Acid/base and metal complex solution chemistry of sulfonated polyacrylate copolymer versus temperature and ionic strength.

Sulfonated polyacrylate copolymer (also known as vinyl sulfonated co-polymer; VS-Co) have been widely used in mineral scale control. However, the speciation chemistry of such polymers in solution is not fully understood. In this paper, the acid-base and calcium complex solution chemistry of a VS-Co has been determined from 0.01 to 2 m ionic strength and from 25 to 90 °C by combining electrostatic theory with potentiometric titrations. To process the titration data, VS-Co is treated as a hypothetical, averaged monoacid, HA, with the same concentration of the active carboxylic functional groups of VS-Co. The acid and calcium dissociation reactions of this acid are simply considered as 1:1 type hypothetical reactions, namely HA↔H + + A − and Ca(A⋯A)↔Ca 2+ + (A⋯A) 2− , with (A⋯A) 2− as an arbitrary combinations of two dissociated A − units. The microconstants of the acid dissociation reaction are fitted with a linear electrostatic model with p K a = p K a , intr + b e l e c θ A − , where p K a , intr is an intrinsic constant referring to the condition of zero dissociation, θ A − is the deprotonated fraction of carboxylic functional groups and b elec is an electrostatic factor based on polyelectrolyte theory. Similarly, the microconstants of the Ca 2+ dissociation reaction are fitted with p K CaA 2 = p K CaA 2 , intr + 2 b elec θ A − with doubled electrostatic effect since the complexation of Ca 2+ with the polymer is considered to neutralize two negative charges. To quantitatively describe the speciation of VS-Co at various conditions, the p K a , intr , p K CaA 2 , intr , and b elec values are fitted empirically as a function of temperature ( T , K), and ionic strength ( I , m): p K a , intr = 5.068 − 128.398 T − 0.924 × I 1 / 2 + 0.311 × I p K CaA 2 , intr = 5.754 − 888.644 T − 5.749 × I 1 / 2 + 2.221 × I b e l e c = 3.234 − 1.321 × I 1 / 2 + 0.399 × I . Fitted results suggests no significant effect of temperature on the electrostatic factor b elec , which is consistent with electrostatic theory. Results from this study can be used to predict the equilibria of VS-Co in a solution, at various temperature, ionic strength, pH, and metal concentrations. [ABSTRACT FROM AUTHOR]