活性炭による六価クロム水溶液の還元

抄録

Cr (VI) in sulfuric acid solutions was reduced with activated carbons (initial solution; 2.5×10^-3 mol/500ml as K₂Cr₂O₇). Reduction rate of Cr (VI) and chemisorption of Cr (total) varied considerably with the various types of activated carbons. The results obtained in these experiments can be summarized as follows;
1) Remaining Cr (VI) and Cr (total) decreased rapidly in the initial reaction period (several minutes). The reduction rate of Cr (VI) with the activated carbons decreased gradually in the course of the reaction, while the remaining Cr (total) stayed constant.
2) Remaining Cr (VI) decreased with an increase in reaction temperature, and with an increase in the amount of activated carbons, and was propotional to the amount of fine sized particles. However, there was no detectable variation with increasing of Cr (III)/Cr (VI) mole ratio in the initial solution.
3) Remaining Cr (total) reached a minimum value at pH 3-4 in the reaction solutions (initial pH; about 2.5). From calculation of all the chemical species in the initial chromate-dichromate solution, it was considered that the predominant species on activated carbons were HCrO₄-and Cr₂O₇^2-.
4) The following eouation can be suonosed for the reduction of aqueous dichromate solutions with activated carbons. 2Cr₂O₇^2-+3C+16H+→4Cr³⁺+8H₂O+3CO₂