A new sequential and simultaneous speciation analysis of thallium in coal effluents by graphite furnace atomic absorption spectrometry after a novel ligandless mixed micelle cloud point extraction

ABSTRACT

A novel sequential/simultaneous extraction procedure was developed for determining Tl(I) and Tl(III) and total Tl in coal mine effluents. In this method, the selective formation of anionic species of Tl(I) and Tl(III) with HCl and diethylenetriamine pentaaceticacid (DTPA), respectively, were introduced in a mixed micelle cloud point extraction. An Aliquat-336 and Triton X-114 aggregates acted as ion-pair and extracting agents. In sequential extraction, the hydrophilic Tl(III)-DTPA²⁻, first reacted with cationic aggregate through electrostatic interaction and extracted into a small aggregate rich phase and leaves the cationic Tl(I) in supernatant. This was subjected to a similar extraction after converting Tl(I) into TlCl₃²⁻ on addition of HCl. In simultaneous extraction, total Tl was extracted by adapting a similar extraction, adding HCl and DTPA, avoiding the chelating and oxidation/reducing agents. Parameters affecting the process are optimised using GFAAS. Under the optimised conditions, the detection limit and pre-concentration factor were 15 pg mL⁻¹ and 25^, respectively for both sequential and simultaneous extractions. The recoveries of Tl(III) and Tl(I) were between 85% and 104% in the range of 0.5 to 3 ng mL⁻¹. A certified reference material, NIST 1643c, was used to verify the accuracy of the procedure. The method was applied to natural waters and coal effluents.

KEYWORDS:

• Thallium speciation analysis
• sequential and simultaneous analysis
• mixed micelle cloud point extraction
• coal effluent samples

Disclosure statement

No potential conflict of interest was reported by the authors.