Zinc Patent Granted in USA

3 February 2015

Alexander Mining plc

("Alexander" or the "Company")

Patent Granted in United States for a Method for Leaching Zinc from a Zinc Ore

The Company is pleased to report that it has received notification that its MetaLeach Limited ("MetaLeach") subsidiary has been granted a patent in the United States for a Method for Leaching Zinc from a Zinc Ore. The patent, number 8,871,001, has a standard term of 20 years from the effective date of 19 February 2010 (being the date of original filing of the PCT Application from which the United States patent is derived).

Description

The patent, the Australian equivalent of which was granted on 30 August 2012, describes a method for leaching zinc from zinc-bearing carbonate ore. The method comprising the steps of: subjecting a material consisting essentially of a zinc-bearing ore containing the zinc-bearing carbonate ore to elevated temperatures of between about 300 °C and about 900 °C in the absence of additional reactive reagents, thereby producing a decomposed material and carbon dioxide; subjecting the decomposed material to an aqueous acid or alkali leach thereby producing an aqueous zinc solution; and subjecting the aqueous zinc solution to a zinc recovery step.

Background

Sulphide deposits have dominated production of primary zinc. Current estimates are that approximately 95% of the zinc mined worldwide is mined from sulphidic ore deposits, in which the ore is typically mixed with sulphides of copper, lead and/or iron. After grinding the ore, froth flotation is used to separate minerals from the gangue, taking advantage of differences in their hydrophobicity. The concentrate is either smelted or undergoes roasting (to produce zinc oxide and sulphur dioxide), acid leaching (typically using at least some of the sulphur dioxide to produce acid) then electro-winning to recover zinc.

Unlike sulphides, zinc oxide is not readily separated from gangue materials by gravimetric means. Accordingly, the zinc oxide component of a mixed zinc oxide-zinc sulphide ore is typically discarded. However, increasing zinc demand has resulted in increased interest in recovering zinc from non-sulphide zinc ores, such as oxides and carbonate ores.

This patent complements those in the AmmLeach® family by expanding the range of ores which can be treated. Where zinc is present in combination with other metals the pre-treatment separates the zinc rendering it leachable. The patent is primarily intended for and complementary to use in combination with AmmLeach®.

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