The making of time-dependent kaolin suspensions in the structural rejuvenation mode

Time-dependent structural rejuvenation process in both ageing and stepdown shear rate modes, was postulated to require that both the silica and alumina faces of the kaolin platelets be negatively charged so as to produce strong EDL repulsive interaction in the face-face configuration to slow down the bonding process and to form the open network structure with (+)edge-(-)face bonds. Currently, the rapid unlike charge silica alumina face-face attraction prevents such structural organization. The use of adsorbed P2O74- additive and high pH are two simple methods that can make the alumina face negatively charged. It was found that both treatment methods did produce time-dependent behaviour characterizing the structural rejuvenation process for both the high defect KGa-2 and low defect KGa-1b kaolin suspensions. This confirmed that the underlying principle of our premise is correct. The KGa-1b kaolin with a lower content of permanent or layer positive charge required a smaller amount of adsorbed P₂O₇^4- and a lower pH to bring about the time-dependent behavior. High pH treated KGa-2 kaolin suspension also display time dependent behaviour in ageing. Addition of 0.002M NaCl to the high pH-treated KGa-2 kaolin suspension hastened the structural rejuvenation process and increased the ageing yield stress. The oscillatory behaviour in the stepdown shear stress was eliminated by removing either the (+)alumina-(-)silica face-face attraction or all the fixed charged-base face-face interactions. The large layered agglomerates was markedly decreased by P2O74- treatment for KGa-2 kaolin suspension based on size distribution data. A clay-rich iron ore tailings was similarly treated and became time-dependent in both ageing and stepdown shear rate modes.