Factors Governing the Performance of Bauxite for Fluoride Remediation of Groundwater

Transcription

1 SUPPORTING INFORMATION Factors Governing the Performance of Bauxite for Fluoride Remediation of Groundwater Katya Cherukumilli *,, Caroline Delaire, Susan Amrose, Ashok J. Gadgil,Ψ Department of Civil and Environmental Engineering, University of California, Berkeley, California , United States Ψ Energy Technologies Area, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States *Corresponding Author: Department of Civil and Environmental Engineering, University of California, Berkeley, California , United States. Phone: ; Address: 410 O Brien Hall, Berkeley, CA Number of Pages: 7 Number of Tables: 2 Number of Figures: 4 S1

2 Contents 1. Bauxite Ore Pictures and SEM Images (Fig. S1) S3 2. Points of Zero Charge (ph PZC ) of Adsorbents (Fig. S2) S3 3. Detailed Experimental Summary (Table S1) S4 4. Solution Preparation (Table S2) S5 5. Determination of Min. Bauxite Dose to Reach WHO-MCL (Fig. S3) S6 6. XRD, BET, and FTIR Sample Preparation S6 7. Increase in Equilibrium ph due to Calcite Dissolution S6 8. Kinetics of Fluoride Removal (Fig. S4) S7 9. References S7 S2

3 1. Bauxite Ore Images A B C B Figure S1. Images of raw bauxite ores shown A) before ball milling, B) after ball milling, and C) at 8K magnification using a Scanning Electron Microscope (SEM). Sources of bauxite ores as presented from left to right in each panel : USA, Guinea, Ghana, and India. Zetapotential in DI (mv) 2. Points of Zero Charge (phpzc) of Adsorbents n 50 u 30 p AA India Bauxite Ghana Bauxite Guinea Bauxite USA Bauxite PZC ph Figure S2. The zetapotentials of all adsorbent materials used in this study were measured using a Malvern Zetasizer Nano ZSP, with a matrix containing deionized (DI) water and an adsorbent solid:volume ratio of 0.05mg/L to maintain a stable suspension of particles. The ph of the test solutions was adjusted approximately to ph 2, 4, 6, 8, and 12 using 1M HCl and 1M NaOH stock solutions. We present averages of points of zero charge (phpzc) and standard errors from duplicate experiments. S3

4 The differences in PZC cannot account for the lower performance of India bauxite in comparison to Ghana, Guinea, and USA bauxites (Fig. 1a). The measured PZC of India and Ghana bauxites (6.8 and 7.2) are higher than the PZC of Guinea and USA bauxites (5.0 and 5.3), indicating that bauxites from India and Ghana may have higher surface charge in our electrolytes, which should have a positive (if any) effect on fluoride adsorption, not a detrimental effect. 3. Detailed Experimental Summary Table S1. Detailed Summary of Experimental Conditions Used in This Study Goal of Experiments Electrolyte Composition Initial ph; ph held Constant? Adsorbent Used; Dose (g/l) # of Replicates Corresponding Figure Minimum Dose Sri Lankan Groundwater (Table S2) 2-11 g/l 2 1a, S2 Dissolved Al/Fe Measurements NaF (10 mg/l) NaCl (35 mm) HCO 3- (5 mm) DI Water (Binary-Solute matrix, Table S2) 10 g/l 2 - Adsorption Isotherms NaF ( mg/l) NaCl (1-6 mm) MES (50 mm) HCO 3- (5 mm) 6, Yes 4/L 2 2a Adsorption Envelopes NaF (10 mg/l) NaCl ( mm) Varying Buffers HCO 3- (5 mm) 4-8, Yes 6/L 2 2b Equilibrium ph NaCl (35 mm) - 1 g/l 2 Table1 Calcium and Carbonate Measurements No 4 g/l 2 Table 1 FTIR NaF (100 & 500 mg/l) - Guinea bauxite 2 g/l 2 3a Effect of Ionic Strength Cost Calculations NaF (10 mg/l) NaCl (1-100 mm) HCO 3 - (5 mm) Synthetic and Real groundwater matrices (Table S2) Guinea bauxite 10 g/l Guinea bauxite & AA; 2-11 g/l 3 3b 2 4, S3 Kinetics Sri Lankan Groundwater (Table S2) Guinea bauxite & AA; 10 g/l & 4 g/l 2 S4 S4

5 4. Solution Preparation. Recipes for synthetic Ghana, Sri Lanka, and Tanzania groundwater matrices are shown in Table S2. These groundwater matrices were developed based on British Geologic Survey (BGS) 1 measurements and prepared using stock solutions of 100 mm CaCl 2, 100 mm MgCl 2, 200 mm NaHCO 3, 100 mm Na 2 SO 4, 10 mm SiO 2 (Na 2 SiO 3-5H 2 O), and 10 mm NaNO 3. Intial fluoride concentrations of all lab-synthesized groundwaters were set to 10 mg F - /L using a stock solution of 100 mg/l NaF. Real groundwater samples from Telangana (Nalgonda District) and West Bengal (South Dinjapur District), India, were collected after flushing the tubewells for several minutes and stored in sealed plastic bottles until later characterization. Initial ph of all tested waters was set to 6 (± 0.1) by addition of drops of 1M HCl or 1M NaOH, as necessary. Concentrations of ions (e.g., Fe, Ca, Mg, Si, and P) were characterized in real groundwater samples using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) following US-EPA Method Reported error for ICP-AES is ±10%. Table S2. Chemical Composition of Synthetic and Real Groundwater Matrices Used in This Study a Component Synthethic Groundwater Real Groundwater b (mg/l) Binary Solute Ghana Sri Lanka Tanzania West Bengal Telangana F ±.62 c 8.4 ± 0.8 Ca ± ± 2.0 Mg ± ± 3.5 Si ± ± HCO SO NO 3- as N NaCl Fe ± ± 0.01 P ± ± 0.01 (a) Values reported are gravimetric target concentrations or measured concentrations with errors (b) Dashes indicate that the ions were not expected or measured (c) Errors represent the larger of the standard deviation from repeated tests and ICP-AES measurement errors S5

6 5. Determination of Minimum Bauxite Dose to Reach Fluoride WHO-MCL. Figure S3 shows an example of the method used to calculate minimum doses of adsorbents required to reach the WHO-MCL. Equilibrium Fluoride Concentration (mg F - /L) Replicate 1 Replicate Adsorbent Dose (g/l) WHO-MCL (1.5 mg F - /L) Minimum Dose = 4g/L Figure S3. Replicate data on the fluoride removal performance of three different adsorbent doses are plotted and the x value for y = 1.5 (WHO-MCL) is determined using linear regression. 6. XRD, BET, and FTIR Sample Preparation. XRD patterns were collected using a coupled scan with 4 frames at 300 seconds/frame (θ1 & θ2 ranging from 10,10 to 40,40). XRD peaks for each bauxite sample (processed as g of dry powder) were integrated and merged using Diffrac Eva and the peaks were identified using the Jade software program. For BET surface area analysis, approximately g of bauxite powder was added to glass tubes, dried overnight in a vacuum at 100 C, and analyzed using nitrogen gas sorption. ATR-FTIR analysis was conducted by setting a force gauge to 60N to press 0.1 g of each dry powdered bauxite sample completely flat on a glass slide. 7. Increase in Equilibrium ph due to Calcite Dissolution. We estimated the increase in ph resulting from the dissolution of calcium carbonate observed in our experiments with India bauxite in 35 mm NaCl, assuming an open system with zero initial alkalinity. Since the open system has to S6

7 be electrically neutral, 2*[Ca 2+ ] + [H + ]= [OH - ]+ [HCO - 3 ]+ 2[CO 2-3 ]. Assuming [Ca 2+ ] = M (measured value), [OH - ]=10-14 /[H + ], [HCO - 3 ]= /[H + ], and [CO 2-3 ]= /[H + ] 2, we can calculate the value of [H + ] using a cubic function. We found that under these conditions, the dissolution of 334 µm of CaCO 3 is theoretically expected to increase the solution ph to 8.1, equal to our average measured value reported in Table Kinetics of Fluoride Removal Fluoride Concentration ( mg F - /L) Activated Alumina Guinea Bauxite Contact Time (hours) Figure S4. Fluoride concentration as a function of contact time for Activated Alumina and Guinea Bauxite (respective doses: 4 and 10 g/l) in synthetic Sri Lankan groundwater (Table S2). Doses used correspond to the minimum required doses to reduce initial fluoride concentrations of 10 mg/l to the WHO-MCL (1.5 mg/l) after 24 hours of contact time. We present averages and standard errors from duplicate experiments. 9. References 1. Edmunds, W.; Smedley, P.L. Chapter 12: Fluoride in Natural Waters. In Essentials of Medical Geology; Selinus, O., Ed.; Springer Netherlands: Dordrecht 2013; pp US EPA Clean Water Act Analytical Method 200.7: Determination of Metals and Trace Elements in Water and Wastes by Inductively Coupled Plasma-Atomic Emission Spectrometry; Rev S7