Studies on the thermal decomposition of alkali metal thiosulphatobismuthates(III)

Abstract The thermal decomposition of thiosulphatobismuthates(III) of alkali metals was investigated. The general formulae of the thiosulphatobismuthates are M 3 [Bi(S 2 O 3 ) 3 ]·H 2 O where M = Na, K, Rb or Cs, and M 2 Na[Bi(S 2 O 3 ) 3 ]·H 2 O where M = K or Cs. Typical thermal curves for thiosulphatobismuthates(III) and the results obtained in thermal, X-ray, chemical and spectrophotometrical analyses of the decomposition products are shown. The results were used to determine three stages of the thermal decomposition. At the first stage, at about 200°C, hydrated compounds are dehydrated. At the second stage, above 200°C, there is a rapid decrease in mass which is caused by evolving sulphur dioxide; bismuth sulphide and an intermediate decomposition product are formed. At about 320°C the thermal decomposition products are bismuth sulphide and alkali metal sulphate.