Evaluation of Electrochemical Treatment for Removal of Arsenic and Manganese from Field Soil

Soils containing inorganic compounds are frequently encountered by transportation agencies during construction within the right-of-way, and they pose a threat to human health and the environment. As a result, construction activities may experience project delays and increased costs associated with management of inorganic compounds containing soils required to meet environmental regulations. Recalcitrance of metal-contaminated soils toward conventional treatment technologies is exacerbated in clay or organic content-rich fine-grained soils with low permeability and high sorption capacity because of increased treatment complexity, cost, and duration. The objective of this study was to develop an accelerated in situ electrochemical treatment approach to extract inorganic compounds from fine-grained soils, with the treatment time comparable to excavation and off-site disposal. Three reactor experiments were conducted on samples collected from two borehole locations from a field site in Illinois that contained arsenic (As)(~7.4 mg/kg) and manganese (Mn)(~700 mg/kg). A combination of hydrogen peroxide (H2O2) and/or citrate buffer solution was used to treat the soils. A low-intensity electrical field was applied to soil samples using a bench-scale reactor that resembles field-scale in situ electrochemical systems. For the treatment using 10% H2O2 and citrate buffer solution, average removal of 23% and 8% were achieved for Mn and As, respectively. With 4% H2O2 and citrate buffer, 39% and 24% removal were achieved for Mn and As; while using only citrate buffer as the electrolyte, 49% and 9% removal were achieved for Mn and As, respectively. All chemical regimes adopted in this study reduced the inorganic compound concentrations to below the maximum allowable concentration for Illinois as specified by the Illinois Environmental Protection Agency. The results from this work indicate that electrochemical systems that leverage low concentrations of hydrogen peroxide and citrate buffer can be effective for remediating soils containing manganese and arsenic.

Magnesium Hydride-Mediated Sustainable Hydrogen Supply Prolongs the Vase Life of Cut Carnation Flowers via Hydrogen Sulfide

Magnesium hydride (MgH2) is a promising solid-state hydrogen source with high storage capacity (7.6 wt%). Although it is recently established that MgH2 has potential applications in medicine because it sustainably supplies hydrogen gas (H2), the biological functions of MgH2 in plants have not been observed yet. Also, the slow reaction kinetics restricts its practical applications. In this report, MgH2 (98% purity; 0.5–25 μm size) was firstly used as a hydrogen generation source for postharvest preservation of flowers. Compared with the direct hydrolysis of MgH2 in water, the efficiency of hydrogen production from MgH2 hydrolysis could be greatly improved when the citrate buffer solution is introduced. These results were further confirmed in the flower vase experiment by showing higher efficiency in increasing the production and the residence time of H2 in solution, compared with hydrogen-rich water. Mimicking the response of hydrogen-rich water and sodium hydrosulfide (a hydrogen sulfide donor), subsequent experiments discovered that MgH2-citrate buffer solution not only stimulated hydrogen sulfide (H2S) synthesis but also significantly prolonged the vase life of cut carnation flowers. Meanwhile, redox homeostasis was reestablished, and the increased transcripts of representative senescence-associated genes, including DcbGal and DcGST1, were partly abolished. By contrast, the discussed responses were obviously blocked by the inhibition of endogenous H2S with hypotaurine, an H2S scavenger. These results clearly revealed that MgH2-supplying H2 could prolong the vase life of cut carnation flowers via H2S signaling, and our results, therefore, open a new window for the possible application of hydrogen-releasing materials in agriculture.