The influence of sodium carboxymethylcellulose and sodium chloride on the precipitation of calcium sulfate from its supersaturation solutions

Abstract

The crystallization of gypsum from supersaturated solutions in dependence on the molar [Ca2+] : [SO42−] ratio 0,26 : 0,15 and 0,35 : 0,15 in the presence of the sodium carboxymethylcellulose (CMC, with the degree of polym- erization of 1000 units) and NaCl was investigated at 25C. The efficiency of inhibition was estimated from measure- ments of change in Ca2+ concentration during the precipitation process. It was found that increasing the calcium ions content in solution compared to sulfate ions results in decrease in the induction period of crystallization. At a polymer concentration of 1,0 g/L and sodium chloride concentration of 0,7 mol/l the induction period of gypsum crystallisation in a supersaturation of the calcium sulfate solution with the molar rate of [Ca2+] : [SO42−] of 0,35 : 0,15 increases from several minutes to one hour. Further increasing the sodium chloride concentration up to 2,0mol/l did not result in change in the induction period of crystallization. This enables the preparation of supersaturated calcium chloride solu- tions using brines for the sealing of porous rocks, cracks, and joints of soil formations.The results of the phase analysis confirmed that salt precipitates in the form of gypsum.