| Antimony cementation by iron in hydrochloric acid solution was carried out using rotating disc technique to study the effect of disc rotating speed, reaction temperature, initial Sb (III) ion concentration and atmosphere on the rate of cementation. The results obtained in this experiment are as follows; 1) Two reaction rate periods were found in the cementation: ie, an "initial" slow rate and a "final" enhanced rate periods. These are first-order reaction rate processes and can be expressed by the following equation. d/dt[Sb^(+++)] = -[Sb^(+++)] k·A. 2) The cementation rate increased with increasing temperature and initial Sb (III) ion concentration because the morphology of antimony deposit became porous. 3) In case of the excess existence of non-cementable ions such as Fe^(++), Fe^(+++), the cementation rate docreased with the ionic strength increment of solution. 4) Under oxygen containing atmosphere, Fe(II) ions are oxidized to Fe(III) ions and these oxidized ions are reduced by Fe disc to Fe(II) ions. These reactions interfere with antimony cementation reaction. 5) The apparent activation energy was found to be 3.2 ㎉/mole in initial rate period, in enhanced rate period 2.2 ㎉/mole above 40℃. Therefore, the rate controlling step is supposed to be diffusion through boundary layer, whereas it changes to surface reaction in enhanced rate period below the temperature of 30℃. |
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