Fenton/Fenton-like processes with in-situ production of hydrogen peroxide/hydroxyl radical for degradation of emerging contaminants: Advances and prospects.

Hydroxyl radicals (•OH) play a crucial role in the fate of redox-active substances in the environment. Studies of the •OH production in nature has been constrained to surface environments exposed to light irradiation, but is overlooked in the subsurface under dark. Results of this study demonstrate that abundant •OH is produced when subsurface sediments are oxygenated under fluctuating redox conditions at neutral pH values. The cumulative concentrations of •OH produced within 24 h upon oxygenation of 33 sediments sampled from different redox conditions are 2-670 μmol •OH per kg dry sediment or 6.7-2521 μM •OH in sediment pore water. Fe(II)-containing minerals, particularly phyllosilicates, are the predominant contributor to •OH production. This production could be sustainable when sediment Fe(II) is regenerated by the biological reduction of Fe(III) during redox cycles. Production of •OH is further evident in a field injection-extraction test through injecting oxygenated water into a 23-m depth aquifer. The •OH produced can oxidize pollutants such as arsenic and tetracycline and contribute to CO2 emissions at levels that are comparable with soil respiration. These findings indicate that oxygenation of subsurface sediments is an important source of •OH in nature that has not been previously identified, and •OH-mediated oxidation represents an overlooked process for substance transformations at the oxic/anoxic interface.

Production of Abundant Hydroxyl Radicals from Oxygenation of Subsurface Sediments.

Application of iron sulfide particles for groundwater and soil remediation: A review.

The kinetics of base cation release due to chemical weathering

Activated persulfate oxidation is an effective in situ chemical oxidation process for groundwater remediation. However, reactivity of persulfate is difficult to manipulate or control in the subsurface causing activation before reaching the contaminated zone and leading to a loss of chemicals. Furthermore, mobilization of heavy metals by the process is a potential risk. An effective approach using iron electrodes is thus developed to manipulate the reactivity of persulfate in situ for trichloroethylene (TCE) degradation in groundwater and to limit heavy metals mobilization. TCE degradation is quantitatively accelerated or inhibited by adjusting the current applied to the iron electrode, following k1 = 0.00053·Iv + 0.059 (-122 A/m(3) ≤ Iv ≤ 244 A/m(3)) where k1 and Iv are the pseudo first-order rate constant (min(-1)) and volume normalized current (A/m(3)), respectively. Persulfate is mainly decomposed by Fe(2+) produced from the electrochemical and chemical corrosion of iron followed by the regeneration via Fe(3+) reduction on the cathode. SO4(•-) and ·OH cocontribute to TCE degradation, but ·OH contribution is more significant. Groundwater pH and oxidation-reduction potential can be restored to natural levels by the continuation of electrolysis after the disappearance of contaminants and persulfate, thus decreasing adverse impacts such as the mobility of heavy metals in the subsurface.

/pdf/electrolytic-manipulation-of-persulfate-reactivity-by-iron-5fhtj230xl.pdf

Electrolytic manipulation of persulfate reactivity by iron electrodes for trichloroethylene degradation in groundwater.

The transformation of trichloroethylene (TCE) in natural mineral iron disulfide (pyrite) aqueous suspension under different oxygen conditions was investigated in laboratory batch experiments. TCE t...

Trichloroethylene Transformation by Natural Mineral Pyrite: The Deciding Role of Oxygen

Kinetics of trichloroethene dechlorination with iron powder.

Sodic alteration assemblages including clinoptilolite, mordenite, analcime and Na-montmorillonite were locally observed in sediments in the eastern part of the Hachimantai geothermal region, northeast Japan. This study investigated the mechanisms of sodic enrichment in the sediments during alteration. Kinetic results for water/rock interaction experiments are reported here. Batch-type experiments were conducted at 150–250°C under saturated vapor pressure. Pyroclastic rocks dissolved incongruently in these experiments, and the solubility and dissolution rates among elements varied as follows: the apparent steady-state concentrations of major elements are Si > Na ≫ K > Ca > Al and the order of the dissolution rates is Si > Al > Na ≫ K > Ca. Na had the highest steady-state concentration and fastest dissolution rate of the alkali and alkali earth metal ions. Based on surface analysis of plagioclase, dissolution was effected via a reaction layer of Na-montmorillonite on the mineral surface. Additionally, a reaction model constructed based on the experimentally observed reaction mechanism quantitatively explains the dissolution behavior. These results show that Na-montmorillonite can be precipitated by pyroclastic rock/meteoric water interactions without seawater involvement: the Na is derived from the host rocks.

An experimental and modeling study of Na‐rich hydrothermal alteration

PROBLEM TO BE SOLVED: To provide a method for cleaning polluted soil which is environmentally friendly and safe and can clean to a further fine particle size.SOLUTION: The invention relates to the method for cleaning polluted soil that cleans soil polluted by a heavy metal by acidic electrolytic water produced by electrolyzing a potassium chloride solution.

Method for cleaning polluted soil

The spent adsorbents left after treating arsenic-contaminated water contain large amounts of arsenic. These spent adsorbents may come into contact with silicic acid leached from soil or cementitious solidification materials in the disposal environment. Thus, it is important to evaluate the effects of silicic acid on spent adsorbents containing arsenic. In this study, the effects of silicic acid on spent Mg-based adsorbents (magnesium oxide (MgO) and magnesium hydroxide (Mg(OH)2)) containing arsenite were investigated. The arsenic leaching ratios of both spent adsorbents decreased slightly with an increase in the initial silicic acid concentration of the eluent. The arsenic leaching ratio decreased from 1.24% to 0.69% for MgO and from 5.97% to 4.71% for Mg(OH)2 at an initial Si-normalized concentration of 100 mg/L. The primary mechanism behind the inhibition of arsenic leaching by silicic acid was determined to be the difficulty of arsenic desorption due to the coating effect following the adsorption of silicic acid species. The results indicate that the arsenic leaching related to the ion exchange reaction with silicic acid hardly occurred for the spent Mg-based adsorbents. Compared with various spent Mg-based and Ca-based adsorbents, the spent MgO adsorbent exhibited the highest environmental stability and best performance.

/pdf/effects-of-silicic-acid-on-leaching-behavior-of-arsenic-from-2s3rka1z.pdf

Effects of Silicic Acid on Leaching Behavior of Arsenic from Spent Magnesium-Based Adsorbents Containing Arsenite

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