Preparation of silica powder with high whiteness from palygorskite

Silica powder with high whiteness was prepared from calcined and acid-activated palygorskite. The effect of calcination temperature, mass ratio of ammonium sulfate to palygorskite, acid concentration and leaching time on the chemical composition, the whiteness and the specific surface area (SBET) of the products were investigated. The suitable conditions for preparing silica powder with high whiteness from palygorskite were as follows: calcination temperature at 560 °C, mass ratio of ammonium sulfate to palygorskite of 3:1, H2SO4 concentration of 0.5 M and leaching time of 2 h. Under the proper conditions, the silica content, the whiteness and the specific surface area of the product were 85%, 92% and 308 m2/g, respectively. The solid products consisted mainly of amorphous silica with a small amount of quartz. The silica particles maintained the fibrous morphology of palygorskite and a few particles with 10–20 nm in diameter were observed. The length of the fibrous particles decreased from micrometer dimension to about 100–200 nm as the intensity of the modification reactions was increased. The silica products are promising materials as adsorbents, catalyst supports and fillers of plastics.