EFFECT OF ADDITIVES ON THE CRYSTALLIZATION OF BARIUM-SULFATE

The kinetics of crystallization of barium sulphate for both seeded and unseeded systems in presence of additives have been studied by follow ing the changes in ionic conductivity in supersaturation solutions con taining stoichiometric concentrations of the lattice ions at 298 K. Th e additives investigated include: 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), hexamethylenediaminetetramethylenephosphonic acid (HMNTM P), ethylenediaminetetramethylenephosphonic acid (ENTMP) and nitrilotr imethylene-phosphonic acid (NTMP). The effect of these additives on th e growth kinetics has been studied at several inhibitor concentrations . The retarding effect of these inhibitors is interpreted in terms of adsorption of inhibitor ions at the active crystal growth sites follow ing the Langmuir isotherm. The order, in terms of decreasing the inhib itory effect on the rate of growth of barium sulphate of the studied a dditives is HEDP >HMNTMP >ENTMP >NTMP. This order holds for both seede d and unseeded systems.