Detoxification of Heavy Metal Contaminated Soils

Abstract

The concentration of the heavy metals in the soils from the strong affected zones because of the mining and metallurgical industry, Baia Mare and Zlatna (Romania), is significant due to the high values of the contents and association of the four metals Pb, Cu, Zn, Cd. The efficacy of the natural zeolites in heavy metals immobilization from the studied soils was evaluated in experiments in which the plant growth was observed. Heavy metals contaminated soils have been treated with a mixture of organic substance and zeolites (organo - zeolitic material). Zeolitic tuffs were roll-crushed and ground in small grains with dimensions between 0.05 and 2.0 mm. Clinoptilolite is the predominant zeolite and appears as compact masses of tabular and prismatic micron - sized crystals that are evident in SEM images. In the mixture, the polluted soil represents 83% and the organo - zeolitic material represents 17%. The soils used in the experiment are excessive contaminated with Pb (40375- 1054ppm) in association with Zn (1175-490ppm), Cd (24.2-13.2ppm) and Cu (409.5-37.6ppm) in Baia Mare zone and with Cu (7000-360ppm) in association with Zn (3100-1900ppm), Cd (80-40ppm) and Pb (2000-50ppm) in Zlatna zone. The original soil and the treated soil have been planted with Lolium perenne. The growth of the plants has demonstrated that the soil treated with organo-zeolitic material allows the growth of vegetation much faster than the original soil. These results show that growth of the plants was possible because the organo-zeolitic material mixed with the soil provides the substances necessary for the plants to develop (ammonium, humus, potassium, calcium). At the same time, heavy metals that inhibit the plant development are blocked through the cationic exchange mechanism that makes them enter the zeolites structure and they no longer directly have access to the plant roots.