RELATIONS BETWEEN SUSPENSION PH AND ZINC SOLUBILITY IN ACID AND CALCAREOUS SOLLS

Abstract

Four acid soils from Hawaii and three calcareous soils from Pakistan were used to study the effect of suspension pH on Zn solubility. The soils, at different pH values, were equilibrated with added Zn for 6 days at 25°C. After equilibration, Zn concentrations in the supernatants were determined by atomic absorption spectrophotometry. The effect of suspension pH was quantitatively evaluated by plotting the negative log Zn in solution (pZn) against pH. A linear relationship was observed up to pH 7.0 for acid soils. As the system passed neutrality, a general increase was noted in the amounts of Zn in solutions for the soils high in organic matter. The increase in Zn solubility over the alkaline range was assumed to be due to dispersion of organic matter, which either released complexed Zn or provided chelating agents for added Zn and reduced adsorption or precipitation.For the calcareous soils, the relationship between Zn solubility and pH was nonlinear. It was assumed that at higher pH, Zn in solutions precipitated as Zn(OH)2, ZnCO3, or Ca-zincate. There was no indication of colloidal peptization or formation of soluble zincate ions with NaOH. Four acid soils from Hawaii and three calcareous soils from Pakistan were used to study the effect of suspension pH on Zn solubility. The soils, at different pH values, were equilibrated with added Zn for 6 days at 25°C. After equilibration, Zn concentrations in the supernatants were determined by atomic absorption spectrophotometry. The effect of suspension pH was quantitatively evaluated by plotting the negative log Zn in solution (pZn) against pH. A linear relationship was observed up to pH 7.0 for acid soils. As the system passed neutrality, a general increase was noted in the amounts of Zn in solutions for the soils high in organic matter. The increase in Zn solubility over the alkaline range was assumed to be due to dispersion of organic matter, which either released complexed Zn or provided chelating agents for added Zn and reduced adsorption or precipitation. For the calcareous soils, the relationship between Zn solubility and pH was nonlinear. It was assumed that at higher pH, Zn in solutions precipitated as Zn(OH)2, ZnCO3, or Ca-zincate. There was no indication of colloidal peptization or formation of soluble zincate ions with NaOH. © Williams & Wilkins 1977. All Rights Reserved.