In mining, high levels of capital investment are often a barrier to entry for junior miners or small ore bodies. In addition, expensive processes place immense pressure on operations, driving profits down and negatively affecting the bottom line.

Thankfully, the process of agglomeration is a highly effective, economical method to extract precious metals. According to Theo Winterbach, Mechanical and Bulk Materials Handling Manager at SENET, this is one of the key benefits of the agglomeration process – along with its ability to improve the leaching properties on the heap.

What is Agglomeration?

Hugo Bronkhorst, Product Specialist at SENET describes the agglomeration process as a wet process whereby material fines are rolled into uniformed pellets with the aid of binding agents, to achieve the tackiness needed for material to stick to the coarser particles. The efficiency of the heap leaching process relies on the process of quality agglomerate particles. This increases the ore permeability, drives proper percolation, and minimises segregation during the handling and stacking of the agglomerate, prior to loading on the heap leach pad.

“Heap leaching is a relatively low capital investment option for extracting lean-grade metals, like Gold, Nickel, Uranium, or Copper, from the ore body,” confirms Winterbach. “A low operational cost offers the opportunity for new entrants to grow in mining.” He adds that agglomeration is not recommended for high grade ore, which would be better suited to the carbon-in-leach (CIL) extraction process.

The Steps in the Agglomeration and Related Processes

Winterbach simplifies the complex agglomeration and related processes into three steps:

  1. Ore Preparation & Crushing – following tests conducted on the ore to determine the desired particle size, crushing can commence. The average agglomerate is approximately 30mm in diameter, which offers a good size for percolation in the heap leach process. A key focus during crushing is to ensure that the ore is not crushed too fine, as fines can clog the system and prevent effective percolation and extraction.

  1. Agglomeration

  • A series of short conveyors transport ore to the heap
  • Solution such as sulfuric acid, water or cement is fed at predetermined rates into a rotating drum via a spray bar system
  • A chemical reaction bonds the fines together
  • The rolling action in the drum causes them to stick to larger particles and increase in size
  • Once optimum residence time has been achieved (ensuring particles do not degrade or segregate) and the agglomerates have formed to the desired size and the required particle strength, they are fed from the drum onto the conveyor to proceed with the stacking process

  1. Conveying and Heap Leach Stacking – the agglomerates are sent to the heap leach pads via conveyors, where they’re stacked. A strong agglomerate ensures that the heap leach pad is stable, comprising multiple layers. The heaped ore is then irrigated with a liquid to dissolve the metals and generate the leachate, which is how the precious metals are extracted.

Why Seek Expert Advice for Agglomeration?

 It is widely recognised that the efficiency of the heap leaching process relies heavily on the process of quality agglomerate particles. With expert guidance and accurate testing, mines are better able to determine the best process and equipment for extracting their particular precious materials.

“An experience-based approach is critical to success,” believes Bronkhorst. “A myriad of factors influences agglomerate characteristics – from variable drum speed to ore type and moisture content, feed rates and residence times. Agglomeration has the potential to maximise recovery rates, but only if the necessary factors are considered, and the correct processes are followed.”

Blinding the heap with fines means losing the recovery of the precious metals, wasting much energy, and little return on investment. “This is not true agglomeration. Proper processes must be followed to ensure a good agglomerate is added to the heap leach pad. With this approach, the best solution is used to ensure cost savings and maximum profitability,” concludes Bronkhorst.

For more information from SENET’s agglomeration experts, contact Theo Winterbach (t.winterbach@senet.co.za) or Hugo Bronkhorst (h.bronkhorst@senet.co.za).

 

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