Immobilization Of Heavy Metals In Soil Research Articles

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.

Application of heavy metal immobilization in soil by biochar using machine learning

Biochar application is a promising strategy for the immobilization of heavy metal (HM)-contaminated soil, while it is always time-consuming and labor-intensive to clarify key influenced factors of soil HM immobilization by biochar. In this study, four machine learning algorithms, namely random forest (RF), support vector machine (SVR), Gradient boosting decision trees (GBDT), and Linear regression (LR) are employed to predict the HMimmobilization ratio. The RF was the best-performance ML model (Training R2 = 0.90, Testing R2 = 0.85, RMSE = 4.4, MAE = 2.18). The experiment verification based on the optimal RF model showed that the experiment verification was successful, as the results were comparable to the RF modeling results with a prediction error<20%. Shapley additive explanation and partial least squares path model method were used to identify the critical factors and direct and indirect effects of these features on the immobilization ratio. Furthermore, independent models of four HM (Cd, Cu, Pb, and Zn) also achieved better model prediction performance. Feature importance and interactions relationship of influenced factors for individual HM immobilization ratio was clarified. This work can provide a new insight for HM immobilization in soils.

Effect and mechanism of biochar as a support on immobilization of different heavy metals by iron oxides in a multi-contaminated soil

The effect and mechanism of biochar as a support on immobilization of different heavy metals (HMs) by iron oxides (FexOy) were still poorly understood. Herein, biochar-supported zero-valent iron (ZVI/BC) was fabricated via the simple one-step thermal reduction approach and applied to a soil multi-contaminated with cadmium (Cd), zinc (Zn), and lead (Pb) for 60-d. Results showed that individual pyrogenic FexOy effectively immobilized Cd but facilitated the release of Pb and Zn in soils. Biochar as a support compromised the immobilization of Cd by FexOy, possibly ascribing to cationic competition effect. ZVI/BC can synergistically immobilize Zn and Pb with the immobilization effectiveness of 33.7 % and 11.9 %, respectively owing to the dispersion effect of BC on ZVI. ZVI/BC addition increased soil pH, but soil pH increase can be not the key factor for the immobilization of HMs in soils. Moreover, biochar increased the diversity of soil bacteria community, but pyrogenic FexOy significantly lowered it. Further, ZVI/BC supplementation significantly stimulated the relative abundances of Fe(Ⅲ)-reducing bacteria (e.g., Geobacter and Acinetobacter) and sulfate-reducing bacteria (e.g., Desulfosporosinus and Desulfurispora) in soils, boosting the microbial reduction of Fe(Ⅲ) minerals and increasing the HCl-extractable Fe(Ⅱ) concentration. The adsorption/co-precipitation of secondary Fe minerals and formation of metal sulfide precipitates could play an important role in immobilization of HMs in soils. Overall, the present study highlighted the coupling of biotic and abiotic processes for stabilization remediation of HMs multi-contaminated soils by ZVI/BC.

Novel application of xanthan gum-based biopolymer for heavy metal immobilization in soil

The sorption reaction between xanthan gum-based biopolymer and Cd, Cu, Pb, and Zn was verified through contact time, initial concentration, and pH alteration. The biopolymer has a negative surface charge in the pH range of 1–8.5, and contains three dominant functional groups (i.e., OH, C-H, and CC bonds). The equilibrium time of Cd, Cu, Pb, and Zn concentration on the biopolymer was 10 min, and was followed by a pseudo-second-order kinetic reaction. The maximum sorption capacities (qm) of Cd, Cu, Pb, and Zn were 16.0 mg/g, 8.5 mg/g, 38.3 mg/L, and 7.2 mg/L, respectively. The Langmuir sorption isotherm was found to be more appropriate than the Freundlich model. Furthermore, the immobilization of heavy metals in the biopolymer-added soil was assessed using HCl and NaH2PO4 extraction. It was observed that 20% and 90% of Cu was immobilized in the soil, and the immobilization rate increased with the biopolymer mixing ratios. This study suggests that the biopolymer could be removed Cd, Cu, Pb, and Zn from solution, and the biopolymer could be applied as an additive for the immobilization of heavy metals in soil.

Bio-Mediated Method for Immobilizing Copper Tailings Sand Contaminated with Multiple Heavy Metals

Microbial induced carbonate precipitation (MICP) is a natural bio-mediated process that has been investigated for soil stabilization and heavy metal immobilization in soil and groundwater. This study analyzed the effect and mechanism of MICP for the solidification/stabilization of tailings sand with multi-heavy metals. When the concentration of cementation solution (CS) is 1.0 mol/L and the optical density(OD600) is 1.6, the unconfined compressive strength of tailings sand treated by MICP is the largest, and the solidification efficiency of heavy metals in tailings sand is also the highest. The macroscopic and microscopic observations reveal that the mechanism of MICP solidification of tailings is bacterial outer oxide, hydroxide, alkaline carbonate, and carbonate precipitation.

Development of phosphorus composite biochar for simultaneous enhanced carbon sink and heavy metal immobilization in soil

As a porous and carbon material, biochar is focused on respectively in sequestrating carbon and stabilizing metals in soil, while few studies attempted to design biochar for simultaneously achieving these two targets. This study proposed to produce phosphorus-composite biochar for synchronously enhancing carbon sequestration and heavy metals immobilization. Two phosphorus materials from tailings, Ca(H2PO4)2 and Ca5(PO4)3(OH), were selected as modifier to load into biomass prior to pyrolysis. Results showed that incorporating P not only increased pyrolytic C retention in biochar by 36.1–50.1%, but also obtained biochar with higher stability by chemically formation of COP, C-PO3 and C2-PO2. After 90-day incubation with soil, more C was sequestrated in the P-biochar amended soil (59.6–67.0%) than those pristine biochar (43.2–46.6%). Highly soluble Ca(H2PO4)2 was more efficient than Ca5(PO4)3(OH) in this regard. Meanwhile, these P-composite biochar exhibited more Pb/Cd immobilization (31.3–92.3%) compared with the pristine biochar (9.5–47.2%), which was mainly due to the formation of stable precipitates Pb5(PO4)3Cl and Cd3(PO4)2, especially for Ca5(PO4)3(OH) modification. Additionally, P-composite biochar “intelligently” altered soil microbial community, i.e., they suppressed Actinobacteria proliferation, which is correlated to carbon degradation, while promoted Proteobacteria growth, facilitating phosphate dissolution for ready reaction with heavy metals to form precipitate, benefiting the Pb and Cd immobilization. A dual functions biochar was engineered via simply loading phosphorous prior to pyrolysis and simultaneously enhanced carbon sequestration and heavy metal immobilization.

Evaluating the remediation potential of MgFe2O4-montmorillonite and its co-application with biochar on heavy metal-contaminated soils

In this work, a novel and efficient magnesium ferrite-modified montmorillonite (MgFe2O4-MMT) compound was prepared. MgFe2O4-MMT and biochar were mixed at 0:10, 1:9, 3:7, 4:6, and 10:0 w/w combinations and were used for heavy metal immobilization in soil polluted with multiple heavy metals. MgFe2O4-MMT can significantly increase soil alkalinity, and it exhibited the most optimal effect in immobilization of heavy metals in soil. The amounts of Cd, Pb, Cu, and Zn that were extracted by the toxicity characteristic leaching procedure (TCLP) decreased by 58.4%, 50.3%, 42.9%, and 24.7%, respectively. MgFe2O4-MMT can immobilize heavy metals through electrostatic interactions and cation exchange processes. Although, the immobilization of potentially toxic elements by MgFe2O4-MMT and biochar was inferior to that by MgFe2O4-MMT. The combined application of MgFe2O4-MMT and biochar dramatically increased the diversity and richness of the soil bacterial community. The Chao1 index for M3B7 treatment group was 1.7 and 1.2 times higher than that for the control and MgFe2O4-MMT treatment groups, respectively. The combination of biochar and MgFe2O4-MMT might be a cost-effective and ecological remediation approach for mild Pb and Cd contamination.

Restoration of heavy metal-contaminated soil and water through biosorbents: A review of current understanding and future challenges.

Heavy metal pollution in soil and water is a potential threat to human health as it renders food quality substandard. Different biosorbents such as microbial and agricultural biomass have been exploited for heavy metal immobilization in soil and sorptive removal in waters. Biosorption is an effective and sustainable method for heavy metal removal in soil and water, but the inherent challenges are to find cheap, selective, robust, and cost-effective bioadsorbents. Microbial and agricultural biomass and their modified forms such as nanocomposites and carbonaceous materials (viz., biochar, nanobiochar, biocarbon), might be useful for sequestration of heavy metals in soil via adsorption, ion exchange, complexation, precipitation, and enzymatic transformation mechanisms. In this review, potential biosorbents and their metal removal capacity in soil and water are discussed. The microbial adsorbents and modified composites of agricultural biomasses show improved performance, stability, reusability, and effectively immobilize heavy metals from soil and water. In the future, researchers may consider the modified composites, encapsulated biosorbents for soil and water remediation.

The performance of emerging materials derived from waste organism blood and saponified modified orange peel for immobilization of available Cd in soil.

Waste organism blood (WOB) and orange peel are emerging stabilization materials obtained as by-products from agricultural processes, which are quite suitable for heavy metal immobilization in soil. In this work, waste organism blood and chemically modified orange peel (SOP) were investigated as potential sorbents for immobilization of available Cd in soil. Application of 5% WOB and SOP effectively immobilized cadmium (Cd) with an associated regulation of soil pH, among which the pH of acidic soil increased most significantly. While the application of 3% SOP alone stabilized almost the same amount of available Cd compared to WOB, it caused the highest stabilization rate of 58.85% when applied at 5%. By contrast, SOP combined with WOB (the mass ratio of the material is 1 : 1) at a 5% addition rate stabilized the available Cd in soils remarkably, with a stabilization rate of 57.74%. This study revealed that the soil particles after stabilization have a more compact and flaky structure, and the SOP and WOB had a particular pore structure, which was helpful for the adsorption of available Cd in soil. This study put forward new insights into the potential effects of Cd immobilization in contaminated soil by newly emerging stabilization biomass materials (WOB and SOP).

Immobilization of heavy metals in contaminated soils by modified hydrochar: Efficiency, risk assessment and potential mechanisms

The modified hydrochar was prepared by a facile one-pot lime-assisted hydrothermal synthesis approach and the modified hydrochar and pristine hydrochar were investigated to immobilize the heavy metals (HMs) of Pb and Cd in contaminated soils. The results showed that the modified hydrochar exerted significantly enhanced effectiveness in immobilizing Pb and Cd comparing to pristine hydrochar, resulting from the increased surface functionality and non-crystalline properties, increased pH value and enhanced electronegativity of hydrochar. By introduction with 5% modified hydrochar, the contaminated soils showed the highest value of 34.5% (Pb) and 8.1% (Cd) reductions in leaching toxicity, and significant improvements of 95.1% (Pb) and 64.4% (Cd) were observed. In addition, the concentrations of acid soluble fraction were remarkably reduced by 54.0% (Pb) and 27.0% (Cd), and the reductions were much higher than that of 29.5% (Pb) and 8.3% (Cd) for 5% pristine hydrochar treatment. The enhanced surface complexation, precipitation and cation-π interaction played an important role in the immobilization of HMs in soils. The present study offered a novel and cost-effective approach to prepare soil amendment from waste biomass towards HMs immobilization in contaminated soils.

Immobilization of heavy metals in vegetable-growing soils using nano zero-valent iron modified attapulgite clay

Nowadays, the problem of heavy metal pollution in vegetables is received wide attention. In this work, attapulgite clay (ATTP), as a cheap and readily available inorganic mineral material, was modified with nano zero-valent iron (nFe0@ATTP) for heavy metal immobilization in soil. Batch experiments were employed to evaluate the optimal remediation performance by ATTP before and after modified with nFe0 through planting Pakchoi (Brassica chinesis L.) in Cd, Cr, and Pb contaminated soil from Changsha. The results showed that amendments can all increase the pH value of soils, and notably decrease the concentration of extractable Cd, Cr, and Pb in soil. The germination rate and root length of Pakchoi were promoted, and the activities of peroxidase (POD), catalase (CAT), and malondialdehyde (MDA) contents were notably reduced besides superoxide dismutase (SOD) activity after treatments with ATTP and nFe0@ATTP. Vicia faba-micronucleus test indicated that the application of amendments reduced the toxicity of heavy metals on the genetic material of Vicia faba root tip cells. The nFe0@ATTP were found to well convert Cd, Cr, and Pb into less bioavailable state in soil, thus blocking heavy metal uptake by plants. This material could be a promising amendment for heavy metals contaminated soil.

Ameliorative Effects of Biochar on Rapeseed (Brassica napus L.) Growth and Heavy Metal Immobilization in Soil Irrigated with Untreated Wastewater

Untreated wastewater carries substantial amount of heavy metals and causes potential ecological risks to the environment, food quality, and soil health. The pot study was established to evaluate the effectiveness of woodchip-derived biochar (BC) on rapeseed biomass, photosynthetic pigments, antioxidant enzyme activities, such as peroxidase (POD), ascorbate peroxidase (APX), polyphenol peroxidase (PPO), catalase enzyme (CAT), and heavy metal-induced phytotoxicity under untreated domestic (DWW) and industrial (IWW) wastewater irrigation. Biochar was applied at three levels (0, 1, and 2%) combined with DWW and IWW treatments. Wastewater analysis indicated higher heavy metal concentrations than the safer limits set by FAO. Results revealed that DWW and IWW treatments without biochar incorporation adversely affected the rapeseed growth performance, photosynthetic pigments, and antioxidative defense system. Compared with DWW and IWW treatments, BC at 2% rate significantly enhanced shoot fresh biomass (41% and 72%), root fresh biomass (34% and 62%), total chlorophyll (79% and 85%), total pigments (77% and 108%), carotenoids (74% and 94%), and lycopene concentration (43% and 61%), respectively. In addition, BC also improved the antioxidant enzymes activities by reducing the heavy metal-induced oxidative stress in rapeseed leaves. Similarly, AB-DTPA extractable Cd was decreased by (44% and 26%), Pb (51% and 54%), Ni (59% and 56%), and Cu (45% and 41%) in soil when BC was applied at 2% application rate along with DWW and IWW treatments and thereby reduced their uptake in shoots and roots of rapeseed. Therefore, BC can be considered an efficient strategy to ameliorate the hazardous effects of untreated DWW and IWW wastewater and to enhance rapeseed biomass, physiological attributes, and antioxidant enzyme activities.

Spectroscopic analyses to study the effect of biochar and compost on dry mass of canola and heavy metal immobilization in soil

ABSTRACTThis research was conducted to use spectroscopic analysis to evaluate the effect of biochar and compost application on heavy metal immobilization during the canola plants grown in the contaminated soil using X-Ray Diffraction (XRD), Energy Dispersive spectroscopy by X-rays (EDX) and Fourier Transmission Infrared Spectroscopy (FTIR). The results showed that the cadmium (Cd) and lead (Pb) concentrations in the root and shoot of canola plants significantly decreased with the addition of rice straw compost (RC) and biochar (RB) to contaminated soil. The use of spectroscopic analysis observed the precipitation, inner-sphere complex reaction, and electrostatic attraction are the dominating mechanisms for heavy metals immobilization with organic amendments. Our results indicate that the rice straw biochar and compost can immobilize heavy metals and improve dry weight of canola plants. Moreover, the spectroscopic analysis is a simple method and can be effective to understand the mechanism of heavy metals immobilization.

A new insight into the immobilization mechanism of Zn on biochar: the role of anions dissolved from ash.

Biochar is considered to be a promising material for heavy metal immobilization in soil. However, the immobilization mechanisms of Zn2+ on biochars derived from many common waste biomasses are not completely understood. Herein, biochars (denoted as PN350, PN550, WS350, and WS550) derived from pine needle (PN) and wheat straw (WS) were prepared at two pyrolysis temperatures (350 °C and 550 °C). The immobilization behaviors and mechanisms of Zn2+ on these biochars were systematically investigated. The results show that compared with biochars produced at low temperature, biochars produced at high temperature contained higher amounts of ash and exhibited much higher sorption capacities of Zn2+. By using Zn K-edge EXAFS spectroscopy, we find that the formation of various Zn precipitates/minerals, which was caused by the release of OH−, CO32−, and Si species from biochar, was the immobilization mechanism of Zn2+ on PN and WS biochars. Hydrozincite and Zn(OH)2 were the main species formed on PN350, PN550, and WS350; while on WS550, besides hydrozincite, a large fraction of hemimorphite was formed. The occurrence of hydrozincite and hemimorphite on biochar during Zn2+ immobilization is firstly reported in our study, which provides a new insight into the immobilization mechanism of Zn2+ on biochar.

Heavy metal immobilization in soil near abandoned mines using eggshell waste and rapeseed residue

Heavy metal contamination of agricultural soils has received great concern due to potential risk to human health. Cadmium and Pb are largely released from abandoned or closed mines in Korea, resulting in soil contamination. The objective of this study was to evaluate the effects of eggshell waste in combination with the conventional nitrogen, phosphorous, and potassium fertilizer (also known as NPK fertilizer) or the rapeseed residue on immobilization of Cd and Pb in the rice paddy soil. Cadmium and Pb extractabilities were tested using two methods of (1) the toxicity characteristics leaching procedure (TCLP) and (2) the 0.1 M HCl extraction. With 5 % eggshell addition, the values of soil pH were increased from 6.33 and 6.51 to 8.15 and 8.04 in combination with NPK fertilizer and rapeseed residue, respectively, compared to no eggshell addition. The increase in soil pH may contribute to heavy metal immobilization by altering heavy metals into more stable in soils. Concentrations of TCLP-extracted Cd and Pb were reduced by up to 67.9 and 93.2 % by addition of 5 % eggshell compared to control. For 0.1 M HCl extraction method, the concentration of 0.1 M HCl-Cd in soils treated with NPK fertilizer and rapeseed residue was significantly reduced by up to 34.01 and 46.1 %, respectively, with 5 % eggshell addition compared to control. A decrease in acid phosphatase activity and an increase in alkaline phosphatase activity at high soil pH were also observed. Combined application of eggshell waste and rapeseed residue can be cost-effective and beneficial way to remediate the soil contaminated with heavy metals.

Enhanced heavy metal immobilization in soil by grinding with addition of nanometallic Ca/CaO dispersion mixture

This study investigated the use of a nanometallic Ca and CaO dispersion mixture for the immobilization of heavy metals (As, Cd, Cr and Pb) in contaminated soil. Simple grinding achieved 85–90% heavy metal immobilization, but it can be enhanced further to 98–100% by addition of a nanometallic Ca/CaO dispersion mixture produced by grinding. Observations using SEM-EDS elemental maps and semi-quantitative analysis showed that the amounts of As, Cd, Cr, and Pb measurable on the soil particle surface decrease after nanometallic Ca/CaO treatment. The leachable heavy metal concentrations were reduced after nanometallic Ca/CaO treatment to concentrations lower than the Japan soil elution standard regulatory threshold: <0.01mgL−1 for As, Cd, and Pb; and 0.05mgL−1 for Cr. Effects of soil moisture and pH on heavy metal immobilization were not strongly influenced. The most probable mechanisms for the enhancement of heavy metal immobilization capacity with nanometallic Ca/CaO treatment might be due to adsorption and entrapment of heavy metals into newly formed aggregates, thereby prompting aggregation of soil particles and enclosure/binding with Ca/CaO-associated immobile salts. Results suggest that the nanometallic Ca/CaO mixture is suitable for use in immobilization of heavy-metal-contaminated soil under normal moisture conditions.