Flocculation Value and Gel Structure of Sodium/Calcium Montmorillonite and Illite Suspensions1
- J. D. Oster,
- I. Shainberg and
- J. D. Wood2
The flocculation value, the minimum salt concentration which causes flocculation within 24 hours, was determined for mixtures of Na- and Ca-montmorillonite (API-25) and Fithian illite (API-35). The equivalent fraction of exchangeable Na+, ENa, varied from 0 to 1. We prepared Na/Ca clay suspensions by adding the appropriate amounts of homoionic dry clays to a series of Na/Ca chloride solutions (0.2 to 80 molc m−8; 0.2 to 80 meq liter−1) with appropriate sodium adsorption ratio and shaking the mixture for 1 hour. The flocculation value of Ca-montmorillonite (0.25 molo m−3) increased rapidly with small amounts of exchangeable Na+: the flocculation value for an ENa of 0, 0.2, 0.4, and 1 was 0.25, 6, 9, and 12 molc m−3, respectively. The flocculation values for Ca- and Na-illite were 0.25 and 55 molo m−3, respectively, and increased linearly with ENa. Van der Waals attraction forces are mainly responsible for flocculation of Ca-montmorillonite and illite systems. Edge-to-face attraction is dominant in flocculating Na-montmorillonite. The large effect of small amounts of exchangeable Na+ in montmorillonite suspensions results from demixing of exchangeable ions whereby Na+ is the predominant cation on the external surfaces when ENa < 0.20.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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