ZINC SORPTION BY KAOLINITE: INFLUENCE OF pH, ELECTROLYTE, AND INITIAL Zn CONCENTRATIONS WITH SIMULTANEOUS RELEASE OF Mg, Ca, Mn, AND Cu IONS

Abstract

The present study deals with: (a)The influence of pH values, different electrolyte concentrations (ionic strength) and different initial Zn concentrations on Zn sorption by kaolinite, (b)The possible fit of sorption data to known sorption isotherms. (Langmuir, Freundlich, Tempkin and Sposito), and (c) The simultaneous release of other ions (Mg, Ca, Mn, and Cu) as a result of Zn sorption by Kaolinite and its possible implications. Experiments were carried out by using five different initial Zn concentrations (from 4.05×10−5 to 5.17×10−4), two different electrolyte concentrations (10−3 and 10−2 M KNO3) and different pH values (3.5 to 8.5). The results, in general, show an increase of Zn sorption as pH and initial Zn concentrations increase, with simultaneous decrease in electrolyte concentration. Langmuir equation was found to describe Zn sorption data better at pH 4.5 and 7.5 in the presence of 10−2 and 10−3 M KNO3. Maximum Zn sorption was found to be 498 and 921 mg kg−1 at pH 7.0, in the presence of 10−2 and 10−3 M KNO3 respectively. The other equations (Freundlich, Tempkin and Sposito) were found to describe better the Zn sorption data in the presence of 10−2 M KNO3 and with less success in the presence of 10−3 M KNO3. At constant Zn initial concentration, as pH increased and molarity of electrolite decreased there was a decrease in the amount of Mg, Ca, Mn, and Cu released in a result of Zn sorption by kaolinite. When the initial concentration of Zn increases, at different pH values from 4.0 to 8.0 with constant KNO3 concentration (10−3 M), there is an overall increase in ion concentration (Mg, Ca, Mn, and Cu). At 10−2 M KNO3 and with different initial Zn concentrations and pH values as described before, the following were observed. Increase of Cu release at pH 5.5 to 6.5, decrease at pH 4.0 and 7.0 and no change at pH 8.0. Increase of Mn release at pH 4.0 to 6.0 and 8.0 decrease at 6.5 and no release at pH 7.0. Increase of Ca release at pH 4.0 to 6.5 and 8.0 and decrease at pH 7.0. Decrease of Mg release at all studied pH values. These observations should probably be taken into account when availability of these ions to plants is studied.