Editor’s note: The following is a selected portion from the upcoming 2025 Edition of the Pit & Quarry University Handbook. The full handbook is slated for release this November, at which time additional content will also be published online. Be sure to check back for more content as it’s made available!
Maintaining clean wash water is essential to those operating with a wet process.
Whether adding a first wash plant or tweaking an existing one, operators should follow a series of best practices to avoid common pitfalls in wet processing.
“It’s a whole new world out there in wet processing,” says Lauren DeBow, washing applications engineer at Superior Industries. “Most ‘easily mined’ reserves are long gone, and we’re short on aggregate folks who’ve washed rocks all their lives.”
DeBow and her team assist producers with thorough applications analysis and customized wash plant solutions.
“Washing is a unique process for each and every operation,” she says.
According to DeBow, producers who reuse dirty water in their wash system are essentially putting all the dirt, debris, clay and fines right back onto the product they’re trying to clean. At the same time, this causes wear, tear, clogging and buildup on equipment, water pipes and spray bars.
As DeBow describes, there are three common methods of recycling and reusing wash water: traditional settling ponds, ultra-fines recovery systems (UFRs) and clarification systems.
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Settling ponds
While pumping dirty water to a settling pond is a simple concept, particles settle out naturally with time and gravity, allowing fresh water to float to the next level of the pond to be reused. The disadvantages, however, are space requirements and permitting restrictions that make it harder to establish these ponds.
There are also evaporation issues and maintenance costs involved, according to DeBow. The costs can be hefty when having to dig out sediments to ensure the needed depth for required settling.
On the plus side, settling ponds can work well for operations that have a larger footprint and can successfully use flocculants to achieve greater settling efficiencies.
UFRs
A UFR system, meanwhile, offers the advantage of removing a good portion of material down to a #400 mesh, keeping more fines out of the pond. This results in less digging during pond maintenance.
Additionally, a UFR provides a stackable material that can become a saleable product, resulting in minimized waste. Also, the water remains much cleaner and requires less processing before reusing it.
One of the downfalls of UFRs is an occasional situation where wastewater travels too far downstream in the pond, requiring additional flocculants to separate particles. In this event, enough larger particles are not present to stimulate the settling process.
The latter results in a “double dipping” during the process. Still, if a UFR can minimize the need to dig out the pond, a savings in operating costs can be achieved.
Clarification systems
Growing in use, clarification systems start with something as simple as a thickener or the use of a clarification tank.
No matter the option, clarification systems have space and flocculant requirements. Clarification systems are becoming more popular, though, as they’re less likely to incur permitting issues. They also allow operations to eliminate settling ponds.
Clarification systems discharge a sludge waste product that’s typically pumped to a designated area, where it must sit and dry. Sometimes, this waste product requires the use of filter or belt presses that pull out extra moisture, creating a solid, stackable cake that’s potentially used as a fill product.
The biggest drawback of a clarification system is the capital investment required. But, depending on the cycle time of the complete clarification system (which can create a bottleneck), it delivers extremely clean water back into the wash circuit.
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Finding the right solution
Efficiency improves when optimizing all the equipment in the wash plant.
For example, if sand screws are not running properly, an operation may be washing valuable product and sending it to the pond. Conduct a thorough plant audit to evaluate the performance of each piece of equipment in the plant.
Again, each wet processing operation is different, and the right solutions depend on parameters such as material type, moisture content, specification requirements, size of footprint, permitting restrictions, financial limitations, water rates, water availability and more. Proper analysis by an experienced applications engineer is advised.
More from the P&Q University Handbook: Safety | P&Q University Handbook
Carol Wasson is a veteran freelance writer for the aggregate and construction equipment industries.
