Recovery of Boric Acid from Aqueous Solutions Using Polycondensation Anion Exchangers

Abstract

The sorption behavior and mechanism of boric acid recovery on polymerization anion exchangers of both strongly and weakly basic types are now fairly well understood, while a current knowledge of the sorption of boric acid on polycondensation anion exchangers is limited. The present investigation was carried out to establish influences of temperature, concentration and pH of boric acid on its sorption behavior. It was used polycondensation anion exchangers based on monoethanolamine and epichlorohydrin (SB-1, SB-2) and pyrocatechol and formaldehyde (SB-7, SB-8). It has been revealed that anion exchangers in the hydroxyl form containing alcohol and aminooxyethyl functional groups possess high sorption activity and selectivity for boron. When sorption of boric acid from solutions at a concentration more than 0.057 M, pH 5.0-7.5, the exchangers have been shown to possess unusually high sorption capacity for boron. It has been established that the mechanism of boric acid sorption on the hydroxyl-form polycondensation anion exchanger has the mixed nature owing to the fact that it was observed two simultaneous processes: first, chemisorption of boric acid molecules by the hydroxyl groups of the anion exchangers, coupled with the accumulation of tetraborate anions [B4O5(OH)4]2- in the sorbent phase, and second, complex formation of polynuclear boron compounds.