Enhancement of clay zeta-potential by chelating agents

Significant enhancement of the zeta-potential (ζ) in heavy loam type soil samples treated with solutions of 1-hydroxypropane-1,1-bisphosphonic acid (HEDPA), 1,2-diaminoethane-N,N,N′,N′-tetraethanoic acid (EDTA), citric acid, and succinic acid was observed for a relatively broad range of concentrations and pH. An observed increase of zeta-potential in the samples treated with varying concentrations of HEDPA (0.0001–0.1 M) revealed a well-pronounced broad maximum at 0.05 M. Data also indicates that the enhancement of zeta-potential imparted by HEDPA treatment was not very strongly dependent on the pH of the treated clay suspension, showing only a weakly pronounced maximum at pH 6. It was established that the observed significant increase of zeta-potential, from −16 up to −40 mV, qualitatively correlates with a specific complex formation ability of the studied chelating agents. The relative broadness of the maximum of the zeta-potential within a wide concentration range of HEDPA could be associated with an intensive dissolution and complex formation of background cations, such as Fe(III), Al(III), Ca(II), Zn(II), Mg(II), and Mn(II) while observed increase of zeta-potential at pH 6 could be explained by sorption of studied complexing agents on the surface of clay particles.