Critically evaluate the introduction of vacuum-distillation technology for refining of crude selenium

Sublimation and distillation in vacuum, as well as in an atmosphere of indifferent gases — carbon dioxide, nitrogen, argon, helium — is most often used to purify selenium.

Sublimation is carried out at ~ 400 °. However, in the presence of sulfur, arsenic, tellurium, and mercury in the initial selenium, sublimation is ineffective, since the impurities of these elements also evaporate. Oxygen impurity, which reduces the resistance of products, is not separated. To separate traces of oxygen, heating of selenium in evacuated ampoules at 700 ° C is used. With rapid cooling, traces of oxygen in the form of selenium dioxide are condensed on the cooled walls of the ampoule.

Selenium of high purity with high resistance is obtained by distillation at 700 °. Apply quartz distillers with dephlegmators.

Attempts to apply zone melting to purify selenium were unsuccessful due to supercooling of selenium and its ability to become glassy.

Purification of tellurium is carried out by both chemical and physical methods. The number of chemical methods should include fractional recovery and redeposition of tellurium dioxide. From physical methods, recrystallization of the main nitrate of tellurium, telluric acid and other compounds, as well as sublimation and zone smelting, is used. Fractionated reduction is used to separate selenium. It is based on the difference in the redox potentials of tetravalent tellurium and selenium. When recovering from a solution containing 28% hydrochloric acid, the recovery of selenium goes well. At the same time, tellurium is not restored. After diluting the solution, tellurium can be isolated from it.

Tellurium can be separated from impurities of heavy metals and selenium due to amphotericity. Tellurium dioxide is dissolved in alkali, insoluble metal hydroxides are separated, and then tellurium dioxide is separated from the solution.

For separation from impurities of various metals from tellurium dioxide and arsenic, its treatment with nitric acid is used. At the same time, soluble metal nitrates are formed. Tellurium dioxide dissolves poorly in nitric acid.

 

Explain the importance of recycling secondary minerals and industrial waste.

Recycling should be distinguished from recycling. The purpose of processing is the conversion of waste into secondary raw materials [⇨], energy [⇨] or products with certain consumer properties.

Recycling may or may not include their treatment - activities aimed at changing the physical, chemical or biological state of the waste to ensure subsequent work on waste management. A variety of waste materials are processed, including glass, paper, aluminum, asphalt, iron, fabrics, various types of plastic and organic waste (sources of numerous harmful substances and even bacteria and viruses). In some cases, individual waste treatment processes are not technically feasible or economically unprofitable due to the exorbitant costs of material, transport, financial and human resources.Recycling may generate waste.

Many types of waste can be recycled, and for each type of waste there is an appropriate recycling technology. For the separation of waste material used different types of separation. For example, magnets are used to extract black metals from trash. Chlorine vinyl, low density polyethylene, polypropylene and food sources are also recyclable, although they are usually not sorted. These are substances of uniform consistency, which makes it possible to easily produce new materials from them. Recycling of multi-component items (for example, computers and other electrical equipment) is rather difficult, due to their dismantling and separation.

⇐ Предыдущая123

Поделиться: