Studies On The Development Of The Trace Boron Adsorbents And The Mechanism For The Removal Of Nature Water

Trace boron element is an essential nutrient element for organisms. However, excess boron will cause toxicological response to organisms. With the development of mental smelting, glass, cosmetic and pharmaceutical industries, boron pollution in nature water is worsening. In addition, seawater desalination and utilization is also hampered by high boron content. Therefore, research of boron removal technologies in nature water is getting more and more attention from experts and scholars. Boron specific resin is one of the best boron removal methods, research and development of boron specific resin with high adsorption capacity and good selectivity is significant.The removal principle of boron specific resin method is based on the boron adsorption by resin and the complexation reaction of polyhydroxyl groups in the resin with boric acid/borate. According to two complexation mechanisms of polyhydroxyl groups with boric acid/borate:the complexation of alkaline polyhydroxyl groups with borate B(OH)4" and complexation of acid polyhydroxyl groups with boric acid B(OH)3, this paper selected two typical polyhydroxyl compounds:2,3-dihydroxynaphthalene-6-sulfonic acid sodium salt and gallic acid and research the adsorption mechanism for boric acid/borate.1. The complexation of B(OH)4-with2,3-dihydroxynaphthalene-6-sulfonic acid sodium salt in aqueous solution was examined thoroughly by11B NMR measurements. It was confirmed that boric acid reacted with2,3-dihydroxynaphthalene-6-sulfonic acid sodium salt to form two five-membered ring complexes with1:1and1:2stoichiometries, and the formation constant of the two complexes were logβ=5.22and logβ2=6.10. A novel boron selective adsorbent presorbed2,3-dihydroxynaphthalene-6-sulfonic acid sodium salt was prepared by using ion exchange method, and amount of1.20mmol/g2,3-dihydroxynaphthalene-6-sulfonic acid sodium salt were loaded on the adsorbent. Bath experiments were conducted to evaluate the performance of the adsorbent for removal of boron from water, and the effects of pH value and initial concentration of the boron solution, contact time and bath temperature on the removal efficiency were investigated. Boron removal optimum conditions were as follows:pH value was8.9, the initial boron concentration was0.05mol/L,24h could reach equilibrium. The adsorbent’s adsorption capacity was estimated to be about0.67mmol/g. The thermodynamics and kinetics research of boron adsorption by adsorbent showed that the boron adsorption on adsorbent conformed to pseudo-second-order rate equation, and it was a chemical and physical adsorption process, the adsorption rate was mainly controlled by chemical adsorption mechanism. B(OH)4-was bouded to the adsorbent mainly in the form of1:1complex and electrostatic attraction.2. The11B NMR results of the complexation of H3BO3with gallic acid showed that in aqueous solution H3BO3reacted with gallic acid to form1:1and1:2five-membered ring complexes and the formation constant were logβ1=3.79and logβ=4.10. A novel boron selective adsorbent presorbed gallic acid by loading amount of0.81mmol/g gallic acid was prepared by using ion exchange method. Research of the effects of pH value and initial concentration of the boron solution, contact time and bath temperature on the removal efficiency showed that boron removal optimum conditions were as follows:pH value was6.5, the initial boron concentration was0.025mol/L,24h could reach equilibrium. The adsorbent’s adsorption capacity was estimated to be about0.39mmol/g. Boron adsorption process on the adsorbent could be well described with Langmuir equation, Freundlich equation and pseudo-second-order rate equation, which was a spontaneous chemical process with monomolecular layer. Boron was bouded to the adsorbent mainly in the form of1:1complex.During the boron removal research by using above adsorbents, relevant complexation mechamism research played an important role.