COMPARATIVE ANALYTICAL DETERMINATION OF THORIUM IN MEDIUM AND LOW-GRADE MINERALS AND ORES USING SEMIMETHYLTHYMOL BLUE

The composition, stability constants and molar absorption coefficient of the chelate of thorium ion with Semimethylthymol Blue, SMTB is determined spectrophotometrically in a medium of perchloric acid and sodium perchlorate solution (pH 2.0). In the thorium-SMTB system, a purple red Th(SMTB) chelate is formed with logarithmic overall stability constant of 20.76 +/- 0.01 and molar absorption coefficient of 1.44x10(4) (560 nm) dm(3) mol(-1) cm(-1). SMTB was proposed as a new reagent for the spectrophotometric determination of micro-molar amounts of thorium at lambda(max) 560 nm. The colour development depends on time, temperature, pH and buffer species. The interferences of different anions, cations and organic acids on thorium determination were also investigated. Beer's law was obeyed for 11.6-104.4 mu g Th(IV)/25 ml(0.46-4.18 ppm). SMTB was used for the spectrophotometric determination of thorium in medium and low-grade minerals and ores and the results were reproduciable and satisfactory. Comparative study including different statistical tests between the spectrophotometric and complexometric determinations of thorium in its minerals and ores using SMTB has been carried out.