Silica in soil

Dixon JB (1989) Kaolin and serpentine group minerals. In Dixon JB, Weed SB (eds) Minerals in Soils. Soil Science Society of America, Madison, Wl, pp 468-527 Dress LR, Wilding LP, Smeck NE, Senkayi AL (1989) Silica in Soils Quartz and disordered silica polymorphs. In Dixon JB, Weed SB (eds.) Minerals in Soil Environment, 2edn. Soil Science Society of America, Madison, Wl. 

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. 

Meunier J. C., Colin F., and Alarcon C. (1999) Biogenic storage of silica in soils. Geology 27, 835-838. 

According to Jones and Handreck (1967), silica in soil solutions is entirely in the monomeric form Si(OH)4 (monosilicic acid) and is present in concentrations generally ranging from 7-80 jug g , but always less than the saturation value (about 120 pgg" ). The concentration of dissolved silica in soils depends on those factors which control dissolution rates of polymeric silica and on those which control the rate of removal of monosilicic acid from solution. 

Crystallinity. Non-crystalline forms will dissolve more rapidly than crystalline forms the vast majority of biogenic silica in soils is non-crystalline. 

Specific surface area. The higher the specific surface area (surface area volume ratio) of silica particles, the greater their dissolution rate will be in general, it is also true that smaller particles will dissolve more rapidly than larger particles (as much as 50-75% of biogenic silica in soils may be in the <5/im size fraction). 

Soil microorganisms. Many reports have documented the ability of certain soil microorgEmisms (especially bacteria such as Bacillus siliceous, which is used as a fertilizer in some parts of the Soviet Union (Cooper, 1959)) to depolymerize silica and convert it to the soluble monomeric form (see e.g., Lauwers and Heinen, 1974, and references therein) thus, the presence or absence of these oi anisms can be expected to play an important role in determining the concentration of dissolved silica in soil solutions. 

Adsorption. Monomeric silica can be removed from solution by adsorption onto surfaces of sesquioxide minerals (e.g., AljOa, FejOa) through pH-dependent reactions that apparently involve hydrogen bonding (see Jones and Handreck, 1967, and references therein) such reactions, especially with AI2O3, seem to exert a major control over the concentration of dissolved silica in soil solutions. 

Formation of clay minerals. It is generally agreed that some of the dissolved silica in soils is utilized in the formation of authigenic clay minerals however, the quantitative significance of this process is unclear (McKeague and Cline, 1963). 

The silica in soil moisture in temperate humid climates may reach saturation with amorphous silica, probably because of evaporative concentration (Sears and Langmuir 1982). Mean or median silica concentrations in soil moisture are poorly known. The median value of 54 ppm in Table 7.4 is from a study of C-horizon (deep) soils in central Pennsylvania (Sears and Langmuir 1982),... 

Continued dissolution of K-feldspar as the water moves downward through the soil tends to raise the pH and concentrations of both dissolved potassium and silica in soil waters. At point B saturation with kaolinite is reached, and the weathering reaction along line B —> C is... 

The proof of reversibility in primary mineral weathering would be instances where primary mineral structures have formed under earth-surface conditions. There are reports that secondary quartz can slowly precipitate at room temperature from solutions supersaturated with monosilicic acid. More typically, however, precipitated silica in soils is structurally disordered, in the form of chalcedony or opal. In fact, as long as alumina is present, silica does not precipitate as a separate phase, reacting instead to form aluminosilicates (layer silicates, imogolite, or allophane). 

Wilding, L. P., N. E. Smeck, and L. R. Drees (1977). Silica in soils Quartz, cristobalite, tridymite, and opal. In "Minerals in Soil Environments" (J. B. Dixon and S. B. Weed, eds.), pp. 471-552. Soil Science Society of America, Madison, Wisconsin. 

Previous Work. Information pertinent to this investigation has been drawn from three types of data the large body of published stream-water analyses, the basic work on solubilities of crystalline and amorphous silica and of various silicates, and a group of recent reports on dissolved silica in soil waters. 

The rapid achievement of a constant value of silica in soil water demonstrates that the opportunity for equilibration exists, but the electrolytes do not show any signs of reaching a plateau concentration. The electrolytes apparently do not equilibrate with the soil during or shortly after a storm period. Thus, during storm runoff, when more than 75% of the annual discharge occurs, there is not sufficient time for chemical equilibrium of the electrolytes to be reached in soil water, and it appears that reaction kinetics must be an important factor in determining the concentrations of the electrolytes. 

All of the organic matter and part of the aluminosilicates, hydroxyoxides, and silica in soil exist in structures too small or too poorly crystalline to be detectable by x-ray diffraction, These amorphous materials are not well understood, but they should logically be among the most reactive of soil components, because their structure is so open and their surface area so great, They represent a transition state between unweathered parent materials and well-crystallized secondary soil minerals. 

The x-ray amorphous silica in soils includes opaline silica in the form of plant phytoliths. During plant growth, silica precipitates on the walls of plant cells. After death and organic decay of the plant, the silica phytoliths remain in the soil for many year s as accurate representation of the cell wall. Phytoliths are visible under the microscope and can identify the plants in which they formed. 

Silica is a mineral that is found in stone, soil and sand. The amount of silica in soil and rock may vary widely depending on the local geology Breathing in silica dust can cause silicosis, a serious lung disease. 

Beckwith RS, Reeve R (1964) Studies on soluble silica in soils. II. The release of monosilicic acid from soils. Aust J Soil Res 1 157-168 Bennett PC (1991) The dissolution of quartz in organic-rich aqueous systems. Geochim Cosmochim Acta 55 1781-1797... 

The occurrence of amorphous silica in soil clays appears to be associated frequently with parent material for instance, it is commonly observed in New Zealand soils of volcanic origin (Fieldes and Swindale [1954]). The clay from the A2 horizon of a Kaieri podzol (Fieldes and Williamson [1955]) provides an unusual example, consisting essentially of silica, an appreciable proportion of which is amorphous. The silica, in addition, tends to be grouped into very thin sheets in contrast to the clustered aggregates noted when silica gel is associated with aluminum and iron oxides. Hydrated silica gel has also been reported in Japanese soils developed on pumice (Kanno [1959] Matsui [1959]), but the morphology is not described. 

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... 

Acquaye, D. K., and J. Tinsley, 1965. Soluble silica in soils. In Experimental Pedology. E. G. Halls-worth and D. V. Crawford, ed. London Butterworths, p. 126. 

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