Silica sand is a natural siliceous mineral, which is often used as filter material in water treatment, chemical industry and other fields.

Silica sand particles have a hard structure and relatively narrow size distribution. Which can remove larger impurity particles and suspended solids in water, and can adsorb some dissolved substances, such as heavy metal ions.

Washed sand is a kind of filter material processed by artificial or mechanical processing of natural river sand or quartz sand. 

The particles of washed sand are slightly larger than silica sand. And the distribution is relatively wide. However, after washing and screening, the surface is smooth, which can ensure that no fine particles or impurities will be produced during the water treatment process. Therefore, it is also widely used in some fields, such as steel, construction and other industries.

To sum up, although both silica sand and washed sand can be used as filter materials, because of their slightly different particle characteristics and uses, it is necessary to select the appropriate filter material according to the specific application.