φ-pH diagram of As-N-Na-H2O system for arsenic removal during alkaline pressure oxidation leaching of lead anode slime

In order to illustrate the thermodynamic characteristics of arsenic during alkaline pressure oxidation leaching process of lead anode slime (NaNO3 as oxidant; NaOH as alkaline reagent), the φ-pH diagrams of As-Na-H2O, N-H2O, As-N-Na-H2O systems at ionic mass concentration of 0.1 mol/kg and temperatures of 298, 373, 423 and 473 K were established according to thermodynamic calculation. The results show that the existence forms of arsenic are associated with pH value, which mainly exists in the forms of H3AsO4, H2AsO4−, HAsO42−, and As2O3 in lower pH region, while it mainly exists in the form of when pH>11.14. High alkali concentration and high temperature are advantageous to the arsenic leaching. The alkaline pressure oxidation leaching experiments display that the tendency of arsenic leaching rate confirms the thermodynamic analysis results obtained from the φ-pH diagrams of As-N-Na-H2O system, and the highest leaching rate of arsenic reaches 95.85% at 453 K.