Modern Mining July 2024

CRUSHING & SCREENING

Vibration in motion: resolving downtime in the screening process By Larry Horrie: Account Manager, Martin Engineering

After fresh water, sand is the most widely consumed natural resource on the planet. The annual world consumption of sand is estimated to be >15 billion tons, with a respective trade volume of 70 billion dollars.

Inland sand is extracted and placed in stockpiles for transport to the processing plant.

W hether extracted from a dry inland quarry or underwater resource, impurities and biological material must be removed, otherwise the sand can contaminate the end process. Removing impurities from the product further saturates it, causing it to enter the processing and drying system as a slurry. Although some end users don’t require dried sand, most do, so the water needs to be extracted. To remove water, the sand is passed through a screening process involving industrial vibrators. The volume and sustained operation of the process can put a lot of strain on the vibrators, so it is not uncommon for them to break down. This is accompanied by downtime and lost production, which makes lead time in being able to replace units and reliability of the vibrators extremely important. This article walks through the process of one of the largest sand mining operations in the Southern United States

and discusses the impact that quality vibration has on the operation. Clean sand makes strong concrete The first stop for mined and quarried sand is the sanitisation plant, where the sand is washed of impurities including clay, silt, salts and mica, as well as organic matter which can propagate the growth of bacteria. Along with improving the adhesive quality of the product, the removal of organic impurities and bacteria improves the curing of concrete or mortar, weakening the final product. For construction purposes, 75-85 percent clean sand is sufficient for cement. Having a larger surface area than sand, clay creates a filmy barrier around sand particles which prevents or reduces the adhesion of cement by increasing the amount of water needed, in turn lessening the strength of concrete or mortar. A high presence of mica can have structural implications due to the smooth surface of the particulate. Because

of the corrosive effect on reinforcement, the sand also needs to be tested periodically for coal residues. Bouncing particles The processing plant that services the sand mine has three dewatering racks with sloped screens covered with a specially made porous cloth that allows moisture, but none of the fines, to pass through. The racks sit on spring stabilisers to absorb the force output of the two high powered electric vibrators mounted on top that counter-rotate to create a linear force through the rack’s centre of gravity, with enough torque to bounce and move tons of wet material up and down. Several tons per hour of heavy wet granules are vibrated across the screens, so the water extraction process needs to be fast to meet production demands. It is then dropped on a conveyor to be transported either to the drying kiln or the outdoor storage area.

36  MODERN MINING  www.modernminingmagazine.co.za | JULY 2024