LABORATORY METHODS – PRACTICAL ASSIGNEMENT INTERACTION BETWEEN GYPSUM AND A P-BEARING AQUEOUS SOLUTION INSTRUCTIONS: Please follow the guidelines described in the tasks. Your assignment should be delivered in hardcopy, including your name, student ID number and the answers clearly listed by task. Failure to comply with communicated deadlines will involve a -10% per delayed day penalty on assignment mark. Experimental device The followed experimental procedures consisted on the immersion of fragments of exfoliation of natural gypsum in 100 ml of a 75 mM phosphoric acid (H 3PO4) aqueous solution, previously neutralized with sodium hydroxide (NaOH) until the desired initial pH value of 6 was attained. The experiments took place inside polypropylene batches, closed with Parafilm film in order to avoid dissolution evaporation, and were maintained at constant temperature of 25 ± 0.1 ºC and 1 atm of pressure. The dissolutions remained at constant 25 rpm stirring during the experiments, using floating stirrers covered with Teflon. Figure 1 shows a schematic representation of the used experimental device. These experiments were designed to study the evolution of the aqueous solution chemistry during the interaction process. In this case, the grain sizes were selected to have diameters ranging from 1.0 to 1.5 mm. The duration of these experiments was of 72 hours, and dissolution samples were collected at 2, 4, 6, 8, 10, 12, 24, 36, 48, 60, 72 hours of elapsed time after inserting the gypsum grains in the reaction batch. Finally, each experiment was repeated three times in order to examine the reproducibility of the process. 100 ml of H3PO4 at 75 mM Figure 1. Experimental device used for interaction experiments. I – ANION CONCENTRATIONS IA. Analytical methods The measure of total phosphate and sulphate concentrations in the aqueous dissolution was carried out by means of ionic chromatography, using a Metrohm Advanced Compact 861 IC chromatographer. Samples collected during the experimental stage were diluted and compared with six reference dissolutions with different concentrations. These dissolutions were prepared using standard dissolutions of Na 2SO4 and KHPO4, both having 1000 ± 2 ppm (Panreac) concentration. An anion column (6.1006.520 Metrostep A SUPP 5 – 150) was used and the applied eluent was a dissolution of 15 mM of NaOH and 2.0 mM Na2CO3, with a flux velocity of 1.0 ml/min. and 5 MPa of pressure. The suppressor consisted of a solution with 100 mM of H2SO4. IB. Calibration lines In ion chromatography, aqueous concentrations are measured in a chromatogram of retention time versus detector response (Figure 2). In this graphical representation, the retention time enables the identification of the component in question, while its concentration is proportional to the corresponding peak’s area. For more information on ion chromatography, please consult Harvey, 2000. Figure 2. Schematical representation of a typical chromatogram (CHROMacademy.com). In the present case, we intend to measure sulphate and phosphate concentrations, and the results obtained from standard solutions are presented in table 1. Table 1 – Obtained chromatographic retention peak areas for standard phosphate and sulphate aqueous solutions. Phosphate (ppm) 10.2250 20.1456 40.0920 60.0871 79.7783 99.9175 Sulphate (ppm) 10.2723 19.9471 40.0898 60.0498 80.4411 99.4190 Run 1 24.3419 49.6771 105.6500 167.8710 232.9210 301.2880 Run 1 76.2839 148.6670 319.1340 501.0630 688.3830 865.2370 Peak Area Run 2 24.2887 49.4130 106.0560 168.0300 232.6120 301.7820 Run 2 75.4431 149.0850 319.7000 501.9080 688.9800 863.6050 Run 3 24.1368 49.6346 106.4140 168.2220 232.9320 302.0426 Run 3 76.0087 149.4590 320.2160 501.1660 690.7540 863.2410 TASK 1: Using the average value for the obtained areas, plot the results versus the concentrations of each standard solution and extract the corresponding trendline equations for sulphate and phosphate calibrations. What is the precision (in % of the mean) of the method in both cases? Don’t forget to present the calculations. IC. Batch experiment results – phosphate and sulphate concentrations TASK 2: in the Appendix: Data you may find the measured chromatographic results, regarding the evolution of sulphate and phosphate concentrations as a function of time, for the 3 replicated experiments. Determine the missing concentrations in mM ( 103mol/L) applying the expressions of the calibration lines. For each experiment present the precision as % of the average areas. II – CALCIUM CONCENTRATIONS IIA. Analytical methods The concentrations of total calcium in dissolution were measured with a PYE-UNICAM SP9 atomic absorption/emission spectrophotometer equipped with an acetylene burner. The analyses were carried out using a calcium light bulb (422.7 nm of wave length). Each sample was analysed eight times and the detection limit for calcium is 2 ppm. The reference dissolutions applied for all experiments were prepared using a standard dissolution of 1000 ppm (Panreac). IIB. Calibration lines Atomic Absorption Spectrometry (AAS) is a method requiring frequent re-calibration during operation procedures and for the sake of simplicity you will not be asked to perform the tedious task of finding a new calibration expression every 10 measurements. The final results for each of the 3 experiments are included in the Appendix: Data section. III – INTEGRATION OF RESULTS TASK 3 – Build tables with the averaged results of mM concentrations of calcium, sulphate and phosphate for the 3 repeated experiments, including the standard deviation. TASK 4 – plot your results in a graph of concentration versus time and include error bars in your data points. TASK 5 – plot your pH measurements vs time. IV – INTERPRETATION AND FOLLOW UP TASK 6 – explain the variation of concentrations as a function of time in the experiments. TASK 7 – as the experiments proceeded, gypsum grains were also sampled and imaged with the aid of a Scanning Electron Microscope (Figure 3). The micrographs reveal a progressive coating of gypsum by newly formed crystals. In your opinion, what would be the next analytical steps to be pursued? Figure 3. Coating of tabular crystals overgrowing a gypsum grain, ~10 hours into the experiment. APPENDIX: DATA Experiment B Experiment A 1. Chromatographic results for phosphate Sample P6-A1 P6-A2 P6-A3 U6-A1 U6-A2 U6-A3 U6-A4 U6-A5 U6-A6 U6-A7 U6-A8 Sample P6-B1 P6-B2 P6-B3 U6-B1 U6-B2 U6-B3 U6-B4 U6-B5 U6-B6 U6-B7 U6-B8 Time (h) 2 4 6 8 10 12 24 36 48 60 72 Time (h) 2 4 6 8 10 12 24 36 48 60 72 Dilution 98.59 99.78 100.42 99.63 99.94 99.05 95.91 100.41 96.75 97.93 97.42 Dilution 100.09 100.48 100.07 100.06 100.25 97.94 96.98 98.63 97.67 99.78 97.46 1 179.375 155.228 55.3493 167.292 166.444 168.109 173.767 161.428 169.279 170.23 168.392 Peak areas 2 180.409 168.873 160.995 167.063 166.631 168.678 174.311 164.881 169.52 168.66 169.294 3 181.727 164.889 162.436 167.607 167.194 168.925 173.734 164.953 170.306 169.024 168.976 Average 180.504 166.881 161.716 mM 66.586 62.635 61.222 STD 1.179 2.817 1.019 1 162.317 154.455 158.453 167.793 168.15 171.916 174.649 171.783 170.994 168.193 173.135 Peak areas 2 169.259 164.506 160.37 167.63 169.492 172.498 174.795 171.891 171.491 167.693 173.951 3 168.961 165.17 161.868 167.864 170.017 172.433 175.102 171.183 171.976 169.052 174.184 Average 169.110 164.838 160.230 mM 63.610 62.356 60.489 STD 0.211 0.470 1.712 Experiment C Sample P6-C1 P6-C2 P6-C3 U6-C1 U6-C2 U6-C3 U6-C4 U6-C5 U6-C6 U6-C7 U6-C8 Time (h) 2 4 6 8 10 12 24 36 48 60 72 Dilution 96.33 100.07 99.33 97.73 99.3 100.34 97.96 100.21 98.93 97.17 97.69 1 193.526 162.538 174.18 172.895 170.75 165.649 170.673 167.641 169.647 173.668 172.164 Peak areas 2 190.926 174.462 170.41 172.677 170.813 166.701 171.28 167.58 170.87 174.449 172.566 3 187.894 172.311 162.219 172.406 171.453 166.791 170.652 166.694 170.642 174.491 171.04 Average 190.782 169.770 168.936 mM 68.523 63.828 63.067 Experiment B Experiment A 2. Chromatographic results for sulphate Sample S6-A1 S6-A2 S6-A3 U6-A1 U6-A2 U6-A3 U6-A4 U6-A5 U6-A6 U6-A7 U6-A8 Sample S6-B1 S6-B2 S6-B3 U6-B1 U6-B2 U6-B3 U6-B4 U6-B5 U6-B6 U6-B7 U6-B8 Time (h) 2 4 6 8 10 12 24 36 48 60 72 Time (h) 2 4 6 8 10 12 24 36 48 60 72 Dilution 20.21 19.8 19.95 99.63 99.94 99.05 95.91 100.41 96.75 97.93 97.42 Dilution 19.95 19.9 19.93 100.06 100.25 97.94 96.98 98.63 97.67 99.78 97.46 1 281.149 638.07 821.308 129.049 143.836 156.579 199.932 197.523 205.054 207.104 205.449 Peak areas 2 281.5 638.493 822.034 129.338 144.105 156.781 200.035 198.061 205.107 206.791 205.821 3 281.747 639.07 823.04 129.349 144.366 157.031 200.048 198.57 205.378 207.312 205.806 Average 281.465 638.544 822.127 mM 7.174 15.198 19.545 STD 0.301 0.502 0.870 1 482.986 684.922 818.39 147.532 162.499 177.197 206.857 207.325 208.192 205.289 210.639 Peak Areas 2 485.712 685.514 821.578 147.928 162.997 177.604 206.971 206.79 208.819 205.528 210.959 3 486.466 686.328 823.942 147.675 163.176 177.593 207.125 207.027 208.728 205.625 211.336 Average 485.055 685.588 821.303 mM 11.775 16.356 19.506 STD 1.831 0.706 2.786 STD 2.819 1.521 2.666 Experiment C Sample S6-C1 S6-C2 S6-C3 U6-C1 U6-C2 U6-C3 U6-C4 U6-C5 U6-C6 U6-C7 U6-C8 Time (h) 2 4 6 8 10 12 24 36 48 60 72 Dilution 19.91 20.03 19.98 97.73 99.3 100.34 97.96 100.21 98.93 97.17 97.69 1 231.086 403.425 575.428 163.278 174.149 179.066 202.986 202.663 207.439 211.602 209.022 Peak areas 2 231.587 404.035 575.708 163.329 174.464 179.296 203.374 202.958 207.759 212.106 209.55 3 231.888 404 576.755 163.468 174.192 179.348 203.264 202.429 207.61 211.97 209.295 Average 231.520 403.820 575.964 Experiment B Experiment A 3. Results for calcium concentrations Sample A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 Sample B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 t (h) 2 4 6 8 10 12 24 36 48 60 72 t (h) 2 4 6 8 10 12 24 36 48 60 72 Average (mM) Std (mM) 2.93 0.34 5.51 0.30 8.54 0.44 11.29 1.65 12.72 2.01 11.68 2.15 16.53 2.25 16.56 2.07 16.54 2.10 17.08 2.07 16.80 2.29 Average (mM) 4.38 6.70 8.51 12.35 14.81 14.42 16.95 17.26 17.45 17.84 18.19 Std (mM) 0.42 0.15 0.25 1.21 1.36 0.94 1.12 1.14 1.36 1.46 1.43 mM 5.918 9.942 13.891 STD 0.405 0.343 0.699 Experiment C Sample C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 t (h) 2 4 6 8 10 12 24 36 48 60 72 Average (mM) 2.27 3.62 4.92 7.19 8.72 9.12 14.02 18.13 22.27 26.43 30.54 Std (mM) 1.99 3.29 4.24 5.61 6.82 7.19 11.72 17.45 23.69 30.20 36.87 4. Evolution of pH Time (h) 2 4 6 8 10 12 24 36 48 60 72 pH 5.95 5.69 5.39 5.07 4.78 4.64 4.35 4.32 4.31 4.30 4.31 References: Harvey, D. (2000) Modern Analytical Chemistry, McGraw Hill, 795pp. LABORATORY METHODS – PRACTICAL ASSIGNEMENT INTERACTION BETWEEN GYPSUM AND A P-BEARING AQUEOUS SOLUTION INSTRUCTIONS: Please follow the guidelines described in the tasks. Your assignment should be delivered in hardcopy, including your name, student ID number and the answers clearly listed by task. Failure to comply with communicated deadlines will involve a -10% per delayed day penalty on assignment mark. Experimental device The followed experimental procedures consisted on the immersion of fragments of exfoliation of natural gypsum in 100 ml of a 75 mM phosphoric acid (H3PO4) aqueous solution, previously neutralized with sodium hydroxide (NaOH) until the desired initial pH value of 6 was attained. The experiments took place inside polypropylene batches, closed with Parafilm film in order to avoid dissolution evaporation, and were maintained at constant temperature of 25 ± 0.1 ºC and 1 atm of pressure. The dissolutions remained at constant 25 rpm stirring during the experiments, using floating stirrers covered with Teflon. Figure 1 shows a schematic representation of the used experimental device. These experiments were designed to study the evolution of the aqueous solution chemistry during the interaction process. In this case, the grain sizes were selected to have diameters ranging from 1.0 to 1.5 mm. The duration of these experiments was of 72 hours, and dissolution samples were collected at 2, 4, 6, 8, 10, 12, 24, 36, 48, 60, 72 hours of elapsed time after inserting the gypsum grains in the reaction batch. Finally, each experiment was repeated three times in order to examine the reproducibility of the process. 100 ml of H3PO4 at 75 mM Figure 1. Experimental device used for interaction experiments. I – ANION CONCENTRATIONS IA. Analytical methods The measure of total phosphate and sulphate concentrations in the aqueous dissolution was carried out by means of ionic chromatography, using a Metrohm Advanced Compact 861 IC chromatographer. Samples collected during the experimental st age were diluted and compared with six reference dissolutions with different concentrations. These dissolutions were prepared using standard dissolutions of Na2SO4 and KHPO4, both having 1000 ± 2 ppm (Panreac) concentration. An anion column (6.1006.520 Metrostep A SUPP 5 – 150) was used and the applied eluent was a dissolution of 15 mM of NaOH and 2.0 mM Na2CO3, with a flux velocity of 1.0 ml/ min. and 5 MPa of pressure. The suppressor consisted of a solution with 100 mM of H2SO4. IB. Calibration lines In ion chromatography, aqueous concentrations are measured in a chromatogram of retention time versus detector response (Figure 2). In this graphical representation, the retention time enables the identification of the component in question, while its concentration is proportional to the corresponding peak’s area. For more information on ion chromatography, please consult Harvey, 2000. Figure 2. Schematical representation of a typical chromatogram (CHROMacademy.com). In the present case, we intend to measure sulphate and phosphate concentrations, and the results obtained from standard solutions are presented in table 1. Table 1 – Obtained chromatographic retention peak areas for standard phosphate and sulphate aqueous solutions. Phosphate (ppm) 10.2250 20.1456 40.0920 60.0871 79.7783 99.9175 Sulphate (ppm) 10.2723 19.9471 40.0898 60.0498 80.4411 99.4190 Run 1 24.3419 49.6771 105.6500 167.8710 232.9210 301.2880 Run 1 76.2839 148.6670 319.1340 501.0630 688.3830 865.2370 Peak Area Run 2 24.2887 49.4130 106.0560 168.0300 232.6120 301.7820 Run 2 75.4431 149.0850 319.7000 501.9080 688.9800 863.6050 Run 3 24.1368 49.6346 106.4140 168.2220 232.9320 302.0426 Run 3 76.0087 149.4590 320.2160 501.1660 690.7540 863.2410 TASK 1: Using the average value for the obtained areas, plot the results versus the concentrations of each standard solution and extract the corresponding trendline equations for sulphate and phosphate calibrations. What is the precision (in % of the mean) of the method in both cases? Don’t forget to present the calculations. IC. Batch experiment results – phosphate and sulphate concentrations TASK 2: in the Appendix: Data you may find the measured chromatographic results, regarding the evolution of sulphate and phosphate concentrations as a function of time, for the 3 replicated experiments. Determine the missing concentrations in mM ( 103mol/ L) applying the expressions of the calibration lines. For each experiment present the precision as % of the average areas. II – CALCIUM CONCENTRATIONS IIA. Analytical methods The concentrations of total calcium in dissolution were measured with a PYE-UNICAM SP9 atomic absorption/ emission spectrophotometer equipped with an acetylene burner. The analyses were carried out using a calcium light bulb (422.7 nm of wave length). Each sample was analysed eight times and the detection limit for calcium is 2 ppm. The reference dissolutions applied for all experiments were prepared using a standard dissolution of 1000 ppm (Panreac). IIB. Calibration lines Atomic Absorption Spectrometry (AAS) is a method requiring frequent re-calibration during operation procedures and for the sake of simplicity you will not be asked to perform the tedious task of finding a new calibration expression every 10 measurements. The final results for each of the 3 experiments are included in the Appendix: Data section. III – INTEGRATION OF RESULTS TASK 3 – Build tables with the averaged results of mM concentrations of calcium, sulphate and phosphate for the 3 repeated experiments, including the standard deviation. TASK 4 – plot your results in a graph of concentration versus time and include error bars in your data points. TASK 5 – plot your pH measurements vs time. IV – INTERPRETATION AND FOLLOW UP TASK 6 – explain the variation of concentrations as a function of time in the experiments. TASK 7 – as the experiments proceeded, gypsum grains were also sampled and imaged with the aid of a Scanning Electron Microscope (Figure 3). The micrographs reveal a progressive coating of gypsum by newly formed crystals. In your opinion, what would be the next analytical steps to be pursued? Figure 3. Coating of tabular crystals overgrowing a gypsum grain, ~10 hours into the experiment. APPENDIX: DATA Experiment B Experiment A 1. Chromatographic results for phosphate Sample P6-A1 P6-A2 P6-A3 U6-A1 U6-A2 U6-A3 U6-A4 U6-A5 U6-A6 U6-A7 U6-A8 Sample P6-B1 P6-B2 P6-B3 U6-B1 U6-B2 U6-B3 U6-B4 U6-B5 U6-B6 U6-B7 U6-B8 Time (h) 2 4 6 8 10 12 24 36 48 60 72 Time (h) 2 4 6 8 10 12 24 36 48 60 72 Dilution 98.59 99.78 100.42 99.63 99.94 99.05 95.91 100.41 96.75 97.93 97.42 Dilution 100.09 100.48 100.07 100.06 100.25 97.94 96.98 98.63 97.67 99.78 97.46 1 179.375 155.228 55.3493 167.292 166.444 168.109 173.767 161.428 169.279 170.23 168.392 Peak areas 2 180.409 168.873 160.995 167.063 166.631 168.678 174.311 164.881 169.52 168.66 169.294 3 181.727 164.889 162.436 167.607 167.194 168.925 173.734 164.953 170.306 169.024 168.976 Average 180.504 166.881 161.716 mM 66.586 62.635 61.222 STD 1.179 2.817 1.019 1 162.317 154.455 158.453 167.793 168.15 171.916 174.649 171.783 170.994 168.193 173.135 Peak areas 2 169.259 164.506 160.37 167.63 169.492 172.498 174.795 171.891 171.491 167.693 173.951 3 168.961 165.17 161.868 167.864 170.017 172.433 175.102 171.183 171.976 169.052 174.184 Average 169.110 164.838 160.230 mM 63.610 62.356 60.489 STD 0.211 0.470 1.712 Experiment C Sample P6-C1 P6-C2 P6-C3 U6-C1 U6-C2 U6-C3 U6-C4 U6-C5 U6-C6 U6-C7 U6-C8 Time (h) 2 4 6 8 10 12 24 36 48 60 72 Dilution 96.33 100.07 99.33 97.73 99.3 100.34 97.96 100.21 98.93 97.17 97.69 1 193.526 162.538 174.18 172.895 170.75 165.649 170.673 167.641 169.647 173.668 172.164 Peak areas 2 190.926 174.462 170.41 172.677 170.813 166.701 171.28 167.58 170.87 174.449 172.566 3 187.894 172.311 162.219 172.406 171.453 166.791 170.652 166.694 170.642 174.491 171.04 Average 190.782 169.770 168.936 mM 68.523 63.828 63.067 Experiment B Experiment A 2. Chromatographic results for sulphate Sample S6-A1 S6-A2 S6-A3 U6-A1 U6-A2 U6-A3 U6-A4 U6-A5 U6-A6 U6-A7 U6-A8 Sample S6-B1 S6-B2 S6-B3 U6-B1 U6-B2 U6-B3 U6-B4 U6-B5 U6-B6 U6-B7 U6-B8 Time (h) 2 4 6 8 10 12 24 36 48 60 72 Time (h) 2 4 6 8 10 12 24 36 48 60 72 Dilution 20.21 19.8 19.95 99.63 99.94 99.05 95.91 100.41 96.75 97.93 97.42 Dilution 19.95 19.9 19.93 100.06 100.25 97.94 96.98 98.63 97.67 99.78 97.46 1 281.149 638.07 821.308 129.049 143.836 156.579 199.932 197.523 205.054 207.104 205.449 Peak areas 2 281.5 638.493 822.034 129.338 144.105 156.781 200.035 198.061 205.107 206.791 205.821 3 281.747 639.07 823.04 129.349 144.366 157.031 200.048 198.57 205.378 207.312 205.806 Average mM STD 281.465 7.174 0.301 638.544 15.198 0.502 822.127 19.545 0.870 1 482.986 684.922 818.39 147.532 162.499 177.197 206.857 207.325 208.192 205.289 210.639 Peak Areas 2 485.712 685.514 821.578 147.928 162.997 177.604 206.971 206.79 208.819 205.528 210.959 3 486.466 686.328 823.942 147.675 163.176 177.593 207.125 207.027 208.728 205.625 211.336 Average mM STD 485.055 11.775 1.831 685.588 16.356 0.706 821.303 19.506 2.786 STD 2.819 1.521 2.666 Experiment C Sample S6-C1 S6-C2 S6-C3 U6-C1 U6-C2 U6-C3 U6-C4 U6-C5 U6-C6 U6-C7 U6-C8 Time (h) 2 4 6 8 10 12 24 36 48 60 72 Dilution 19.91 20.03 19.98 97.73 99.3 100.34 97.96 100.21 98.93 97.17 97.69 1 231.086 403.425 575.428 163.278 174.149 179.066 202.986 202.663 207.439 211.602 209.022 Peak areas 2 231.587 404.035 575.708 163.329 174.464 179.296 203.374 202.958 207.759 212.106 209.55 3 231.888 404 576.755 163.468 174.192 179.348 203.264 202.429 207.61 211.97 209.295 Average mM STD 231.520 5.918 0.405 403.820 9.942 0.343 575.964 13.891 0.699 Experiment B Experiment A 3. Results for calcium concentrations Sample A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 Sample B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 t (h) 2 4 6 8 10 12 24 36 48 60 72 t (h) 2 4 6 8 10 12 24 36 48 60 72 Average (mM) Std (mM) 2.93 0.34 5.51 0.30 8.54 0.44 11.29 1.65 12.72 2.01 11.68 2.15 16.53 2.25 16.56 2.07 16.54 2.10 17.08 2.07 16.80 2.29 Average (mM) 4.38 6.70 8.51 12.35 14.81 14.42 16.95 17.26 17.45 17.84 18.19 Std (mM) 0.42 0.15 0.25 1.21 1.36 0.94 1.12 1.14 1.36 1.46 1.43 Experiment C Sample C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 t (h) 2 4 6 8 10 12 24 36 48 60 72 Average (mM) 2.27 3.62 4.92 7.19 8.72 9.12 14.02 18.13 22.27 26.43 30.54 Std (mM) 1.99 3.29 4.24 5.61 6.82 7.19 11.72 17.45 23.69 30.20 36.87 4. Evolution of pH Time (h) 2 4 6 8 10 12 24 36 48 60 72 pH 5.95 5.69 5.39 5.07 4.78 4.64 4.35 4.32 4.31 4.30 4.31 References: Harvey, D. (2000) Modern Analytical Chemistry, McGraw Hill, 795pp. Lab Methods Practical Assignment Research Question: How does gypsum (CaSO4.2H2O) interact with aqueous phosphate? Experimental device - Repeated 3x - Total duration of 72 h (Check hand out for sampling times) - pH initial =6 PO43- 100 ml of H3PO4 at 75 mM Ca2+ SO42- - Analytical techniques: - IC and AAS (for liquid) - SEM-EDS XRD (for solids) Gypsum 2g; 1.0
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