sulphide versus oxide, page-3

Poet.. that's a murky can 'o worms you've opened there..

Copper Oxides and Carbonates generally are secondary replacement minerals from leached/weathered primary sulphide minerals and to some extent are formed and laid down in similar manner to Iron Ore deposits as discussed elsewhere: occasionally deposited from aqueous hydrothermal fluids too.

They don't predominate and so chalcopyrite remains the principal copper ore. Sulphide process plants and assocated metallurgy are geared towards recovery of copper via flotation using reagents which act on the sulphur molecule. To some extent oxides can be floated too though few metallurgists have much experience of this and it remains something of a dark art perfected within mines sharing both types of ores. Often the experience gained at one mine is irrelevant at another.. The other problem is that when you mix reagents to capture both the sulphides and oxides you tend to lose selectivity and, although Rougher/Scavenger (ie the primary float) recovery may be adequate it's often impossible to get the final con grade up to an acceptable level for smelters..

If the oxide and sulphide ores occur together there is little choice but to process them together. Where they occur separately the preferred route is to treat them separately. If the deposit and mill throughput is large enough it pays to process the oxide ores first by leaching and concentrating to copper cathode via Solvent Extraction and Electro Winning and then floating the sulphide ores later in a separate plant to concentrate to either smelt to metal or roast off the sulphur to oxidise the ore and then process through the leach plant. Gold generally follows the sulphur and recovered in credits from the smelter. If associated with oxide it is often lost as the leach residue is rarely processed but 'stored' in settlement ponds (for ever and a day).

I guess it could be possible to float the oxide ores and sulphide ores separately in the same plant (like in Pb/Zn flotation) but I have no experience of this as a process and don't know if it exists.. don't see why it couldn't though.

Another possibility if the scale of operation is small is to leach the copper from the oxides with acid and generate copper sulphate which is dried into crystal form and sold to chemical companies for onward resale as.. copper sulpate crystals or powder. I would anticipate this to be an option for the oxides at AN/AS if they are near surface and separate to the deeper sulphides. Not too much equipment is required

Hope this helps

BT