Semi-batch crystallization of gypsum from calcite and sulfuric acid

International audienceOne of the most important environmental issues for decades to come is the treatment of industrial wastewaters containing salts (sulfates, chlorides, sodium, magnesium ...) which can lead to strong perturbations affecting the fauna and flora when highly concentrated at the discharge point. Different processes used to separate the dissolved salts from the liquid matrix may be encountered depending on the nature and the composition of the effluent. One major objective in the R&D sectors of water and environment is to optimize such processes, while another is to promote the treated wastewaters by recycling the cleared liquid phase or reusing some compounds they contain in other production processes. The latter is of great interest, both to limit the amount of waste and to save natural resources including rare metals but also less noble materials whose amount consumed each year is very important, but the one available not unlimited. Gypsum, the most important raw material of plaster's industry, is a rather interesting example from this point of view as world's known resources are estimated at 2.34 billion tons, which roughly represents 25 years of operation. The industry of plaster will therefore meet in the coming decades a decrease in resources for the commodity, especially in some countries where gypsum deposits will eventually become out of reach or completely depleted