Silica sand is used in various applications and each use requires specific characteristics. In this article, we will provide a detailed explanation of the specifications required for silica sand used in water filtration.
Where Did the Idea of Silica sandFiltration Come From?
The idea of sand filtration dates back to ancient times, specifically ancient Egyptian civilization. Archaeological evidence in Alexandria shows that ancient Egyptians used sand filters to purify water.
Thousands of years later, scientist John Gibb designed an experimental silica sand filter model. Between 1829 and 1855, this idea was developed significantly, especially as cholera outbreaks pushed governments to regulate water quality. This led to the introduction of the Metropolitan Water Act, the first law to regulate clean water.
Countries like England and Scotland initially relied on slow sand filters. However, because they required large spaces, scientists, including engineer Patrick Clark, worked on developing more efficient versions. Clark successfully increased filtration rates and reduced the space needed, leading to the invention of rapid sand filters.
Since then, sand filtration systems have evolved in design, filtration rate and water flow direction—making them more efficient and versatile.
What Are the Specifications of Filter Sand?
Extensive research has been conducted to determine the ideal filtration media. Scientists tested several materials in lab experiments, including:
- Silica sand
- Anthracite coal
- Crushed granite
- Ilmenite (Iron titanium oxide)
Among these, silica sand is the most widely used in Egypt due to its durability, affordability and wide availability.
The key specifications of silica sand used in filters include:
- High strength and hardness
- Controlled particle size distribution
- SiO₂ content between 90–99%
- Specific gravity between 2.0 – 4.0
- Ideal grain size: 1.2 mm
- Acid solubility (20% HCl for 24 hrs) should not exceed 2%
- Abrasion loss: Less than 2% by weight
- Ferric oxide (Fe₂O₃): 0.011%
- Chromium oxide (Cr₂O₃): < 0.0001%
- Titanium dioxide (TiO₂): < 0.001%
- Aluminum oxide (Al₂O₃): 0.1%
- Calcium oxide (CaO): 0.05%
- Magnesium oxide (MgO): 0.03%
- Loss on ignition (LOI): 0.117%
Are There Different Sizes of Silica Sand?
Yes. After mining, silica sand is processed and sorted based on:
- Grain size
- Silica content
- Level of impurities
Grain sizes are sorted using a set of sieves arranged from coarse to fine. Each sieve captures a specific size, allowing accurate classification.
In filter sand, the effective size is defined as the sieve opening through which 10% of the total sand weight passes or the size that retains 90% of the weight.
Types of Sand Filters
There are several types of sand filtration systems, including:
- Pressure filters
- Slow sand filters
- Rapid sand filters
Purpose of Filters
Sand filters are widely used due to their high efficiency in water purification. Silica sand is a key component in:
- Filtering groundwater and rainwater
- Treating wastewater
- Purifying drinking water
The main function of the filter is to capture suspended impurities and particles as water passes through the sand media.
Conclusion
Filter sand must be made from pure quartz or silica, with high mechanical strength and precise particle sizes. It should be free from clay, carbon and other contaminants. The combination of physical strength, chemical purity and proper sizing makes silica sand the ideal filtration medium in a wide range of water treatment applications.
