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Factors Affecting the Ratio of Cation Exchange Capacity to Clay Content in Lignite Overburden

Department of Soil and Crop Sciences, Texas A&M University, College Station, TX 77843

View larger version (16K): [in a new window]   Fig. 1. Distribution of cation exchange capacity (CEC) and percent clay values reported by a commercial laboratory for 50 overburden samples selected for general study.

View larger version (16K): [in a new window]   Fig. 2. Comparison of percent organic C determined by a commercial laboratory (organic Cc) and percent organic C determined in the present study by difference in total C and inorganic C.

View larger version (19K): [in a new window]   Fig. 3. Comparison of percent clay determined by a commercial laboratory (clayc) and percent clay determined after intensive dispersion.

View larger version (17K): [in a new window]   Fig. 4. Estimated pH-dependent charge of overburden clay and the organic fraction.

View larger version (16K): [in a new window]   Fig. 5. The relationship between the estimated cation exchange capacity (CEC) of the clay fraction after accounting for CEC due to organic C and percent clay following intensive dispersion.

View larger version (26K): [in a new window]   Fig. 6. X-ray tracing of the fine (<0.2 µm) and coarse (0.2–2.0 µm) clay fractions from a sample dominated by smectitic clay.

View larger version (28K): [in a new window]   Fig. 7. X-ray tracing of the fine (<0.2 µm) and coarse (0.2–2.0 µm) clay fractions from a sample dominated by kaolinitic clay.

View larger version (140K): [in a new window]   Fig. 8. Scanning electron micrographs of shale fragments from the silt fraction of high cation exchange capacity (CEC) to percent clay samples of lignite overburden. (a) Shale fragment following overnight shaking in sodium hexametaphosphate. (b) Shale fragment following overnight shaking in sodium hexametaphosphate. (c) Shale fragment following destruction of CaCO3, organic C, Fe oxides, sonication, and shaking overnight in sodium hexametaphosphate. (d) Shale fragment following destruction of CaCO3, organic C, Fe oxides, sonication, and shaking overnight in sodium hexametaphosphate.