Environmental characterization of ferrochrome arc furnace dust and its stabilization

ABSTRACTMASTER THESISENVIRONMENTAL CHARACTERIZATION OF FERROCHROME ARC FURNACEDUST AND ITS STABILIZATIONÜlkü BULUTFırat UniversityGraduate School of Natural and Applied SciencesDepartment of Environmental Engineering2006, Page: 68In this study, dissolution properties under different conditions and pollution potential byTCLP of arc furnace dust generated in ferrochrome, which is a raw material of stainless steelproduction, production were examined and some stabilization/solidification techniques wereapplied to the dust depending on contaminants determined. Dissolution properties and pollutionpotentials of all the stabilized/solidified materials prepared were also studied under the similarconditions.In the dissolution experiments, it was determined that except for chromium and zinc,metallic components concentration dissolved from AFBT were below the detection limits.However, chromium and zinc in different concentrations released into the solution depending onpH, contact time and liquid/solid ratio. The chromium concentration dissolved from AFBT byTCLP was found to be 9.8 mg/l, is higher than the maximum allowable concentration of 5 mg/l.According to TCLP test results, it was concluded that the AFBT has an important pollutionpotential, it was a hazardous waste.For the stabilization/solidification of the AFBT, Portland cement, Portland cement-FeSO4, Portland cement-sand, Portland cement-sand-FeSO4, fly ash and fly ash-FeSO4 mixtureswere tested and it was found the following results:IWhen the Portland cement was only used, it was determined that although metal ions incationic form were stabilized, Cr(VI) in the sample was not changed depending on Portlandcement addition and remained in the soluble chromate form. Also, weak structural integrity wasobserved due to non-pozzolanic properties of AFBT.In the stabilization/solidification experiments carried out with Portland cement-FeSO4mixture, the stabilization efficiency of Cr(VI) increased by the increasing amounts of Portlandcement and FeSO4. Optimum Portland cement and FeSO4 dosage was determined to be 30 %and 5 times of stoichiometric amount calculated from Cr(VI) reduction stoichiometry by ferrousiron with respect to Cr(VI) content of AFBT, respectively. Even though effective stabilizationof AFBT under the conditions investigated was established, monolithic solid residue could notbe obtained.In order to both stabilize and solidify to the AFBT, Portland cement-sand, Portlandcement-sand-FeSO4 mixtures were also tested. Results expected for Cr(VI) stabilization was notobtained by using Portland cement-sand. However, when the 5 times of stoichiometric amountof FeSO4, 30 % Portland cement and 16 % sand mixture was added to the AFBT, the beststabilization/solidification of AFBT was accomplished.In the stabilization/solidification experiments which were fly ash and fly ash-FeSO4mixtures were used, it was found that the results were similar to that of Portland cement andPortland cement-FeSO4 mixtures.Keywords: Ferrochrome, arc furnace dust, hexavalent chromium, stabilization, solidification,TCLP.II