| A large number of abandoned tailings produced by mining in the long-term rainfall leaching effect,a large number of heavy metal leaching on the surrounding soil,water environment caused serious pollution.Guizhou Province is rich in heavy metal mineral resources(mercury ore,antimony ore,manganese ore,lead-zinc ore,etc.),and due to the waste tailings from mining,Guizhou Province as one of the provinces with the most serious heavy metal exceedances.Therefore,the study of leaching of heavy metals from tailings and their migration and transformation characteristics in soil plays a crucial role in the environmental management and remediation strategies of abandoned tailings ponds.In this study,the leaching characteristics of heavy metals in tailings and the migration and transformation characteristics of heavy metals in soil were investigated by field samples combined with tailings-soil leaching system simulation experiments,utilizing the tailings and surrounding soils of typical mercury(Hg),antimony(Sb)and manganese(Mn)tailings ponds in Guizhou.The main conclusions are as follows.(1)X-ray diffraction(XRD)characterization showed that the minerals in the Hg tailings were mainly quartz,illite,calcite and dolomite;the Sb tailings were mainly quartz,illite,gypsum and kaolinite;and the Mn tailings were mainly quartz,illite and calcite.Scanning electron microscopy energy spectroscopy(SEM-EDS)characterization showed that all three tailings contained eight heavy metals,including mercury(Hg),manganese(Mn),antimony(Sb),copper(Cu),lead(Pb),zinc(Zn),chromium(Cr),and nickel(Ni).The contents of heavy metals in the Hg tailings were in the order of Mn(205.40mg/kg)> Cr(102.78 mg/kg)> Zn(52.06 mg/kg)> Ni(51.54 mg/kg)> Sb(50.61mg/kg)> Pb(51.54 mg/kg)> Cu(28.66 mg/kg)> Hg(3.19 mg /kg).The contents of heavy metals in Sb tailings were in the order of Sb(81.46 mg/kg)> Mn(66.71mg/kg)> Zn(56.00 mg/kg)> Cr(51.09 mg/kg)> Ni(32.59 mg/kg)> Cu(25.97mg/kg)> Pb(25.57 mg/kg)> Hg(0.06 mg/ kg).The contents of heavy metals in Mn tailings were in the order of Mn(298.00 mg/kg)> Cr(192.34 mg/kg)> Zn(137.55mg/kg)> Ni(90.35 mg/kg)> Sb(27.86 mg/kg)> Cu(24.46 mg/kg)> Pb(3.71mg/kg)> Hg(0.04 mg /kg).(2)The soils around the Hg and Mn tailings ponds are weakly alkaline(p H 7.97 and 7.01,respectively)and the soils around the Sb tailings ponds are weakly acidic(p H 6.46).The average content pattern of heavy metals in soils around the Hg tailings pond was Mn(221.26 mg/kg)> Pb(194.49 mg/kg)> Cu(126.81 mg/kg)> Cr(123.75mg/kg)> Zn(123.53 mg/kg)> Ni(49.73 mg/kg)> Sb(20.34 mg/kg)>Hg(3.53mg/kg),where Hg,Sb,Cu,Pb,Zn,Cr,and Ni exceeded the background values of Guizhou soil by 32.1,12.6,4.0,5.5,1.2,1.3,and 1.3 times,respectively.The average content pattern of heavy metals in soils around the Sb tailings pond was Pb(221.56mg/kg)> Mn(159.49 mg/kg)> Cr(123.33 mg/kg)> Cu(115.38 mg/kg)> Zn(69.17mg/kg)> Sb(97.59 mg/kg)> Ni(32.31 mg/kg)> Hg(0.26 mg/kg),where Hg,Sb,Cu,Pb and Cr exceeded the background values of Guizhou soil by 2.4,60.2,3.6,6.3 and1.3 times,respectively.The average content pattern of heavy metals in soils around the Mn tailings pond was Mn(321.76 mg/kg)> Pb(192.76 mg/kg)> Cr(149.59mg/kg)> Cu(142.80 mg/kg)> Zn(127.64 mg/kg)> Ni(65.76 mg/kg)> Sb(2.56mg/kg)> Hg(0.44 mg/kg),where Hg,Sb,Cu,Pb,Zn,Cr and Ni exceeded the background values of Guizhou soil by 4.0,1.6,4.5,5.5,1.3,1.6 and 1.7 times,respectively.The farther the distance from the tailings pile,the lower the content of heavy metals in the soil.Based on the risk assessment,the soils in each mine are contaminated with a combination of Hg,Cu,Sb and Pb.(3)According to the content of heavy metals in leachate of tailings and soil,it is concluded that the content of heavy metals in leachate varies irregularly with time.With the increased rainfall,only Mn and Cu in Hg tailings leachate showed an increased trend,and only Sb and Cu content in Mn tailings leachate showed an increased trend.The time to reach the maximum value of heavy metals in each tailings leachate was different.After 12 months of leaching,the average content of heavy metals in tailings leachate was greater than the average content of heavy metals in tailings-soil leachate,indicating that the soil played a certain role in retaining the migration of heavy metals.(4)The tailings-soil leaching experiment showed that the migration capacity of heavy metals varies with increasing soil depth.Under the influence of Hg tailings,the contents of Hg,Mn,Cr and Ni showed a decreasing trend,the contents of Sb and Cu showed an increasing trend,and the contents of Pb did not change much with the increase of soil depth.Under the influence of Sb tailings,with the increase of soil depth,the contents of Sb,Cu and Pb showed a decreasing trend,the contents of Zn and Hg showed an increasing trend,the contents of Mn and Cr showed a decreasing trend and then an increasing trend,and the contents of Ni did not change much.Under the influence of Mn tailings,the contents of Zn,Ni,Cu,and Pb showed a decreasing trend,the contents of Hg,Mn,and Sb showed a rising and then decreasing trend,and the contents of Cr showed a decreasing and then increasing trend as the depth of soil layer increased.After 12 months of leaching,the highest mean migration rates were observed for Mn followed by Cr in soils(0-60 cm)under Hg,Sb and Mn tailings.It showed that Mn and Cr are more likely to leach in the soil and migrate deeper under the rainwater leaching effect.(5)The heavy metals leached from the tailings were all present in the soil mainly in the stable residue state(F5).The proportions of residue state(F5),organic bound state(F4),Fe-manganese oxide bound state(F3),carbonate bound state(F2)and exchangeable state(F1)of each heavy metal did not change significantly with increasing depth.The proportion of the five forms of each heavy metal changed less with time.Under the tails,the fractions of potentially available and bioavailable fractions of Mn in the soil were higher at the third month of leaching,and the fractions of bioavailable and potentially available fractions of Zn and Pb were higher during the 12 months of leaching.The ratios of the 5 fractions of Mn,Pb,and Zn did not change significantly with increasing depth.As the soil was alkaline,heavy metal elements were easily fixed by forming stable precipitates in the alkaline soil,prompting the migration and transformation ability of heavy metal elements to be significantly weakened.In summarized,different heavy metals leached from tailings exist in different forms in the soil environment and have different ion release potential. |
PDF Full Text Request