Thermochemical Arsenate-Oxide Equilibria in the System Fe–As–O Determined Electrochemically between 317 and 536°C

Abstract

An electrochemical technique has been applied to the determination of the ferric arsenate-ferric oxide equilibrium in the temperature range 3l7-536°C.Equilibrium electrochemical potentials were measured in an oxygen concentration cell which consisted of (a) an oxygen reference electrode, (b) a solid calcia-stabilized zirconia electrolyte, and (c) a ferric arsenateferric oxide mixture over which was passed argon containing a known partial pressure of As40 6 (g).The free energy of decomposition of ferric arsenate as a function of temperature, the thermochemical properties of ferric arsenate and Fe-As-O predominance area diagrams of interest in pyrometallurgical processes were calculated from the experimental data and from data available in the literature.For the reaction: FeAs04(s) = 1/2 Fe203(s) + 1/4 As406(g) + 1/2 Olg), /)'G~= 159,654-124.921 T(K), J/mol for 590~T~725 and /)'G~= 125,337-77.5850 T(K), llmol for 725~T~809.