I often get questions about the purpose of agglomeration in heap leaching operations so I thought this blog post would be a good opportunity to give a brief overview of the agglomeration process as well as talk about when it is and isn't necessary. When an ore is crushed, often a lot of fine particles are created. These particles can prevent leaching solution from moving evenly through a heap and this can dramatically decrease recovery. Agglomeration solves this problem by sticking the fine particles either to each other or to larger particles in the ore so that the leach solution can flow evenly through the ore for maximum recovery. Continue reading for a more detailed explanation . . . 

To step back for a moment let's take a look at heap leaching in general. To stat a heap leach, crushed ore is piled onto an area that has been prepared for the leaching process. Lixiviant (typically cyanide for gold ores and sulfuric acid for copper ores) is dripped onto the top of the heap and then slowly flows through the heap by gravity while leaching out the target metal in the ore. Once the lixiviant (and dissolved metal) makes it to the bottom of the heap it is recovered by a fluid collection system. This fluid which now contains the dissolved metal (called pregnant solution) is typically sent to a hydrometallurgical process to recover the metal.

So what part does agglomeration play in all this? Well, in order for the lixiviant to extract the metals in the ore it needs to be able to get in contact with the metals. In many cases this requires crushing of the ore so that the particles are small enough for the lixiviant to contact most of the metal in the ore. When crushing takes place this typically generates fines, which can be a big problem for the heap leaching process. The fines basically plug the holes in the heap that the lixiviant needs to flow evenly to the bottom - this is where agglomeration comes to help.

Agglomeration is the process of taking the fine particles and either attaching them to each other or attaching them to larger particles in the ore. This keeps the metal in the fines available for the lixiviant and at the same time allows the lixivant to flow smoothly and evenly through the heap. The agglomeration process takes place after crushing and before the material is piled into the heap; it is typically done in an agglomeration drum which is a large, open-ended rotating drum (seen in the picture above) that continually rolls all of the particles together. Typically a binding agent (like cement) is added to the material to help it stick together, along with some addition of the lixiviant to get an early start on the leaching. 

Agglomeration is not necessary for all ores as some ore do not need to be crushed before leaching and some ores just don't generate many fines through crushing. However, when there are a lot of fines in the heap material it is critical that agglomeration is used to ensure even lixiviant flow and maximum recovery.

Sepro manufactures agglomeration drums both for cyanide and acid leaching so if you have any questions about the process or the equipment please don't hesitate to contact us!