Application of apatite particles for remediation of contaminated soil and groundwater: A review and perspectives

Impacts of sugarcane bagasse-derived biochar and apatite on heavy metal speciation in incubated heavy metal-contaminated soil

Heavy metal contamination in soils poses significant environmental and health risks, necessitating effective remediation strategies. This study investigates the time-dependent effects of sugarcane bagasse-derived biochar and apatite as soil amendments on the chemical speciation of heavy metals in polluted soil. Despite their known efficacy, the specific influence of these amendments on the distribution of heavy metal chemical fractions over time remains underexplored. Incubated experiments were conducted over one month using soil samples spiked with Biochar and apatite. Pb- and Zn-contaminated soils were incubated with biochar and apatite at varying ratios: biochar at 5% and 10%, and biochar/apatite mixtures at 2.5:2.5% and 5:5% ratios (in mass). Changes in heavy metal speciation were analyzed using Tessier's sequential extraction procedure. Results demonstrate significant shifts in the distribution of heavy metals across soil phases, suggesting potential reductions in bioavailability and environmental mobility. Incubation with varying application rates of biochar and apatite revealed diverse effects on Pb and Zn chemical fractions. Amendments reduced the exchangeable fraction of Pb and Zn by up to 38.5% and 47.7%, respectively, while increasing their more stable F4 and F5 fractions. Proposed mechanisms likely include cation exchange (swapping of ions between the soil and amendments), precipitation (formation of solid compounds), complexation with functional groups/minerals, and physical adsorption (attachment of metal ions) on biochar surfaces The efficacy of biochar and apatite underscores their promise for remediating Pb and Zn in contaminated soils, though variability in efficacy across different soil types warrants further investigation. These findings indicate the potential for practical applications in large-scale soil remediation projects. Further research is needed to assess the persistence of heavy metal stabilization over time and under varying environmental conditions.

Bacterial activation level determines Cd(II) immobilization efficiency by calcium-phosphate minerals in soil

Soil mineral properties significantly influence the mobility of Cd(II) within the soil matrix. However, the limited understanding of how microbial metabolism affects mineral structure at the microscale poses challenges for in situ remediation. Here, we designed a model calcium-phosphate system in a urea-rich environment to explore the impact of different microbial activation levels on Cd(II) fixation at mineral interfaces. Findings indicate that bacteria affected the morphological structure of the minerals and the amount of carbonate incorporation (average 5.4 %), thereby enhancing Cd(II) immobilization capacity (up to 9.6 times). This process is influenced by the intensity of bacterial activation, as reflected in their urease activity. Extracellular substances secreted by bacteria are also essential for activating minerals, contributing to a sustained decrease in their surface potential. The introduction of activated minerals in potting experiments markedly stimulated the soil urease activity, promoting the enrichment of functional bacteria and facilitating Cd(II) passivation, thereby reducing Cd(II) uptake by vegetables. An extensive soil survey further corroborated a linkage between soil total phosphorus and urease activity, indirectly emphasizing the universality of phosphate mineral-urease microbial interactions and their critical role in the morphological transformation of Cd(II). Our findings highlight the functional dynamics of urease microorganisms in shaping soil mineral landscapes and regulating heavy metal mobility, with broad implications for soil microscale remediation strategies.

Optimized immobilization of lead and cadmium in soil using dithiocarboxy functionalized silica: A long-term effectiveness study

The efficient immobilization of heavy metals often requires a high dosage of remediation material, resulting in increased remediation costs and potential ecological risks. In this study, we developed a novel silica-based material, RNS-TS, characterized by a high density of dithiocarboxy groups, aimed at remediating Pb and Cd contaminated soils and evaluating the long-term efficacy via aging experiments. The synthesized RNS-TS achieved a functional group density of 2.59 mmol/g. At a concentration of 1 %, it effectively reduced the content of bioaccessibility Pb, Cd, and Cu in slightly contaminated soil by 86 %, 82 %, and 100 %; in moderately contaminated soil by 94 %, 75 %, and 100 %; and in heavily contaminated soil by 68 %, 60 %, and 100 %. Furthermore, the remediation process was relatively fast, with equilibrium achieved within one day after adding the RNS-TS. Aging experiments revealed that the remediated products exhibited excellent stability under simulated climate conditions such as extreme temperatures, freeze-thaw cycles and dry-wet cycles etc. Field experiments demonstrated that a 0.2 wt% application of RNS-TS reduced the content of bioaccessible Cd from 0.6 mg/kg to 0.3 mg/kg (approximately 50.8 % reduction), while Cd content in wheat grains decreased from 0.18 mg/kg to 0.08 mg/kg (approximately 54.4 % reduction). This successful application ensured safe wheat production. This material shows great promise as a risk element stabilization agent for heavy metal-contaminated soils.

Effects of coexisting goethite or lepidocrocite on Fe(II)-induced ferrihydrite transformation pathways and Cd speciation

The efficacy of ferrihydrite in remediating Cd-contaminated soil is tightly regulated by Fe(II)-induced mineralogical transformations. Despite the common coexistence of iron minerals such as goethite and lepidocrocite, which can act as templates for secondary mineral formation, the impact of these minerals on Fe(II)-induced ferrihydrite transformation and the associated Cd fate have yet to be elucidated. Herein, we investigated the simultaneous evolution of secondary minerals and Cd speciation during Fe(II)-induced ferrihydrite transformation in the presence of goethite versus lepidocrocite. The presence of goethite resulted in a more pronounced ferrihydrite transformation than lepidocrocite because goethite facilitates electron transfer. Coexisting goethite promoted the production of secondary goethite with different morphology by triggering template-directed nucleation and growth of labile Fe(III) derived from ferrihydrite and intermediate lepidocrocite, respectively. However, coexisting lepidocrocite impeded goethite formation from ferrihydrite and acted as the template to facilitate secondary lepidocrocite production. Furthermore, variations in the crystallinity of coexisting lepidocrocite influenced the particle size and crystallinity of the secondary lepidocrocite, reflecting different dominant mechanisms in secondary lepidocrocite formation. Despite partial Cd mobilization into the solution due to Fe(II)-induced ferrihydrite transformation, secondary goethite and lepidocrocite re-sequestered Cd through lattice Fe(III) substitution, indicated by an increased structural Cd proportion, expanded lattice spacing, and reduced hyperfine field intensity. Additionally, secondary goethite was more effective than secondary lepidocrocite in sequestering Cd. Coexisting goethite increased the structural Cd proportion by 3.5-fold compared to coexisting lepidocrocite, demonstrating the superior ability of coexisting goethite in enhancing Cd stability during Fe(II)-induced ferrihydrite transformation in natural soils. These findings highlight the impact of template-driven mineralogical transformation on Cd fate in polluted soils and provide crucial implications for toxic metal remediation using mineral amendments.

Unveiling the Structural, Electronic and Magnetic Properties of Gd4.5A0.5Si3O13 (A = K, Na, and Li) Oxides With Promising Potential for Low-Temperature Magnetic Cooling

The growing demand for solid-state magnetic cooling, leveraging the magnetocaloric effect requires the discovery of high-performing magnetocaloric materials (MCMs). Herein, a family of Gd-containing MCMs is provided, specifically the Gd4.5A0.5Si3O13 (A = K, Na, and Li) oxides, which demonstratse exceptional low-temperature magnetocaloric performance. Through comprehensive experimental investigations and theoretical calculations on their structural, electronic, and magnetic properties, it is unequivocally confirmed that all of them crystallize in a hexagonal apatite-type structure (space group P63/m), exhibiting an antiferromagnetic semiconductor ground state with magnetic ordering temperatures below 1.8 K (typically ≈0.7 K for Gd4.5K0.5Si3O13). Furthermore, their remarkable maximum magnetic entropy change (-ΔSM max) values of 31.85 and 58.22 J kgK-1 for Gd4.5K0.5Si3O13; 25.31 and 55.01 J kgK-1 for Gd4.5Na0.5Si3O13; and 25.15 and 55.77 J kgK-1 for Gd4.5Li0.5Si3O13, under the magnetic field changes of 0-2 and 0-5 T, respectively, surpass those of prominent low-temperature MCMs, including the commercialized Gd3Ga5O12 (≈14.6 and 32.8 J kgK-1) paramagnetic salt. These findings in addition to their high environmental stability position these Gd4.5A0.5Si3O13 oxides as exceptionally promising for practical magnetic cooling applications.

Sustainable Nanotechnology Based Techniques for Mitigating the Pollutants from Pulp and Paper Industry

Paper mills inevitably produce various pollutants, including chlorolignin, chlorophenols, chloroguaiacol, furan, cyanide, and heavy metals. These pollutants cause significant threats to aquatic and terrestrial life. The pulp and paper industries are looking for eco-friendly solutions for the disposal of effluents during paper processing. Moreover, environmental management practices are a key concern that may be addressed by removing these effluents using suitable bioremediation techniques. Therefore, we have discussed several eco-friendly nanotechnology based sustainable bioremediation technologies like the use of nanoparticles, nanomaterials, nanocomposites, nanoadsorbents, and several advanced methods such as electrocoagulation and photocatalysis, which may be utilized for the elimination of hazardous pollutants from paper industry effluents. This review finally includes critical insight into the potential use of the above-mentioned nanotechnology based interventions for mitigation of contaminants from the paper industry. Nevertheless, there are a few limitations and challenges toward implementation of such technologies, which are also discussed in this review.

Polystyrene microplastics as carriers for nano-hydroxyapatite particles: Impact of surface functionalization and mechanistic insights

The potential of microplastics (MPs) to act as carriers for contaminants or engineered nanomaterials is of rising concern. However, directly determining the vector effect of polystyrene (PS) MPs towards nano-hydroxyapatite (nHAP) particles, a typical nano phosphorus fertilizer and soil remediation material, has been rarely studied. In this study, the interaction of differentially surface functionalized PS MPs with nHAP were investigated through batch experiments under different solution chemistry conditions. The results demonstrated that nHAP had the highest attachment/adsorption affinity onto carboxyl-functionalized PS, followed by bare PS and amino-functionalized PS under near-neutral pH conditions. Adsorption of nHAP exhibited a strong pH-dependent behavior with PS MPs, increasing under acidic-neutral pH (3-7) and decreasing at higher pH values. The presence of humic acid and NaCl hindered the adsorption of nHAP onto MPs. Scanning electron microscopy observations revealed a rod-like morphology for adsorbed nHAP, which was randomly distributed on MPs surface. Surface complexation and cation-π interaction were mainly responsible for the adsorption of nHAP as revealed by multiple spectroscopic analyses. These results provide mechanistic insights into nHAP-PS interactions and expound the effect of surface functionalization of PS on binding mechanisms, and thus bring important clues for better understanding the vector effects of MPs towards nanoparticles.

Non-phytoremediation and phytoremediation technologies of integrated remediation for water and soil heavy metal pollution: A comprehensive review

Since the 1980s, there has been increasing concern over heavy metal pollution remediation. However, most research focused on the individual remediation technologies for heavy metal pollutants in either soil or water. Considering the potential migration of these pollutants, it is necessary to explore effective integrated remediation technologies for soil and water heavy metals. This review thoroughly examines non-phytoremediation technologies likes physical, chemical, and microbial remediation, as well as green remediation approaches involving terrestrial and aquatic phytoremediation. Non-phytoremediation technologies suffer from disadvantages like high costs, secondary pollution risks, and susceptibility to environmental factors. Conversely, phytoremediation technologies have gained significant attention due to their sustainable and environmentally friendly nature. Enhancements through chelating agents, biochar, microorganisms, and genetic engineering have demonstrated improved phytoremediation remediation efficiency. However, it is essential to address the environmental and ecological risks that may arise from the prolonged utilization of these materials and technologies. Lastly, this paper presents an overview of integrated remediation approaches for addressing heavy metal contamination in groundwater-soil-surface water systems and discusses the reasons for the research gaps and future directions. This paper offers valuable insights for comprehensive solutions to heavy metal pollution in water and soil, promoting integrated remediation and sustainable development.

Innovative remediation strategies for persistent organic pollutants in soil and water: A comprehensive review

Persistent organic pollutants (POPs) provide a serious threat to human health and the environment in soil and water ecosystems. This thorough analysis explores creative remediation techniques meant to address POP pollution. Persistent organic pollutants are harmful substances that may withstand natural degradation processes and remain in the environment for long periods of time. Examples of these pollutants include dioxins, insecticides, and polychlorinated biphenyls (PCBs). Because of their extensive existence, cutting-edge and environmentally friendly eradication strategies must be investigated. The most recent advancements in POP clean-up technology for soil and water are evaluated critically in this article. It encompasses a wide range of techniques, such as nanotechnology, phytoremediation, enhanced oxidation processes, and bioremediation. The effectiveness, cost-effectiveness, and environmental sustainability of each method are assessed. Case studies from different parts of the world show the difficulties and effective uses of these novel techniques. The study also addresses new developments in POP regulation and monitoring, highlighting the need of all-encompassing approaches that include risk assessment and management. In order to combat POP pollution, the integration of diverse remediation strategies, hybrid approaches, and the function of natural attenuation are also examined. Researchers, legislators, and environmental professionals tackling the urgent problem of persistent organic pollutants (POPs) in soil and water should benefit greatly from this study, which offers a complete overview of the many approaches available for remediating POPs in soil and water.

Effects of temperature-related changes on charred bone in soil: From P release to microbial community

Phosphorus (P) is one of the most common limited nutrients in terrestrial ecosystems. Animal bones, with abundant bioapatite, are considerable P sources in terrestrial ecosystems. Heating significantly promotes P release from bone bioapatite, which may alleviate P limitation in soil. This study aimed to explore P release from charred bone (CB) under heating at various temperatures (based on common natural heating). It showed that heating at ∼300 °C significantly increased the P release (up to ∼30 mg/kg) from CB compared with other heating temperatures. Then, the subsequent changes of available P and pH induced evident alternation of soil microbial community composition. For instance, CB heated at ∼300 °C caused elevation of phosphate-solubilizing fungi (PSF) abundance. This further stimulated P mobility in the soil. Meanwhile, the fungal community assembly process was shifted from stochastic to deterministic, whereas the bacterial community was relatively stable. This indicated that the bacterial community showed fewer sensitive responses to the CB addition. This study hence elucidated the significant contribution of heated bone materials on P supply. Moreover, functional fungi might assist CB treated by natural heating (e.g., fire) to construct P "Hot Spots".