The Role of Clay Minerals in Activating and Neutralizing Reactions

3 THE ROLE OF CLAY MINERALS IN ACTIVATING AND NEUTRALIZING REACTIONS 

For a substance to act as an activating agent, it must react with natural substances to produce one or more soluble substances that increase the cation and anion contents of water. For example, zinc sulphide is an activating agent as it produces highly soluble zinc sulphate which increases Zn into water. But the clay minerals rarely act as activating agents in nature, as explained below. 

As shown in Table 1.4 (Part I, Chapter 1), clay minerals are among the most stable minerals in the condition prevailing at the Earth s smface. Therefore they are not likely to react with water or atmospheric gases to produce other substances. Moreover, they are insoluble in water (though may create a colloid solution in water for their extremely fine grainsize), thus incapable of changing the water quality. One clay mineral may be transformed to another 

Leachates form by the interaction of rainwater with the waste materials of mine or industrial waste dumps. The constituents of the leachates depend on the compositions of the waste materials in the waste dumps, and some of them may be potential pollutants or contaminants of water. When the leachate flows over the ground surface, it passes through the soil and some of the dissolved substances present in it are removed by the clay minerals present in the soil. Thus fewer amounts of pollutants and contaminants reach the smface water bodies. Therefore the surface water bodies distant from the waste dump are generally less polluted or contaminated than those that are close to the waste dump. 

Similarly, when a part of leachate percolating downward through the vadose zone passes through the clay-rich subsurface layers, the clay minerals remove a part of dissolved substances from it, preventing or decreasing the pollution or contamination of ground water. 

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