Pilot scale production of Mg(OH)2 compounds from a real industrial reverse osmosis desalination brine

Abstract

Brine valorisation technologies have gained substantial interest in the last decade, particularly with respect to the recovery of valuable minerals within integrated schemes. Within this context, several studies have investigated at the laboratory scale the extraction from brines of magnesium hydroxide, Mg(OH)2, a compound widely adopted in several industrial fields. The present work aims at thoroughly assessing, for the first time, the synthesis of Mg(OH)2 from a real industrial reverse osmosis desalination brine at a semi-industrial scale. The brine produced by the industrial seawater reverse osmosis plant installed on the island of Lampedusa was treated in situ by adopting a pilot-scale Multi Feed Plug Flow Reactor with and without specific pre-treatments to enhance the product purity. High-purity (>98 %) values for the Mg(OH)2 solids were achieved; the higher the reaction pH, the higher the Mg2+ conversion; settling and filtration features exhibited a maximum rate at pH 11.2, while the lower the brine flow rate the higher the settling and filtration properties of Mg(OH)2 suspensions. Finally, an economic analysis of the Mg(OH)2 production scheme showed the feasibility of the proposed approach, highlighting the large potential for this brine valorisation strategy.