Alkaline-earth metal ion adsorption

It was shown that the strong chemisorption of CN ions results in a significant increase of the Ca adsorption in an alkaline medium leading to a potential dependence of Cd adsorption that is characteristic for the potential dependence of the adsorption of CN ions. This result confirms the assumption that the unexpected potential dependence of alkaline earth metal ions (increasing adsorption with increasing potential) in alkaline medium is a result of their induced adsorption via adsorbed OH species. 

J.T.G. Overbeek, Electrokinetic phenomena, in Colloid Science, Vol. I (H. R. Kruyt, ed.). Elsevier, Amsterdam, 1952. R. O. James and T. W. Healy, Adsorption of hydrolyzable metal ions at the oxide-water interface. II Charge reversal of SiOa and Ti02 colloids by adsorbed Co(II), La(III), and Th(IV) as model systems, J. Colloid Interface Science 40 53 (1972). C.-P. Huang and W, Stumm, Specific adsorption of cations on hydrous a-Al203, /. Colloid Interface Science 43 409 (1973). S. L. Swartzen-Allen and . Matijevid, Colloid and surface properties of clay suspensions. II Electrophoresis and cation adsorption of montmorillonite, /. Colloid Interface Sci. 50 143(1975). G. R. Wiese, R. O. James, D. E. Yates, and T. W. Healy, Electrochemistry of the colloid-water interface, in Electrochemistry (J. O M. Bockris, ed.). Butterworths, London, 1976. D, W. Fuerstenau, D. Man-mohan, and S. Raghavan, The adsorption of alkaline-earth metal ions at the rutile/aqueous solution interface, in P. H. Tewari, op. cit. ... 

A similar interpretation of the data in Fig. 4.7 is given in D. W. Fuerstenau, D. Manmohan, and S. Raghavan, the adsorption of alkaline-earth metal ions at the rutile/aqueous solution interface, in P. H. Tewari, op. cit. ... 

The adsorption of N2 and O2 on ion exchanged type X zeolite was studied, independently, by McKee (1964) and Habgood (1964). In both studies, the sorbents were commercial type X zeolite with Si/Al 1.25, and the zeolite was ion-exchanged with both alkali and alkaline earth metal ions. Li+ was one of the ions included in both studies. These studies were performed at 1 atm pressure. The highest N2/O2 selectivities were obtained for Ba + > Sr + > Li+ > Ni + (McKee, 1964). 

The adsorption of the alkali metal and alkaline-earth metal ions by adsorbents e.g. precipitated silica, is interesting since it reveals the effects of the size and charge of the ions on the energetics of adsorption. Precipitated silica has a high adsorptive capacity and is a suitable candidate for the study. 

Zeolites are naturally occurring hydrous aluminum-sodium silicates in porous granule form. They are capable of exchanging their sodium base for calcium or magnesium and of expelling these alkaline earth metals for sodium by treatment with salt. Thus, they are a type of ion-exchange media. (Some zeolites act as molecular sieves by adsorption of water and polar compounds.)... 

Determination of trace metals in seawater represents one of the most challenging tasks in chemical analysis because the parts per billion (ppb) or sub-ppb levels of analyte are very susceptible to matrix interference from alkali or alkaline-earth metals and their associated counterions. For instance, the alkali metals tend to affect the atomisation and the ionisation equilibrium process in atomic spectroscopy, and the associated counterions such as the chloride ions might be preferentially adsorbed onto the electrode surface to give some undesirable electrochemical side reactions in voltammetric analysis. Thus, most current methods for seawater analysis employ some kind of analyte preconcentration along with matrix rejection techniques. These preconcentration techniques include coprecipitation, solvent extraction, column adsorption, electrodeposition, and Donnan dialysis. 

Barium reacts with metal oxides and hydroxides in soil and is subsequently adsorbed onto soil particulates (Hem 1959 Rai et al. 1984). Adsorption onto metal oxides in soils and sediments probably acts as a control over the concentration of barium in natural waters (Bodek et al. 1988). Under typical environmental conditions, barium displaces other adsorbed alkaline earth metals from MnO2, SiO2, and TiO2 (Rai et al. 1984). However, barium is displaced from Al203 by other alkaline earth metals (Rai et al. 1984). The ionic radius of the barium ion in its typical valence state (Ba+) makes isomorphous substitution possible only with strontium and generally not with the other members of the alkaline earth elements (Kirkpatrick 1978). Among the other elements that occur with barium in nature, substitution is common only with potassium but not with the smaller ions of sodium, iron, manganese, aluminum, and silicon (Kirkpatrick 1978). 

Most of electrodecarboxylations have been carried out with partially neutralized carboxylic acid. Alkaline and alkaline earth metal as well as ammonium (pyridinium) carboxylates work efficiently as supporting electrolytes. Some metal ions (such as Fe " and Co " ) are found to favor selectively radical reactions in electrodecarboxylation. Addition of certain salts, such as perchlorate, fluoroborate, sulfate, dihydrogen phosphate, bicarbonate, and fluoride, tends to inhibit the radical reaction and favor the formation of cation intermediates [28-31]. The remarkable effects of the salts are well explained in terms of competitive adsorption between the anions and carboxylates. 

Figure 2.3. Surface complexation phenomena in the retention or desorption of metals from mineral surfaces. Nonspecific (exchangeable) adsorption consists of electrostatic bonds only and the ions retain their hydration sphere (outer-sphere complexes) specific (nonexchangeable) adsorption requires removal of the hydration sphere (inner-sphere complexes). Alkali and alkaline earth metals tend to form outer-sphere complexes, hence their tendency to be loosely bound and readily exchangeable with other ions in solution. Transition metals tend to form inner-sphere complexes, which are more strongly bound and less exchangeable (Cotter-Howells and Paterson, 2000). Representation of (a) an outer-sphere complex, (b) an inner-sphere complex, and (c) a solution complex (see also Figure 2.2). The solid substrate is textured with the solution above this. Unlabeled spheres represent oxygen atoms, and the spheres labeled M represent metals in the substrate or in solution. Smaller shaded spheres labeled H are hydrogen atoms. (Adapted from Brown et al., 1999 Cotter-Howells and Paterson, 2000.)...

Il in, Turutina, and co-workers (Institute of Physical Chemistry, the Ukrainian S.S.R. Academy of Sciences, Kiev) (113-115) investigated the cation processes for obtaining crystalline porous silicas. The nature of the cation and the composition of the systems M20-Si02-H20 (where M is Li+, Na+, or K+) affect the rate of crystallization, the structure, and the adsorption properties of silica sorbents of a new class of microporous hydrated polysilicates (Siolit). These polysilicates are intermediate metastable products of the transformation of amorphous silica into a dense crystalline modification. The ion-exchange adsorption of alkali and alkaline earth metals by these polysilicates under acidic conditions increases with an increase in the crystallographic radius and the basicity of the cations under alkaline conditions, the selectivity has a reverse order. The polysilicates exhibit preferential sorption of alkali cations in the presence of which the hydrothermal synthesis of silica was carried out. This phenomenon is known as the memory effect. 

Azo dyes supported on silica gel were prepared and then-adsorption behavior toward metal ions were investigated. The l-(2-pyridylazo-2-naphthol)-immobilized silica gel and 2-(2-thiazolylazo)-p-cresol-immobilized silica gel showed greater affinity for UO(III) compared with Cu, Cd, Fe, and alkaline earths. Trace uranyl was quantitatively retained on the column at neutral pH. Matrix components in seawater did not interfere and the spiked recovery of uranyl in artificial seawater was found to average 98.6% with a relative standard deviation of 1.08%. ... 

Guan et al. (2009) removed trivalent chromium ions from waste water using synthetic zeolites. It was observed that zeolite can selectively adsorb chromium even in the presence of other alkali and alkaline earth metal cations including sodium and potassium. Xie et al. (2012) stated that if zeolites are modified with chitosan by forming a monolayer of chitosan on zeolite surface their adsorption capacities increases and they can preferentially adsorb phosphorous along with many other heavy metals from waste water. It was attributed to the increased porous structure of zeolites and non-zeolite fraction of different oxides. Monolayer of chitosan acted as binding material for adsorption of different heavy metal ions. 

The quantity dyl3 In a2 at the potential of the electrocapillary maximum is of basic importance. As the surface charge of the electrode is here equal to zero, the electrostatic effect of the electrode on the ions ceases. Thus, if no specific ion adsorption occurs, this differential quotient is equal to zero and no surface excess of ions is formed at the electrode. This is especially true for ions of the alkali metals and alkaline earths and, of the anions, fluoride at low concentrations and hydroxide. Sulphate, nitrate and perchlorate ions are very weakly surface active. The remaining ions decrease the surface tension at the maximum on the electrocapillary curve to a greater or lesser degree. 

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