磷酸对八宝景天热解过程中As、Pb迁移转化的影响

Influence of phosphoric acid on migration and transformation of arsenic and lead during pyrolysis of Sedum spectabile

本文利用管式炉在不同温度下对八宝景天进行直接热解和磷酸预处理热解,研究了As、Pb的迁移特性和形态分布.结果表明:生物炭中As的回收率随温度升高波动,Pb的回收率随温度升高先增大后减小,As、Pb的回收率均在500℃时达到最大,分别为66.2%和73.08%.添加8%磷酸后As、Pb回收率在一定温度范围内增加,并在300℃时达到最大值,分别为83.75%和92.78%.热解温度由300℃升到600℃时,生物炭中As的稳定形态(F4+F5)由不足20%增加到70%左右,Pb的最稳定形态(F5)由3%增加到32%.添加8%磷酸热解后,生物炭中As的稳定性小幅增加,500和600℃时F5分别增加20%和5%;Pb的稳定性显著增加,(F4+F5)均达到90%以上.磷酸添加量对重金属形态分布无明显影响.实验结果表明采用磷酸预处理用于修复植物热解可提高生物炭中重金属As、Pb的回收率及稳定性,并可降低其生态风险指数.

The pyrolysis experiments with or without phosphoric acid pretreatment of Sedum spectabile were conducted at different temperatures in a tube furnace to study the migration characteristics and speciation distributions of As and Pb.The results showed that the recovery rate of As fluctuated and the recovery rate of Pb was increased firstly and then decreased with the increase of temperature.The recovery rate of As and Pb both reached maximum at 500℃ with 66.2%and 73.08%respectively.The recovery of As and Pb was increased after adding 8%phosphoric acid in a certain temperature range and reached maximum at 300℃ with 83.75% and 92.78% respectively.When the pyrolysis temperature was increased from 300℃ to 600℃,the stable form(F4+F5)of As in biochars was increased from less than 20% to about 70%,and the most stable form(F5)of Pb was increased from 3% to 32%.After the pyrolysis with 8% phosphoric acid pretreatment,the stability of As in biochar was increased slightly with F5 increasing by 20% and 5%respectively at 500℃ and 600℃;and the stability of Pb was increased remarkably with(F4+F5)reaching more than 90%.The dosage of phosphoric acid had no significant effect on the distribution of heavy metals.These results indicated that phosphoric acid pretreatment could be used for pyrolysis of phytoremediation plants to increase the recovery and stability of heavy metals in the biochars.In the meantime,the potential ecological risk index was also reduced.