Czasopismo | RUDY I METALE NIEŻELAZNE | Rocznik 2012 - zeszyt 1

ROASTING SELENIUM FROM COPPER REFINERY ANODE SLIMES

nr katalogowy: 65538

Selenium is present in the slimes fed to roasting process mostly as copper and silver selenides as well as elementary sele‐nium, depending on the processing steps prior to the deselenisation. The decomposition of silver (Ag2Se), copper (Cu2Se) and mixed (AgCuSe) selenides is a necessary step in the roasting, before the oxidation of selenium to SeO2 can take place. Vapour pressure of elementary selenium or that in its intermetallic compounds is much lower than that of pure SeO2(g). Thus, the oxidation of selenium bound in selenides must occur on the surfaces of the intermetallic compounds, where for‐mation of complex selenium oxides with silver or copper is possible. The selenium roasting of anode slimes is a complex process where the deselenisation rate is linked with the chemical form of selenium present in the slime. Elemental sele‐nium is removed from the slime easily at low temperatures, around 200 °C, where its oxidation starts. Silver selenide Ag2Se is oxidized to selenite Ag2SeO3 almost quantitatively, and no gaseous selenium dioxide is released from slime to the roaster gas. The reaction rate is low, due to the small decomposition pressure of silver selenite. Copper selenides if present in the anode slime react much in the same way in oxygen as silver selenides. Due to the higher decomposition pressure only a fraction is oxidized directly to Cu2SeO4 or CuSeO3, and selenium is released as SeO2(g) to the gas phase. In SO2‐bearing roaster atmospheres, the stable forms of copper and silver are their sulphates. Thus the gravimetric data of slime roasting is a combination of oxidation, deselenisation and sulphation reactions. The reaction rates in O2+SO2 atmospheres are en‐hanced by porosity and cracks formed in reaction scales which allow the gas transport between the reaction atmosphere and selenite. This feature of the roasting products explains the beneficial properties of sulphur dioxide in the anode slime roasting comp[...]

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2012-1

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