Process & contact
Member of DPP
Input: sewage sludge incineration ash, from sewage works using biological and/or chemical P-removal.
- phosphoric acid (technical grade, some Fe and Al remain)
- iron and aluminium salts
- mineral ash residues
1) ash is leached using phosphoric acid, so solubilising phosphorus and calcium but not most of the iron or heavy metals
2) addition of sulphide to precipitate heavy metals and maximise the proportion of these which stay in the leached ash (solid fraction)
3) solid-liquid separation
4) from the liquid fraction (enriched phosphoric acid), calcium is precipitated as gypsum, by addition of sulphuric acid, and the gypsum is separated out by vacuum belt filter and water washing.
5) the resulting phosphoric acid is partially returned back to leaching process. The additional acid production is purified by ion-exchanger and optionally nano-filtration membrane
6) the resulting purified phosphoric acid is then concentrated (preferably using secondary heat, e.g. from a sludge incinerator)
7) regeneration of the ion-exchange resin produces (using hydrochloric acid) produces a metal salt solution, which can be potentially recycled to sewage works for phosphorus removal
Pilot plant: Hamburg, Germany and Elverlingsen, Germany, 50 kg/h ash (photo)
Full scale plant: Hamburg, Germany (started October 2023) Throughput: 20,000 t/y ash, output 7000 t/y of technical phosphoric acid (57% H3PO4). Initially (Nov 2023) at 1/3 of capacity. See Scope 80 Newsletter
Further full scale plants are in project phase in Kiel, (Germany), Lünen (Germany) and Moerdijk (The Netherlands).