ALKALINITY EXCHANGE PROCESS FOR IMPROVING THE EXTRACTION OF PRECIOUS AND RARE METALS

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By the process of the present invention the cyanide leaching of precious and platinumgroup metals is improved by using sodium hydroxide to dissolve the mineral matrix thatencapsulates the pay metals and their respective containing minerals allowing for thepenetration of the leaching reagent whilst dispersing the fine materials hence enhancingthe rate and extent of dissolution of the said pay metals and their transfer into the aqueousphase. A process wherein the sodium hydroxide is produced on site through an alkalinityexchange process comprised of carbonation using carbon dioxide followed by liming-caustification of the carbonated slurry using calcium hydroxide. The resulting limed-causticslurry is subjected to solid-liquid separation and subsequent washing producing a solutioncontaining sodium hydroxide. Sodium cyanide is added to the aforementioned sodiumhydroxide solution which therefore becomes fresh lixiviant that is directed to the leaching ofthe pay metals contained in the orebody.