Abstract Experimental Procedures Reinier Hernandez_ Prabhakar Pant

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					                                                                                  Characterization of Iron Phosphate Precipitation
                                                                                                                                                                                  Reinier Hernandez, Prabhakar Pant, PhD.
                                                                                                                                                                           Applied Research Center, Florida International University

Abstract                                                                                    Results                                                                                                                                                                                                                                                 Conclusions
Nowadays heavy metals and specifically uranium contamination,                               The results for both titrations were recorded simultaneously. The                                                                                                     From the results given in Figure 3, the iron (III) and phosphate                  This current work complements a prior study performed on a
                                                                                            two curves are shown in Figures 1 and 2.                                                                                                                              ratio at which the maximum precipitation is attained, can be                      similar system. Some of the findings, such as those obtained with a
has become a major environmental concern. Within the frame
                                                                                            Fig 1. Conductivity curve of iron-monophosphate complex formation                                                                                                     determined. These results are in good accordance with those                       radiotracer experiment, were corroborated by using conventional
of implementation of polyphosphate technology for uranium                                                                      2.9
                                                                                                                                                                                                                                                                  obtained by the radioactive tracer precipitation experiment.                      analytical techniques. Additional observations were made which
decontamination,       the      formation          of    iron      (III)        phosphate                                      2.7
                                                                                                                                                                                                                                                                                                                                                    enhanced the understanding of this particular system.
                                                                                                                                                                                                                                                                  The SEM analysis allowed us to analyze the surface properties

                                                                                               Specific Conductivity (uS/cm)
complexes as a possible source of interference has been widely                                                                 2.5
                                                                                                                                                                                                                                                                  and elemental composition of the samples.
                                                                                                                                                                                                                                                                                                                                                     The stoichiometry and reaction mechanism of iron phosphate
analyzed. This work intends to further previous studies on iron                                                                2.3
                                                                                                                                                                                                                                                                      Fig 4. X-ray fluorescence spectrum of Fe phosphate precipitate
                                                                                                                               2.1                                                                                                                                                                                                                     formation was determined.
(III) phosphate complex formation. The reactions of Fe3+ with
                                                                                                                               1.9                                                                                                                                                                                                                   The stoichiometric ratio Fe/PnOm in the precipitate follows the
different phosphate species (mono, pyro, tri) were characterized                                                               1.7                                                                                                                                                                                                                     order: Fe/PO43- > Fe/P2O54- > Fe/P3O75- .
by electrometric and atomic absorption methods. An elemental                                                                   1.5
                                                                                                                                                      0             2000   4000    6000         8000   10000     12000     14000   16000   18000      20000                                                                                          Elemental analysis using X-ray fluorescence yielded a varied
and surface analysis was performed in the precipitates obtained.                                                                                                                                Volume KH2PO4(uL)
                                                                                                                                                                                                                                                                                                                                                       precipitate composition.

Experimental Procedures                                                                                                                                                                                                                                                                                                                              The hydrolysis process of the polyphosphate species plays an
                                                                                                                                                                Ion                   Fe3+                Cl-            Na+         H2PO4-                  H+
Conductometric/Potentiometric Titration                                                                                        Ionic Molar conductivity
                                                                                                                                                                                                                                                                                                                                                       important role in determining the precipitate composition.
                                                                                                                                                                                          68             76.31       50.08            36                349.65
                                                                                                                                   (10–4 m2Smol–1)
The titrations (potentiometric and conductometric) were performed                                                                                                                                                                                                                                                                                    Precipitate surfaces were found very similar in all studied cases.
simultaneously using a set up similar to Figure 1. A 400 ml beaker was                      The shape of the conductivity curve is explained by the ion

used as a conductivity/potentiometric cell. 100 mL of deionized water was                   balance presented in the reaction. The conductivity raises                                                                                                            The composition of the precipitate is given by the ratio between                  References
added to the titration cell followed by 3 mL of         Fe3+    0.1 M stock solution.       because of the increment on the H+ species in solution; notice                                                                                                        the peaks corresponding to each element.                                            Corbridge, D.E.C. “Phosphorus: An Outline of its Chemistry,
The mixture was titrated using NaHPO4 0.1 M at a stirring rate of 2 rps.                    the high molar conductivity of H+.                                                                                                                                                       Table 3. Precipitate composition                                 Biochemistry, and Technology”. 4th ed. Elsevier, Amsterdam,
The data was collected manually and analyzed in an Excel spread sheet.                                     Fig 2. pH curve of iron-monophosphate complex formation                                                                                                       Sample     P/Fe ratio   O/Fe ratio   O/P ratio   precipitate composition
                                                                                                                                                                                                                                                                         mono 3       1.96          9.1         4.64
                                                                                                                                2.7                                                                                                                                                                                                                   De Jager, H., and A.M. Heyns. “Study of the hydrolysis of sodium
FAA & SEM Analysis of Iron-Polyphosphate Precipitation                                                                                                                                                                                                                   mono 4       0.95         2.98         3.15
                                                                                                                                                                                                                                                                         pyro 5       1.96         6.91         3.52                                  polyphosphate in water using Raman spectroscopy”. Applied
A ten point iron calibration curve (0.5 ppm, 0.75 ppm, 1.0 ppm, 1.5 ppm,                                                        2.6

                                                                                                                                                                                                                                                                         pyro 6       1.67         4.75         2.85
                                                                                                                                                                                                                                                                                                                                                      Spectroscopy, 52:808-814, 1998.
2.0 ppm, 2.5 ppm, 3.0 ppm, 3.5 ppm, 4.0 ppm, 5.0 ppm) was prepared                                                                                                                                                                                                        tri 5       1.54         5.75         3.73

                                                                                                                                                                                                                                                                          tri 6        2.3          7.8         3.39
                                                                                                                                                                                                                                                                                                                                                      Ed. David R. Lide. "Equivalent Conductivity of Electrolytes In
in each case. A total of 26 precipitation experiments were prepared by                                                         2.45
                                                                                                                                                                                                                                                                                                                                                      Aqueous Solution." CRC Handbook of Chemistry and Physics
                                                                                                                                                                                                                                                                  The variation in precipitate composition corresponds to the
mixing in a 50 mL centrifuge tube, different volumes of iron stock (25

                                                                                                                                                                                                                                                                                                                                                      90th Edition Internet Version 2010. 2010. Web.
                                                                                                                                                                                                                                                                  presence of different phosphate species within the crystal.
mM) and the respective phosphate species for a given molar fraction.
                                                                                                                                                       0                    5000                 10000             15000              20000                                  Fig 5. SEM images of Fe/phosphate precipitates.
                                     Phosphate molar fraction                                                                                                                       KH2PO4 Volume (uL)                                                                (A,B) Mono 500X. (C,D) Pyro 500X. (E) Tri 150X. (F) Tri 1000X.                  Knox, A.S., R.L. Brigmon, D.I. Kaplan, and M.H. Paller, 2008.
           Sample    monophosphate     pyrophosphate             triphosphate
                                                                                                                                                                                                                                                                  A                                       B
             1           0.83               0.83                    0.83                                                                                                                                                                                                                                                                              “Interactions among phosphate amendments, microbes and
             2            0.8                0.8                     0.8
             3           0.75               0.75                    0.75
                                                                                            The pH trend presented in Figure 2 supports the reaction                                                                                                                                                                                                  uranium mobility in contaminated sediments”. Science of the
             4           0.66               0.66                    0.66                    mechanism proposed before in ec. 1.                                                                                                                                                                                                                       Total Environment 395:63–71.
             5            0.5                0.5                     0.5
             6           0.33               0.33                    0.33                                                       Fig 3. pH curve of iron-monophosphate complex formation
                                                                                                                                                                                                                                                                  C                                       D
             9           0.16                                       0.16                                                                                                                                                                                                                                                                            I would like to acknowledge the contribution to this work from Ms.
After 72 hours, the samples were centrifuged at 4500 rpm for 15 minutes                                                                                80                                                                                                                                                                                           Alejandro Amor and Dr. Prabhakar Pant (Mentor).
and the precipitate separated from the supernatant. The precipitates                                                                                                                                                                                                                                                                                Special thanks to the DOE/FIU Science and Technology Workforce
                                                                                                                                % of Iron remaining

were dried in a vacuum oven at 130 C and kept in a desiccator. The                                                                                     60
                                                                                                                                                                                                                                                                                                                                                    Development Program and all of its members for their guidance
supernatants were filtered through a 0.45 µm membrane filter and                                                                                                                                                                              pyrophosphate
                                                                                                                                                                                                                                                                  E                                       F                                         and support.
diluted accordingly. Iron concentration was measured using a Flame
Atomic Absorption Spectrophotometer and measuring the absorbance at
248.3 nm; deuterium lamp background correction was used.

Two precipitate samples of each phosphate were analyzed for elemental                                                                                     0
                                                                                                                                                              0.0          0.2            0.4             0.6            0.8        1.0
composition and surface properties in the Scanning Electron Microscope.                                                                                                              Phosphate molar fraction

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