Magnesium recovery from exhausted brine

Abstract

Mg and MgCO3 are among the 20 EU critical raw materials. Interestingly, Mg can be found at very high concentration in brines generated as waste stream from salt works. Literature works have demonstrated the feasibility of Mg extraction from brines [1–3] by reactive precipitation, for the production of Mg(OH)2. Here we present an overview of the experimental campaigns carried out using 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 and tested, eventually leading to a continuous process by a quasi-PFR pilot reactor. Different alkaline solutions have been adopted in order to analyse their influence on the process, looking in particular at the product purity (affected by possible by-products co-precipitation) but also at the economic profitability. A late development focused on the development of a membrane crystalliser reactor using ionic exchange membranes (CrIEM) [4]. In the CrIEM the precipitation reaction occurs avoiding the direct contact between feed brine and alkaline solution, thus allowing in principle the use of any alkaline species, minimising the risk of by-products co-precipitation. In preliminary tests 99.5 % pure Mg(OH)2 was produced using cheap reactant, opening room for the development of a novel and economically profitable process