title: Sequential electrodialytic recovery of phosphorus from low-temperature gasification ashes of chemically precipitated sewage sludge.
abstract: Phosphorus recycling from secondary materials like sewage sludge ashes offers an alternative to mining of phosphates from primary resources and a mean to counteract the current phosphorous rock depletion concern. A separation of P from the bulk ash is normally required, due to its low plant availability and the presence of heavy metals. Previously, more than 80% of P was recovered from incineration sewage sludge ashes using a two-compartment electrodialytic cell. In contrast, the recovery was below 30% for ashes from low-temperature gasification using the same setup. The low recovery was due to a high presence of Al- and Fe(III)-P bindings. In the present study, an electrodialytic process combining sequentially a pair of two-compartment cells allowed a recovery of up to 70% of phosphorus from these ashes. The use of a second cell, where the ash was suspended in an alkaline solution, allowed the P solubilisation from aluminium and ferric phosphates. In addition, P was separated from most metals as they became insoluble under the prevailing chemical environment. The obtained ratio of Al, Fe, Mg and most heavy metals to P was comparable to wet process phosphoric acid. Therefore, this sequential process was found to be suitable to recycle P and potentially use it in the production of common fertilizers like diammonium phosphate.
authors.affiliation: Department of Civil Engineering, Technical University of Denmark, Building 118, 2800 Kongens Lyngby, Denmark. Electronic address: rapv@byg.dtu.dk.
authors.forename: Raimon
authors.initials: R
authors.lastname: Parés Viader
authors.affiliation: Department of Civil Engineering, Technical University of Denmark, Building 118, 2800 Kongens Lyngby, Denmark.
authors.forename: Pernille Erland
authors.initials: PE
authors.lastname: Jensen
authors.affiliation: Department of Civil Engineering, Technical University of Denmark, Building 118, 2800 Kongens Lyngby, Denmark.
authors.forename: Lisbeth M
authors.initials: LM
authors.lastname: Ottosen
authors.affiliation: Department of Chemical and Biochemical Engineering, Technical University of Denmark, Building 313, 4000 Roskilde, Denmark.
authors.forename: Jesper
authors.initials: J
authors.lastname: Ahrenfeldt
authors.affiliation: Department of Environmental, People and Technology, Roskilde University, 4000 Roskilde, Denmark.
authors.forename: Henrik
authors.initials: H
authors.lastname: Hauggaard-Nielsen
mesh_terms: D017607:Aluminum Compounds / Q000032:analysis; D011232:Chemical Precipitation; D055664:Electrochemical Techniques; D005290:Ferric Compounds / Q000032:analysis; D010710:Phosphates / Q000032:analysis; D010758:Phosphorus / Q000737:chemistry*; D012722:Sewage / Q000737:chemistry*; D013696:Temperature; D018505:Waste Management / Q000379:methods*
chemical_list: D017607:Aluminum Compounds; D005290:Ferric Compounds; D010710:Phosphates; D012722:Sewage; D010758:Phosphorus; C012714:aluminum phosphate; C035885:ferric phosphate
keywords: Electrodialysis; Heavy metals; Iron phosphates; Low-temperature gasification; Phosphorus; Sewage sludge ash