The effect of stabilizing additives on the rheology and sedimentation stability of alumina-water slurry was investigated. Three kinds of stabilizing additives, synthetic smectite clay; TXP, carboxymethyl cellulose; CMC#1, and native gellan gum; LT-100, were used in this study. The equilibrium flow curves obtained with a rheometer for aqueous solutions of these additives showed that both TXP and LT-100 give typical shear thinning properties with significant thixotropic behavior. The rheological measurements and sedimentation stability tests for alumina-water slurries suggested that the magnitude of structural stress may be related to the stability of slurries. This information is useful for the preparation and stability evaluation of alumina-water slurries.
A new evaluation technique has been developed for the characterization of slurry compressibility by hydrostatic pressure measurement. Slurry was poured into a test tube, and the change in hydrostatic pressure at the bottom was measured during the gravitational sedimentation. In order to investigate the effect of flocculation degree on the sedimentation behavior, pH values were changed using hydrochloric acid. It was found that the hydrostatic pressure of strongly flocculated slurry decreased faster than that of well-dispersed slurry. It was also shown that the hydrostatic pressure of weakly flocculated slurry decreased like well-dispersed slurry at initial stage of sedimentation, however it decreased rapidly after a certain time. This result suggests that the flocculation proceeded during the sedimentation for the weakly flocculated slurry. The results obtained from the hydrostatic pressure measurement were found to agree well with DLVO theory.
A new evaluation technique has been developed for the characterization of slurry compressibility by using conventional constant pressure filtration. In order to estimate the packing fraction of formed cake, we modified Ruth equation and the experimental results were analyzed by using the modified equation based on not the filtrate but the particle volume of formed cake. The cake packing fractions estimated by this equation agreed fairy well with those obtained by measuring the volume and weight of the cake, and therefore this method is useful for the evaluation of the slurry compressibility. Furthermore it was shown that the packing fraction decreased drastically at certain initial slurry concentration for strongly flocculated slurry.