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

To: Al Cern who wrote (2574)	5/5/1998 11:22:00 PM
From: E. Charters	Read Replies (2) \| Respond to of 3744

After comminution or grinding to release size of the majority of the desired economic particles, the process of concentration begins. This varies according to the mineral. In the case of sulphide minerals this may be a process of flotation of the valuable sulphides by oil bubble flotation. Rejection of the gangue minerals such as quartz and iron minerals is accomplished in this step. This will produce for instance, a float concentrate of perhaps 27% copper. The ground slurry is introduced into cells where a froth is created and the rising froth attaches itself, if chemically prepared, preferentially to the desired product. Some minerals will not respond to flotation although a wide variety do. Other techniques involve gravity separation and cyanidation or solvent extraction techniques. Oxide minerals lend themselves to solvent extraction directly. Gold is frequently solvent extracted by cyanide directly on the ore after grinding. Silver may be cyanided or floated. Nickel and copper, cobalt, and platinum minerals respond to flotation. After the substance is concentrated it is dried by dewatering in tanks and later in filters. The filtercake is then ready to be pelletized for solvent electrolytic refining or furnace smelting. An excellent book to read on the process of mining, concentration and smelting is "The Winning of Nickel". It is the story of Sudbury mining and milling methodology. Recovery percentages ranging from 68% to 96% should always be viewed with suspicion. It may be that on a very good day, but I am sure you will find that a very good review of the tails percentages reveal a discrepancy between the claims of the milling people and the actual recovery. Here is a list of usual recoveries claimed on primary ores: Copper: 88% Gold: 85 to 96% Silver: 80% to 90% Zinc: 85% Iron Ore: 65% to 90% Nickel: 88% But this is very general. Complex ores with multi metals have a very different recovery for each metal. Some precious metals may suffer in polymetallic ores. Copper Nickel ores are harder to recover than others. Cost are higher in refining these ores too. Costs to concentrate, grind and smelt each ore is on the merits of that ore. It requires individual study. Many ores are impossible to recover economically although they are very rich because they are too fine grained. echarter@vianet.on.ca The Canadian Mining Newsletter