Study On Environmental Characteristics Of Soil Heavy Metal Speciation In Duolong Mine Concentration Area,Tibet

The Duolong deposit is the first world-class super-large copper deposit found in China in recent years.The proven copper resources reach 20 million tons,but it still has great prospecting potential,which has been designated as the strategic reserve base of mineral resources by the state.At present,a large number of researchers have carried out work on the Duolong ore concentration area,but most of the previous work has tended to geological mineralization and prospecting,environmental work is less,and the existing environmental research is less involved in soil heavy metal speciation.In this paper,we analyzed the speciation of soil heavy metals by means of Tessier seven-step method,and studed the speciation characteristics,preliminarily discussed the migration and release rules of heavy metals in the mining area,and evaluated its ecological risk,so as to provide reference for the green exploitation of the deposit in the future.The main insights are as follows:(1)The Tessier seven-step method divided the soil heavy metal speciation into seven kinds,including water-soluble state,ion-exchange state,carbonate state,humic acid state,iron and manganese oxidation state,strong organic state and residue state.The water-soluble state,ion-exchange state and carbonate state are relatively unstable.In the improved BCR method,they are also called acid-soluble state,and the residue state is very stable.In Duolong ore concentration area,Cu,Cd and Hg elements have a high proportion of acid-soluble state,which poses a certain ecological risk.The remaining elements mainly exist in the form of residue,which is very stable.At the same time,different forms of Cu,Cd and Hg also have good correlations,and are prone to mutual transformation under certain conditions,with great potential environmental hazards.(2)The Duolong deposit is mainly of porphyry type and epithermal type,the examples are the Duobuza and Rongna deposit.A large number of oxidized ores are distributed on the surface of the mining area.Among them,the oxidized ores on Duobuza mining area are formed by oxidation of exposed minerals.The migration sequence of heavy metals in the mining area is as follows: primary ore ? surfacesoil ? river ? river sediment.The surface oxidized ore in Rongna mining area is indirectly formed by acid spring,and its origin is closely related to the shallow low-temperature hydrothermal deposit.The migration sequence of heavy metals in the mining area is as follows: primary ore ? spring ? surface soil;Primary ore ?spring ? Rongna River ?river sediment.(3)The results of comprehensive fuzzy evaluation showed that all 7 heavy metal elements in the soil of Dulong mining area have certain ecological risk,among which Cu?Pb?Zn?As?Cr element risk grade are II(low-medium)and Cd?Hg element risk grade are III(medium),and the ecological risk of Cd element is higher than Hg element.Therefore,Cd ? Hg element need to pay more attention,beware of their ecological impact.