Silica Continue ...
Industrial Sand Applications : continues....
Oil and Gas Recovery: Known commonly as proppant, or “frac sand,” industrial sand is pumped down holes in deep well applications to prop open rock fissures and increase the flow rate of natural gas or oil. In this specialized application round, whole grain deposits are used to maximize permeability and prevent formation cuttings from entering the well bore. Silica’s hardness and its overall structural integrity combine to deliver the required crush resistance of the high pressures present in wells up to 2,450 meters deep. Its chemical purity is required to resist chemical attack in corrosive environments.
Recreational: Industrial sand even finds its way into sports and recreation. Silica sand is used for golf course bunkers and greens as well as the construction of natural or synthetic athletic fields. In golf and sports turf applications silica sand is the structural component of an inert, uncontaminated, growing media. Silica sand is also used to repair greens and to facilitate everyday maintenance like root aeration and fertilization. The natural grain shape and controlled particle size distribution of silica provides the required permeability and compaction properties for drainage, healthy plant growth and stability.
Scope for substituting different grades of silica glass
Sand suitable for one use can normally be used for any other application with a higher permitted level of iron. Thus, flint glass sand can be used to make float glass or colouredcontainer glass (since iron can be added to the batch if needed to produce the required colour). As sands with lower levels of iron usually command a premium price, this may not be economically viable unless there are compensating savings, say, in the form of lower transport costs than an alternative quarry.
On the other hand, if a glassmaker wished to use sand with a higher level of iron for a lower-iron-level application, the quarry would have to introduce additional processing. This might, for example, take the form of acid leaching to remove deposits of iron from the surface of the grains of sand. The extent of the capital investment and operating costs needed to do this would determine whether it was an economic proposition. In some locations, it might not be possible for the quarry operator to secure planning permission for the additional plant. Where the iron content occurs as inclusions within the grains, it is often
difficult for a quarry operator to reduce the iron specification significantly. Consequently, much sand suitable for coloured-glass containers is not capable of being processed to meet the requirements for float glass or flint glass. It is sometimes possible to produce a number of different grades of silica sand from a single quarry by selective quarrying of different parts of the deposit.
Cleaning the quartz grains and increasing silica content is achieved by washing to remove clay minerals and scrubbing by
attrition between particles. Production of the optimum size distribution is achieved by screening to remove unwanted coarse
particles and classification in an upward current of water to remove unwanted fine material. Quartz grains are often iron
stained and the staining may be removed or reduced by chemical reaction involving sulphuric acid at different temperatures.
Impurities present as separate mineral particles may be removed by various processes including gravity separation, froth flotation and magnetic separation. For the highest purity, for electronics applications, extra cleaning with aggressive acids such as hydrofluoric acid combined with thermal shock may be necessary. After processing, the sand may be dried and some applications require it to be ground in ball mills to produce a very fine material, called silica flour. Also, quartz may be converted to cristobalite in a rotary kiln at high temperature, with the assistance of a catalyst. Some specialist applications require the quartz to be melted in electric arc furnaces followed by cooling and grinding to produce fused silica.
