Alkali-treated yttrium-containing chitosan-based hydrogels for phosphate recover with highly selective in wide pH aqueous solution

Excessive discharge of wastewater containing phosphorus is the leading cause of water eutrophication. In this study, yttrium ions were embedded in chitosan/polyvinyl alcohol hydrogel beads by adsorption of amino functional groups. After alkali treatment, a new chitosan-based yttrium hydrogel adsorbent (PC-Y-OH) with porous channels was perpetrated. The results showed that alkali treatment reduced the protonation of amino functional groups in hydrogel and made PC-Y-OH have stable adsorption of phosphate in the initial solution of pH 4 similar to 10. Compared with hydrogel beads without alkali treatment (PC-Y3+), the inhibition of high concentration bicarbonate and sulfate of PC-Y-OH was reduced by 47 % and 43 %, respectively, under acidic conditions (initial pH of 3). In weak acid (initial pH of 6) or alkaline (initial pH of 8) conditions, its adsorption capacity is almost uninhibited by co-existing substances. After regenerating the adsorbent with an alkali solution 7 times, the adsorption capacity was still over 80 % of the first adsorption. The adsorption kinetics and thermodynamics results indicated that PC-Y-OH could reach the adsorption equilibrium within 2 h, and the adsorption process was a spontaneous exothermic process with a maximum adsorption capacity of 62.36 mg-P/g. Surface chemical analysis of the adsorbent indicated that phosphate adsorption on the adsorbent was primarily driven by chemical complexation. Moreover, this provides a promising adsorbent for recovering phosphorus from aquatic environments.