Trivalent exchange

In the presence of di- and trivalent exchangeable cations many anions are precipitated as insoluble salts (e.g., calcium dodecylsulfate). When this possibility is not considered, adsorption data are misinterpreted. (It was reported [60] that dodecylsulfate anions were adsorbed in the interlayer space of calcium montmorillonite. However, the (001) reflections observed and ascribed to the calcium montmorillonite surfactant complex d (001) = 30 A) are the reflections of calcium dodecylsulfate. Anionic pesticides may be partially inactivated by precipitation as insoluble Ca , AF", Fe etc. salts (e.g., acifluorfen [61]).)... 

Separation Processes. The product of ore digestion contains the rare earths in the same ratio as that in which they were originally present in the ore, with few exceptions, because of the similarity in chemical properties. The various processes for separating individual rare earth from naturally occurring rare-earth mixtures essentially utilize small differences in acidity resulting from the decrease in ionic radius from lanthanum to lutetium. The acidity differences influence the solubiUties of salts, the hydrolysis of cations, and the formation of complex species so as to allow separation by fractional crystallization, fractional precipitation, ion exchange, and solvent extraction. In addition, the existence of tetravalent and divalent species for cerium and europium, respectively, is useful because the chemical behavior of these ions is markedly different from that of the trivalent species. 

Corrective Action Application At a RCRA site in the southwest, a waste stream containing hexavalent chromium was reduced to the trivalent form. The trivalent chromium was then removed using ion exchange. The influent hexavalent chromium... 

R indicates the organic portion of the resin and SO3 is the immobile portion of the ion active group. Two resin sites are needed for nickel ions with a plus 2 valence (Ni ). Trivalent ferric ions would require three resin sites. As shown, the ion exchange reaction is reversible. The degree the reaction proceeds to the right will depend on the resins preference, or selectivity, for nickel ions compared with its preference for hydrogen ions. The selectivity of a resin for a given ion is measured by the selectivity coefficient. K. which in its simplest form for the reaction... 

Another point of contention has been the extent to which, if any, SbFj is reduced to SbFs upon intercalation. Although chemical analyses have shown an F Sb ratio of 5 1 (Lll, M5), Sb Mossbauer measurements (B24) indicated partial reduction of Sb(V) to Sb(III). On the other hand, mass-spectral measurements as a function of temperature (S15) showed only SbFs, evolved in stages, with no fluorocarbons emitted at any time. The latter are usually an indication of partial reduction of the intercalant and fluorination of the graphite host. Wide-line, F-NMR chemical-shifts are consistent with either SbFj or SbFe, but not with SbFs, but the occurrence of fluorine exchange could produce minor amounts of trivalent species (FI 1) this point is thus still controversial, and will be alluded to again. 

In the preparation of Mo/HUSY, the cluster 1 amounting to 2.5 wt% (as molybdenum metal) of HUSY was added to the suspension of HUSY 92% of the molybdenum was loaded onto HUSY. The Cl/Mo ratio of Mo/HUSY was found to be 0.34, suggesting that in ion exchange the cluster 1 acted as a trivalent cation on the average. These findings indicate that the protons in HUSY are less exchangeable by the cluster cation than the Na cations in NaY. 

F. Solvent Exchange on Octahedral Trivalent Transition Metal Ions... 

H. Solvent Exchange and Ligand Substitution on Trivalent Transition Metal Aquapentaammine Complexes... 

Parameters for Solvent Exchange on Trivalent Octahedral Transition Metal Species and Related Species... 

The selected treatment option involves the reduction of hexavalent chromium to trivalent chromium either chemically or electrochemically. The reduced chromium can then be removed using a conventional precipitation-solids removal system. Alternative hexavalent chromium treatment techniques include chromium regeneration, electrodialysis, evaporation, and ion exchange.16... 

The acidic character of 5A zeolite as a function of the calcium content has been explored by different techniques propylene adsorption experiments, ammonia thermodesorption followed by microgravimetry and FTIR spectroscopy. Propylene is chemisorbed and slowly transformed in carbonaceous compounds (coke) which remain trapped inside the zeolite pores. The coke quantities increase with the Ca2+ content. Olefin transformation results from an oligomerization catalytic process involving acidic adsorption sites. Ammonia thermodesorption studies as well as FTIR experiments have revealed the presence of acidic sites able to protonate NH3 molecules. This site number is also correlated to the Ca2+ ion content. As it has been observed for FAU zeolite exchanged with di- or trivalent metal cations, these sites are probably CaOH+ species whose vas(OH) mode have a spectral signature around 3567 cm"1. 

Di or trivalent cations are able to induce the dissociation of coordinated water molecules to produce acidic species such as MOH+ (or MOH2+ for trivalent metal cations) and H+. Several infrared studies concerning rare-earth or alkali-earth metal cation exchanged Y zeolites have demonstrated the existence of such species (MOH+ or MOH2+) [3, 4, 5, 6]. However, the literature is relatively poor concerning the IR characterization of these acidic sites for LTA zeolites. The aim of the present work is to characterize 5A zeolite acidity by different techniques and adsorption tests carried on 5A zeolite samples with different ion exchange. 

The overall distribution of lanthanides in bone may be influenced by the reactions between trivalent cations and bone surfaces. Bone surfaces accumulate many poorly utilized or excreted cations present in the circulation. The mechanisms of accumulation in bone may include reactions with bone mineral such as adsorption, ion exchange, and ionic bond formation (Neuman and Neuman, 1958) as well as the formation of complexes with proteins or other organic bone constituents (Taylor, 1972). The uptake of lanthanides and actinides by bone mineral appears to be independent of the ionic radius. Taylor et al. (1971) have shown that the in vitro uptakes on powdered bone ash of 241Am(III) (ionic radius 0.98 A) and of 239Pu(IV) (ionic radius 0.90 A) were 0.97 0.016 and 0.98 0.007, respectively. In vitro experiments by Foreman (1962) suggested that Pu(IV) accumulated on powdered bone or bone ash by adsorption, a relatively nonspecific reaction. On the other hand, reactions with organic bone constituents appear to depend on ionic radius. The complexes of the smaller Pu(IV) ion and any of the organic bone constituents tested thus far were more stable (as determined by gel filtration) than the complexes with Am(III) or Cm(III) (Taylor, 1972). 

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