Grinding Circuit Optimization

For optimizing the comminution circuit, some surveys are conducted followed by a complete mass balance and model fit, and these are utilized to investigate possible circuit changes and alternative operating strategies. Several options should be investigated using available equipment. Further simulations were performed to evaluate a circuit expansion, resulted in significant improvement in overall comminution performance.
Representative ore samples should be collected from determined sample points during the complete comminution survey for breakage and grinding characteristics. The survey data should be mass balanced using a reliable software like JKSimMet to confirm the data quality and estimate any stream flow rates that could not be measured.  ore characterization results are used as JKSimMet inputs to analyze the effect of the ore variability in the circuit in terms of throughput and final product.
Then simulations were conducted to assess if a finer final product and higher performance may be achievable with the current equipment as obtained in the survey. Mostly two items should be considered for optimizing grinding circuit, first simulating models to achieve the correct circuit may by adding some other equipment or only by modifying the current equipment; second, is optimizing the mill performance itself sometimes according to the ore characterization, we need to optimize the ore behaviors in the mill, one solution is to modify the profile design of liners especially discharge grates and pulp lifters which play the main roll for accurate exit of grind ore from the SAGmill. Consequently, other mill parameters such as mill speed should be adjusted in a way that cause the integrated optimum performance for a mill. Many simulations with different considerations help to find optimum points.
As mentioned above, finding the correct circuit is one of the main jobs in optimization project. The correct circuit help us to achieve finer product with higher throughput or even with the same throughput. In a typical grinding circuit with SAGmill, ballmills, screens and hydro cyclones, mostly below changes can help to provide with finer product; nevertheless, it should be thoroughly studied case by case and there are not any same solutions for all the grinding plants.
1-Changing in SAGmill’s grate slot, screen aperture or cyclone vortex; most of the times by decreasing these mentioned items, the circulating load will increase, however, the P80 will decrease in a way can increase the performance of whole processing plant.
 2- Ball reduction size, usually as decreasing the ball size in ball mills, we can increase the ball charge and will have the finer product.
3- Increase ball charge; increasing the ball charge cause to fully utilized the installed power and increasing the utilization of mill which cause significantly decrease in product size. And also, Ball size measurements indicated that there is s systematic decrease in ball size towards the exit diaphragm, this shows a proper performance of balls reduction size during the retention time in the mill.
 4- crushing more than grinding; usually using a crusher for oversize material help to increase the capacity of grinding circuit which by considering other items even can lead to finer product, and also, significantly decrease the energy consumption.
 5- Partial split of classifiers underflow; by splitting the flow streams, can release some capacity, and reduce the product size.
As a conclusion, for optimizing the grinding circuit it is necessary to consider all the parameters integrated, there are many changes that can help a plant to modify, the changes should be simulated many times to find the optimum model and see the synergism of changes and determine the cost and benefit of each solution and model.