溴化铵改性膨润土脱除气态单质汞的特性及机理分析

采用溴化铵对钠基膨润土进行改性制得脱汞吸附剂,在固定床实验装置上对所制备的吸附剂进行脱汞性能测试。脱汞实验结果表明,钠基膨润土较钙基膨润土在脱汞性能上提高不大,而溴化铵改性的钠基膨润土(Br-Ben/Na)脱汞性能得到明显提高,脱汞效率达到97.7%。吸附温度的升高有利于对Hg0的脱除,在140℃下,10%Br-Ben/Na吸附剂的脱汞率能长时间保持在90%以上,说明在此吸附过程中化学吸附占主导性作用。通过N2吸附/脱附、X射线衍射(XRD)、元素分析仪和傅里叶变换红外光谱(FT-IR)分析等结果表明,改性后的膨润土比表面积下降,平均孔径增大;铵根离子进入到膨润土的层间置换出层间钠离子,煅烧活化过程中层间的铵根离子并未分解,而在层间与膨润土结合为某吸附活性组分协助Br-与Hg0反应,提高了膨润土的脱汞性能。

Adsorption performance and mechanism of bentonite modified by ammonium bromide for gas-phase elemental mercury removal

Bentonite was modified with ammonium bromide to enhance its adsorption performance for the removal of elemental mercury. The adsorbents were characterized by N₂ adsorption/desorption, X-ray diffraction (XRD), elemental analysis, and Fourier transform infrared spectroscopy (FT-IR); the adsorption test was carried out in a laboratory-scale fixed-bed reactor. The results showed that the performance of sodium bentonite in mercury removal is only slightly higher than that of calcium bentonite; however, its performance in mercury removal can be greatly enhanced through the modification with ammonium bromide. The mercury removal efficiency reaches 97.7% over the sodium bentonite modified with ammonium bromide (Br-Ben/Na). High temperature may promote the removal of Hg⁰ and the mercury removal efficiency remains higher than 90% over the 10% Br-Ben/Na adsorbent for a long time at 140 ℃, suggesting that chemical adsorption played a dominant role in the adsorption process. Through the modification with ammonium bromide, the sodium ions were replaced with the ammonium ions added to the bentonite layers; the specific surface area of the modified bentonite is decreased, whereas the average pore size is increased. During the calcination activation process, the ammonium ions may combine with bentonite within the layers, forming the adsorption active centers, which promotes the reaction between Br^- and Hg⁰ and then enhance the adsorption performance of bentonite in the removal of mercury.