硫化第一鉄による六価クロム水溶液の還元

抄録

In order to examine the suitability of ferrous sulfides as a reductant of dichromate, the reduction characteristics of dichromate by ferrous sulfides in an acidic solution were investigated by doing the determination of reaction rate, the measurements of rest potential, and so on. The main results obtained are as follows:
(1) Both of the acid decomposition rate of ferrous sulfides and the reduction rate of dichromate by ferrous sulfides are influenced greatly by the stoichiometry of ferrous sulfides. Reaction with stoichiometric ferrous fulfide proceeds faster than that with iron-deficient ones.
(2) Sulfur species in the reacted products of non-oxidizing acid decomposition and of oxidation reaction of ferrous sulfide are affected by its stoichiometry. Sulfur in iron-deficient ferrous sulfides is oxidized more readily. From the differences in the reaction rate, reaction products and rest potential, we may propose the different meahnisms of oxidation reaction to the stoichiometric and non-stoichiometric ferrous sulfides.
(3) Oxidation reaction as well as non-oxidizing acid decomposition reaction of ferrous sulfides can be predicted by knowing their rest potential values.
(4) The reduction rate of dichromate solution with ferrous sulfides is accelerated by either increasing acid concentration, raising temperature or lowering rest potential. However, the efficient reduction of dichromate is associated with the evolution of hydrogen sulfide, suggesting that ferrous sulfide is not an attractive reductant of dichromate waste water.