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Processing of the sand after excavation began as a basic procedure to remove grit and unwanted material but, when the uses for sand expanded, processing became more complex. In the early days of quarrying processing was as basic as a casual throw of the sand through an angled sieve placed over the wagon that the dobber was loading.

Unwanted material fell to the ground and the sand dropped through into the wagon.
When demand for sand increased in the early 20th century processing began to be mechanized. An early machine, known as a ‘shaker’, consisted of a vibrating mesh screen with 1/2 inch holes, ideal for screening coarse building sand.

Some customers began to want a more pure, more finely graded sand, so processing methods began to be refined. Also, higher prices could be asked for sand that was processed and so processing plants were established in or adjacent to the quarries.

1986 Double Arches, aerial view of new drying plant. By kind permission WBB Minerals

Washing
During WW1 the foundries making armaments needed large amounts of sand free from impurities to make their castings, so the sand began to be routinely washed. In a machine known as a ‘Niagara’ the sand was washed by a stream of water on to a vibrating 1/2 inch mesh screen which removed la rger particles like gravel The finer sand particles fell through the mesh on to a 1/8 inch mesh screen made of piano wire, to further refine it. The refined sand was washed into a tank where it was stirred and the silt pumped away. A bucket conveyor then lifted the sand from the washing tank to a chute which fed the waiting wagons. The buckets were perforated to allow excess water to drain away; the wagons also had holes in the bottom for further drainage.

The ‘Niagara’ was later replaced by barrel washers which worked on much the same principle but the sand was fed by conveyor into slowly revolving drums containing sieves of varying mesh size. Water for washing came from deep pools at the washing plant.

Modern quarries use attrition scrubbers which remove silt and gravel from the sand particles using the abrasive power of water and hydro-cyclone systems, which in turn use pressurized water jets to float the fine grains of sand away from the coarse grains. Solid particles that are separated from the finer sand particles are allowed to settle in silt lagoons. Mindful of recycling and energy efficiency, the silt can be reused in quarry restoration and some of the water can be reused for washing.

Grovebury Quarry Sandpit Machinery Sand dewatering Tower circa 1990
by kind permission of Garside Sands

Drying
In the early days of the quarries, sand was transported to the customer in its wet form, but there began to be a demand for a dry product that could be used immediately. At the processing plants, drying sheds housed large coal-fired ovens for this purpose. In a modern processing plant a system of conveyors feed the wet sand into gas and oil fired dryers, each costing £750,000.

After it is dried, the sand is graded to produce the grain size needed for a particular purpose. Vibrating rotex screens made from metal or plastic are used to screen the sand; these can be changed to produce the different grain sizes. In a modern processing plant many different grain sizes can be selected. The graded sand is then conveyed to storage silos or on to a bagging shed. The whole operation is controlled from a central diagnostic desk, controlling flow and storage.

The sand is tested several times at various stages of the process to ensure that it conforms to the specifications of that particular grade of sand.

Once washed, dried, graded and tested the sand is bagged ready for transportation. In the old days hessian sacks were filled by hand in a bagging shed and teams of women employed to mend them. Old coffee sacks were often used and one worker remembers a woman being employed to turn the sacks inside out so that the sand would not be contaminated with coffee. Today’s bagging operation is very different: robotic bagging systems reduce all the manual labour to the touch of a button. The correct weight of sand is deposited into each polythene sack, which is sealed and sprayed with a batch number, date and grade and moved by forklift truck to the waiting lorries.

2009. Garside Sands. grading machine. By kind permission Susannah Oliver

Specialist Processing
In the modern sand industry customers often require a product that needs special processing. This may take place on-site or be done by specialist companies. Organic pigments may be added, for example, to colour the sand for use in sports pitches and arenas. A specific terracotta colour often used in sporting arenas is achieved by burning the sand. In other uses, for example in the manufacture of colourless glass, complex processes may be needed to remove certain stubborn particles. These can involve hot sulphuric acid leaching to remove iron and iron oxides. Soil may be added to the sand for use in horticulture, something which is done on-site at Garside’s Grovebury quarry.

 
 
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