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

Abstract

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.