| With the continuous development of social economy,mining had brought about a series of environmental problems.Heavy metal pollution had great harm to the surrounding environment and human health.As an important source of heavy metal pollution,tailing pond release characteristics and migration rules of heavy metals had been widely studied.Due to the rich mineral resources in western China,the heavy metal pollution in the tailing pond was serious.Heavy metal pollution in tailing was mainly affected by wind erosion and water erosion.Although the precipitation in western China was low,the concentrated sudden rainstorm was significant,which can easily cause loss of heavy metal in tailing pond.Therefore,this paper choose Ningxia central a copper silver mine tailing as the research object,using indoor simulation experiment,using static extraction and dynamic leaching experiment method,tailing heavy metal dissolution characteristics and migration characteristics,the geological accumulation index method of tailing and soil heavy metal pollution level,using the potential ecological hazard index method of tailing and soil heavy metal potential ecological risk evaluation,finally through the risk assessment method of tailing and soil heavy metal ecological risk level evaluation,the main conclusions were as follows:(1)Through the indoor physical and chemical experiment to study the basic properties of tailing and soil,the results show that:① The study tailing and soil were sandy loam,coarse texture,alkaline,low nutrient level and high salt content of tailing.②Cu,Zn,As,Cd and Pb exceed the background value of heavy metal elements in Ningxia tailing,Cu,As and Cd were high,and more polluted;Zn,As and Pb were not exceeded,and the Cu and Cd was low.③Cu,Cd and Pb in tailing were mainly in carbonate binding forms,accounting for 75.99%,72.74%and 50.63%respectively.Zn was mainly found in carbonate and iron and manganese oxidation forms.As exists in the tailing in the exchange state and residue form,the other four heavy metals were mainly found in residue forms.(2)Based on descending meteorological characteristics in Ningxia,the static extraction and dry and wet alternating dynamic dissolution experiment results,the results show that the tailing of five heavy metals(Cu,Cd,As,Pb and Cd)the dissolution rules as follows:① different size as leaching concentration in the tailing,followed by Cu and Zn,the smallest leaching concentration of Pb and Cd.The leaching concentration of Cu elements in the coarse size(>0.25mm)and fine diameter(<0.10mm)was high,the concentration of Pb and Zn elements in the coarse size immersion solution was high,and the smaller the particle size,the higher the concentration of As and Cd,indicating the strongest leaching capacity of As.② Under the conditions of solid-liquid ratio 1:2.5,1:5 and 1:10,the concentration of 5 heavy metals was As>Cu>Zn>Pb>Cd,and the leaching concentration of 5 kinds of heavy metals was solid-liquid ratio 1:1:5:1.5>1:10,indicating that the greater the solid-liquid ratio,the higher the leaching concentration of heavy metals.③ Under the initial conditions of pH=5.5>8.5,the leaching concentration of five heavy metals was As>Cu>Zn>Pb>Cd,Cu under different pH conditions,Zn was less likely to leach under alkaline conditions,and As was easier to release from the tailing at pH=8.5,and the overall leaching amount of Pb and Cd elements was low.④The pH and conductivity values of tailing leach decreased with the increase of leaching,and the concentration of heavy metals in leach decreased first with the increase of leaching.The concentration of heavy metals in leach was As>Cu>Cn>Pb>Zn N>Cd,indicating that the level of heavy metal content in tailing affected the concentration of heavy metals in leaching,but did not play a decisive role.The cumulative release of heavy metals in tailing increased gradually with the number of leaching times,increasing Zn and Cd faster,indicating a large release rate.The release rate of five heavy metals,Cd>Zn>Pb>As>Cu,indicates strong Cd release capacity and high risk of leaching.(3)In Ningxia central rainfall data for the experimental parameters setting,using static extraction and dry and wet alternately dynamic leaching experiment method results show:① the tailing As leaching concentration,Cu elements in coarse size(>0.25mm)and fine diameter(<0.10mm)component leaching concentration was higher,Pb and Zn elements in the coarse diameter leaching liquid concentration was higher,the smaller the particle size As and Cd leaching,the higher the concentration was higher,the particle size of tailing heavy metal leaching influence was bigger.②Under the conditions of solid-liquid ratio 1:2.5,1:5 and 1:10,the concentration of 5 kinds of heavy metals was As>Cu>Zn>Pb>Cd,and the leaching concentration of 5 kinds of heavy metals was solid-liquid ratio 1:2.5>1:10.The greater the greater the solid-liquid ratio,the higher the leaching concentration of heavy metals.③Under the initial pH of the extract=5.5,7.0 and 8.5,the leaching concentrations of five heavy metals were As>Cu>Cd>Zn>Pb>Cd,the leaching concentration of Cu under different pH conditions was not different,and As was easier to be released from the tailing in the extract pH=8.5.④ The concentration of heavy metals in the tailing leaching liquid decreased with the increase of the number of leaching.The amount of heavy metal release of Zn and Cd was large,and the release rate was from large to small:Cd>Zn>Pb>As>Cu,and the maximum release capacity of Cd was the strongest.(4)The degree of pollution,potential ecological risk level and ecological risk of heavy metals in tailing,leaching and soil were evaluated.The single factor index evaluation results show that Cu,Zn,Cd and Pb in leaching solution and leaching solution do not exceed the Comprehensive Sewage Discharge Standard(Class Ⅰ)and Copper,nickel and cobalt industrial pollutant discharge standard,As and Cd exceed the Surface Water Environmental Quality Standard(Class)and Groundwater Environmental Quality Standard(Class),and the As exceeding rate was high.The excess rate of heavy metals in soil leaching liquid was lower than that of tailing leaching liquid,so the soil can adsorb heavy metals and reduce the risk of downward migration of heavy metals.The geological accumulation index evaluation results show that Cu in tailing before leaching was extremely pollution level,and all heavy metals in soil samples were no pollution level;Cu in tailing after leaching was still extremely strong pollution,and Cu and As in some soil samples become mild pollution level,indicating that tailing heavy metal pollution was serious,Cu and As were the main pollution elements,and leaching causes soil heavy metal pollution.The evaluation results of potential ecological hazard index show that Cu in tailing was a very high ecological risk,and the risk level of Cd decreases from high ecological risk to high ecological risk after leaching,As from high ecological risk to moderate ecological risk;soil heavy metals before and after leaching were slightly ecological risk,and the risk index of Cu,As and Pb in soil after leaching;the high ecological risk area was 0-30cm,and Cu was the key ecological risk factor of heavy metals in tailing,which can reduce the ecological risk level of heavy metals and increase the ecological risk of soil heavy metals.The coding results of ecological risk assessment showed that Cd,As,Cu and part of Pb in tailing were extremely high risk and Zn was high risk.Cd in soil was extremely high risk,some soil Cu was high risk,and Pb and Zn were low risk.Cd and Cu decreased to high risk in tailing after leaching,while As,Zn and Pb decreased to intermediate risk.Leaching will reduce the effective proportion of heavy metals in tailing and reduce their ecological risk. |
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