Kyoungphile Nam

Life Cycle Assessment (LCA), a systematic method of evaluating the environmental impacts of an entire process, will be employed in this study to compare four soil remediation scenarios. In this study, we apply LCA on the Janghang Songrim Forest in South Korea, a site contaminated by arsenic from historical smelting operations. The environmental impacts of soil remediation techniques are critical in selecting sustainable methods for contaminated sites. A thorough understanding of these impacts enables the identification of the most environmentally responsible strategies for site restoration. We examine four techniques, in-situ solidification/stabilization using iron oxide injection, excavation & refill, soil washing, and the combined approach reflecting actual on-site practices implemented on the site around 2010. The assessment is performed with Simapro software 9.6.0.1 using ReCiPe2016 impact assessment method, supported by data from field measurements, Ecoinvent database, relevant literature, and site-specific information from the Janghang Songrim Forest. This study models and assesses the environmental trade-offs of each remediation scenario from a cradle-to-gate perspective, analyzing every stage from material extraction and transportation to remediation processes. The comparative analysis aims to guide future decisions on sustainable soil remediation by identifying low impact, effective techniques for sites with similar contamination profiles. The goal of this study is to conduct a comparative assessment of the environmental impacts of four remediation methods especially focusing on greenhouse gas emissions, resource depletion, and effect on human health. Although the results are based on a case in Janghang Songrim Forest, we intend to extend this approach to propose pathways for enhancing low-impact technologies informed by the results.

Precipitating cadmium in groundwater as sulfide using calcium polysulfide (CPS) has advantages over hydroxide precipitation, as it is less affected by pH variations and exhibits a lower solubility product constant. However, dissolved oxygen (DO) in groundwater can oxidize the precipitated cadmium sulfide (CdS), leading to its remobilization. From this perspective, this study aimed to evaluate the long-term stability of cadmium precipitated by CPS and to elucidate the stabilization mechanisms. First, under anoxic conditions, Cd²⁺ (100 mg/L) was completely precipitated as CdS by adding CPS. The precipitates were then oxidized in ambient air in two different conditions: (1) with the supernatant (SN) and (2) without the supernatant (in deionized water, DI). Both conditions were subjected to stirring at 250 rpm to maximize DO contact. After 27 days of exposure, the Cd release was only 4.2% in SN, while in DI, 60.5% of the Cd2+ was re-dissolved, indicating more than 10 times greater dissolution. In addition, X-ray photoelectron spectroscopy (XPS) analysis revealed that the Cd in SN remained consistent with the CdS reference peaks. Based on the measurements of pH, DO, ion chromatography (IC), and zeta potential results, it was concluded that polysulfide (Sx2-) and bisulfide (HS-) in the SN supernatant reacted with DO, preventing CdS oxidation. Moreover, the formation of elemental sulfur (S0) from Sx2- and HS- oxidation contributed to physical sequestration, which inhibited the dissolution of CdS. The experiments were conducted under higher DO levels than typical groundwater, creating a more oxidative environment. Thus, our research suggests that CPS could effectively stabilize cadmium in groundwater, with minimal risk of remobilization under the presence of DO.

Per- and polyfluoroalkyl substances (PFAS), particularly perfluorooctanoic acid (PFOA, C7F15COOH), have been widely used in industry due to their high stability and heat resistance. Their release during manufacturing and treatment processes has led to contamination of aquatic systems and groundwater. While PFOA is generally resistant to degradation under typical aqueous environments, it can be degraded in the presence of catalysts or strong oxidizing / reducing agents. Previous studies have reported that PFOSA derivatives could be transformed into PFOA and shorter-chain PFCAs in the presence of montmorillonite under sunlight irradiation. The Fe3+-containing material mentioned above are widely distributed in natural environments, indicating that the potential for PFOA to undergo photocatalytic degradation facilitated by natural media. This study aims to investigate the potential role for photocatalytic transformation of PFOA using various forms of Fe3+ found in natural environments (structural iron in clay minerals, magnetite, goethite, etc.) under both 254 nm UV light and natural sunlight conditions (including UV radiation of 290-400 nm). When 50 μM PFOA and 500 μM Fe3+-containing montmorillonite were exposed to 254 nm UV light for 3 days at pH 7, a defluorination ratio of 18.2 % was achieved. Future studies will aim to investigate the photocatalytic behavior of structural iron containing clay minerals under natural sunlight irradiation. The photocatalytic reaction between PFOA and nontronite (22.3 wt%), which contains approximately ten times higher structural iron (Fe3+) content than montmorillonite (2.3 wt%) will be investigated. To further understand the potential of PFOA phototransformation under natural conditions, reaction mixtures will be prepared with various forms of naturally occurring Fe3+ media, such as iron oxides to simulate environmental conditions.

The environmental hazards associated with nuclear power plants, specifically the release of fission byproducts such as strontium (Sr) and cesium (Cs) are highlighted for their harmful attributes, even in non-radioactive forms owing to their physicochemical characteristics and potential health risks. Sr and Cs exhibit significant physicochemical resemblances to calcium (Ca) and potassium (K), respectively. These similarities are so pronounced that the human body often confuses Sr and Cs with Ca and K, leading to their accumulation. This accumulation can give rise to detrimental health conditions, including leukemia, thyroid cancer, bone marrow cancer, and general paralysis. In this study, a soil washing method was employed to eliminate Sr and Cs contaminants from the soil. We hypothesize that the efficiency of Sr and Cs removal is influenced by the resemblance in physicochemical properties. Physicochemical properties such as atomic radius, hydrated radius, electronegativity, and electron affinity of Sr, Cs, Na, Mg, K, Ca, Ba, and Al were carefully studied and summarized for the investigation. Subsequently, solutions with Na, Mg, K, Ca, Ba, and Al at concentrations of 0.1 and 0.01 M, with a pH of 7, were tested for their efficacy in removing Sr and Cs from the soil. The results showed that the greater similarity in hydrated radius between heavy metals and ions appears to be responsible for increased removal efficiencies. For example, both Ca and Sr share the same hydrated radius of 0.412 nm. Interestingly, Ca exhibited the highest efficiency in removing Sr compared to Na, K, Mg, Ba, and Al. Additionally, Ba, with a hydrated radius of 0.404 (the second closest to Sr), demonstrated the second-highest efficiency in Sr removal. Examining results for other heavy metals (i.e., Cd, Co, Cu, Ni, Pb, and Zn), a heightened resemblance in hydrated radii between the heavy metal and ion corresponded to increased removal efficiency, indicating a strong positive correlation. Overall, this study contributes valuable insights into effective strategies for mitigating the environmental impact of nuclear power plant activities on soil contamination.