The preparation of hydroxypropyl starch grafted acrylamide and its enhancement on flocculation of coal slime water

Natural starch is a rich polysaccharide biopolymer, which has received more and more attention in the field of water and tailings treatment. However, it has some disadvantages, such as small molecular weight, poor water solubility, and lack of electric charge. Therefore, it is gradually modified to obtain specific properties. Starch-modified flocculant is an environment-friendly flocculant with good flocculation performance for wastewater. In this study, hydroxypropyl starch (HPS) and acrylamide (AM) were used as raw materials, and ceric ammonium nitrate was used as the initiator to synthesize hydroxypropyl starch grafted acrylamide (HPS-AM) by aqueous polymerization method. Taking monomer conversion rate, grafting rate, and grafting efficiency as evaluation indicators, the effects of initiator dosage, reaction temperature, reaction time, and the dosage ratio of starch to AM on the graft copolymer were studied by single factor experiments. The optimal synthesis conditions were temperature 55℃, reaction time 2 h, the mass ratio of HPS/AM 1:3, and initiator dosage 0.045 g. The graft copolymer products were characterized by infrared spectroscopy and differential scanning calorimetry, and the flocculation sedimentation experiments were carried out on coal slime water using HPS-AM, HPS, and polyacrylamide (PAM). When the dosage of HPS-AM was 4 mL, the minimum turbidity of the slime water was about 30.19 NTU, and the flocculation efficiency was about 78%; while when the dosage of PAM was 6 mL, the minimum turbidity of the slime water was 115.12 NTU, and the flocculation efficiency was about 40%. HPS has no flocculation performance. Therefore, compared with PAM and HPS, HPS-AM has better flocculation performance in the treatment of coal slime water.