Heavy Metals' Structural And Potential Risks In Lead Zinc Ore Tailings

The structure of Pb, Zn, Cu and Cd in lead zinc are tailing soils in Yongzhou, Hunan. is analyzed by the preferred BCR sequential extraction procedure. In the first study, EDTA, HNO3 and CaCl2 were used as extractants to remove Pb, Zn and Cu from tailing soils. The content and proportion of heavy metals of the mine are measured. Meanwhile, the ecological risks are evaluated with the help of Lars Hakanson's potential ecological risk exponential method. Analysis shows that the content of heavy metals is very high, going to such an extent as to cause serious pollution. The metals are listed here in order of ponderance: Cd>Pb>Cu>Zn. On the other hand, it is very possible that the heavy metals may combine together as compounds or cling to the crystal form of clay. Since the form of soluble acid and free metals are very little, it is no easy job for metal eluting nor restoration of plants. Yet it is possible to take out those heavy metals adopting the chemical extraction technology. DTPA and EDTA, indicated by a research, both have iterative value and strong conformity effect. So they are effective filters to restore the polluted soil. Here,on the base of precious studies, the redistributions of Pb, Zn and Cu were determined using the sequential extraction procedure of the optimized European Community Burean of Reference (BCR) before and after extraction. The results indicated that EDTA was effective extracting agents, Percentage extractabilities of metal followed the sequence of Cd > Zn > Cu > Pb. The four fractions of metal (Acid dissolution condition, hard - manganese oxide compound union condition, sulfide and organic synthesis condition and residual condition)could be extracted by EDTA.Basing on the research ago, EDTA got from the above experiments was used as the best extractant to perform experiments on soil columns on the tailing soil of Yong zhou lead cupper mine,further study the change rule of EDTA extraction efficiency with the different depths of soil columns and Migration transformation characteristic of fractions of metal before and after extraction. The extraction efficiency of EDTA on the acid-extractable fraction was significant in shallow soil column, And the acid-extractable fractions were more easily desorption by soil particles with the depth of the soil columns increased., while in deeper soil column, a descend of the extraction efficiency on reduced, oxidizable and residual fractions was abtained. After extraction ,with the depth of the soil columns increased,the extraction efficiency of all fractions of metal dropped.There are three main causes:â‘ With the depth of the soil columns increased,the consistency of EDTA reduced,the extraction efficiency reduced with it,too.â‘¡desorption by soil particles with the depth of the soil columns increased.,tiny soil particles are easily to desorptIon condition and chela gathering condition (Me-EDTA) metal,so the acid-extractable fraction metals consistency increased considerably with the increase of consistency.â‘¢Soil permeability not too good, the water power function is not big, the extract fluid total quantity is not big, causes the extract speed to be slower, is left by the extract the metal to have the sufficient time again by the soil granule adsorption.