Caiman | Crushing | Equipment

The copper extraction process begins at an open cut mine where Copper Ore is blasted and removed via Excavators and Tip Trucks. The ore is fed to a Crusher where it is broken down to a specified maximum size and passed through to a conveyor. When the crushed ore falls onto the conveyor it is transported to a Ball Mill to have its particle size reduced further. During transportation the ore on the conveyor has grinding medium added to it, with the quantity added determined by the ores volumetric flow rate.

The Ball Mill is best seen as a large rotating drum on its side. The conveyor deposits crushed ore and the included grinding medium inside the Mill at one end. As the Mill revolves, the grinding medium smash and crush the ore into finer particles, until such time as the ore is of sufficient size to exit the other end. Grinding medium is not removed from the Mill but smashed to pieces and exits as part of the output feed. A cyclone separator is used on the Mill’s output feed to remove the oversized particles. These are returned back to the Ball Mill for further crushing. The sized particles are collected in leaching tanks where they are submerged in sulphuric acid to begin the leaching process (where copper ions dissolve into the acid solution).

The sulphuric acid and crushed ore mixture is now referred to as a Process Slurry. The Slurry is pumped first into a Thickener tank and then a Clarifier. The thickener tank is used to gravity separate the clay particles from the desired leached solution. Flocculants and Coagulants (artificial additives that promote amalgamation of fine particles into larger heavier ones) are added to the mixture to decrease the settling time. Once enough time has expired for the clays to sufficiently settle, the overflow (top part of the solution within the tank) is then pumped to the Clarifier. As a general rule Clarifiers will have a lower residence time and produce a thicker underflow solution. Flocculants will again be added and a settling time is allowed for. The end result is the Clarifiers overflow stream consisting of a High Grade Copper Leached solution. This solution is now referred to as a Pregnant Leach Solution and will be treated for copper extraction. The underflow stream of the Clarifier is pumped back to the original Thickener for further processing.

Returning to the original Thickener tank, let’s now address its underflow stream (the solution within the tank pumped from the bottom). Here we have a much lower concentration and further treatment needs to occur in order for high grade copper to be extracted. The underflow of the Thickener tank is passed through a series of additional Thickeners (five in total, referred to as CCD No.1 to No.5). More flocculants and coagulants are added and further separation occurs between the clay and copper impregnated leached solution. A second Clarifier is introduced and a Low Grade Copper Leach Solution is produced (also referred to as a Pregnant Leached Solution, often prefixed with either LG or HG).

The final two stages of the copper extraction process are Solvent Extraction (SX) and Electrowinning (EW).

The first stage (SX) is a two step process. First the Pregnant Leached Solution is injected with an organic solvent which has the beneficial property of attracting copper atoms to its molecular structure, especially in low acid – low copper leach solution. Copper ions transfer between the two solutions and once completed, we declare the organic solution to be loaded. This step is referred to as Extraction. Then the organic solution is contacted with a concentrated sulphuric acid. Copper is released from the loaded organic and the end result is a sulphuric acid solution containing very high concentrations of copper. This is referred to as Stripping. The final solution after Stripping is called a Strong Electrolyte and it is this which will be used in the Electrowinning process. The remaining solution, containing the now unloaded organic solvent, goes through a recycling process to be reclaimed for later reuse.

The Electrowinning process is essentially a series of cell batteries. Each cell is comprised of electrodes (in the form of removable anode and cathode plates), and is filled with the Strong Electrolyte solution (from the Stripping process). A potential DC voltage is applied to the cells and, much like the charge cycle of a battery, current flows. Current flows due to chemical reactions occurring within the electrolyte, and a consequence of this action is the accumulation of copper onto the electrode plates. When sufficiently coated, the plates are removed from the solution by a system of hooks and overhead crane and taken to a stripping and washing bay where the copper is removed, and the plates washed and returned (at a later date) for the process to be repeated.

Figure 2: General flow diagram of the copper extraction process

Last update: February 21, 2012

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