Influence of pH and ionic strength on flocculation of clay suspensions with cationic xylan copolymer

Abstract

In this work, the influence of pH and ionic strength on the flocculation performance of cationic xylan copolymer in kaolin and bentonite suspensions was systematically investigated. The cationic xylan was produced via copolymerizing xylan with 2-(methacryloyloxy ethyl) trimethylammonium chloride (METAC), and the cationic xylan copolymer (CMX) showed a maximum adsorption of 4.6 and 1.8mg/g on kaolin and bentonite particles at the CMX dosage of 8mg/g, pH 10, 30°C and 1h, respectively. The reduction in charge density of CMX from 2.66 to 2.48meq/g was observed, with an increase in pH of CMX solution to from 2 to 10. The maximum increase in the zeta potential of kaolin (+54mV) and bentonite (−3mV) suspensions and the highest removal of kaolin (75%) and bentonite (96%) from the suspensions were obtained at 8mg/g CMX and pH 7. Stability studies revealed that pH had a noticeable influence on the sedimentation of kaolin and bentonite particles. CMX increased the destabilization index of kaolin (0.4–45) and bentonite (0.2–51) suspensions by increasing the floc size of kaolin and bentonite particles to 9.5μm and 12.7μm, respectively. CMX removed more of bentonite than kaolin at any pH under static and dynamic conditions. The impact of inorganic salts on the removal of kaolin particles was also studied. CMX exhibited better performance than a commercial flocculant (PDADMAC) in flocculating the commercially produced effluent.