Sung-Ho Kong

Treatment of petroleum-contaminated soils using iron mineral catalyzed hydrogen peroxide

Abstract Naturally-occurring iron minerals, goethite and magnetite, were used to catalyze hydrogen peroxide and initiate Fenton-like reaction of silica sand contaminated with diesel and/or kerosene in batch system. Optimum reaction conditions were investigated by varying H2O2 concentrations (0, 1, 7, 15, and 35wt%) and iron mineral contents (0, 1, 5 and 10wt%). Contaminant degradation in silica sand-iron mineral-H2O2 system was identified by determining total petroleum hydrocarbon (TPH) concentration with gas chromotography. Iron mineral system was less aggressive in contaminant degradation but it was more efficient than FeSO4 system. Magnetite system provided more strong oxidation condition than goethite system due to coexistence of Fe+2 and Fe+3 and dissolution of iron. The results indicate that iron mineral catalyzed H2O2 system would have a promising application to site remediation since natural soils generally contain 0.5–5 wt% of iron minerals.

Hydrogen peroxide decomposition in model subsurface systems.

Rates of hydrogen peroxide decomposition, hydroxyl radical production, and oxygen evolution were investigated in silica sand-goethite slurries using unstabilized and stabilized hydrogen peroxide formulations. The goethite-catalyzed decomposition of unstabilized hydrogen peroxide formulations resulted in more rapid hydrogen peroxide loss and oxygen evolution relative to systems containing a highly stabilized hydrogen peroxide formulation. Systems at neutral pH and those containing higher goethite concentrations were characterized by higher rates of hydrogen peroxide decomposition and by more oxygen evolution. The stabilized hydrogen peroxide formulation showed greater hydroxyl radical production relative to the unstabilized formulations. Furthermore, hydroxyl radical production rates were greater at neutral pH than at the acidic pH regimes. The results suggest that when stabilized hydrogen peroxide is injected into the subsurface during in situ bioremediation, naturally occurring minerals such as goethite may initiate Fenton-like reactions. While these reactions may prove to be toxic to microorganisms, they have the potential to chemically oxidize contaminants in soils and groundwater.

Hydrogen peroxide decomposition on manganese oxide (pyrolusite): kinetics, intermediates, and mechanism.

The objective of this study is the kinetic interpretation of hydrogen peroxide decomposition on manganese oxide (pyrolusite) and the explanation of the reaction mechanism including the hydroperoxide/superoxide anion. The decomposition of hydrogen peroxide on manganese oxide at pH 7 was represented by a pseudo first-order model. The maximum value of the observed first-order rates constants (k(obs)) was 0.741 min(-1) at 11.8 of [H(2)O(2)]/[triple bond MnO(2)] when [H(2)O(2)]/[triple bond MnO(2)] were ranged from 58.8 to 3.92. The pseudo first-order rate constants (kMnO(2)) approximated as the average value of 0.025 (min mM)(-1) with a standard deviation of 0.003 at [H(2)O(2)]/[triple bond MnO(2)] ranged from 39.2 to 11.8. When [H(2)O(2)]/[triple bond MnO(2)] was 3.92, the rate constants (kMnO(2)) was 0.061 (min mM)(-1) as maximum. Oxygen production showed that the initial rates increased with decreasing [H(2)O(2)]/[triple bond MnO(2)] and the total amounts of oxygen was slightly less than the stoichiometric value (0.5) in most experiments. However, oxygen was produced at more than 0.5 in low [H(2)O(2)]/[triple bond MnO(2)] (i.e. 3.92 and 9.79). The relative production of hydroperoxide/superoxide anion implied that the production increased with low [H(2)O(2)]/[triple bond MnO(2)], and the existence of anions suggested that the mechanism includes propagation reactions with intermediates such as hydroperoxide/superoxide anion in solution. In addition, both [H(2)O(2)] decomposition and the production of anion were accelerated in alkaline solution. Manganese ion dissolved into solution was negligible in neutral and alkaline conditions, but it greatly increased in acidic conditions.

Application of a peroxymonosulfate/cobalt (PMS/Co(II)) system to treat diesel-contaminated soil

We investigated the feasibility of using peroxymonosulfate (PMS) with transition metals (PMS/M(+) system) for remediation of diesel-contaminated soils. To the best of our knowledge, this is the first attempt to apply a PMS/M(+) system for the treatment of diesel-contaminated soils. Two well-known transition metals, Fe(II) and Co(II), used to activate PMS including the effect of co-existence of counter anions (Cl(-) and SO(4)(2-)) were tested and it revealed that the most effective degradation of diesel was achieved with cobalt chloride. The effect of PMS (i.e. 0-500 mM) indicated that the increasing the molar ratio of PMS/diesel increased degradation of diesel on soils. The effect of Co(II) (i.e. 0-4mM) showed that at least 2mM of Co(II) was needed to degrade above 30% of diesel. Moreover, a maximum diesel degradation of 47% was achieved at a single injection of PMS/Co(II) (i.e. 500 mM/2mM). Assessments of system pH showed that diesel degradation was higher under acidic conditions (pH 3) possibly due to the dissolution of metal ions from soils that are not possible at other pHs (pH 6 and 9). Sequential injections of both PMS and Co(II) were employed to improve the level of remediation (approximately 90% degradation). The degradation of diesel increased as much as 88% when PMS/Co(II) was sequentially injected. This indicates that PMS/Co(II) systems are applicable for remediation of soil contaminated with diesel fuel as an aspect of in situ chemical oxidation.

Effect of metal oxides on the reactivity of persulfate/Fe(II) in the remediation of diesel-contaminated soil and sand

The effect of metal oxides on the ability of persulfate (PS) with Fe(II) to remediate diesel-contaminated soil was investigated. In both natural soil and purchased sand, the highest diesel degradation occurred at pH 3 and the optimum molar ratio of PS/Fe(II) was 100:1 (i.e. 500 mM PS to 5 mM Fe(II)). Moreover, adding Fe(II) increased PS reactivity more in soil than it did in sand, indicating the involvement of metal oxides in the soil matrix. Evaluating the effects of metal oxides (i.e. goethite, hematite, magnetite, and manganese oxide) on the reactivity of PS with/without Fe(II) in a system containing diesel-contaminated sand revealed that manganese oxide increased PS activity the most and that the highest diesel degradation by PS occurred when both manganese oxide and Fe(II) were used as activators. XRD did not show the transformation of manganese oxide in the presence of Fe(II). SEM-EDS showed the association of Fe(II) on the surface of manganese oxide, and ICP analysis revealed that almost all the added Fe(II) adsorbed to manganese oxide but almost none adsorbed to iron oxides under acidic conditions. Therefore, the high reactivity of PS could be due to the high density of Fe(II) over the surface of manganese oxide.

Persulfate activation by iron oxide-immobilized MnO2 composite: identification of iron oxide and the optimum pH for degradations.

Iron oxide-immobilized manganese oxide (MnO2) composite was prepared and the reactivity of persulfate (PS) with the composite as activator was investigated for degradation of carbon tetrachloride and benzene at various pH levels. Brunauer-Emmett-Teller (BET) surface area of the composite was similar to that of pure MnO2 while the pore volume and diameter of composite was larger than those of MnO2. Scanning electron microscopy couples with energy dispersive spectroscopy (SEM-EDS) showed that Fe and Mn were detected on the surface of the composite, and X-ray diffraction (XRD) analysis indicated the possibilities of the existence of various iron oxides on the composite surface. Furthermore, the analyses of X-ray photoelectron (XPS) spectra revealed that the oxidation state of iron was identified as 1.74. In PS/composite system, the same pH for the highest degradation rates of both carbon tetrachloride and benzene were observed and the value of pH was 9. Scavenger test was suggested that both oxidants (i.e. hydroxyl radical, sulfate radical) and reductant (i.e. superoxide anion) were effectively produced when PS was activated with the iron-immobilized MnO2.

Feasibility study on an oxidant-injected permeable reactive barrier to treat BTEX contamination: adsorptive and catalytic characteristics of waste-reclaimed adsorbent.

The adsorptive and catalytic characteristics of waste-reclaimed adsorbent (WR), which is a calcined mixture of bottom-ash and dredged-soil, was investigated for its application to treating BTEX contamination. BTEX adsorption in WR was 54%, 64%, 62%, and 65%, respectively, for a 72 h reaction time. Moreover, the catalytic characteristics of WR were observed when three types of oxidation systems (i.e., H(2)O(2), persulfate (PS), and H(2)O(2)/Fe(III)/oxalate) were tested, and these catalytic roles of WR could be due to iron oxide on its surface. In PS/WR system, large amounts of metal ions from WR were released because of large drops of solution pH, and the surface area of WR was also greatly reduced. Moreover, the BTEX that was removed per consumed oxidant (ΔC(rem)/ΔOx) increased with increasing PS. In H(2)O(2)/Fe(III)/oxalate with WR system, the highest BTEX degradation rate constants (k(deg)) were calculated as 0.338, 0.365, 0.500 and 0.716 h(-1), respectively, when 500 mM of H(2)O(2) was used, and the sorbed BTEX on the surface of WR was also degraded, which suggests the regeneration of WR. Therefore, the oxidant-injected permeable reactive barrier filled in WR could be an alternative to treating BTEX with both adsorption and catalytic degradation.

Synthesis of iron composites on nano-pore substrates: Identification and its application to removal of cyanide

Two types of nano-pore substrates, waste-reclaimed (WR) and soil mineral (SM) with the relatively low density, were modified by the reaction with irons (i.e. Fe(II):Fe(III)=1:2) and the applicability of the modified substrates (i.e. Fe-WR and Fe-SM) on cyanide removal was investigated. Modification (i.e. Fe immobilization on substrate) decreased the BET surface area and PZC of the original substrates while it increased the pore diameter and the cation exchange capacity (CEC) of them. XRD analysis identified that maghemite (γ-Fe(2)O(3)) and iron silicate composite ((Mg, Fe)SiO(3)) existed on Fe-WR, while clinoferrosilite (FeSiO(3)) was identified on Fe-SM. Cyanide adsorption showed that WR adsorbed cyanide more favorably than SM. The adsorption ability of both original substrates was enhanced by the modification, which increased the negative charges of the surfaces. Without the pH adjustment, cyanide was removed as much as 97% by the only application of Fe-WR, but the undesirable transfer to hydrogen cyanide was possible because the pH was dropped to around 7.5. With a constant pH of 12, only 54% of cyanide was adsorbed on Fe-WR. On the other hand, the pH was kept as 12 without adjustment in Fe-WR/H(2)O(2) system and cyanide was effectively removed by not only adsorption but also the catalytic oxidation. The observed first-order rate constant (k(obs)) for cyanide removal were 0.49 (± 0.081) h(-1). Moreover, the more cyanate production with the modified substrates indicated the iron composites, especially maghemite, on substrates had the catalytic property to increase the reactivity of H(2)O(2).

PCE DNAPL degradation using ferrous iron solid mixture (ISM)

Ferrous iron solid mixture (ISM) containing Fe(II), Fe(III), and Cl was synthesized for degradation of tetrachloroethene (PCE) as a dense non-aqueous phase liquid (DNAPL), and an extraction procedure was developed to measure concentrations of PCE in both the aqueous and non-aqueous phases. This procedure included adding methanol along with hexane in order to achieve the high extraction efficiency, particularly when solids were present. When PCE was present as DNAPL, dechlorination of PCE was observed to decrease linearly with respect to the total PCE concentration (aqueous and non-aqueous phases) and the concentration of PCE in the aqueous phase was observed to be approximately constant. In the absence of DNAPL, the rate of PCE degradation was observed to be the first-order with respect to the concentration in the aqueous phase. A kinetic model was developed to describe these observations and it was able to fit experimental data well. Increasing the concentration of Fe(II) in ISM increased the values of rate constants, while increasing the concentration of PCE DNAPL did not affect the value of the rate constant. The reactivity of ISM for PCE dechlorination might be close to that of Friedels salt, and the accumulation of trichloroethylene (TCE) might imply the lower reactivity of ISM for degradation of TCE or the necessity of large amount of Fe(II) in ISM. TCE (the major chlorinated intermediate), ethene (the major non-chlorinated compound), acetylene and ethane were detected, which implied that both hydrogenolysis and beta-elimination were pathways of PCE DNAPL degradation on ISM.

Degradation of multi-DNAPLs by a UV/persulphate/ethanol system with the additional injection of a base solution

This study was conducted to investigate the inhibited influences on and solution to the degradation of four types of dense non-aqueous phase liquids (DNAPLs) (i.e. perchloroethylene [PCE], trichloroethylene [TCE], chloroform [CF], and carbon tetrachloride [CT]) all at the same instance in groundwater (GW). Degradations of DNAPLs in de-ionized water (DW) and GW were carried out by applying an ultraviolet radiation-activated persulphate (UV/PS) system. PCE and TCE were degraded by over 90% and CT was only degraded by 25% in both DW and GW. However, CF was degraded by over 90% in DW, while it was only degraded by 50% in GW. First of all, degradations with an inorganic anion (either Cl− or ) indicated that the lower degradation of CF in GW was caused by the existence of the chloride ion. Moreover, the low CF degradation in GW was overcome by the additional injection of a base solution (sodium hydroxide [NaOH]) into the UV/PS system. The results showed that PCE, TCE, and CF were degraded by over 90%, respectively, when a molar ratio of [base]0:[PS]0 was larger than 0.5:1, but CT was still not effectively degraded in the UV/PS system. To achieve effective CT degradation, UV/PS with the ethanol (EtOH) system was evaluated and it was found that it degraded CT over 90%. However, at this time, CF was not effectively degraded in the UV/PS/EtOH system. Finally, degradations of DNAPLs in the UV/PS/EtOH system with the additional injection of a base solution were conducted and it showed that multi-DNAPLs were degraded by over 90%, respectively, when the molar ratio of [PS]0:[EtOH]0:[base]0 was 1:1:3.