Adsorption of Chloride,Nitrate and Perchlorate by Variable Charge Soils

Two cells consisting of a chloride-selective eloectrode and a nitrate-selective electrode or of a chloride-selectrive electrode and a perchlorate-selective electrode were directly put in the soil suspension to determine the concentration rations Cl^-/NO3^- or Cl^-/ClO4^- for studying the adsorption of the three anions by variable charge soils.It was found that all the concentration ration CCl^-/CNO3^- and CCl^-/CClO4^- in suspension were smaller than unity when soil samples were in equilibrium with mixed KCl and KNO3 or KCl and KClO4 solutions of equal concentration.The order of the amount of chloride,nitrate and perchlorate adsorbed by variable charge soils was Cl^->NO3^->ClO4^- when the soils adsorbed these anions from the solution containing equal concentrations of Cl^-,NO3^- and ClO4^-.Such factors as the pH of the suspension,the iron oxide content of the soil etc.Could affect the amounts and the ratios of anions adsorbed.The adsorption was chiefly caused by coulombic attraction,but a covalent force between the anion and the metal atom on the surface of soil particles may also be involved,at least for Cl^- ions,even for NO3^- ions.