The traditional process for recovering gold from ore is by way of cyanide leaching.

When the ore contains high concentration of sulphides, an oxidative thermal or a chemical pretreatment is often required. The recovery of gold from soil and rock containing gold sulphides using existing techniques has not however been found to be particularly efficient. In addition, the currently known techniques suffer from several drawbacks particularly with regard to the bi-products produced as a result of the recovery process.

It is an object of the present invention to provide an improved method and apparatus for use in the recovery of gold from source material containing gold sulphides which alleviates one or more of the drawbacks of currently known techniques.

According to one aspect of the present invention there is provided apparatus suitable for use in the recovery of gold from a source material containing gold sulphides, the apparatus including a heated retort for receiving the source material so as to separate it into a solids component and a volatiles component, a high temperature filter arranged for receiving the volatiles component from the retort and separating it into a primarily gaseous mixture which includes sulphur dioxide gas and particulates, and scrubbing means for receiving the gaseous mixture and removing selected components therefrom so that the resultant gaseous mixture may be vented to atmosphere.

The apparatus may further include cooling means for cooling the gaseous mixture exiting from the high temperature filter. The cooling means may be in the form of a condenser and more preferably, a condensing column. The gases exiting the high temperature filter pass through the condensing column where they undergo a rapid cooling treatment. This cooling prevents the formation of dioxins and furanes. The gases may for example, enter the

condensing column at about 1000°C and exit at about 120°C. This rapid cooling as well as preventing the formation of the above chemicals also allows any arsenic present to condense as arsenic trioxide. A spray nozzle may be provided which injects a controlled volume of treatment fluid such as for example, water and air in such a way that an extremely fine mist is produced which the hot gases pass through. By controlling the air and water it can be insured that the bottom of the condensing column stays dry by having all the water turn into a gas vapour. With the water exiting the condensing column at 120°C a gaseous state can be maintained until enters the scrubbing means.

The apparatus may further include filtering means for substantially removing any remaining particulate matter from the gaseous mixture prior to entry to the scrubbing means.

The filtering means may be in the form of a low temperature filter and preferably, a bag house.

In one preferred form, the gases entering this unit from the condensing column are maintained at about 120°C through the filter. This prevents the binding of the bags with moisture. As previously mentioned, any matter that may have condensed into particulate form such as for example, arsenic is trapped in this unit which prevents the emission of these particulates to atmosphere.

The apparatus may further include means for reducing the size of the particles of source material prior to entering the retort. Preferably, the source material is reduced to particles sizes ranging from 40 to 50 micron.

The high temperature filter may be for example, of the type described in International Patent Specification No. PCT/AU96/00628 (W097/13594). The retort may be an indirectly fired vertical or horizontal retort and may, for example, be of the type also described in the aforementioned specification or a retort of the type described in International Patent Specification No. PCT/AU93/00646 (WO 94/15150). Preferably, the retort and high temperature filter are heated to a temperature from 700 to 800°C. Preferably, the scrubbing means is heated to a temperature of 130°C. In one preferred form, the scrubbing means includes an alkali liquid including water and caustic soda which is sprayed onto the gaseous mixture in order to dissolve the sulphur dioxide gas.

The solids and particulates in the high temperature filter and the retort may be collected and subsequently used in a gold extraction process such as, a carbon in pulp recovery process or carbon in leach recovery process.

The scrubbing means may be adapted to remove the sulphur dioxide from the gaseous mixture. The gases entering this unit from will be acid in nature. To prevent any acid emissions the scrubber is kept charged with a base water solution. As the acid gases come in contact with the base water they neutralise each other out and we are left with a salt water solution. The pH level of the scrubber water is constantly monitored to insure that it does not become neutral. The scrubber water is pumped through two nozzles that spray onto two separate pads. The first may for example, be about 600mm above the base water level and the second about 1200mm above the first. Between the fine spray of water from the nozzles and the permanently soaked pads all of the acid gases are effectively neutralised.

According to another aspect of the present invention there is provided a method suitable for use in the recovery of gold from a source material containing gold sulphides, the method including steps of feeding the source material to a heated retort so as to separate it into a solids component and a volatiles component transforming the volatiles component to a high temperature filter and separating it into a primarily gaseous mixture which includes sulphur dioxide gas and particulates scrubbing the gaseous mixture so as to remove selected components therefrom so that the resultant gaseous mixture can be vented to atmosphere.

A preferred embodiments of the invention will be hereinbefore described with reference to the accompanying drawing and in that drawing there is shown a schematic circuit diagram of treatment apparatus according to the present invention.

Referring to the drawing there is shown apparatus generally indicated at 10 which comprises a feed hopper 12 for delivering solid source material to a retort 16 via line 15 and rotary valve 13. Liquid source material may be fed to the retort 16n along line 17 via variable speed drive 18 and rotary valve 19. The retort 16 includes a screw 26 driven by motor 27 and

a heating chamber 28 heated by LPC from source 29. The volatile components which contain the sulphur in the form of sulphur dioxide are transferred via line 20 to high temperature filter 23. The remaining solids are transferred from the retort via a rotary valve to collecting receptacle 25.

The high temperature filter 23 separates a substantial portion of the particulates from the volatiles. these particulates being transferred to the collecting receptacle 32. Nitrogen is fed to the high temperature filter 23 from source 34. The resultant treated gas is passed via fan 33 from the high temperature filter 23 to a condensing column 35 which cools the gas and removes any or the majority of arsenic from the gas. Water is fed to the spray head 37 in the condensing column 35 from source 50. Compressor 39 provides for the productions of water spray at the spray head. The remaining gases pass to a low temperature filter in the form of a bag house 42 which will remove substantially all of any remaining particulate matter which is deposited at collecting vessel 44. The gas then exist the bag house 42 and passes through a scrubber 48 which dissolves the sulphur dioxide so that the gas can then be vented to atmosphere via 49.

Neutralising agent is fed to the scrubber from source 47.

Finally, it is to be understood that various alterations, modifications and/or additions may be incorporated into the various constructions and arrangements of parts without departing from the spirit or ambit of the invention.