Trichloroethylene Degradation by Various Forms of Iron Activated

Article pubs.acs.org/IECR

Trichloroethylene Degradation by Various Forms of Iron Activated Persulfate Oxidation with or without the Assistance of Ascorbic Acid Ya-Ting Lin,† Chenju Liang,*,‡ and Chun-Wei Yu‡ †

Department of Environmental Engineering, Chung Yuan Christian University, 200 Chung Pei Road, Chung Li District, Taoyuan City 320, Taiwan ‡ Department of Environmental Engineering, National Chung Hsing University 250 Kuo-kuang Road, Taichung 402, Taiwan S Supporting Information *

ABSTRACT: The oxidation of trichloroethylene (TCE), by Fe2+ activated persulfate (PS) to generate the sulfate radical (SO4−•) is limited due to the scavenging of SO4−• by excess Fe2+. This study focused on evaluating the potential for TCE oxidative degradation by iron activated persulfate (IAP) (including soluble iron and solid iron minerals), with the assistance of ascorbic acid (AsA). AsA, a water-soluble twoproton donor, may act as a reductant and a chelator, which may reduce iron oxides or complex soluble iron for PS activation. The results indicated that PS oxidation and various types of iron (Fe2+, Fe3+, FeOOH, Fe2O3) activated PS are able to degrade TCE in the presence or absence of AsA and are dependent upon the PS concentrations applied. Furthermore, the TCE degradation could be accelerated in the iron minerals activated PS system with the assistance of AsA. In addition, synthesized iron minerals with higher specific surface area resulted in a higher PS activation efficiency (i.e., lower PS consumption) and exhibited a higher degree of TCE degradation than that observed in commercial iron minerals activated PS systems. Therefore, maintaining a suitable concentration of Fe2+ during the IAP process to avoid unnecessary SO 4 −• consumption, thereby enhancing oxidative efficiency toward target contaminants is critical. We note that reducing SO4−• scavenging by excess Fe2+ can be achieved by adding a chelating agent to regulate quantities of Fe2+ or, using different sources of Fe2+ such as iron minerals for effective PS activations. Several studies attempted to investigate the iron (e.g., dissolved iron or iron mineral) complex with citric acid (CA),9,10 ethylenediaminetetraacetic acid (EDTA),9−12 and sodium thiosulfate (Na2S2O3),7,10 as activators in the IAP system, to increase the rate and/or percentage of contaminant degradation. The use of chelating agents should (1) be effective in metal buffering (i.e., the maintenance of metal ions in either oxidized or reduced forms), (2) increase resistance to destruction by oxidation to a certain extent, and (3) pose low risk to the environment as a remedial additive. The abovementioned chelating agents may not be optimum choices as iron complex activators, for example, EDTA is an environmentally harmful and biodegradation resistant compound. Therefore, efforts are still needed to find the best chelating agents for use in the IAP process.

1. INTRODUCTION Trichloroethylene (TCE) has been widely used as a commercial and industrial degreasing agent. Historically, significant quantities of TCE have been released to the environment, resulting in extensive contamination of soils and groundwater. TCE has been found in at least 1045 of the 1699 National Priorities List sites regulated by the United States Environmental Protection Agency.1 Among current commonly used in situ chemical oxidation (ISCO) oxidants, the application of persulfate (PS) (S2O82−), with a redox potential of 2.01 V, has gained attention for the treatment of chlorinated solvents.2 One of mechanisms to increase PS reactivity is via transition metal (e.g., Fe2+) activation of PS (eq 1) to generate a stronger oxidant known as the sulfate radical (SO4−•) with Eo = 2.4 V vs NHE.3 Iron minerals such as zerovalent iron as a source of ferrous ion have been used for PS activation.4−6 It has been well reported that TCE could be rapidly degraded by the iron activated PS (IAP) process; however, there would be incomplete TCE destruction due to SO4−• scavenging by excess Fe2+ (eq 2), which exhibits a greater reaction rate constant.7,8 Fe2 + + S2 O82 − → Fe3 + + SO4 −• + SO4 2 − k = 2.0 × 101 M−1 s−1

(1) Received: Revised: Accepted: Published:

SO4 −• + Fe 2 + → Fe3 + + SO4 2 − k = 4.6 × 109 M−1 s−1 © 2016 American Chemical Society

(2) 2302

November 17, 2015 January 31, 2016 February 6, 2016 February 7, 2016 DOI: 10.1021/acs.iecr.5b04352 Ind. Eng. Chem. Res. 2016, 55, 2302−2308

Article

Industrial & Engineering Chemistry Research

solution. Thereafter, 3 M NaOH solution was slowly introduced into the mixed solution. The resulting solution was then calcined in a furnace (CF-66, CHUNG-CHUAN), in which the temperature was ramped from ambient 25 to 120 °C at a rate of 3 °C/min to remove any moisture, held for 24 h and allowed cool naturally. Goethite powder was collected and washed with RO water and ethanol for three cycles. The goethite was then dried at 50 °C for 24 h prior to storage in a desiccator. For the preparation of hematite, the dried goethite was mixed in ethanol solution, which was then calcined in a furnace with the temperature ramped from ambient 25 to 65 °C at a rate of 2 °C/min, and held for 2 h. Then, it was increased to 500 °C at a rate of 5 °C/min, held for 6 h, and allowed cool naturally. After the furnace was cooled to room temperature, hematite was collected and washed for three cycles as described earlier. The hematite was then dried at 50 °C for 24 h prior to storage in a desiccator. 2.3. Experimental Procedure. TCE solution was prepared at an initial concentration of 0.46 mM by adding the required amount of pure TCE to a 2 L borosilicate reservoir with no headspace and stirring overnight at 20 °C in a temperaturecontrolled chamber. Thereafter, a predetermined amount of PS was added to the reservoir and mixed for a few minutes to reach the designated PS concentrations (1, 10, and 100 mM). Before filling a series of 60 mL amber screw top PTFE/silicone septum glass reaction bottles (no headspace), the required amount of AsA powders (10 mM) and various forms of iron minerals were added into each 60 mL sample bottle as listed below: • 0.5 g of each iron mineral (i.e., commercial or synthetic FeOOH and Fe2O3) • 10 mM of Fe2+ (iron(II) sulfate) • 10 mM of Fe3+ (iron(III) sulfate) or • 10 g soil All reaction bottles were shaken continuously on an IKA HS 250 reciprocating shaker at 20 °C. Control tests without PS or AsA, or with various forms of iron minerals without PS, were also carried out in parallel. All experiments were performed in duplicate to ensure the reproducibility of experimental results. Average data was reported. 2.4. Analytical Methods. TCE in solution was extracted with n-heptane and the extract was analyzed using a gas chromatograph (GC, Agilent 7890A) with an Agilent J&W Scientific DB-624 column (60 m × 0.25 mm i.d.) and a mass spectrometer in electron impact mode (MS, Agilent 5975C) in accordance with the method for analyzing volatile organic compounds in aqueous phase established by the Taiwan National Institute of Environmental Analysis (Method W785.54B). For analysis of AsA, aqueous samples were filtered using a polytetrafluorethylene filter (0.2 μm) placed within a stainless syringe holder (Advantec, KS-13) and then measured using a high-performance liquid chromatograph (HPLC, Agilent 1100) equipped with UV detector (210 nm) and a Agilent Zorbax Sb-Aq column. The mobile phase was 20 mM phosphate salt solution/acetonitrile (99/1, v/v) at a flow rate of 1.0 mL/min and the effluent was monitored by the UV detector at a wavelength of 210 nm. The concentration of phenol was determined by HPLC/UV at a wavelength of 254 nm, using an Agilent Model Eclipse XDB-C18 column. The mobile phase was methanol/water (60/40, v/v) at a flow rate of 0.8 mL/min. The concentration of NB was also determined in accordance with the procedure for phenol analysis with the

Vitamin C (a.k.a. ascorbic acid (AsA), C6H8O6) is a wellknown essential nutrient for humans and also a natural antioxidant. AsA is a bidentate ligand with a bifunctional enediol group built into a heterocyclic lactone ring, which could coordinate metal ions to form chelates.13,14 It is also a twoelectron reductant that will reduce high oxidation states of metals15−17 and organic compounds.18−21 Sun and Pignatello22 investigated complexing Fe3+ with different organic ligands for catalytic hydrogen peroxide (H2O2) oxidization of 2,4-D herbicide. Their results showed the successful use of organic ligands (such as AsA) complexed with Fe3+ as a catalyst assisting transformation and mineralization of 2,4-D by H2O2. Moreover, when the pH is greater than the pKa2 (11.79) of AsA, dissociated dianionic AsA could readily release two electrons for the transformation of each chlorinated solvent molecule such as carbon tetrachloride (CT).18,21 Also, the reduction rate of CT by alkaline AsA could be enhanced in the presence of iron minerals (e.g., Fe2O3, Fe3O4, FeS2, FeOOH) via three mechanisms: dissolution by acid, detachment of Fe3+ by adsorbed AsA, and Fe3+ reduction by AsA.18 In order to reduce SO4−• scavenging by excess Fe2+ (an activator for PS) in the IAP process, this research evaluated the degradation of TCE by the IAP process with AsA mediating various forms of iron complexes as activators. To explore the treatment performance, this study experimentally tested the feasibility of these IAP oxidation systems with the goal of understanding (1) the effect of various forms of iron activators including Fe2+, Fe3+, and the commercial iron minerals (FeOOH, and Fe2O3) and (2) the effect of the synthetic forms of the iron minerals (FeOOH and Fe2O3) on PS activation.

2. EXPERIMENTAL METHODS 2.1. Chemicals and Materials. Trichloroethylene (C2HCl3, ≥99.5%) and iron(III) sulfate hydrate (Fe2O12S3, >76.0%) were obtained from Fluka. Sodium persulfate (Na2S2O8, PS, >99.0%) and nitrobenzene (C6H5NO2, NB, ≥99.0%) were obtained from Merck. L-Ascorbic acid (C6H8O6, 99.7−100.5%), sodium hydroxide (NaOH, ≥99.0%), and goethite (FeOOH, ∼35.0% Fe) were obtained from SigmaAldrich. Iron(II) sulfate heptahydrate (FeSO4·7H2O, 99.0− 103.4%), n-heptane (C7H16, min 99%), and sodium thiosulfate pentahydrate (Na2S2O3·5H2O, 99.5%) were obtained from Riedel-deHaën. Hematite (Fe2O3, 97.0%, ∼45 μm) was obtained from Alfa Aesar. Phenol (C6H5OH, 99.2%), ferric nitrate 9-hydrate (Fe(NO3)3·9H2O, 99.8%), ethanol (C2H5OH, min 99.9%), and acetic acid (CH3COOH, >80%) were obtained from J. T. Baker. Methanol (CH3OH, 99.9%) was obtained from ECHO. n-Hexane (C6H14, min 95.0%) was obtained from Tedia. Acetonitrile (C2H3N, ≥99.9%) was obtained from Aencore. Sodium bicarbonate (NaHCO3, 99.6− 100.3%) and potassium iodide (KI, >99.5%) were obtained from Union Chemical Work. Sodium dodecyl sulfate (C12H25NaSO4, SDS, 95.0%) was obtained from Scharlau. FerroVer Iron Reagent (total iron analysis) and Ferrous Iron Reagent (ferrous ion analysis) were obtained from Hach Company. Water was purified using a Sky water reverse osmosis (RO) purification system. 2.2. Synthesis of Goethite and Hematite. A surfactantassisted goethite and hematite synthetic procedure, which was modified from the procedure established by Madal and Muller,23 was used in this study. In brief, 1.707 M of Fe(NO3)3·9H2O solution was mixed with 33 wt % of SDS 2303

DOI: 10.1021/acs.iecr.5b04352 Ind. Eng. Chem. Res. 2016, 55, 2302−2308

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Industrial & Engineering Chemistry Research

Figure 1. TCE degradation by various forms of iron activated persulfate oxidation in the presence or absence of AsA with initial PS concentrations of (a) 1, (b) 10, and (c) 100 mM. [TCE]0 = 0.46 mM; [AsA]0 = 10 mM; [Fe2+]0 and [Fe3+]0 = 10 mM; [iron mineral] = 0.5 g/60 mL; [soil] = 10 g/60 mL; reaction time = 72 h.

exception that a wavelength of 275 nm was used. The Fe2+ and total iron concentrations were colorimetrically determined using a Hach DR 2400 spectrophotometer, in accordance with Hach methods 8146 and 8008, respectively. The concentration of PS was spectrometrically determined using a spectrophotometer (Hach DR/2400) in accordance with the procedure developed by Liang et al.24 The specific surface areas of iron minerals were measured using a nitrogen sorption technique at 77 K (BET Sorptometer, CBET-201A, Porous Materials, Inc.). The pH was measured using a pH meter (Thermo Orion 720A+) equipped with a Mettler Toledo Inlab 437 pH combination electrode. Oxidation−reduction potential (ORP)

was measured using a pH/Conductivity meter (Eutech Instruments CyberScan PC 5000) equipped with a Mettler Toledo Inlab Redox combination electrode. The crystal structure was analyzed using PANalytical X’Pert Pro MRD Xray diffraction (XRD, using Cu Kα radiation at 1.54 Å).

3. RESULTS AND DISCUSSION 3.1. Effects of Various Forms of Irons. The PS activation effect of various forms of iron minerals in the presence or absence of AsA on TCE degradations was assessed. The degradation of TCE (0−30%) occurred under 1 mM PS and various forms of iron with and without 10 mM AsA (see Figure 2304

DOI: 10.1021/acs.iecr.5b04352 Ind. Eng. Chem. Res. 2016, 55, 2302−2308

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Industrial & Engineering Chemistry Research

Figure 2. Variations of (a) TCE, (b) PS, (c) pH, and (d) ORP as a function of reaction time in the iron mineral/AsA/PS system. [TCE]0 = 0.46 mM; [PS]0 = 10 mM; [AsA]0 = 10 mM; [iron mineral] = 0.5 g/60 mL.

was seen that in the presence of AsA, TCE degradations reached 46% by Fe2+ and 76% by Fe3+ activated PS oxidation. These results showed that TCE degradation was lower using Fe2+ activation when compared to Fe3+ activation. On the other hand, the presence of AsA appeared to effectively regulate the available iron activator and resulted in a higher TCE degradation percentage when Fe3+ was used instead of Fe2+ (i.e., 76% (Fe3+) vs 46% (Fe2+) TCE degradations). It was also evident that TCE was significantly reduced (nearly complete TCE degradation, 92−99%) by iron minerals activation in the presence of AsA. Table S1 (SI) lists the molar ratio of persulfate decomposed, versus TCE degraded (ΔPS/ΔTCE), for the IAP system with the assistance of AsA (data also presented in Figure 1). It can be seen that at a 1 mM PS concentration, for several species of iron, there was no TCE degradation (Figure 1), and therefore ΔPS/ΔTCE could not be calculated. When comparing PS in the 10 mM to 100 mM PS systems, ΔPS/ΔTCE ratios in all IAP processes increased with increasing PS concentration. This was most evident in the homogeneous soluble ferrous and ferric ions activation systems where the ΔPS/ΔTCE ratio in the PS 100 mM system was 4−7 times larger than those in the PS 10 mM system. For comparison, note that the ΔPS/ΔTCE ratio in the heterogeneous iron mineral activation systems was approximately 3 times larger. In the homogeneous dissolved iron activation system, the presence of AsA significantly enhanced the amount of iron available for PS decomposition. However, the excess iron induced greater PS or SO4−• consumption during the IAP process, thereby decreasing the

1a). However, it was seen that PS was completely decomposed under the condition of 1 mM PS/10 mM Fe2+ without AsA while other conditions exhibited slight persulfate decompositions (0−20%). The reduced form of dissolved Fe2+ is the working activator and a 10/1 molar ratio of Fe2+/PS is far higher than the stoichiometric molar ratio (i.e., 2) (eq 3) required for complete decomposition of PS. Also, the excess Fe2+ resulted in significant SO4−• scavenging; thereby inhibiting TCE degradation. On the other hand, the presence of AsA is capable of reducing the oxidized forms of iron minerals to Fe2+15,16,25 which will react with PS. However, due to a limited PS concentration and the excess presence of Fe2+, only slight TCE degradation was observed. It should be noted that when comparing the effect of AsA in the absence of iron minerals on PS decomposition, it was found that AsA would react with PS. It has been reported that AsA can act as a pro-oxidant to react with PS to generate SO4−• (eq 4), but higher concentrations of AsA may favor the reaction between AsA and SO4−• (eq 5) and limit the reaction between PS and target contaminants.26,27 2Fe2 + + S2 O82 − → 2Fe3 + + 2SO4 2 −

(3)

S2 O82 − + C6H8O6 → SO4 −• + C6H6O6−• + SO4 2 − + 2H+ SO4 −• + C6H8O6 → C6H6O6−• + SO4 2 − + 2H+

(4) (5)

When PS concentration increased from 1 to 10 mM, the degradation of TCE was increased markedly (see Figure 1b). It 2305

DOI: 10.1021/acs.iecr.5b04352 Ind. Eng. Chem. Res. 2016, 55, 2302−2308

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Industrial & Engineering Chemistry Research

Figure 3. XRD patterns of (a) goethite and (b) hematite and (c) degradation of TCE and decomposition of PS in the presence of synthetic iron minerals under iron mineral/AsA/PS system. [TCE]0 = 0.46 mM; [PS]0 = 10 mM; [AsA]0 = 10 mM; [iron mineral] = 0.5 g/60 mL; reaction time = 72 h.

of organic substances. Therefore, except for a PS/AsA molar ratio of 1/10, the other solutions have higher PS and lower AsA (PS/AsA of 10/10 and 100/10), which are within the threshold level of AsA (i.e., AsA/PS greater than 4). Control tests containing only AsA, with no PS or iron minerals, showed almost no TCE degradation (90%) than those in the iron minerals/PS systems (∼50% TCE degradation at the end of 72 h reaction time). As seen in Figure 2b, complete PS decomposition was rapidly achieved in the presence of AsA, despite the presence or absence of iron minerals. It was noticed that consumption of PS by AsA occurred and this interaction resulted in a more rapid TCE degradation than the PS only reaction. Note that AsA was also rapidly decomposed in the AsA/iron minerals solution (see Figure S3 (SI), which shows variations of TCE, PS, AsA, total iron and ferrous ion as a function of reaction time in the iron mineral/AsA/PS systems). However, when PS was exhausted, little further degradation of TCE occurred. Figure 2c and d shows the variations of pH and ORP in solutions. The pH

efficiency of the TCE degradation. It appears that the use of iron minerals resulted in an improved aqueous TCE degradation in the heterogeneous IAP system, with the assistance of AsA. Without the assistance of AsA, PS alone would also result in substantial TCE degradations (22−78%). Moreover, in the higher PS concentration (i.e., 100 mM) system, complete TCE degradation (see Figure 1c) was observed regardless of the presence or absence of various form of iron minerals and AsA. The pH variation corresponding to Figure 1 is presented in Figure S1. It can be seen that the pHs generally ranged between 3 and 4 for all experimental conditions with or without AsA. Iron cations may be released from iron minerals at acidic pH. However, in the IAP system, the release of iron cation (II or III) from iron minerals in a solution depends on the solution’s pH and also redox potential (Eh). Elevated ORP may limit acid dissolution of iron. Liang et al.7 reported that the acidic pH is not a critical condition in governing available Fe2+ in solution in the IAP process. Overall, in the iron minerals/AsA/PS system, AsA acts as a pro-oxidant (e.g., by forming chelated Fe2+, note: a fixed AsA/Fe2+ molar ratio of 1/1 was used in this study.) enhancing the IAP process. Huling et al.27 suggested that at an AsA/PS molar ratio of greater than 4, excess AsA would inhibit SO4−• or PS oxidative reactions with organic contaminants such as TCE. Then, AsA can be used for scavenging PS or radical oxidants, and preserving aqueous samples containing PS during analysis 2306

DOI: 10.1021/acs.iecr.5b04352 Ind. Eng. Chem. Res. 2016, 55, 2302−2308

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Industrial & Engineering Chemistry Research Table 1. Surface Characteristics of the Commercial and Synthetic Iron Mineralsa surface area (m2/g) b

pore volume (cm3/g)

material

SBET

Smeso

commercial synthetic

29.67 226.32

29.44 226.10

0.23 0.23

commercial synthetic

24.44 98.15

24.25 97.76

0.19 0.39

Smacro

Vtotal

Vmeso

Vmacro

avg pore sizec (Å)

0.28 0.38

0.19 0.37

0.09 0.02

370.96 67.57

0.29 0.48

0.20 0.40

0.09 0.08

471.69 195.37

Goethite

Hematite

Micro size of surface area and pore volume for all samples are zero (T-plot method). bSmeso = Smeso+macro − (Vmacro/avg pore size). cAvg pore size: median pore diameter (based on pore vol). a

powders are poorly crystallized when compared to the commercial iron minerals. The synthetic FeOOH apparently exhibits an amorphous material and the further calcinated Fe2O3 product shows obvious intense XRD reflections. Based on the full width at half-maximum (fwhm) of the XRD reflections (i.e., two stronger peaks at 2θ = 33.22 and 35.42 corresponding to the (104) and (110) diffraction planes of synthetic using Debye−Scherrer formulas (eq 6), the obtained crystallite sized for the synthesized Fe2O3 are 0.368 and 0.255 nm. In addition, the crystallite sizes for the commercial FeOOH and Fe2O3 calculated from fwhm data (i.e., stronger peaks at 2θ = 21.378 and 2θ = 33.216 for the commercial FeOOH and Fe2O3, respectively) are 0.409 and 0.827 nm, respectively.

decreased from 6.8 to around 3 in the presence of PS and there was increased pH reduction in the system with the presence of AsA, mainly due to the dissociation of AsA to produce H+. It should be noted that the IAP process would simultaneously degrade TCE and AsA, and when AsA is exhausted the remaining PS is still capable of degrading TCE. At the end of experimental runs of PS/AsA/FeOOH and PS/AsA/Fe2O3 experiments (Figure 2), aqueous samples were analyzed for possible organic intermediates, based upon Taiwan’s EPA method NIEA W785.55B (Purge and Trap pretreatment). The results demonstrated that no significant quantities of volatile organic compounds (a total of 60 VOCs listed in the EPA 524.2 VOC mix standard) were detected except for the residual target TCE. It is possible that intermediates were destroyed by oxidation in the IAP system as soon as they were formed. Additionally, the ORP of above 500 mV in the PS/iron mineral or PS alone systems implies higher oxidizing conditions as compared to ∼350 mV in the TCE only solution. However, the presence of AsA, regardless of the presence of PS, generally lead to lower ORP, which resulted in higher TCE degradation. That is because of the reductive property of AsA, which promotes higher oxidative efficiency in the IAP process. These observations are similar to those reported in the IAP system with a persulfate-thiosulfate redox couple, where the thiosulfate (i.e., a reducing agent) reductively recycled Fe2+ for persulfate activation and enhanced TCE degradation.7 Moreover, it was evident that the presence of AsA resulted in higher concentrations of dissolved iron minerals (e.g., the concentrations of Fe2+ in the presence of goethite and hematite are 1.1−15.3 and 1.0−2.0 mg L−1, respectively, during the course of the reaction) as compared to those detected in the absence of AsA (i.e., Fe2+ below 0.1 mg L−1) (see Figures S3d and e (SI) for remaining concentrations of total iron and ferrous ion in solutions at different reaction time, respectively). AsA is capable of maintaining available iron for PS activation, and it can be speculated that the interaction between AsA and iron minerals through formation of a surface Fe3+-AsA complex produces Fe2+ on the surface by electron transfer, thereby releasing Fe2+ from the iron mineral surface into solution.15 Aqueous Fe3+ could also be reduced to Fe2+ in the presence of AsA. This process likely produces the degradation of TCE, by PS in the presence of iron minerals with AsA participating in the recycling of Fe2+. 3.2. Effects of Synthetic Iron Minerals. Figure 3a and b shows the XRD patterns of synthetic/commercial goethite and hematite, respectively, and standard XRD patterns from the International Centre for Diffraction Data (ICDD), powder diffraction file (PDF) cards 03-0249 and 24-0072, respectively,28 are also plotted in the figures for comparison. The weak peaks indicate that the synthetic goethite and hematite

t=

Kλ Bcos θB

(6)

Where t is the mean size of the crystalline, K is the shape factor (typical value of 0.89), λ is the X-ray wavelength, B is the line broadening half the maximum intensity in radians, and θ is the Bragg angle. The surface area and pore volume of commercial iron minerals range from 24 to 30 m2 g−1 and from 0.28 to 0.29 cm3 g−1, respectively (reported in Table 1). It was seen that the surface area and pore volume for the synthetic iron minerals significantly increased to 98−226 m2/g and 0.38−0.48 cm3/g, respectively. In addition, the average pore sizes of commercial and synthetic iron minerals are 370−472 and 68−195 Å, respectively, and the mesopore appears to be the main pore in these iron minerals. The TCE degradation and PS decomposition in the synthetic iron minerals activated PS system with or without AsA are shown in Figure 3c. The results show that the degradations of TCE by synthetic iron mineral activations were similar to the degradation of TCE by commercial iron minerals (see Figure 1b) in the absence or presence of AsA (e.g., 99% (commercial) vs 94% (synthetic) TCE removal in the Fe2O3/AsA/PS system). However, there is an exception for the FeOOH system without AsA (i.e., 68% (commercial) vs 32% (synthetic) TCE degradations). Moreover, it was seen that the decomposition of PS by synthetic iron minerals was generally lower than those by commercial iron minerals in the iron mineral/AsA/PS system. Note that the decomposition of PS was minor (