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| NIRE Annual Report | 
| 1998 |
Removal of Selenium(VI) by Reduction Method with
Rare Metals Division |
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Objectives
Selenium occurs in many kinds of sulfide ores and is contained in waste water in smelting processes. Especially, selenium(VI) is difficult to be removed. It is well known that selenium(IV) is much easier to be removed than selenium(VI). Therefore, reduction of Se(VI) to Se(IV) was examined with reducing agents. Ferrous ion is used as a useful reducing agent in many metallurgical processes. The present study was conducted to obtain a fundamental understanding of the reaction kinetics of reduction of Se(VI) with ferrous chloride in hydrochloric acid solution.
Results
Fig. 1 shows a time variation of the concentration of Se(IV), Se(VI) and selenium in an aqueous solution at 343 K in 0.5 kmol m-3 FeCl2 - 1.0 kmol m-3 HCl solution, respectively. Initial concentration of Se(VI) was 100 g m-3. Concentration of Se(VI) decreased with time and reached 3.5 g m-3 after 9 hours reaction. On the other hand, Se(IV) increased for approximately 2 hr , thereafter gradually decreased with time. Selenium concentration in aqueous solution, which was the sum of the concentration of Se(IV) and Se(VI), decreased with time, and amorphous selenium was precipitated. From these results, reaction rate was found to be of first order with respect to Se(VI) concentration. Therefore, reaction rate may be written as
Fig. 2 shows the relationship between k1 and C(FeCl2). A good linear relationship was obtained over the concentration range from 0.1 to 0.5 kmol m-3, the slope of the graph being 2.0. This indicates that the rate constant is of a second order with respect to ferrous chloride concentration.
