The concept for an ED-RO integrated system for boron removal with simultaneous boron recovery in the form of boric acid

The concept of an integrated membrane system for boron removal, concentration and boric acid recovery was presented. In this system boron and polyol (e.g. d-mannitol) containing water is first desalinated by electrodialysis (ED) and then, after alkalization, concentrated by reverse osmosis (RO) in a two-stage system. The 1st RO stage permeate contains less than 1 mg/L of boron and can be then discarded to the environment or used as feed for the ED concentrate compartment. In the 2nd RO stage boron rich alkaline solution is concentrated to a retentate boron content of 10.8 g/L or more. The alkaline retentate is neutralized with a strong mineral acid and then solid boric acid crystallizes. After separation of the solid, the supernatant solution (not only saturated with boric acid but also containing alcohol and salts) is recycled back to the ED desalination step. The above concept was discussed based on the results of the design of an exemplary system in which a wastewater of 75 mg/L of boron and TDS of 1.8 g/L is treated.