Dynamics of boric acid sorption by boron-selective SB-type anionite

Abstract

Investigation and choice of an effective sorbent are significant for protection of water bodies against boron The boron high concentration in natural waters produces toxic impact on aquatic biota due to its high biological activity. This paper studied the dynamics of boric acid sorption from aqueous solutions by polycondensation anionite SB-1 synthesized on the base of monoethanolamine and epichlorohydrin. The anion exchanger contained aminooxyethyl and alcohol functional groups in its structure. Methods. It has been established the influences of the ion form of the anionite on the dynamic characteristics of boron sorption from both a model boric acid aqueous solution (0.43 mol/dm3) and an industrial wastewater effluent after boric acid production (0.47 mol/dm3), other things being equal (pH = 5.0; the volume rate of the solution passing through the anionite layer = 1.5 ml/min∙cm2; t = 20 0C). Structural studies to determine the form of boron in the anionite phase were performed using the IR spectroscopic method. Dynamic characteristics of boron sorption (the cation and overall ion-exchange capacity values, period of the protecting effect of the filter) were determined graphically from the sorption curves. Results. It has been found that the hydroxyl form of the anion exchanger SB-1, in comparison with the chlorine form, performs superequivalent boron sorption while boron sorption from both a model and real production solutions. For the first time we have demonstrated that at the initial stage, boric acid sorption is carried out owing to the chemisorption, resulting to the formation of stable hydroxoborate forms [B(OH)4]– in the ionite phase. As the anionite is being saturated and the concentration of free functional hydroxyl groups is decreasing, the formation of polynuclear forms of boric acid [B4O5(OH)4]2– occurs in the anionite phase by sorption of boric acid molecules on free tetrahydroxoborate anions and, further, the complex formation of polynuclear forms of boron by the nitrogen atom of aminooxyethyl functional groups. It has been stated that desorption of boron from anionite is considered to be effective when carried out with a 2 n. NaOH solution with a regeneration degree of 0.995.