The dissolution of mild steel by warm sulphuric acid with and without organic inhibiting additions has been studied by means of simultaneous measurements of corrosion rate and corrosion potential, and by the determination of true anodic and cathodic polarization curves in the neighbourhood of the natural corrosion potential.Quinoline, 2 : 6-dimethylquinoline, a-and p-naphthoquinolines, N-ethylquinoline, thiourea, methylthiourea, ethylthiourea and 0-, m-and p-tolylthioureas inhibit the dissolution of mild steel by 5% (w/v) sulphuric acid at 70" and 40", being increasingly effective in the order given above. The quinolines are primarily anodic inhibitors, but at high concentrations they limit the cathodic reaction also; the thioureas inhibit both cathodic and anodic reactions, the cathodic the more at low concentrations, the anodic the more at high.The results are interpreted by a modified adsorption theory and are discussed in terms of recent fundamental views of electrode reactions. Some practical implications are pointed out.

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Removal of iron to low residual levels is essential in preparation of AICI3 feed for chloride electrolysis cells for Al production. The number and complexity of systems affording possibilities for beneficiation of bauxite by gassolid reaction is such that computer techniques are needed to analyze them in an ordered way. Predominance area diagrams have been used in conjunction with free energy minimization calculations to define routes for selective removal of iron. The systems AI/Fe-CI-O, Al/Fe-S-O, AI/Fe-S-CI and AI/Fe-S-CI-0 have been analyzed in this way. Several indirect routes in which Fe203 is first converted to an easily chlorinated compound have been identified; in particular, sulfidization by S02-C0 mixtures of high sulfur potential appears attractive.Other routes involve direct chlorination of Fe203 to FeCI2 or FeCI3 under conditions where Al203 is nonreactive. Volatilization of AICI3 with retention of FeS is possible in principle with gas reactants based on K2S-CI2 mixtures.

carried out using a relatively high discard level of the order of atm for all species, and this served to establish an accurate estimate of the input distribution for a second run. The second calculation was then able to establish equilibrium levels of gaseous species to below atm. This was the fundamental feature that enabled a predominance area diagram to be used for a wide range of gas compositions.The method of checking the accuracy of calculation of these low component levels may be demonstrated by referring to Figure 4. The triple point for Fe-FeS-FeO was calculated by conventional means, using data from Kubaschewski et al. (1967). The unique values for sulfur and oxygen pressures at equilibrium a t lOOOOK were 0.96 X 10-lo and 2.33 X atm, respectively. The triple point could be reproduced by the minimization program by equilibrating a closed system containing 3.6 mol of SO2, 6.4 mol of CO and excess iron. The equilibrium distribution was found to contain the solid components a t sulfur and oxygen pressures of 1.2 X and 2.4 X atm, respectively. This degree of precision was attained in other similar systems, confirming that the use of the low calculated partial pressures was justified. Literature CitedBuntin, A,, et al., Tr. Tomsk. Gos. Univ.: Ser. Khim., 154, 52 (1962).Conditions for preparation of AIC13 of low iron content were studied in a thermogravimetric apparatus designed so that sensitive components were shielded from the gaseous reagents. Reaction of natural bauxite pisolites of diameters between 1.5 mm and 12 mm with gaseous reagents based on S02-C0, HCI-CO, HCI, HPS-CI~, S2C12-CO, S02-C12 and CO-CI2 was analyzed. Predictions that Sop-CO mixtures of high sulfur potential would be particularly suitable for preparation of FeS were confirmed. Maximum sulfidization rates occurred at the SO21 CO ratio of 3565. Rates were proportional to (p(S2)2 + p(COS).p(Sd + p(COS)2). FeS could be rapidly removed to residual Fe levels of 0.1 to 0.3% by direct chlorination below 750OC. Direct chlorination of FepO3 using CO-CI2, HCI, or HCI-CO gave much less favorable results. The possibility of removing AIC13 while retaining FeS is unique to the H2S-C12 reagent system, but the reaction kinetics were unfavorable. The sulfidizationchlorination route appears to afford the best combination of characteristics sought in a beneficiation process suitable for integration with AIC13 production.T h e authors wish to thank Comalco Ltd., 95 Collins St., Melhoume. for financial assistance toward this work.