Reactivity Of Different As(Ⅲ)-Pyrites In The Oxidative Dissolution Processes

Natural pyrites contain different species of As(Ⅲ),which affect the oxidation reactivity of pyrite.In this study,the oxidation reactivity of different pyrites,namely,pure pyrite[Py-free],As(Ⅲ)-adsorbed pyrite[Py*-As(Ⅲ)],As(Ⅲ)-soluble pyrite[Py-As(Ⅲ)diss]and As(Ⅲ)-structurally-incorporated pyrite[Py-As(Ⅲ),including Py-0.02 and Py-0.04]will be compared.By means of kinetic experiments and electrochemical experiment to study the reactivity of different As(Ⅲ)-pyrites.The effects of As(Ⅲ)on the secondary minerals after oxidation of pyrites are studied by XRF,XRD,XPS,SEM,TEM and FTIR solid characterization methods.In Py-As(Ⅲ),As(Ⅲ)replaces S(-Ⅰ)and changes the relative ratio of Fe:S.The increasing contents of surface Fe(Ⅲ)-S(-Ⅱ)and Fe(Ⅱ)-S(-Ⅰ)[Py-0.04>Py-0.02>Py-free>>Py*-As(Ⅲ)]in the XPS results reveal that Py-As(Ⅲ)with more As carries more surface defects and is resistant to oxidation during the preparation process.The oxidation rates in the order of Py-0.04>Py-0.02>Py-free>Py*-As(Ⅲ)>Py-As(Ⅲ)diss at pH 2.5 and of Py-0.04>Py-0.02>Py-As(Ⅲ)diss>Py*-As(Ⅲ)>Py-free at pH 7.0 and 9.0 imply that structurally-incorporated As(Ⅲ)always enhances the oxidation rates of pyrite,whereas adsorbed As(Ⅲ)does not.The electrochemical analyses further support that As in Py-As(Ⅲ)decreases the charge transfer resistance on the pyrite surface and facilitates the two-electron transfer reaction between dissolved oxygen and the pyrite surface,thus enhancing the oxidation rates of pyrites.Compared with Py-As(Ⅲ),As in As(Ⅲ)*-pyrite is more readily to be mobilized,with more As(Ⅴ)being detected at pH 2.5.Subsequent decreases of As(Ⅲ)and As(V)suggest re-immobilization of the released As via the adsorption and/or co-precipitation pathways.At pH 2.5,the oxidized product mainly contains S(0)and unreacted pyrite,while at pH 7.0 and 9.0,TEM and SEM results demonstrate that the lepidocrocite is the primary oxidation product,and Rod-shaped goethite is found at pH 7.0,and magnetite is found at pH 9.0.Solid characterizations further reveal that dissolved and/or adsorbed As(Ⅲ)significantly inhibit the development of lepidocrocite,goethite and magnetite,whereas structurally-incorporated As(Ⅲ)does not,triggering differences in the speciation of secondary Fe minerals.