THE INHIBITION OF GYPSUM AND BARITE NUCLEATION IN NACL BRINES AT TEMPERATURES FROM 25-DEGREES-C TO 90-DEGREES-C

The inhibition of gypsum and barite nucleation in NaCl brines by phosp honates and polycarboxylates was studied at 25, 50, 70 and 90 degrees C in terms of the prolonged induction period. Hexamethylene-diaminetet ra(methylene phosphonic) acid (HDTMP) was found to be an effective inh ibitor for the scaling of calcium sulfate dihydrate. Hydroxyethylene-1 , 1-diphosphonic acid (HEDP) and phosphinopolycarboxylic acid (PPPC) w ere found to be effective inhibitors for barium sulfate scaling. The i nhibition of nucleation through prolongation of the nucleation inducti on period likely resulted from an increase in the interfacial tension between the crystal and aqueous solution due to the presence of the in hibitors. It was observed that the inhibition of nucleation depends hi ghly on the lattice cation/anion molar ratio and the pH of the solutio n as well as the degree of supersaturation and temperature for a given inhibitor.