Immobilization Of Heavy Metals Research Articles

Montmorillonite-coupled microbially induced carbonate precipitation (MICP) enhanced contaminant removal and carbon capture in cyanide tailings

Microbial induced carbonate precipitation (MICP) technology is an effective method for immobilization of heavy metals in tailings. However, how to sustainably improve the removal of contaminants and the carbon capture capacity of tailings is a current concern. In this study, montmorillonite-coupled MICP (Mt-MICP) process is proposed to solidify cyanide tailings by improving mineralization properties, heavy metal and cyanide removal, and carbon capture. The results showed that Mt -MICP increased the amount of mineralized precipitation by 0.16–1.33 times; Total cyanide (T-CN) and free cyanide (F-CN) concentrations were reduced by 82.00 and 97.14 %, respectively; Cr, Zn, Cu and Pb leaching concentrations were reduced by 87.18, 42.85, 60.56 and 88.79 %, respectively. Characterizations results such as X-computed tomography (X-CT) confirmed that Mt enhanced the uniformity of the bio-cementation. Furthermore, the Mt-MICP process increased CO2 capture from tailings by 27.15∼34.55 %. Density Functional Theory (DFT) and thermogravimetry (TG) showed that Mt increased the adsorption energy of tailings for CO2 and was converted to CaCO3 by urea catalysis. This work provided new insights into the harmless treatment of CT and microbial carbon capture.

Biochar Blended with Alkaline Mineral Can Better Inhibit Lead and Cadmium Uptake and Promote the Growth of Vegetables.

Three successive vegetable pot experiments were conducted to assess the effects on the long-term immobilization of heavy metals in soil and crop yield improvement after the addition of peanut shell biochar and an alkaline mineral to an acidic soil contaminated with lead and cadmium. Compared with the CK treatment, the change rates of biomass in the edible parts of the three types of vegetables treated with B0.3, B1, B3, B9, R0.2 and B1R0.2 were -15.43%~123.30%, 35.10%~269.09%, 40.77%~929.31%, -26.08%~711.99%, 44.14%~1067.12% and 53.09%~1139.06%, respectively. The cadmium contents in the edible parts of the three vegetables treated with these six additives reduced by 2.08%~13.21%, 9.56%~24.78%, 9.96%~35.61%, 41.96%~78.42%, -4.19%~57.07% and 12.43%~65.92%, respectively, while the lead contents in the edible parts reduced by -15.70%~59.47%, 6.55%~70.75%, 3.40%~80.10%, 55.26%~89.79%, 11.05%~70.15% and 50.35%~79.25%, respectively. Due to the increases in soil pH, soil cation-exchange capacity and soil organic carbon content, the accumulation of Cd and Pb in the vegetables was most notably reduced with a high dosage of 9% peanut shell biochar alone, followed by the addition of a low dosage of 1% peanut shell biochar blended with 0.2% alkaline mineral. Therefore, the addition of a low dosage of 1% peanut shell biochar blended with 0.2% alkaline mineral was the best additive in increasing the vegetable biomass, whereas the addition of 9% peanut shell biochar alone was the worst. Evidently, the addition of 0.2% alkaline mineral can significantly reduce the amount of peanut shell needed for passivating heavy metals in soil, while it also achieves the effect of increasing the vegetable yield.

The potential of magnetic biochar prepared by a solvent-free method as a soil amendment: Metal immobilization performance, soil microbial co-occurrence network and community assembly mechanism

Magnetic biochar (MBC) is widely recognized as an effective soil amendment for the immobilization of heavy metals in soils. However, the most commonly used methods currently for manufacturing MBC necessitate the use of iron salt solutions, leading to energy consumption for dehydration and potential environmental risks. Here, we fabricated a magnetic biochar based on the solvent-free method and applied it as a soil passivator at a rate of 5 % (w/w) for 90 days. The metal immobilization performance of MBC was investigated, together with its soil micro-ecological effects including the impacts of MBC application on soil microbial community diversity, composition, co-occurrence network pattern and assembly mechanism. The results showed that MBC treatment significantly decreased the DTPA-extractable Cd and Zn by 54.1 % and 59.5 % (P<0.05) after the 90-day incubation, respectively, higher than that of biochar (BC) treatment (25.6 % for Cd and 50.4 % for Zn). The transformation of Cd, Zn and Pb from labile fractions to residual fraction was facilitated in MBC treatment. Besides, MBC application significantly increased soil pH, soil organic matter content and cation exchange capacity (P<0.05). The addition of MBC considerably altered the soil bacterial community diversity and composition. Both soil environmental variables and bioavailability of metals shaped microbial communities, while the latter explained more. Compared to CK, the complexity and stability of the co-occurrence network in MBC-amended soil were enhanced. Null model analysis implied that the microbial community assembly was governed by the stochastic process in MBC treatment, while the deterministic process was the dominant mechanism initially. Overall, our findings provide insight into the ecological mechanisms and interactions of soil microbial communities in response to MBC application and demonstrate that MBC is a promising amendment for metal-contaminated soil remediation.

Effects of biochar and magnesium oxide on cadmium immobilized by microbially induced carbonate: Mobilization or immobilization in alkaline agricultural soils?

Microbially induced carbonate precipitation (MICP) is a promising technique for remediating heavy metal-contaminated soils. However, the effectiveness of MICP in immobilizing Cd in alkaline calcareous soils, especially when applied in agricultural soils, remains unclear. Biochar and magnesium oxide are two environmentally friendly passivating materials, and there are few reports on the combined application of MICP with passivating materials for remediating heavy metal-contaminated soils. Additionally, the number of treatments with MICP cement and the concentration of calcium chloride during the MICP process can both affect the effectiveness of heavy metal immobilization by MICP. Therefore, we conducted MICP and MICP-biochar-magnesium oxide treatments on agricultural soils collected from Baiyin, Gansu Province (pH = 8.62), and analyzed the effects of the number of treatments with cement and the concentration of calcium chloride on the immobilization of Cd by MICP and combined treatments. The results showed that early-stage MICP could immobilize exchangeable cadmium and increase the residual cadmium content, especially with high-concentration calcium chloride MICP treatment. However, in the later stage, soil nitrification and exchange processes led to the dissolution of carbonate-bound cadmium and cadmium activation. The fixing effect of MICP influence whether the MICP-MgO-biochar is superior to the MgO-biochar. Four treatments with cement were more effective than single treatment in MICP-biochar-magnesium oxide treatment, and the MICP-biochar-magnesium oxide treatment with four treatments was the most effective, with passivation rates of 40.7% and 46.6% for exchangeable cadmium and bioavailable cadmium, respectively. However, attention should be paid to the increase in soil salinity. The main mechanism of MICP-magnesium oxide-biochar treatment in immobilizing cadmium was the formation of Cd(OH)2, followed by the formation of cadmium carbonate.

Immobilization of Heavy Metals by Phosphorus-solubilizing Bacteria and Inhibition of Cd and Pb Uptake by Wheat

Phosphorus-solubilizing microorganisms convert insoluble phosphorus in the soil into phosphorus that can be absorbed by plants. Soluble phosphate combines with heavy metals to form precipitation, reducing the content of available heavy metals, thereby reducing the absorption of heavy metals by crops, which plays an important role in the remediation of heavy metal-contaminated soil. The effects of the immobilization of Cd and Pb and the release of PO43- by the phosphorus-solubilizing bacterium Klebsiella sp. M2 were studied through solution culture experiments. In addition, the effects of strain M2 on wheat uptake of Cd and Pb and its microbiological mechanism were also explored through pot experiments. The results showed that strain M2 reduced the concentrations of Cd and Pb and increased the concentration of PO43- in the solution through cell wall adsorption and induced phosphate precipitation. Pot experiments showed that compared to those in the CK group and inactivated strain M2 group, inoculation with live strain M2 significantly increased （123%-293%） the contents of Ca2-P and Ca8-P in rhizosphere soil, decreased the content of DTPA-Cd （34.48%） and DTPA-Pb （36.72%） in wheat rhizosphere soil, and thus hindered the accumulation of Cd and Pb in wheat grains. Moreover, high-throughput sequencing results showed that strain M2 significantly increased the diversity of wheat rhizosphere bacterial communities； increased the relative abundance of Proteobacteria, Gemmatimonadetes, and Bacteroidota in wheat rhizosphere soil； and increased the proportion of heavy metal-immobilizing and phosphorus-promoting bacteria in wheat rhizosphere soil （mainly Sphingomonas, Nocardioides, Bacillus, Gemmatimonas, and Enterobacter）. These bacterial genera played an important role in immobilizing heavy metals and preventing wheat from absorbing heavy metals. These results provide bacterial resources and theoretical basis for the bioremediation of heavy metal-contaminated farmland.

Novel strategy for efficient energy recovery and pollutant control from sewage sludge and food waste treatment

Considering the high organic matter contents and pollutants in sewage sludge (SS) and food waste (FW), seeking green and effective technology for energy recovery and pollutant control is a big challenge. In this study, we proposed a integrated technology combing SS mass separation by hydrothermal pretreatment, methane production from co-digestion of hydrothermally treated sewage sludge (HSS) centrate and FW, and biochar production from co-pyrolysis of HSS cake and digestate with heavy metal immobilization for synergistic utilization of SS and FW. The results showed that the co-digestion of HSS centrate with FW reduced the NH4+-N concentration and promoted volatile fatty acids conversion, leading to a more robust anaerobic system for better methane generation. Among the co-pyrolysis of HSS cake and digestate, digestate addition improved biochar quality with heavy metals immobilization and toxicity reduction. Following the lab-scale investigation, the pilot-scale verification was successfully performed (except the co-digestion process). The mass and energy balance revealed that the produced methane could supply the whole energy consumption of the integrated system with 26.2 t biochar generation for treating 300 t SS and 120 t FW. This study presents a new strategy and technology validation for synergistic treatment of SS and FW with resource recovery and pollutants control.

Effects of enzyme-induced carbonate precipitation technique on multiple heavy metals immobilization and unconfined compressive strength improvement of contaminated sand

Enzyme-induced carbonate precipitation (EICP) has been studied in remediation of heavy metal contaminated water or soil in recent years. This paper aims to investigate the immobilization mechanism of Zn2+, Ni2+, and Cr(VI) in contaminated sand, as well as strength enhancement of sand specimens by using EICP method with crude sword bean urease extracts. A series of liquid batch tests and artificially contaminated sand remediation experiments were conducted to explore the heavy metal immobilization efficacy and mechanisms. Results showed that the urea hydrolysis completion efficiency decreased as the Ca2+ concentration increased and the heavy metal immobilization percentage increased with the concentration of Ca2+ and treatment cycles in contaminated sand. After four treatment cycles with 0.5 mol/L Ca2+ added, the immobilization percentage of Zn2+, Ni2+, and Cr(VI) were 99.99 %, 86.38 %, and 75.18 %, respectively. The microscale analysis results presented that carbonate precipitates and metallic oxide such as CaCO3, ZnCO3, NiCO3, Zn(OH)2, and CrO(OH) were generated in liquid batch tests and sand remediation experiments. The SEM-EDS and FTIR results also showed that organic molecules and CaCO3 may adsorb or complex heavy metal ions. Thus, the immobilization mechanism of EICP method with crude sword bean urease can be considered as biomineralization, as well as adsorption and complexation by organic matter and calcium carbonate. The unconfined compressive strength of EICP-treated contaminated sand specimens demonstrated a positive correlation with the increased generation of carbonate precipitates, being up to 306 kPa after four treatment cycles with shear failure mode. Crude sword bean urease with 0.5 mol/L Ca2+ added is recommended to immobilize multiple heavy metal ions and enhance soil strength.

Structural studies of calcium silicate hydrate modified with heavy metal cations

This study investigates the immobilization mechanisms of heavy metal ions in the C-S-H phase. Synthetic C-S-H phases were prepared via the precipitation method, incorporating five different ions (Pb(II), Cd(II), Ni(II), Zn(II), and Cr(III)). Structural analysis of the obtained material was conducted using vibrational spectroscopy (both FT-IR and Raman), X-ray photoelectron spectroscopy, and X-ray diffraction. Spectroscopic methods were primarily employed to evaluate the structural effects and polymerization degree of the resulting C-S-H phase. Morphological changes were characterized using scanning and transmission electron microscopy (SEM and TEM, respectively). Our findings reveal several mechanisms for immobilizing heavy metal cations: precipitation of insoluble compounds (particularly notable for Ni(II) and Cr(III)), replacement of Ca(II) ions within the silicate structure (evident in the crystallization of Ca(OH)2 in samples containing Cd(II), Ni(II), and Zn(II) in minimal quantities), and strong bonding of certain metals (such as Pb(II)) with the C-S-H phase structure. These insights contribute to understanding the potential applications of C-S-H phases in heavy metal immobilization.

Isolation of biocrust cyanobacteria and evaluation of Cu, Pb, and Zn immobilisation potential for soil restoration and sustainable agriculture

Soil contamination by heavy metals represents an important environmental and public health problem of global concern. Biocrust-forming cyanobacteria offer promise for heavy metal immobilisation in contaminated soils due to their unique characteristics, including their ability to grow in contaminated soils and produce exopolysaccharides (EPS). However, limited research has analysed the representativeness of cyanobacteria in metal-contaminated soils. Additionally, there is a lack of studies examining how cyanobacteria adaptation to specific environments can impact their metal-binding capacity. To address this research gap, we conducted a study analysing the bacterial communities of cyanobacteria-dominated biocrusts in a contaminated area from South Sardinia (Italy). Additionally, by using two distinct approaches, we isolated three Nostoc commune strains from cyanobacteria-dominated biocrust and we also evaluated their potential to immobilise heavy metals. The first isolation method involved acclimatizing biocrust samples in liquid medium while, in the second method, biocrust samples were directly seeded onto agar plates. The microbial community analysis revealed Cyanobacteria, Bacteroidota, Proteobacteria, and Actinobacteria as the predominant groups, with cyanobacteria representing between 13.3 % and 26.0 % of the total community. Despite belonging to the same species, these strains exhibited different growth rates (1.1–2.2 g L−1 of biomass) and capacities for EPS production (400–1786 mg L−1). The three strains demonstrated a notable ability for metal immobilisation, removing up to 88.9 % of Cu, 86.2 % of Pb, and 45.3 % of Zn from liquid medium. Cyanobacteria EPS production showed a strong correlation with the removal of Cu, indicating its role in facilitating metal immobilisation. Furthermore, differences in Pb immobilisation (40–86.2 %) suggest possible environmental adaptation mechanisms of the strains. This study highlights the promising application of N. commune strains for metal immobilisation in soils, offering a potential bioremediation tool to combat the adverse effects of soil contamination and promote environmental sustainability.

The role of soil structure on the cracking and cadmium leaching behavior of biochar-amended fine-grained soils

Biochar has shown promising potential for soil remediation, yet its impact on heavy metals (HMs) immobilization often overlooks soil structure, which could influence soil cracking behavior and HMs transport. To address this gap, this study investigates the role of soil structure (dry density and aggregate size) on the cracking and cadmium (Cd) leaching behavior of biochar-amended fine-grained soils. A series of semi-dynamic leaching tests were conducted on samples with and without wetting-drying (W-D) cycles. Based on the proposed improved method for quantifying the effective diffusion coefficient (De) of Cd in unsaturated soils and microstructural analyses, we found that: (1) Higher dry density and larger aggregate generally resulted in smaller De by decreasing soil pore volume. (2) Biochar could connect isolated pores within large aggregates through its internal pores, yielding greater increases in De (294.8%–469.0%) compared to small aggregates (29.1%–77.4%) with 3% biochar. However, further increases in biochar dosage led to decreased De, primarily due to the dense pore structure. (3) Biochar effectively inhibited soil cracking, achieving the highest reduction of 36.8% in surface crack ratio. (4) After W-D cycles, samples exhibited higher De with increasing dry density, with aggravated cracking being the primary cause, suggesting preferential flow within the cracks, particularly those penetrating the soil. This study highlights the importance of careful consideration of soil structure and cracking potential before in situ field application of biochar as a remediation agent for HMs-contaminated fine-grained soils.

Efficient Immobilization of heavy metals using newly synthesized magnetic nanoparticles and some bacteria in a multi-metal contaminated soil.

Simultaneous application of modified Fe3O4 with biological treatments in remediating multi-metal polluted soils, has rarely been investigated. Thus, a pioneering approach towards sustainable environmental remediation strategies is crucial. In this study, we aimed to improve the efficiency of Fe3O4 as adsorbents for heavy metals (HMs) by applying protective coatings. We synthesized core-shell magnetite nanoparticles coated with modified nanocellulose, nanohydrochar, and nanobiochar, and investigated their effectiveness in conjunction with bacteria (Pseudomonas putida and Bacillus megaterium) for remediating a multi-metal contamination soil. The results showed that the coatings significantly enhanced the immobilization of heavy metals in the soil, even at low doses (0.5%). The coating of nanocellulose had the highest efficiency in stabilizing metals due to the greater variety of surface functional groups and higher specific surface area (63.86 m2 g-1) than the other two coatings. Interestingly, uncoated Fe3O4 had lower performance (113.6 m2 g-1) due to their susceptibility to deformation and oxidation. The use of bacteria as a biological treatment led to an increase in the stabilization of metals in soil. In fact, Pseudomonas putida and Bacillus megaterium increased immobilization of HMs in soil successfully because of extracellular polymeric substances and intensive negative charges. Analysis of metal concentrations in plants revealed that Ni and Zn accumulated in the roots, while Pb and Cd were transferred from the roots to the shoots. Treatment Fe3O4 coated with modified nanocellulose at rates of 0.5 and 1% along with Pseudomonas putida showed the highest effect in stabilizing metals. Application of coated Fe3O4 for in-situ immobilization of HMs in contamination soils is recommendable due to their high metal stabilization efficiency and suitability to apply in large quantities.

Harnessing Biochar in Contaminated Soil for Heavy Metal Immobilization, Soil Health Enhancement, and Carbon Sequestration

Harnessing Biochar in Contaminated Soil for Heavy Metal Immobilization, Soil Health Enhancement, and Carbon Sequestration

Reactivity of air granulated basic oxygen furnace steel slag and its immobilization of heavy metals

Air granulation of basic Oxygen furnace slag can improve its hydraulic potential to enhance recycling potential. The hydration behaviour of the slag has been investigated via isothermal calorimetry, QXRD, and TG/DTG analysis. The air granulated slag exhibited improved early-age hydration and led to the formation of C–S–H, hydrogarnet, and hydrotalcite phases. The slag reactivity is controlled by the dissolution of SiO2 and Fe2O3 bearing phases as observed by SEM-EDX-based PARC analysis and the hydration degree reaches up to 41% after 28 days curing. The hydrated slag features an improved immobilization of V and Cr as confirmed by ICP-OES analysis.

Ash from gasification of poultry feathers for heavy metal immobilization under assisted phytostabilization in soils

The carried-out experiment aimed to assess the influence of ash derived from the thermochemical conversion of feathers (AGF) as a soil amendment, and Dactylis glomerata L. as a test plant in aided phytostabilization of soil strongly contaminated by Cu, Cd, Pb and Zn. The influence of AHG on the chemical properties of soil (pH as well as total and CaCl2-extracted heavy metals) as well as the plant yield and concentration of heavy metals in the roots and shoots. The applied soil amendment influenced an increase in the pH values of soil (by 0.4 units) and a reduction in CaCl2-extractable forms of Zn (25%), Cu (23%), Cd (20%) and Pb (12%), as well as total forms of Cu (35%), Zn (35%), Pb (20%) and Cd (17%) in the soil. The plant yield of the shoots of Dactylis glomerata L. following the application of AGF was 31% higher when compared to the control series. The roots of the tested plant in the AGF series contained higher values of the analyzed heavy metals in relation to the shoots, which was especially visible in the case of Pb (more than twice as high) and Cd (37%).

Heavy metal immobilization and radish growth improvement using Ca(OH)2-treated cypress biochar in contaminated soil

Heavy metal contamination poses a significant threat to soil quality, plant growth, and food safety, and directly affects multiple UN SDGs. Addressing this issue and offering a remediation solution are vital for human health. One effective approach for immobilizing heavy metals involves impregnating cypress chips with calcium hydroxide (Ca(OH)2) to enhance the chemical adsorption capacity of the resulting woody charcoal. In the present study, un-treated cypress biochar (UCBC) and calcium-treated cypress biochar (TCBC), were introduced into pristine and contaminated soil, at rates of 3, 6, and 9% (w/w). Both BCs were alkaline (UCBC pH: 8.9, TCBC pH: 9.7) with high specific surface area, which improved the soil properties (pH, EC, and OM). Radish (Raphanus sativus) cultivated in pots revealed that both UCBC and TCBC demonstrated significant improvements in growth attributes and heavy metal immobilization compared to the control, with TCBC exhibiting superior effects. The TCBC surface showed highly active nanosized precipitated calcium carbonate particles that were active in immobilizing heavy metals. The application of TCBC at a rate of 9% resulted in a substantial reduction in Zn and Cu uptake by radish roots and shoots. In contaminated soil, Zn uptake by radish roots decreased by 55% (68.3–31.0 mg kg−1), and shoots by 37% (49.3–31.0 mg kg−1); Cu uptake decreased by 40% (38.6–23.2 mg kg−1) in roots and 39% (58.2–35.2 mg kg−1) in shoots. Uptake of Pb was undetectable after TCBC application. Principal component analysis (PCA) highlighted the potential of TCBC over UCBC in reducing heavy metal concentrations and promoting radish growth. Future research should consider the long-term effects and microbial interactions of TCBC application.

A novel approach to heavy metal immobilization in municipal solid waste incineration fly ash: Investigating the use of chicken eggshell waste and CaO addition

Municipal solid waste incineration (MSWI) fly ash is a significant byproduct of waste-to-energy processes, and poses substantial environmental and health hazards if not treated properly. The process of Stabilization/Solidification (S/S) efficiently immobilizes hazardous elements present in the fly ash through a combination of physical and chemical mechanisms. The objective of this research is to thoroughly examine the feasibility of using chicken eggshell waste powder as a stabilizing agent for heavy metals, specifically targeting Pb, in MSWI fly ash. Experimental analysis involved varying eggshell waste to fly ash weight proportions, extending from 0.0 (control group), 7:3 up to 9.5:0.5 ratio, with designated curing durations of 2 and 72 hours, and maintaining a liquid-to-solid (L/S) ratio at 1.0 mL/g. In the two-hour curing period, the immobilization efficiency of Pb reached 100% with the addition of only 1.5% eggshell waste. Optimal ratios for Pb stabilization in MSWI fly ash were identified: maximum 2% eggshell waste for 2-hour curing and 1.5% for 72 hours due to elevated Pb and Cd levels of 7:3 ratio. Adding CaO mitigated these levels, enhancing stabilization and compliance with landfill criteria. The results demonstrated that the addition of CaO led to efficient immobilization of Pb, achieving approximately 99%. In addition, the observed enhancement in compressive strength resulting from the incorporation of CaO highlights its effectiveness in enhancing the stabilizing process of MSWI fly ash. By demonstrating the effectiveness of eggshell waste and CaO in stabilizing hazardous elements, this study advocates for scalable solutions and further research on long-term stability and environmental impacts.

Properties of artificial lightweight aggregates prepared from coal and biomass co-fired fly ashes and sewage sludge fly ash

The use of solid waste such as coal and biomass co-fired fly ashes and sewage sludge fly ash instead of clay and other non-renewable resources to produce lightweight aggregates (LWAs) is conducive to sustainable development. In this study, the effects of co-fired fly ashes, sewage sludge fly ash and quartz sand proportion, sintering temperature and sintering time on the physical properties and microstructure of LWAs are studied by single factor experiment. Experimental results show that the optimal experiment conditions are the raw material ratio of co-fired fly ashes: sewage sludge fly ash: quartz sand = 9: 1: 4, 2 wt% SiC as an expansion agent, and sintering at 1060 °C for 10 min. The LWAs obtained under the above conditions have a bulk density of 0.85 g/cm3, an apparent density of 1.84 g/cm3, a 1-h water absorption of 2.71 %, and a compressive strength of 8.68 MPa, which are in accordance with the GB/T17431.1–2010 standard. Besides, the heavy metal immobilization effect of the LWAs is satisfying, where the heavy metal leaching concentrations meet the standard of GB5085.3–2007. In conclusion, it is feasible to use the raw materials to prepare the LWAs under the above sintering conditions, and the prepared LWAs have high strength and low water absorption.

Heavy metals immobilization and bioavailability in multi-metal contaminated soil under ryegrass cultivation as affected by ZnO and MnO2 nanoparticle-modified biochar

Pollution by heavy metals (HMs) has become a global problem for agriculture and the environment. In this study, the effects of pristine biochar and biochar modified with manganese dioxide (BC@MnO2) and zinc oxide (BC@ZnO) nanoparticles on the immobilization and bioavailability of Pb, Cd, Zn, and Ni in soil under ryegrass (Lolium perenne L.) cultivation were investigated. The results of SEM–EDX, FTIR, and XRD showed that ZnO and MnO2 nanoparticles were successfully loaded onto biochar. The results showed that BC, BC@MnO2 and BC@ZnO treatments significantly increased shoots and roots dry weight of ryegrass compared to the control. The maximum dry weight of root and shoot (1.365 g pot−1 and 4.163 g pot−1, respectively) was reached at 1% BC@MnO2. The HMs uptake by ryegrass roots and shoots decreased significantly after addition of amendments. The lowest Pb, Cd, Zn and Ni uptake in the plant shoot (13.176, 24.92, 32.407, and 53.88 µg pot−1, respectively) was obtained in the 1% BC@MnO2 treatment. Modified biochar was more successful in reducing HMs uptake by ryegrass and improving plant growth than pristine biochar and can therefore be used as an efficient and cost effective amendment for the remediation of HMs contaminated soils. The lowest HMs translocation (TF) and bioconcentration factors were related to the 1% BC@MnO2 treatment. Therefore, BC@MnO2 was the most successful treatment for HMs immobilization in soil. Also, a comparison of the TF values of plant showed that ryegrass had a good ability to accumulate all studied HMs in its roots, and it is a suitable plant for HMs phytostabilization.

Influence of EMR–Phosphogypsum–Biochar Mixtures on Sudan Grass: Growth Dynamics and Heavy Metal Immobilization

This study investigates the growth dynamics and heavy metal immobilization in Sudan grass cultivated on substrates composed of electrolytic manganese residue (EMR), phosphogypsum, and chili straw biochar. Pot experiments revealed that a substrate with phosphogypsum constituting 75% of the mix hinders Sudan grass seed germination. Compared with sole EMR utilization, the composite substrates notably enhanced plant growth, evidenced by increases in plant height and fresh weight. The integration of these substrates led to a significant elevation in total chlorophyll content (up to 54.39%) and a reduction in malondialdehyde (MDA) levels (up to 21.66%), indicating improved photosynthetic activity and lower oxidative stress. The addition of biochar reduced the content of Zn, Cd, and Mn in the roots of Sudan grass by up to 25.92%, 20.00%, and 43.17%, respectively; and reduced the content of Pb, Mn, and Cr in the shoot by up to 33.72%, 17.53%, and 26.32%, respectively. Fuzzy membership function analysis identified the optimal substrate composition as 75% EMR and 25% phosphogypsum, with 5% chili straw biochar, based on overall performance metrics. This study adopts the concept of “to treat waste with waste”. The approach is to fully consider the fertility characteristics of EMR, phosphogypsum, and biochar, underscoring the potential for utilizing waste-derived materials in cultivating Sudan grass and offering a sustainable approach to plant growth and heavy metal management.

Valorization of biomass bottom ash in alkali-activated GGBFS-fly ash: Impact of biomass bottom ash characteristic, silicate modulus and aluminum-anodizing waste

Growing production of green energy from biomass has led to a surge in biomass bottom ash (BBA) generation, often relegated to landfills due to high leachable heavy metal content. This study proposed solidifying BBA in alkali-activated granulated ground blast furnace slag (GGBFS) and class F fly ash (CFA) blended binders. Investigations into the influence of BBA content, fineness, silicate modulus of activators, and aluminum-anodizing waste (AAW) on solidification performance were conducted, focusing on reaction mechanisms, phase assemblages, mechanical properties and leaching behavior. Results indicate relatively low reactivity of BBA and high leachable chloride (Cl-), sulphate (SO42-), chromium (Cr), molybdenum (Mo), lead (Pb) and zinc (Zn) contents from BBA. Increased BBA substitution leads to strength deterioration, while ground biomass bottom ash (GBBA) improves the mechanical performance slightly. This improvement is attributed to the increased reactive aluminosilicate content and an enhanced packing system resulting from finer particles. However, GBBA induces an increased heavy metals leaching. Higher silicate modulus activators enhance mechanical properties and reduce the leaching of Mo and Cl-, while lower silicate modulus activator accelerates the reaction process, promoting the formation of hydrotalcite-like phases and reducing the leaching of Cr and SO42-. Incorporating 0.5 wt% aluminum-anodizing waste improves immobilization efficiency of toxic ions, but further increases in dosage lead to higher leaching due to weakened mechanical performance. Overall, hybrid binders with 10 wt% G/BBA exhibit desirable mechanical properties, along with sufficient immobilization of leachable heavy metals, enabling their use as potential construction materials.