Comparison of Direct Pressure Leaching with Atmospheric Leaching of Zinc Concentrates

Both pressure leaching of zinc concentrate, in an autoclave, and atmospheric leaching, in stirred tanks, have been employed in the expansion of zinc production at plants employing roast-leach-electrowin technology. These direct leaching methods result in the conversion of the sulphur in the feed to the elemental form, rather than to sulphur dioxide, decoupling zinc production from acid production. Atmospheric and pressure leaching methods are also readily implemented over a wide range of production rates. In choosing the best technology for expansion, capital and operating costs, zinc recovery, byproduct quality and the compatibility of recycle streams with the existing refinery must be compared. Leach testwork with several zinc concentrates using both methods has been performed by Dynatec. Recent results are presented, along with a discussion of their implications for process selection.