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Process & contact


P-recycling from ashes and precipitates


Updated 2/2022

Input materials

Sewage sludge incineration ash, struvite.

Planned: other phosphate-rich materials with low levels of organics, e.g. vivianite.

Output products

Phosphoric acid, or mono- or diammonium phosphate (fertilizer or flame retardant quality).

Iron / aluminium salts as aqueous solution: can be recycled to sewage works for P-removal.

Solid magnesium sulphate salts (if struvite is input), recycled by sewage works for struvite precipitation.34susphos

Inert mineral material stream (containing sand, gypsum, iron oxides) can be used in the construction industry.

Process description

The input materials are attacked with concentrated sulphuric acid.

The resulting phosphoric acid is purified using a proprietary organic solvent extraction process, without requiring ion-exchange or membrane filters. The acid has low levels of impurities and concentration >50% P2O5 (from ash), because the only water input is in the sulphuric acid.

The process requires very little heat to achieve dry solids or a concentrated phosphoric acid, and can be run largely on waste heat. 

Iron and aluminium are c. 99% removed from the phosphoric acid, and partly recovered for recycling, partly fixed in the insoluble minerals stream.

Mono- or diammonium phosphate can be precipitated from the phosphoric acid by reaction with ammonia gas.

Heavy metals are largely removed and rendered inert in insoluble calcium minerals: e.g. >95% of Cd, Hg, Cu, Zn …

Operating status

25 kg/day pilot operated in Leeuwarden (NL) for 8 months for struvite and tests with sewage sludge incineration ash are underway since May 2021.

A full scale plant of 50 000 t/y is planned in The Netherlands, with objective of operation in 2023-2024

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