A simulation tool for ion exchange membrane crystallization of magnesium hydroxide from waste brine

Increasing attention is nowadays paid to the management and valorisation of industrial waste brines aiming also at the recovery of raw materials. Magnesium has been listed as a Critical Raw Material by EU, prompting researchers to investigate novel routes for its recovery. Within this framework, a novel Crystallizer with Ion Exchange Membrane (CrIEM), is proposed as an innovative way to recover magnesium from industrial waste brines exploiting low-cost alkaline reactants. In the present work, a novel mathematical model of the CrIEM process is proposed to provide a useful tool for its design in different working conditions. Batch and feed & bleed continuous configurations have been investigated taking into account: (i) the variation of the alkaline and brine concentration in their own collection tanks over time and (ii) the spatial mono-dimensional (1D) steady-state description of the main phenomena that occur inside the CrIEM. Original experimental data, from ad-hoc laboratory tests, and literature information were used to validate the proposed model both in the batch and continuous feed & bleed configuration. A good agreement between model predictions and experimental/literature data was found for both cases, thus proving the reliability of the proposed model for the design of the CrIEM reactor.