Determination of the crystal structure of the mono-caesium derivative of the macrocyclic tetraphenol p-tert-butylcalix[4]arene shows the metal atom to be bound within the cup formed by the ligand; the metal is thereby in much closer proximity to the aromatic carbon atoms than to the phenolic oxygens, indicating that it is involved in polyhapto bonding to a delocalised anionic ligand.

Removal of arsenate anion from aqueous solution by coprecipitation with ferrihydrite has been studied under conditions in which the Fe/As ratio is maintained at a constant level, while the degree of supersaturation with respect to the iron oxide precipitate is varied. An Fe/As ratio of 12 was chosen, and supersaturation was controlled by varying the iron concentration or the pH. The relationship between supersaturation and arsenic removal was found to follow an exponential curve, with greater arsenic removal occurring at higher supersaturation ratios for each of the pH values tested. Higher supersaturation ratios were required to achieve a given level of arsenic removal at pH 7 than would be required to achieve the same level of removal at pH 3.5. The results provide important guidelines for selection of appropriate concentrations of iron(III) required for arsenic removal under various circumstances. Powder XRD analysis of the arsenate-ferrihydrite precipitates showed an increasing degree of structural order with decreasing levels of supersaturation. TEM images of the precipitates revealed that aggregates with a morphology similar to that of schwertmannite are formed in some samples at low supersaturation levels. The results described in this paper indicate that the overall efficiency of arsenic removal involves a combination of both supersaturation and pH effects, with pH controlling the affinity of arsenate for the ferrihydrite surface, and supersaturation controlling the surface area and physical properties of the ferrihydrite product.

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The adsorption of phosphonate molecules onto mineral surfaces is of interest due to their use as scale inhibitors. Molecular modeling is an important tool that can aid the fundamental understanding of how these inhibitors operate. This paper presents an empirical molecular mechanics study of the adsorption of a series of straight chain phosphonate molecules onto barium sulfate. It has been found that inhibition can be predicted for this straight chain series of molecules, which differ by the number of phosphonate groups present as well as by the chain length. Even more importantly, the modeling results can predict which faces will be preferred, and this has been verified by scanning and transmission electron microscopy on the resultant barite particles. It has been found that, in general, lattice matching results in the lowest replacement energy for all of the organic molecules investigated. The agreement between the experiment and the model confirms that the dominant mechanism of interaction for the additives on barium sulfate is via the deprotonated phosphonate groups with the barium ions on the surface.

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