Thermochemical reduction of pelletized gypsum mixed with carbonaceous reductants
2015
Motaung, SR(Council for Scientific and Industrial Research DST/CSIR National Centre for Nanostructured Materials ,Tshwane University of Technology Department of Environmental, Water and Earth Science) | Zvimba, JN(Council for Scientific and Industrial Research, CSIR Natural Resources and the Environment) | Maree, JP(Tshwane University of Technology Department of Environmental, Water and Earth Science) | Kolesnikov, AV(Tshwane University of Technology Department of Chemical and Metallurgical Engineering)
The recovery of better quality waste gypsum during acid mine drainage (AMD) neutralization is one step closer to achieving downstream waste gypsum beneficiation for recovery of valuable materials. This can facilitate recovery of treatment costs and prevention of environmental pollution from gypsum waste-dumps. Thermal reduction using rotary kilns to recover valuable materials from waste gypsum remains a critical and controversial process because of waste gypsum handling problems, environmental pollution due to dust and gaseous emissions and poor conversion yields. In order to mitigate these problems and improve waste gypsum conversion yields, pelletization of waste gypsum in the presence of binders (starch and cellulose) was investigated. A laboratory-scale disc pelletizer was used to produce pellets from a mixture of coal and commercial gypsum or waste gypsum, generated during AMD neutralization, with starch and micro-crystalline cellulose used as binders. The pellets were subjected to high-temperature thermal treatment in a tube furnace to generate calcium sulphide (CaS), an important intermediate for waste gypsum beneficiation. The kinetics of thermal conversion of pelletized waste gypsum to CaS were found to be highly dependent on furnace temperature. Results also showed that pelletization affords improved handling of waste gypsum while use of binders as additives significantly improved the CaS yield, with starch giving the better yield compared to cellulose.
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