Silicates lime-rich

In the study of the lime-natural pozzolan systems, lime-rich and lime-poor calcium silicate hydrates have been differentiated by The endothermal peak at 90°C was attributed to the lime-rich C-S-H phase, and that at 125°C, to the lime-poor C-S-H phase. An exothermic peak that appears in this system at about 850°C is caused by the crystallization of wollastonite. 

Terre verte or Veronese earth is a magnesium clay coloured by ferrous silicate. It is very rich in silica and poor in alumina and usually contains, besides magnesia, also small quantities of alkali, and sometimes lime and carbonic acid. 

Various methods for the removal of As from geothermal waste waters have been investigated at theoretical, laboratory, pilot plant and full plant scales. These include adsorption onto Fe-oxide floe and subsequent separation by dissolved air flotation (De Carlo and Thomas, 1985 Shannon et al., 1982) and co-precipitation with lime to form an As-rich calcium silicate (Rothbaum and Anderton, 1976). In both cases, effective removal was achieved only after oxidation of As" to As, For Fe-oxide floe treatment, competitive adsorption of silica inhibits As adsorption, particularly that of As" (Swedlund and Webster, 1999), suggesting that prior removal of silica would help optimise As removal efficiency. The use of ion selective chelating resins for As" removal from geothermal waters has also been successfully tried (Egawa et al, 1985). 

The interaction of zeolite-rich materials with Ca(OH)2 is of special interest, because zeolites, like other reactive aluminosilicate systems, e.g., crushed bricks, give rise to calcium silicates and aluminates, which are able to harden upon hydration in both aerial and aqueous environments. This behaviour, already known in ancient times, is typical of a volcanic, mostly glassy material, called pozzolana, which is the genetic precursor of the mentioned Neapolitan yellow tuff, widely spread in the surroundings of Naples, Italy [61]. That is why every material able to behave as pozzolana is called "pozzolanic material" and the property to react with lime is called "pozzolanic activity". 

Cu and Zn in concentrations up to three times those of granites. Mg-rich silicate rocks, such as peridotites and. serpentinites, typically enrich. soils, plants and waters with very high amounts of Mg, Fe, Cr, Co, Ni and V, but other trace elements remain very low. Al-rich silicate rocks, such as shales and micaschists, are often rich in sulfur and metal traces such as Zn, Pb, and Cd. In contra.st, carbonate dominated rocks, such as lime.stones or sulfate bearing dolomites, typically contribute to enrich their environment with Mn, F, S, Cl, Ba, Sr, As, Cd and radon. In conclusion, in.sujficient knowledge of this natural contribution can lead to misinterpretations of contaminated sites, e.specially for elements such as Ni, Cr, Zn, V, Cd and As. 

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