Novel HCN sorbents based on layered double hydroxides: sorption mechanism and performance

Layered double hydroxides (LDHs) and layered double oxides (LDOs) have been prepared and used as sorbents for hydrogen cyanide (HCN). Based on results from sorbent optimization experiments, the optimal performance for HCN removal was found in Ni-Al LDH. As evidenced by fixed-bed sorption studies, the Ni-Al LDO with the greatest surface area showed better performance and outperformed products calcined at 200, 400, or 500 °C, whereas, the Ni-Al LDH showed a more twofold higher sorption capacity than the Ni-Al LDO. Investigation of the mechanisms between HCN and sorbents reveals that the HCN removal by the Ni-Al LDH and Ni-Al LDO leads to the formation of the complex anion, [Ni(CN)4](2-). Nevertheless, the [Ni(CN)4](2-) can enter interlayer region of the Ni-Al LDH due to its anion exchangeability, which endows this LDH with more binding sites, not only on its external surfaces, but also on its internal surfaces located in the interlayer region. In contrast, [Ni(CN)4](2-) were only adsorbed on the external surface of the Ni-Al LDO. As a result, the sorption capacity of the Ni-Al LDH for HCN is twice as high as that of the Ni-Al LDO, which is at 21.55 mg/g.