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Process & contact

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Updated 01/24

Input materials

Input: sewage sludge incineration ash, from sewage works using biological and/or chemical P-removal.

Output products

- phosphoric acid (technical grade, some Fe and Al remain)Tetraphos HPHOR AussenansichtSmaller
- gypsum
- iron and aluminium salts
- mineral ash residues

Process description

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

TetraPhos Anlage Hamburg1

Operating status

Pilot plant: Hamburg, Germany and Elverlingsen, Germany, 50 kg/h ash

Full scale plant: Hamburg, Germany (started October 2023) - photos: outside (above), exchange colums (right), ash leaching unit and vacuum belt filter for the residue (below).
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), L√ľnen (Germany) and Moerdijk (The Netherlands).


                                                                                                                                ion exchange columns


TetraPhos Anlage Hamburg2














                              Digestion / leaching unit (centre) and belt filter for the residue (right) 

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