VOLUME 19 (Supplement)

Immobilization of arsenate and fluoride from alkaline industrial wastes via induced hydrotalcite and brucite formation: Implications for the solidification of radioactive waste

Coal fly ash and granulated blast furnace slag (GBFS) can potentially be utilized as highly effective binders for the solidification and stabilization of radioactive waste. This study investigated a novel immobilization strategy by inducing the formation of magnesium-bearing minerals, specifically hydrotalcite and brucite, through the addition of magnesium oxide (MgO) and magnesium nitrate [Mg (NO₃)₂]. Mineralogical transformations were monitored over two weeks with varying Mg-source ratios (10%–30%). Results showed that MgO addition successfully induced stable hydrotalcite and brucite phases, significantly enhancing fluoride removal in GBFS from 53% to over 97%. In contrast, Mg nitrate led to pH reduction and the formation of less stable hydrocalumite. Selective dissolution and leaching tests confirmed that anions co-precipitated with hydrotalcite remained sequestered at pH as low as 5.6, whereas calcium-bearing minerals dissolved at pH 9, releasing sorbed anions. These findings demonstrate that controlling pore-water chemistry through slightly soluble MgO provides a possible long-term sequestration mechanism for arsenate and fluoride as analogues of highly mobile radioactive oxyanions, highlighting the potential of industrial by-product-based binders for radioactive waste solidification applications.