THE EFFECT OF CATIONIC POLYMER AS FLOCCULANT ON BENTONITE AGGREGATION UNDER DIFFERENT PH AND THE STUDY OF AGGREGATION MECHANISM

Abstract

Cationic polymer of poly((N,N-dimethylamino)ethyl methacrylate) (PDMA) as flocculant was used for treating bentonite suspension with pH 3–11, and the effect of PDMA on sedimentation rate, the size of aggregates and floating bentonite ratio in supernatant was investigated. Furthermore, the PDMA amount in aggregates by thermogravimetry and d(001) of bentonite by X-ray diffraction were measured. When pH of the bentonite suspension decreased, the sedimentation rate of bentonite aggregates increased and the floating bentonite ratio in supernatant solution decreased with only a small amount of PDMA. However, when more than optimum amount of PDMA was added, the sedimentation rate decreased and the floating bentonite ratio increased. Also, bentonite aggregates became the largest by adding optimum amount of PDMA, while they became smaller by using an excessive amount of PDMA. These phenomena were explained by the interaction between PDMA and bentonite surface. That is, in the case of strong interaction, the size of bentonite aggregate was large and the sedimentation rate was fast. On the contrary, in the case of weak interaction, bentonite was difficult to aggregate and the sedimentation rate was slow.