Correlation between flocculation and adsorption of cationic polyacrylamides on precipitated calcium carbonate
The study of each stage of the flocculation process is essential to better understand and predict flocculation mechanisms. The adsorption of cationic polyacrylamide derivatives (C-PAM) onto precipitated calcium carbonate (PCC) has been investigated systematically as a function of the C-PAM characteristics including molar mass, chain architecture, and charge density. The adsorption results show that, for C-PAM of similar molar mass, highly branched architectures reach the equilibrium faster than linear C-PAM. Similarly, the flocculation rate is higher for the branched C-PAM, which may be indicative of the predominance of the bridging mechanism. In terms of the molar mass, lower molar mass leads to lower adsorption rates and slower flocculation. Adsorption isotherms of C-PAM onto precipitated calcium carbonate could be described by the Langmuir isotherm model. The maximum amount of C-PAM that adsorbs on the particle surface as a monolayer, obtained from adsorption tests through the Langmuir isotherm linear fit, could be correlated with the structure of the aggregates, obtained from flocculation experiments. Moreover, a good correlation was obtained between the adsorption results and the kinetics of the first stage of the flocculation process dominated by particle aggregation. (c) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.