Recovery of selenium from electrolytic copper refinery slimes

Claim 1

A PROCESS FOR THE RECOVERY OF SELENIUM FROM SELENIUM-BEARING ANODE SLIMES CONTAINING A SUBSTANTIAL AMOUNT OF TELLURIUM PRODUCED IN THE ELECTROLYTIC REFINING OF COPPER WHICH COMPRISES MIXING SAID ANODE SLIMES WITH AT LEAST THE STOICHIOMETRIC AMOUNT OF SODIUM CARBONATE TO CONVERT ALL OF THE SELENIUM TO SELENATE AND SUFFICIENT WATER TO FORM A THICK PASTE AT A TEMPERATURE ABOVE THE TRANSITION TEMPERATURE OF SODIUM CARBONATE HEPTAHYDRATE TO SODIUM CARBONATE MONOHYDRATE, EXTRUDING THE PASTE ABOVE SAID TEMPERATURE THROUGH ORIFICE MEANS WHEREBY FORMING SAID PASTE INTO AN ELONGATE EXTRUDED PRODUCT, FORMING SAID EXTRUDED PRODUCT INTO A BED OF PREFORMED MASSES OF PASTE HAVING MACRO-POROUS SPACES THEREIN, DRYING THE BED OF PREFORMED PASTE MASSES HAVING MARCO-POROUS SPACES THEREIN AND THEREBY REMOVING THE WATER OF HYDRATION OF THE SODIUM CARBONATE THUS FORMING A DRIED MARCO-POROUS BED OF MICRO-POROUS PREFORMED MASSES OF SLIMES-SODA ASH MIXTURE, ROASTING SAID RESULTING DRIED MACRO-POROUS BED OF MICRO-POROUS PREFORMED MASSES OF DEHYDRATED SLIMES-SODA ASH MIXTURE BY CIRCULATING THERETHROUGH OXIDIZING GASES MAINTAINED AT A TEMPERATURE SUFFICIENTLY HIGH TO OXIDIZE THE OXIDIXABLE CONSTITUENTS IN SAID BED BUT BELOW A TEMPERATURE WHICH WILL CAUSE THE MATERIAL IN SAID BED TO REACH ITS FUSION TEMPERATTURE FOR A PERIOD OF TIME SUFFICIENT TO OBTAIN SUBSTANTIALLY COMPLETE OXIDATION OF THE OXIDIZABLE CONSTITUENTS OF THE MATERIAL IN THE BED THEREBY CONVERTING SELENIUM THEREIN TO A WATER-SOLUBLE SELENIUM COMPOUND, LEACHING THE ROASTED PRODUCT WITH WATER TO DISSOLVE THE WATER SOLUBLE SELENIUM COMPOUND, NEUTRALIZING THE LEACH LIQUOR WITH INORGANIC ACID, PURIFYING THE RESULTING LEACH LIQUOR AFTER SAID NEUTRALIZING BY THE ADDITION OF SUFFICIENT SODIUM METABISULFITE TO PRECIPITATE ANY TELLURIUM PRESENT IN THE LEACH LIQUOR AND TO CONVERT ANY ALKALI METAL-SELENITE PRESENT IN THE LEACH LIQUOR TO ELEMENTAL SELENIUM TO PRECIPITATE IT OUT OF THE LEACH LIQUOR, FILTERING THE RESULTING LEACH LIQUOR SOLUTION TO OBTAIN A PURIFIED SELENIUM-RICH LEACH LIQUOR AND RECOVERING THEREFROM A SELENIUM SLUDGE OF HIGH PURITY.