2006•Soil and Sediment Contamination An International JournalRequires access
Clay Mineralogy of Central Victorian (Creswick) Soils: Clay Mineral Contents as a Possible Tool of Environmental Indicator
Khawar Sultan
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Abstract
The clay mineralogy and heavy metal/metalloid (As, Pb and Cu) contents of soils developed on the various rock units in a central highlands environment in Victoria (Creswick, Australia) have been investigated. The clay minerals identified showed an order of abundance as: kaolinite ≫ illite > smectite > mixed-layer (ML) ≈ vermiculite. The soil clay mineralogy did not change systematically with depth (0∼ 10, 10∼ 20 and 20∼ 30 cm) and showed large variations spatially. The high proportion of kaolinite was probably due to the removal of 2:1 phyllosilicates by the formation of 1:1 kaolinite through weathering, which also reduced the cation exchange capacity (CEC) and electrical conductivity (EC, soil: water ratio of 1:5) of soils by aging. Soils were classified as silty loam to loam with a low clay size (≤ 2μ m) fraction. The soils were acidic to moderately acidic with pH ranging from 4.5 to 7.1, averaging 5.7. Concentrations of As, Pb, and Cu (average values 24.3, 16.7 and 11.0 mg/kg, respectively) did not show an association with the clay mineral contents except vermiculite. The occurrence of smectite and mixed-layer clay contents, although far lower than kaolinite and illite, contributed significantly to CEC of soils. The study area was affected by mining, high natural background As values dominate the area and the role of clay minerals in fixation of metalloid/metals was found to be less significant. Low organic matter content (average ∼ 6.5%), low soil surface area (average ∼ 1.0 m2/g) and the high proportion of kaolinite mineral content result in a limited ability to fix heavy metals. The role of Fe oxides appeared to be a key influence in the fixation of As and other potentially toxic metals, rather than the clay minerals, and therefore requires further research. This work highlighted the importance of the determination of types and amounts of clay minerals of natural soils in environmental management.