Risk minimisation of FGD gypsum leachates by incorporation of aluminium sulphate

• Published in: The Science of the total environment Vol. 406; no. 1; pp. 69 - 75
• Main Authors: Álvarez-Ayuso, E., Querol, X., Ballesteros, J.C., Giménez, A.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15.11.2008; [Amsterdam; New York]: Elsevier Science; Elsevier
• Subjects: Alum Compounds - chemistry; Aluminium sulphate; aluminum sulfate; Applied sciences; Calcium Sulfate - chemistry; Disposal; Exact sciences and technology; FGD gypsum; Fluoride; fluorides; Fluorides - chemistry; Fluorides - isolation & purification; gypsum; Hydrogen-Ion Concentration; Kinetics; landfill leachates; Leaching; Other wastes and particular components of wastes; Pollution; pollution control; Risk Assessment; risk reduction; soil pollution; Stabilization; waste disposal; Waste Disposal, Fluid - methods; Waste Management - methods; Wastes; Water Pollutants, Chemical - chemistry; Water Pollutants, Chemical - isolation & purification; Fluoride; Disposal; Aluminium sulphate; Stabilization; FGD gypsum; Leaching; Desulfurization; Waste dumping; Pollution prevention; Treatment residue; Gypsum; Hazardous waste; Fluorides; Soil pollution; Waste disposal; Additive; Lixiviation; Water pollution; Flue gas purification; Leachate; Aluminium sulfate
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2008.08.010

The incorporation of aluminium sulphate to (flue gas desulphurisation) FGD gypsum before its disposal was investigated as a way to minimise the risk supposed by the high fluoride content of its leachates. Using a bath method the kinetic and equilibrium processes of fluoride removal by aluminium sulphate were studied at fluoride/aluminium molar concentration (F/Al) ratios in the range 1.75 10 − 2 –1.75 under the pH conditions (about 6.5) of FGD gypsum leachates. It was found that fluoride removal was a very fast process at any of the (F/Al) ratios subject of study, with equilibrium attained within the first 15 min of interaction. High decreases in solution fluoride concentrations (50–80%) were found at the equilibrium state. The use of aluminium sulphate in the stabilization of FGD gypsum proved to greatly decrease its fluoride leachable content (in the range 20–90% for aluminium sulphate doses of 0.1–5%, as determined by the European standard EN 12457-4). Such fluoride leaching minimisation assures the characterization of this by-product as a waste acceptable at landfills for non-hazardous wastes according to the Council Decision 2003/33/EC on waste disposal. Furthermore, as derived from column leaching studies, the proposed stabilization system showed to be highly effective in simulated conditions of disposal, displaying fluoride leaching reduction values about 55 and 80% for aluminium sulphate added amounts of 1 and 2%, respectively.