Kaolinite suspension treatment using cellulose dissolved in sodium hydroxide as flocculant

Abstract Kaolinite is clay used in various industries that forms turbid dispersions and disrupts aquatic ecosystems if not separated from process waters before discharge. Conventional coagulation chemicals, such as alum and polyacrylamides could be used to improve separation, but they contain long-term risks to human health and the environment. In this study, we show that cellulose dissolved in aqueous sodium hydroxide can be used to increase the particle size and the settling rate of kaolinite suspension. The effect is further enhanced when the cellulose solution is used together with magnesium chloride. Response surface models were made to evaluate the effect of cellulose and magnesium chloride doses on kaolin suspension turbidity after 10 min and after 20 h of settling. An effective dose was determined and a 0.5 wt% kaolinite suspension with initial turbidity of 3200 NTU was treated with 20 ppm of dissolved cellulose and 0.5 mM of magnesium chloride to achieve turbidity of 7.3 NTU after 2 min of settling and 4.7 NTU after 10 min of settling. Additionally, it was shown that the cellulose solution largely retains its ability to flocculate the kaolin suspension in saline waters at least up to 0.5 M of sodium chloride content. These results could have applications especially in industries where both kaolinite and cellulose are present, such as pulp and paper industry.