Abstract: A method and filter bed for removing impurities from liquids wherein the filter bed comprises a mixture of treated filter aid material and an active particulate material having opposite surface charges in aqueous suspension. The filter aid material has been treated to produce the desired surface charge. The identity of the active particulate material depends on the application. Examples are organic polymeric absorbents, zeolites, bentonite, zirconium oxide, zirconium phosphate, activated alumina, ferrous sulfide, activated carbon and diatomaceous earth.

Abstract: A method for preparing an improved filter material, together with the improved material prepared thereby and an improved method for removing impurities from a liquid. The filter material comprises a mixture of ion exchange resin particles and treated filter aid material. In the preferred embodiment, the ion exchange resin particles comprise a mixture of anion and cation exchange resin particles, and the filter aid material is treated with a chemical compound to produce a positive surface charge thereon. The filter aid material may be further treated with a second compound to produce an enhanced negative surface charge.

Abstract: Impurities are removed from a liquid by passing the liquid through an improved filter bed. The filter bed comprises a mixture of oppositely charged particles of filter aid material, the particles normally having a surface charge in aqueous solution. A portion of these particles are treated with a chemical compound to produce a surface charge that is opposite from the normal surface charge. These oppositely charged particles clump in aqueous suspension, and produce a filter bed which is capable of removing suspended particles with very high efficiency, while maintaining a relatively low pressure drop across the filter bed.