title: Comparison of immobilisation of air pollution control residues with cement and with silica.
abstract: Cement as agent for immobilising Pb from air pollution control residues is compared with the use of different silica-containing materials. The DIN 38414-S4 leaching test was used to control Pb leachability and to compare obtained Pb leachate concentrations with the landfill limit of 2 mg/l for Pb. Firstly, one scrubber residues was treated with cement and micro-silica. With cement, the Pb leachability could be reduced with a factor ranging from 3 to 50 depending on the type and amount of cement used and depending on the curing time. The landfill limit of 2 mg/l was, however, never attained. From all tested silica-containing additives, aerosil could reduce the initial Pb leaching (101.3mg/l) to below the detection limit at a dosage of 0.13 g aerosil/g residue. Second best and an economically preferable silica-containing additive was micro-silica: a reduction from 101.3 to 0.7 mg/l was observed at a dosage of 0.4 g micro-silica/g residue. The formation of Ca-silicates was found to be responsible for the decreased Pb leachability. To generalise the findings, the Pb leachability of five cement-treated and five micro-silica-treated air pollution control residues were compared. For three scrubber residues, 2-20 times lower Pb leachate concentrations were measured for micro-silica-treated samples (cured for 5 weeks) than cement-treated samples. For a fly ash and a boiler ash the difference was, respectively, 48 and 17 times. pH-dependent leaching tests showed that at pH=2.5, Pb leaching is 250 times lower for the micro-silica-treated residue than for the cement-treated residue and almost seven times lower at pH 12.4.
authors.affiliation: Department of Chemical Engineering, K.U. Leuven, de Croylaan 46, B-3001 Leuven, Belgium. daneel.geysen@cit.kuleuven.ac.be
authors.forename: D
authors.initials: D
authors.lastname: Geysen
authors.forename: C
authors.initials: C
authors.lastname: Vandecasteele
authors.forename: M
authors.initials: M
authors.lastname: Jaspers
authors.forename: G
authors.initials: G
authors.lastname: Wauters
mesh_terms: D000393:Air Pollutants / Q000737:chemistry*; D000397:Air Pollution / Q000517:prevention & control*; D006863:Hydrogen-Ion Concentration; D019216:Metals, Heavy / Q000032:analysis / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry*
chemical_list: D000393:Air Pollutants; D019216:Metals, Heavy; D012822:Silicon Dioxide