Dr. C. Crăciun’s research while affiliated with National Research and Development Institute for Soil Science, Agrochemistry and Environmental Protection and other places

Zlatna area is a high polluted zone with heavy metals due to industrial activity (extraction and processing of non-ferrous area). In spite of the fact that industrial activity was stoped for 2-3 years, the effect of pollution are still obvious. The aim of this paper is to make evident some aspects concerning the impact of pollution on the mineralogical composition of the clay fraction (below 2µ) from some soils belonging to dystric cambisol and luvisol type. From the chemical point of view, the effect of pollution is the acidifiation and depletion of bases, reflected by the decrease of values of indices which express soil reaction (pH) and soil exchange properties, especially in the surface horizon. From mineralogical point of view, the acidifiation determines a strong alteration of primary minerals (micas and feldspars) and just of secondary minerals (illite), evolution beeing towards hydroxy interlayered minerals (intergrade) and kaolinite. As result of this alteration the content of kaolinite increases, achiving a double content in the surface horizon of some polluted soils. Sometimes kaolinite becomes the dominant mineral in the clay fraction of some strong polluted soil.

The mineralogical investigation of the 33 profiles of vertisol from Romania indicated that there are two principal geographical zones with vertisols (West and South) which present some quantitative mineralogical differences at the colloidal level. In spite of the fact that in all investigated profiles, the quantitative mineralogical composition of the clay fraction (below 2μ) was the same, (smectite, illite and kaolinite) the vertisols from the western zone show a higher content of smectite (montmorillonite) and a lower content of illite in comparison with vertisols from southern zone. The correlations between some physical indices of soil and smectite quantity indicated that an increase of soil smectite content determines an increase of bulk density and compaction degree, concomitantly with a decrease of total porosity and air porosity. The established relationships between some chemical indices and mineralogical parameters indicated that cation exchange properties and reaction of these soils appear more closely related to the quality (mineralogical composition) than to the quantity of clay fraction. The empirical relationships established between physical and chemical indices of vertisols and mineralogical parameters suggest that in some cases, considered favorable, the clay mineral information could allow some predictions on the physical and chemical properties, in spite of the fact that such of predictions have a limited value from quantitative point of view.

The study by X-ray diffraction of clay below 2µm from 27soil profiles belonging to different soil types gave some useful information concerning the clay mineralogical composition and the influence of parent material on the clay quality. The identified clay minerals also distinct phases from soils of Banat area are illite, smectite, chlorite and kaolinite. With exception of luvosols in which all clay minerals are present, in other soil types illite, smectite and kaolinite were identified. The quantitative mineralogical differences between soil profiles referring to the contents of the clay minerals can be due to parent material and pedogenesis. The dominant clay minerals are illite and smectite (exception luvosols) their ratio (S/I) indicating a decrease trend to the profile surface. The most reduced of value of his ratio in the surface horizon could be related to natural (a stronger alterations of K-bearing minerals, preferential migration of the smectite) and artificial (K-fertilization) causes. The established positive relationship between the soil clay content on the side and the clay content of smectite, and smectite/illite ratio on the other side suggests that between a clay quantity and clay quality is a direct relation due to a textural influence of the parent material. The direct established relationship between the content of each clay mineral from the clay of the surface horizon and from the deep horizon considered as belonging to parent material indicates the mineralogical influence of the parent material on the clay mineralogy.