Chemical State of Chromium, Sulfur, and Iron in Sewage Sludge Ash based Phosphorus Fertilizers

As an essential element of all life forms, phosphorus (P) is vital to the fertilizer industry. With decreasing quantity and quality of phosphate rock resources, recycling P-fertilizers from wastewater is of increasing interest. The P-fertilizer products of a recently developed thermochemical process...

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Bibliographic Details
Published inACS sustainable chemistry & engineering Vol. 3; no. 10; pp. 2376 - 2380
Main Authors Vogel, Christian, Radtke, Martin, Reinholz, Uwe, Schäfers, Franz, Adam, Christian
Format Journal Article
LanguageEnglish
Published American Chemical Society 05.10.2015
Subjects
Chromium
Sewage sludge ash
sulfur
Iron
X-ray absorption near-edge structure (XANES) spectroscopy
Phosphorus recovery
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Summary:As an essential element of all life forms, phosphorus (P) is vital to the fertilizer industry. With decreasing quantity and quality of phosphate rock resources, recycling P-fertilizers from wastewater is of increasing interest. The P-fertilizer products of a recently developed thermochemical process for P recovery from sewage sludge ash (SSA) were investigated by chromium, sulfur, and iron K-edge X-ray near-edge structure (XANES) spectroscopy. This paper focuses the formation and prevention of toxic chromium­(VI) and toxic sulfides during the thermochemical processes. Reducing conditions prevent the oxidation of chromium­(III) in the SSA to toxic chromium­(VI). Sulfides formed under the reducing conditions are nontoxic iron sulfides. Hematite (Fe2O3) present in the SSA is reduced to magnetite (Fe3O4). A gentle post-treatment at 400 °C under oxidizing conditions converts the iron sulfides into plant-available iron sulfates. This oxidative post-treatment does not form undesired chromium­(VI) compounds.
ISSN:2168-0485
2168-0485
DOI:10.1021/acssuschemeng.5b00678