Behaviour of quartz suspensions in the presence of calcium ions and acrylate polymers

Abstract

The effect of acrylate polymers on the behaviour of quartz-slime suspensions, in the presence or in the absence of calcium ions, is considered. Results of dispersion tests with polyacrylates of various molecular weights show that acrylates are capable of extending the pH range in which quartz is dispersed to weakly acid pH values: between 3.5 and 4.5, if calcium ions are not added to the system. On the other hand, in the presence of calcium ions, the dispersed state can be maintained only in a narrow pH range, between 4, 5 and 6 to 8.5, the latter value being reached only in the case of very low molecular weight polymer (5.400). At higher pH values, flocculation takes place, more intensively as the pH becomes more basic and the molecular weight of polymer higher. The mechanism by which dispersion or flocculation occurs is interpreted on the basis of experimental results of dispersion tests and zeta potential measurements. From these data, it is concluded that electrostatic effects and steric hindrance phenomena must not be ignored in explaining the behaviour of mineral suspensions, chiefly when a very low molecular weight is used. Adsorption of calcium ions on quartz surfaces appears also to play a fundamental part in the flocculation mechanism at basic pH values.