FLOCCULATION AND COAGULATION BEHAVIOR OF A KAOLIN - A COMPARATIVE-STUDY

A comparative study of the flocculation and coagulation response of a kaolin suspension using different flocculants and coagulants was made. The flocculants and coagulants tested include cassava starch, which is a polymer (oxidised, charged and uncharged; and causticised), salts of divalent and trivalent metals (magnesium chloride hexahydrate - MgCl2 . 6H2O and aluminium nitrate (nanohydrate - AI(NO3)3 . 9H2O), and the presence of these metal ions in causticised cassava starch. Results show that well flocculated suspensions were obtained in the alkaline pH region (pH > 8) and that charged oxidised cassava starch proved to be the most effective flocculant. The investigation also reveals that the presence of metal cations in causticised cassava starch significantly contributed to the existence of low settling rates at high supernatant clarity often observed in some clay slurry treatment systems by flocculation and sedimentation method. The study further revealed that in some flocculation systems fast settling corresponds to high sediment volume whereas in others, the opposite applies. It is therefore concluded that this phenomenon should be taken into consideration for the proper design and operation of clay slurry treatment facilities.