Effect of anionic polyelectrolytes on the dissolution of magnetite in thioglycolic acid solutions

Abstract

A detailed study of the influence of some anionic polyelectrolytes on the dissolution of magnetite (Fe₃O₄) in thioglycolic acid (HTG) is presented. At pH values between 2 and 7, polyacrylic acid (HPA) inhibits the reaction as it is adsorbed strongly on the oxide surface; the inhibitory effect increases with HPA concentration. Polymethacrylic acid (HPMA) and sodium poly(styrene sulfonate)(NaPSS) do not have any effect on the dissolution rate, probably because of lower adsorption resulting from the greater rigidity of the polymeric chains. No effect on the specific rate constant values is observed with changes in the molecular weight of HPA. Addition of NaCl decreases the rate of dissolution in HPA at low concentrations but does not affect the inhibitory effect at higher HPA concentrations. The Arrhenius activation energy was evaluated for the dissolution reaction in the presence of HPA, HPMA and NaPSS and in the absence of polyelectrolyte, and no differences were found, suggesting that the inhibition, observed in the case of HPA, is probably due to the blocking of the reactive sites on the oxide surface by polyelectrolyte adsorption.