Photooxidation of Natural and Waste Cr(III)-Bearing Hydroxides in Water and Ice: Cr(III)-O Complex-Mediated Oxidation and the Effect of Natural Organic Matter.

The photooxidative dissolution of Cr(III)-bearing hydroxides (Cr(OH) and FeCr(OH)) is proposed as a potential abiotic source of Cr(VI) in environments. Compared to the dark oxidation of Cr(OH) by O, photoirradiation enhanced Cr(VI) production in both aqueous and frozen solutions. In the presence of natural organic matter (NOM), the photoproduction of Cr(VI) was significantly promoted in aqueous solution but hindered in frozen solution.

Freeze-induced crystallization: An overlooked pathway for mineral genesis in natural waters.

Natural ice plays salient roles in making the Earth habitable and sustainable. Previously overlooked, its role in chemical processes is now of emerging interest, particularly due to the freeze concentration effect, which can substantially promote chemical reactions during ice formation. We demonstrate here that ice formation can serve as a dynamic and unique pathway for mineral genesis.

Rhodochrosite Oxidation by Dissolved Oxygen and the Formation of Mn Oxide Product: The Impact of Goethite as a Foreign Solid Substrate.

Rhodochrosite conversion to Mn (oxyhydr)oxides significantly affects the fate and transport of various substances in the environment. We examined rhodochrosite oxidation by dissolved oxygen and the oxidation product formation with an emphasis on the effects of goethite substrate. Without goethite, rhodochrosite oxidation was slow as no detectable change was observed for 28 d with microscopic and spectroscopic analyses, except a minor change in X-ray diffraction.

Cr(VI) Formation via Oxyhalide-Induced Oxidative Dissolution of Chromium Oxide/Hydroxide in Aqueous and Frozen Solution.

The oxidative dissolution of Cr(III) species (CrO and Cr(OH)) by oxyhalide species, which produces hexavalent chromium (Cr(VI)), was studied in aqueous and frozen solution. The oxyhalide-induced oxidation of Cr(III) in frozen solution showed a different trend from that in aqueous solution. Cr(VI) production was higher in frozen than aqueous solution with hypochlorous acid (HOCl) and bromate (BrO) but suppressed in frozen solution with hypobromous acid (HOBr) and periodate (IO).

Stability of Sn-Pd-Kaolinite catalyst during heat treatment and nitrate reduction in continuous flow reaction.

In this study, a novel and highly reactive Sn-Pd catalyst supported by environmentally benign kaolinite (Sn-Pd-kaolinite) was developed and evaluated for stability for effective nitrate (NO) reduction in batch and continuous mode. Complete NO removal with fast reduction kinetics (k = 18.16 × 10 min) and 71% selectivity toward N were achieved by the Sn-Pd-kaolinite catalyst during batch reactions.

Correction to: Potential CO intrusion in near-surface environments: a review of current research approaches to geochemical processes.

In the original publication of the article, the third author name has been misspelt. The correct name is given in this correction. The original version of this article was revised.

Potential CO intrusion in near-surface environments: a review of current research approaches to geochemical processes.

Carbon dioxide (CO) capture and storage (CCS) plays a crucial role in reducing carbon emissions to the atmosphere. However, gas leakage from deep storage reservoirs, which may flow back into near-surface and eventually to the atmosphere, is a major concern associated with this technology. Despite an increase in research focusing on potential CO leakage into deep surface features and aquifers, a significant knowledge gap remains in the geochemical changes associated with near-surface.

Defluoridation of water by Tea-bag model using La(3+) modified synthetic resin@chitosan biocomposite.

The aim of this work is to gain a better understanding of the formation of lanthanum complex onto iminodiacetic acid and chitosan (CS@La-IDAMP) composite for effective removal of fluoride from aqueous solution using a tea-bag model for the first time. The surface textural and chemical properties of the synthesized composites were characterized by FTIR, SEM with EDAX and mapping images. The experimental data revealed that the fluoride adsorption was rapid, maximum fluoride removal could be removed within 12min contact time at neutral pH in room temperature under batch equilibrium model.

Geochemical characteristics and microbial community composition in toxic metal-rich sediments contaminated with Au-Ag mine tailings.

The effects of extreme geochemical conditions on microbial community composition were investigated for two distinct sets of sediment samples collected near weathered mine tailings. One set (SCH) showed extraordinary geochemical characteristics: As (6.7-11.

Cr(OH)3(s) oxidation induced by surface catalyzed Mn(II) oxidation.

We examined the feasibility of Cr(OH)3(s) oxidation mediated by surface catalyzed Mn(II) oxidation under common groundwater pH conditions as a potential pathway of natural Cr(VI) contaminations. Dissolved Mn(II) (50 μM) was reacted with or without synthesized Cr(OH)3(s) (1.0 g/L) at pH 7.

Reduction of Chromium(VI) mediated by zero-valent magnesium under neutral pH conditions.

In an effort to assess the potential use of ZVMg in contaminant treatments, we examined Cr(VI) reduction mediated by ZVMg particles under neutral pH conditions. The reduction of Cr(VI) was tested with batch experiments by varying [Cr(VI)](0) (4.9, 9.

Geochemical implications of gas leakage associated with geologic CO2 storage--a qualitative review.

Gas leakage from deep storage reservoirs is a major risk factor associated with geologic carbon sequestration (GCS). A systematic understanding of how such leakage would impact the geochemistry of potable aquifers and the vadose zone is crucial to the maintenance of environmental quality and the widespread acceptance of GCS. This paper reviews the current literature and discusses current knowledge gaps on how elevated CO(2) levels could influence geochemical processes (e.

Defluoridation from aqueous solutions by granular ferric hydroxide (GFH).

This research was undertaken to evaluate the feasibility of granular ferric hydroxide (GFH) for fluoride removal from aqueous solutions. Batch experiments were performed to study the influence of various experimental parameters such as contact time (1 min-24h), initial fluoride concentration (1-100 mgL(-1)), temperature (10 and 25 degrees C), pH (3-12) and the presence of competing anions on the adsorption of fluoride on GFH. Kinetic data revealed that the uptake rate of fluoride was rapid in the beginning and 95% adsorption was completed within 10 min and equilibrium was achieved within 60 min.

Metal release from bottom sediments of Ocoee Lake No. 3, a primary catchment area for the Ducktown Mining District.

Ocoee Lake No. 3 is the first reservoir receiving suspended sediments contaminated with trace metals discharged by acid mine effluents from the Ducktown Mining District, Tennessee. Bottom sediments (0-5 cm) from the lake were sampled to assess the potential for future adverse environmental effects if no remediation controls or activities are implemented.

Oxidative dissolution of chromium(III) hydroxide at pH 9, 3, and 2 with product inhibition at pH 2.

Hexavalent chromium, Cr(VI), can be immobilized under neutral to alkaline conditions by reduction to Cr(III); similarly, the mobility of naturally occurring Cr in soils and sediments can be limited by its occurrence in the +III oxidation state. Conversely, the oxidation of Cr(IIi) to Cr(VI) increases both its toxicity and often its mobility. Dissolution of Cr-(OH)3(s) in 0.