Scheelites

Luminescence spectrum of scheelite with a broad gate width of 9 ms is shown in Fig. 4.9d. The narrow lines at 490 and 572 nm are usually ascribed to Dy and the lines at 607 and 647 nm to Sm . Nevertheless, the relative intensity of the line at 607 nm compared to the line at 647 nm is lower at longer delay times (Fig. 4.9e,f). Besides that with a shorter gate width of 1 ps, when the relative contribution of the short lived centers is bigger, the characteristic lines of Sm at 647 nm and Dy at 575 nm disappear while the lines at 488 and 607 nm remain. Such luminescence is characteristic of Pr , which was confirmed by a time-resolved luminescence study of scheelite artificially activated by Pr and Sm (Fig. 5.5). Unlike in apatite, the phenomenon exists not only under 308 nm, but also under 337 nm excitation due to the higher energy 

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Sal soda, see Sodium carbonate 10-water Saltpeter, see Potassium nitrate Scacchite, see Manganese chloride Scheelite, see Calcium tungstate(VI)(2—)... 

Tungsten concentrate Scheelite from iron oxides and other conductor minerals Roll 1,50 -0.6 1.0-1.5. 3... 

In 1781 Scheele, and also T. Bergman, isolated another new oxide, this time from the mineral now known as scheelite (CaW04) but then called tungsten (Swedish tung sten, heavy stone). Two years later the Spanish brothers J. J. 

Tungsten occurs in the form of the tungstates scheelite, CaW04, and wolframite, (Fe,Mn)W04, which are found in China (thought to have perhaps 75% of the world s reserves), the former Soviet Union, Korea, Austria and Portugal. 

Scheel-skure./. tungstio acid, -spat, m. scheelite. 

Fig. 7—9. Comparison of x-ray and wet analytical results for scheelite and synthetic samples. Triangles = scheelite ores dots = synthetic samples. (Fagel, Liebhafsky, and Zemany, Anal. Chem., 30, 1918.)...

The flotation of sulfidic, oxidic, and salt-type ores and, in special cases, silicate ores can be improved by the use of ether carboxylates as collectors [221,222]. In particular, the flotation of fluorite, barite, and scheelite is mentioned. Special synergistic combinations of ether carboxylates with fatty acids [223] and with vinyl- or alkylsulfonic acid polymer [224] are described. 

Molybdates and tungstates Scheelite, powellite, wulfenite, ferrimolybdite... 

Monazite Bastnasite Scheelite Magnetite Ferberite Wolframite Gold... 

The electrostatic separation method is the exclusive choice in some specific situations, for example in the cases of rutile and ilmenite deposits. These deposits generally contain minerals of similar specific gravities and similar surface properties so that processes such as flotation are unsuitable for concentration. The major application of electrostatic separation is in the processing of beach sands and alluvial deposits containing titanium minerals. Almost all the beach sand plants in the world use electrostatic separation to separate rutile and ilmenite from zircon and monazite. In this context the flowsheet given later (see Figure 2.35 A) may be referred to. Electrostatic separation is also used with regard to a number of other minerals. Some reported commercial separations include those of cassiterite from scheelite, wolframite from quartz, cassiterite from columbite, feldspar from quartz and mica, and diamond from heavy associated minerals. Electrostatic separation is also used in industrial waste recovery. 

Those minerals whose solubilities are greater than those of most oxides and silicates, but lower than those of soluble salt minerals, are grouped as semisoluble salt minerals (also called salt-type minerals). The list comprising this particular minerals group is calcite, dolomite, magnesite, barite, gypsum, scheelite, carbonate, phosphate, sulfate and some others. These minerals are characterized mainly by their tonic bonding and as has already been pointed out, by their moderate solubility. 

Another reducing agent relevant to chlorination reactions is sulfur dioxide. When the material to be chlorinated contains calcium oxide, it is advantageous to convert it to calcium sulfate rather than to calcium chloride. The advantages are less chlorine consumption and easy disposal of calcium sulfate (which is water-insoluble). The chlorination of scheelite is an important example of the use of the sulfur dioxide chlorine reagent ... 

Complex oxides Chromite niobite-tantalite pyrochlore ilmenite wolframite scheelite... 

In order to make scheelite decomposition irreversible, quartz sand is added to the charge in an amount sufficient to bind calcium as an insoluble silicate. Alternatively, scheelite concentrates are directly decomposed with hydrochloric acid according to the reaction ... 

As a result of the decomposition, calcium chloride and other soluble impurities pass into solution, while tungstic acid, together with silica and undecomposed scheelite, remain in the residue. The technical grade tungstic acid thus obtained is purified using the ammonia-cal method. 

Fig. 12. Unit cell volume vs. for MM0O4 scheelite compounds...

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