Ever wondered what happens in the process between gold ore discovery and the creation of a gold bar? You are not alone. The process is a lot more interesting than most people think, and two of the most important techniques in modern gold processing are called CIL ( Carbon-in-Leach) and CIP (Carbon-in-Pulp)
They sound almost identical, and in some ways they are, but the difference between them matters enormously, and is dependent on the mineralogy of the ore discovered. Let’s break it down.
Gold Extraction
Gold is extracted from alluvial or primary deposits. Alluvial gold is found in river sediments or soil from shallow earth deposits that contain small particles or nuggets of gold—sometimes known as ‘free’ gold as the gold particles have been released from the host rock after millennia of natural weathering. Primary deposits of gold are those in which the gold is still embedded in the ore (i.e., the gold is not ‘free’) and are mostly found underground in quartz seams.
Once the ore is dug up and crushed into a fine slurry (think of a very thick, gritty smoothie), the next challenge is separating the gold from everything else. This is where both CIL and CIP gold processing come in.
Both methods use a chemical called cyanide solution to dissolve the gold out of the crushed rock. Cyanide is a reagent that is used to leach, often in tanks. Cyanide has a natural affinity for gold, and when the two meet in the right conditions, the gold dissolves into the liquid. At that point, you need something to grab the dissolved gold out of the liquid and hold onto it so you can recover it later. That “something” is activated carbon, tiny black granules that act like a sponge specifically for dissolved gold.
So far, CIL and CIP sound identical. Here’s where they diverge.
CIP: Carbon in Pulp
In a Carbon in Pulp circuit, the process happens in two distinct stages. First, the crushed ore slurry goes through a series of leaching tanks where cyanide does its job, dissolving the gold into solution. This leaching process is allowed to largely complete before anything else happens.
Then, in a separate set of tanks, activated carbon is added to the already gold-rich solution to adsorb (pull out) the dissolved gold.
CIL: Carbon in Leach
Carbon in Leach runs both processes at the same time, in the same tank. The cyanide is dissolving the gold while the activated carbon is simultaneously pulling it out of solution. Leaching and adsorption happen together, in parallel, through a series of tanks where carbon moves counter-current to the slurry flow. The simultaneous leach and absorption phases of the CIL process were developed for processing gold ores that contain preg-robbing materials such as natural absorptive carbon. These reduce the gold yield by attracting gold meant for the activated carbon. Simultaneous leaching and absorption help minimize the problem.
By having carbon present during leaching, you’re essentially outcompeting those minerals in real time, capturing the gold before the rock can steal it back. In high preg-robbing ores, CIP can result in significant gold losses. CIL can recover gold that CIP simply cannot.
So Why Pick One Over The Other?
The distinction has real consequences for how efficiently gold is recovered and how much it costs to do it. CIP is more practical and cost-effective when preg-robbing isn’t a concern, which is why Mwamba employs this method of gold processing at our plant in Buziba, Northern Tanzania. Keeping the stages separate can make the circuit easier to manage and control, and it often requires less carbon inventory in the system at any given time.
In both cases, once the gold is sitting on the activated carbon, it goes through a process called elution to strip it off, then electrowinning to plate it out as a sludge, and finally smelting to produce the doré bar you might actually recognize as gold.
The choice between CIL and CIP isn’t about one being universally better than the other. It’s about understanding your ore, knowing what’s in the rock you’re dealing with, and designing a circuit that recovers the maximum amount of gold for the minimum cost.
That’s what good metallurgy looks like, and it’s the kind of thinking that goes into every tonne of ore we process.
Mwamba Group operates gold processing facilities in Tanzania. We share insights like these because we believe transparency and education are part of being a responsible mining company.
