Central Soil Salinity Research Institute, Regional Research Station, Bharuch, Gujarat, 392012
1Present address: Central Soil Salinity Research Institute, RRS, 21/467, ICCMRT Building, Indira Nagar, Lucknow, Uttar Pradesh, 226016
The effect of electrolyte concentration, sodium adsorption ratio, (Ca:Mg) ratio on flocculation-dispersion behaviour of some swelling clays was investigated. The soil clay fractions were extracted from four different soils, viz. Sodic Haplusterts, Sodic Natraquerts and Aquic Salusterts collected from Gujarat and Typic Haplusterts collected from Maharashtra. The clays were made homoionic by saturating them with 1 M NaCl and CaCl2, respectively. The critical coagulation concentrations (CCC) were investigated with four levels of SAR (10, 20, 40 and 60) and two levels of (Ca:Mg) ratios (1:1 and 1:8). The electrolyte concentration of equilibrating solutions ranged from 5 to 60 meq L·1. The flocculation rates of different clay suspensions were determined by measuring the height of the gel and that of the clear solution at 24 h of shaking the suspension. The CCC values increased with increasing SAR and decreasing (Ca:Mg) ratio. Even though Ambheta and Devaliya clay had the same levels of montmorillonite, presence of higher amount of illite in Ambheta clay resulted in a higher CCC value. The CCC values of the clays containing greater percentage of montmorillonite and lower kaolinite per cent exhibited greater incremental change in CCC values in the lower SAR range. Whereas, clays containing higher per cent kaolinite and illite, the greater incremental changes in CCC values were observed at higher SAR. The effect of Mg in increasing the CCC values was more pronounced in the clays with higher illite contents. The relative gel volume of the clay suspension increased with the increase in clay content, SAR and (Mg:Ca) ratio.
Critical coagulation concentration, settling rate, swelling clay, clay minerals, SAR, Ca:Mg ratio
