The chemistry of silica surfaces

Holt, P. F.; King, David T.

doi:10.1039/jr9550000773

Cited by 49 publications

(18 citation statements)

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“…However, account has not been taken here of the considerable release of native silica from some clays. Holt and King (1955) reported sorption of .silicic acid on finely ground quartz at pH 8 but not at pH 4 and sorption of monosilicic acid on clay crystal faces cannot be ruled out. Further investigations are being carried out on this problem.…”

Section: Discussionmentioning

confidence: 74%

Studies on soluble silica in soils. I. The sorption of silicic acid by soils and minerals

Beckwith¹,

Reeve²

1963

Soil Res.

119

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Soils, representing a variety of great soil groups, were shaken with solutions containing monosilicic acid at concentrations not exceeding 135 p.p.m. The residual concentrations of monosilicic acid under near-equilibrium conditions depended on the nature of the soil, the level of added monosilicic acid, the solution : soil ratio and the pH of the soil suspension. The experimental results indicate that the residual concentration of monosilicic acid is controlled by an adsorption equilibrium which is dependent on pH; with acidification below pH 8-9 the residual concentration in soil suspensions steadily increases.Several samples of oxides and hydroxides of iron and aluminium were also shown to sorb monosilicic acid from solution. This sorption resembled that recorded for soils in its strong dependence on pH in the range 4-9. Sesquioxides appear to be responsible for much of the capacity of soils to sorb monosilicic acid. Wyoming bentonite and two kaolinite samples also sorbed monosilicic acid, at least from suspensions of pH above 7, and some natural and synthetic carbonates sorbed monosilicic acid at their natural pH values. Such minerals may contribute to the ability of some alkaline soils to sorb monosilicic acid.The avidity with which some soils sorb added monosilicic acid suggests that some native silica occurs in soils in the sorbed state. Some implications of this suggestion and of the other results are discussed in relation to some previous work on soils and natural waters, possible adsorption mechanisms, and some pedogenetic processes.Considering the abundance of silicon in the earth's crust surprisingly little attention has been given to its reactions in soils. The less abundant element aluminium, for example, has received much more investigation in recent years, presumably because of its importance to the chemistry of phosphorus in soils. However, there have been several indications of important effects of reactive silica in soils. Thus, among others, Dutt (1947) and Laws (1950) have reported beneficial effects of alkali metal silicates on soil physical properties and claims of decreased phosphate requirements of plants as a result of applications of silicates to soils have been made during several decades (e.g. Toth 1939). From such experiments it seems that reactive silica, resulting from hydrolysis of the metal silicates, can affect the properties of soils, for neither the pH change nor the addition of alkali metal ions would produce the observed results. Nevertheless the influence of native silica on the properties of field soils has apparently been considered unimportant by most workers (see, for example, Mehta et al. 1960).

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Section: Discussionmentioning

confidence: 74%

Studies on soluble silica in soils. I. The sorption of silicic acid by soils and minerals

Beckwith¹,

Reeve²

1963

Soil Res.

119

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“…Holt and King (1955) have shown that silica surfaces usually carry an incomplete monolayer of silicic acid which can be removed only by preliminary treatment by sodium hydroxide. This surface layer dissolves rapidly and provides much of the silica found in the solution.…”

Section: Particle Size and Solubilitymentioning

confidence: 99%

Metamorphic Reactions and Metamorphic Facies

Fyfe¹,

Turner²,

Verhoogen³

1958

Geological Society of America Memoirs

232

111

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This book presents a detailed discussion of a few selected topics in metamorphism. Chapter I (Turner) is a historical account of the development of the facies concept. A new definition of metamorphic facies is formulated.Chapters II to IV (Fyfe and Verhoogen), each of which ends with a summary in nontechnical language, deal respectively with certain thermodynamic and kinetic aspects of metamorphic-reactions. In Chapter II, the authors consider successively the magnitude of the free energy of metamorphic reactions, methods for computing approximate values of the entropies of silicates, a definition of the pressure variables in metamorphism, the role of surface films, and structural aspects of metamorphic mineralogy. The conclusion of Chapter III, which is devoted to a study of kinetics, is that reaction rates in systems containing water are generally such as not to lead to difficulties or inconsistencies in the interpretation of metamorphic facies. The role of water in metamorphic reactions is stressed again. This leads to a closer study of systems containing water, which are discussed in Chapter IV. Some properties of water are evaluated, such as its dielectric constant and ionic product, at high pressures and temperatures. A model is set up by which thermodynamic functions for hydration-dehydration reactions can be evaluated. There follows a discussion of solubility in aqueous systems and of variations of pH under natural conditions. _ In Chapter V, Fyfe and Turner correlate field and experimental data on the stability of critical mineral assemblages in metamorphic rocks. They conclude that there are at present no major inconsistencies between field and experimental data. Metamorphic facies, defined by mineralogical and field criteria, can still be interpreted in terms of a few intensive physical variables.The role of water and heat in metamorphism is considered in Chapter VI (Fyfe and Verhoogen). Regional metamorphism is not a normal phenomenon, in the sense that it would occur wherever rocks are buried to sufficient depth. On the contrary, it appears that regional metamorphism can occur only where the heat flow is notably increased and where water, probably of juvenile origin, is abundant.Chapter VII (Turner) is a revision of individual metamorphic facies. In the light of new experimental and mineralogical data the limits of some facies and subfacies are redefined, and a few new divisions are proposed.

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“…Sua retenção, comprovada por Holt & King (1955) por meio do Si 31 (radioativo), ocorre por adsorção específica às superfícies dos óxidos de Fe, à semelhança do P (Hingston et al, 1972). Fósforo e silício competem entre si pelos mesmos sítios de adsorção, de maneira que o segundo pode deslocar (dessorver) o primeiro, e vice-versa, da fase sólida para a líquida (Obihara & Russel, 1972;Oliveira, 1984;Leite, 1997).…”

Section: Introductionunclassified