Concentrator design has a large impact on the flow in production because oversizing in one area will push problems downstream. The challenge is to strike the right balance between equipment flow and recovery of concentrate ore grades.
One way to overcome bottlenecks is to include a consistent design factor throughout the engineering process. This requires solid knowledge of the ore, open and transparent cooperation and sharing of expectations between the mine owner, engineers and equipment suppliers. Setting the design criteria based on shared expectations and common ground enables the parties to design a solution with focus on total cost of ownership, rather than lowest capital investment.
“A consistent design factor on all equipment might mean a slightly larger initial investment. However, it is much more costly to shut down operations and replace undersized equipment at a later stage. The primary reason for focusing on the design factor in comminution is to accommodate periods of harder ore, where the circuit otherwise is designed to process at average rates,” says Dave Rose, Global Process Director for Concentrators at FLSmidth.
For instance, a copper comminution circuits in the range of 100,000 t/d typically have a design factor of 15 percent and this design factor often leads to a production of 115,000 t/d. Consequently, this creates bottlenecks elsewhere in the production line.
Keep it floating
To make sure that the design criteria meets the need of the specific mine - and that all equipment meet these criteria, too - FLSmidth has the advantage over most suppliers by being a full flow sheet provider.
“Since we develop, supply, install and maintain all the necessary equipment and workflow, our customers are sure that all equipment function well together and are sized according to the needs. To meet their needs, we continuously develop new equipment or make improvements on existing equipment, for example our new nextSTEP™ rotor/stator flotation device. Dewatering circuits are generally pretty forgiving on the performance if oversized, but are extremely unforgiving if undersized”, says Rose
The balance between the percent solids, the head grade and the recovery grade is essential. Using too high a design factor in the flotation circuits can introduce other concerns, including recovery and concentration grade because of the change in retention time in the cells.
“While rougher flotation may have high grade and recovery, the cleaners may exhibit negative performance because of higher tonnage rates or higher grade feeding into the cleaners than what was designed for. The volumetric balance is very important. We regularly visit plants where the ore head grade is high and a properly designed flotation circuit is underperforming because the ore does not match the design criteria provided for the circuit. The big challenge with higher head grade is not overloading the cleaner circuits. Concentrate grade may be better but the recovery will be lower, as there are higher value minerals lost in the circuit,” he says.
The best design is made by considering various scenarios in a step-by-step manner through the flowsheet, starting with the comminution circuit. The design has to combine the ore and mineralogy characteristics with the client’s expectations.
The next step in the process is recovery, which has to include consideration of the ore grade, recovery variance, as well as operational conditions, such as slurry, density, reagent addition, etc. Next to consider is the variation in recovery and feed rates to determine the best option for sizing of the dewatering equipment.
Key benefits of the nextSTEP™ rotor/stator**
• Significant improvement in both metallurgical performance and energy efficiency
• Lowest operating power of any mechanical flotation mechanism on the market
• Dramatic improvements in attachment rates, which translates into significant recovery increases
• Better wear distribution increases product lifecycle and improve total cost of ownership
• Designed to be retrofitted in all forced air machines, regardless of make or model
Lowest power consumption flotation technology on the market
The nextSTEP rotor/stator from FLSmidth reduces power requirements by 15-40 percent and has a better wear distribution, which therefore increases the life span and reduces the total cost of ownership. With reduced OPEX through energy efficiency and significantly improvement of recovery rates and concentration grades, the nextSTEP™ rotor/stator is a step change in flotation.
It is possible to retrofit the nextSTEP rotor/stator into existing flotation cells up to 660m3. The conversion process is simple, low risk, for all makes and models, and proven already with a large number of successfully completed retrofits for flotation cells ranging in size from 5m3 to 250m3.
Dave Rose, Global Process Director, Concentrators