Scandium, recovery

The scandium recovery process is ouUined schematically in Figure 5. The tungsten ore tailings are dissolved in the hydrazin sulfuric reagent, the pH is adjusted to 2.0, and the resulting solution is checked for the presence of ferric ion colorimetrically using the thiocyanate spot test. Any ferric ion content is reduced to the ferrous state by the addition of elemental iron as per the following equation ... 

The scandium retained on the strong cationic resin is eluted quantitatively with 6 N HCl. In the process, the resin is regenerated by the strong acid and can be used again at undiminished capacity. The scandium is then precipitated by the addition of saturated oxalic acid. The precipitate is filtered, washed, and converted to SC2O3 by calcination at elevated temperatures. The scandium recovery process is very efficient in that 99% of the Sc retained on the initial extraction column is recovered in the sesquioxide product. The overall recovery of the Sc present in the initial feed solution is determined solely by the point at which the extraction process is stopped. 

Due to absence of rich scandium raw minerals, scandium extraction is a complex process closely connected with the separation from impurities present on the leaching solutions. Chloride wastes after titanium-magnesium production (TMP) may be considered as a resource for scandium recovery. These wastes are highly mineralized hydrochloric pulps containing 0.08-0.1 g/L of Sc, more than 8 mol/L of HCl, and a large quantity of solid particles. 

The high extraction and kinetic properties of TVEX-TBP allowed for the development of and introduction to technology of selective scandium recovery ( TVEX-Sc-process [19,27]) from hydrochloric pulps obtained by leaching of accumulated mine wastes and salt chlorinators during titanium production. 

The recovery ratios indicate that the added traces of cadmium, cerium, copper, lanthanum, manganese, scandium, and zinc are quantitatively recovered. The recoveries of barium, cobalt, bromium, iron, uranium, and vanadium were also satisfactory. 

S. Kobayashi, T. Busujima, S. Nagayama, Scandium Triflate-Catalyzed Strecker-Type Readions of Aldehydes, Amines, and Tributyltin Cyanide in Both Organic and Aqueous Solutions. Achievement of Com-plde Recovery of the Tin Compounds toward Environmentally Friendly Chemical Processes Chem. Commun 1998, 981-982. 

To date, reports have involved palladium catalysts for Suzuki and Sono-gashira coupling reactions [63-66], rhodium catalysts for silylations of alcohols by trialkylsilanes [67,68], and tin-, hafnium-, and scandium-based Lewis acid catalysts for Baeyer-Villiger and Diels-Alder reactions [69]. Regardless of exact mechanism, this recovery strategy represents an important direction for future research and applications development. Finally, a particularly elegant protocol where CO2 pressure is used instead of temperature to desorb a fluorous rhodium hydrogenation catalyst from fluorous silica gel deserves emphasis [28]. 

The ore thortveitite may be cracked by fusion with sodium carbonate or by heating with hydrofluoric acid. In a series of steps, scandium is precipitated as hydroxide or oxalate, which on thermal decomposition forms lower yield of oxide. This recovery, however, is tedious and is now obsolete. 

In most recovery processes, scandium oxide is converted to its fluoride salt. The fluoride salt is the end product. The fluoride is converted to metallic scandium by heating with calcium in a tantalum crucible at elevated temperatures. A similar reduction is carried out with most rare earths. The metal is purified by distillation at 1,650 to 1,700°C under high vacuum in a tantalum crucible. 

The oxidizing atmosphere during the pretreatment of the ore helps to break up chemically the naturally occurring stable bonds in the solid, resulting in better dissolution rates. In a process developed for the recovery of scandium from uranium plant iron sludges (R15), the calcination of the sludge at 250°C was found to be very effective in the removal of organic materials and appreciably decreased the consumption of acid. 

In another attempt. Song et al. reported that ionic liquids [bmim]PF act as powerful media in scandium triflate catalyzed Diels-Alder reactions not only for the facilitating of catalyst recovery but also for the accelerating of the reaction rate and improving of selectivity (Scheme 17.5). Various dienes and dienophiles provided excellent yields and selectivity at room temperature in 4 h [47]. 

While use of trimethylsilyl cyanide (TMSCN) as a cyano anion source provides promising and safer routes to these compounds, TMSCN is easily hydrolyzed in the presence of water, and it is necessary to perform the reactions under strict anhydrous conditions. On the other hand, tributyltin cyanide (B SnCN) (Luijten and van der Kerk 1955, Tanaka 1980, Harusawa et al. 1987) is stable in water and is a potential cyano anion source, although there have been no reports of Strecker-type reactions using Bu3SnCN. In this section, we report scandium triflate-catalyzed Strecker-type reactions of aldehydes, amines, and Bu3SnCN in both organic and aqueous solutions. Complete recovery of the toxic tin compounds is also described. 

The recovery of Be compounds from gadolinlte is described in the section on scandium, jdtrium and rare earth metals. 

Non-chloroaluminate ILs, which are in general poor nucleophiles, have proven to be attractive alternative media for Lewis acid catalyzed reactions. ILs may have a reaction rate accelerating effect, and they may improve selectivity and facilitate catalyst recovery. This is the case for scandium triflate catalyzed Diels-Alder cycloaddition [8,9], three-component (aldehyde, aniline, triethylphosphite) synthesis of a-aminophosphonates [10], Claisen rearrangement and cyclization reactions [11], or Friedel-Crafts reactions [12, 13]. 

Zirconium-containing raw is a promising scandium source [19-23]. It was established that Sc is accumulated in carbon-containing residue after chlorination [21] and in manifold after separation of base zirconium sulfate [22-23], The extraction technology used for Sc recovery is based on leach neutralization, sludge separation, sludge leaching by nitric or hydrochloric acid, and scandium extraction by TBP solution in kerosene. The treated solution free of Sc is a valuable source of Zr and Hf. 

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