Valorization of saltwork brines for the production of acid and base using electrodialysis with bipolar membranes

Abstract

Valorization of brines, usually considered as wastes, has become an alternative to extract critical and valuable raw materials, but also for energy recovery and generation of reactants. Within this context, the H2020 SEArcularMINE project aims to recover from saltwork brines Mg(II), Li(I) and some trace elements (B(III), Co(II) and Sr(II), among others), all of them listed as critical raw materials by the European Union [1]. Due to the fact that the technologies devoted to the recovery of the above mentioned elements require acid and bases, the SEArcularMINE project aims to produce them in-situ (HCl and NaOH) from exhausted brines (free of Mg(II) and Ca(II)) using Electrodialysis with Bipolar Membranes (EDBM), promoting in this way a fully circular scheme. The aim of this work is to evaluate the performance of a laboratory EDBM unit (equipped with membranes supplied by SUEZ-WTS) for the production of NaOH and HCl, mimicking conditions (in terms of solution composition and flows arrangements) expected within the treatment chain. Moreover, experiments were carried out with real pre-treated brines (Mg(II) and Ca(II) < 10 mg/L), and the transport of the above-mentioned trace elements was studied in detail. All the experiments were performed in a lab-scale unit (Electromat MkI ED STACK) with an active area of 0.028 m2 operated at 300 A/m2. In order to compare experiments, several performance parameters were calculated, such as the specific energy consumption (SEC), current efficiency and acid and base purities. Experimental results showed the possibility of producing NaOH and HCl (>1 M), with SEC values ranging between 2.05 and 2.39 kWh/kg NaOH and current efficiencies higher than 70%.