The kinetics of gypsum precipitation, the inhibiting effect of citric acid and its use in the differential precipitation of Mg(OH)₂ from CaSO₄·2H₂O

Abstract

The crystallization of solids from supersaturated solutions is a source of numerous complications during a range of industrial processes: undesirable precipitates may clog pipelines, foul membranes, contaminate the target compounds of a process, lower the effectiveness of heat-exchange via scale formation, etc. Calcium sulfate dihydrate (CaSO4·2H2O or gypsum) is one of the most common of such solids, therefore during the last decades, numerous studies were dedicated to the investigation of the precipitation kinetics and method development potentially suitable for precipitation control and inhibition. In the experimental work leading to this dissertation, the kinetics of gypsum precipitation was studied in the entire experimentally available concentration range. The impact of citric acid (or citrate ion) on the reaction was investigated in detail including some experiments in unconventional media. The acquired experience was used to optimize the differential precipitation of magnesium hydroxide from gypsum, which provides a promising method to improve the treatments of acidic wastewaters economically and in environmentally friendly way, and could also be useful in desalination processes.