Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning

Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning 2017-04-21T02:33:06+00:00
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Gold Lock-up; carbon loading & inventory problem (2 replies)

9 months ago
Madungo 9 months ago

Hello, I need help to releasing gold lock up from my CIL circuit's carbon. I want to run more frequent elution in order to get more gold out but we seem to only recover what we're putting in only. My gold locks up in the tanks and it increases each month. I and at the point where I want to keep it where it is or decrease it. Plant feed grade is stable.

My elution efficiencies are between 85 and 93%. My biggest challenge is the carbon concentration in tanks is very high hence more gold on inventory but reasons for the high concentration is due to that there's too much sand in my system currently caused by the bad grind I've had recently so all the carbon settles at the bottom of the tanks with the sand particles.

I've tried picking up densities to reclaim all the carbon that is at the bottom of the tanks but it's not coming up as expected or as seen from the samples taken at the tanks drain valves. And the loadings on those samples are high but I can't elute the carbon as it is not reporting to the loaded carbon vessel.

What do I do next? Thank you.

9 months ago
ThabisoKwenane 9 months ago

Hello. Try installing air injection pipe in each of your CIL tank(s) to help in agitating the slurry/sand. That might help in keeping your carbon in suspension next time you experience a similar challenge. 

Your relative density of the slurry to CIL should be atleast between 1.38 - 1.42 t/m3. Check if whether it's between that range. Also do ask your supplier, what is your "wetted carbon density"; Your slurry density should just be a bit above the wetted carbon density for your carbon to be on suspension. 

9 months ago
Cyanide 9 months ago


Good practice to do monthly gold inventory so you can track circuit inventory and establish good optimum. Most of it is carbon related. Gold on slurry normally only in circuit for 24 hours but in carbon probably 2 weeks. Can pull carbon inventory down with more elation if you have capacity but it's a trade-off between elation cost and solution grade. One other variable is carbon concentration in tanks. Most circuits tend to optimize around 14 days carbon residence. If you're much higher, will have more gold on inventory.

Also, adjust your CIL density/viscosity until your carbon is dispersed. If it keeps settling towards the bottom get longer carbon advance pumps. Reduce the amount of carbon in your circuit as long as you don't start having tails, and speed up your strips. You can add air sparges to the bottom to mix and lift carbon, also air should increase your do.

Bypass primary CIP tank and empty it out to recover any trapped carbon is the only real solution. Then if grinding is a problem, track sanding by using a weighted measure (heavy mill ball or any heavy item on line to detect and measure any sand build up to indicate further sanding events. To lift carbon from "sanding events" only works if slurry is return to normal densities immediately but every low density event will always leave some carbon inert at the CIP tanks. Carbon stripping is not a accountable problem, solution in m3/hr, grade g/t, solution out g/t is sufficient. Assay of pregnant and barren carbon should also agree.

I noted that the carbon loading on extracted from the bottom high is high. What is the operation carbon loading in contrast? One way to decrease gold inventory, if there is a temporary peak of gold loading on the pregnant carbon, is too increase the stripping rate as most of the gold report to metal in the first few hours, so one can return "stripped" carbon at higher gold tail concentration than optimum, and then add the "stripped" carbon to the CIP tank with similar carbon gold values.

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