Magnesium recovery from exhausted brine

Mg and MgCO3 are among the 20 EU critical raw materials. Interestingly, Mg can be found at veryhigh concentration in brines generated as waste stream from salt works. Literature works havedemonstrated the feasibility of Mg extraction from brines [1–3] by reactive precipitation, for theproduction of Mg(OH)2. Here we present an overview of the experimental campaigns carried outusing exhausted brine from real salt works (Italy) to produce Mg(OH)2 with high purity and conversion.Lab – and pilot-scale batch and semi-continuous CSTR crystallisers were developed andtested, eventually leading to a continuous process by a quasi-PFR pilot reactor. Different alkalinesolutions have been adopted in order to analyse their influence on the process, looking in particularat the product purity (affected by possible by-products co-precipitation) but also at the economicprofitability. A late development focused on the development of a membrane crystalliser reactorusing ionic exchange membranes (CrIEM) [4]. In the CrIEM the precipitation reaction occurs avoidingthe direct contact between feed brine and alkaline solution, thus allowing in principle the useof any alkaline species, minimising the risk of by-products co-precipitation. In preliminary tests99.5 % pure Mg(OH)2 was produced using cheap reactant, opening room for the developmentof a novel and economically profitable process