THE HEAVY METALS IMMOBILIZATION IN POLLUTED SOILS FROM ROMANIA BY THE NATURAL ZEOLITES USE

The effect of heavy metals' immobilization with natural zeolitic tuffs and with organo-zeolitic material in soils polluted by Pb, Zn, Cu and Cd affected by the nonferrous metallurgy industry it has been studied in an experiment with Lolium perenne in laboratory and greenhouse conditions. Surface soil samples (0-20 cm) of 100 kg each (as global sample) from four different types of soils in vicinity of Pb and Cu smelters in Baia Mare locality and Cu smelter in Zlatna locality were used in the experiment. The concentration of Pb, Zn, Cu and Cd in those four types of soils: (eutricambosol, BMR-O and luvosol, BMC-O in Baia Mare; dystricambosol, ZT-O and anthrosol-Z2T-O, in Zlatna) exceeds Romanian references limits. Within the experiment, from each global sample there have been realized two experimental options: first (I) treated experimental option of soil (polluted soil + zeolitic tuffs); second (II) treated experimental option of soil (polluted soil + organo-zeolitic material) in proportion of 82%-18%. Each experimental option of treatment was replicated three times. The mixtures of the two experimental options have been used to test the amendments effect for the plants growing, in comparison to the untreated soil (original soil). The experiment for the treatment of polluted soils, with natural zeolitic tuffs and with organo-zeolitic material was realized in pots of 6.5 kg, using as plant Lolium perenne. The experiment took place on a period of one year and six months. Natural zeolitic tuff was added as crushed with 2 mm in size, and also as an organo-zeolitic material (crushed tuff mixed with poultry manure). The zeolites used for the treatment of soils are characterized by high cation exchange capacity, high content of clinoptilolite>90%. Exchanged cations are represented by (Ca +/- Mg, K and Na). The organo-zeolitic material determined the increase of pH from the untreated soil to the first and second treated experimental option of soil in all four types of soil used in the experiment. The growth of humus content is significant in the second treated experimental option of soil by passing from high content class to very high content over 5% for ZT-II sample and from low content class to moderate content for BMR-II and Z2T-II, with mentaining of the high content class, over 4%, for BMC-II sample. Both amendments have increased the cation exchange capacity of 2.54 times compared with the untreated soil. From the analysis of heavy metals concentrations from plants in three harvests, it has been demonstrated that Pb and Cd have reduced their contents in the treatment experimental options, which is associated with a bigger affinity of the zeolites structure for these two metals. In comparison with the aerial part of the plants, the roots extracted higher concentration of Pb and Cd. The concentration of heavy metal in roots is higher in the untreated soil than in both treated soil experimental options. Instead, Cu and Zn present higher contents in the aerial part, which would be a proof of selective accumulation of these metals, being used in the process of growing. The second experimental option of treatment for all soils ensured the conditions for the biomass growing and the roots development. In the EDX spectrum of the zeolitic tuff from the second treated experimental option of soil, there were obtained distinct peaks for Pb, Cu and Zn in the appropriate zones of Na, Ca and K peaks. The X-ray diffraction spectrum obtained on the zeolitic tuffs particles from the second treated soil experimental option showed the structural parameters change of the clinoptilolite. The reticular distance (d) from 8.9447 of the initial zeolitic tuff sample to 9.0916 of the zeolitic tuff used in the second treated experimental option of soil (BMR-II sample) demonstrated that the clinoptilolite cations were changed by Pb. These results can be considered a solution to reduce heavy metal uptake in plants due to the amendments based on the natural zeolites.