Investigation of the properties of Mg(OH)₂ extracted from magnesium-rich brine via the use of an industrial by-product

Compared with magnesium oxide (MgO) produced through the dry route, the wet route production can lead to MgO with a high purity and reactivity. During this process, the use of chemical alkalis to precipitate the precursor, magnesium hydroxide (Mg(OH)₂), is the highest contributor to cost and energy consumption. This study proposes a low-cost and sustainable way to recover Mg(OH)₂ from simulated reject brine using concrete wash water (CWW). Mg(OH)₂, with a purity of 94 % and a recovery degree of 98 % was synthesized at room temperature. Higher stirring speed and use of low pH CWW increased the impurity (CaCO₃) content. The synthesized Mg(OH)₂ showed a similar reactivity to MgO synthesized from reject brine with chemical bases due to its high specific surface area (102.8 m²/g). The calcination of the synthesized Mg(OH)₂, led to MgO with a higher reactivity than similar ones obtained through the wet-route. Furthermore, the textural properties of Mg(OH)₂ synthesized under different conditions were evaluated to establish a correlation between the reaction conditions and reactivity of Mg(OH)₂. Increase in reaction temperature led to a small crystalline size, whereas the aging process resulted in the agglomeration of the synthesized Mg(OH)₂, influencing its reactivity. The findings presented in this study can pave the way for the sustainable recovery of Mg(OH)₂ and its direct use as a binder or as a precursor for the production of reactive MgO.