Effects Of Biochar On Heavy Metals Fractions Change And Vertical Migration In Soil

The special characteristics of biochar,such as lots of pores,high adsorption capacity,and rich surface functional groups were high efficiency on improving soil physical and chemical properties,and reduced pollutant bioavailability and changed the fractions.At present,biochar applied in the field pollution remediation has been one of hotspot in soil remediation.However,the effect of biochar on soil heavy metals fractiosn changes and vertical migration was still unclear.The factors of biochars types from different feedstocks,soil types and WSOM?Water-solube Organic Matter?with different leaching solution influenced the heavy metals vertical migration with lab soil column experiment.The heavy metals fractions change and vertical migration was also reasearched with biocahr application in field long-term experiment,which offered the theoretical basis for the biochar environmental behavior,process of pollution remediation and mechanism reasearching.The specific conclusions are as follows:?1?Effects of biochar on cadmium?Cd?uptake by various vegetables and downward movement in saline-alkali soil was stutied.The experiment was carried out in a polluted pilot plant with boxes dimensions of 1m?wide?×2 m?long?×1 m?high?.The concentration of Cd was detected in different tissues of vegetables.The fractions and distribution of Cd in soil was analyzed by European Community Bureau of Reference?BCR?method.The results showed that the biomass of vegetables was significantly increased by 16.9%-519.9%,while the Cd concentration in green pepper and eggplant fruits were decreased by 6.8%-11.5%and 15.1%-15.4%with biochar application compared to control,respectively.The concentration of Cd in Chinese cabbage root was decreased by 1.6%after biochar addition.After two different vegetables growth,Cd in contaminated soil profile was transferred from topsoil?0⁶ cm?to subsoil?6¹2 cm?.The concentration of Cd transferred to subsoil was 14.30±4.17 mg kg^-1.Meanwhile the concentrations of Cd were decreased as exchangeable,reducible and oxidizable fractions in soil and vegetables.The residual Cd tranfer was decreased by 0.3 to 20.1%over time with biochar application in topsoil and bottom soil.Hence,the biochar was effective in mitigating the soil Cd vertical migration and preventing depth soil Cd pollution.?2?The effect of biochar on Cd and Pb pollution in different soil types was showed in follow.The results indicated that soluble heavy metals concentration of filtrate water was decreased by 89.0⁹5.7%?Cd?and 93.2⁹9.3%?Pb?with biochar application compared with control.The 2.3⁹.8%Cd and Pb of surface soil converting to insoluble fractions with added biochar.The bioavailable Cd and Pb concentration were reduced by 4.5¹0.7%?Cd?and 11.7¹6.4%?Pb?in surface soil?0⁴ cm?with biochar application.With the increase of paddy soil ratio,the bioavailability of Cd and Pb concentration was decreased by 13.8¹6.2%?Cd?and 4.0¹3.4%?Pb?in 4⁸ cm soil,indicating that the amount of heavy metals transferred downward was decreased.With 100%quartz sand treatment,the application of biochar effectively reduced the downward migration of heavy metals,and the conversion of 100.0%and 95.0%exchangeable Cd and Pb fractions was converted to 13.1⁴3.9%residual Cd and 11.6¹00.0%residual Pb.The soil organic matter?SOM?and pH were also increased by 1.2².3 g kg^-1 and 0.01⁰.31 unit with biochar application,respectively.So,the biochar has great effects as soil conditioner with heavy metals polluted amendment.With increase paddy soil ratio,the content of SOM was increased,which was high efficiency on fixed heavy metals compared with quartz sand.The application of biochar was another factor that effectively increased the content of SOM and stabilized heavy metals and prevented the migration of Cd and Pb.The leacheate solution went through soil and changed the forms of heavy metals with biochar application.So,the biochar was high efficiency on stabilized the heavy metals in different soil types.?3?Effects of different biochars and leaching solution on heavy metals vertical migration and fraction distribution in lab soil columns.This study was performed in 5cm×25cm lab soil column,and the content of Cd and Pb was analyzed in the contaminated soil column.The European Community Bureau of Reference?BCR?method was used to analyze the Cd and Pb fractions and distribution in soil column.The results showed that the wheat straw and bush biochar treatment?such as Z2,Z3?in 4⁸cm soil,the Pb content was increased by 0.4%³.5%and 11.7%¹6.4%,respectively.Overall,biochar changed the fraction of Pb in profile soil.The water-soluble organic matterm?WSOM?was produced by simulating biochar leaching was leached.The effect of high WSOM concentration on heavy metal migration was better than low WSOM concentration.This phenomenon is obvious in both citric acid and sodium humate solution.Low concentration of sodium humate solution did not significantly affect the heavy metals'migration.When the solution concentration reaches 10 mM,the Cd and Pb migration speed were accelerated.Increased heavy metal content in the underlying soil,increasing the risk of contamination.However,it also increased the proportion of residual fraction in the bottom soil to a certain extent,which had a good effect on the transfer of non-bioavailable heavy metals'forms.In general,the migration of Cd was greatly affected by the concentration of the leaching solution,and the migration of Pb was greatly affected by the kinds of organic matter in the leaching solution.?4?After 9 years of long-term experiment,the application of biochar in the field could effectively improve the SOM and pH in paddy soil.With the increase of biochar rates,the SOM was also on the inceased by 3¹3 g kg^-1.The total Cd and Pb were decreased by 7.6³4.65%and 6.1¹7.6%gradually with increase biochar application rates.Biochar had significant changes in the forms of Pb and Cd during field heavy metal-contaminated paddy soil amendment.The fractions changes of Pb and Cd indicated that the biochar had long-term effects on keeping the heavy metals fractions stability after change and decreased their bioavailability during the wheat and rice growth periods.