Synthesis of 3D calcium-modified microspheres for fast purification of simulated phosphate wastewater

Abstract

Adsorption is one of the most promising techniques for large-scale application in phosphate-containing wastewater treatment and the synthesis of efficient adsorbents is the core of the process. High efficiency adsorbent include inorganic adsorbents and organic adsorbents, and the chitosan performs better adsorption capacity because of readily biodegradable and abundant amino functional groups. In this work, a kind of calcium-modified chitosan microspheres (Ca-CTS gel) has been gained through in-situ precipitation for absorbing phosphate from simulation wastewater. The influence factors of the synthesis conditions including crosslinking agent addition, mental ions types, and Ca2+ loading amount, etc., on the adsorption efficiency have been researched. The results showed that the metal ions modified chitosan represented by La3+ modified chitosan was significantly different from Ca2+ modified chitosan in loading principle. The characterization results indicated that the adsorption mechanism belonged to the precipitation conversion between Ca(OH)2 and CaHPO4·2H2O. The adsorption kinetics and thermodynamics results showed that the adsorption reaction was endothermic and spontaneous, and the Langmuir-fitted maximum adsorption capacity was 23.7 mg/g at 25 °C. The adsorption experiment results also showed that the other anions, i.e., SO42− and CO32− have a negative influence on phosphate removal, attributing to the smaller Ksp values of their calcium salts. In addition, the dynamic phosphate-adsorption curves have been obtained under different operating conditions for evaluating the industrial application prospect of the as-prepared Ca-CTS gel.