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Gold/Mining/Energy : ECHARTERS -- Ignore unavailable to you. Want to Upgrade?

To: Al Cern who wrote (2099)	12/31/1997 8:14:00 PM
From: E. Charters	Read Replies (1) \| Respond to of 3744

1. Release size. Amount of grinding. Bears on media use and electricity. Also fines production plays havoc on flotation and Merril Crowe cyanide system. Many factors here. 2. Metallurgy. Is gold accompanied by sulfides, what kind? copper, zinc? Carbon? Can kill cyanide. Reagant consumption. Cyanide costs money. Sulfide are also extremely hard to grind. 3. Bond work index of ore? Is the ore hard, tough, expensive to grind? 4. Is gold atomically bound by arsenides or pyrite. Will take autocalving or acid treatment. That is the free milling versus semi refractory concept. There are a wide variety of types of ore as well as recovery techniqes and costs. Gold can be leached from some very porous but hard ores that only ahve to be crushed. Capital costs and thoughput is very simple. Other ores require a lot of crushing and grinding and chemical treatment. Then there is mining. Its quite another thing. And there are many many factors here that inter-relate. EC<:-}

To: Al Cern who wrote (2099)	1/2/1998 7:43:00 PM
From: Bill Jackson	Read Replies (2) \| Respond to of 3744

Al, Usually the rock has to be crushed to 200-400 mesh. This is to provide the maximum surface area for later chemical processes. Some rocks are hard but shatter easily, and others are softer but tougher so they have to be worked harder. The composite of the hardness/toughness etc is called the grinding index. It generally comes out as an energy figure per ton to a certain mesh. Since smaller costs more, but smaller also gives more surface area you must balance costs versus gain. A side though is the amount of clay or 'slime' forming material at what grind size. Excessive clay or slime tends to slow any settling, clog filters and adsorb gold, and so this goes into the equation. Grind too fine and if you do a flotation it all floats. In addition gold bound with tellurium or pyrite mey be resistant to chemiacl extraction(cyanide) as the layers are intimately involved, and you must bake it in an autoclave to turn the sulfide into SO2 allowing you to extract the gold. This stage can be done by bacteria also. In essence you are smashing all the rock to powder and picking out the lumps with tweezers in a free milling gold system, where the gold once broken free can be picked up by gravity tables, tweezers(joke), of a centrifugal concentrator. Obviously it is harder to smash rubbery rock, it absorbs the blows, and you must use more energy. For sulfide it must be crushed and placed into water with a frothing agent and a flotation aid. ( stuff you add to the podwer so when you make bubbles the sulfide sticks to the bubbles and they float to the top with the ore attached to them. The non sulfide sinks, as it does not stick to the flotation aid. It is a complex brew to make a flotation circuit work at highest recovery. There are many rocks, many types of flotation aids and foaming agents. Bill