Thallium is mainly recovered from the smelting process of non-ferrous heavy metal sulfide ore as a by-product. The oxide of thallium is thallium oxide (or thallium trioxide) and thallium oxide (or thallium monoxide) are highly volatile. During roasting, sintering and smelting, most of the ore volatilizes into the smoke and dust. For example, during lead smelting, about 60% to 70% of thallium enters the sintering and roasting fumes. The thallium content of the lead blast furnace dust accounts for about 23% of the thallium content in the concentrate. When roasting pyrite in a sulfuric acid plant, the thallium-rich fumes of the furnace gas purification system can also be used as the raw material for extracting thallium.
The content of thallium in smelting raw materials is very low and must be enriched first. Pyroconcentration can increase the thallium content of the material by more than 10 times. Most of the thallium in the smoke is thallium oxide, thallium sulfate and thallium chloride. When dilute sulfuric acid is used to leaching thallium-containing fumes, zinc, cadmium, iron and other elements enter the solution at the same time. Dilute solution containing 0.05～1g/L of thallium can use potassium permanganate to oxidize TI+ to Tl3+. According to the principle of thallium, zinc, and cadmium precipitation in different pH solutions, sodium hydroxide is used to neutralize the pH of the solution to 4～ 5. Heat to 70～80℃ to make thallium precipitate out of the solution in the form of thallium hydroxide. If the solution contains more than 5g/L of thallium, add excess sodium chloride at 20°C to precipitate the thallium in the form of insoluble thallium chloride.
There are many ways to recover thallium in industry. Take the recovery of thallium from lead sintering fume as an example: after lead sintering fume is smelted and enriched in a reverberatory furnace, thallium-rich ash containing about 2% thallium is obtained, which is leached with sulfuric acid with a concentration of 120–150 g/L , The solid-liquid ratio is 1:5, the temperature is 90℃, and the stirring is 4h, the leaching rate is above 95%. Using the by-products of the metal smelting process such as aluminum, zinc, copper, manganese, etc. as raw materials, thallium metal is produced through hydrometallurgy. The wet method uses the by-products of the non-ferrous metal smelting process as raw materials. When sulfuric acid is added for extraction, thallium sulfate is generated, and then zinc powder is used to make spongy thallium, and sulfuric acid is added to dissolve the sponge thallium, and sodium carbonate is added to react to generate thallium carbonate. Sulfuric acid is added, and the resulting solution is treated with zinc to obtain a purity of 99%.
High-purity thallium can be refined by electrolysis. The thallium prepared by the general method still contains impurities such as copper, lead, and cadmium. It is first smelted with alkali and sodium nitrate and metal thallium to make the lead form sodium lead (Na2PbO2) and be removed. If the lead content exceeds 0.03%, You need to smelt twice. In this way, copper and cadmium can be removed as hydroxides. During electrolytic refining, pure thallium or tantalum sheets are used for the cathode, the thallium content in the electrolyte is 30–40 g/L, the sulfuric acid concentration is 70 g/L, the temperature is 55–60°C, the cathode current density is 100A/m2, and the anode current density It is 200A/m2, and the anode is covered with cloth. After two to three electrolytic refining, 99.999% high-purity thallium can be obtained.
Medical applications
Thallium was originally used in medicine to treat tinea capitis and other diseases. Later, it was found to be highly toxic and used as an anti-rodent, insecticide, and anti-mold agent, and was mainly used in agriculture. During this period, many patients were poisoned. With more in-depth research and understanding of the side effects of thallium toxicity in the future. Since 1945, countries around the world have cancelled the use of thallium in these areas in order to prevent thallium from polluting the environment. Thallium pesticides have been restricted or banned in many countries due to the secondary pollution of the environment during their use, but they are still used today in some developing countries.
In modern medicine, the Tl isotope thallium-201 as a radionuclear element is widely used in the detection and diagnosis of diseases such as the heart, liver, thyroid, melanoma, and coronary arteries. Studies have found that thallium can delay the growth of certain tumors while reducing the frequency of tumor occurrence. Before technetium-99 was widely used in nuclear medicine, thallium-201, which has a half-life of 73 hours, was once the main radioisotope used in core angiography. Today, Thallium-201 is also used in stress tests for risk stratification of coronary heart disease.
Industrial application
Thallium is very important for thallium alloys in the industry. Alloys made of thallium have many characteristics such as increasing the strength of the alloy, improving the hardness of the alloy, and enhancing the corrosion resistance of the alloy. Thallium-lead alloys are mostly used in the production of special fuses and high-temperature solders; the alloy of thallium-lead-tin 3 metals can resist acid corrosion and is very suitable for key parts of mechanical equipment in acidic environments; thallium amalgam has a low melting point of -60℃ , Used to fill low-temperature thermometers, can be used in polar regions and other high-altitude low-temperature layers; thallium tin alloy can be used as a superconducting material; thallium cadmium alloy is an important material in the atomic energy industry.
High temperature superconductor
Thallium is the third high-temperature superconductor discovered in 1988 after yttrium and bismuth. Four superconducting phase powders have been synthesized: Tl-1212, Tl-1223 (TlBa2Ca2Cu3O8, TC =110K), Tl-2212 (Tl2Ba2CaCu2O8+x, TC =85K) and Tl-2223 (Tl2Ba2Ca2Cu3O10, TC =125K). In recent years, studies on thallium-based high-temperature superconducting materials have shown that they are promising to obtain high TC thin films, polycrystalline, thick films and strips.
National defense military
The sulfide of thallium is particularly sensitive to infrared rays that are invisible to the naked eye. The photosensitive photoelectric tube made with it can receive signals and carry out reconnaissance in the dark night or dense fog atmosphere, and can also be used to make infrared photosensitive cells; thallium halide crystals can be manufactured Various high-precision optical prisms, lenses and special optical instrument parts. During the Second World War, mixed crystals of thallium chloride were used to transmit ultraviolet rays, and to detect enemy situations or self-internal communication late at night; in recent years, optical fibers made of thallium bromide and thallium iodide were used for CO2 lasers. The filtration is much better than that of quartz optical fiber, and it is very suitable for long-distance, non-interrupted, multi-channel communication.
Optical applications
The high-pressure mercury thallium lamp filled with thallium iodide is a green light source, which is widely used in the production of signal lamps and special luminous light sources for light reactions in the chemical industry; in the glass production process, adding a small amount of thallium sulfate or thallium carbonate will have a large refractive index Improve, it can be comparable to gems.
About us
As a global Contract Research Organization (CRO), headquartered in New York, USA, Alfa Chemistry has served the pharmaceutical and biotechnology industries for years. Today, Alfa Chemistry is specialized in organic chemistry, material chemistry, and medicinal chemistry. Here are some our products, such as Terbium Catalysts, 2,2'-Bi-4-lepidine, Diethylenetriamine, Tris 2-aminoethyl amine, etc.