Désirée Nordmark

Carbon speciation in ash, residual waste and contaminated soil by thermal and chemical analyses.

Carbon in waste can occur as inorganic (IC), organic (OC) and elemental carbon (EC) each having distinct chemical properties and possible environmental effects. In this study, carbon speciation was performed using thermogravimetric analysis (TGA), chemical degradation tests and the standard total organic carbon (TOC) measurement procedures in three types of waste materials (bottom ash, residual waste and contaminated soil). Over 50% of the total carbon (TC) in all studied materials (72% in ash and residual waste, and 59% in soil) was biologically non-reactive or EC as determined by thermogravimetric analyses. The speciation of TOC by chemical degradation also showed a presence of a non-degradable C fraction in all materials (60% of TOC in ash, 30% in residual waste and 13% in soil), though in smaller amounts than those determined by TGA. In principle, chemical degradation method can give an indication of the presence of potentially inert C in various waste materials, while TGA is a more precise technique for C speciation, given that waste-specific method adjustments are made. The standard TOC measurement yields exaggerated estimates of organic carbon and may therefore overestimate the potential environmental impacts (e.g. landfill gas generation) of waste materials in a landfill environment.

Mobility and fractionation of arsenic, chromium and copper in thermally treated soil.

Thermal treatment is used to remediate soil co-contaminated with organic and inorganic contaminants. It destroys organic contaminants, but the remaining inorganic contaminants require further treatment. In this study the effects of thermal treatment on the mobility, speciation and chemical fractionation of As, Cr and Cu in a CCA-polluted soil were evaluated by leaching tests, As speciation assays and a sequential extraction procedure. The soil was sieved into four size fractions (<0.125, 0.125—0.250, 0.250—0.500 and 0.500—1.0 mm), each of which was treated at 800°C and analysed in comparison with the untreated soil. The leaching of As and Cr increased by factors of 18—40 and 2—23, respectively, while the mobility of Cu decreased 12—14-fold after treatment. The concentration of As(V) in pore water of the finest soil fraction increased 19-fold, whereas that of As(III) remained constant. The treatment reduced As, Cr and Cu associated with the reducible soil fraction. In addition, it increased the proportions of As and Cr (slightly) associated with the exchangeable and acid-soluble soil fractions, and the proportions of Cu and Cr (substantially) associated with the residual fraction.

Geochemical Behavior of a Gravel Road Upgraded with Wood Fly Ash

AbstractAn insufficient bearing capacity of gravel roads is a common problem in Sweden during thaw periods. In this study, a gravel road at Timra in central Sweden was mechanically stabilized by mixing 30% wood fly ash into the road base material. Testing of pollutant mobilization was performed both in the lab and at the field site over three years. The differences at a given liquid-to-solid ratio reached several orders of magnitude for some elements. K, Ca, Cl, and SO4 were easily mobilized and found at elevated concentrations in leachate from the road one year after the road was stabilized. Two years after stabilization, the concentrations had returned to background levels. The stabilization also impacted the infiltration capacity of the road, reducing it by a factor of four. The weathering of Mg, Cu, and Zn from surrounding soil was higher, while the leaching of Al and K was higher from the amended road. Using fly ash in this fashion did not result in any noticeable adverse environmental impacts.

Controlling the mobility of chromium and molybdenum in MSWI fly ash in a washing process

Fly ash from a cogeneration plant near Sundsvall in Sweden was treated in an ash-washing facility. The leaching of chromium (Cr) and molybdenum (Mo) from the ash residue exceeded the limit values for non-hazardous landfills. In this study factors that influence the leaching of Cr and Mo were identified and methods that can reduce the leaching were evaluated. The results revealed that the mobility of Cr and Mo are mainly controlled by pH and redox reactions and sequential extraction tests also showed that the fraction of highly soluble species of Cr and Mo increased after washing due to pH reactions in the ash during the process. Stabilization of the pH at ∼8 through carbonation of the washed ash and a lowering of the redox potential by adding ferrous iron to the process resulted in decreased leaching. Treatment with carbon dioxide yielded a decrease (from 10.7 to 8.2) in the pH and, hence, the leaching of Cr and Mo by 93 and 91%, respectively. And the addition of ferrous iron reduced the leaching of Cr by 50%. Carbonation of the ash can be achieved via treatment with flue gases from the power plant or treatment with landfill gas at the disposal site.