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Black plate (276,1) nitrous oxide. This to my mind suggests the involvement of hydroxyl radicals the yield of which is enhanced in N2O saturated aqueous media189. It’s an interesting paper but the method it describes will never become a practical decontamination method on the large scale, since it is too demanding in terms of electricity and only small volumes of liquid could be sensibly treated by means of it. Unmodified zeolite surfaces show no affinity for anions, and in fact repel them because of the formal negative framework electric change. However, if the zeolite is initially exchanged with particular cations which form practically insoluble complexes with those anions it is desired to remove from a particular aqueous medium, the resulting complexes will precipitate within the zeolite matrix and tend to remain there. When chromate anions were sorbed by clinoptilolite, the degree of uptake was found to be proportional to the solubility product (Ksp) of the particular chromate salt, and to the amount of the exchangeable cation present in the zeolite. In the series of cations studied, Pb2þ was found most effective in removing chromate190. The removal of iodide anions, particularly 131I with a half-life of just 8 days (hence highly radioactive) formed in 2.77% yield among the products from the fission of 235U, using zeolites has been investigated. It was found that clinoptilolite is a more promising material for this purpose than natrolite, and that the adsorption was highest in its Ag þ , Pb2 þ and Tl þ -exchanged forms191. Faghihian et al. based in Tehran, have reported the following studies, which may be taken as representative of the field of environmental decontamination using zeolites as a whole: adsorption of arsenate anions by Fe, Pb and Ag-exchanged clin- optilolites192, uptake of cerium cations by zeolite A prepared from natural tuffs193, thorium cation uptake again using zeolite A prepared from natural clinoptilolite tuffs194, removal of cyanide anions from industrial liquid wastes using cation-exchanged clin- optilolite (the cobalt form of the zeolite showed the highest uptake of 1.95 meq of cyanide per gram of zeolite, whereas the uptake of natural forms is 0.070 meqyg) 195, synthesis of Na-P-c zeolite from perlite and its use in cyanide adsorption196, removal of radioactive iodide anions using a surfactant-modified zeolite (SMZ) 197, adsorp- tion of molybdate anions by natrolite and clinoptilolite-rich tuffs198. Catalytic converters are implemented into the exhaust-systems of vehicles to reduce their toxic gas emissions, especially NOx. Cu- ZSM-5 catalysts are used for direct NO decomposition of which it is found that Cu-SZM-11 and Cu-SZM-12 have about twice the efficiency of Cu-ZSM-5 for this purpose199. In a following paper, it 276 Christopher J. RhodesPDF Image | Properties and applications of zeolites
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