Determination of Tellurium in Coal Samples by Means of Graphite Furnace Atomic Absorption Spectrometry after Coprecipitation with Iron(III) Hydroxide

A simple and accurate method for the determination of tellurium in coal samples was investigated by the combustion of samples under a high pressure of oxygen and coprecipitation with Fe(OH)3, followed by a measurement by graphite furnace atomic absorption spectrometry (GF-AAS). About 0.5 g of an accurately weighed ground coal sample and 0.5 g of starch were combusted in an oxygen combustion bomb filled with oxygen to 3 Mpa and added with 3 ml of water as a absorbing solution. The formed tellurium trioxide TeOs dissolved in water as TeO42-, which was in turn reduced to TeO32- by heating. After diluting the above-mentioned solution up to about 50 ml with water, Fe(OH)(3) is formed upon adding Fe(NO3)(3) and sodium hydroxide solutions at pH 8-9 and left standing overnight. After dissolving the precipitate by HCl, the solution was diluted to 10 ml with water and the concentration of tellurium was measured by GF-AAS at a wavelength of 214.3 nm. The standard addition method was employed for the determination of tellurium in real coal samples, because those processes for the formation of tellurium(VI) oxide and coprecipitation with Fe(OH)3 were interfered by matrices. For NIST SRM 1632c, the standard coal sample tellurium content of 0.057 +/- 0.004 mg kg(-1) was in good agreement with the information value of 0.05 mg kg(-1) with 7% of RSD in five replicate analyses. The tellurium contents in 20 real coal samples given by Center for Coal Utilization, Japan were also determined. The tellurium contents in these samples were scattered over the narrow range between 0.032 and 0.100 mg kg(-1).