Precious metal recovery

Claim 1

IN A METHOD FOR RECOVERING AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF GOLD, SILVER, PLATINUM, IRIDIUM, RHODIUM, RUTHENIUM, OSMIUM AND PALLADIUM FROM A BITUMINOUS SHALE CONTAINING SAID METAL TOGETHER WITH SILICA, SAID METAL BEING ENTANGLD WITH SAID SILICA, THE STEPS INCLUDING: DIGESTING THE SHALE WITH AN AQUEOUS SOLUTION OF AN ALKALINE SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF AMMONIUM CARBONATE, SODIUM CARBONATE, POTASSIUM CARBONATE, AMMONIUM HYDROXIDE, SODIUM HYDROXIDE, POTASSIUM HYDROXIDE, LITHIUM HYDROXIDE, LITHIUM CARBONATE, CALCIUM HYDROXIDE, SODIUM BICARBONATE, POTASSIUM BICARBONATE, CALCIUM HYPOCHLORITE, SODIUM HYPOCHLORITE, LITHIUM HYPOCHLORITE AND MIXTURES THEREOF, TO INCREASE THE SUSCEPTIBILITY OF SAID METAL TO DISSOLUTION IN AN AQUEOUS ACID SOLUTION CONTAINING SULFATE, NITRATE AND CHLORIDE ANIONS; SEPARATING AN INSOLUBLE RESIDUE FROM THE ALKALINE DIGESTION MIXTURE; DIGESTING THE RESIDUE FROM THE ALKALINE DIGESTION WITH AN AQUEOUS ACID SOLUTION CONTAINING SULFATE, NITRATE AND CHLORIDE ANIONS; SEPARATING A CLEAR AQUEOUS SOLUTION CONTAINING SAID METAL FROM THE ACID DIGESTION MIXTURE; CONTACTING THE CLEAR SOLUTION WITH SULFIDE ANIONS WHILE MAKING THE SOLUTION FIRST ALKALINE AND THEN ACID TO PRECIPITATE SAID METAL AS ITS SULFIDE; SEPARATING THE PRECIPITATED METAL SULFIDE FROM THE ACID SOLUTION; ROASTING THE SEPARATED METAL SULFIDE IN AN OXIDIZING ATMOSPHERE AT A TEMPERATURE ABOVE ABOUT 500 DEGREES C. TO CONVERT THE METAL ESSENTIALLY TO ITS OXIDE; AND REDUCING THE ROASTED PRODUCT IN AN HYDROGEN ATMNOSPHERE AT A TEMPERATURE BETWEEN ABOUT 800 DEGREES C. AND ABOUT 1200 DEGREES C. TO REDUCE THE METAL COMPOUND TO THE FREE METAL.