Effects Of Environmental Materials And Plants On Heavy Metal Migration In Soil Of Mining Areas

At present,the remediation of heavy metal contaminated soil in mining areas has become an important aspect of environmental control in China.In this paper,the heavy metal contaminated soil in Bayan Obo mining area of Inner Mongolia was taken as the research object.Through the systematic investigation of soil and plant in the mining area,the pollution status and form distribution characteristics of heavy metal in soil were analyzed,and the ecological risk status was evaluated.In view of the remediation of heavy metal contaminated soil in the mining area,potted experiments about phytoremediation were carried out for two consecutive years with native plants Caragana microphylla Lam,Medicago sativa L.and Lolium perenne L.The effects of biofertilizers and fulvic acids on heavy metal migration in soil were studied,and the optimal parameters of remediation amount of environmental materials were selected.A field block experiment was conducted to study on the synergistic effect of environmental materials combined with shrub-grass on heavy metal migration in polluted soil of mining area.These provides some reference for the theory and practice of soil remediation in mining areas in China.(1)The heavy metal pollution elements in the soil of Bayan Obo mining area were Pb,Cu,Zn,Mn,Ni and As,among them,Pb and As exceed the national screening values of soil pollution risk,while do not exceed the risk control values;as other pollutants,Cu,Zn and Ni were higher than their screening values for risk,all of which had pollution risk.The Main mine,East mine,tailings pond and dumps were all heavily polluted areas,among them,Pb and Zn were heavily polluted,Cu and Ni were moderately polluted,As was slightly polluted,and Mn content was higher,which could also be used as the main pollutant;the distribution of Pb,Zn and Mn was mainly residual and reducible forms,the form distribution of Cu,Cr,Ni and As was mainly residual.The content of soil organic matter,available NPK and cation exchange capacity was low,fertility was poor.(2)Twenty-four suitable plants were recorded through vegetation survey in mining area,accounting for 45.83%of the total species.There were some differences in heavy metal enrichment ability of aboveground of different plants,and the aboveground parts of Caryopteris mongholica Bunge,Xanthium sibiricum Patrin ex Widder,Ammopiptanthus mongolicus(Maxim.ex Kom.)Che,Achnatherum splendens(Trin.)Nevski,Gypsophila davurica Turcz.ex Fenzl had strong enrichment ability to Pb,Cu,Zn,Mn and Ni respectively,transport capacity of most suitable plants was relatively strong,which could be used as some suitable phytoremediation materials for the above five heavy metals in this mining area.(3)Pot experiments were conducted to study the effects of biofertilizers and fulvic acids combined with plants on heavy metal migration in contaminated soil of two mining areas for two consecutive years.The phytoremediation effect of heavy metal contaminated soil and planting soil in the mining area was better under the configuration of 1:1,after two years of restoration,the fastest rates of Pb,Cu,Zn,Mn and Ni in 1:1 soil decreased from 1054.00,253.70,2440.00,7864.00 and 472.50 mg/kg before restoration to 511.89,128.56,1271.16.5567.12 and 228.58 mg/kg,respectively;under the condition of single and simultaneous addition of two environmental materials,the combined with Caragana microphylla Lam,Medicago sativa L.and Lolium perenne L.had better effects on the migration of five heavy metals in soil,the highest accumulations of Pb,Cu,Zn,Mn and Ni in Medicago saliva L.restoration for 2 years were 11658.72,3159.77,31142.10,40863.84 and 6500.09?g/pot,respectively;in the single application,biofertilizers with(B5)1 OOg/pot or(B5)200g/m2 was combined with three plants to reduce the efficiency and extract the five heavy metals,and F3(150mg/L)with fulvic acids was combined with three plants to reduce the efficiency and extract the five heavy metals,respectively;as a whole,the combined application of 100 g/pot B+100 mg/L F(T6)or 200 g/m2 B+100 mg/L F(T6),i.e.high concentration of BF+medium concentration of FA,had better phytoremediation effect on heavy metal migration in contaminated soil.(4)Pot experiments were conducted for two consecutive years to study the changes of soil fertility in heavy metal contaminated soils treated with two kinds of environmental materials and three kinds of phytoremediation.The comprehensive fertility index IFI of both configured soils increased with time,IFI of heavy metal contaminated soils was slightly higher which were allocated according to 1:2 ratio of heavy metal contaminated soils and planting soils from mining areas;The effect of mixed application was obvious,adding biofertilizers and fulvic acids combined with Medicago sativa L.to remediate heavy metal contaminated soil allocated according to 1:2 ratio of heavy metal contaminated soils and planting soils from mining areas for two years,IFI were 82.87 and 142.61,respectively,soil fertility changed from grade ? to grade ?,and soil fertility was in good condition;as a whole soil pH decreased,and organic matter and available NPK increased significantly with time prolonging;the number of microorganisms in soil increased significantly under the treatment of T5 and T6,and the number of bacteria,fungi and actinomycetes increased overall under the continuous remediation of Medicago saliva L.;after two years of continuous restoration,the growth of the three plants was obviously promoted by T5 and T6.(5)Field block experiment under shrub-grass cooperative rehabilitation model showed that the aboveground and total dry weight of shrub-grass increased significantly after 2 season,when 200g/m2 B+100mg/L F(T6)was added together with fulvic acid and shrub-grass to remediate heavy metal contaminated soil;the contents of five heavy metals in soil decreased in varying degrees,the removal efficiency of Pb and Zn was better,the average reduction efficiency was 37.32%and 35.74%respectively;the forms of the five heavy metals had changed significantly,showing the transformation from residual and oxidizable to reducible and exchangeable;the contents of five heavy metals in shrubs and grasslands increased significantly after two seasons of restoration,the average contents of Pb,Zn and Mn in the aboveground part of shrubs and grasslands were higher.Under 200g/m2 B+100mg/L F(T6)treatment,the average total uptake of five heavy metals was about 590.09 mg/season in the aboveground part of each square metre of shrub-grass.