The recovery of phosphorus from source-separated urine by repeatedly usable magnetic Fe3O4@ZrO2 nanoparticles under acidic conditions
2020
Guan, Tong | Kuang, Yue | Li, Xiaodi | Fang, Jing | Fang, Wenkan | Wu, Deyi
The separation of urine at source for phosphorus (P) recovery is attractive taking into account the high P concentration and small volume. However, the treatment of urine is still challenging due to its unpleasant odor and hygiene problems. Because the above problems could be solved by acidification to keep the pH of urine below 4, we propose a novel strategy to recover P from acidified urine using tailored hydrous zirconia-coated magnetite nanoparticles (Fe₃O₄@ZrO₂). This strategy involves the selective adsorption of phosphate by easily separable and reusable Fe₃O₄@ZrO₂, the desorption of adsorbed phosphate, and the precipitation of desorbed phosphate as calcium phosphate fertilizer. The results indicated that at pH 4, the P in synthetic urine was selectively adsorbed and could be exhausted using Fe₃O₄@ZrO₂. Nearly all (>97.5%) of the sequestered P on the Fe₃O₄@ZrO₂ nanoparticles was stripped using ≥1 M NaOH solution and ~100% of the stripped P was then successfully transformed into calcium phosphate, upon adding CaCl₂ at pH >12 and a Ca/P molar ratio of 3. The liquid/solid (Fe₃O₄@ZrO₂ particles) mixture could be conveniently separated for reuse using an external magnetic field. The reusability of the Fe₃O₄@ZrO₂ nanoparticles in the extraction of P from synthetic urine was confirmed using five cycles of the adsorption-desorption process and their performance validated using real urine samples. The mechanism of phosphate adsorption was investigated using XPS, FTIR and zeta potential measurements, showing that phosphate was chemically adsorbed on the surface through direct coordination to zirconium atom via ligand exchange.
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