The invention discloses a method for preparing a
quaternary ammonium cationic
starch flocculant in a DMSO / H2O / NaOH
system. The method comprises following steps: 1), NaOH is dissolved in water, DMSO and
starch are added, a mixture is heated, stirred and subjected to
reflux condensation for a reaction, and a
starch activation liquid is obtained; 2), the starch activation liquid obtained in the step 1) is cooled to 60-75 DEG C, then an etherifying agent activation liquid is added and stirred, and a reaction is performed for 0.5-1 h; 3), the white powdery
quaternary ammonium cationic starch flocculant is obtained through cooling, purification and
drying. According to the method, the starch is pre-activated in the DMSO / H2O / NaOH
system, the reactions are performed in a homogeneous
system, so that the starch has higher
plasticity, active sites for combination of an etherifying agent and the starch are increased, the activated starch can react with the cationic etherifying agent rapidly, the
quaternary ammonium cationic starch flocculant prepared with the method can be completely dissolved in water,
colloid particles can be clustered through
flocculation under the sufficient bridging and cross-linking actions, and the
flocculation effect cannot be influenced by a settlement action of the flocculant.