Nickel sorption reactions

As indicated, Ni forms generally weak complexes with common inorganic ligands. However, complexes of sizeable stability are formed with many organic ligands and a considerable portion of this study has been devoted to their effects on nickel-sorption reactions. Those ligands specifically studied were sulfate (804 ), citrate, nitrilotriacetate (NTA), glycine, and cyanide. Appropriate data are summarized in Table I. These data were obtained from Baes and Mesmer (14), Sillen and Martell (15, 16), and Smith and Martell (17). 

Reactions of metal ions in aqueous media have been show n to be strongly influenced by surface sorption reactions. The adequate description of metal ion behavior in systems where particulates have been included is an important step in the application of laboratory data to natural systems of wide environmental interest. In this study, data on the adsorption of aqueous nickel, Ni, onto oxides of silica and iron is presented. Of special interest are the effects which various ligands have on the adsorption reactions. Data are analyzed through the use of the chemical equilibrium computer model REDEQL2 making use of the solvent-ion model of adsorption. 

Because of the delay in decomposition of the peroxide, oxygen evolution follows carbon dioxide sorption. A catalyst is required to obtain total decomposition of the peroxides 2 wt % nickel sulfate often is used. The temperature of the bed is the controlling variable 204°C is required to produce the best decomposition rates (18). The reaction mechanism for sodium peroxide is the same as for lithium peroxide, ie, both carbon dioxide and moisture are required to generate oxygen. Sodium peroxide has been used extensively in breathing apparatus. 

If the specifications for diesel fuels become even more strict in the future and sulfur levels less than 0.05% S (500 ppm) must be achieved, it may be more reasonable to remove the sulfur by means other than hydrotreating. At the level of 500 ppm, selective stoichiometric reactions or selective sorption may be worth considering, even if the sorptions are irreversible. It should be recalled that benzene was for many years freed of thiophene by stoichiometric removal by Raney nickel, as pointed out by Startsev (2). 

NaY (Katalistiksj Si/Al=2 56) was used as a starting material for preparation of NH, K, Cs exchanged samples and three series of stab.lliJed Y-zeolites. Nickel was introduced before molybdenum by ion-exchange from Wi(NO )2 solution. Molybdenum was incorporated into the zeolite by sublimation of Mo(CO) in hydrogen stream at room temperature. Sulfided and non-sulfided Mo Y and Ni-Mo-Y samples were characterized with XRD, ND sorption capacity and FTIR spectroscopy. Each sample (0.25 g. 0.5-1 mm grains) was partially decarbonylated at 425 K before the WGS reaction and next presulfided with 1 2 vo1 %)/H2 mixture at 675 K, Catalysts after pre-... 

The degree of reversibility can depend on the amount of time that the pollutant has been in contact with the solid. Sorption onto iron hydroxides, organic matter and metal carbonate minerals is often observed to be irreversible over time spans exceeding years (Brady etal. 1999). Immobilization reactions are indicated by slow reaction kinetics as found, for example, for the binding of nickel, zinc, and cadmium to different soil constituents which (Gerth 1985). When in contact with iron oxides, these elements are immobilized by matrix diffusion (Briimmer etal. 1988 Gerth etal. 1993). 

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