Retention of Cu and Zn by H‐Montmorillonite

Abstract

Abstract Studies were conducted on the retention of Cu and Zn by H‐montmorillonite in relation to associated anion, salt concentration reaction time, pH of the equilibrium solution, and techniques. Under conditions where the pH of the equilibrium solution was too acid for formation of Cu(OH) 2 , the amounts of Cu and Zn retained were similar for Cl, NO 3 , and SO 4 salts and equal to the cation‐exchange capacity (CEC) as measured with NH 4 + . Detailed studies of metal retention in relation to pH of equilibrium solutions for Cl systems revealed no retention of Cu or Zn in excess of the CEC provided the pH of the system was below 5.5 to 6.5. The exact pH favoring excess retention varied according to salt concentration and the metal in question. Retention of the metals in excess of the CEC was explained in terms of precipitation of Cu(OH) 2 and Zn(OH) 2 in the clay systems. In the acetate systems, Cu and Zn retention was usually greater than the CEC even under acid conditions. As the pH of the systems increased, metal retention increased. In addition to metal retention, acetate retention was measured. Acetate retention was found to be related to the concentration of acetate and essentially independent of the quantity of metal retained.