Explain differences of purification methods of gallium.
Gallium is a typical scattered element. It is found in the form of an isomorphous impurity (at concentrations of 0.04 to 0.001%) in many aluminum and iron minerals and in zinc blende. Only one gallium mineral, 339 gallite (CuGaSz), is known (it was discovered in 1958). The mineral germanite has a relatively high gallium content.
Gallium of a high degree of purity (99.9999%) is usually produced by a combination of several purification methods: a) electrolytic refining; b) vacuum distillation of the impurities; c) zone melting.
The process of gallium purification is very laborious and it has many stages. It has been used the impure metallic gallium. For purification we have used the following scheme:
1. Acid treatment with concentrated mineral acids. An acids mixture of HCl and HNO3 has been used in various proportions and concentrations, at 35oC. The ratio of the acid solution at metallic gallium was 0.8 ml / 1 g Ga.
2. Filtration. The liquid metallic gallium was vacuum filtrated through the glass or quartz porous plates in teflon apparatus. The average diameter of the filter pores is 15 - 40 µm for a vacuum filtration.
3. Electrolytic process in alkaline solution. As electrolyte a 25 % KOH solution has been used at a temperature of 60 - 70 o C. The electrolytic cell comprises a circulating system for the electrolyte. A mean current of about 3-ampere is set up. The resulting deposition is about 2 g/h, and the calculated current yield is about 90 %. The apparatus can be operated continuously and without servicing for a long time.
4. Vacuum distillation. The process of distillation was based on the fact that the vapor pressure of Ga at high temperature remains almost constant. The work has been done a temperature of 750 - 1000oC, in quartz apparatus, in high vacuum for 24 hours.
5. Horizontal melting zone technique. The material was purified in vacuum by the horizontal melting zone method. The velocity of the melted zone was 12 - 15 mm/h and 25 passing were made. The purity of the material was investigated by chemical analysis. We have determined the content of metallic impurities using an emission spectroscopy technique.
Explain technological schemes of rhenium from Zhezkazgan ore, sources loss of rhenium and methods to reduce losses
Significant resources are concentrated in some deposits of copper, is a type of copper sandstone and copper schists. This type includes Dzhezkazgan ore deposits in which it was found a high rhenium content.
The rhenium content varies:
• in the wash sulfuric acid from 100 to 250 mg/L,
• in the electrostatic dust: from 140 to 320 g/t,
• in the slime from 400 to 900 g/t.
At the present time wash sulfuric acid is the only source of its industrial production in Kazakhstan. There is another valuable element, an stable isotope of osmium 187, in the wash sulfuric acid and slime. Its content is 0.3-0.8 mg/L and 50-90 g/t, respectively.
Overall recovery of rhenium to commercial ammonium perrhenate from the solution according to the technology is 98,05 %.
The rhenium recoveries for each stage in the process are:
• extraction - 99,5%;
• solid phase stripping – 99,36%, of which 89,1% in crude ammonium perrhenate and 10,26% in mother liquor;
• dissolution of the pulp with formation of crude ammonium perrhenate – 92,27%;
• re-crystallization of crude ammonium perrhenate into commercial salt – 99,99%;
• precipitation of complex salt - Zn(NH3)4(ReO4)2 from mother liquor of solid phase rhenium re-extraction, mother liquor from pulp dissolution and wash solution – 88,7%;
• decomposition of complex rhenium salt during separation of rhenium (solution) and zinc (precipitate) – 99,3%;
• evaporation of rhenium containing solution after the decomposition and crystallization of crude ammonium
perrhenate – 89,40 %.
17. Specify loss of rhenium in the waste during the flotation of copper ore and methods of increasing the extraction of rhenium.
When enriching the flotation of copper ores, where almost no molybdenum, rhenium’s large part goes into copper concentrates.
The behavior of rhenium at roasting of copper concentrates
When the reflectivity smelting of copper concentrates as a result of the low oxidizing atmosphere from 50 to 80% Re is carried away with flue gases, are not fully fumed rhenium goes into matte (штейн). In electric furnaces, where the atmosphere is more reducing, sublimate 35-40% Re when converting copper matte rhenium almost completely sublimated. Its concentration in the dusts of converters can reach hundredths of a percent.
Catching rhenium from gases reflective furnaces copper smelting factory – a very difficult task because of the high temperature and a large amount of gas. Assume for that goal to use solid adsorbents – coal, coke, ashes, etc., which are introduced in the form of dust in the gas stream, and then catching by conventional means. If the furnace and converter gases are used to produce sulfuric acid, rhenium is concentrated in the acid wash electrostatic precipitators. The concentration of H2SO4 500-600 g / l.
The distribution of during melting between different products, as well as the incomplete catching of of gases make the desired pre-extraction of rhenium from copper concentrates before they are melting.