As tariffs begin to take hold — impacting both supplies and costs of various metals and minerals imported for construction and manufacturing — pressure is ramping up to increase throughput of domestic mines.
Though there are a number of promising mining projects on the boards that will one day increase domestic U.S. production of copper, nickel, zinc, molybdenum and other critically needed metals and minerals, the reality is that it will be many years before those new mines are fully operational.
In the interim, mining companies are carefully looking at existing operations to push production rates as high as possible. This is a challenging proposition, however, as ore grades trend lower, requiring more tonnage that needs to be processed by aging concentrators to maintain status quo for the volume of processed materials needed in a variety of sectors.
Concentrators Are Pivot Point
Once ore has been drilled and blasted, it is hauled away to the concentrator, an important stage in the mining process where it enters intense crushing and grinding processes that will ultimately liberate the desired metals or minerals from the gauge waste surrounding it.
Once the ore has achieved the desired particle size it can move through the separation process where the valuable minerals can be separated from the waste rock into a higher-grade concentrate. Froth flotation is a common method to achieve this goal and does so by creating a slurry of ore and water. At this stage, specialty chemical reagents are added, making the desired mineral particles hydrophobic. When air is added to the slurry to generate bubbles the particles attach, forming a froth rich in concentrate that is skimmed off the lips of the tank. The undesired gangue leaves through the bottom of the flotation tank and becomes tailings.
Once the concentrate has gone through sufficient stages of froth flotation to achieve the desired concentrate grade, it can be dewatered and shipped out to smelters or reductive leaching for final processing into refined metals in pure form.
Optimization and Debottlenecking
As existing operations push more production through their existing circuits, it rarely happens without consequences. Increasing throughput often sends coarser feed to flotation and decreases retention time, resulting in a drop in recovery. Additional signs your plant may be reaching its limits can be traced to some common symptoms including overloaded conveyor belts, tanks and sumps spilling over, pipes/chutes plugging, pumps/control valves operating at 100% most of the time and increases in unplanned downtime.
Both optimization and debottlenecking are essential activities that improve safety, production and profitability of the concentrator.
Concentrator optimizations start by having a robust data set and understanding of ore characteristic. A strong mine-to-mill team can communicate upcoming ore and develop key strategies like blending ore. OPEX investments can then be made to install needed instrumentation and automated process-controls to assist operators. A comprehensive optimization program for all concentrators across the entire plant is a great way to see productivity gains.
Meanwhile, debottlenecking is the term commonly applied to projects that address the current design limits of various processes of the concentrator flowsheet to gain more productivity. A bottlenecked grinding circuit often may be identified by an increase in spillage coming off conveyor belts. Similarly, bottlenecked processes at the flotation stage can result in spillage coming from pump boxes/launders. It also may result in a drop in recovery rates, or even curtailments to mill throughputs. Bottlenecking is an issue that may commonly occur if a key performance indicator is deemed a priority and pushed harder than it should be.
As metallurgists begin diving into these improvement projects, it is important to consider the load to utility systems, where aggressive throughput metrics begin taxing the power and water systems, bogging down and slowing process operations. Engaging your frontline operators and engineering teams early is an essential step to understand the scope of the projects. It’s often the case that a seemingly straightforward project will result in unexpected complications, and those who know the plant best often can come up with workable solutions.
Balancing Quick Wins with the Long View
It’s essential for mine managers to integrate planning groups with a well-thought-out geo-metallurgy program in order to balance long-term priorities with short-term needs. This will result in an accurate understanding of expected returns on investment for longer-term capital projects, as well as surfacing any issues that could be faced.
It is often the case that debottlenecking of current operations could result in improvements that could be integrated with a prudent strategy of broad plant improvements — all leading to a step-change in productivity.
For example, if the material hardness and grindability characteristics see a sustained increase in later years, mine managers may find themselves behind the eight ball if they have not anticipated and planned for those changes. Urgent and costly upgrades to grinding and crushing operations could be the result. Taking a longer-term view of those changes means that engineering and procurement of costly new equipment can be done with adequate time needed to manage long-lead equipment and installation.
It should be remembered that the purpose of a concentrator is not to mill the most tons or to scape the last bit of metal from the lip of the flotation cell. It is instead to maximize the amount of salable concentrate for the given ore type. When an operator begins the journey to optimize and debottleneck, it is critical to not get tunnel vision on one process, but to understand the overall impacts to the system.
Success Factors
Though every mine manager wants to see improved productivity and profit, none of those projects can be considered a success if they create safety issues for employees on the front lines of operations.
A successful debottlenecking or optimization project will improve safety metrics because they will address spillage issues that often expose workers to hazards or result in them facing risks from emergency projects to restore an equipment breakdown. Safety can never be compromised over a goal of increased tonnage.
When employees are able to leave on time at the end of their shifts, getting home safely and on time, plant morale is likely to benefit due to an improved quality of life in the workplace.
