Simultaneous determination of nucleation and crystal growth kinetics of gypsum

The chemical treatment of industrial effluent, containing sulphuric acid, is typically completed by neutralising it with lime through solid/liquid separation. The mineral precipitation processes developed by Veolia Environnement use sludge recirculation. The production of a high sludge density characterises these processes, at a minimum of at least 25% weight in solids. The first laboratory tests studied the precipitation reaction, confirming the production of gypsum (CaSO4·2H2O). Then the precipitation mechanisms, nucleation and crystal growth kinetics, are determined in order to establish a model which predicts population density in reactor in accordance with fluid dynamics. The determined nucleation and growth kinetics are then used to feed a reaction model, coupling computational fluid dynamics (CFD) and population balance modelling to simulate the precipitation process.