Abstract: Adsorption isotherms of HCN by Cu- and Ca-montmorillonites show that water present in the interlayer space decreases HCN adsorption.
For Ca-montmorillonite, i.r. spectra permit distinguishing between HCN interacting with the cations and molecules filling the interlayer space. Both types are removed upon outgassing. The residual water is not displaced by HCN.
On Cu-montmorillonite, species (presumably CN− ions) strongly held by the cations are observed in addition to adsorbed HCN molecules. The residual hydroxyls retained in the interlayer space are removed by the adsorption of HCN. These hydroxyls, either OH− or H2O, are characterized by two well defined stretching bands.
Infra-red spectra of samples heated below 200°C show that adsorbed HCN is involved in chemical reactions. For both clays, bands appear in the region characteristic of carbonyl and carboxyl groups; the production of ammonium is detected for Cu-montmorillonite. The reactions and the observed spectral features could be accounted for by the formation of formamide.