This study investigates using an iodide-enhanced solution at the cathode during electrokinetic treatment to optimize the removal of mercury from soils. The experimental program consisted of testing two types of clayey soils, kaolin, and glacial till, that were initially spiked with 500 mg/kg of Hg͑II͒. Experiments were conducted on each soil type at two voltage gradients ͑1.0 or 1.5 VDC/cm͒ to evaluate the effect of the voltage gradient when employing a 0.1 M KI solution. Additional experiments were performed on each soil type to assess the effect of using a higher iodide concentration ͑0.5 M KI͒ when using a 1.5 VDC/cm voltage gradient. The tests conducted on the kaolin soil showed that when the 0.1 M KI concentration was employed with the 1.0 VDC/cm voltage gradient, approximately 97% of the mercury was removed, leaving a residual concentration of 16 mg/kg in the soil after treatment. The tests conducted on glacial till indicated that it was beneficial to use the higher ͑0.5 M KI͒ iodide concentration and the higher ͑1.5 VDC/cm͒ voltage gradient to enhance mercury removal, because, under these conditions, a maximum of 77% of the mercury was removed from the glacial till, leaving a residual concentration of 116 mg/kg in soil after electrokinetic treatment. Compared to kaolin, the lower mercury removal from the glacial till soil is attributed to the more complicated soil composition, such as the presence of carbonates and organic matter, which caused Hg͑II͒ to adsorb to the soil and/or exist as an immobile chemical species.

Numerous sites have been polluted with mercury as a result of accidental spills and improper disposal practices, and these mercury-contaminated sites may have adverse effects on human health and the environment. Innovative and cost-effective remediation techniques are urgently needed, and this study was performed to investigate the use of electrokinetics for mercury-contaminated soils. Initially, batch tests were performed on two soils, kaolin and glacial till, spiked with mercury(II) to investigate mercury desorption and complexation under different pH environments (pH range 2-12). The complexing agents included disodium ethylenediaminetetraacetate (Na-EDTA), potassium iodide (KI), and sodium chloride (NaCl), and these solutions were used at a concentration of 0.1 M. In addition, deionized water was used for comparison purposes. Based on the batch tests, Na-EDTA and KI were identified as the complexing agents with the greatest potential. The removal efficiency of these complexing agents was then examined by conducting electrokinetic experiments that employed the same solution concentration (0.1 M) and voltage gradient (1.0 VDC/cm) conditions. These tests indicated that for both soils, KI was a more effective complexing agent than Na-EDTA under electrokinetics. For the kaolin soil, the electrokinetic treatment using KI removed approximately 97% of the initial contaminant present (500mg/kg of Hg(ll)), leaving a residual concentration of 16 mg/kg of Hg in the soil, whereas on the glacial till soil, KI removed only 56% of the initial contaminant present (500mg/kg of Hg(II)), leaving a residual concentration of 220 mg/kg of Hg in the soil. The lower Hg removal from glacial till is attributed to the presence of organic matter, which increased mercury adsorption or the formation of insoluble mercury surface complexes.

With increasing commercialization of high volume, two-dimensional carbon nanomaterials comes a greater likelihood of environmental release. In aquatic environments, black carbon binds contaminants like aromatic hydrocarbons, leading to changes in their uptake, bioavailability, and toxicity. Engineered carbon nanomaterials can also adsorb pollutants onto their carbon surfaces, and nanomaterial physicochemical properties can influence this contaminant interaction. We used 2D graphene nanoplatelets and isometric carbon black nanoparticles to evaluate the influence of particle morphology and surface properties on adsorption and bioavailability of benzo(a)pyrene, a model aromatic hydrocarbon, to brine shrimp (Artemia franciscana) and a fish liver cell line (PLHC-1). Acellular adsorption studies show that while high surface area carbon black (P90) was most effective at a given concentration, 2D graphene nanoplatelets (G550) adsorbed more benzo(a)pyrene than carbon black with comparable surface area (M120). In both biological models, co-exposure to nanomaterials lead to reduced bioavailability, with G550 graphene nanoplatelets cause a greater reduction in bioavailability or response than the M120 carbon black nanoparticles. However, on a mass basis the high surface area P90 carbon black was most effective. The trends in bioavailability and adsorption were consistent across all biological and acellular studies, demonstrating the biological relevance of these results in different models of aquatic organisms. While adsorption is limited by surface area, 2D graphene nanoplatelets adsorb more benzo(a)pyrene than carbon black nanoparticles of similar surface area and charge, demonstrating that both surface area and shape play important roles in the adsorption and bioavailability of benzo(a)pyrene to carbon nanomaterials.