RESUMEN

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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RESUMEN

Magnetite core/zirconia shell nanocomposite (abbreviated as Fe3O4@ZrO2 hereafter) was obtained using one-step co-precipitation method and its performance for removal of fluoride ion from water was studied. The results showed that the Langmuir maximum adsorption capacity of fluoride ion by Fe3O4@ZrO2 was 35.46 mg·g-1, which was far higher than those of magnetite, activated alumina and activated carbon. Studies of adsorption kinetics indicated that the adsorption of fluoride ion by Fe3O4@ZrO2 was fast and could be well described by the pseudo-second-order model. The adsorption process of fluoride ion was an endothermic reaction. The adsorption of fluoride ion by Fe3O4@ZrO2 decreased with increasing pH. Chloride, nitrate and sulfate anions, which commonly coexist in drinking water, had little effect on F- adsorption, although the coexistence of HCO3- and CO32- reduced the adsorption significantly by increasing the pH of the solution system. The fluoride adsorbed by Fe3O4@ZrO2 could be successfully desorbed with 1 mol·L-1 NaOH solution as desorption agent. The desorption rate reached 99.5%-99.6%. The F--desorbed Fe3O4@ZrO2 could be reused for the removal of F- after regeneration via restoring the protonation status of surface hydroxyl groups on hydrous zirconia. The removal efficiency of fluoride by Fe3O4@ZrO2 from actual well water was lower than that from pure water, but concentration limit for fluoride in drinking water could still be attained by increasing the dosage to a sufficiently high level. Fe3O4@ZrO2 is a promising material for fluoride removal due to its good performance, simple preparation method and easy separation from water by providing an external magnetic field.

RESUMEN

Eutrophication has become a worldwide environmental problem and removing phosphorus from water/wastewater before discharge is essential. The purpose of our present study was to develop an efficient material in terms of both phosphate adsorption capacity and magnetic separability. To this end, we first compared the performances of four spinel ferrites, including magnesium, zinc, nickel and copper ferrites. Then we developed a copper ferrite-based novel magnetic adsorbent, by synthesizing 1,6-hexamethylenediamine-functionalized copper ferrite(CuFe2O4) via a single solvothermal synthesis process followed by LaCl3 treatment. The materials were characterized with X-ray diffraction, transmission electron microscope, vibrating sample magnetometer, Fourier transform infrared spectra and N2 adsorption-desorption. The maximum adsorption capacity of our material, calculated from the Langmuir adsorption isotherm model, attained 32.59mg/g with a saturation magnetization of 31.32emu/g. Data of adsorption kinetics were fitted well to the psuedo-second-order model. Effects of solution pH and coexisting anions (Cl-, NO3-, SO42-) on phosphate adsorption were also investigated, showing that our material had good selectivity for phosphate. But OH- competed efficiently with phosphate for adsorption sites. Furthermore, increasing both NaOH concentration and temperature resulted in an enhancement of desorption efficiency. Thus NaOH solution could be used to desorb phosphate adsorbed on the material for reuse, by adopting a high NaOH concentration and/or a high temperature.

RESUMEN

A novel magnetic core/shell structured nano-particle Fe3O4@ SiO2phosphor-removal ahsorbent functionalized with hydrous aluminum oxides (Fe3O4@ SiO2@ Al2O3· nH2O) was synthesized. Fe3O4@ SiO2@ Al2O3· nH2O was characterized by XRD, TEM, VSM and BET nitrogen adsorption experiment. The XRD and TEM results demonstrated the presence of the core/shell structure, with saturated magnetization and specific surface area of 56.00 emu · g⁻¹ and 47.27 m² · g⁻¹, respectively. In batch phosphor adsorption experiment, the Langmuir adsorption maximum capacity was 12.90 mg · g⁻¹ and nearly 96% phosphor could be rapidly removed within a contact time of 40 mm. Adsorption of phosphor on Fe3O4@ SiO2@ Al2O3 · nH2O was highly dependent on pH condition, and the favored pH range was 5-9 in which the phosphor removal rate was above 90%. In the treatment of sewage water, the recommended dosage was 1.25 kg · t⁻¹. In 5 cycles of adsorption-regeneration-desorption experiment, over 90% of the adsorbed phosphor could be desorbed with 1 mol · L⁻¹ NaOH, and Fe3O4@ SiO2@ Al2O3· nH2O could be reused after regeneration by pH adjustment with slightly decreased phosphor removal rate with increasing recycling number, which proved the recyclability of Fe3O4@ SiO2@ Al2O3· nH2O and thereby its potential in recycling of phosphor resources.

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