Acid/basic potentiometric titration can be used to quantify the red mud surface charge properties.The amount of surface active -OH groups and surface charge density on the red mud particles generated from Chinese diaspore bauxite were evaluated from the acid/basic potentiometric titration data in 0.1 mol/L or 0.5 mol/L NaCl solution.The results show that the adsorption of sodium polyacrylate(SPA) on the red mud surface causes the increase of the surface active -OH groups,which makes the point of zero charge(PZC) shift to a lower pH value.However,the adsorption of polyacrylamide(PAM) causes little change.As the concentration of NaCl solution increases,the surface charge becomes more positive in acidic solution and more negative in alkaline solution,which can be attributed to the presence of a porous surface gel coating on the red mud particles.
Gibbsite crystals display large varieties of shapes and sizes when grown from sodium aluminate solution. The usage of gibbsite is partly determined by morphology,therefore,controlling the gibbsite morphology in accordance with usage arrests interests of both merchants and scientists. In present study,the effects of organic additives with various functional groups,oleic acid,1-octadecanol and stearic acid on gibbsite morphology were investigated at the concentration of 0.1 g/L. Experiments were performed at the temperature of 65 ℃. Samples of gibbsite crystals were obtained from the decomposition of the unseeded synthetic sodium aluminate solution. The morphologies of these gibbsite crystals were examined with SEM,which shows that functional groups influence gibbsite morphology intensively. The morphologies of gibbsite nucleated from the pure solution and solution containing oleic acid,1-octadecanol and stearic acid are as follows:mosaic gibbsite consisting of various shapes of crystals,radial agglomerate consisting of hexagonal pallets,mosaic and ball like agglomerate consisting of block crystals and loose,radial crystal consisting of irregular tiny nuclei. The facts indicate that it is possible to control gibbsite morphology at the presence of additives with various functional groups. The action mechanism of functional group to morphology was also proposed.
