The continuous depletion of minerals caused by land mining and the increase in their demand have pushed the development of novel sustainable technological processes for mineral recovery from unconventional sources. In this context, magnesium (Mg) has gained considerable attention for its peculiar properties and high relevance of its compounds, such as magnesium hydroxide, Mg­(OH)2. In the present work, the influence of several operating conditions on the Mg­(OH)2 precipitation process was thoroughly investigated by adopting a novel multiple feed-plug flow reactor. The influence of (i) initial Mg2+ concentrations in the feed stream; (ii) brine and alkaline flow rates; and (iii) the product recycling strategy (seeded crystallization) was considered. The results marked the possibility of improving sedimentation and filterability properties of Mg­(OH)2 suspensions by adopting the recycling strategy to overcome industrial issues associated with the production of Mg­(OH)2 suspensions using NaOH solutions.

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 monodimensional (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.

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