| It's extremely important to search the efficient and cheap materials for remediating soil contaminated by heavy metals.In this study,four kinds of agricultural wastes such as rice straw,rice husk,wheat straw,and sugarcane bagasse feedstocks were selected for biochar production.Finally,RS,RH,WH and SC biochars were produced at 500? for 2 h and used to immobilize the lead,cadmium,copper and zinc in paddy soil.The content of exchangeable heavy metals in soil were studied.The effects of biochars from different feedstocks on the physicochemical properties and the effectiveness of remediating heavy metal in paddy soils were studied.In addition,effects of rice straw biochars prepared at 300?,500? and 700? for 2 h labeled as RS300,RS500 and RS700 on the physicochemical properties and heavy metals(Pb,Cd,Cu and Zn)availability in contaminated paddy soil were studied.The effects of biochars on Pb,Cd,Cu and Zn in polluted soil were explored,aiming to provide the reference for the application of biochars on the remediation of soil.The main results were as follows:(1)The elements and properties of biochars were closely related to the feedstocks and pyrolysis temperatures.The pH of RS,RH,WH and SC was about 6.9-10.0,the pH and yield of RS were the highest.The ash,N content,O content,H/C,O/C and(O+N)/C of WH were higher than other biochars.The pH,ash content,yield,N content,O content,O/C and(O+N)/C of SC were the lowest.The morphology of biochars had obvious honeycomb structure.With the increasing of pyrolysis temperature,the pH,ash and C content of biochars increased,while,the yield,H content,O content,H/C,O/C and(O+N)/C contents of biochars decreased with increasing temperatures.With the increasing of pyrolysis temperatures,the pore structure of biochar became more and more obvious,and the whole structure of biochar prepared at 700? was collapsing.(2)The feedstocks of biochars had influence on the remediation of heavy metals in contaminated soil.Four kinds of biochars could increase the pH,electrical conductivity,available phosphorus content and water-soluble organic carbon content of soil.Compared to CK,the addition of biochars were 1.5% and 3%,and the soil pH increased by 0.1-0.7 units,and the content of available phosphorus increased by 14.3%-93.8% and water-soluble organic carbon increased by 7.0%-55.7%.With increasing biochars content,the soil pH,electrical conductivity,the contents of available phosphorus and water-soluble organic carbon increased.Compared to CK,biochars significantly reduced the content of exchangeable heavy metals in soil(p<0.05).In all treatments,the reduction of exchangeable Pb,Cd,Cu and Zn content more than 60%,when treated with WH3,RS3 and WH1.5.RS,WH and SC were more effective on Cd immobilization than RH in soil.RS and WH were more effective on Cu and Zn immobilization than RH and SC in soil.Biochar additions at 3% for heavy metals immobilization were better than that of 1.5% application rate.In general,WH and RS were relatively suitable as remediating agents for Pb,Cd,Cu and Zn immobilization in soil.(3)The pyrolysis temperature of biochars influenced the immobilization of heavy metals in soil.Compared to CK,biochars prepared at different temperatures could significantly(p<0.05)increased the soil pH,electrical conductivity,available phosphorus content and water-soluble organic carbon content of soil.Results showed that biochars prepared at the higher pyrolysis temperature could increase the soil pH and electrical conductivity,while there is no significant difference was observed for available phosphorus and water-soluble organic carbon in contaminated soil relative to control.Compared to CK,the pH,the electrical conductivity,the content of available phosphorus and water-soluble organic carbon of soil increased.The bioavailable portion of Pb,Cd,Cu and Zn decreased by 10.2%-24.2%,10.7%-25.2%,12.8%-27.6% and 4.2%-4.9%,with the addition of RS300,RS500 and RS700,respectively,relative to control.The decreasing of bioavailable Zn was lower than that of the other heavy metals.RS300 derived biochar showed greater immobilizaing efficiency for Pb and Cd.RS700 showed the best effeciency to immobilize Cu in soil.RS700 and RS300 had better effectiveness on the remediation of heavy metals than RS500.RS300 showed better immobilizaing effect for Pb and Cd,while RS700 performed better for Cu immobilization.However,biochars prepared at different temperatures showed no significant effect for Zn immobilization in contaminated soil.(4)WH and RS had higher ash content,pH and O/C than RH and SC,and had greater effect on soil pH than RH and SC.WH and RS had stronger ability to immobilize the heavy metals than RH and SC.The effect of RS300 on immobilization of Pb and Cd in soil was better,due to the higher O/C ratio of RS300.The effect of RS700 on immobilization soil Cu was better maybe due to its higher pH and ash content.The results of this study had important practical value for the application of biochars and for using the agricultural wastes reasonably and remediating heavy metal combined pollution. |
PDF Full Text Request