KINETICS OF REDUCTION OF ARSENI (V) WITH SULFUR DIOXIDE GAS IN AQUEOUS SULFURIC ACID SOLUTION

摘要

The reduction of arsenic(V) to arsenic(III) in aqueous sulfuric acid solutions with sulfur dioxide gas was investigated. In this work, six variables were considered as those affecting the rate of reduction: (1) initial arsenic(V) concentration, (2) initial arsenic(III) concentration, (3) aqueous sulfur dioxide concentration, (4) pH and sulfuric acid concentration, (5) temperature and (6) addition of various sulfates. The reaction was found to be first order with respect to concentration of both arsenic(V) and aqueous sulfur dioxide and zero order with respect to arsenic(III) concentration. The rate of reaction in sulfuric acid solution at 25 deg C is given by:(H_2SO_4)<1.5 mol/L -d(As(V)/dt=k_1 (As(V))(SO_2(aq))/(H_2SO_4)~(0.4)(H_2SO_4)<1.5 mol/L -d(As(V)/dt=k_1 (As(V))(SO_2(aq))/(H_2SO_4)~(2.5)where the rate constant k_1 depends on temperature. The apparent activation energies were found to be 9.5 kcal/mol from 25 to 60 deg C and 4.8 kcal/mol from 60 to 80 deg C in 1 moll H2S04. The reduction reaction in aqueous solution was suppressed by hydrogen ion.