Silicate calcium

3 Stabilization of Lead with Calcium Silicate and Other Additives 

Bhatty [14] has stabilized solutions containing salts of cadmium, chromium, lead, mercury, and zinc with tricalcium silicate. Bhatty proposes that, in water, tricalcium silicate becomes calcium silicate hydrate, which can incorporate in its structure metallic ions of cadmium and other heavy metals. 

Komameni and colleagues [15-17] have suggested that calcium silicates exchange Ca + in the silicate structure for Pb. Their studies have shown that at least 99% percent of the lead disappears from a solution as a lead-siUcate-complex precipitate. 

Hock and colleagues [13] have suggested a more complex mechanism to explain why cement stabilizes lead the formation of lead carbonates. When cement is added to water, the carbonates are soluble. Meanwhile, the lead ions become soluble because lead hydroxides and lead oxides dissociate. These lead ions react with the carbonates in the solution and precipitate as lead carbonates, which have limited solubility. Over time, the environment in the concrete changes the lead carbonates dissolve, and lead ions react with silicate to form an insoluble, complex lead silicate. The authors point out that no concrete evidence supports this mechanism however, it agrees with lead stabilization data in the literature. 

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Cements are commonly made by heating a mixture of limestone and clay to about 1700 C. The product is ground with gypsum. Chemically cements consist of a mixture of calcium silicates and aluminates with some sulphate present. World production 1976 730 megatonnes. 

Brunauer and co-workers [129, 130] found values of of 1310, 1180, and 386 ergs/cm for CaO, Ca(OH)2 and tobermorite (a calcium silicate hydrate). Jura and Garland [131] reported a value of 1040 ergs/cm for magnesium oxide. Patterson and coworkers [132] used fractionated sodium chloride particles prepared by a volatilization method to find that the surface contribution to the low-temperature heat capacity varied approximately in proportion to the area determined by gas adsorption. Questions of equilibrium arise in these and adsorption studies on finely divided surfaces as discussed in Section X-3. 

Reaction (13.4) is exothermic and reversible, and begins at about 700 K by Le Chatelier s Principle, more iron is produced higher up the furnace (cooler) than below (hotter). In the hotter region (around 900 K), reaction (13.5) occurs irreversibly, and the iron(II) oxide formed is reduced by the coke [reaction (13.6)] further down. The limestone forms calcium oxide which fuses with earthy material in the ore to give a slag of calcium silicate this floats on the molten iron (which falls to the bottom of the furnace) and can bo run off at intervals. The iron is run off and solidified as pigs —boat-shaped pieces about 40 cm long. 

Calcium Silicate Brick. Sand—lime brick is used ia masonry ia the same way as common clay brick. The bricks, molded from a wet mixture of sand and high calcium hydrated lime, are heated under pressure ia a steam atmosphere. Complex hydrosiUcates are formed that give the bricks high dimensional stabiUty (6). 

Calcium Silicates. Cements aie hydiated at elevated tempeiatuies foi the commercial manufacture of concrete products. Using low pressure steam curing or hydrothermal treatment above 100°C at pressures above atmospheric, the products formed from calcium siUcates are often the same as the hydrates formed from their oxide constituents. Hence lime and siUca ate ftequendy used in various proportions with or without Portland cement in the manufacture of calcium siUcate hydrate products. Some of these compounds are Hsted in Table 6. 

Table 6. Calcium Silicate Hydrates Formed at Elevated Temperatures ...

AfwiUite can also be formed, and appears to be the thermodynamically stable calcium silicate hydrate in pure systems, at room temperature. 

Boron carbide from boron oxide and carbon Calcium silicate from lime and silica Calcium carbide by reaction of lime and carbon Leblanc soda ash... 

Container Insulation Tanks containing materials above atmospheric temperature may require insulation to reduce loss of heat. Almost any of the commonly used insulating materials can be employed. Calcium silicate, glass fiber, mineral wool, cellular glass, and plastic foams are among those used. Tanks exposed to weather must have jackets or protective coatings, usually asphalt, to keep water out of the insulation. 

Recommended Thickness of Insulation Indoor insulation thickness appears in Table II-2I, and outdoor thickness appears in Table 11-22. These selections were based upon calcium silicate insulation with a suitable aluminum jacket. However, the variation in thickness for fiberglass, cellular glass, and rockwool is minimal. Fiberglass is available for maximum temperatures of 260, 343, and 454°C ( 500, 650, and 850°F). Rock wool, cellular glass, and calcium sihcate are used up to 649°C (I200°F). 

Aluminum-jacketed calcium silicate insulation with an emissivity factor of 0.05. To convert inches to miUimeters, multiply by 25.4, to convert dollars per 1 miUion British thermal units to dollars per 1 nulhon kilojoules, multiply by 0.948, = 5/9 ( F — 32). 

Ca +, Fe + etc. which are the cationic species in the slag phase). Fellner and Krohn (1969) have shown that the removal of phosphorus from iron-calcium silicate slags is accurately described by the Flood-Grjotheim equation widr... 

For equivalent particle size the carbon blacks are the most powerful reinforcing fillers. However, fine particle size silicas can be very useful in non-black compounds whilst other fillers such as aluminium hydroxide, zinc oxide and calcium silicate have some reinforcing effect. 

Some commonly used insulating materials are calcium silicate, mineral slagwool, glass fiber, cellular glass, and polyurethane. 

The usual extraction procedure is to roast the crushed ore, or vanadium residue, with NaCl or Na2C03 at 850°C. This produces sodium vanadate, NaV03, which is leached out with water. Acidification with sulfuric acid to pH 2-3 precipitates red cake , a polyvanadate which, on fusing at 700°C, gives a black, technical grade vanadium pentoxide. Reduction is then necessary to obtain the metal, but, since about 80% of vanadium produced is used as an additive to steel, it is usual to effect the reduction in an electric furnace in the presence of iron or iron ore to produce ferrovanadium, which can then be used without further refinement. Carbon was formerly used as the reductant, but it is difficult to avoid the formation of an intractable carbide, and so it has been superseded by aluminium or, more commonly, ferrosilicon (p. 330) in which case lime is also added to remove the silica as a slag of calcium silicate. If pure vanadium metal is required it can... 

More advanced insulations are also under development. These insulations, sometimes called superinsulations, have R that exceed 20 fthh-°F/Btu-m. This can be accomplished with encapsulated fine powders in an evacuated space. Superinsulations have been used commercially in the walls of refrigerators and freezers. The encapsulating film, which is usually plastic film, metallized film, or a combination, provides a barrier to the inward diffusion of air and water that would result in loss of the vacuum. The effective life of such insulations depends on the effectiveness of the encapsulating material. A number of powders, including silica, milled perlite, and calcium silicate powder, have been used as filler in evacuated superinsulations. In general, the smaller the particle size, the more effective and durable the insulation packet. Evacuated multilayer reflective insulations have been used in space applications in past years. 

Calcium silicate Foam glass Mineral wool... 

Assume a 3-in. line. Design process temperature 320°F (Tp). Insulation 1 V2 -in- thick calcium silicate. Steam temperature 366°F (TJ. Ambient temperature 0°F (L,). 

L.F. Insulate 4" pipe and fit with calcium silicate, V thick, alum fin. 53.0... 

Silicates at about 20-40 p.p.m. are also used in cooling-water treatment although the build-up of protection can be slow. At higher temperatures calcium silicate may be deposited from hard waters. 

The calcium oxide formed reacts with impurities in the iron ore to form a glassy material called slag. The main reaction is with Si02 to form calcium silicate, CaSi03 ... 

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