Recovery of phosphorus from Sewage Sludge Ash (SSA) by heat treatment followed by high gradient magnetic separation and flotation

Recovering phosphorus from unconventional sources has gained attention recently due to some estimates predicting a decline in phosphate rock production in the years to come. Recovery of phosphorus from Sewage Sludge Ash (SSA) coming from municipal sewage incineration plants arises as a promising alternative. Nonetheless, the use of simple, straightforward mineral processing techniques for that purpose has not been explored on its entirety yet. This research work studies the recovery of phosphorus from a Japanese SSA via heat treatment followed by the use of High Gradient Magnetic Separation (HGMS) and flotation. The heat treatment was carried out using the addition of 5% of carbon and exposure to temperatures of 540 degrees C and 680 degrees C for 30 min. Measurements using a Vibrating Sample Magnetometer showed that magnetization of SSA increases at higher temperatures, at higher carbon additions, and when a N-2 atmosphere is used. On the other hand, when 5% of Fe2O3 was also added before the heating step, the previously detected aluminum-phosphate phase (Ca9Al(PO4)(7)) is replaced by an iron-phosphate phase (Ca9Fe(PO4)(7)). HGMS trials using this specimen, pointed out that the "nonmagnetic-rich" fraction was enriched by 7% on a relative basis of P2O5 content. Further treatment of this portion, using flotation at pH 10, revealed that an additional enrichment (i.e. 19% in relative P2O5 content) occurs in the froth when compared with the tailings. The results show evidence that it is possible to promote phosphorus recovery from SSA using a heating treatment followed by these mineral processing methods. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.