How fines recovery systems can benefit aggregate processors
Settling ponds can end up being more of a chore than a solution for aggregate waste
Wash plants used by aggregate operations to create clean sand and rock will produce a waste stream. This waste stream consists of the water used to clean the material as well as any silts, fines and clays that are removed in the process. The waste stream is typically thought to contain no value, and is often disposed of in the cheapest and easiest way possible - an earthen containment known as a settling pond.
But when these ponds fill up, the settled solids have to be removed or the surface water has to be pumped off to make room for the incoming waste. Undertaking this task can be both time consuming and expensive, says Eagle Iron Works, an equipment provider for the aggregates industry for over 145 years. Depending on the size of the operation, ponds may require cleanout several times a week. These costs can add up in the long run, making ponds more of a chore than a solution for waste.
Fines recovery systems
Fines recovery systems, such as EIW's Hawk Fines Recovery Plant, help to alleviate the burden of settling pond maintenance by reducing the volume of material going into the pond.
These systems feature a sump, pump, hydrocyclones, and dewatering screen. The waste stream from the wet processing plant enters the sump of the fines recovery system, where it is pumped up to the hydrocyclones. Hydrocyclones used for fines recovery are specifically designed to capture fine particles down to 400 mesh. These particles are then discharged onto a dewatering screen to remove additional moisture for conveying and stacking the material.
Particles smaller than 400 mesh and water are then sent to the settling pond or downstream processing equipment, such as a thickener or filter press.
Benefits of fines recovery
The benefits of fines recovery systems are many but largely include:
- Reduction in pond cleanout/maintenance costs
Pond cleanout can be costly, both from an equipment standpoint and a labor standpoint. Mucking out a pond requires an excavator, which not all operations may have in their fleet, so renting the required equipment costs money. Even if a site has its own excavator, the excavator needs fuel, so operational expenses are incurred there. - Reduction in operator time
The operator spends time running the equipment to clean out the pond, time that could be spent doing other tasks elsewhere on site. By reducing the volume of material that goes to the settling pond by first processing it through a fines recovery system like EIW's Hawk Plant, aggregate producers can reduce their pond cleanout frequency. Reducing pond cleanout frequency saves money on fuel and equipment rental fees as well as allows a better, more productive use of personnel time. - Reduction in load on downstream equipment
If an aggregate site has installed tailings management and water recycling equipment, such as a thickener and/or filter press to recycle water or to reduce pond size, or if a site is considering adding one or both of these pieces of equipment to a new build, a fines recovery system can be a big benefit.
Adding a fines recovery system reduces the solid material that is sent to the thickener or filter press, reducing the size or number of units required. Ultimately, this can save on capital equipment costs as well as maintenance costs from component wear and tear.
In a process flow, the fines recovery unit follows the wet plant but precedes the thickener and filter press. The waste stream is processed in the fines recovery unit, which removes particles greater than 400 mesh. The minus 400 mesh and water leftover exits out the top of the Hydrocyclone and is sent to the downstream tailings equipment for further liquid-solid separation.
Creation of a saleable product
Fines recovery systems remove particles greater than 400 mesh from the waste stream and discharge it as a drip-free solids material. This material can potentially be sold as back fill or pond lining, adding an additional revenue stream from what would have once been disposed of as waste. In some cases, the material discharged from the Hawk can be mixed into a product stream without knocking the product out of spec.
However, if the material can't be sold or mixed in with a product for sale, it's possible it could be used for site reclamation to help restore the area back to its original state. Regardless, the solids material is much easier to handle and manage in this form than as part of a waste slurry from a pond.
Who can benefit from fines recovery?
Fines recovery equipment is beneficial for any aggregate application with a waste stream and a settling pond. It is a good consideration when planning for a new build, but it can also be added to any existing site, even those already operating thickeners and/or filter presses.
By installing a fines recovery system, aggregate producers can spend less time and money on settling pond maintenance, reduce the load on downstream processing equipment and potentially create a usable, if not saleable, product.
