Stabilization of ZnCl2-containing wastes using calcium sulfoaluminate cement: Leaching behaviour of the solidified waste form, mechanisms of zinc retention
Résumé
To assess the potential of calcium sulfoaluminate cement to solidify and stabilize wastes containing high amounts of soluble zinc chloride (a strong inhibitor of Portland cement hydration), a simulated cemented waste form was submitted to leaching by pure water at a fixed pH of 7 for three months, according to a test designed to understand the degradation processes of cement pastes. Leaching was controlled by diffusion. The zinc concentration in the leachates always remained below the detection limit (2μmol/L), showing the excellent confining properties of the cement matrix. At the end of the experiment, the solid sample exhibited three zones which were accurately characterized: (i) a highly porous and friable surface layer, (ii) a less porous intermediate zone in which several precipitation and dissolution fronts occurred, and (iii) the sound core. Ettringite was a good tracer for degradation. The good retention of zinc by the cement matrix was mainly attributed to the precipitation of a hydrated and well crystallized phase with platelet morphology (which may belong to the layered double hydroxide family) at early age (≤1 day), and to chemisorption onto aluminum hydroxide at later age. © 2011 Elsevier B.V.
Mots clés
diffusion
ester
experimental study
hydration
hydroxide
leachate
pH
retention
tracer
concentration (parameters)
solidification
precipitation
surface property
waste management
building material
chemistry
Aluminum Compounds
Calcium Compounds
Chlorides
Construction Materials
Hydrogen-Ion Concentration
Sulfur Compounds
Zinc Compounds
aluminum hydroxide
inorganic compound
cement
Degradation process
Detection limits
Early age
Ettringites
Intermediate zone
Layered double hydroxides
Leachates
Platelet morphology
Pure water
Solid samples
Solidified waste forms
Surface layers
Three zones
Waste forms
Zinc concentration
Chemisorption
Chlorine compounds
Ion beams
unclassified drug
Portland cement
zinc chloride
aluminum derivative
Cement matrix
Cement paste
Cement hydration
calcium sulfoaluminate cement
calcium derivative
sulfur derivative
article
chloride
stabilization
calcium sulfoaluminate
waste treatment
dissolution
leaching
zinc
zinc derivative
aluminum compound
calcium
concentration (composition)
crystallization
degradation
detection method