The sorption of ammonia on californian chrysotile treated with boiling water and with aqueous solutions of sodium nitrate

Abstract

Californian chrysotile asbestos modified by hydration treatments with boiling water and with aqueous solutions of sodium nitrate was applied as an adsorbent for ammonia at 298 K. Heats of adsorption and differential molar entropies of adsorption were determined through adiabatic calorimetry for low surface coverages of adsorped ammonia up to 12 μmol m -2. Nitrogen adsorption-desorption isotherms, pore size distributions and electron micrographs were also obtained. The very large heats of adsorption created by the initial doses of ammonia are thought to be related to the formation of ammonium hydroxide at high energy sites such as at vicinal hydroxyl groups generated during the hydration treatments. The singular effect of sodium ion inclusion was most noticeable at 15 kPa and above when the amount of ammonia adsorbed fell to a level close to 70% of that measured for the water-treated chrysotile. Ammonia adsorbed on the water-treated chrysotile was more mobile and gave values of the experimental differential molar entropy which were from 6 to 10 J K -1 mol -1 higher than those of the samples treated with an aqueous solution of sodium nitrate, depending on the surface coverage. Although surface chemical changes were induced by both treatments, the essentially fibrous physical structure of chrysotile asbestos appeared to be undisturbed.