The colloid and surface chemistry of clays in natural waters

The colloid and surface chemistry of clays is discussed based on recent work of the authors. The aim is to test the predictability of the role and fate of suspended matter in natural waters, transforming a reductionistic approach into a holistic picture. Most of the information is based on model substances and model clay minerals, for which electrokinetic properties, ion exchange capacities, and enthalpies of wetting were measured. It has been shown that mimicking the disintegration of particles, accomplished by milling, new positively charged surfaces can be created. Beidellite, a model smectite mineral, is the prevailing type of clay minerals by its large specific surface area, large ammonia saturation indexes, and high specific enthalpies of wetting, however with little contribution to new amphoteric surfaces as a result of milling. In ripidolite, a chlorite, all these values are much lower, however the creation of amphoteric surfaces through milling is strongly expressed. Indeed, ripidolite is a unique example of clays that can exhibit positively charged surfaces. Adsorption of fulvic acid, a widespread detrital organic, obscures the differences by producing commonly observed negatively charged surfaces of natural suspended matter and sediments