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The routine dredging of waterways produces huge volumes of sediments. Handling contaminated dredged sediments poses significant and diverse challenges around the world. In recent years, novel and sustainable ex situ remediation technologies for contaminated sediments have been developed and applied. This review article focuses on cement-based binders in stabilizing contaminants through the stabilization/solidification (S/S) technique and the utilization of contaminated sediments as a resource. Through S/S techniques, heavy metals can be solidified and stabilized in dense and durable solid matrices, reducing their permeability and restricting their release into the environment. Industrial by-products like red mud (RM), soda residue (SR), pulverized fly ash (PFA), and alkaline granulated blast furnace slag (GGBS) can immobilize heavy metal ions such as lead, zinc, cadmium, copper, and chromium by precipitation. However, in a strong alkali environment, certain heavy metal ions might dissolve again. To address this, immobilization in low pH media can be achieved using materials like GGBS, metakaolin (MK), and incinerated sewage sludge ash (ISSA). Additionally, heavy metals can be also immobilized through the formation of silicate gels and ettringites during pozzolanic reactions by mechanisms such as adsorption, ion exchanges, and encapsulation. It is foreseeable that, in the future, the scientific community will increasingly turn towards multidisciplinary studies on novel materials, also after an evaluation of the effects on long-term heavy metal stabilization. [ABSTRACT FROM AUTHOR]

Environmental context: Mitigating the environmental fallout of industrial accidents is crucial. In a recent study, researchers conducted tests on model substrates to explore the effectiveness of bioremediation in treating complex refinery contaminants resulting from both accidental and deliberate facility damage. The research reveals that bioremediation can be a promising, eco-friendly solution for cleaning up such pollutants, aligning with broader efforts to combat environmental harm resulting from industrial incidents. Rationale: Bioremediation harnesses microorganisms' diverse metabolic abilities to detoxify and eliminate pollutants, particularly hydrocarbon-based ones such as oil. This natural biodegradation process performed by microorganisms is a cost-effective method for environmental cleanup compared to other remediation technologies. Methodology: In this study, we examined the fate of heavy metals, cobalt and molybdenum, by the analysis of the basic chemical parameters of other sample components, such as n -hexane extractable substances and total petroleum hydrocarbons. The metal content was determined using inductively coupled plasma–optical emission spectrometry (ICP-OES). Exchangeable (loosely bound to the surface of particles and due to its high mobility and availability is crucial for understanding the potential immediate impact of metal contamination) and more stable fractions of the metal and the metal forms were determined using a sequential extraction method. The phase composition of the samples was determined by X-ray diffraction. Results: In our microbiological analysis, we isolated various cultures from a consortium of microorganisms. Basic chemical analysis indicators, such as n -hexane extractable substances, total petroleum hydrocarbons and humic acids, reflected robust microbiological activity. During the study, metals in exchangeable form decreased and those in more stable forms increased. Discussion: The sequential extraction of cobalt and molybdenum revealed shifts in various metal fractions within the bioaugmented substrate post-bioremediation, differing from the initial substrate. These alterations in metal fractions are likely attributable to microbial actions, leading to the formation of more stable metal fractions throughout the bioremediation process. Environmental context. Mitigating the environmental fallout of industrial accidents is crucial. In a recent study, researchers conducted tests on model substrates to explore the effectiveness of bioremediation in treating complex refinery contaminants resulting from both accidental and deliberate facility damage. The research reveals that bioremediation can be a promising, eco-friendly solution for cleaning up such pollutants, aligning with broader efforts to combat environmental harm resulting from industrial incidents. [ABSTRACT FROM AUTHOR]

The most common contaminants in the earth's crust are heavy metals. Remediation is a technique to immobilize, remove, or detoxify these metals in contaminated environments. However, after decades using conventional remediation techniques, new scientific findings indicate that these remediation operations can promote adverse impacts. Given this perspective, a sustainable remediation approach that minimizes environmental, social, and economic impacts has been growing. The objective of this work was to evaluate the chemical immobilization provided by a steel mill industrial waste from the Acid Recovery Plant (ARP) as an alternative to remediate sediments affected by cadmium, lead and zinc. The experiment consisted in adding increasing doses of an ARP industrial residue, consisting mostly of iron oxide, to sediment samples contaminated by a metallurgical industry. After the incubation period, samples from each treatment were removed and submitted to simple extractions (water, acetic acid, DTPA and sodium nitrate) and total pseudo digestion (nitro-perchloric) to determine the bioavailability of Cd, Pb and Zn. The application of the ARP residues provided the formation of complexes associated with the most stable chemical fractions, such as the fraction associated with Fe oxides (F4) and the residual fraction (F5). Treatment with 5% ARP residue was sufficient to reduce the solubility of Cd, Pb and Zn in the sediment studied. Chemical containment proved to be a promising alternative for minimizing the impact of potentially toxic elements (PTEs) in contaminated soils and sediments, as well as being viable from a sustainable point of view. [ABSTRACT FROM AUTHOR]

This article gives a brief review of the use of algae for remediation, including an introduction to its general principles, reported applicability, and utilization. Algae comprises of a broad fusion of photosynthesizing organisms. Based on size and morphology, algae are classified into macro- and microalgae. Algae were the first photosynthetic inhabitant on the earth surface as a result of their ability to utilize sunlight for synthesis of carbon dioxide, nutrients, water and the ability to increase atmospheric oxygen levels. Algae's growth within the environment is determined by the availability of nitrogen, carbon, phosphorous compounds, and other essential trace nutrients within the ecosystem. In line, algae enhance the air with oxygen (O2) synthesized from the photosynthetic mechanism. Phycoremediation have always utilized algae species in the clean-up of various domestic, agricultural, municipal, and industrial wastewaters. Therefore, unlike conventional technologies that have the potential for secondary pollution, high operating costs, insufficient utilization of the natural resources, and a general public health burden brought on by the potential waterborne diseases, phycoremediation technology offers a sustainable, economical, and environmentally friendly method of remediating wastewater pollutants. [ABSTRACT FROM AUTHOR]

Heavy metal contamination has occurred as a result of industrial civilization. Zinc, copper, chromium, and lead are the most prevalent heavy metal pollutants. Heavy metal contamination has arisen as a significant environmental issue on a global scale. Human and environmental health is at risk when soils are contaminated. as well as having poor engineering qualities. Solidification/Stabilization is a critical remediation strategy for polluted soils which is both efficient and cost-effective. The solidification/stabilization approach has been frequently used to rehabilitate heavy metal-contaminated areas. First, The use of gypsum to strengthen and leach polluted soils was reviewed. Also, cement/fly ash-solidified/stabilized soils have better engineering qualities. On the other hand, the global output of phosphogypsum surpasses 300 million tons, raising disposal and environmental problems every year. The efficiency of the phosphogypsum-based stabilization/solidification technique was investigated, and the methods employed biochar and chemical agents such as citric acid and FeCl3. This review examines various remediation options as well as innovative soil amendments. [ABSTRACT FROM AUTHOR]

• A novel strategy, classification, grading, and zoning (CGZ) can reduce the environmental impact of remediation by 24 %. • Pre-remediation survey, stabilizer selection and farmer compensation are key influencing factors for the CGZ strategy. • High-density sampling (e.g., 20 m) in complex/marginal areas offers enhanced life cycle environmental benefits. • Crop's bioconcentration factors may be a tradeoff factor for stabilization and crop substitution in remediation. Sustainable remediation is crucial for agricultural soil in China as 19.4 % of soil samples are contaminated by toxic substances. Current remediation strategies, classification management and pollution grading, cannot support sustainable remediation because of lacking refined zoning and over-engineering. To address these shortcomings, we synthesized a new strategy: classification, grading, and zoning (CGZ), and performed a life cycle assessment to determine its benefits. The results showed that the CGZ strategy reduced environmental impacts by 24 % and 19 % when applied in 1.45 km2 of contaminated land (3 years from survey to remediation). These reductions were attributed to optimizing remediation technologies for various planting zones and minimizing the remediation area through balancing the primary and secondary impacts of pre-surveys and the remediation itself. Meanwhile, sustaining these remediation efforts over the long term must include equitable farmer compensation based on crop type to mitigate future environmental consequences associated with farmers switching crops. [Display omitted] [ABSTRACT FROM AUTHOR]

Heavy metal contamination has occurred as a result of industrial civilization. Zinc, copper, chromium, and lead are the most prevalent heavy metal pollutants. Heavy metal contamination has arisen as a significant environmental issue on a global scale. Human and environmental health is at risk when soils are contaminated. as well as have poor engineering qualities. Solidification/Stabilization is a critical remediation strategy for polluted soils which is both efficient and cost-effective. The solidification/stabilization approach has been frequently used to rehabilitate heavy metal-contaminated areas. First, The use of gypsum to strengthen and leach polluted soils was reviewed. Also, cement/fly ash-solidified/stabilized soils have better engineering qualities. On the other hand, the global output of phosphogypsum surpasses 300 million tons, raising disposal and environmental problems every year. The efficiency of the phosphogypsum-based stabilization/solidification technique was investigated, and the methods employed biochar and chemical agents such as citric acid and FeCl3. This review examines various remediation options as well as innovative soil amendments.

Extensive research to date has focused on the coagulation-flocculation and biosorption properties of the invasive Opuntia ficus-indica (L.) Mill. to remove metals from water. However, no studies have reported on the use of O. ficus-indica extract as a leaching agent to remove metals from contaminated soil. In the present work, a new environmentally friendly method for lead-contaminated soil remediation is evaluated. The method involves the use of cladode extract from O. ficus-indica as a soil washing agent. This new technique can serve to mitigate against the potential deterioration of soil quality and other secondary environmental impacts that result from the use of inorganic acids and/or chelating agents. Extractions from cladodes harvested during both day and night crassulacean acidic metabolism (CAM) phases were evaluated for treatment of lead contamination in three different soils including kaolinite, montmorillonite and a field-natural soil sample. Lead removal rates, which ranged from 44 to 100%, were significantly impacted by the intrinsic properties of the soils, the leachate dosage, the plant harvest phase, and the soil washing duration. Fourier-transform infrared spectroscopy (FTIR) characterization of the leachates indicated that functional groups present in the O. ficus-indica extracts played an essential role in the removal process. Results suggest that this species possesses promising potential to be used as a sustainable basis for the abatement of lead contaminated soil. [ABSTRACT FROM AUTHOR]

Many agricultural areas are contaminated by heavy metals to such a level that the growth of plants is drastically reduced. Based on the site's specific characteristics, feasibility studies were carried out to choose the most effective technologies. Feasibility tests showed that soil washing and phytoremediation technologies could be used at the agricultural site under study. The efficiency of the technologies is highly dependent on soil characteristics, which determine the chemical form of the metals. The results indicate that water-based soil washing can be successfully used with the possibility of reaching the remediation objectives quickly. However, the technology in the first step essentially breaks down the soil. Moreover, phytoremediation cannot be used directly to overcome the toxicity derived from the very high bioavailability of the heavy metals. Still, there is the need to use "assisted" phytoremediation by adding compost that reduces metal bioavailability, allowing phytoextraction. In this case, a longer time is needed to reach the remediation target. The results provide a preliminary scenario for decision-makers and stakeholders to assess possible technologies applicable and a possible scheme to be applied in similar cases of polluted agricultural areas. [ABSTRACT FROM AUTHOR]

Multi-criteria analysis and detailed impact analysis were carried out to assess the sustainability of four remedial alternatives for metal-contaminated soil/sediment at former timber treatment sites and harbour sediment with different scales. The sustainability was evaluated in the aspects of human health and safety, environment, stakeholder concern, and land use, under four different scenarios with varying weighting factors. The Monte Carlo simulation was performed to reveal the likelihood of accomplishing sustainable remediation with different treatment options at different sites. The results showed that in-situ remedial technologies were more sustainable than ex-situ ones, where in-situ containment demonstrated both the most sustainable result and the highest probability to achieve sustainability amongst the four remedial alternatives in this study, reflecting the lesser extent of off-site and on-site impacts. Concerns associated with ex-situ options were adverse impacts tied to all four aspects and caused by excavation, extraction, and off-site disposal. The results of this study suggested the importance of considering the uncertainties resulting from the remedial options (i.e., stochastic analysis) in addition to the overall sustainability scores (i.e., deterministic analysis). The developed framework and model simulation could serve as an assessment for the sustainability likelihood of remedial options to ensure sustainable remediation of contaminated sites. [ABSTRACT FROM AUTHOR]

A new concept of removal and recovery of heavy metals and simultaneous regeneration and reuse of ethylenediamine-tetraacetic acid (EDTA) in soil washing effluent containing metal-EDTA complexes is proposed, which is used to remediate heavy metal contaminated soil. To achieve this goal, soil washing approach coupled with rectangular wave asymmetrical alternative current electrochemistry (RW-ACE) equipped with amidoxime-functionalized electrodes (Ami-CF) is employed. With high hydrophilicity and strong binding affinity, Ami-CF could specifically compete for heavy metals over EDTA under electric field. RW-ACE system is found successfully to achieve the non-destructive decomplexation of heavy metal-EDTA, and then regenerate EDTA for highly recycling, which saves as high as 98.9 % EDTA consumption compared with conventional washing method. Moreover, more than 90% of heavy metals are recovered and deposited on the electrode with a majority of them existed as zero-valence state as evidenced by XPS. The RW-ACE method is universal for various heavy metals such as Cu2+, Zn2+, Cd2+, and Pb2+ in an authentic contaminated soil, and the loss of soil nutrient is very limited. Along with long-term assessment and operation cost estimation, the RW-ACE method is a sustainable remediation approach for the heavy metal polluted wastewater and soils, and easily scaled up for field practice. [Display omitted] Heavy metal contaminated wastewater and soil has become a serious worldwide problem that endangers both the environment and human health. The newly developed rectangular wave asymmetrical alternative current electrochemistry (RW-ACE) equipped with amidoxime-functionalized electrodes (Ami-CF) makes great process in sustainable decontamination of heavy metal in wastewater and soil, achieving simultaneous recovery of heavy metals and ethylenediamine-tetraacetic acid (EDTA) in wastewater or soil washing solutions containing metal-EDTA complexes. Long-term performance and economic feasibility assessment validated that RW-ACE is highly cost-efficient and sustainable, which could potentially be as next-generation method for remediation of heavy metal contaminated soil and corresponding water purification. • A novel rectangular wave alternative current electrochemical (RW-ACE) system was proposed. • Non-destructive decomplexation of heavy metal-EDTA was achieved by RW-ACE system. • Universal soil washing coupled with RW-ACE achieved sustainable soil remediation. • As high as 98.9% EDTA consumption was saved compared with conventional soil washing. • RW-ACE method greatly retained soil nutrients while efficiently removed heavy metals. [ABSTRACT FROM AUTHOR]

Red mud and phosphogypsum are voluminous industrial by-products worldwide. They have long been disposed of in landfills or open storage, leading to a waste of resource and environmental pollution. This study provides a novel approach to recycle these industrial by-products as sustainable red mud-phosphogypsum-Portland cement (RPPC) binders for stabilization/solidification (S/S) of multimetal-contaminated soil. The physical strength, metal leachability and microstructure of S/S soil were investigated after 7-day and 28-day curing, as well as freezing-thawing (F-T) cycle and wetting-drying (W-D) cycle. The results show that the strength of soil treated by all binders fulfilled the uniaxial compressive strength requirement (350 kPa) of S/S waste in landfills. Microstructural analyses show that the main hydration products of the RPPC S/S soil are ilmenite, ettringite, anhydrite and hydrated calcium silicate. The 10% and 15% RPPC binders have a competitive metal immobilization ability compared with 10% PC, but the immobilization priority is different: Pb > Zn > Cd in RPPC system and Zn > Cd > Pb in PC system, respectively, probably due to the precipiataion of Pb2+ with the abundant SO 4 2− in phosphogypsum in RPPC system. The strength of RPPC and PC treated soil was still higher than 350 kPa except for RPPC7.5 after 10 freeze-thaw or 10 wetting-drying cycles. The RPPC binder performed worse than PC binder after both freeze-thaw and wetting-drying cycles, especially at a lower dosage. Only the metal leaching concentrations of samples treated by RPPC15 and PC10 could fulfil the Chinese standards for hazardous wastes. [Display omitted] • Red mud and phosphogypsum were recycled into a sustainable binder for S/S. • RPPC binder showed an excellent efficiency for heavy metal immobilization. • Immobilization priority of heavy metals in RPPC system is Pb > Zn > Cd. • RPPC binder showed comparable durability, especially against freeze-thaw cycles. Red mud and phosphogypsum were recycled into a sustainable binder for stabilization/solidification of multimetal-contaminated soil. [ABSTRACT FROM AUTHOR]

Among the toxic metals, hexavalent chromium [Cr(VI)] has attracted much attention due to its high mobility and toxicity, rendering considerable challenges for long-term remediation. In this study, the soil was collected from a dichromate contaminated industrial site in Liaoning Province, a seasonally frozen area in northern China, and subjected to frequent freeze-thaw cycles. Three additives, including (i) ferrous sulfate; (ii) calcium polysulfide; and (iii) combined biochar and calcium polysulfide were applied to reduce and immobilize Cr(VI) in the soils. The samples underwent 28 days of incubation followed by 16 freeze-thaw cycles. The toxicity characteristic leaching procedure (TCLP) and simulated acid rain leaching were adopted to test the remediation performances. It was observed that all three treatments can significantly reduce and immobilize Cr(VI) after short-term incubation, while biochar with abundant functional groups could adsorb and reduce Cr(VI) effectively. Notably, the concentration of Cr(VI) in TCLP leachates after incubation in combined treatment decreased by 67.87% and 37.27%, respectively, compared with the application of ferrous sulfate or calcium polysulfide alone. Freeze-thaw cycles induced the disintegration of soil particles and increased the risk of contaminant mobilization. Conversely, biochar particles has become finer and even produced nanoparticles with ageing, accompanied by the increase in oxygen-containing surface functional groups. Additionally, the specific surface area increased with the pyrolysis of biochar, which further enhanced the retention of soil colloidal particles and suppressed the migration of contaminants. Therefore, the cumulative release of Cr(VI) in the combined treatment (i.e., 10.97 ~ 32.97 mg/kg) was much lower than that of the other two treatments after freeze-thaw ageing. Overall, the combination of biochar and calcium polysulfide displayed advantages in the reduction and immobilization of Cr(VI), and offered a long-term, effective strategy for the remediation of Cr(VI) contaminated soils in cold regions. [Display omitted] ● Application of biochar plus calcium polysulfide enhanced Cr(VI) immobilization. ● Immobilization was associated with reduction and surface complexation. ● Freeze-thaw ageing re-mobilized soil Cr(VI). ● Biochar particles became finer and even produced nanoparticles with ageing. ● This amendment is suitable for long-term remediation of seasonally-frozen areas. [ABSTRACT FROM AUTHOR]

In washing soils contaminated with toxic metals, the replacement of recalcitrant EDTA with biodegradable chelators has gained high expectations. Herein we investigated the feasibility of using EDTA and biodegradable GLDA, EDDS and IDS under conditions pertinent to operational remediation technology, in a pilot-scale experiment. GLDA and IDS did not precipitate from process solutions, which lessened their recyclability. In other process parameters, chelator supplement, Na-saturation of process solutions and processing time, EDTA outperformed biodegradable chelators. Treatment with EDTA was also the most effective in total Pb and Zn removal and least impacted soil properties. GLDA was slightly better in Cd removal. EDDS and IDS were inefficient. All chelators effectively removed easily-available Pb, Zn and Cd from the exchangeable soil fraction. EDTA was the most efficient chelator in reducing the bioaccessibility of Pb and GLDA in reducing the bioaccessibility of Cd from simulated human gastrointestinal tract. Treatment with GLDA had an edge in reducing plant bioaccessibility of toxic metals, but induced worrying leachability of Pb. This was 8.3-times higher than with the process with EDTA and 3.4-times higher than in original soil. In general, our results demonstrate the advantage of EDTA over tested biodegradable chelators in process and remediation efficiency and environmental safety. Image 1 • In soil washing biodegradable chelators are often preferred over persistent EDTA. • Current knowledge is based on data from small-scale soil extraction experiments. • EDTA and biodegradable chelators were tested in operational soil-washing process. • Recyclability, efficiency, soil impact and safety of chelators were assessed. • In most aspects EDTA outperformed biodegradable chelators GLDA, EDDS and IDS. [ABSTRACT FROM AUTHOR]