GWA Group Ltd V.GWA

Where does the Autoclave fit in the process?

[Mechadvice]

Thank-you for the positive comments. I am not familiar with the process of using an autoclave. I have spent the last 10 years in straight forward milling work. I hope that someone can weigh in on this question and provide their thoughts. However, I have asked my peers and also done some reading on autoclaves. Here is what I have found: The autoclave is required because of the nature of the refractory ore that is at the Bradshaw deposit. The ore is difficult to separate without first putting the ore through the autoclave process. Where does this fit in the flowsheet? From what I can see it comes after the grinding process and likely before the flotation separation process. So for the ore from Bradshaw in the Redstone Mill it might look like this: Prior to the AutoClave: The concentrator consists of two buildings, namely the crusher house and the mill building. At the crusher house ore falls through a grizzly into a coarse ore bin with a capacity of approximately 100 live tonnes. The 24 minus material is conveyed by a 42X16 Simplicity pan feeder to a 30X42 Birdsboro Jaw Crusher that crushes the ore to 3 to 4 minus. The crushed material is then conveyed to the Gator Double Deck vibrating screen which feeds the oversized material on a conveyor equipped with a self-cleaning magnet for tramp steel removal, over to the Metso HP 400 cone crusher. The HP 400 is a safe, modern and dependable cone crusher and is readily available in todays market. The crushing plant is fully automated with VFD (Variable Frequency Drives) for operational flexibility. All equipment can be energized from a PLC in a control booth. To ensure the health and safety of the operator, any airborne dust particulate is collected by a KTM AA 19/30 dust collector system. The crushed ore at 5/8" minus is conveyed from the crusher house to two fine ore bins located in the mill building through a conveyor galley way. Conveyors underneath the 800 mt fine ore bins feed the grinding circuit which consists of two Dominion Engineering 10x13 and one 10.5x13 ball mill. The ore can feed one or two primary ball mills as the three ball mills can work either in series as a primary, secondary and tertiary grind or as two primary mills for a secondary grind. This flexibility allows two different types of feed (low grade and high grade or custom ore) to be processed at the same time. Cyclones work in conjunction with the ball mills to achieve the grinds required for flotation. At this point in the process the ore is reduced down to tiny particles that would normally go through a floatation process. Chemicals would be added and the minerals separated via gravity and floatation. Here is where the AutoClave comes into play: With the refractory ore the normal process for separating minerals does not work as effectively. Recovery % is very low unless something like an autoclave process is used. So at this point the ore is likely treated with a chemical and then passed through an autoclave where it is pressurized and the temperature is elevated. The reaction in the autoclave will depend on the ore being processed. I cannot speak to the type of reaction that will be sought when it comes to the Bradshaw ore. The end result of the autoclave process is to liberate the gold from what is entraining it. After this is complete the gold can then be further separated using a flotation process. After the AutoClave they may then be able to use a flotation process. But this will take some process flowsheet work to make it suit the Bradshaw ore The finely ground ore passes from the cyclone overflow into conditioning prior to the rougher flotation tank cells. Chemicals are added for conditioning purposes prior to the rougher cells. Cleaning of the sulphides is achieved by scavenger and cleaner cells with appropriate chemical and mechanical action. The flotation concentrate and tailings are then pumped to two different thickeners in the mill building. A 40' dia. high density cone tails thickener removes a large amount of water from the tailings leaving a "tooth-paste-like" material consisting of about 25% solids which is pumped into the tailings area. The concentrate is pumped to a 26' diameter conventional concentrate thickener which also removes water from the slurry. The thickened concentrate is then pumped into a surge tank feeding the Larox Press Filter which produces a concentrate of 9% moisture. The concentrate is then conveyed into a concentrate holding bay. The concentrate is weighed and sampled upon shipping. The moisture content and payable metal grade of each shipment is then determined at Northern Sun's laboratory in the mill building. Disclaimer: This is a data from the Northern Sun Mining website. I added in comments with regards to the autoclave. I do not have experience with autoclaves. These are only my thoughts based on opinions of peers and from what I have read. Autoclaves are being successfully used by some large cap gold companies to process refractory ores.