Synthesis and Characterisation of Chromium-Containing Amorphous Aluminosilicates

Synthesis of amorphous sodium aluminosilicates containing up to 4% of chromium are carried out with the aim of producing amorphous Cr(III)-containing aluminosilicates having slightly basic properties. The procedure involves direct reaction of solutions of sodium silicates, aluminate and chromate. By allowing additional reaction time after the rapid initial precipitation, maximum chromium concentrations of 4.0 wt.% were achieved. In contrast to chromium-containing aluminosilicates obtained by complete ion exchange, those obtained by this method exhibit basic properties when in aqueous suspension (p H = 10), and show different redox characteristics. The thermal conversion of Cr(III) to Cr(IV) in these alkaline forms contrasts with the thermal stability of the ion-exchange synthesised products. 20 ref.--M.J.W.