The influence of sodium carboxymethylcellulose and sodium chloride on the precipitation of calcium sulfate dihydrate

Abstract

The inhibition of gypsum was investigated at 25C in aqueous 0,7 and 1,5 mol/l NaCl solutions by so- dium carboxymethylcellulose (CMC-1000, with the degree of polymerization of 1000 units).The efficiency of inhibition was estimated from measurements of the calcium concentration in the supersaturated calcium sulfate solutions (0,15 mol/l) during the precipitation process by the standard procedure of complexometric titration. It was observed that the presence of NaCl exhibits synergistic effect on the performance of CMC-1000. In the presence of CMC-1000 at 0,5 g/l inhibitor concentration and sodium chloride at 0,7 mol/l concentration induction time, preceding the formation of the gypsum, increases from 100 (without NaCl) to 630 min. Induction times at 0,1 g/l CMC-1000 and sodium chloride at 0,7 and 1,5 mol/l concentrations are 60 and 32 min respectively. The results of X- ray powder diffraction indicated that dihydrate calcium sulfate and sodium chloride present in solid phase.