A Study on Soil Clay Minerals and the Distribution of Heavy Metals in Soils Derived from Black Shale and Black Slate in Dukpyoung Area

충북 괴산 덕평리 일대 흑색셰일 및 흑색점판암기원 토양의 점토광물 조성 및 중금속원소의 분산

Concentrations of several heavy metals in soils derived from black shale and slate have been reported to be higher than the average concentrations in non-polluted soils. This study describes and characterizes soil minerals, and investigates the distribution of heavy metals in soils, and then examines their relationship. Soils in the study area are mainly consist of guartz and feldspars with minor amount of kaolin, illite, vermiculite, chlorite and illite-vermiculite interstratified minerals. Mineral compositions are similar in mountain-, farmland-, and paddy-soils. The residual soils derived from sandy phyllites contain less illites than those from black shale and black slate. Heavy metals appear to be more concentrated in soils than in rocks. The concentrate ratios in soils to rocks ranges 1.1 times for Cr, 2 for Cu, 1.4 for Ni. The contour maps of Cd, Zn, Pb, Cu contents using 0.43N $HNO_3$-extraction imply that these elements are highly concentrated in the soils near the past uranium exploration region, coal seams, black slate beds and tailings than other parts of the study area. The proportions of the day in most soils are less than 10%. In spite of small proportions of the clay, the concentrations of heavy metals from clay fractions to the total concentrations are high: 1~2.4 times for Co, 1.4~2.5 for Cu, 1.2~2.6 for Ni, 1~5 for Pb, 1~2.7 for Zn and 1.6~1.8 for Cr and V. The contents of organic carbons in clay fractions are also 1.5~3.9 times higher than in silt and sand fractions. Cu, Pb and organic carbons show positive relationship in all size fractions. In the size-fractionated soil profile samples, the contents of heavy metals and organic carbons show analogous trends with depth. For the clay fractions of soil profile samples, the contents of heavy metals with depth have analogous trends to abundances of vermiculites, which have the high CEC in main clay minerals.