Gypsum Determination in Soils by Conversion to Water-Soluble Sodium Sulfate
1994
Berigari, M. S. | Al-Any, F. M. S.
Precise and accurate determination of gypsum in soils has been difficult by the wet-chemical methods, based on its solubility in water. In this work, 2-g samples of three Typic Gypsiorthids were washed once with 25-mL portions of 50% (v/v) ethanol to selectively remove nongypsic soluble sulfates. Soil gypsum was subsequently converted to CaCO₃(s) and Na₂SO₄ by ultrasonic dispersion of the samples twice with 25-mL increments of 0.5 M Na₂CO₃ solution. The SO²⁻₄ in the supernatant solution was centrifuge separated and analyzed by the standard gravimetric BaSO₄ (A) and turbidimetric (B) methods to obtain the gypsum content of the samples. The agreement between the data of Methods A and B was excellent where the best-fitted regression line coincided with the 1:1 line in a scattergram. Soil gypsum was also extracted with water, then determined by turbidimetric SO²⁻₄ (C) and the Bower-Huss conductometric (D) methods for comparison. Statistical analyses of the data showed higher values (P = 0.05) of gypsum in soils obtained by the proposed method than by water extraction even when the same method of SO²⁻₄ analysis was applied. The efficiency of the proposed method was 25 to 31 times greater than that achieved by water. The proposed method of gypsum extraction and its determination in soils from turbidimetric SO²⁻₄ analysis was applied. The efficiency of the proposed method was 25 to 31 times greater than that acheived by water. The proposed method of gypsum extraction and its determination in soils from turibidimetric SO²⁻₄ analysis is simple, rapid, and quite accurate for soil taxonomy, land reclamation, and other engineering purposes.
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