Processing

The extent of processing required will depend on the nature of the deposit and the end uses for which the mineral is used. The provision of the necessary processing plant requires high capital expenditure.

Processing can involve improving both the physical and chemical properties of the raw material to meet specific market demands. Normally several grades of silica sand will be produced at one quarry.

Processing will normally involve washing to remove impurities such as clay and size classification to remove coarse and fine fractions and to produce a sand of the required particle size distribution. Most processing will also involve attrition scrubbing to remove the more stubborn impurities which can be ‘stuck’ to the sand grains.

High grade uses such as colourless glass and many industrial uses may involve increasingly complex and expensive processing techniques to remove impurities. These processes can involve hot sulphuric acid leaching to remove iron and iron oxides and froth flotation and gravity separation techniques to remove heavy iron and chromite particles.

Quartz is converted to cristobalite by calcination which is a higher temperature form of silica used in the ceramics. Silica can also be milled to produce silica flour used as an industry filler in paints, adhesives etc.

The processed sand is often dried and transported to the customer by tanker or is bagged for sale.

Silica sand used for horticultural and sports uses may be blended with soil to produce a growing medium. Recently a member has developed a product for the sports surfaces which involves blending with polypropylene fibres with the growing medium to provide a high wearing sports field surface.