Detoxification of Soils, Polluted Jointly by Heavy Metals, Acid Wastes and Acid Precipitations

Some theoretical premises on detoxification of soils, acidified and contaminated by heavy metals from mining activities are subject of general discussion on the results obtained in Bulgaria. Presented results are obtained, both, by model pot experiments and field trials in some mining areas, contaminated mainly with copper and others including radioactive elements, cadmium and lead. The methods described are given briefly in their chemistry of treatments. They are restricted to: (1) Suppression the availability of contaminants to plants, based to the neutralization of exchangeable acidity of soil (liming ); (2) Capsulation of a polyvalent metal between the structural composites in an organic– mineral complex, i.e. liming and addition of an organic or/and mineral waste (peat, coal dust, wasted ferric hydroxide); (3) Microbial in situ detoxification based on a biochemical acidicy or slightly alkaline dissolution of the ore waste on the surface layer of soil and biochemical reductive precipitation of metal ions, transferred and located in a deeper soil horizon (B2). Each one of methods discussed, reveals its effectiveness, depending on the material used for detoxification, its dose, level of contamination, and the biology of tested plant. Liming as an independent action versus the toxic acidity of soil, promises to become enough for restoration of soils at moderate levels of heavy metal pollution. However, at higher pollution levels, liming must be done versus the total acidity of soil and by addition to soil other amendments also. The microbial treatment, compare to the traditional ones, outlines as a new highly effective approach, because of its opportunity to remove although a part of heavy metals from ploughed soil surfaces. It is a convenient method, particularly for soils, strongly polluted with ore wastes.