Kinetic experiments are reported on the chemical formation of AgI layers on polycrystalline silver substrates. The AgI layers, up to several micrometres in average thickness, were grown under ambient conditions by reacting a rotating silver disc with solutions of iodine dissolved in ethanol and with aqueous triiodide solutions. The morphology and structural identity of the AgI layers were determined by scanning electron microscopy and powder X-ray diffraction, respectively. Depending upon the growth conditions employed, either porous or compact AgI deposits could result, and thus the rate of formation of AgI could be limited by a diffusion step in solution, or by some slower transport step across the layers. The AgI layers were inhomogeneous, and often consisted of discrete crystallites. Thus, the metal oxidation theories developed for planar and isotropic product layers could not be applied to the formation of AgI layers under ambient conditions.

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By means of the miscible-displacement approach, investigations have been carried out on cadmium adsorption-desorption by mixtures of freeze-dried montmorillonite and freshly precipitated humic acid. Low Cd surface loadings were employed and acidic (pH 4.5-5) solution conditions were maintained during both adsorption and desorption cycles. Compared with montmorillonite, Cd adsorption by humic acid was much greater so that clay-humic mixtures containing only a few per cent w/w humic acid removed appreciably more Cd from solution than that by clay alone. However, this greater Cd uptake by humic acid was offset by the susceptibility of bound Cd to desorb once the supply of Cd in the column ihput solutions was removed. Thus, both montmorillonite and undissolved humic acid had a limited ability to fix Cd, a result which may have some implication to mechanisms of Cd binding by natural clay-humic mixtures in acidic soil environments. The miscible-displacement approach appears to be well suited to examining solute interactions with poorly soluble, high molecular weight soil humic materials.

This work extends a previous study on the electrochemistry of silver electrodes in aqueous sulfide solutions. It has been found that the voltammograms for the silver-sulfide system have additional features to those reported earlier. The nature and interpretation of the additional features is described. Peaks due to silver oxides, and chemically formed silver sulfide, are identified and discussed. Further evidence for the presence of α- and β-Ag2S in the layer deposited during anodic oxidation of the silver was obtained from chronopotentiometric and diffraction studies.

The growth of Agl on a rotating Ag disc is found to be much slower in a 12/ EtOH solution than in an aqueous I3′ solution.