Reaction between hydrosulfide and iron/cerium (hydr)oxide: hydrosulfide oxidation and iron dissolution kinetics

摘要

Hydrosulfide oxidation and iron dissolution kinetics were studied at normal pressure,under inert (N_2) atmosphere,in a liquid-solid mechanically-stirred slurry reactor.The kinetic variables undergoing variations were: hydrosulfide initial concentration (0.90-3.30 mmol/L),oxide initial surface area (16-143 m~2/L) and pH (8.0-11.0).The hydrosulfide consumption and products (thiosulfate and polysulfide) formation were quantified by means of capillary electrophoresis,while iron dissolution was monitored through atomic absorption spectroscopy.Most of Fe(II) produced at pH = 9.5 remained associated with the oxide surface in the time-scale of the experiments.The hydrosulfide oxidation by the iron/cerium (hydr)oxide was found to be surface-controlled,with rates (R_i) of both sulfide oxidation and Fe(II) dissolution expressed in terms of an empirical rate equation: R_i = k_i[HS~-]_(t=0)~(0.5)[A]_(t=0)[H~+]_(t=0)~(0.5),where k_i represents the apparent rate constants for the oxidation of HS~- (k_(HS)) or the dissolution of Fe(II) (k_(Fe)),[HS~-]_(t=0) is the initial hydrosulfide concentration,[A]_(t=0) is the initial Fe/Ce (hydr)oxide surface area and [H~+ ]_(t=0) is the initial proton concentration.The rate constant,k_(HS),for the oxidation of hydrosulfide at pH = 9.5 was (3.4219 +- 0.65) x 10~(-4) mol~2 L~(-1) m~(-2) min~(-1),with the rate of hydrosulfide oxidation being ca.10 times faster than the rate of Fe(II) dissolution (assuming a 1:2 stoichiometric ratio between HS~- oxidized and Fe(II) produced;k_(Fe) = (3.9116 +- 0.41) x 10~(-5) mol~2 L~(-1) m~(-2) min~(-1)).