Stabilisation of heavy metal containing dusts by reaction with phosphoric acid: study of the reactivity of fly ash.
Water-washed fly ash was reacted with phosphoric acid in order to transform available heavy metals into insoluble metal phosphate compounds. The temperature, pH and concentration of free phosphate were monitored during the first 80 min of reaction. Phosphoric acid reacted rapidly with second order kinetics and an apparent rate constant of 0.015 l/(mol s m2). Analysis of the evolution of the concentrations of other major elements of fly ash shows that the reaction follows a dissolution-precipitation type mechanism. The solubility of trace heavy metals tends to increase at low pH values. Various heat and mass transfer coefficients are derived and help understand the phosphate stabilisation procedure and design industrial reactors for this purpose. Calcium phosphates are formed which can trap heavy metals in a stable apatite mineral structure.
Bournonville
Blandine
B
Laboratoire de Génie des Procédés des Solides Divisés UMR CNRS 2392, Ecole des Mines d'Albi-Carmaux, Campus Jarlard, Route de Teillet, 81013 ALBI CT Cedex 09, France.
Nzihou
Ange
A
Sharrock
Patrick
P
Depelsenaire
Guy
G
D002244:Carbon / Q000737:chemistry*; D003031:Coal; D060729:Coal Ash; D004787:Environmental Pollution / Q000517:prevention & control; D006863:Hydrogen-Ion Concentration; D007220:Industrial Waste; D007700:Kinetics; D019216:Metals, Heavy / Q000737:chemistry* / Q000302:isolation & purification*; D052638:Particulate Matter; D010756:Phosphoric Acids / Q000737:chemistry*; D013696:Temperature
D003031:Coal; D060729:Coal Ash; D007220:Industrial Waste; D019216:Metals, Heavy; D052638:Particulate Matter; D010756:Phosphoric Acids; D002244:Carbon; C030242:phosphoric acid