Membrane electrolysis for the removal of Na+ from brines for the subsequent recovery of lithium salts

Membrane-based technology in water and resources recovery from the perspective of water social circulation: A review

In this review, the application of membrane-based technology in water social circulation was summarized. Water social circulation encompassed the entire process from the acquirement to discharge of water from natural environment for human living and development. The focus of this review was primarily on the membrane-based technology in recovery of water and other valuable resources such as mineral ions, nitrogen and phosphorus. The main text was divided into four main sections according to water flow in the social circulation: drinking water treatment, agricultural utilization, industrial waste recycling, and urban wastewater reuse. In drinking water treatment, the acquirement of water resources was of the most importance. Pressure-driven membranes, such as ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) were considered suitable in natural surface water treatment. Additionally, electrodialysis (ED) and membrane capacitive deionization (MCDI) were also effective in brackish water desalination. Agriculture required abundant water with relative low quality for irrigation. Therefore, the recovery of water from other stages of the social circulation has become a reasonable solution. Membrane bioreactor (MBR) was a typical technique attributed to low-toxicity effluent. In industrial waste reuse, the osmosis membranes (FO and PRO) were utilized due to the complex physical and chemical properties of industrial wastewater. Especially, membrane distillation (MD) might be promising when the wastewater was preheated. Resources recovery in urban wastewater was mainly divided into recovery of bioenergy (via anaerobic membrane bioreactors, AnMBR), nitrogen (utilizing MD and gas-permeable membrane), and phosphorus (through MBR with chemical precipitation). Furthermore, hybrid/integrated systems with membranes as the core component enhanced their performance and long-term working ability in utilization. Generally, concentrate management and energy consumption control might be the key areas for future advancements of membrane-based technology.

Effect of [Na+]/[Li+] concentration ratios in brines on lithium carbonate production through membrane electrolysis

Lithium is a fundamental raw material for the production of rechargeable batteries. The technology currently in use for lithium salts recovery from continental brines entails the evaporation of huge water volumes in desert environments. It also requires that the native brines reside for not less than a year in open air ponds, and is only applicable to selected compositions, not allowing its application to more diluted brines such as those geothermally sourced or waters produced from the oil industry. We have proposed an alternative technology based on membrane electrolysis. In three consecutive water electrolyzers, fitted alternately with anion and cation permselective membranes, we have shown, at proof-of-concept level, that it is possible to sequentially recover lithium carbonate and several by-products, including magnesium and calcium hydroxide, sodium bicarbonate, H2 and HCl. The big challenge is to bring this technology closer to practical implementation. Thus, the issue is how to apply relatively well-known electrochemical technology principles to large volumes and to a highly complex and saline broth. We have studied the application of this new methodology to ternary mixtures (NaCl, LiCl and KCl) with constant LiCl and KCl composition and increasing NaCl content. Results showed very similar behaviour for systems containing [Na+]/[Li+] concentration ratios ranging from 1.24 to 4.80. The voltage developed between the anode and cathode is almost the same in all systems at roughly 3.5 V when a constant current density of 50 A m-2 is applied. The three monovalent cations migrate with different rates across the cation exchange membrane, with Li+ being the most sluggish and thus crystallization of Li2CO3 only occurs close to completion of the electrolysis. The dimensionless concentration profiles are almost indistinguishable despite the changes in total salinity. The solids crystallized from different feeds showed higher Na+ and K+ contents as the initial Na+ concentration was increased. However, solids with over 99.9% purity in Li2CO3 could be obtained after a simple re-suspension treatment in hot water. The electrochemical energy consumption greatly increases with higher Na+ concentrations, and the amount of fresh water that can be recovered is diminished.