“…However, the quality of the end-product containing vivianite depends on the source material qualities, which is problematic due to the presence of heavy metals and other potential contaminants. Vivianite itself has been reported to have qualities as a slow-release fertilizer [59,60], so purifying it by another process step seems necessary for legislative requirement in agriculture applications and/or a positive image as a fertilizer. Vivianite can also have other uses, such as art pigments [61].…”