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It will take an average of 25 to 50 years to purify the remaining wastewater from mining operations. It will also need to seal off billions of gallons of valuable water resources and discard them. According to the University of Florida, the separation system developed by researchers at the university has greatly shortened the purification time of mining waste water - only 2 to 3 hours, which may be a great news for mining companies and water shortage regions around the world.
Mining companies use water to treat ore, suppress dust, and use it for slurry transportation. After these operations are completed, the water will contain a large amount of mineral by-product particles to form a slurry. These milk-like muds are found throughout Florida's phosphate mining area. They are injected into sedimentation ponds about one square mile deep and 40 feet deep, waiting for the mineral particles to sink to the bottom. In Florida alone, the total area of ​​such sedimentation ponds exceeds 150 square miles, about half the size of the New York City.
But particles are charged, which makes them repel each other and float in water. It is a long process to settle to the bottom of the water. The mining company can only reuse the small amount of water at the top, and the water containing particles can not only be used but also occupy large areas of land. As early as the 1990s, people used electric fields to separate the mud and water from the mud, but this method was considered uneconomical.
The separation system designed by Marc Oralem, a professor of chemistry at the University of Florida's Herbert Wertheim School of Engineering, is different from the past in that it has two layers of upper and lower plates as electrodes that can continuously inject mud into it. Energization between the electrodes generates an electric field, and charged particles move toward the bottom, forming a paste-like solid. In the dehydration zone of the mud, the particles cannot move, pushing the water to the top. Dewatered mud paste can be used to fill potholes left by mining. The purified water can also be reused to process the ore produced.
"It would be better to recycle the water after it has been built up with so many sedimentation tanks," said Oraem. His team has built a laboratory-scale prototype, and the next step is to gradually increase the scale to the critical point, making it practical in reality.
Although this design is for Florida's phosphate mines, Olaem says it can be used anywhere else, especially in arid North Africa. In Morocco and the Western Sahara, phosphate reserves account for 85% of the world total, and there is a very shortage of water there. (Reporter Chang Lijun)
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