Silicic acid sorption

Miller, D. M., Miller, W. P., and Sumner, M. E. (1986). Kinetics of silicic acid sorption by goethite using a flow-through cell. Agron. Abstr. p. 169. 

The kinetics of sorption of arsenite and arsenate in the presence of sorbed silicic acid have been only recently examined (Waltham and Eick 2002). These authors demonstrated that the sorption of silicic acid (added 60 h before arsenic) decreased the rate and the total amount of arsenic sorbed. The amount of arsenite sorbed decreased as the surface concentration of silicic acid increased. Furthermore, the inhibition of arsenite sorbed ranged from about 4% at a pH of 6 and 0.1 mM silicic acid up to 40% at a pH of 8 and 1 mol IT1 silicic acid. In contrast, silicic acid reduced the rate of arsenate sorption which decreased by increasing pH and silicic acid concentration, but the total quantity of arsenate sorbed remained nearly constant, indicating that arsenate was able to replace silicate. 

Violante A, Krishnamurti GSR, Pigna M (2008) Mobility of trace elements in soil environments. In Violante A, Huang PM and Gadd G (eds) Wiley-JUPAC series on biophysico-chemical processes of metals and metalloids in soil environments. John Wiley Sons, Hoboken, USA Waltham AC, Eick MJ (2002) Kinetic of arsenic adsorption on goethite in the presence of sorbed silicic acid. Soil Sci Soc Am J 66 818-825 Waychunas GA, Fuller CC, Rea BA, Davis J (1996) Wide angle X-ray scattering (WAXS) study of two-line ferrihydrite structure Effect of arsenate sorption and counterion variation and comparison with EXAFS results. Geochim Cos-mochim Acta 60 1765-1781... 

Compounds known to undergo changes in their absorption spectra upon sorption onto a solid surface are termed adsorptiochromic, and such effects would be ideally studied by means of diffuse reflectance spectroscopy. In one such study, the absorption of various spiropyrans onto many different solids was investigated [35]. For the compounds studied, the reflectance spectra were dominated by bands at 550 nm and in the range of 400-500 nm (most often at 472 nm). As an example, the reflectance spectra obtained for 6-nitrobenxospir-opyran are shown in Fig. 5. When the difference spectrum was taken between the spectrum of the pure compound and that obtained after sorption onto silicic acid, the bands characteristic of the adsorbed species were clearly evident. 

Fig. 5 Diffuse reflectance spectra of 6-nitrobenxospiropyran (A) in pure form and (B) after its sorption onto silicic acid. (Data adapted from Ref. 35.)...

Beckwith, R.S. Reeve, R. (1963) Studies on soluble silica in soils. I. The sorption of silicic acid by soils and minerals. Aust. J. Soil Res. 

TABLE 5.3. Rate and Quantity of Chromate Sorption in the Presence of Silicic Acid as a Function of pH... 

At the present moment we have at our disposal satisfactorily founded information on the structure of cellulose and a detailed picture of fibre structure which would seem to correspond rather well with the truth. On account of this knowledge, which is much more advanced than that on the actual structure of silicic acid gels, we may endeavour to give another more adequate interpretation of the sorption phenomena in cellulose... 

Iron Oxide Hydrogels. — Van Bemmelen f has investigated the dehydration of the gel of iron oxide and obtained curves similar to those of silicic acid. The water content decreases continuously with the decrease of vapor tension. The transition point is less pronounced than in the case of silicic acid gel. The course of the dehydration and the read-sorption is shown by the curves in Fig. 29. 

Sorption reactions of silica in soils were postulated many years ago (Sreenivasan [1935]). In the early work, however, somewhat high concentrations of sodium and potassium silicates were used, and such systems would be subject to hydrolysis and polymerization reactions and also to pH changes. Thus, in recent studies on the sorption of soluble silica by soils (Eliassaf [1962] Beckwith and Reeve [1963] McKeague and Cline [1963]), dilute solutions (100 to 135 ppm) of monomeric silicic acid have been employed, and results indicate that the residual concentration of monosilicic acid is controlled by an adsorption equilibrium which is pH dependent. Sesquioxides make a considerable contribution to the capacity of soils to sorb soluble silica (Nejegebauer [1958] Beckwith and Reeve [1963]), and the apparent increase in solubility of silica in soil suspensions with increased acidity has been discussed in terms of... 

The effect of other inorganic anions (sulfate, molybdate, silicate), low molecular mass organic ligands (LMMOLs, such as oxalate, malate, citrate, tartrate and succinate), and fulvic or humic acid on the sorption of arsenate and arsenite onto variable charge minerals and soils has been studied (Roy et al. 1986 Grafe et al. 2001 Liu et al. 2001 Violante et al. 2005a,b). 

Silicate, chromate, molybdenate, and humic acids also may create significant interferences with the sorption of As(V) and As(III) on zerovalent iron (Su and Puls, 2001b Giasuddin, Kanel and Choi, 2007). Interferences from borate and sulfate, however, were negligible with As(V) and only minor with As(III). Some interferences with As(III) and As(V) sorption occurred with carbonate and nitrate (Su and Puls, 2001b). Similarly, Farrell et al. (2001) concluded that carbonate and nitrate could hinder the efforts of zerovalent iron to lower As(V) concentrations in water to below 5 pgL-1. 

Some characteristic properties of bentonites (CEC, sorption properties) are mainly governed by the montmorillonite content and the layer charge of montmorillonite. Other properties, however, depend on the circumstances under which the rock is formed. These are particle size distribution, external specific surface area, and surface acid-base properties. The quantity of the edge sites mainly depends on the specific surface area. The protonation and deprotonation reactions take place on the edge sites of other silicates and aluminosilicates present beside montmorillonite, so their effects manifest via surface reactions. Consequently, the origin of bentonite determines all properties that are related to external surfaces. 

The sorption of uranium from acid sulfate leach liquors by strong base anion exchange resins is unusual since complexes of the type [U02(S04) ] " may be sorbed by both ion exchange and addition mechanisms. High concentrations of other species are present in the leach solution due to dissolution of pyritic and siliceous components of the ore, but, apart from iron, they do not interfere with the sorption of uranium as a complex anion. Iron(III) also forms an anionic sulfate complex, but is only weakly held by the resin and is displaced ahead of the uranium. The sorption of uranium may be represented by equations of the type ... 

It is shown that the solubility of siliceous rocks was 18.6 times higher than the solubility of quartz but 2.3 times lower than the solubility of amorphous silica. The soluble form of silica, monosilicic acid, is unstable. First the concentration of silica in solution increases and reaches a maximum then it decreases because of processes of sorption and polycondensation of soluble forms. 

Most of the recent adsorption literature has emphasized the importance of the acid-base properties of oxide surfaces when explaining or estimating their sorption behavior. However, Sveijensky (1993) has shown that log values for the adsorption of a specific cation by multiple mineral sorbents are a simple linear function of l/e, where e is the dielectric constant of each mineral. He has used this approach to estimate CC and TL model K"" values for the adsorption of up to 18 cations on 7 oxide and silicate mineral surfaces. 

---