The mechanism of fluidization of concentrated calcium carbonate slurries by poly(oxyethylene) diphosphonates

Nonionic poly(oxyethylene) polymers having a diphosphonate group at one cha in end strongly adsorb onto CaCO3 particles. The main consequence is a cons iderable lowering of the viscosity of concentrated slurries. This effect oc curs because of the break up and redispersion of aggregates of flocculated CaCO3 particles by the polymer adsorption. The mechanism of colloidal stabi lization is steric, the particles becoming uncharged as the polymer adsorbs at their surface. As a consequence, the colloidal suspensions remain stabl e and fluid at high volume fractions and at high ionic strengths. On the ot her hand, because of the strong affinity of these polymers for CaCO3 surfac es, the larger part of the polymer is adsorbed until the coverage of the pa rticles reaches completion. The easy to handle polymer-to-solid weight rati o can then be used as a formulation parameter. The depletion flocculation b y the nonadsorbed polymer is avoided.