Calcium Composites

TOMLINSON You spoke about the addition of calcium carbonate to agricultural soils. For the Cranberry Lake area we heard from Dr. Bloomfield yesterday that the calcium composition of the water in the rivers was essentially the same as in the rain. But, some years ago, measurements were made on the various minerals in forest soil in Northern Quebec. The amount of calcium available was really not enough for another crop of trees, but the area is being cropped. It was indicated in this study that the inputs of calcium from the atmosphere would be very helpful based on values that were averaged from England and places where they d measured dust fall. From more recent measurements of the rain input into Northern Quebec, it s evident there is very little calcium added in this way, far less than there is in industrial areas closer to various sources of calcium input to the atmosphere. In addition, there is the leaching of calcium from the soil. I feel we may be in for some major problems. Have you any specific data on that type of area, where the calcium budget is low in the soil ... 

Polymer compositions containing pentaerythritol are also used as secondary heat-, light-, and weather-resistant stabilizers with calcium, zinc, or barium salts, usually as the stearate, as the prime stabilizer. The polymers may be in plastic or fiber form (87—89). 

A typical slag (specific gravity 3.6) contains complex siUcates of iron, calcium, 2iac, magnesium, and aluminum oxides. The quantity of fluxes (compounds added to lower the melting poiat) added depends on the feed composition, and is calculated to ensure a fluid slag at the operating temperature. 

Tia is also used as an ahoyiag element ia lead—antimony alloys to improve fluidity and to prevent drossiag, ia lead—calcium alloys to improve mechanical properties and enhance electrochemical performance, ia lead—arsenic alloys to maintain a stable composition, and as an additive to low melting alloys. 

Quicklime and hydrated lime are reasonably stable compounds but not nearly as stable as their limestone antecedents. Chemically, quicklime is stable at any temperature, but it is extremely vulnerable to moisture. Even moisture in the air produces a destabilizing effect by air-slaking it into a hydrate. As a result, an active high calcium quicklime is a strong desiccant (qv). Probably hydrate is more stable than quicklime. Certainly hydrated lime is less perishable chemically because water does not alter its chemical composition. However, its strong affinity for carbon dioxide causes recarbonation. Dolomitic quicklime is less sensitive to slaking than high calcium quicklime, and dead-burned forms are completely stable under moisture-saturated conditions. 

Recovery from Brines. Natural lithium brines are predominately chloride brines varying widely in composition. The economical recovery of lithium from such sources depends not only on the lithium content but on the concentration of interfering ions, especially calcium and magnesium. If the magnesium content is low, its removal by lime precipitation is feasible. Location and avadabiHty of solar evaporation (qv) are also important factors. 

Tricalcium phosphate, Ca2(P0 2> is formed under high temperatures and is unstable toward reaction with moisture below 100°C. The high temperature mineral whidockite [64418-26-4] although often described as P-tricalcium phosphate, is not pure. Whidockite contains small amounts of iron and magnesium. Commercial tricalcium phosphate prepared by the reaction of phosphoric acid and a hydrated lime slurry consists of amorphous or poody crystalline basic calcium phosphates close to the hydroxyapatite composition and has a Ca/P ratio of approximately 3 2. Because this mole ratio can vary widely (1.3—2.0), free lime, calcium hydroxide, and dicalcium phosphate may be present in variable proportion. The highly insoluble basic calcium phosphates precipitate as fine particles, mosdy less than a few micrometers in diameter. The surface area of precipitated hydroxyapatite is approximately... 

Fig. 12. Phase diagram of the CaO—H2O—P20 (calcium orthophosphate) system where the circle represents the variable hydroxylapatite composition and...

Tricalcium Phosphate. Commercial tricalcium phosphate (TCP) is actually an amorphous basic calcium phosphate close to hydroxyapatite in composition. Because of its extremely low solubiUty in water, TCP is precipitated almost quantitatively from dilute phosphate solutions with a slurry of hydrated lime. TCP is separated by dmm-, spray-, or flash-drying the TCP slurry, with or without intermediate sedimentation or filtration steps. It is used as an industrial-grade flow conditioner and parting agent. 

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