title: Chemical state of mercury and selenium in sewage sludge ash based P-fertilizers.
abstract: Phosphorus-fertilizers from secondary resources such as sewage sludge ash (SSA) will become more important in the future as they could substitute conventional fertilizers based on the nonrenewable resource phosphate rock. Thermochemical approaches were developed which remove heavy metals from SSA prior to its fertilizer application on farmlands. We analyzed the chemical state of mercury and selenium in SSA before and after thermochemical treatment under different conditions for P-fertilizer production by X-ray absorption near edge structure (XANES) spectroscopy. In some incineration plants the mercury loaded carbon adsorber from off-gas cleaning was collected together with the SSA for waste disposal. SSAs from those plants contained mercury mainly bound to carbon/organic material. The other SSAs contained inorganic mercury compounds which are most probably stabilized in the SSA matrix and were thus not evaporated during incineration. During thermochemical treatment, carbon-bound mercury was removed quantitatively. In contrast, a certain immobile fraction of inorganic mercury compounds remained in thermochemically treated SSA, which were not clearly identified. HgSe might be one of the inorganic compounds, which is supported by results of Se K-edge XANES spectroscopy. Furthermore, the chemical state of selenium in the SSAs was very sensitive to the conditions of the thermochemical treatment.
authors.affiliation: Division 4.4 Thermochemical Residues Treatment and Resource Recovery, Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, 12205 Berlin, Germany. Electronic address: cv.vogel@yahoo.de.
authors.forename: Christian
authors.initials: C
authors.lastname: Vogel
authors.affiliation: Division 4.4 Thermochemical Residues Treatment and Resource Recovery, Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, 12205 Berlin, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Krüger
authors.affiliation: Division 4.4 Thermochemical Residues Treatment and Resource Recovery, Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, 12205 Berlin, Germany.
authors.forename: Hannes
authors.initials: H
authors.lastname: Herzel
authors.affiliation: ESRF-The European Synchrotron, 71 Avenue des Martyrs, 38000 Grenoble, France.
authors.forename: Lucia
authors.initials: L
authors.lastname: Amidani
authors.affiliation: Division 4.4 Thermochemical Residues Treatment and Resource Recovery, Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, 12205 Berlin, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Adam
keywords: Mercury; Mercury selenide (HgSe); Phosphorus recovery; Selenium; Sewage sludge ash; X-ray absorption near edge structure (XANES) spectroscopy