Strontium carbonate, SrCO

Strontium Carbonate. Strontium carbonate, SrCO, occurs naturally as strontianite in orthorhombic crystals and as isomorphs with aragonite, CaCO, and witherite, BaCO. There are deposits in the United States in Schoharie County, New York in WestphaUa, Germany and smaller deposits in many other areas. None is economically workable. Strontianite has a specific gravity of 3.7, a Mohs hardness of 3.5, and it is colorless, gray, or reddish in color. 

The two principal strontium minerals are its carbonate, strontianite, SrCOs, and the more abundant sulfate mineral celestite, SrS04. 

Strontium occurs chiefly as sulfate (celestite, SrSO,i) and carbonate (strontianite. SrCO ) although widely distributed in small concentration. The commercially exploited deposits are mainly in England. The sulfate or carbonate is transformed into chloride, and the electrolysis of die fused chloride yields strontium metal,... 

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. 

Strontium Hexaferrite. Strontium hexaferrite [12023-91 -5] SrO-6 Fe2 03, is made by combining powdered ferric oxide, Fe203, and strontium carbonate, SrCO, and calcining the mixture at ca 1000°C in a rotary kiln (9). The material is cmshed, mixed with a binder, and pressed or extmded into... 

Strontium carbonate (SrCO ) is used to make radiation-resistant glass and TV picture tubes, as well as pyrotechnics. 

Elemental composition Sr 59.35%, C 8.14%, 0 32.51%. SrCOs is dissolved in dilute acid and carbon dioxide liberated is identified by the lime-water test (turns lime water milky). Strontium in solution is analyzed by various methods mentioned earlier (See Strontium). 

Some substitution of strontium (up to 14 mol.%), of lead (2 mol.% reported) but no barium has been reported in aragonite, although investigations at elevated temperatures and pressures show almost complete miscibility of these elements in the structure (Gaines et al., 1997, p. 442), and SrCOs (strontionite), BaCOs (witherite), and PbCOs (cerussite) are common minerals. A calculated plot (Figure 3(b)) for cations in ninefold coordination shows that this coordination theoretically allows trivalent rare earth elements and quadravalent and many other elements to be substituents in the structure. Ytterbium, europium, samarium, and radium carbonates with aragonite structure have been synthesized (Spear, 1983). 

Judd and Pope [36] conclude that because the activation energies for decompositions of CaCOj, SrCO, and BaCOj are all close to the corresponding enthalpies of dissociation (apparent values of , are 180,222 and 283 kJ mol and A//, 178, 235 and 269 kJ mol, respectively) the mechanisms of decomposition in all three substances are the same as that proposed by Hills [18] for calcite. Strontium carbonate [37] generally resembles the calcium salt in that an increase in sample size results in a decrease in reaction rate. Differences in behaviour were ascribed [37] to the occurrence of a crystallographic transformation and to fusion. 

For example, potassium nitrate is denoted by lA which means KNO3 or Strontium carbonate by 3D which means SrCOs. 

The four main components of fireworks are a container, a fuse, a bursting charge, and stars. Stars contain the chemical compoimds needed to produce light of brilliant colors. Many of these compounds contain alkaline earth metals, such as barium chloride (BaCl2), strontium carbonate (SrCOs), and calcium chloride (CaCla). The table identifies which metals are needed to make the colors seen during a fireworks display. 

Occurrence Strontium is present in the Earth s crust at an average concentratiOTi of 0.04% and is therefore 15th in abundance. Of the naturally occurring strontium compounds, only the minerals strontianite (strontium carbonate, SrCOs) and celes-tite (strontium sulfate, SrS04) are of economic importance. 

Black Ash Method, Reduction with Carbon. To enable the chemical reduction of SrSo4, celestite is mixed with powdered coal and then heated up to about 1,100°C. The chemical reaction follows the equation SrS04 + 2C SrS + 2CO2 and produces carbon dioxide and strontium sulfide. In the next process step, the strontium sulfide is dissolved in water, before carbon dioxide passes through SrS + H2O + CO2 SrCOs + H2S the solution, forming and precipitating strontium carbonate firom the solution. The by-product sulfur is recovered as elemental sulfur. 

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