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Environmental and Engineering Geoscience

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Some Practical Observations on the Use of Bentonite

¹ Biomin, Inc., P.O. Box 20028, Ferndale, MI 48220

Key Words: Bentonite • Swelling • Organoclay • Contaminants • Hydrated Radius • Water

The first 20% of the full text of this article appears below.

	INTRODUCTION

 
There are two types of bentonite: (1) the sodium, high-swelling type, derived from volcanic ash that was deposited in marine environments; and (2) the calcium, low-swelling type, which evolved from volcanic ash deposited in freshwater environments. Bentonites are used in industry as drilling muds, foundry sand binders, animal feed binders, binders and carriers for pesticides and drugs, binders for iron ore pelletizing (taconite), landfill and pond liners, thickeners for slurry trenches, and flocculents. There is an extensive body of literature available related to the swelling properties of montmorillonite extending back to 1954 (Norrish, 1954; Odom and Low, 1978). Practical observations, however, are seldom included, probably because those who are active in that field do not publish their observations.

A high-quality industrial bentonite is very pure, typically consisting of 95 percent montmorillonite, plus 5 percent shale, feldspar, goethite, gypsum, celestite, and/or cristobalite. It has a cation ion exchange capacity of 70–90 meq/100 g. An early article by Alther (1986) showed that the ratio of sodium to calcium and magnesium on the surface of a clay platelet determines the quality of a bentonite as a drilling mud, landfill liner, and other applications that require a large swelling capacity (i.e., maximum dispersion of the clay platelets upon wetting [a high level of purity is assumed]). These bentonites are usually yellow in color and rich in oxidized iron. They occur in seams near the ground surface where percolating groundwater delivers dissolved oxygen, which oxidizes the iron. By contrast, specifications for bentonites for steel foundries (Steel Foundries Society of America, 1965) require a gray colored bentonite with a high methylene blue cation exchange capacity (commonly 100 meq/g or more), a high-swelling capacity (17 mL/g of clay or more), high liquid limits (600 or more), very low filter loss, and relatively low Fann . . . [Full Text of this Article]