FORMATION OF A POROUS SILICA-RICH MATRIX FROM CHRYSOTILE-ASBESTOS WASTE FOR POTENTIAL APPLICATION IN SILICON REMOVAL FROM PROCESS SOLUTIONS

Abstract

Silicon-containing species in uranium-bearing process solutions can accumulate on ion-exchange materials, impairing mass transfer and sorption efficiency. Inexpensive porous inorganic materials for preliminary silicon removal are therefore of practical interest. This study aimed to evaluate how thermal, chemical and mechanical post-treatment affects the porous structure of a silica-rich product obtained by hydrochloric acid leaching of chrysotile-asbestos waste, in order to select a promising matrix for sorption studies. Raw material underwent magnetic separation followed by HCl leaching. Five products were examined: material calcined at 650 °C; material calcined at 850 °C (1 h) and modified with 5% NiSO₄ and 10% MoO₄; material calcined at 650 °C for 52 h; leached product before attrition; and the same product after attrition. Textural properties were assessed via low-temperature N₂ adsorption using BET, Langmuir, t-plot and BJH methods. The BET specific surface area of the samples varied from 56.55 to 169.02 m²/g. The most favorable textural characteristics were observed for the leaching product without additional grinding: the specific surface area was 169.02 m²/g, the micropore area was 44.72 m²/g, the t-plot micropore volume was 0.0180 cm³/g, and the average pore diameter was 3.89 nm. After attrition, surface area remained high (165.99 m²/g) while total pore volume increased to 0.1951 cm³/g. Calcination at 650 °C and prolonged 52-h calcination reduced surface area to 106.61 and 91.41 m²/g, respectively; combined 850 °C treatment with Ni–Mo modification gave the lowest value (56.55 m²/g). HCl leaching was the key step forming the porous silica matrix. The unattrited leached product was selected as the most promising matrix for silicon removal from uranium solutions.