Heavy Metal Concentration to Clay Minerals in Aqueous Solutions (1)

Suspension pH and Metal Contents of Sericite

Abstract

When clay minerals are suspended in aqueous solutions containing metal ions, the metals concentrate remarkably to the solid (clay minerals). Using sericite (2M1 muscovite) from the Hikawa mine, Shimane Prefecture, southwest Japan, degrees of the concentration of some heavy metals such as cobalt, copper, zinc, (arsenic), cadmium and lead were examined as functions of the duration of time, metal contents in solutions and pH. A term "suspension pH" is designated in this paper, which represents the pH of sericite-suspension during stirring the suspension. As the amount of sericite in suspension increases, the value of the suspension pH increases until 3 gr. per 100 cc water. The value of the suspension pH coincides well with that of pH of the solution in acid condition (pH<7.0). In alkaline conditions, the suspension pH gradually closes to the abrasion pH as the duration of time increases. However, even after one year duration, the value of the suspension pH does not achieve an equilibrium.
The maximum adsorption of heavy metals in sericite occurs within an hour and as the duration of time increases, the amount of the metal content in sericite decreases. With increasing the contents of metals in solution, the amount of metals in sericite increases to ceratin amount. As the numbers of kind of metal ions in solution increases, the content of each metal decreases keeping the total content of metals in sericite almost constant. Zinc, cobalt and arsenic concentrate more in solid rather in solution, while cadmium and lead remain rather in solution. Experimental techniques affecting the content of heavy metals in sericite such as washing of sericite are examined. Based on the experimental results, considerations on the mechanism of the adsorption of heavy metals, significance of the suspension pH and aging effect of clay minerals in aqueous solution were presented.