Thallium, chemical symbol Tl, atomic number 8 1, is a group Ⅲ A element in the sixth period of the periodic table of elements, and its content is very low in the natural environment, so it is an associated element. Thallium salts are generally colorless and odorless crystals, which form thallium compounds after being dissolved in water, and are more stable in water or paraffin than in air.

Thallium reacts rapidly with wet air or oxygen-containing water to form TlOH. Thallium reacts easily with halogen at room temperature, but it can react with sulfur and phosphorus at high temperature, but it does not react with hydrogen, nitrogen, ammonia or dry carbon dioxide. Thallium dissolves slowly in sulfuric acid and hardly in hydrochloric acid and hydrofluoric acid, because insoluble salts are formed on the surface.

preparation method

Thallium is mainly recovered as a by-product in the smelting process of nonferrous heavy metal sulfide ore. Thallium oxides, thallium oxide (or thallium trioxide) and thallium oxide (or thallium monoxide) are highly volatile, and most of them volatilize into smoke and dust during roasting, sintering and smelting of copper, lead and zinc sulfide concentrates. For example, in the lead smelting process, about 60% ~ 70% thallium enters the sintering and roasting dust.

Thallium content in lead blast furnace dust accounts for about 23% of thallium content in concentrate. When roasting pyrite in sulfuric acid plant, thallium-rich flue gas discharged from furnace gas purification system can also be used as raw material for extracting thallium.

Thallium is very low in smelting raw materials and must be enriched first. Pyrolysis enrichment can increase thallium content in materials by more than 10 times. Thallium in soot is mainly thallium oxide, thallium sulfate and thallium chloride. When leaching thallium-containing dust with dilute sulfuric acid, zinc, cadmium, iron and other elements simultaneously enter the solution.

The dilute solution containing thallium 0.05 ~1g/l can be oxidized from TI+ to Tl3+ by potassium permanganate. According to the principle that thallium, zinc and cadmium are precipitated in solutions with different pH values, the pH value of the solution is neutralized to 4 ~ 5 with sodium hydroxide and heated to 70 ~ 80℃ to precipitate thallium from the solution in the form of thallium hydroxide.

Refer to the above content: Baidu Encyclopedia-Thallium