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FEATURE - Mining world seeks natural remedy for toxic waste

23.10.2001  |  125× přečteno      vytisknout článek

FEATURE - Mining world seeks natural remedy for toxic waste LONDON - Using materials such as bonemeal or seaweed, scientists hope natural waste will one day serve to combat dangerous mining waste that can cause serious illness in humans and kill plant and animal life. Many of the metals found in the acidic waste from mining operations - or tailings - such as cadmium, arsenic or lead can be lethal if allowed to enter the environment in large amounts. \"There\'s no such thing as an impermeable landfill or a container that is insoluble enough not to release metal,\" said Dr Eva Valsami-Jones, who heads the environmental mineralogy programme at Britain\'s Natural History Museum in London. Tailings are usually stored in large pits, but a spate of serious accidents involving toxic spills will force the mining world to review its waste management policy. \"The only safe tailings dam is one that doesn\'t exist. You can store a couple of weeks\' worth of water but basically you cannot go on storing billions of litres of water, because sooner or later, whether by accident or carelessness or natural disaster, it\'s going to fail,\" said Professor David McConchie, of the Australian green-technology firm Virotec. Rather than neutralising the tailings with acid, the new remedies use the chemical powers of natural waste to trap heavy metal atoms, and slowly release them into the environment in such tiny amounts that they no longer pose a threat. \"The key questions are - do these methods work, are they cost-effective, are they better than what already exists and can operations be carried out in a way that minimises environmental harm?\" said Charles Secrett, head of the British-based environmental lobby Friends of the Earth. In a reflection of the ancient Greek practice of homeopathy - treating like with like - researchers have come up with three methods utilising waste products that promise to be cheap and sustainable to remediate, or clean, contaminated soil and water. Caustic red mud can make acidic mine water clean enough to drink, while bonemeal and seaweed could one day be used together to clean the most polluted old mine sites. LOCK UP THOSE ATOMS! The Natural History Museum\'s team is currently studying the effectiveness of bonemeal, used as a common garden fertiliser because of its high phosphate content, in treating soil contaminated by inorganic material like heavy metals. The bonemeal dissolves in the soil and its alkaline phosphate binds with the metal to form a chemical micro-barrier. \"The metal phosphate is very insoluble. Once it forms, it is no longer available as a contaminant, it\'s as if it is locked up in a mineral cage,\" Valsalmi-Jones said. \"The first stage of our research actually demonstrated in the lab that there was a wide range of metals we could remediate, which included the standard nasties like lead, cadmium and also things like uranium, nickel and cobalt - all the metals one would want to remediate,\" she added. Research is still at an early stage, but this method may one day provide a safe, sustainable solution to waste and could even be used in tandem with other ecological methods to treat areas polluted by both organic and inorganic substances, she said. \"Anything that is safe for environmental or human health and closes the loop in terms of residue is in principle a good thing. But all too often we class residues as \'waste\' that actually have demonstrable uses,\" said FOE\'s Secrett. CLOSING THE LOOP McGill University in the Canadian city of Montreal is also moving closer to closing the environmental loop with the use of dead plant life to rid tailings water of metal. Professor Bohumil Volesky of McGill\'s department of chemical engineering found biomass such as dead seaweed removed heavy metals from water and like a sponge, was then easily rinsed out and reused and the metals could be recovered and resold. \"Heavy metals are toxic and the problem with them is that they are persistent. A metal is a metal is a metal. It doesn\'t change and the only way to remove the toxicity associated with it is to remove the metal from the environment,\" he said. Water is poured through a column of biomass, which collects the heavy metals through a process called biosorption. Once the biomass is saturated, a mild acid is used to wash out the metals in a highly concentrated form, and can be used time and again. \"Eventually the material deteriorates and what you do is give it the last wash so it\'s totally metal free. Then you can use it as fertiliser or...as straw or hay,\" Volesky said. With the metal-laden soil and water taken care of at the mining site, the earth must be packed with nutrients so that it can regenerate and encourage new plant growth. PLANT REGENERATION WITH RED MUD Virotec, a former Australian gold mining firm, made a breakthrough when it found that the red muddy residue from alumina refining could remove heavy metals and then be used for revegetation. \"We take one waste product from the alumina refineries, physically and chemically change it, and then apply it without leaving another environmental problem behind,\" said Virotec executive chairman Brian Sheeran. The product bauxsol takes its name from the aluminium ore bauxite. Once treated seawater, bauxsol cleans the tailings water by capturing the metal, leaving behind a small amount of inert red sediment on which plants can thrive. \"Even when we plant plants on the used bauxsol, they don\'t get hit with an overload of metals,\" Professor McConchie, who developed the product, said. \"They love it.\" Bauxsol contains a cocktail of harmless minerals, some of which are even used in common indigestion tablets, he said. \"The minerals react with the metals and the acid extremely well and form these new minerals that have a low solubility and are very stable...when we leach the used bauxsol with very acid solutions, we still don\'t recover the metals,\" McConchie said. Bauxsol was recently show-cased in Baia Mare in Romania, the site of one of the industry\'s worst toxic spills last year. The downsides? \"If you use it on your vegetable garden at home...just make sure you don\'t have a family dog and white carpets!\" McConchie said. Story by Amanda Cooper REUTERS NEWS SERVICE

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