The effect of mechanochemical treatments on clay minerals and the mechanochemical adsorption of organic materials onto clay minerals

The present paper reviews investigations on the mechanochemical reactions occurring during the grinding of kaolinite and the mechanochemical adsorption of polar organic compounds by expanding and nonexpanding clay minerals, carried out in our laboratory by IR spectroscopy, supplemented by XRD and TG-DTA techniques. Kaolinite was ground in the absence and presence of diluents (alkali halides) and IR spectra were recorded after different grinding periods. The mechanochemical reactions can be classified into four groups, diffusion of atoms (mainly protons, "prototropy"), delamination, layer breakdown, and adsorption of atmospheric water by the amorphous product. In the mechanochemical adsorption study of phenol and dichlorophenol by smectites (montmorillonite, beidellite, saponite, and Laponite), the mineral was ground with excess phenol. Spectra of ground phenol-smectite mixtures were recorded in KBr disks, after leaving the disks for 3 days in a vacuum furnace at 115°C for the evolution of the excess phenol. In most cases, the first 5 min of grinding led to an increase in the adsorption of phenol. An additional 5 min of grinding resulted in a decrease of the phenol adsorption. In the mechanochemical adsorption study of stearic acid by nonexpanding clay minerals (sepiolite, playgorskite, talc, pyrophyllite, and allophane), the mineral was treated with molten acid. Disks were prepared with NaCl, KCl, and CsCl. Each disk was crushed, reground, and repressed an additional four times. Grinding the products converted some of the adsorbed acid into the stearate anion.