| In the historical period,large-scale indigenous zinc smelting activities were conducted in the northwest of Guizhou.A large amount of lead-zinc smelting slag producted in smelting activities accumulated on the hillside and the surrounding farmland for a many years.The high content of heavy metal remaining in the slag is easy to through the way such as wind power diffusion and surface runoff migrated to the surrounding atmosphere,water,soil,crops and so on environment medium,pose a serious threat to the surrounding and downstream water quality safety,food safety and regional ecological security of agricultural products,and finally enters the body through the food chain or direct absorption,increase the human health risk of exposure.Phytoremediation as an effective and sustainable restoration method can control the diffusion of heavy metals and reduce the potential toxicity,so as to minimize the erosion of the waste residue yard.The key to control the diffusion of heavy metal pollution is to restore the vegetation of waste residue dump.However,in the ecological reconstruction of slag by plants,the presence of organic compounds secreted by microorganisms and plant roots,especially organic acids,can activate the heavy metals in the slag in the rhizosphere environment and enhance the activity,thus increasing the possibility of heavy metals movement and infiltration in the slag.In addition,the poor environment with high content of heavy metals,poor physical structure,low water-holding and fertilizer retention capacity,and serious lack of organic matter and essential nutrients for plants restricts the process of vegetation restoration of lead-zinc smelting waste residue.Therefore,amnetments should be added to inhibit the activation of plant-induced heavy metals in the process of plant stability restoration to reduce the movement and infiltration of heavy metals to alleviate the plant toxicity of heavy metals,and at the same time improve the extreme habitat of waste residue yard.In this study,we used a bare earth smelting residue that had been stored for many years in Houchang Town,Weining County,western Guizhou as the research object,and simulated the addition of different amendments,including biogas residue(BR),activated phosphate rock powder(APT)a combination the mixture of the above two substances,were used in the indigenous zinc smelting slag,set up the control group without modifier,and planted L.perenne for pot experiment.The effects of different amendments on the availability and migration of heavy metals in indigenous zinc smelting slag were studied,by changing the physicochemical and microbiological characteristics of the waste residue matrix and promoting the plant growth.The results showed:(1)Compared with the control,The addition of the amendments can effectively improve the extreme habitat of lead-zinc smelting slag and significantly increase the content of nutrient elements(N,P and organic matter).Among them,the active phosphorus phosphate tailing(APT)increased the effective phosphorus in the waste residue significantly higher than other improved treatments,and the improvement effect on the total nitrogen,available nitrogen,organic matter and available potassium of the waste residue matrix were BR? CA3? CA1? CA2? APT,and the combined amendments(CA3,CA2,CA1)treatments have better effect on total phosphorus than the APT and BR treatments.(2)The amendments significantly increase the urease,catalase,sucrase,alkaline phosphatase activity,respiratory intensity and the numbers of bacteria,fungi and actinomycetes in the waste residue matrix.Among them,under the treatments of CA3 and BR,the improvement of enzyme activity and microbial activity were better than that of CA1,CA2 and APT.The correlation analysis showed that the nutrient content in the waste residue was the main factor affecting the enzyme activity,the quantity and the activity of the microflora,and the improvement of the microbiological characteristics of the waste residue was also the main factor affecting the nutrient accumulation in the waste residue.(3)With the addition of amendments,the total concentrations of Cu,Cd,Pb and Zn in the waste residue decreased to different extents compared with the control.And altered the distribution of the chemical fractions of major heavy metals and promoted a change from the the aci-extractable fraction into residual fraction,which decreased the bioavailability of heavy metals in the rhizosphere.However,acid soluble Cd and Zn are still the main forms of waste residue after the treatment with the modifier.PCA principal component analysis showed that 7%,9% of the BR,CA1,CA2,CA3 treatment group of nutrients and waste residue and microbiological characteristics have strong correlation,and the control group and 1% of APT,BR,CA1 and CA2,CA3 treatment group and the correlation of heavy metals from waste acid soluble state strong,with the increase of conditioner added proportion residual matrix nutrient content,enzyme activity and microorganism quantity and activity increased gradually,and to a certain extent,reduce the acid soluble heavy metal content.(4)The heavy metal content(Cu,Cd,Zn,Pb)in L.perenne was relatively high in the waste residue of the control group.After the addition of the modifier,the heavy metal content in the aboveground and underground parts of the plant gradually decreased with the increase of the addition of the modifier.Under 9% BR treatment,the content of Cd in some parts of ryegrass was the lowest,and that of Cu and Zn in overground parts was the lowest in 7% CA3 treatment group.The content of Cu and Zn in the underground part was the lowest in the 9% CA3 treatment group.The addition of CA2 had the most significant reduction effect on Pb in ryegrass,especially in the 7% and 9% CA2 treatment groups.The correlation analysis showed that the content of acid soluble heavy metals in the waste residue was the main factor affecting the absorption and accumulation of heavy metals in plants.With the decrease of acid soluble heavy metals in the waste residue,the content of heavy metals in ryegrass also decreased correspondingly.(5)The application of amendments significantly increased the plant height,root length,fresh weight and total chlorophyll content of perenne L.relative to the control,and and CA3 rates of 7%,and 9% were the most effective.The amendments can significantly decrease the activity of CAT,SOD,POD and MDA in leaves,after that,with the increase of the amount of modifier,there was a certain upward trend.The correlation analysis showed that heavy metal content in plant is the activity of antioxidant enzymes in plants(SOD,CAT and POD)and MDA content change and limiting factors of the development of plant growth,antioxidant enzyme system can be as the change of heavy metal content in the body to make the corresponding stress reaction in order to reduce the heavy metal stress on plant growth,relieve lipid membrane peroxidation damage of tissue cells,promote the growth of plants.What ’s more,each treatment of the modifier is an increase in the chemical form ratio of Cu,Cd,Pb,and Zn which is weak in various parts of the plant,and the proportion of chemical forms with strong heavy metal activity is reduced,which enhances the distribution of heavy metals in non-metabolically active tissues,and alleviates or avoids.(6)Principal component analysis was carried out on the nutrient,microbiological characteristics,bioavailable heavy metals and plant growth of the zinc residue from the soil.The results showed that 5%,7%,9% of BR and CA3 and 7% and 9% of the CA1 treatment group Strong correlation with TN,AN,AK,OM,TP,urease,invertase,alkaline phosphatase,respiratory intensity,bacteria,fungi,actinomycetes,fresh weight,root length,plant height,total chlorophyll 7%,9% of the CA2 treatment group showed a strong correlation with catalase,EC,AP,TP,while the control group(CK),1%,3%,7%,9% of APT,1% of BR and CA3,1%,3% of CA1,CA2 treatment groups showed strong correlation with heavy metals in waste slag acid and heavy metals in plants.It indicates that the addition of modifiers can significantly increase the nutrient content of lead and zinc smelting waste residue matrix,significantly increase the enzyme and microbial activity in the waste residue matrix,and effectively reduce the bioavailability of heavy metals.The factor scores showed that 7% and 9% of CA3 treatments were the best,followed by 7%,9% of BR and 5% of CA1 treatment groups.In summary,the biogas residue and activated phosphate tailing are used as an inexpensive and excellent improver for the ecological restoration of the zinc slag residue,which can provide the necessary nutrients for the physiological growth of the repaired plant and improve the physical and chemical properties of the waste residue.The chemical and microbiological properties reduce the content of aci-extractable heavy metals in the slag and the absorption of heavy metals by plants,thus effectively promoting the growth and development of plants.Moreover,the biogas residue and phosphate tailing are organic or industrial wastes,and the cost is much lower than the use of chemical fertilizers and other organic fertilizers,which can effectively reduce the cost of matrix improvement in the ecological restoration process of the mine,and ultimately ―to waste waste treatment‖ "The win-win goal." When the biogas residue and the activated phosphate tailing are mixed and applied in a mass ratio of 2:1,the improvement effect is best when the residue is added in a ratio of 7% to 9%,which can be used as a reference ratio mode for improving the lead and zinc smelting slag. |
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