| Rare earth is an important strategic resource for transforming traditional industries and developing high-tech industries.It is widely used in the defense industry and high-tech fields.Its mineral types can be divided into weathering and mineral types.Ion-type rare earths are present in the mineral environment in the ionic phase,so the mining method is ion exchange leaching.At the same time,the heavy metal ions in the ore body environment are also activated by ion exchange,and migrate to the water body and soil environment,together with the ion-type rare earth mining and processing,a large amount of waste containing heavy metals will be produced,causing serious heavy metals in the mine and its surrounding environment(soil,water).This subject takes Longnan Zudong mining area in Ganzhou as the research object,and scientifically selected research areas,including rare earth mine production area,tailings area,surrounding residential living area and farmland,with a total of 66 research sample sites.Firstly,the current situation of heavy metal pollution in the sample area was investigated,and the source of heavy metals was analyzed.At the same time,the status of heavy metal pollution and potential ecological risk were evaluated.Secondly,the Pb,which is seriously polluted in the sample area,is taken as the research object to explore the regularity of its morphological distribution with time under natural conditions when water-soluble state enters the soil environment.Finally,the effects of the concentration of nitride,rare earth ions and heavy metals on the transformation/aging process of Pb were investigated under the action of ammonium sulfate and acid rain.Mainly draw the following main research conclusions:(1)Through field investigation and sampling in the research area,the content of heavy metals was surveyed.The sources of heavy metals were analyzed by correlation analysis,principal component analysis and spatial analysis.At the same time,the pollution degree and potential ecological hazards of heavy metals in the research area were evaluated.The results showed that: The average contents of Cd,Hg,As,Pb,Zn and Tl in the soil of the research area were 0.27,1,32.64,135.91,113.19 and 2.34 mg/kg,respectively,which were higher than the background values of the soil environment in Jiangxi Province,showing a high degree of accumulation characteristics and pollution status.Referring to the national secondary standards,the over-standard rates of Cd,Hg,As,Pb and Tl in Farmland Soils in the study area were 15%,97.83,30.40,71.7% and 100% respectively,which seriously threatened human health.according to the national secondary standard,13.64% of the research samples belong to the warning level,42.42% belong to mild pollution,12.12% belong to moderate pollution,and 31.82% belong to heavy pollution;Based on the background value of soil environment,the proportions of light pollution,moderate pollution and heavy pollution were 1.52%,28.79% and 69.7%,respectively.The comprehensive potential ecological hazard coefficient(RI)shows that the average potential ecological risk coefficient of five heavy metals in the research area is 634.50,and the heavy metal pollution in the soil environment is at a strong ecological hazard level.(2)Through laboratory incubation experiments,water-soluble heavy metals were added to farmland soils to explore the transformation process of exogenous heavy metals into soil environment,and the dynamics model was used to fit it.The results showed that: The aging process in the short-term(60d) is mainly reflected in the conversion of mild acid-soluble fraction to oxidisable fraction.At the initial stage of culture(10d),the mild acid-soluble fraction was rapidly converted into reducible fraction,and then the conversion rate gradually decreased,and finally it became balanced.The Elovich equation best fits the short-term aging process of heavy metals in the soil environment,which indicates that this process is a heterogeneous dispersion process.There are mainly mechanisms such as surface aggregation,precipitation,diffusion and organic matter encapsulation,but its dominant position is not yet clear.(3)Response Surface Methodology(RSM) was used to investigate the effects of different concentrations of ammonium sulfate,yttrium and lead on soil environment and aging degree of lead.The results showed that: Under the interaction of ammonium sulfate,yttrium and lead,the soil environmental pH value is inversely proportional to the content of ammonium sulfate,directly proportional to the content of yttrium and inversely proportional to the content of lead in a certain content range.Eh is inversely proportional to the content of ammonium sulfate,inversely proportional to the content of strontium,and proportional to the content of lead.Under the interaction of ammonium sulfate and yttrium,the aging degree of lead is proportional to the content of yttrium,and decreases first and then increases with the increase of the content of ammonium sulfate;under the interaction of ammonium sulfate and lead,the aging degree of lead increases with the increase of its content,while ammonium ion has little effect on it;under the interaction of yttrium and lead,the aging degree of lead increases slightly with the increase of yttrium content.(4)Response surface methodology(RSM) was used to investigate the effect of ammonium sulfate,yttrium and lead on lead activation.The results showed that: With ammonium sulfate as activator,under the interaction of ammonium sulfate,yttrium and lead,the activation degree of lead is directly proportional to the content of ammonium sulfate,inversely proportional to the content of yttrium and inversely proportional to the content of lead;with acid rain as activator,under the interaction of ammonium sulfate,yttrium and lead,within a certain content range,the activation degree of lead is directly proportional to the content of ammonium sulfate,inversely proportional to the content of yttrium,and inversely proportional to the content of lead.The activation degree of lead is inversely proportional to yttrium and lead under the interaction of yttrium and lead. |
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