Poly(acrylic acid) as an effective inhibitor to inhibit mineral scale crystallization: molecular weight investigation

In this research, constant amount of two poly(acrylic acid) (PAA) polymers with molecular weights of ~ ۲۰۰۰ and ~۱۰۰۰۰۰, were added to calcium sulfate dihydrate (gypsum) formation solution as antiscalant. The crystallization kinetics was also probed by in situ UV-Vis spectrophotometry. XRDand SEM were used for phase and morphological studies of the formed crystals. The surface adsorption of the additives was evaluated by XPS analysis. The comparison showed that the presence of the low molecular weight PAA increased the induction time by ~ ۸۰ times and decreased thecrystallisation kinetics far more than the larger molecular weight PAA. When the pH in the reacting solution was changed from ~ ۴ to ~ ۷, the efficiency of the low molecular weight PAA in inhibiting gypsum formation increased, while in the presence of the higher molecular weight PAA the oppositeeffect was observed. Taken together, the turbidity plots, the XPS data and the morphological changes in shape and size, all infer that the additives adsorbed to the surfaces of the growing crystals

Keywords:

crystallization , calcium sulfate dihydrate , antiscalant , surface adsorption , poly(acrylic acid) , XPS