Activation of gypsum anhydrite-slag mixtures

The potential for using slags activated with near neutral salts as immobilisation matrices for nuclear wastes containing reactive metals

“…In their studies they found that C-S-H and ettringite were the main hydration products formed and that monosulfate was absent at all ages. The presence of these hydration products is corroborated by other researchers [47,[52][53][54], although other hydrates such as C 4 AH 13 have been reported [54], as has the formation of gypsum from systems activated using anhydrite [55]. Matschei et al [51] described the mechanism of SSC hydration where alkali ions entered solution directly after mixing, causing an increase in pH.…”

“…Nonetheless, it has been indicated [50,64] that by using anhydrite or hemihydrate (CaSO 4 Á0.5H 2 O) directly without additional additives, a hardened activated slag system with reasonable strength could still be produced, with anhydrite usually producing a better system. This is probably partly due to the formation of additional gypsum from anhydrite [55]. However, by using hemihydrate rather than anhydrite , a saving in thermal energy during processing was achieved [54].…”

Mineral Sequestration of Carbon Dioxide in Circulating Fluidized Bed Combustion Boiler Bottom Ash

“…Ca 2 Al(AlSiO 7 ) + CaSiO 3 + 2CO 2 → 2CaCO 3 + CaAl 2 Si 2 O 8 (5) Similarly, the peaks corresponding to lime and gehlenite in C2 disappeared after wet carbonation, whereby a strong calcite peak was observed, indicating that lime and gehlenite were consumed to produce calcite via the wet carbonation reaction, as expressed in Equations (3) and (4) (Figure 3b). In addition, anhydrite (CaSO 4 ) in C2 was hydrated and formed gypsum (CaSO 4 ·2H 2 O) after wet carbonation, as shown in Equations (6) and (7) [39]. Meanwhile, no significant changes were observed in P1, even after dry and wet carbonation, indicating that the carbonation reaction barely occurred in this sample.…”

Hemihydrate or waste anhydrite in composite binders with blast-furnace slag: Hydration products, microstructures and dimensional stability

“…The commercial gypsum pastes were added with 10% of Portland cement, as chemical activator, referred to the weight of the GGBFS + pozzolans, and 0.2% of malic acid as setting retarder as reported elsewhere [16]. The fluorgypsum pastes were added with 1-3% of Ca(OH) 2 and aluminum and potassium sulphates as chemical activators for anhydrite and GGBFS + pozzolans based on laboratory experience from the authors and as reported elsewhere [3,17]. The water/binder ratios were established for good workability at 0.43 for commercial gypsum and 0.3 for fluorgypsum binders.…”