United Rock Products Recovers Over 90% Water For Reuse with McLanahan Thickener

Based in Irwindale, Calif., United Rock Products is a Colas company with over 100 years of experience in manufacturing aggregate products for construction, ready-mix and asphalt applications.

United Rock mines from an alluvial fan deposit that has been operating since the early 1900s. The site mines material from multiple pits and produces various products, including concrete sand, pea gravel, plaster sand, asphalt and fill materials, as well as recycled concrete and miscellaneous base products.

Challenge

One of United Rock’s main goals is to recycle process water for reuse throughout the plant. The site initially used a clarifier that was outdated and needed a replacement.

“It was pretty rudimentary, pretty basic on the technology” said Brett Rankin, Project Engineer at United Rock.

The original clarifier used couldn’t meet expectations for water recovery, which is a crucial part of cost savings to the site. Water is an expensive but necessary resource for aggregate processing, so it’s important to save money where possible.

The previous clarifier also required frequent cleaning, as excess mud would enter the water tank.

“With the old system, we would get mud into the tank,” Rankin explained. “We cleaned it out every three months.”

United Rock is reclaiming the pits as they are mined, so it’s important for the site to achieve maximum solids retention for site reclamation. United Rock decided to work with Aggregate Crusher Specialists (ACS), a McLanahan dealer, to find a solution for its needs.

Solution

McLanahan supplied United Rock with a High-Rate Thickener to increase water recovery and solids retention.

Using chemical reagents, High-Rate Thickeners separate liquids and solids through hindered settling. Slurry enters the feed well and is mixed with chemicals or flocculant. As the solution is mixed, larger particles settle to the bottom of the tank and are moved toward the center to be discharged.

Clean water overflows weirs around the perimeter of the tank and fills a process water tank. The overflow, or process water, is ready for reuse while the underflow, the thickened slurry, can be further processed or used for site reclamation.

The McLanahan High-Rate Thickener has more advanced technology than the United Rock’s previous equipment, allowing for easier operation and better results.

“The driving force for us was to use that technology to recycle more water,” explained Rankin. “Water is really expensive in this area and so if we can recover 10% more, it’s a big savings.”

United Rock recirculates the process water through the wash plant and has plans to eventually use it to cool crushers.

“We’re pumping the water back to the wash plant, and we’re using it throughout the wash plant – on the spray bars, the dewatering screens, the sand screws,” Rankin said. “Right now, we’re using fresh water to cool our crushers, and we’re looking at different systems that can utilize our recycled water for that as well.”

As for the solids reclaimed, they are being used to fill and reclaim the pit.

Results

Rankin explained that this project has numerous benefits.

“It’s kind of a double green project, as Colas would call it. It’s an environmental stewardship and corporate social responsibility, so we’re taking care of the environment, recycling water that’s a scarce resource in this area,” he said. “The second part of the green is that it’s saving us money.”

The McLanahan High-Rate Thickener has provided United Rock with an increase in both water recovery and solids retention, recovering about 93% water and 30 to 32% solids. 
“The biggest impact of the McLanahan High-Rate Thickener is the results of the water and how much we’ve been recycling,” Rankin explained. “Our water, I’ve noticed, is a lot cleaner than that previous water.”

With an increase in water recovery, United Rock has saved money on water and lowered maintenance costs. The High-Rate Thickener has also required little maintenance and is almost self-sufficient.

“The performance is doing quite well,” said Rankin. “It’s pretty hands off at this point, so it’s basically running itself. The operator only has to check on it every couple hours to make sure there’s no upset conditions and everything’s running smooth.”

Before the McLanahan High-Rate Thickener, United Rock cleaned the clarifier’s water tank every three months to remove mud and sludge. Since installing the new High-Rate Thickener over a year ago, the site has yet to clean out the process water tank, reducing costs for labor and maintenance.

“That’s kind of a direct impact,” said Rankin. “We don’t have the cost of a clam shell coming in every three months on a consistent basis.”

The advanced technology of the High-Rate Thickener allows for easy adjustments to meet the desired outcome.

“It’s pretty easy to make a change and see the results go up and down,” explained Rankin. “We would change the torque and increase the percentage on the rigs until we got the percent solids density that we were looking for.”

Working with both McLanahan and ACS, United Rock received support throughout the development of the project.

“ACS as a whole has been a crucial part of the implementation and support of this project,” Rankin said.

McLanahan’s process engineers and electrical design specialists worked with the team at United Rock to help optimize the operation with the McLanahan High-Rate Thickener, as well as provide maintenance support when needed.