We go over here to the section on cyanidation plus gravity. There’s a bit less of a benefit here overall. So then flotation: we’re saying for every 10% of recovery – again, this is empirical just due to plant survey – just from plant surveys, 0.2% to 1% overall gold recovery. First off, you will get some particles that you might not get in flotation: large particles, large nuggets that need a long retention time. And honestly, lowering the load on the cyanidation circuit is going to improve performance. But for me, the largest benefit or the biggest reason here to look at gravity recovery in a cyanidation circuit is because often free gold is going to cause – let’s look here.
This is grade. This is time. It’s often the free gold that’s going to cause the variability in feed grade. And let’s say you’re not even detecting some of these, but you’re getting these grade spikes from free gold that you’re either running into periodically, or there are lenses of free gold in the deposit, that kind of thing. Good luck trying to run a circuit efficiently in that sort of variable environment. Whereas a gravity circuit is going to knock down these peaks by recovering the significant large portions of free gold and lower the overall feed grade. So you’re going to end up with something that looks more like this going to the cyanidation circuit. And now you’re just having to optimize the circuit in a much less variable environment. So reagents are going down, residence time can go down, and you have much tighter control over the operation of that cyanidation circuit.
So for me, this is the biggest economic benefit of a gravity circuit because in a lot of cases, most of the gold, you’re probably going to end up putting into solution anyway, but from a process control standpoint, there is a very strong argument for adding a gravity circuit to a cyanidation plant based on the reduction of variability to the downstream process.
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