Paper presented by Dr Jeff Claflin at MetPlant2017, Perth, September 2017
Best practice gold recovery is not an accident. It is the result of proper operation of the adsorption circuit using good quality activated carbon. In-house testing of carbon relative activity permits optimisation of the plant kiln. However, a conventional carbon ‘regeneration’ kiln cannot process carbon fouled with floatation chemicals and achieve best practice gold recovery. A high temperature, controlled atmosphere carbon ‘reactivation’ kiln is required.
Carbon circuit design allows for low quality carbon by increasing the carbon advance rate and setting an easily achieved and commercially prudent solution tails target of typically 0.02 ppm Au. These design criteria are important to ensure the commercial success of the gold operation in the first instance. Most carbon ‘regeneration’ kilns will produce carbon of sufficient quality to achieve a 0.02 ppm Au solution tail in the absence of flotation reagents.
Best practice recovery is considered less than 0.005 ppm Au in solution reporting to tails. If the carbon is heavily fouled, as it will be if used for flotation leach circuits, then a ‘regeneration’ kiln cannot achieve world’s best practice recovery no matter how much carbon is advanced. World’s best practice gold recovery requires a carbon ‘reactivation’ kiln and the whole of the carbon circuit operated optimally.
The competing reactions occurring in a carbon ‘reactivation’ kiln are presented and discussed in terms of kiln design and operation. New industrial and laboratory findings are presented to fill gaps in the body of knowledge and identify that a large reduction in residence time at temperature will not significantly impair reactivation, but can significantly reduce the size and cost of the kiln or permit significantly increased carbon throughput.
The carbon circuit performance is modelled in terms of gold adsorption, as a function of carbon reactivation using ‘simulation of carbon-in-leach/carbon-in-pulp circuits’ (SIMCIL). An optimum carbon advance rate is identified as a function of optimum carbon ‘reactivation’ kiln operation to achieve 0.005 ppm Au in the tails solution. A conventional carbon ‘regeneration’ kiln is compared to a state-of-the-art carbon ‘reactivation’ kiln in terms of reactivation performance and gold recovery.