Manuscript title: In situ nanoscale imaging of struvite formation during the dissolution of

Transcription

1 Supporting Information Manuscript title: In situ nanoscale imaging of struvite formation during the dissolution of natural brucite: implications for phosphorus recovery from wastewaters. Authors: Jörn Hövelmann 1, Christine V. Putnis 2,3 Address: 1 German Research Centre for Geosciences (GFZ), Interface Geochemistry, Potsdam, Germany, 2 Institut für Mineralogie, University of Münster, Münster, Germany, 3 The Institute for Geoscience Research (TIGeR), Department of Chemistry, Curtin University, Perth 6845, Australia Journal: Environmental Science and Technology Figures: 5 Tables: 5 No. of pages: 9 S1

2 Figure S1: Time-lapse in situ AFM deflection images of a brucite surface during dissolution in (A-C) 5 mm, (D-F) 10 mm and (G-I) 20 mm (NH4)2HPO4 (ph 8.5). White arrows serve as reference points. Etch pit spreading velocity is clearly increased with increasing ammonium phosphate concentration. S2

3 Table S1: Log activities of P, N and Na species in the initial solutions used during AFM experiments (calculated using PHREEQC) initial solution H3PO4 H2PO4 - HPO4 2- PO4 3- NH4 + NH3 Na + NaH2PO4 NaHPO4 - NaPO4 2- NaH2PO4, ph mm mm mm mm mm NH4H2PO4, ph mm mm mm mm mm (NH4)2HPO4, ph mm mm mm mm mm NH4H2PO4, 20 mm ph ph ph ph Figure S2: Log activities of (A) H 2 PO 4 -, HPO 2 - and PO 4 3- vs. total P concentration, (B) NH 4 + and NH 3 vs. total N concentration, (C) H 2 PO 4 -, HPO 2 - and PO 4 3- vs. ph and (D) NH 4 + and NH 3 vs. ph. S3

4 Table S2: Distribution of species in 20 mm (NH 4 ) 2 HPO 4 (ph 8.5) before and after equilibration with brucite (calculated with PHREEQC) 20 mm (NH4)2HPO4, ph mm (NH4)2HPO4, ph 8.5 initial solution after equilibration with brucite ph 8.5 ph 9.78 Mg 1.38e-02 mol/l Species Molality Activity Mg(HPO4) 7.64e e-03 Mg e e-03 Mg(PO4) e e-03 Mg(NH3) e e-05 Mg(OH) e e-05 Mg(H2PO4) e e-07 Mg(NH3) e e-08 Mg(NH3) e e-10 Mg4(OH) e e-12 N(-3) 4.00e-02 mol/l N(-3) 4.00e-02 mol/l Species Molality Activity Species Molality Activity NH e e-02 NH3 2.98e e-02 NH3 5.25e e-03 NH e e-03 Mg(NH3) e e-05 Mg(NH3) e e-08 Mg(NH3) e e-10 Na 4.73e-03 mol/l Na 4.73e-03 mol/l Species Molality Activity Species Molality Activity Na e e-03 Na e e-03 Na(HPO4) e e-04 Na(HPO4) e e-04 NaH2PO4 3.95e e-06 NaPO e e-06 NaPO e e-07 NaH2PO4 1.30e e-07 P 2.00e-02 mol/l P 2.00e-02 mol/l Species Molality Activity Species Molality Activity HPO e e-03 HPO e e-03 H2(PO4) e e-04 Mg(HPO4) 7.64e e-03 Na(HPO4) e e-04 Mg(PO4) e e-03 PO e e-06 Na(HPO4) e e-04 NaH2PO4 3.95e e-06 PO e e-05 NaPO e e-07 H2(PO4) e e-05 H3(PO4) 1.86e e-10 NaPO e e-06 Mg(H2PO4) e e-07 NaH2PO4 1.30e e-07 H3(PO4) 3.03e e-13 S4

5 Table S3: Mg concentrations in AFM outflow solutions (measured by ICP-OES) and average saturation indices with respect to struvite (calculated with PHREEQC) exp. no. inflow solution struvite 13 NH4H2PO4, ph 8.5 Mg concentration in outflow [mg/l] aliquot no. #1 #2 #3 #4 avg. struvite 5 mm <0.001 <0.001 <0.001 < mm <0.001 <0.001 <0.001 < mm <0.001 <0.001 <0.001 < mm <0.001 <0.001 < mm <0.001 < struvite 16 (NH4)2HPO4, ph mm <0.001 < mm <0.001 < mm <0.001 < mm <0.001 < mm <0.001 < struvite 22 (NH4)2HPO4, ph 8.5 struvite 21 struvite 15 struvite 14 5 mm mm < mm mm <0.001 < NH4H2PO4, 20 mm ph ph ph ph NH4H2PO4, 50 mm ph 9.5 <0.001 < ph 9.0 <0.001 < ph 8.5 < ph 8.0 < ph NH4H2PO4, 50 mm ph 9.5 <0.001 < ph 9.0 <0.001 < ph 8.5 <0.001 < ph 8.0 <0.001 < ph struvite 20 NaH2PO4, 10 mm, ph NH4H2PO4, 10 mm, ph (NH4)2HPO4, 10 mm, ph S5

6 Figure S3: Mg concentrations in AFM outflow solutions after interaction of brucite with 10 mm NaH 2 PO 4 (black), NH 4 H 2 PO 4 (blue) and (NH 4 ) 2 HPO 4 (red). Measured values tended to be highest in (NH 4 ) 2 HPO 4 and lowest in NaH 2 PO 4 indicating that brucite dissolution is promoted in the presence of NH 4 + and/or NH 3. S6

7 Figure S4: PHREEQC simulations showing the evolution of ph and values of relevant phases as a function of Mg added to (A) 10 mm NH 4 H 2 PO 4 (initial ph 8.5), (B) 20 mm NH 4 H 2 PO 4 (initial ph 8.5), (C) 10 mm (NH 4 ) 2 HPO 4 (initial ph 8.5) and (D) 20 mm NH 4 H 2 PO 4 (initial ph 6). The simulations were run by adding brucite in small steps to the reactant solution. After each step, the and ph values were calculated and plotted against the amount of Mg released. In all simulations supersaturation with respect to struvite, newberyite, trimagnesium phosphate (TMP) and bobbierite is reached before brucite saturation. For initial ph values > 6 (A-C), struvite is always the first phase that becomes stable. For ph values 6, newberyite becomes stable first (D). The amount of Mg that needs to be added to reach struvite saturation decreases with increasing total P (cf. A, B) and N concentration (cf. A, C). S7

8 Table S4: Theoretical Mg concentrations in the reactant solutions at struvite saturation and corresponding amounts of brucite dissolved into a solution volume of 38 µl ( volume of the fluid cell) initial solution Brucite dissolved [mol] total Mg concentration [mg/l] Struvite Bobbierite TMP Newberyite Brucite NH4H2PO4, ph mm -3.53e mm -1.83e mm -9.18e mm -3.76e mm -1.97e (NH4)2HPO4, ph mm -1.99e mm -9.47e mm -4.61e mm -1.87e mm -9.78e NH4H2PO4, 20 mm ph E ph e ph e ph e ph e NH4H2PO4, 50 mm ph E ph E ph E ph E ph E S8

9 Bulk powder experiments. A set of bulk powder experiments was performed complementary to our AFM experiments. For these experiments, ~0.25 g of brucite powder (grain size fraction: µm) was filled into small plastic containers (volume: 10 ml) together with 8 ml of either 10 mm NH 4 H 2 PO 4 or 10 mm (NH 4 ) 2 HPO 4 solution. The initial ph of the solution was adjusted to 8.5 using NaOH. The containers were subsequently sealed with a lid and shaken a few times to disperse the powder. For each of the two solutions we prepared 4 aliquots that were allowed to react for different time periods (i.e., 22 h, 29 h, 44 h and 52 h). Each container was shaken 3 times a day. Upon termination of an experiment, the container was opened and the supernatant solution withdrawn using a syringe. The solution was then filtered using 0.45 µm syringe filters and stored for later ICP-OES analysis. The reacted brucite powder was immediately spread on a filter paper to remove adsorbed water as quickly as possible and then allowed to dry in air at room temperature before XRD analysis. XRD analyses were done using a Brukeraxs D8 X-ray Microdiffractometer. Measurements were performed with a Cu-radiation source and data were collected from 4.6 to 85 2θ using a step size of θ and a counting time of 58.4 s per step. Table S5: Mg concentrations in solution after interaction of brucite powder with 10 mm NH 4 H 2 PO 4 and (NH 4 ) 2 HPO 4 (both ph 8.5) and corresponding values for struvite (calculated with PHREEQC) reaction time [h] 10 mm NH4H2PO4, ph mm (NH4)2HPO4, ph 8.5 Mg concentration [mg/l] struvite Mg concentration [mg/l] struvite Figure S5: XRD patterns obtained of non-reacted brucite powder (black) and brucite powders reacted in 10 mm (NH 4 ) 2 HPO 4 (purple) and 10 mm NH 4 H 2 PO 4 (blue) for 44 h. In the 2θ range from 15 35, the patterns of the reacted samples show several peaks that are not observed in the nonreacted sample. These peaks match well with the most intense peaks for struvite. A reference pattern of struvite is shown in green. S9