Methods of increasing the extraction of rhenium
The main sources of rhenium now – wash acid, the dust from the roasting of molybdenite, electrostatic sulfuric acid plants copper smelting factory.
18.Compare and describe modern technologies of processing of mineral raw materials containing titanium.
Titanium is the ninth most abundant element on Earth. It is almost always present in igneous rocks and the sediments derived from them. It occurs in the minerals ilmenite, rutile and sphene and is present in titanates and many iron ores.
Three types of products are obtained directly from the titanium concentrates titanium tetrachloride, titanium dioxide, and ferrotitanium.
General flow sheet of the production of titanium tetiachloride and titanium dioxide from ilmenite concentrates (sulfuric acid method)
Pigment grade titanium dioxide (titanium white) contains from 94 to 98.57% TiO2 and some oxide admixtures (ZnO, Al2O3, SiO2 and occasionally Sb203), which are introduced in order to obtain the required structure and physico-chemical properties. Some pigment brands have the structure of rutile, others of anatase.
On the scheme seen that titanium chloride is produced by chlorination of titanium slags (75 to 85% TiO2) formed in the smelting of ilmenite concentrates. Two methods are used for the production of titanium dioxide: a) direct decomposition of ilmenite concentrates (or titanium slags) with sulfuric acid followed by precipitation of metatitanic acid from the sulfate solution; b) hydrolytic decomposition (or "burning") of titanium tetrachloride.
Chloride process
19. Show the differences in modern technology in the processing of zirconium and hafnium containing rare metal raw materials.
A very complex industrial processing route for the separation of Zr and Hf is described in Figure. Starting from ore (zircon), the first step consist of a chlorination in the presence of carbon, according to the reaction:
ZrO2(+ SiO2 + HfO2) + 2C +2Cl2 = ZrCl4 + HfCl4 + SiCl4 + 2CO
This operation is carried out in a tube furnace on a bed fluidized by chlorine gas, at a temperature of about 1470K. A selective condenser allows a first purification by fractionate condensation of the chlorides and collection of the mixed Zr + Hf chloride. The separation of Zr and Hf by distillation of the chlorides at atmospheric pressure is not practicable, due to the small difference is sublimation temperatures: 604K for ZrCl4 and 592K for HfCl4.
For the separation, two process are currently in use:
By addition of water, the chlorides are transferred into the oxychlorides ZrOCl2 + HfOCl2 . There are separated by liquid extraction with methyl isobutyl ketone (MIBK) in the presence of thiocyanate. The Hf passes into the organic phase, whereas the Zr remains in the aqueous phase. Both the Hf – containing and the Zr – containing phases are then treated with sulfuric acid and ammonia, and calcinated to form pure ZrO2 or HfO2. The oxides are chlorinated again to obtain pure water – free, ZrCl4 and HfCl4. This process has some inherent environmental problems: the high aqueous solubility and low flashpoint of MIBK, and the formation of possible gaseous contaminants generated by the decomposition of the thyocyanic complexes in the acid medium (H2S. HCN, mercaptans). It was shown that these problems can be avoided by using organophosphorous extractants instead of MIBK.
Extractive distillation of the chlorides in a bath molten KCl-AlCl3 at 623 K under atmospheric pressure.