Modelling dewatering behaviour through an understanding of solids formation processes. Part I--Solids formation considerations.

An understanding of the mechanisms which control solids formation can provide information on the characteristics of the solids which are formed. These characteristics will in turn impact on dewatering behaviour. In this paper a model for solids formation is proposed. The first part of the model considers the hydrodynamics in the precipitation vessel, from which a reactant mixing model is developed. Spatially variant solution conditions are quantified (dynamically) using an equilibrium speciation model. These calculations are performed in conjunction with an adsorption model, accounting for equilibria involving adsorbed species. The kinetics of solids formation, including nucleation, growth and aggregation, are described empirically using spatially variant supersaturation profiles. These, together with moment transformations of the solids population balance, describe the evolution of particle sizes throughout the precipitation process. Precipitation of nickel hydroxide is explored experimentally, and models developed are fitted to the results. Comments are offered on the impact of simplifications required for computational reasons, and assumptions required due to lack of information, on the accuracy of the model. In part II of this paper, the use of model outputs in predicting filtration behaviour is explored.