SCI SINTERING 56 04 2024 07 Supplementarypdf
SCI SINTERING 56 04 2024 07 Supplementarypdf
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  1. Science of Sintering, 56 (2024) 485-503________________________________________________________________________ _____________________________ *) Corresponding author:m.bugarcic@itnms.ac.rs https://doi.org/10.2298/SOS231107063B UDK: 66.081; 628.4.043 Phyllosilicate-Based Adsorbents Decorated with Iron Oxyhydroxides: Application for Lead, Chromates and Selenites Removal Mladen Bugarčić1*), Zlate Veličković2, Željko Radovanović3, Milena Milošević4, Slavko Mijatov5, Jovica Stojanović1, Aleksandar Marinković61Institute for Technology of Nuclear and Other Mineral Raw Materials, 86 Bulevar Franše d’Eperea Street, 11000 Belgrade, Serbia 2University of Defence in Belgrade, Military Academy, 33 Pavla Jurišića Šturma, Belgrade, 11000, Serbia 3Innovation Center of the Faculty of Technology and Metallurgy Ltd, 4 Karnegijeva, Belgrade, 11000, Serbia 4University of Belgrade - Institute of Chemistry, Technology and Metallurgy - National institute of the Republic of Serbia, Department of Ecology and Technoeconomics, 12 Njegoševa, 11001 Belgrade, Serbia5Military Technical Institute, 1 Ratka Resanovića, Belgrade 11000, Serbia6University of Belgrade, Faculty of Technology and Metallurgy, 4 Karnegijeva, Belgrade 11060, SerbiaSupplementary material S2. Experimental section S2.1. Materials List of substance used in experiments: •Iron(II) sulfate heptahydrate (Laphoma Skopje, p.a.) •Iron(III) nitrate nonahydrate (Fisher Scientific Loughborough, p.a.) •Hydrogen peroxide (Fisher Scientific Loughborough ,30 wt% p.a.) •Hydrofluoric acid (Merck Darmstadt, 40 wt% p.a.) •Hydrochloric acid (Zorka Šabac, 37 wt% p.a.)•Sulfuric acid (NPK engineering Belgrade, 95 wt% p.a.) •Tetraethyl orthosilicate (TEOS) (Merck Darmstadt, 98 wt% chemical grade) •Toluene (Sigma Aldrich, 99.9 vol% high performance liquid chromatography (HPLC) purity) •Ethanol (Sani-Hem Novi Bečej, 96 vol%)•Sodium hydrogencarbonate (Laphoma Skopje, p.a.) •Sodium hydroxide (Centrohem Belgrade, 98 wt%) •Potassium hydroxide (Merck Darmstadt, p.a.) •Potassium nitrate (Alkaloid Skopje, p.a.) •Nitric acid (Zorka Šabac, 63 wt%)•Xylene (Zorka Šabac, 90 vol%)
  2. ___________________________________________________________________________2 •Ammonium chloride (Zdravlje Leskovac 99.8 wt% p.a.) •Sodium chloride (Moss Hemoss Belgrade, p.a.) •Lead(II) nitrate (Merck Darmstadt, 99.999 wt%) •Potassium chromate (Centrohem Belgrade, 99.9998 wt%) •Selenous acid (British Drug Laboratory Pool, p.a.) •Deionized water (DW), (18 MΩ cm)•Spectra/Por® Biotech Dialysis Membrane Tubing Regenerated Cellulose (RC) MWCO 3500 S2.2. Samples preparation S2.2.1. Activation of the EVer sample Activation of the EVer sample was performed according to the methodology found in work of Suquet et al.[1] with a few changes in procedure. A sample of EVer weighing 25.0 g and having a particle size in the range from 0.2 mm to 0.5 mm was used. Hydrochloric acid (C= 1.0 mol dm-3, V=250.0 cm3) was employed for the activation. In a three necked flask (V=500 cm3) equipped with Allihn condenser, thermometer, dropping funnel and magnetic stirrer was added EVer sample. Acid is introduced for 5 min and the mixture is heated until it reaches 83 oC, it was continuously stirred for the two hours. After the activation the reaction mixture was cooled to room temperature. (25 oC). The flask contents were filtered using a Buchner funnel and then thoroughly rinsed with DW until negative reaction on chloride ions, thus obtained sample is named as EVera. Following acid activation, 10 g of EVera were modified withvarying amounts of TEOS in absolute toluene (100 cm3). The optimal procedure was determined to be 7.5 % (v/v) TEOS in relation to the inserted hydroxyl group. After 10 hours of silanization on 75 oC, 96 vol% ethanol (7.5 cm3) was added dropwise to the reaction mixture. After cooling, the product was filtered, washed with toluene and ethanol, and dried for 6 hours under vacuum at 50 oC/2000 Pa. Obtained raw sample was named as EVa-25 and larger part of it is sintered on 550 oC for 4 hours on air (sample named as EVa). S2.2.2. Deposition of goethite on the surface of EVa (α-FeO(OH)/EVa) (EV-A)The goethite has been deposited in three successive steps. The overall mass of the reagents used to synthesize goethite was calculated to obtain final goethite deposit ~ 10 wt% in relation to EVa. The EVa sample was etched twice before deposition: •I step using solution of peroxysulfuric acid (ω=1.5 wt%) m(EVa):m(H2SO5)=50 g kg-1 for 15 minutes of gentle stirring (up to 50 rpm) •II step using solution of hydrofluoric acid (ω=3.0 wt%) m(EVa):V(HF(aq))=50 g dm-3for 30 minutes of gentle stirring (up to 50 rpm) After etching, the sample was thoroughly rinsed with DW until negative reaction on fluoride ions, and dried on 80 oC for 3 hours. Concept for preparation of goethite can be found in work of Schwertman and Cornell procedure [2] modified in a few details. In order to obtain EV-A sample 5.0 g of EVa is placed into three-necked flask (V=100 cm3), equipped with condenser, inlet nitrogen tube and thermometer, together with 10 cm3 of xylene, 2 cm3 of nitrogen aerated water solution containing 0.33 g of FeSO4·7H2O and vacuumed (using water pump) for 15 minutes, and sonicated (Ultrasound (US) bath, Bandelin Sonorex RK 100, Germany) another 15 minutes. After that, 0.20 g of NaHCO3 dissolved in 2 cm3 of nitrogen-aerated water (n(FeSO4·7H2O):n(NaHCO3)=1:2) was added to flask providing inert atmosphere for 30 min. Stirring and air bubbling were continued for 48h while the color of material change from green-blue to ocherous. Obtained adsorbent is filtered and rinsed with DW and ethanol
  3. ___________________________________________________________________________3 until a negative reaction to sulfate ions. The procedure for deposition of goethite was repeated three times., and obtained material was stored wet. Drying of the wet EV-A sample was performed at 40 oC for 6 hours and used for characterization. Reactions (S1,2) can be shown as events that take place during the deposition of goethite. 4()+ 23()⟶()2()+24()+ 2()(S1) 4()2()+ 2()⟶ 4()()+ 22()(S2) S2.2.3. Deposition of amorphous iron oxyhydroxide (AIO) on the surface of EVa (Fe2O3·H2O/EVa) (EV-B)Procedure for preparation of 6-line ferrihydrite can be found in the book Iron Oxides in theLaboratory by Schwertman and Cornell [2] with few details changed as follow: In order to wet the base material, 5.0 g of EVa is first measured and put into a tube with 1.0 cm3 of DW. The sample is moistened similarly to the prior instance with the aid of an US bath (Bandelin Sonorex RK 100, Germany) and the application of vacuum. When the reaction mixture reached this temperature, 2.0 g of unhydrolyzed Fe(NO3)3·9H2O was added together with the already wet EVa sample and rapidly agitated for 1 minute in another glass with 10.0 cm3 of xylene and 4.0 cm3 of water. The reaction mixture was then placed into a furnace and preheated on 75 oC. Glass with the reagents are placed back in the oven for an additional 10 minutes after it the polymerization of iron(III) hydroxides is complete. The sample is then rapidly cooled by submerging the glass in cold water, centrifuged (3000 rpm for 3 minutes), the liquid phase is decanted, and the solid raw sample is put into a dialysis bag, where it is dialyzed for 5 days with three changes of water each day. After dialysis, the solid sample is rinsed with DW and ethanol before being dried for six hours at 60 oC. Equation (S3) presents the chemical formula for the synthesis of AIO from iron (III) nitrate. 2(3)3()+ 42()⟶23· 2()+ 63()( S3) S2.2.4. Comparative preparation of iron oxides/oxyhydroxide in two-phase non-miscible water-xylene system Sample of free-standing Goethite, without use of EVa carrier, was prepared in the same way as described in section S2.2.2. Deposition of goethite on the surface of EVa (α-FeO(OH)/EVa) (EV-A). Also, sample of AIO was prepared in the same way as described in section S2.2.3. Deposition of AIO on the surface of EVa (Fe2O3·0.5H2O/EVa) (EV-B) but without addition of EVa in the course of material synthesis. S2.3. Samples characterization In order to determine cation exchange capacity (CEC) mass concentrations of sodium, potassium, magnesium, calcium and iron were done for all samples [3]. Spectrophotometer used for cations determination was Perkin Elmer AAnalyst 300, United States of America. Point of zero charge (pHPZC) was determined by method described by Milonjić et al [4]. Structure and morphology of the EVer and its modifications were done using the Field Emission Scanning Electron Microscopy (MIRA3 TESCAN, Czech Republic) equipped with electron dispersive spectrometer (EDS) (Oxford Instruments XMax 50 mm2, United Kingdom), while determination of samples specific surface area (SSA) was done by Brunauer–Emmett–Teller (BET) methodology on Micrometrics ASAP 2020, United States of America in linear part of nitrogen BET adsorption isotherm on the temperature of nitrogen
  4. ___________________________________________________________________________4 boiling (p = patm). Before nitrogen adsorption all the samples were degassed on vacuum for a 10 h at 150 oC. Adsorption was done using nitrogen 99.9 vol. % purity. Diffractometer Philips PW-1710, Netherlands was used for XRD analysis – automated diffractometer using a Cu tube operated at 40 kV and 30 mA. The diffraction data were assembled in the 2θ Bragg angle range from 4 to 65°, counting for 1 s (qualitative identification) at every 0.02° step. The divergence and receiving slits were fixed at 1 and 0.1 mm, respectively. The Fourier Transformed Infra-Red spectroscopy (FTIR) was used to determine the surface functional groups in samples. The FTIR spectra of all samples were measured before and after adsorption. Thermo Fisher Scientific Nicolet IS-50, United States of America spectroscope was used for FTIR analysis. The analysis was done in ATR mode in the wavenumber range from 4000 to 400 cm-1 with the resolution of 4cm-1 in 32 scans. It is well known that pH value can significantly influence surface complex formation and type of interactions between chromate or selenite ions with adsorbent surface functionalities. For these reasons, adsorption experiments were performed at different pH value. Adsorption experiments were performed on 298 K mads:Vpoll = 8:60 g dm-3 with initial concentration of 50 mg dm-3 of each oxyanion (chromate and selenite). In experiments of chromate adsorption pH is set to: 2.00, 4.00, 6.64 and 8.50 while pH of selenite containing adsorbate was set to 4.74, 6.00, 8.00 and 10.00. S2.4. Adsorption experiments Batch adsorption studies Adsorption experiments are performed in two systems. First set is performed in a batch and second set performed in a fixed bed column (continuous system). Adsorption properties of the obtained adsorbents were checked towards three adsorbate species, two anion species (selenites and chromates) and one cation, i.e. lead (II) - ion. Adsorption in the batch was performed following template provided in Table SI. Tab. SI Adsorption experiments template. Experiment number Temperature / oC Time / min Adsorbent mass/ mg 1 25 90 10 2 25 90 7.5 3 25 90 5.0 4 25 90 2.5 5 35 90 10 6 35 90 7.5 7 35 90 5.0 8 35 90 2.5 9 45 90 10 10 45 90 7.5 11 45 90 5.0 12 45 90 2.5 13 25 5 1 14 25 15 1 15 25 30 1 16 25 90 1 17 35 5 1 18 35 15 1 19 35 30 1 20 35 90 1
  5. ___________________________________________________________________________5 21 45 5 1 22 45 15 1 23 45 30 1 24 45 90 1 The parameters that have been varied were contact time (from 5 to 90 min), adsorbent dosage (8:6 up to 8:60 g/L) and temperature (298, 308 and 318 K). The initial concentration of each toxic element Pb; Cr; Se was set to 9.8; 9.4 and 12.4 mg dm-3, respectively. Adsorption experiments were done in a batch system according to experimental plan given in Table SI. Constant temperature needed for each set of isothermal experiments was provided by water bath. All experiments were done in triplicate for attenuating the measurement uncertainty. According to solubility product of Pb(OH)2 [5], pH value at which the precipitation will occur at 45 μmol dm-3 is equal to 5.52. Similar calculation was performed for chromate and selenite, and accordingly selected operational pHi are given in Table SII (selected so that only adsorption contributes to pollutant removal). The pH values of the adsorbates were set by using diluted aqueous solutions of KOH and HNO3 (0.5 mol dm-3). Preparation of the initial heavy metal solutions (1000 mg dm-3) was done following the method Accu Standard 1000 ppm. Chromium, selenium and lead concentrations were measured by atomic absorption spectrometry method (AAS) using Perkin Elmer AAnalyst 300 spectrophotometer, produced in United States of America. Competitive adsorption of selenite and chromate ions were performed in order to define selectivity towards these anion species. Lead ions were not subject of competitive adsorption studies since it would co-precipitate with Cr (VI) species as well as selenite species. This study was performed on all adsorbents (EVa, EV-A, EV-B), initial concentration of chromium (as chromates) and selenium (as selenites) were set to 10.02 and 10.14 mg dm-3, respectively. Competitive adsorptions were also done according to Table SI template, with exception of experiments: 5-12 and 14-24. Adsorption properties of LDH-EV sample towards anion species (chromates, selenites and dye Acid Green 25(AG 25)) was performed in batch system according to experimental plan given in Table SI. The parameters that have been varied were contact time (from 5 to 90 min), adsorbent dosage (8:6 up to 8:60 g/L) and temperature (298, 308 and 318 K). The initial concentration of each pollutant Cr; Se and AG 25 were set to 10.01; 10.04 and 40.2 mg dm-3, respectively. Adsorption experiments were performed in the same batch system as EVa based adsorbents (7500 μl of adsorbate). Constant temperature needed for isothermal experiments was provided by water bath. All experiments were done in triplicate for attenuating the measurement uncertainty. Chromium and selenium concentration were measured by AAS method using Perkin Elmer AAnalyst 300 spectrophotometer produced in United States of America. Concentration of dye AG 25 during adsorption was measured by UV/Vis spectrophotometer Shimadzu 1800, Japan measuring absorption of the light in the wave length range from 200 to 800 nm on the filtered sample. However, concentrations were calculated by measuring absorbance on 643 nm via Beer-Lambert law equation. Tab. SII Initial pH value for each sorbate solution Heavy metal/s Adsorbate pH Pb2+5.02 H2SeO34.74 K2CrO46.64 H2SeO3, K2CrO43.03 The adsorption capacity was calculated using the following equation (S4):
  6. ___________________________________________________________________________6 =(− )× (S4) Where Ci and Ce (mg dm-3) are initial and equilibrium nickel ion concentration, respectively, M (g) is the mass of adsorbent and V (dm3) is the volume of the adsorbate solution. Estimation of the fitting goodness was performed according to following statistical criteria: R2– coefficient of determination and χ2- "chi-squared" test. Tab. S3 Adsorption model used for experimental data fitting in a batch experiments Equation Parameter Reference Isotherm models Langmuir =1 + qe (mg/g): sorption capacity at equilibrium qmax(mg/g): maximum sorption capacity KL(dm3/mg): Langmuir constant Ce(mg/dm3): equilibrium concentration [6] Freundlich = 1Kf(mg/g)(dm3/mg)1/n: Freundlich constant n: heterogeneity factor [7] Dubinin Radushkevich = −Ɛ2Ɛ = (1 +0) =1√2β (mol2/J2): constant related to sorption energy ε (J/mol): Polanyi potential R: universal gas constant T (K): thermodynamic temperature C0(mg/dm3): initial concentration E (J/mol): Adsorption energy [8] Kinetic modelsPseudo-first order (PFO) = (1 − −1)k1(min-1) the pseudo first order rate constant qe(mg/g): sorption capacity at equilibrium t (min), time qt(mg/g): sorption capacity at specific time [9] Pseudo-second order (PSO) =(122) + ()k2 (g/mg/min): the pseudo-second order rate constant qe(mg/g): sorption capacity at equilibrium[10] Weber – Morris (W-M)= 0.5+ Kid (mg/(min1/2g)): the intra-particle diffusion parameter C (mg/g): intercept [11]
  7. ___________________________________________________________________________7 Modified Freundlich = 1 ⁄kmf (mg/g(min)-1/m): the modified Freundlich diffusion parameter m: Kuo – Lotse paramter [12] Roginsky –Zeldovich –Elovich =( ∗ ∗ )a, b: constants [13] Intraparticular (Dunwald - Wagner) = √(1 − −)=22kDW (min-1): Dunwald –Wagner diffusion rate DDW(m2/min): Dunwald – Wagner coefficient of diffusion R (m): adsorbent particles radius or surface/volume radius [14] Bed column study In purpose to achieve optimal system packing samples was taped (p=0.2 MPa) and packed into glass column. The column was down flow design packed with EV-A (lead and chromates adsorption) and EV-B (selenite adsorption). Continuous adsorption is performed in the tubular column, diameter x height = 0.800×1.000 cm with a PTFE valve and sintered filter, with a layer of sand on the top of the column to prevent uneven distribution of flow. Before initializing adsorption, distilled water was passed over through the column to remove build-up impurities from the rig and then vacuumed to remove trapped air bubbles. The feed water was allowed to pass through the hybrid adsorbent bed using peristaltic pump IsmatecTM, United States of America. The total weight of the adsorbent in the column was 218 and 208 mg for EV-A and EV-B respectively, while the constant adsorbent bed depth was 2 cm, the temperature was set at 25 °C for all experiments. The initial adsorbate concentrations were C0= 2.45, 2.35 and 3.134 mg dm-3 for Pb2+, Cr (VI) and Se (IV), respectively adjusted to pH 4.0 and passed through the column at three different flow rate (Q=0.5, 1.0 and 1.5 cm3min-1). The metal concentrations in effluent were measured at predetermined time intervals by the AAS technique using Perkin Elmer AAnalyst 300, United States of America spectrophotometer. All above-mentioned parameters including an empty bed volume (EBV) were adjusted to obtain optimal empty bed contact time (EBCT). The breakthrough point (BP) was designated as the feed volume supplied to a column up to initial concentration of the pollutants. It was found that the maximum volume of the eluted solution that causes depletion of the column depending on the flow rate (0.5, 1.0 and 1.5 cm3 min-1) for Pb2+ is 8000, 7800 and 7600 cm3, Cr(VI) 9600, 9000 and 8600 cm3 and Se(IV) 10600, 10000 and 8700 cm3, respectively. Empty bed contact time (EBCT) is a measure of the time during which water to be treated is in contact with the treatment medium in a contact vessel, assuming that all liquid passes through the vessel at the same velocity. EBCT (equation S5) is equal to the volume of the empty bed volume (equation S6) divided by the flow rate (0.5, 1 and 1.5 cm3min-1). =(S5) =24ℎ(S6) Three different models i.e. Bohart-Adams, Yoon-Nelson and Thomas were used to compare adsorption isotherm parameters at the equilibrium (Table SIV).
  8. ___________________________________________________________________________8 Tab. SIV The linear forms of the fixed-bed adsorption models Model Linear equation Model parameters Bohart-Adams (0) = ⋅ 0⋅ − ⋅ 0⋅0ct(mol dm-3) concentration of effluent at time tkBA(dm3 mg-1min-1) kinetic constant N0 (mg dm-3) maximum pollutant uptake capacity per unit volume of the adsorbent columnz (cm) bed depth of column, U0(cm min-1) linear velocity of the influent metal solution, Yoon-Nelson (0− ) = ⋅ − ⋅ c0(mol dm-3) initial concentration of metal ct(mol dm-3) concentration of metal at time tt (min) flow time θ (min) time required for 50 % breakthrough KYN (min-1) Yoon-Nelson rate constant, (min-1) Thomas (0− 1) =⋅ ⋅ − ⋅ 0⋅ kT(cm3 min-1 mg-1) Thomas rate constant m (g) mass of the adsorbent Q (cm3 min-1) volumetric flow rate q (mg g-1) adsorption capacity at equilibrium Desorption of the pollutants from the fixed bed saturated column was performed with the same equipment as one used for continuous adsorption experiments. Desorption medium used for desorption was mixture of 0.5 mol dm-3 NaOH(aq) and 0.5 mol dm-3 NaCl(aq) for all pollutants desorption. Desorption experiments were performed on 298 K while flow rate solution was varied (0.5; 1.0 and 1.5 cm3 min-1).S3. Results and discussion S3.1. Chemical and physicochemical analysis From the Table SV, it can be seen that start material (EVer) chemical composition is in accordance with chemical composition of other vermiculite-based samples [15]. In the same table is also chemical composition of acid activated sample (EVa), and as it can be seen from the Table SV, EVa sample has significantly different content of Mg, Fe, Al, Ca, K and Na. Tab. SV Chemical composition of EV samples before (EVer) and after (EVa) acid activation Sample SiO2 wt. % Al2O3 wt. % CaO wt. % MgO wt. % Fe2O3 wt. % K2O wt. % Na2O wt. % TiO2 wt. % LOI wt. % EVer 43.68 7.79 7.67 22.41 7.22 4.07 0.086 0.334 6.73 EVa 40.08 8.86 4.17 27.06 8.14 4.48 0.046 1.16 6.61 1Loss of ignition Tab. SVI Chemical composition of spent liquor obtained after acid activation of Ever. Mass concentration K/g dm-3Na/ mg dm-3Mg/ g dm-3Ca/ g dm-3Fe/ g dm-3Al/ g dm-3Spent liquor solution 2.510 30.5 10.41 0.14 3.500 1.699
  9. ___________________________________________________________________________9 Fig. S1. pHPZC determination for EVa sample. Fig. S2. pHPZC determination for EV-A sample. Fig. S3. pHPZC determination for EV-B sample.
  10. ___________________________________________________________________________10Fig. S4. Speciation diagram for Pb2+, Cr(VI) and Se(IV) ion.
  11. ___________________________________________________________________________11S3.2. XRD analysis Fig. S5. Diffractogram of EVa-25 sample Fig. S6. Diffractogram of Goethite sample.
  12. ___________________________________________________________________________12Fig. S7. Diffractogram of AIO sample. S3.3. FTIR spectra analysis Interestingly in all spectra adsorbed chromate and selenite no significant spectral differences versus pH change was observed. Several mechanisms are possibly involved in overall process the corresponding vibrations of formed complexes/adsorbed species between iron oxyhydroxides surface and oxyanions. Consequently, deconvolution was performed (Figs. S8 and S9) to recognize specific bands related to species bonded in surface complexes. Based on deconvoluted spectra, Fig. S8, it can be seen that similar mechanism was operative for chromate adsorption onto goethite and AIO which include outer-sphere and inner-sphere mono- and bidentate complexes. At pH 4 the Cr–O stretching vibration was found at 906, 810, and 792 cm-1 for monodentate complexes and 955, 810, and 734 cm-1 for bidentate complexes formed at EV-A surface (Fig. S8) [16,17]. With pH increase slight shifting of these peaks and lower intensity was noticed due to decreased efficiency of mono- and bidentate complexes formation, which is in accordance with the previous study [16]. Similar results were observed in the EV-B/chromate spectra. In this region absorption due to surface complexes formation is overlapped with Me-O vibrations Si-O, Al-O, Mg-O) fromvermiculite base. In the case of selenite adsorption at pH 6 onto EV-A (Fig. S9) IR vibrations from the present Se-O bond in monodentate outer-sphere and inner-sphere complexes are observed at 892, 850, 806 and 721 cm-1, while bidentate ones are observed at 940, 765, 677 and 600 cm-1[17–20]. At higher pH, these bands are slightly shifted with observable intensity decrease. Similar bands structure and pH-dependent change, as for selenite/EV-A, were noticed inspectra for selenite/EV-B.
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