Study On The Release Regulation Of Heavy Metal And Phase Transformation Mechanism In A Typical Lead-zinc Mining Waste Rock

During the mining of non-ferrous metal mineral resources,the stripped surrounding rock and gangue are often piled up and discarded in the open-air waste rock pile.After the weathering and oxidation process,the toxic heavy metal elements in them will be activated and released,and they will migrate and transform,causing a series of environmental pollution problems.Aiming at the unclear influence mechanism of waste rock mineral composition and microbial action on the oxidation and release of heavy metals,in this study,a lead and zinc mining site in Jiangxi was selected as a typical research object.First,through continuous chemical extraction and high-throughput sequencing,the distribution characteristics of heavy metal chemical forms and microbial communities in the waste rock dump profile of the site and their relationship with important physical and chemical properties of the profile were studied.Using sequencing batch leaching experiment and high accuracy spectrum characterization,explored the release regulation of arsenic（As）and lead（Pb）from waste rock and their correlation with the occurrence state of heavy metals were proved.reveals the As,Pb mineral phase transformation mechanism of typical sulfide ore.The conclusion is as follows:（1）Toxic heavy metals are mainly concentrated in the upper section（2～30 m）,and the main heavy metal elements exceeding the standard are As,cadmium（Cd）,and Pb.As mainly exists in the residual fraction（13～78%）,Cd mainly exists in the carbonate-bond fraction（22～100%）,and Pb mainly exists in the Fe-Mn-bond fraction（49～74%）.The flow coefficient of heavy metals was significantly correlated with the redox potential（Eh）,electrical conductivity（EC）,clay content,cation exchange capacity（CEC）and total amount of heavy metals.（2）The waste rock heap profile could be divided into eight microbial communities with great differences（P<0.001）.Proteobacteria,Acidobacteria and Firmicutes were the main components of the microbial community in the whole section.The relative abundance of genus was highly correlated with pH,CEC,Eh,SOM and bioavailability of heavy metals.Proteobacteria are correlated with the morphology of As,Cd,Cr,Cu,Ni,Pb and Zn.Tenericutes had positive correlation with Cd and Pb morphology.Gemmatimonadetes were positively correlated with the immovable components of Cr,Cu and Ni.The morphology of Cr and Ni was correlated with Chlamydiae.（3）The main heavy metal pollutants in waste rock accumulated in the site are As and Pb.According to the analysis of related characterization,it is revealed that the release of As and Pb is related to the composition of sulfide ore in waste rock.As and Pb in sulfide ore in waste rock are easier to precipitate than those in silicate and aluminosilicate minerals.Under acidic conditions,As and Pb in the waste rock are easy to dissolve and precipitate with the dissolution of the sulfide ore.Under alkaline condition,As exists in anion form,the release amount of As is higher.（4）Arsenopyrite in waste rock generates realgar,dioecious,sulfur and jarosite in turn in the process of oxidation dissolution,and these products can reduce the oxidation dissolution.When galena exists in waste rock,Pb²⁺released from galena combines with SO₄^2-in the reaction system to form lead sulfate precipitation,which forms passivation film on the surface of arsenopyrite to delay its oxidation dissolution rate.The oxidation of galena is promoted by Fe（Ⅲ）from arsenopyrite.