Calcium: compounds

In addition to the main acidulation reaction, other reactions also occur. Free calcium carbonate in the rock reacts with the acid to produce additional by-product calcium compounds and CO2 gas which causes foaming. Other mineral impurities, eg, Fe, Al, Mg, U, and organic matter, dissolve, the result being that the wet-process acid is highly impure. 

Calcium. Calcium is the fifth most abundant element in the earth s cmst. There is no foreseeable lack of this resource as it is virtually unlimited. Primary sources of calcium are lime materials and gypsum, generally classified as soil amendments (see Calcium compounds). Among the more important calcium amendments are blast furnace slag, calcitic limestone, gypsum, hydrated lime, and precipitated lime. Fertilizers that carry calcium are calcium cyanamide, calcium nitrate, phosphate rock, and superphosphates. In addition, there are several organic carriers of calcium. Calcium is widely distributed in nature as calcium carbonate, chalk, marble, gypsum, fluorspar, phosphate rock, and other rocks and minerals. 

High alpha-ceUulose chemical woodpulp paper, machine-made primarily from fast-growiag softwoods, sized usiag alkaline calcium compounds, and loaded with fillers and other additives, constitutes a presumably more stable material. Different types of paper are used for art, manuscripts, documents, books, etc, each having its own properties of color, texture, feel, etc. 

The FCC is to food-additive chemicals what the USP—NF is to dmgs. In fact, many chemicals that are used in dmgs also are food additives (qv) and thus may have monographs in both the USP—NF and in the FCC. Examples of food-additive chemicals are ascorbic acid [50-81-7] (see Vitamins), butylated hydroxytoluene [128-37-0] (BHT) (see Antioxidants), calcium chloride [10043-52-4] (see Calcium compounds), ethyl vanillin [121-32-4] (see Vanillin), ferrous fumarate [7705-12-6] and ferrous sulfate [7720-78-7] (see Iron compounds), niacin [59-67-6] sodium chloride [7647-14-5] sodium hydroxide [1310-73-2] (see lkaliand cm ORiNE products), sodium phosphate dibasic [7558-79-4] (see Phosphoric acids and phosphates), spearmint oil [8008-79-5] (see Oils, essential), tartaric acid [133-37-9] (see Hydroxy dicarboxylic acids), tragacanth [9000-65-1] (see Gums), and vitamin A [11103-57-4]. 

The principal calcium salt used as a flocculant is calcium hydroxide [1305-62-0] or lime. It has been used in water treatment for centuries (see Calcium compounds). Newer products are more effective, and its use in water and effluent treatment is declining (10). It is still used as a pH modifier and to precipitate metals as insoluble hydroxides. Lime is also sometimes used in combination with polymeric flocculants. 

Precipitated Calcium Carbonate. Calcium carbonate [471-34-1] (Turns), CaCO, is a fine white microcrystaUine powder without odor or taste. It is stable in air. An aqueous suspension is close to neutrality. It is practically insoluble in water, insoluble in alcohol, and dissolves with effervescence in dilute acetic, hydrochloric, and nitric acids (see Calcium compounds, calcium carbonate). 

Alkali metal haHdes can be volatile at incineration temperatures. Rapid quenching of volatile salts results in the formation of a submicrometer aerosol which must be removed or else exhaust stack opacity is likely to exceed allowed limits. Sulfates have low volatiHty and should end up in the ash. Alkaline earths also form basic oxides. Calcium is the most common and sulfates are formed ahead of haHdes. Calcium carbonate is not stable at incineration temperatures (see Calcium compounds). Transition metals are more likely to form an oxide ash. Iron (qv), for example, forms ferric oxide in preference to haHdes, sulfates, or carbonates. SiHca and alumina form complexes with the basic oxides, eg, alkaH metals, alkaline earths, and some transition-metal oxidation states, in the ash. 

Selective Reduction. In aqueous solution, europium(III) [22541 -18-0] reduction to europium(II) [16910-54-6] is carried out by treatment with amalgams or zinc, or by continuous electrolytic reduction. Photochemical reduction has also been proposed. When reduced to the divalent state, europium exhibits chemical properties similar to the alkaline-earth elements and can be selectively precipitated as a sulfate, for example. This process is highly selective and allows production of high purity europium fromlow europium content solutions (see Calcium compounds Strontiumand strontium compounds). 

If ingestion occurs, dilute solutions of calcium compounds (calcium lactate, calcium gluconate, etc) or a large amount of milk followed by magnesium sulfate should be adrninistered (63,64). 

Calcium carbonate, available both from natural sources and as precipitated forms (see Calcium compounds), is most useful in coating because of purity and high brightness, ie, 90—95%. Ground carbonates from marble deposits have high purity levels as do the carbonates from some chalk deposits. 

Such high density salt solutions are extremely expensive. Sodium chloride and calcium chloride are the only salts that are used in large quantities for drilling (see Calcium compounds Sodium compounds). 

Strontium has a valence of +2 and forms compounds that resemble the compounds of the other alkaline-earth metals (see Barium compounds Calcium compounds). Although many strontium compounds are known, there are only a few that have commercial importance and, of these, strontium carbonate [1633-05-2] SrCO, and strontium nitrate [10042-76-9], Sr(N03)2, are made in the largest quantities. The mineral celestite [7759-02-6], SrSO, is the raw material from which the carbonate or the nitrate is made. 

Barium is a member of the aLkaline-earth group of elements in Group 2 (IIA) of the period table. Calcium [7440-70-2], Ca, strontium [7440-24-6], Sr, and barium form a closely aUied series in which the chemical and physical properties of the elements and thek compounds vary systematically with increa sing size, the ionic and electropositive nature being greatest for barium (see Calcium AND CALCIUM ALLOYS Calcium compounds Strontium and STRONTIUM compounds). As size increases, hydration tendencies of the crystalline salts increase solubiUties of sulfates, nitrates, chlorides, etc, decrease (except duorides) solubiUties of haUdes in ethanol decrease thermal stabiUties of carbonates, nitrates, and peroxides increase and the rates of reaction of the metals with hydrogen increase. 

Gypsum [13397-24-5] CaSO 2H20, is a naturally occurring mineral found mainly in the western United States and eastern Canada (see Calcium COMPOUNDS, CALCIUM sulfate). The purer deposits require only minimal beneficiation to get a product pure enough for commercial appHcations. Other... 

The word calcium is derived from calx, the Latin word for lime. The Romans used large quantities of calcium oxide or lime as mortar in constmction (see Lime and limestone). Because calcium compounds are very stable, elemental calcium was not produced until 1808 when a mercury amalgam resulted from electrolysis of calcium chloride in the presence of a mercury cathode. However, attempts to isolate the pure metal by distilling the mercury were only marginally successful. 

Calcium metal and most calcium compounds are nontoxic. In massive pieces the metal does not spontaneously bum in air. Calcium can be touched with dry bare hands without harm. Care must be taken, however, to avoid contact with water owing to the exothermic Hberation of hydrogen and the resulting explosion hazard. Calcium must always be kept dry and preferably sealed in the shipping containers. 

As befits the electron configuration of elemental calcium, the metal is very reactive, readily losing two valence electrons to form the dispositive ion. In aqueous solution and ia its compounds, is colorless. Most calcium compounds ate white, unless the cation is paired with a colored anion. The ion... 

A former commercially important source of calcium chloride was as a by-product of the Solvay process used to produce soda ash (28). Because of environmental concerns and high energy costs, the Solvay process has been discontinued ia the United States though it is stiU used extensively elsewhere ia the world (see Calcium compounds). 

Scmbbers for removing sulfur dioxide from smelter off-gases have been under development for many years. They are widely used in Japan. The calcium sulfate (gypsum) obtained from this process is suitable feed for waUboard production (see Calcium compound, calcium sulfate Sulfur removal and recovery). 

There have been a number of cell designs tested for this reaction. Undivided cells using sodium bromide electrolyte have been tried (see, for example. Ref. 29). These have had electrode shapes for in-ceU propylene absorption into the electrolyte. The chief advantages of the electrochemical route to propylene oxide are elimination of the need for chlorine and lime, as well as avoidance of calcium chloride disposal (see Calcium compounds, calcium CHLORIDE Lime and limestone). An indirect electrochemical approach meeting these same objectives employs the chlorine produced at the anode of a membrane cell for preparing the propylene chlorohydrin external to the electrolysis system. The caustic made at the cathode is used to convert the chlorohydrin to propylene oxide, reforming a NaCl solution which is recycled. Attractive economics are claimed for this combined chlor-alkali electrolysis and propylene oxide manufacture (135). 

Carbon dioxide and calcium carbonate The effect of carbon dioxide is closely linked with the bicarbonate content. Normal carbonates are rarely found in natural waters but sodium bicarbonate is found in some underground supplies. Calcium bicarbonate is the most important, but magnesium bicarbonate may be present in smaller quantities in general, it may be regarded as having properties similar to those of the calcium compound except that on decomposition by heat it deposits magnesium hydroxide whereas calcium bicarbonate precipitates the carbonate. 

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