不同生物质黑碳对土壤中外源镉(Cd)有效性的影响

Impact of Different Biomass Black Carbon Amendments on Retention Capacity of Cadmium in Soil

选取水稻秸秆和樟木枝条两种生物质材料(分别代表农业生态系统和森林生态系统中的废弃生物质材料),分别在300～700℃和500～900℃温度下,采用限氧控温炭化法制备黑碳。为探讨不同生物质材料在不同热解温度下所制黑碳(BC)对污染土壤中镉(Cd)的固持作用,将一系列黑碳分别加入镉(Cd)污染土壤培养,检测重金属Cd形态以及土壤中有机质含量、阳离子交换量(CEC)的变化。结果表明:土壤中有效态Cd含量随着黑碳添加量和热解温度的升高而降低,即土壤对重金属Cd的固持作用增强。700℃水稻BC在添加量为6%时,土壤中有效态Cd含量降幅最大,为47.96%;900℃樟木BC在添加量为6%时,有效态Cd含量也降低了31.91%。土壤培养90d与45d相比,添加水稻BC2%、4%、6%的土壤平均有机质含量分别降低了0.94%、12.93%、17.19%,类似的,添加樟木BC的土壤平均有机质含量分别降低了5.33%、10.68%、20.70%,土壤有效态Cd含量与土壤中有机质的含量呈显著负相关。土壤培养结束后,水稻BC添加量为2%、4%、6%的土壤平均CEC值分别比对照增加了4.71、6.38、7.25cmol·kg-1,樟木BC添加量为2%、4%、6%的土壤平均CEC值分别比对照增加了2.90、8.33、8.52cmol·kg-1。生物质黑碳加入土壤后改变了土壤的基本性状,增强了土壤对Cd的固持作用,降低了土壤介质中有效态Cd的含量,也降低了迁移性和生物毒性,其生态风险性亦相应降低。

Black carbon（BC） were produced from rice straw and camphorwood（represent waste biomass materials in agricultural ecosystem and in forest ecosystem） in the method of controlling pyrolysis temperature and limiting oxygen,at 300~700 ℃ and 500~900 ℃ respectively.To study the immobilization and mechanism to cadmium（Cd） in contaminated soil amended with black carbon（BC） which made from two biomass materials under different pyrolysis temperature.Black carbon were cultivated in Cd pollution soil,to detect changes of heavy metal form,organic matter content and Cation Exchange Capacity of soil.The results showed that：the content of bioavailable Cd in soil was decreased by 47.96% when the adding amount of Rice-BC reaches 6% at 700 ℃,while it was reduced by 31.91% when the adding amount of Camphorwood-BC was 6% at 900 ℃.After 90 days culturing,the content of average organic matter in soil reduced 0.94%,12.93% and 17.19% when the adding amount of Rice-BC varies as 2%,4% and 6%.While for Camphorwood-BC the corresponding decrement was 5.33%,10.68% and 20.70%.It showed a significant negative correlation between the concentration of bioavailable Cd in soil and organic matter content in soil.The average CEC of soil increased 4.71 cmol·kg-1,6.38 cmol·kg-1 and 7.25 cmol·kg-1 when the adding amount of Rice-BC varies as 2%,4% and 6%;and when it refers to Camphorwood-BC that increased 2.90 cmol·kg-1,8.33 cmol·kg-1 and 8.52 cmol·kg-1.The content of bioavailable Cd of most soils had a negative correlation with CEC value of soil.The results indicated that the soil characteristics changed after adding biomass BC,the soil immobilization to Cd was improved and the Cd mobility in soil was reduced,accordingly,its ecological risks were also decreased.