卤化铵改性竹炭对单质汞吸附性能的影响

Effects on elemental mercury adsorption characteristics of bamboo charcoal modified by ammonium halide

为了研究廉价吸附剂竹炭的脱汞性能,将经过CO_2活化并采用NH_4Cl、NH_4I超声浸渍改性的竹炭(BC)应用于单质汞的吸附,并对比不同负载量的NH_4Cl以及NH_4I改性和温度等因素对竹炭的汞脱除性能的影响。采用了元素分析、扫描电镜分析、XPS表征、比表面积及孔径分布等对材料进行研究。结果表明,NH_4Cl和NH_4I改性显著提高竹炭的脱汞能力,并且在同等条件下NH_4I改性剂效果优于NH_4Cl。研究表明提高负载量会造成吸附材料孔堵塞,但在0~8wt.%的负载量情况下,孔道的堵塞不足以抵消化学吸附带来的积极作用,表明改性竹炭对汞的吸附主要表现为化学吸附。同时改性竹炭存在随着温度升高其吸附效率先降低后升高的趋势,暗示竹炭对汞的吸附在低温时物理吸附占优势,温度升高时化学吸附占优势。

To study the mercury removal performance of a low-cost adsorbent, bamboo charcoal （BC） was applied to elemental mercury after activation by CO2 and ultrasonic modification by NH4Cl and NH4I.The loading amount of the modifier and temperature were taken into account.Ultimate analysis, scanning electron microscopy （SEM）, and X-ray photoelectron spectroscopy （XPS） were conducted;specific surface area, and pore size distribution of the materials were studied.The pore structures were investigated based on Brunauer-Emmett-Teller （BET） surface area.The experimental results and characterization data indicate that both NH4Cl and NH4I can significantly improve the mercury removal ability of BC.The BC sample modified by NH4I performed better than the one modified by NH4Cl did, under the same experimental conditions.The modifier may block the fine pores in the BC samples by increasing the concentration of NH4Cl solution, which is not conducive to the physical adsorption of elemental mercury during the initial adsorption period;however, the blockage of the pores of the modified BC was not enough to offset the positive effect of chemical adsorption.This study shows that the mercury adsorption ability of modified BC depended mainly on chemical adsorption rather than physical adsorption.The adsorption efficiency of the modified BC first increased and then decreased, indicating that physical adsorption played a leading role at lower temperatures while chemical adsorption played a major role at higher temperatures.