Ceramisation of hazardous elements: benefits and pitfalls of the inertisation through silicate ceramics

The addition of wastes to silicate ceramics can considerably expand the compositional spectrum of raw materials with a possible inclusion of hazardous components. The present work quantitatively examines relevant literature to determine whether the benefits of incorporating hazardous elements (HEs) into silicate ceramics outweigh the pitfalls. The mobility of various HEs (Ba, Zn, Cu, Cr, Mo, As, Pb, Ni, and Cd) has been parameterised by three descriptors (immobilisation efficiency, mobilised fraction, and hazard quotient) using leaching data. HEs can be incorporated into both crystalline and glassy phases, depending on the ceramic body type. Moreover, silicate ceramics exhibit a remarkably high immobilisation efficiency (often exceeding 99.9%), as accomplished for Ba, Cd, Ni, and Zn elements. The pitfalls of the inertization process include an insufficient stabilisation of incorporated HEs, as indicated by the high hazard quotients (beyond the permissible limits established for inert materials) obtained in some cases for Mo, As, Cr, Pb, and Cu elements. Such behaviour is related to oxy-anionic complexes (Mo, As, Cr) that can form their own phases or are not linked to the tetrahedral framework of aluminosilicate glass. Pb and Cu elements are preferentially partitioned to glass with a low coordination number, while As and especially Mo are not always stabilised in silicate ceramics. These drawbacks necessitate conducting additional studies to develop appropriate inertisation strategies for these elements.