氯盐对含汞土壤热脱附的影响

采用管式电阻炉对不同氯盐调理的含汞土壤进行热脱附实验,研究氯盐种类和炉温等对汞脱除效果的影响,分别从汞脱除率、热重测试和XRD汞形态分析3个方面进行评价。结果表明,不同温度下添加氯盐均对汞脱除率有明显提升。230℃时,添加氯化铁、氯化镁和氯化钙调理相比对照组(不添加氯盐),汞脱除率分别提升66.2%、49.3%和15.8%,即促进效果:FeCl3>MgCl2>CaCl2。在300℃下加热25 min时,添加氯化铁调理的汞脱除率为96.1~96.2%,与对照组相比,最高提升了68.3%。热重测试结果显示,载气对汞的挥发影响较小,湿法投加氯盐效果比干法投加更明显。炉尾晶体XRD分析结果表明,在低温条件下氯盐促进样品中汞向氯化汞转变从而提高了汞脱除率。添加氯盐调理提高了汞脱除率,同时缩短了汞热脱附达到稳定的时间。

Impact of chlorine salt on thermal desorption of mercury contaminated soils

The tests on the decontamination of mercury-polluted soil which was preliminary treated with different chlorides were conducted with tubular resistance furnace heated to evaluate the impact of various chlorides pretreatment and furnace temperatures on the thermal desorption of mercury, based on mercury removal efficiency, TGA and XRD analysis. The results demonstrated that the pretreatment with chlorides led to a significant improvement in the mercury removal efficiency at various furnace temperatures. At 230℃, when mercury-contaminated soil was pre-treated with ferric chloride, magnesium chloride and calcium chloride, the removal rate of mercury, compared with the control test without chloride, increased by 66.2%, 49.3% and 15.8%, respectively. At 300℃, the mercury removal efficiency of the ferric chloride pre-treated sample reached up to 96.1%~96.2%, with an increase about 68.3%. The results of TGA indicated that the carrier gas had less effect on mercury evaporation, and the sample pre-treated with chlorides in wet environment attained better removal efficiency than that in dry. The results of XRD analysis suggested that the improvement of removal rate could be attributed to the cationic exchange of chloride with the mercury from polluted soil. This remediation approach could enhance the decontamination of mercury efficiently as well as shorten the thermal desorption time.