Determination of total thallium in fresh water by electrothermal atomic absorption spectrometry after colloid precipitate flotation.

Tl(I) and Tl(III) are preconcentrated simultaneously from aqueous solutions by colloid precipitate flotation using two collectors: hydrated iron(III) oxide (Fe(2)O(3).xH(2)O) and iron(III) tetramethylenedithiocarbamate (Fe(TMDTC)(3)). After the coprecipitation step and the addition of foaming agents, Tl(I) and Tl(III) were separated from the water by a stream of air bubbles. Various factors affecting Tl(I) and Tl(III) recoveries during the separation from water, including the collector mass, the nature of the supporting electrolyte, pH, zeta potential of the collector particle surfaces, type of tenside, etc., were investigated. Within the optimal pH range (6-6.5), establishing by a recommended procedure, Tl(I) and Tl(III) were separated quantitatively (94.9-100.0%) with 30 mg Fe(III). Both Tl ions were simultaneously separated without any previous conversion of one type of Tl ion to the other. Total Tl determination was performed by electrothermal atomic absorption spectrometry by previous matrix modification of the concentrated samples. The determination limit of Tl by this method is 0.108 mug l(-1).