Introduction
When determining the type of processing plant you want to install at your site, you want a configuration that will give you the highest quality product with the quickest ROI. Here are some factors to take into consideration when designing your new aggregate plant.
1. Prove deposit size and uniformity
It is important to prove reserves for accurate valuation of a mining operation. The most accurate ROI calculations are based on comprehensive drill data throughout the breadth of the deposit. This is common sense to some and overkill to others, but knowledge of the depth, size and mineral the deposit is comprised of gives confidence to investors and insight to your mine planning. The number and location of boreholes required can vary widely among different deposits depending on their size and uniformity, so it is important to consult experts in the field during this process. Once this data is gathered, McLanahan provides assistance in calculating the cost of running and maintaining our equipment so that your profitability expectations are met or exceeded.
A potential advantage to proper valuation of a deposit is determining potential byproducts in addition to the primary aggregate products. These may be a higher value mineral or simply a size fraction that may otherwise go to waste. Identifying the full range of minerals in a deposit with the help of a geologist is the best way to maximize a mine site’s profitability.
2. Design a flexible processing plant
The majority of inquiries received by McLanahan include a single feed gradation or none at all. Final designs should of course be based on run-of-mine feed, but it is important to take into consideration the entire breadth of potential feeds when designing a system. The borehole data from a proven reserve should be analyzed and (discounting overburden) the best and worst feeds should be considered alongside the run of mine feed. This comparison allows for equipment to be selected that can handle anything you throw at it. It also gives insight into production rate variation from various parts of the pit.
In sand deposits, the feed gradations can be compared in an Excel spreadsheet with one standard distribution away from the mean shown as an expected feed and two standard distributions from the mean as an infrequent feed. This will show where bottlenecks may exist in the system and allow some of them to be designed out of the system before the plant is commissioned.
3. Plan for future expansion
Most aggregate producers push their processing plants to the breaking point and then back off enough to prevent continuous breakdowns. Planning on the front end where the bottlenecks should be in the system will make future expansion more affordable while keeping initial costs in check. Site layout is the most critical part of this planning. It is much easier to replace a few pieces of equipment than to rearrange the entire system. Getting bids for a higher feed rate than what is initially required may reveal that some equipment’s capacity is doubled for as little as a 20% increase in price. Upsizing this equipment and the conveyors during the initial build can amount to significant savings when an expansion is added in the future.
4. Schedule maintenance downtime
No one wants to shut down when everything is going right, but that is always the best time to. It is easy to get behind schedule and to put off maintenance until something goes wrong, but experience teaches us that this is always more costly and a less efficient use of time. An unplanned shutdown can mean hours of digging out conveyors and equipment or replacing parts that were never meant to see wear. Planning equipment runtime based on manufacturer-estimated levels allows for scheduled maintenance so that wear parts are replaced rather than the steel body of equipment or beams from the structure. Analyzing wear patterns also gives insight into what parts will need to be replaced next. Long lead time items may then be ordered preemptively, reducing downtime and further improving system uptime. Unplanned shutdowns may still happen, but they are much less likely if proper care is taken of the system.
5. Consider all tailings management options
With the decline of water availability and rise of environmental concerns, the days of sending plant tailings to a pond without another thought are coming to a close. In some parts of this country, we are well past that point. In others, we are only just beginning to consider it. Regardless of where you are, tailings management solutions have come a long way in the past 20 years and can now eliminate settling ponds with high efficiency and reliability. Many aggregate operations are adding fines recovery systems, Thickeners and Filter Presses (or some combination of the three) to reduce costs and/or to produce a sellable product. It is prudent to consider these options during the initial plant design.
A fines recovery system may significantly reduce the amount of fines sent to the pond. This can cut cleanout costs in half and may provide a sellable product, but these results vary based on the deposit, so testing is critical. The next step is to recover the process water and thicken the solids in the tailings to greatly reduce pond size and provide process water at the wash plant, saving horsepower on water pumps. The last stage is to take the thickened solids and press them into a cake. This allows for the complete elimination of settling ponds, opening up land for mining, eliminating costs of cleaning out those ponds and, sometimes, adding a sellable product.
If you need assistance determining the best solution for your new aggregate plant, McLanahan can help.
