Thallium world production

Thallium is likewise recovered from flue dusts emitted during sulfide roasting for H2SO4 manufacture, and from the smelting of Zn/Pb ores. Extraction procedures are complicated because of the need to recover Cd at the same time. There are no major commercial uses for T1 metal world production in 1983 was estimated to be 5-15 tonnes p.a. and the price ranged from 60 to 80 per kg depending on purity and amount purchased. 

The chemistry of thallium has also been studied for its potential contribution to environmental pollution. Even though the annual world production of thallium is probably negligible in this respect (- 1000 times less than mercury, and —1,000,000 times less than lead), the element is released to the environment mainly through coal-burning power plants (33b). Therefore, it has been considered important to follow thallium s further fate in the natural environment, and a large number of thallium compounds have been characterized with this motivation (46-48). 

Thallium sulfate used to be used to kill ants and rats, but the extremely high toxicity levels of T1 compounds are now well recognized and aU Tl-containing species must be treated with caution. The world production of thalhum (15 000 kg in 2001) is far less than that of galhum (Figure 12.3) and indium. Important uses of T1 are in semiconducting materials in selenium rectifiers, in Tl-activated NaCl and Nal crystals in 7-radiation detectors, and in IR radiation detection and transmission equipment. The radioisotope T1 h = 12.2d) is used for cardiovascular imaging. 

In contrast to the small world production of thallium of about 10-15 tons per year, the annual amount of thallium in waste material is estimated to be about 600 tons (Micke et al. 1983). The main anthropogenic occurrence of thallium in the environment results from emissions of the highly volatile metal and its compounds from some industrial processes for example, the smelting of chalcogenic ores - especially lead and zinc sulfides - yields thallium emissions. 

Copper and zinc are the principal metals extracted by electrolysis in aqueous solution the total world production of both approaches 10 ton yr although the electrolytic route accounts for only 10% of the copper and 50% of the zinc produced. Moreover the large electrolytic plants are limited to sites in Africa, Australia and Canada where hydroelectric power is available close to the mines. Cobalt, nickel, chromium, manganese, cadmium, gallium, thallium, indium, silver and gold have also been reported to have been extracted by a hydrometallurgical process but, since these metals are only produced in a low tonnage, the electrolytic processes are on a small scale. 

The polycondensation of BHET to PET proceeds in the melt at temperatures of 270-305 °C, under vacuum (< 1 mbar absolute pressure) and in the presence of Lewis acid metal compounds, such as titanium alkoxides, dialkyltin oxide, gallium oxide, germanium oxide, thallium oxide, lanthanide salts, and most commonly, antimony oxide [1,2, 22-26]. Under polymerization reaction conditions, these catalysts are generally converted to their alkoxides with ethylene glycol. Typical of such alkoxides is antimony(III) glycolate, the active catalyst for the majority of the world s PET production [27] (cf. Structure 1). 

Thallium is prepared from filter dust obtained after roasting of sulfide ores. The dust is dissolved in sulfuric acid. Then thallium co-precipitates with lead sulfate. The lead manufactured by reduction with coke contains thallium metal. Lead is first removed in two electrolytic processes, and in a second step thallium is precipitated on a steel cathode. As an alternative, thallium can be won from a sulfuric acid solution with an ion-exchange technique. The annual production of thallium compounds corresponds to 30 tonnes of thallium, but the production of the metal is not large - in the whole world less than 10 tonnes. 

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