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Following Rembrandt ‘Vivianite is initially colorless, but becomes blue after oxidation and eventually turns black. Rembrandt and Vermeer used the bright blue dye on their canvases’
Phosphate is a scarce raw material that we desperately need for our food supply. At the same time, phosphate is very harmful to the environment in large quantities, causing eutrophication and algal blooms. To avoid its harmful effects, phosphate is removed as best as possible at sewage treatment plants. Recovering phosphate is not easy, however. Existing techniques have limitations in efficiency and area of application, but there are positive developments towards a more circular economy. The mineral vivianite plays a key role in those developments. We interviewed Wetsus scientist Leon Korving. Together with their industrial partners, researchers from Wetsus and TU Delft discovered that the phosphate-rich vivianite is created when iron salts are used to bind phosphate in sewage treatment plants. This is a commonly used technique for phosphate removal, but recovering the phosphate has proven difficult with existing
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techniques. Research by Wetsus showed that vivianite is relatively easy to extract from sewage sludge using a magnetic separation technique borrowed from the mining industry. The technique enables the recovery of up to 80% of phosphate from the sludge.
Recovery Technology
Phosphate is a valuable and scarce raw material (see info box). Sewage plants normally have two methods of removing phosphate. Wetsus scientist Leon Korving clarifies, “You can opt for biological phosphate removal, the advantage being that there are no chemicals necessary.” However,
