Application of Earth ion Exchange Technology to Convert Acid Mine Drainage From Exxaro’s Matla Mine Into Saleable Products

Eutectic freeze crystallisation was compared with evaporative crystallisation as a route for treating hypersaline mine brine. Optimised commercial evaporative crystallisers use 40 to 50 kWh per cubic metre of feed. Laboratory work measured a eutectic temperature of -21.1 degrees Celsius for pure sodium chloride solution, and found that a large difference between coolant and solution caused scaling on the heat exchanger wall.

Ion exchange converted reverse osmosis brine from a power station treating colliery water and cooling tower blowdown into fertiliser and explosives salts, with no liquid effluent left to dispose of. Part of the water rejected by the reverse osmosis stage was also recovered as potable water. Brine is currently used for dust suppression and stored underground.

Testing of 28 coal and coal-shale samples showed the coals to be more liable to spontaneous combustion than the shales, though reactive coal-shales still self-heat and pyrite in them speeds the process. Higher carbon, moisture, hydrogen, volatile matter and nitrogen with lower ash all raised proneness to self-heating, so proximate and ultimate analysis can serve as a screening tool.