Promising method of ion exchange separation of anions before reverse osmosis

A method to improve the quality of purified water, reduce the cost of reagents for the regeneration of resin and create low-waste processes have been developed. This paper presents the results of ion exchange separation of sulfates and nitrates using AV-17-8 anion exchange resin in NO3 form. The efficiency of anion separation on the highly basic anion exchange resin AV-17-8 depends on the magnitude and ratio of their concentrations in water. Separation on the AV-17-8 anion exchange resin has been shown to be effective at concentrations of sulfates up to 800 mg/dm3 and nitrates up to 100 mg/dm3. Conditions for regeneration of 10% NaNO3 anion exchange resin were determined. Reagent precipitation of sulfates from the used regeneration solution in the form of calcium sulfate was carried out. Calcium sulfate precipitate can be used in the manufacturing of building materials. The regeneration solution is suitable for reuse. The developed results will allow to introduce low-waste desalination technology of highly mineralized waters. 94 I. Trus, M. Gomelya, V. Vorobyova, M. Skiba this problem, the processes of ion exchange separation of these ions in the stages preceding the reverse osmosis desalination of water can be used. The most characteristic anions of highly mineralized waters are chlorides, nitrates and sulfates. The use of an anion exchange resin Amberlite IRA 900 allows for the separation of chlorides and nitrates (Berbar, Y. et al. 2008). Today, reverse osmosis methods are preferred for purifying waters with a high content of chlorides and sulfates, (Mubita, T. et al. 2020). These anions can be preliminarily separated on the AV-17-8 anion exchange resin in Cl-form. During the electrochemical separation of chlorides and sulfates in the anode chamber, sulfuric acid is concentrated, and chlorides are oxidized and then released in the form of chlorine gas. It is much more difficult to purify water that contains nitrates along with sulfates. It should be noted that the extraction of nitrates from water with low mineralization is a simple task (Rajca, M. 2012, Wiśniowska E. and Włodarczyk-Makuła M. 2020). Ion exchange is a fairly simple and reliable method that allows to effectively remove nitrates, reducing their concentration in water to acceptable levels. Ion resins are well regenerated with the solutions of sodium, potassium and ammonium compounds. At high concentrations of chlorides and sulfates during their electrochemical separation a mixture of sulfuric and nitric acids will form, which is unsuitable for further use. Therefore, this issue needs to be addressed urgently. However, the processes of regeneration of ion exchangers and utilization of the resulting eluates are insufficiently studied. Therefore, the aim of this work was to study the processes of effective separation of sulfates and nitrates depending on their concentrations in water and to develop a method of processing of eluates, which will allow their reuse to create low-waste water purification processes. The objective of this work is to study the processes of ion exchange separation of sulfates and nitrates on the anion exchange resin AV-17-8 in NO3 form to develop effective methods of anion exchange resin regeneration considering possible directions of processing of the obtained eluates for reuse and to evaluate the prospect of ion exchange separation of anions from the water.