酸性塩化物浴中の鉛精鉱の酸化速度に及ぼす懸濁電位の影響

抄録

Toclarify the potential-dependence of the oxidation rate, 12 kinds of Pbconcentrates were oxidized in an acidic solution containing 3 mol/l NaCl, 13.3g/l PbCl₂, 3.8 g/l Fe, and pH l at 70°C. The potential (Pt vs. SCE) of the suspension was maintained constant at different potentials in the range from 0.25 to 0.45V by addition of KMnO₄ solution. The reaction follows the S°-forming oxidation with concurrent deposition of crystalline PbCl₂.
The results obtained reveal three aspects of the oxidation as follows.
(1) When the sample is repeatedly charged after the completion of oxidation of the first charge in a green solution, the oxidation rate of the second charge differes from that of the first charge. The difference is apparently due to (i) an appreciable waiting time only found in the first reaction, or (ii) the difference of the potential-dependence between the first and second reaction. For the reason of these differences it is considered that an oxidized species of S (may be thianate anion) formed in the first reaction affects the subsequent reaction.
(2) Nearly all of the reaction below 0.35V follow the quasi-first order kinetics. For concentrates with low Cu contents, the potential-dependence is represented by a pseudo-Tafelbehavior (see Fig.16),
E=E'+βlog (1/τ_0.50)
where E is the suspension potential and τ_0.5 is the half life time. The value of E' varies with the sample, while β is a constant at 0.12 V common to the samples. A few concentrates with high Cu contents show exceedingly high rates. The high rate is afttributed to a low value of β.
(3) When the potential is higher than 0.35V, the oxidation with the high rate follows a different kinetics which is independent of the suspension potential.