Enhanced remediation of arsenic-contaminated excavated soil using a binary blend of biodegradable surfactant and chelator

Mechanistic insights into surfactant-induced transformation of chromium-bearing schwertmannite and chromate redistribution during dissolution and recrystallization

Schwertmannite (Sch) is a typical metastable iron hydroxysulfate mineral found in acid sulfate soil and mine drainage, and it is susceptible to environmental factors and the transformation and concomitant release and re-adsorption of trapped heavy metals. Therefore, understanding the mechanism that induces Sch transformation and governs heavy metal redistributions is integral for both environmental science and geochemistry research. Given the widespread environmental accumulation of surfactants through human activities, an important yet understudied question arises: How do surfactants influence the transformation of Sch under such environmental conditions? To answer this query, this study investigated the transformation of chromium (Cr)-bearing schwertmannite (Sch-Cr) induced by anionic and cationic surfactants and the subsequent redistribution of Cr(VI). Both the surfactant type and pH affected the transformation of minerals. Specifically, at pH 3.0, goethite was the final product, in which the anionic and cationic surfactant promoted and inhibited mineral transformation, respectively. At pH 6.5, hematite was the final transformation product and both anionic and cationic surfactants inhibited the transformation of minerals. For the initial fixed Cr(VI), after 20 d of aging in the presence of sodium dodecylbenzesulfonate (SDBS), Cr(VI) mainly existed in the form of a solution, whereas in the presence of cetrimonium bromide (CTAB), Cr(VI) mainly existed in the newly formed secondary minerals. This study reveals the complex geochemical behavior of Sch under environmental disturbances in acid sulfate soils and provides insights into the use and potential exploitation of Sch as an adsorbent for heavy metal elements.

Enhanced fluoride extraction from contaminated soil combining chelator and surfactant: Insights into adsorptive controlment of soil surface charge

Biodegradable chelators and surfactants are promising alternatives to conventional washing agents for remediating soil contaminated with toxic elements, owing to their excellent extractability and environmental compatibility. Most previous studies have primarily aimed at maximizing removal efficiency. However, understanding their underlying extraction mechanism is essential to expand the application potential of chelator- or surfactant-assisted washing systems. This study evaluated the effectiveness of chelators and surfactants in remediating fluoride (F)-contaminated soil and explored their associated extraction mechanisms. Our findings highlight a biodegradable chelator, HIDS (3-hydroxy-2,2'-imino disuccinic acid) as uniquely effective in F extraction with minimal F-bearing minerals dissolution (Ca, Fe, and Al). Chelator recovery rates and zeta potential measurements in post-washed solutions suggests that HIDS adsorbs onto soil surfaces, displacing the originally adsorbed F and enhancing the negative surface charge to inhibit F re-adsorption. Additionally, applying an anionic surfactant to enhance F extraction from soil showed promising results. Notably, a binary blend of HIDS and in-lab designed anionic surfactant, SDT (sodium N-dodecanoyl-taurinate), achieved the highest F removal rate (132 mg kg-1) under optimized washing conditions (HIDS: 10 mmol L-1, SDT: 10 mmol L-1, solution pH: 3, and washing time: 1 h), enhancing F extraction by 22% compared to HIDS-only washing (108 mg kg-1; washing time: 3 h). The FT-IR and zeta potential measurements suggested that SDT adsorbed onto the soil surface. The action of the HIDS-SDT blend towards F extraction involves the complexation and acid dissolution of F-bearing soil minerals, followed by F replacement through chelator and surfactant adsorption. This process mitigated F back-adsorption and enhanced F extraction by generating a negatively charged soil surface.

Remediation of fluoride-contaminated wastes: Chelator-assisted washing and subsequent immobilization using CaO and H3PO4

Fluoride (F) contamination in industrial waste is a significant challenge for sustainable materials recycling. Existing techniques for mitigating F contamination focus on immobilization, converting F compounds to insoluble forms while leaving the total F content untreated. Chelator-assisted washing is considered a promising alternative remediation strategy that can indirectly release F by entrapping and dissolving F-bearing minerals. This study evaluates the effectiveness of chelator-assisted washing in removing F from three real F-contaminated waste samples (TCS-49, TCS-51, and TCS-52) by treating with four different chelators, ethylenediaminetetraacetic acid (EDTA), ethylenediamine N,N'-disuccinic acid (EDDS), diethylenetriaminepentaacetic acid (DTPA), and 3-hydroxy-2,2'-imino disuccinic acid (HIDS). The influence of key washing variables, including chelator type, solution pH, chelator concentration, washing time, and liquid-to-solid (L/S) ratio toward F extraction was assessed and optimized for attaining the maximum extraction. All chelators exhibited the highest F extraction from TCS-49 and TCS-51 at pH 11, whereas in TCS-52 it showed a discrete extraction pattern. Under optimized conditions (concentration, 10 mmol L-1; pH, 11; washing duration, 3 h; and L/S ratio, 10:1), EDTA outperformed the other chelators, enhancing F extraction by 2.1 and 1.2 times for TCS-49 and TCS-51, respectively, compared with those of control treatments. However, for TCS-52, the efficiency of EDTA was analogous to that of the control under the same washing conditions. The linear correlation between the extracted F and F-containing minerals suggests that the chelator-induced F removal from contaminated waste involves the entrapment and dissolution of F-bearing minerals, especially Ca and Fe. The subsequent post-washing immobilization of chelator-washed waste residues using CaO or H3PO4 significantly reduced the content of leachable F under the regulatory limit.

Enhancing lead extraction efficiency from contaminated soil: A synergistic approach combining biodegradable chelators and surfactants

Lead (Pb), a persistent and bio-accumulative contaminant, poses threats to the environment and human health. The effective removal of Pb from contaminated soil proves challenging due to its tendency to form stable complexes with soil components. Chelators have been extensively studied for their ability to extract metal contaminants, including Pb, from soil environment. However, the prolonged environmental persistence of traditional chelators and the high cost of biodegradable alternatives have hindered their practical application in remediation efforts. This study investigated a novel synergistic approach that combined a biodegradable chelator, [S,S]-ethylenediamine succinic acid (EDDS), with cationic and anionic surfactants to enhance Pb extraction efficiency. The study revealed that cationic surfactants, such as cetylpyridinium chloride (CPC) and cetyltrimethylammonium bromide (CTAB), significantly enhanced Pb extraction efficiency when combined with EDDS, whereas anionic surfactants, like sodium N-dodecanoyl-taurinate (SDT) and sodium dodecyl sulfate (SDS), inhibited the extraction process. Specifically, blending 5 mmol L-1 EDDS with 20 mmol L-1 CPC resulted in a 72.6% enhancement in Pb extraction efficiency. The proposed synergistic strategy offers a promising avenue for soil remediation, mitigating Pb contamination while preserving essential soil minerals. By addressing chelator limitations and improving efficiency, this approach presents a viable solution for enhancing soil remediation practices.

Remediation of cadmium-contaminated soil: GLDA-assisted extraction and sequential FeCl3-CaO-based post-stabilization

Cadmium (Cd) contamination of farmland soils is a growing concern because of its highly toxic impact on ecosystems and human health. Chelator-assisted washing and chemical immobilization are effective remediation strategies for Cd-contaminated soils. Ethylenediaminetetraacetic acid (EDTA) has traditionally been used for soil washing, but its persistence in the environment and subsequent toxicity have raised significant ecological concerns. Consequently, biodegradable chelators have gained increasing attention as eco-friendly alternatives to the persistent chelator, EDTA. Therefore, this study evaluated the performance and efficacy of three biodegradable chelators: L-glutamate-N,N'-diacetic acid (GLDA), methylglycine-diacetic acid (MGDA), and 3-hydroxy-2,2'-iminodisuccinic acid (HIDS) in comparison to EDTA for remediating a real Cd-contaminated agricultural soil. The influence of treatment parameters, including chelator variants, washing time, chelator concentration, solution pH, and liquid-to-soil ratio (L/S) on Cd extraction was studied and optimized to attain the maximum removal rate. Following chelator-assisted washing, the efficacy of a stabilization preference combining FeCl3 and CaO in reducing the leaching potential of residual Cd in chelator-washed soil residues was also investigated. GLDA demonstrated comparable Cd extraction efficiency to EDTA, and the Cd extraction efficiency was found to be positively correlated with the soil washing parameters. However, under the optimized conditions (chelator concentration: 10 mmol L-1; washing time: 3 h; solution pH: 3; L/S ratio: 10:1), GLDA exhibited a higher Cd extraction rate than EDTA or the other chelators. Furthermore, a post-treatment process incorporating FeCl3 and CaO substantially diminished the water-leachable Cd content in the resultant soil residues. The proposed remediation strategy, which combines chemically assisted washing and stabilization, could be a practical option for extracting bulk Cd from soil and reducing the leaching potential of residual Cd.

Management of arsenic-contaminated excavated soils: A review

Ongoing global sustainable development and underground space utilization projects have inadvertently exposed many excavated soils naturally contaminated with geogenic arsenic (As). Recent investigations have revealed that As in certain excavated soils, especially those originating from deep construction projects, has exceeded regulatory limits, threatening the environment and human health. While numerous remediation techniques exist for treating As-contaminated soil, the unique characteristics of geogenic As contamination in excavated soil require specific measures when leachable As content surpasses established regulatory limits. Consequently, several standard leaching tests have been developed globally to assess As leaching from contaminated soil. However, a comprehensive comparative analysis of these methods and their implementation in contaminated excavated soils remains lacking. Furthermore, the suitability and efficacy of most conventional and advanced techniques for remediating As-contaminated excavated soils remained unexplored. Therefore, this study critically reviews relevant literature and summarize recent research findings concerning the management and mitigation of geogenic As in naturally contaminated excavated soil. The objective of this study was to outline present status of excavated soil globally, the extent and mode of As enrichment, management and mitigation approaches for As-contaminated soil, global excavated soil recycling strategies, and relevant soil contamination countermeasure laws. Additionally, the study provides a concise overview and comparison of standard As leaching tests developed across different countries. Furthermore, this review assessed the suitability of prominent and widely accepted As remediation techniques based on their applicability, acceptability, cost-effectiveness, duration, and overall treatment efficiency. This comprehensive review contributes to a more profound comprehension of the challenges linked to geogenic As contamination in excavated soils.

Risk assessment of toxic and hazardous metals in paddy agroecosystem by biochar-for bio-membrane applications

Toxic and carcinogenic metal (loid)s, such arsenic (As) and cadmium (Cd), found in contaminated paddy soils pose a serious danger to environmental sustainability. Their geochemical activities are complex, making it difficult to manage their contamination. Rice grown in Cd and As-polluted soils ends up in people's bellies, where it can cause cancer, anemia, and the deadly itai sickness. Solving this issue calls for research into eco-friendly and cost-effective remediation technology to lower rice's As and Cd levels. This research delves deeply into the origins of As and Cd in paddy soils, as well as their mobility, bioavailability, and uptake mechanisms by rice plants. It also examines the current methods and reactors used to lower As and Cd contamination in rice. Iron-modified biochar (Fe-BC) is a promising technology for reducing As and Cd toxicity in rice, improving soil health, and boosting rice's nutritional value. Biochar's physiochemical characteristics are enhanced by the addition of iron, making it a potent adsorbent for As and Cd ions. In conclusion, Fe-BC's biomembrane properties make them an attractive option for remediating As- and Cd-contaminated paddy soils. More efficient mitigation measures, including the use of biomembrane technology, can be developed when sustainable agriculture practices are combined with these technologies.

Evaluation of newly designed flushing techniques for on-site remediation of arsenic-contaminated excavated debris

Excavated debris (soil and rock) contaminated with geogenic arsenic (As) is an increasing concern for regulatory organizations and construction stakeholders. Chelator-assisted soil flushing is a promising method for practical on-site remediation of As-contaminated soil, offering technical, economic, and environmental benefits. Ethylenediaminetetraacetic acid (EDTA) is the most prevalent chelator used for remediating As-contaminated soil. However, the extensive environmental persistence and potential toxicity of EDTA necessitate the exploration of eco-compliant alternatives. In this study, the feasibility of the conventional flushing method pump-and-treat and two newly designed immersion and sprinkling techniques were evaluated at the laboratory scale (small-scale laboratory experiments) for the on-site treatment of As-contaminated excavated debris. Two biodegradable chelators, L-glutamic acid-N,N'-diacetic acid (GLDA) and 3-hydroxy-2,2'-iminodisuccinic acid (HIDS), were examined as eco-friendly substitutes for EDTA. Additionally, this study highlights a useful post-treatment measure to ensure minimal mobility of residual As in the chelator-treated debris residues. The pump-and-treat method displayed rapid As-remediation (t, 3 h), but it required a substantial volume of washing solution (100 mL g-1). Conversely, the immersion technique demonstrated an excellent As-extraction rate using a relatively smaller washing solution (0.33 mL g-1) and shorter immersion time (t, 3 h). In contrast, the sprinkling technique showed an increased As-extraction rate over an extended period (t, 48 h). Among the chelators employed, the biodegradable chelator HIDS (10 mmol L-1; pH, 3) exhibited the highest As-extraction efficiency. Furthermore, the post-treatment of chelator-treated debris with FeCl3 and CaO successfully reduced the leachable As content below the permissible limit.

Agent-assisted electrokinetic treatment of sewage sludge: Heavy metal removal effectiveness and nutrient content characteristics

Sewage sludge (SS) is rich in nutrient elements such as phosphorus (P), nitrogen (N), and potassium (K), and therefore a candidate material for use in agriculture. But high content of heavy metals (HMs) can be a major obstacle to its further utilization. Therefore, an appropriate HM removal technology is required before its land application. In this study, an innovative biodegradable agent (citric acid, FeCl₃, ammonium hydroxide, tetrasodium iminodisuccinate (IDS), and tea saponin) assisted electrokinetic treatment (EK) was performed to investigate the HM removal efficiency (R_HMs) and nutrient transportation. Citric acid, IDS, and FeCl₃-assisted EK showed a preferable average R_HMs (R_ave) reduction of 52.74-59.23%, with low energy consumption. After treatment, the content of Hg (0.51 mg kg^-1), Ni (13.23 mg kg^-1), and Pb (26.45 mg kg^-1) elements met the criteria of national risk control standard, in all cases. Following the treatment, most HMs in SS had a reduced potential to be absorbed by plants or be leached into water systems. Risk assessment indicated that the Geoaccumulation index (I_geo) value of HMs has decreased by 0.28-2.40, and the risk of Pb (I_geo=-0.74) reduced to unpolluted potential. Meanwhile, no excessive nutrient loss in SS occurred as a result of the treatment, on the contrary, there was a slight increase in P content (18.17 mg g^-1). These results indicate that agent-assisted EK treatment could be an environmentally-friendly method for R_HMs and nutrient element recovery from SS, opening new opportunities for sustainable SS recycling and its inclusion into circular economy concepts.

A review for recent advances on soil washing remediation technologies

Contaminated soils have caused serious harm to human health and the ecological environment due to the high toxicity of organic and inorganic pollutants, which has attracted extensive attention in recent years. Because of its low cost, simple operation and high efficiency, soil washing technology is widely used to permanently remove various pollutants in contaminated soils and is considered to be the most promising remediation technology. This review summarized the recent developments in the field of soil washing technology and discusses the application of conventional washing agents, advanced emerging washing agents, the recycling of washing effluents and the combination of soil washing and other remediation technologies. Overall, the findings provide a comprehensive understanding of soil washing technology and suggest some potential improvements from a scientific and practical point of view.