Earth volatiles

In 1768 A. S. Marggraf made the first chemical investigation of fluorite, distinguished it from heavy spar and selenitic spar (sulfates of barium and calcium), and showed that it is not a sulfate (77, 78). When he distilled pulverized fluorspar with sulfuric acid from a glass retort, the glass was badly attacked and even perforated. He noticed that an earth [silica] appeared in the receiver, and therefore concluded that the sulfuric acid had liberated a volatile earth from the fluorspar (77). 

Scheele stated that the acid of fluorspar [hydrofluoric acid] can dissolve siliceous earth and that therefore it is almost impossible to prepare the pure acid. He believed that the earthy deposit in the receiver (Marggraf s volatile earth ) was siliceous earth produced by a reaction... 

Sun, Apollo, Phoebus. The mercurial water and the volatile earth, are always female, often mother, as Ceres, Latona, Semela, Europa, etc. The water is ordinarily designated by the names, daughters, nymphs, naiads, etc. The internal fire is always masculine and active. Impurities are indicated by monsters. 

Achard described a eudiometer using burning phosphorus, investigated the phlogistication of dephlogisticated air, concluded from experiments similar to Priestley s (see p. 345) that nitrogen is a compound of water and the matter of fire, and supposed that fluorspar contains a volatile earth (as Marggraf,... 

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. 

The iodides of the alkaU metals and those of the heavier alkaline earths are resistant to oxygen on heating, but most others can be roasted to oxide in air and oxygen. The vapors of the most volatile iodides, such as those of aluminum and titanium(II) actually bum in air. The iodides resemble the sulfides in this respect, with the important difference that the iodine is volatilized, not as an oxide, but as the free element, which can be recovered as such. Chlorine and bromine readily displace iodine from the iodides, converting them to the corresponding chlorides and bromides. 

Opa.nte. There are two methods used at various plants in Russia for loparite concentrate processing (12). The chlorination technique is carried out using gaseous chlorine at 800°C in the presence of carbon. The volatile chlorides are then separated from the calcium—sodium—rare-earth fused chloride, and the resultant cake dissolved in water. Alternatively, sulfuric acid digestion may be carried out using 85% sulfuric acid at 150—200°C in the presence of ammonium sulfate. The ensuing product is leached with water, while the double sulfates of the rare earths remain in the residue. The titanium, tantalum, and niobium sulfates transfer into the solution. The residue is converted to rare-earth carbonate, and then dissolved into nitric acid. 

Reduction to Gaseous Metal. Volatile metals can be reduced and easily and completely separated from the residue before being condensed to a hquid or a soHd product in a container physically separated from the reduction reactor. Reduction to gaseous metal is possible for 2inc, mercury, cadmium, and the alkah and aLkaline-earth metals, but industrial practice is significant only for 2inc, mercury, magnesium, and calcium. 

The reaction of chlorine gas with a mixture of ore and carbon at 500—1000°C yields volatile chlorides of niobium and other metals. These can be separated by fractional condensation (21—23). This method, used on columbites, is less suited to the chlorination of pyrochlore because of the formation of nonvolatile alkaU and alkaline-earth chlorides which remain in the reaction 2one as a residue. The chlorination of ferroniobium, however, is used commercially. The product mixture of niobium pentachloride, iron chlorides, and chlorides of other impurities is passed through a heated column of sodium chloride pellets at 400°C to remove iron and aluminum by formation of a low melting eutectic compound which drains from the bottom of the column. The niobium pentachloride passes through the column and is selectively condensed the more volatile chlorides pass through the condenser in the off-gas. The niobium pentachloride then can be processed further. 

The acidic character of siUca is shown by its reaction with a large number of basic oxides to form siUcates. The phase relations of numerous oxide systems involving siUca have been summarized (23). Reactions of siUca at elevated temperatures with alkaU and alkaline-earth carbonates result in the displacement of the more volatile acid, CO2, and the formation of the corresponding siUcates. Similar reactions occur with a number of nitrates and sulfates. Sihca at high temperature in the presence of sulfides gives thiosiUcates or siUcon disulfide, SiS2. 

An extensive source of natural pollutants is the plants and trees of the earth. Even though these green plants play a large part in the conversion of carbon dioxide to oxygen through photosynthesis, they are still the major source of hydrocarbons on the planet. The familiar blue haze over forested areas is nearly all from the atmospheric reactions of the volatile organics... 

Figure 4 shows vapor pressure curves of rare-earth metals[24], clearly showing that there is a wide gap between Tm and Dy in the vapor pressure-temperature curves and that the rare-earth elements are classified into two groups according to their volatility (viz.. Sc, Y, La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, and Lu, non-volatile elements, and Sm, Eu, Tm, and Yb, volatile elements). Good correlation between the volatility and the encapsulation of metals was recently... 

As evidenced by their low abundances, carbon compounds, water, and other volatiles such as nitrogen compounds were probably not significantly abundant constituents of the bulk of the solids that formed near the Earth. Many of the carriers of these volatiles condensed in cooler, more distant regions and were then scattered into the region where the Earth was forming. Eragments of comets and asteroids formed in the outer solar system still fall to Earth at a rate of 1 x 10 kg/yr and early in the... 

As can be seen in Fig. 2-1 (abundance of elements), hydrogen and oxygen (along with carbon, magnesium, silicon, sulfur, and iron) are particularly abundant in the solar system, probably because the common isotopic forms of the latter six elements have nuclear masses that are multiples of the helium (He) nucleus. Oxygen is present in the Earth s crust in an abundance that exceeds the amount required to form oxides of silicon, sulfur, and iron in the crust the excess oxygen occurs mostly as the volatiles CO2 and H2O. The CO2 now resides primarily in carbonate rocks whereas the H2O is almost all in the oceans. 

Experimental work can be difficult owing to both the high volatility of the metals and their reactivity toward O2 (e.g., alkali-metals, alkali-earth metals, rare earths). Once reaction begins it often is highly exothermic judging by the enthalpies of formation of borides. ... 

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