Getting Out of the Sand Trap

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GS Materials

By Mark S. Kuhar

In 2013, GS Materials investigated the possibility of a new wash plant that would solve the problems that the company was experiencing with their existing processing system. The plant was more than 40 years old and was not processing clay lumps in the material nor was it recovering fine sand from the waste material. The company came to the conclusion that the wash plant was no longer efficient and they needed to find a new solution.

The efficiency requirements for a new system were threefold. First, GS Materials required a water treatment plant. This was the main requirement as recycling water would result in a significant cost saving for the company. Second, they wanted to recover the fine sand that they were losing, Third, the washed aggregate products should not have any clay lumps but should be washed, sized and saleable.

The product requirements were to produce 200 tph of concrete sand, top size less than 3/8 in. and less than 3 percent below 200 mesh, to produce a USPGA golf sand, a mason sand and 40 tph of aggregate divided into three different sizes.

“As well as production and efficiency requirements we specified that we didn’t want a turnkey system that would take weeks and weeks to design. We wanted an off-the-shelf modular package that was ready to work. CDE could provide this,” explained GS Materials Quarry Manager Troy Russell.

CDE was awarded the contract and the plant was commissioned in December 2013. CDE recognized that GS Materials wanted to see material on the ground in the shortest possible timescale and therefore used the CDE product range as modular components – or individual building blocks – ensuring minimum set up time as well as reducing costs by eliminating the requirement to build supporting structures. These “building blocks” are all from the CDE core product range; the M4500 wash plant, an AggMax 83 integrated scrubbing system, an EvoWash sand plant with an integrated CFCU, and an AquaCycle 600 thickener with a CDE AquaStore for water storage and recirculation around the plant.

The Process
The CDE M4500 modular wash plant processes 270 tph of natural sand and gravel from the Jackson Springs quarry. This raw feed contains high silt content with over 10 percent under 200 mesh.

The integrated L35 hopper on the M4500 modular wash plant is fed via a wheeled loader and has a capacity of 34 tons. The spacings on the hydraulic tipping grid have been specifically selected to ensure that any +5-in. aggregate is immediately rejected by the hopper and does not enter the plant. From the hopper, material progresses up the feed conveyor that is fitted with a belt weigher to monitor the flow of material through the plant and relay real-time capacity information to the plant operator.

The feed conveyor transports the material into the integrated ProGrade P2-75 rinsing screen. The ProGrade has two decks with each screen measuring 5- x 16-ft. The +2-in. material, which amounts to less than 1 tph, is removed on the top deck and stockpiled via the first conveyor on the M4500.

This stone, the first product from the plant, is washed and ready for GS Materials to sell for landscaping projects. Meanwhile, material smaller than 2-in. passes through the top deck of the ProGrade and the 3/8–2-in. product is removed on the bottom deck. This product is transferred via a 30-ft. conveyor to the next stage of processing, the AggMax 83.

Agg Max 83AggMax 83
Material enters the AggMax 83 and is deposited into the back of the RotoMax logwasher where it encounters two counter-rotating spiral shafts which are designed to scrub heavily claybound material. The high chrome cast iron paddles in the RotoMax logwasher force the claybound material to travel along the logwasher while intensely scrubbing it.

During this process the clay and lightweight contaminants are floated off at the back of the RotoMax onto a trash screen that recovers good quality sand from the aggregate fraction while stockpiling the waste material.

The trash screen introduces an additional step to the sand-recovery process, recovering sand that would have previously went to waste. The liberated fine material enters the sump and from here is pumped back to the M4500 ProGrade sump for further processing.

The scrubbed aggregate material travels up the inclined RotoMax logwasher until it reaches the tip and is then discharged from the RotoMax onto a three-deck sizing screen. The first deck removes the 1- to 2-in. aggregate, 1/2- to 7/8-in. is removed on the second deck and the 1/4- to 1/2-in. product is removed on the third deck. These are stockpiled by three 50-ft. mobile conveyors and produce three sized and washed aggregate products for use by GS Materials, as per the company’s initial requirements.

Meanwhile, the fine material from the RotoMax sump joins the material, which earlier passed through the second deck of the ProGrade screen (0 to 3/8-in.), and is pumped to the dual hydrocyclones on the EvoWash sand plant that is integrated on the M4500. The +200 mesh to 1/4in. material is discharged from the bottom of the cyclones onto the EvoWash dewatering screen.

The dewatering screen consists of some large 16-mesh apertures allowing some of the +200 mesh to 1/4-in. to fall into the sump below. However, the majority of the material travels down the screen deck and produces 200 tph of 200 mesh to 1/4-in. concrete sand, which is stockpiled via a 80-ft. radial conveyor and is the fifth product produced from the plant. Meanwhile, the -200 mesh fraction overflows the hydrocyclones and is transferred along with the waste water to the next stage of processing.

EvoWash Sand Plant
The material which passed through the dewatering screen on the M4500 enters the sump and is pumped to the CFCU 70 integrated on the EvoWash B40 sand plant. The Counter Flow Classification Unit is used in the production of the golf sand. It uses upward flow classification to separate particles by density and eliminates the oversize sand particles from the final golf sand product.

The fine material removed in the CFCU through the hydrocyclones is sent to the AquaCycle A600 thickener, along with the overflow from the EvoWash hydrocyclones. The material that is discharged from the bottom of the CFCU is the GS Materials golf sand. It is a 200 to 75 mesh product and is discharged onto one-half of an EvoScreen and then via the sixth conveyor on the plant to produce a golf sand stockpile.

“When we first detailed our requirements for this new wash plant our main aim was to produce high quality concrete sand and capture the fines sand we were losing,” said Russell. “When CDE suggested that we had the capability to also make golf sand we grasped that opportunity. The result is a first class USPGA golf sand which we are now supplying to Pinehurst Golf Resort, one of the preeminent golf resorts in the United States and the site of the 2014 U.S. Open that was held in June 2014.”

He also highlighted the advantages of CDE ProMan which dedicates a project manager to every customer to ensure that the project is delivered on time, to budget and to specification. “Colum Bryson managed our project on our behalf and supplied all required information, including detailed information on golf sand production, ensuring we were aware of all requirements throughout the build, transport, install and commissioning of our wash plant,” Russell said.

CDE has ensured that GS Materials has the option of making a 200 to 75-mesh golf sand or blending their golf sand back into the plant to make a masonry sand. This is the current process as the material from the sump of the CFCU still contains valuable product and therefore is reprocessed through an extra cyclone and the discharge is dewatered onto the second half of the EvoScreen and then to a masonry sand stockpile.

“Masonry sand requires a mix of sizes with a smooth bottom end for building and plastering purposes so we are successfully blending our golf sand and mason sand to produce a final masonry sand,” Russell said.

AquaCycle A600
The final stage of the process is the AquaCycle water treatment system, which receives all the excess fines from the EvoWash and CFCU cyclones. The AquaCycle is a fit-for-purpose steel tank with a feed rate of 2,640 gal./min.

A polyelectrolyte dosing station acts as a delivery system of polyelectrolyte to facilitate the settlement of sludge. “Sludge settles at the bottom of the tank where a set of rakes ensure that the sludge is maintained at an even consistency before it is discharged to ponds,” said Joel Prince, general manager for CDE in North America. “The AquaCycle water treatment system reduces the volume of fresh water required to feed the plant by up to 90 percent while the AquaStore recycles the recovered water around the wash plant.” 

Information for this article courtesy of CDE.

GS Materials Makes it Happen
GS Materials is a family owned sand company that has been in operation since 1984. It is located in Burlington, N.C., with nearby sand quarries in Lemon Springs and Jackson Springs.

GS Materials serves almost the entire state of North Carolina including its capital, Raleigh, and its largest city, Charlotte. Sand and aggregates are also transported to the neighbouring states of South Carolina and Virginia.

The primary product produced by GS Materials is North Carolina Department of Transportation approved concrete sand but the company also supplies a wide range of other sands and aggregates.

Founder and Chairman Tony Convery commented on the first modular wash plant for CDE in the United States. “Our product range has been designed around core themes including rapid deployment, reduced plant footprint and increased production efficiencies all done in partnership with a commitment to ensuring quick, easy and safe maintenance access for all operational personnel,” he said. “We pre-wire and pre-build every unit before it leaves our factory to ensure that once we get to site we can have the plant up and running in the shortest possible time.”

The performance of the CDE wash solution has been extremely positive for GS Materials, as noted by owner, Ronnie Kirkpatrick, “We approached CDE with a number of key requirements in terms of efficiency, performance and modularity,” he said. “It was crucial to us that we would have a water treatment facility and that we could recover the fine sand we were losing with our previous system. The result is in-specification products that are ready for sale and reduced costs in terms of the amount of water required to operate the plant, and significant savings in the management of the sludge lagoons.”

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