $2.24/m3 for acidity greater than 4,000mg/l. .
Lime is typically used to treat acid drainage waters. Waste products including cement-kiln dust, lime kiln dust, calcium magnesium hydrate, or paper mill sludge may be used to treat acid drainage . In Iberia, limestone did not work, so testing of the benefits of a limestone buffered organic substrate was tried-only some of the sulfate reducing bacteria worked . Some insight into the role of sulfate-reducing bacteria in the functioning of permeable reactive biobarriers is provided by testing undertaken at the Colorado State University .
BioteQ Environmental Technologies have developed a process to produce H2S from sulfur at low cost an on site for use in treating acid drainage waters . The process appears to work and is claimed to be cost effective.
Small scale testing of passive treatment systems at two New Zealand mines shows promise-but not full success . Conversely success of a passive treatment system at a remote mine in the cold part of northern Quebec is reported . Observation of the system will continue and upgrades are planned. Effective passive treatment is reported for the Nevada Stewart Mine in Idaho. The treatment medium was fish bone and gravel; the treated water was from a lead-zinc mine .
Once you have treated the drainage, sludge remains. The geotechnical characteristics of the sludge resulting from treatment of acid drainage water are detailed on the basis of one-dimensional laboratory testing. The data may help you consolidate the sludge prior to disposal .
This paper pretty much epitomizes the world-wide situation. The Mount Morgan Mine in Australia operated between 1882 and 1981 . Most of the mine waste is acid generating. Acidic runoff and seepage has heavily impacted the adjacent Dee River. C. Wels in his presentation noted that it will cost over $100 million to clean up, that water treatment will be needed forever, and that right now the federal government has no budget to undertake the work. Dr. Wels is to be commended for his detailed investigation that pinpointed the seepage routes and that makes reasonable and rational suggestions for remedial works. I wonder if they will ever be implemented and if the Dee River will ever run free again.
Other papers describe case histories of the modeling of seepage quantity and quality from a variety of mine waste disposal facilities in various countries and the subsequent impact on local groundwater. Some stories are encouraging: effective controls and a decrease in pollution with time. Others are depressing: ongoing pollution, no cost-effective solution, and calls for more investigations & modeling. I am not going to go through them all-they merely prove the obvious: we can model, we cannot predict, we generally cannot afford the remedial works, and acid seepage will continue for a long time. One more example will suffice.
Twice in the early 1990s I went to Dresden and the mines of Wismut. We stayed in palatial old houses, originally built by wealthy Jewish textile makers, expropriated by the Nazis for their generals, subsequently expropriated by the Russians for the mine managers come to get the uranium from the local mines, and now expropriated by the state and used to house dignitaries come to help clean up the mess. We visited the historic and famous Dresden Opera House, the bombed out palaces, and the ugly soviet new city. We left dispirited; my Spanish client was pessimistic that even German ingenuity and money would succeed, and I was sad because the opera house was closed for repairs.
Currently it is costing fifteen million Euros per year to treat the seepage from the Wismut underground mines . In an attempt to reduce this huge expense, shafts, shallow workings, and exit portals have been plugged, interconnections between workings limited, and to the extent hydrogeologically possible flooding of the underground mines expedited. None of this constitutes success. Work will no doubt continue until the next expropriation of the palatial old houses by the powerful of the next wave of invaders.
The Iberian Pyrite Belt has been mined since prehistoric times . There are no currently active mines. Surface water sampling amply establishes that the watershed is affected by acid drainage from the historic mine workings. A similar tale of catchment-wide surface water pollution by historic underground lead and zinc mines occurs in two watersheds in England . Sadly neither paper tells us which period of historic mining is the greater source nor what is to be done, if anything, to address current conditions.
I read that the Bush Administration is seeking to severely cut funding to the U.S. Geological Survey. This would be a pity (or would it?) when you see the extraordinarily-high-quality work they do. For example consider the time and money spent on the study and the paper , that describes natural acidic impacts on the Colorado Lake Creek watershed by seepage from intensely hydrothermally altered, unexploited, low grade porphyry copper mineralization in the Grizzly Creek Caldera. By law nothing need be done, but I can hear the miner saying that he could mine the deposit and remove the source given the right permits. Maybe that is why the USGS funded the study.
A great success story  is the revegetation of the tailings in the Clark Fork River, Montana superfund site by tilling and addition of lime. Of course it is sad the tailings were allowed to get into the river in the first place: another reason Montana is now a difficult place to start a mine.
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