Precipitation calcium carbonate-magnesium

Fit a 1500 ml. bolt-head flask with a reflux condenser and a thermometer. Place a solution of 125 g. of chloral hydrate in 225 ml. of warm water (50-60°) in the flask, add successively 77 g. of precipitated calcium carbonate, 1 ml. of amyl alcohol (to decrease the amount of frothing), and a solution of 5 g. of commercial sodium cyanide in 12 ml. of water. An exothermic reaction occurs. Heat the warm reaction mixture with a small flame so that it reaches 75° in about 10 minutes and then remove the flame. The temperature will continue to rise to 80-85° during 5-10 minutes and then falls at this point heat the mixture to boiling and reflux for 20 minutes. Cool the mixture in ice to 0-5°, acidify with 107-5 ml. of concentrated hydrochloric acid. Extract the acid with five 50 ml. portions of ether. Dry the combined ethereal extracts with 10 g. of anhydrous sodium or magnesium sulphate, remove the ether on a water bath, and distil the residue under reduced pressure using a Claiseii flask with fractionating side arm. Collect the dichloroacetic acid at 105-107°/26 mm. The yield is 85 g. 

Triturate 20 g. of dry o-toluidine hydrochloride and 35 5 g. of powdered iodine in a mortar and then grind in 17 -5 g. of precipitated calcium carbonate. Transfer the mixture to a conical flask, and add 100 ml. of distilled water with vigorous shaking of the flask. Allow the mixture to stand for 45 minutes with occasional agitation, then heat gradually to 60-70° for 5 minutes, and cool. Transfer the contents of the flask to a separatory funnel, extract the base with three 80 ml. portions of ether, diy the extract with anhydrous calcium chloride or magnesium sulphate, and remove the excess of solvent. The crude 5-iodo-2-aminotoluene separates in dark crystals. The yield is 32 g. Recrystallise from 50 per cent, alcohol nearly white crystals, m.p. 87°, are obtained. 

Barium carbonate prevents formation of scum and efflorescence in brick, tile, masonry cement, terra cotta, and sewer pipe by insolubilizing the soluble sulfates contained in many of the otherwise unsuitable clays. At the same time, it aids other deflocculants by precipitating calcium and magnesium as the carbonates. This reaction is relatively slow and normally requites several days to mature even when very fine powder is used. Consequentiy, often a barium carbonate emulsion in water is prepared with carbonic acid to further increase the solubiUty and speed the reaction. 

For electrical insulation china clay is commonly employed whilst various calcium carbonates (whiting, ground limestone, precipitated calcium carbonate, and coated calcium carbonate) are used for general purpose work. Also occasionally employed are talc, light magnesium carbonate, barytes (barium sulphate) and the silicas and silicates. For flooring applications asbestos has been an important filler. The effect of fillers on some properties of plasticised PVC are shown in Figure 12.21 (a-d). 

Lime is somewhat different from the hydrolyzing coagulants. When added to wastewater it increases pH and reacts with the carbonate alkalinity to precipitate calcium carbonate. If sufficient lime is added to reach a high pH, approximately 10.5, magnesium hydroxide is also precipitated. This latter precipitation enhances clarification due to the flocculant nature of the Mg(OH)2. Excess calcium ions at high pH levels may be precipitated by the addition of soda ash. The preceding reactions are shown as follows ... 

The most commonly observed effect of current flow is the development of alkaline conditions at the cathode. On bare metal this alkaline zone may exist only at the metal surface and may often reach pH values of 10 to 12. When the soil solution contains appreciable calcium or magnesium these cations usually form a layer of carbonate or hydroxide at the cathodic area. On coated lines the cations usually move to holidays or breaks in the coating. On failing asphalt or asphalt mastic type coatings, masses of precipitated calcium and magnesium often form nodules or tubercles several centimetres in diameter. 

The spring waters of the Sierra Nevada result from the attack of high C02 soil waters on typical igneous rocks and hence can be regarded as nearly ideal samples of a major water type. Their compositions are consistent with a model in which the primary rock-forming silicates are altered in a closed system to soil minerals plus a solution in steady-state equilibrium with these minerals. Isolation of Sierra waters from the solid alteration products followed by isothermal evaporation in equilibrium with the eartKs atmosphere should produce a highly alkaline Na-HCO.rCOA water a soda lake with calcium carbonate, magnesium hydroxy-silicate, and amorphous silica as precipitates. 

Most natural waters contain substances which will precipitate at points where polarization occurs in electric membranes units. The most common such substances are calcium carbonate, magnesium hydroxide, and calcium sulfate. Natural waters vary widely in the amounts and proportions of these substances present and accordingly in the ease in which they precipitate salts under polarizing conditions. Accordingly, it is very difficult to predict the performance of spacer-membrane combinations without actual tests on the natural waters of interest. 

In deeper systems dominated by calcium-rich saline fluids, it has been shown that both solubility constraints and silicate reactions act to further remove bicarbonate ions as precipitated calcium and magnesium carbonates, often adjusting pH to levels greater than 9 (Barnes and O Neil, 1971 Fritz et al., 1987a Clauer et al., 1989). For example, during closed-system dissolution of magnesium olivine (forsterite), a major component of many ultramafic rocks, as the silicate water reaction proceeds water breaks down, H" " ions are consumed, carbonates precipitate, and hydroxyl ions force the pH to rise (Barnes and O Neil, 1971 Drever, 1988). 

After a couple of years the outer surface of the saltpetre earth was removed, and the nitrates extracted by lixiviation with water. To the solution potassium carbonate was added, and on concentration and filtering from the precipitated calcium and magnesium salts, the clear solution was evaporated for KNOa. 

Generally, the concentrations of the interfering transition metal ions in the brine are decreased sufficiently by simple adsorption onto the colloidal precipitates of calcium carbonate, magnesium carbonate, and barium sulfate produced by conventional brine pretreatment. The brine is then acidified with hydrochloric acid to about pH 4. This helps to maintain a high hydrogen overvoltage on mercury in order to minimize the formation of hydrogen in the... 

The alkalinity in sea water is almost entirely due to bicarbonate. When the sea water is heated, the bicarbonate breaks down to produce carbon dioxide and carbonate ion. The carbonate can further disproportionate to produce carbon dioxide and hydroxyl ion. The carbonate can react with the dissolved calcium to precipitate calcium carbonate when the solubility is exceeded at the concentrations, temperatures, and pressures at which the evaporation is conducted. Dissolved magnesium can react with the hydroxyl ion to precipitate magnesium hydroxide. 

There are many applications where magnesium is regarded as an undesirable impurity. These include the production of hydrated lime (at atmospheric pressure), aerated concrete, sandlime bricks, and precipitated calcium carbonate, for which MgCOa levels should preferably be less than 2 % and, ideally, less than 1 % in the limestone. 

Hardness caused by calcium and magnesium bicarbonates is referred to as carbonate hardness (formerly called temporary hardness). It can be reduced by boiling the water to drive off carbon dioxide and precipitating calcium and magnesium carbonates (28.3, 28.4). This process causes the lime scale frequently found in kettles and boilers. 

The most common scale found in RO/NF systems is calcium carbonate because it precipitates quickly once concentrated beyond its solubility limit, and also because most natural waters are almost saturated with respect to calcium carbonate (magnesium, barium... 

Brine is treated in a reactor with sodium carbonate and caustic soda to precipitate calcium carbonate and magnesium hydroxide, as shown in Eqs. (1) and (2). 

Calcium and magnesium precipitation Calcium and magnesium ions are precipitated from hard water by adding sodium carbonate and lime. Insoluble calcium carbonate and magnesium hydroxide are precipitated and are removed by... 

The choice of antiblocking additive depends on the polymer, the desired film quality, and whether there is a pigment. Several inorganic substances are used, including synthetic amorphous precipitated silica, diatomaceous earths, nepheline syenite, calcined clay, coated calcium carbonate, magnesium carbonate, magnesium sulphate, mica, talc and various zeolites. Calcium carbonate particles are approximately spherical, but silica ones are irregular mica forms sheets and talc is plate-like. 

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