Kaolinite alkaline leaching

Most kaolinite is formed by the acid leaching of alkaline rocks, primarily the feldspars and micas however, practically any silicate rock or mineral will alter to kaolinite if leaching conditions are suitable for a sufficiently long period of time. Kaolinites that are formed by weathering and remain in place are called residual kaolinites. Those that are transported and sedimented are called sedimentary kaolinites... 

In the present study the behavior of some of the principal coal minerals was traced during alkaline leaching. This was accomplished by leaching several types of coal and by leaching individual minerals, which are commonly present in coal, with various alkalis. Different alkali concentrations and temperatures were employed. The solid reaction products were characterized by x-ray diffraction (XRD) and by dissolution in mineral acids. Results achieved with Illinois No. 6 coal are discussed, since they are representative, and the results of Individually leaching quartz, kaolinite, and iron pyrite... 

In a second set of experiments, -74 pm size kaolin particles were leached with hot alkaline solutions to study the conversion of kaolinite to various sodium hydroaluminosilicate compounds (Table III) under different leaching conditions. In each experiment, 15 g. of kaolin was leached with 120 ml. of alkaline solution. The solid reaction product was recovered by filtration, washed with water, dried in an oven at 95 C, and analyzed by XRD. Although this method of analysis identified the minerals present, it could provide only an approximate indication of the relative proportions of the various minerals present. The amount of quartz was particularly difficult to assess because the method of detection was very sensitive to this mineral. Therefore, the results are reported only in terms of major, minor, and trace quantities present in the product as indicated by XRD (Table IV). Because the small amount of titania in the kaolin was apparently not affected by even the most rigorous leaching conditions, the product always contained a trace of this material and no further mention seems necessary. 

Table III. Various Sodium Hydroaluminosilicates Produced in Leaching Kaolinite with Hot Alkaline Solutions...

The material source of the watershed fault zone is both from host rock and overlying siliceous rocks. The fault zone is an open system with strong chemical weathering, and alkaline condition. Calcium in limestone is leached, the cohesive force of host rock is reduced and formed smectite. It is easy for feldspar transforms to kaolinite under alkaline condition during faulting. Hence, more geochemistry needed to study in the future, to establish qualitative model between chemical compositions and strength of fault rocks. 

---