Immobilization Of Heavy Metals Research Articles

Resource utilization of ultrasonic carbonated MSWI fly ash as cement aggregates: Compressive strength, heavy metal immobilization, and environmental-economic analysis

Ultrasonic carbonation technology is effective for municipal solid waste incineration fly ash (MSWI FA) pretreatment. However, the subsequent disposal route is unclear. In this study, the mechanical strength and heavy metal immobilization effects of raw FA (RFA), washed FA (WFA), conventional carbonated FA (CFA), and ultrasonic carbonated FA (UFA) as cement aggregates in the preparation of concrete were investigated in comparison. The reaction kinetic analysis showed that ultrasonic excitation promoted the internal diffusion phase of the carbonation reaction. The compressive strength of the 28-day solidified bodies was in the order of UFA (32.2 MPa) > CFA (22.8 MPa) > WFA (16.4 MPa) > RFA (12.6 MPa). The 3-day UFA solidified body showed the highest degree of hydration and polymerization through 29Si solid-nuclear-magnetic analysis. The nano-CaCO3 in the UFA provided more nucleation sites and hydration reaction sites for the hydration reaction. In addition, the fine UFA particles filled the pores between cement particles, enhancing the strength of the product. Heavy metal leaching tests described that CFA and UFA met the criteria for resource utilization (HJ/T 1134–2020), and the immobilization efficiency of Cu, Pb, and Zn in the UFA solidified body was above 95.6%, 99.3%, and 99.2%, respectively, mainly by the dual immobilization of carbonate chemical precipitation and cement hydration. Considering 11 environmental impact factors and economic benefits, life-cycle-assessment and cost-benefit analysis were selected. The integrated environmental-economic results show that cement usage is the main influencing factor. UFA scenario was recommended as engineering applications with low global warming potential.

Carbonate-activated binder modified by supplementary materials for mine backfill and the associated heavy metal immobilization effects

Carbonate-activated binder modified by supplementary materials for mine backfill and the associated heavy metal immobilization effects

Effects of chemical composition on lightweight aggregates produced from contaminated soil: Phase regulation, immobilization mechanism and leaching prediction

Contaminated soil induces serious environmental risk due to the presence of hazardous components. The preparation of lightweight aggregate (LWA) is a widely accepted technique to treat contaminated soil. This study investigated the effect of contaminated soil composition on the physical properties and immobilization of heavy metals (Cu, Cr, Pb and Ni) of LWA. Phase regulation, immobilization mechanism and leaching prediction of LWA were analyzed. Results showed that SiO2 and Al2O3 were detrimental to the bloating performance of LWA, whereas fluxing components (Fe2O3, Na2O, K2O, CaO, and MgO) are all conducive. Fluxing components can bring more liquid phase, resulting in a lower density of LWA. The addition of Fe2O3 facilitated the immobilizing Cu and Cr owing to the formation of spinel phases, such as (Mg,Cu)(Fe,Ni)2O4 and Fe(Cr,Al)2O4. Glassy phase could encapsulate heavy metals remarkably, while the high content of fluxing components was unfavorable to the immobilization of Cu and Ni. As network modifiers, Cu and Ni could participate in the formation process of glassy phase, and get encapsulated by liquid phase from fluxing components. Based on the leaching results of Cu, Cr, Pb, and Ni, leaching prediction of LWA was conducted by characteristic indexes and Riley's phase diagram. This research could guide the manufacturing process and leaching control of LWA recovered from contaminated soil.

Effects of biochar and zero valent iron on the bioavailability and potential toxicity of heavy metals in contaminated soil at the field scale

Heavy metals (HMs) such as copper, nickel and chromium are toxic, so soil contaminated with these metals is of great concern. In situ HM immobilization by adding amendments can decrease the risk of contaminants being released. A five-month field-scale study was performed to assess how different doses of biochar and zero valent iron (ZVI) affect HM bioavailability, mobility, and toxicity in contaminated soil. The bioavailabilities of HMs were determined and ecotoxicological assays were performed. Adding 5 % biochar, 10 % ZVI, 2 % biochar + 1 % ZVI, and 5 % biochar + 10 % ZVI to soil decreased Cu, Ni and Cr bioavailability. Metals were most effectively immobilized by adding 5 % biochar + 10 % ZVI, and the extractable Cu, Ni, and Cr contents were 60.9 %, 66.1 % and 38.9 % lower, respectively, for soil with 5 % biochar + 10 % ZVI added than unamended soil. The extractable Cu, Ni, and Cr contents were 64.2 %, 59.7 % and 16.7 % lower, respectively, for soil with 2 % biochar + 1 % ZVI added than unamended soil. Experiments using wheat, pak choi and beet seedlings were performed to assess the remediated soil toxicity. Growth was markedly inhibited in seedlings grown in extracts of soil with 5 % biochar, 10 % ZVI, or 5 % biochar + 10 % ZVI added. More growth occurred in wheat and beet seedlings after 2 % biochar + 1 % ZVI treatment than the control, possibly because 2 % biochar + 1 % ZVI simultaneously decreased the extractable HM content and increased the soluble nutrient (carbon and Fe) content of the soil. A comprehensive risk assessment indicated that adding 2 % biochar + 1 % ZVI gave optimal remediation at the field scale. Using ecotoxicological methods and determining the bioavailabilities of HMs can allow remediation methods to be identified to efficiently and cost-effectively decrease the risks posed by multiple metals in soil at contaminated sites.

Effect of Grain Size Distribution of Soil on Immobilization of Cadmium and Nickel in Contaminated Soil Using Nano Zerovalent Iron: A Factorial Design and Response Surface Methodology Approach

Urban soils get contaminated due to the unscientific disposal of industrial effluents and solid waste, contaminating the soil with heavy metals. Contaminated soils need to be remediated to avoid the ingestion of toxic heavy metals. The immobilization of heavy metals is one of the methods to remediate contaminated soils. The primary purpose of this study was to explore the effect of grain size distribution (GSD) of soil on the efficiency of immobilization of toxic heavy metals in soil when nano zerovalent iron (nZVI) is used to immobilize the metals. Preliminary studies conducted with the 23 factorial design method confirmed that GSD is a significant factor along with the level of contamination and nZVI dosage in the immobilization of heavy metals in soil. Experiments were conducted with cadmium (Cd) and nickel (Ni), the toxic heavy metals, and three soils with different finer particles than 75 µm. Immobilization efficiency was obtained by comparing the leachability of contaminated and treated soil samples using the toxicity characteristic leaching procedure. Reduction in available fraction and variation in the speciation of heavy metals was observed through the sequential extraction procedure. The response surface methodology was adopted for analysis with three levels of GSD, contamination, and nZVI dosage. For Cd, a reduced cubic model was the best fit with a coefficient of determination (R-square) of 0.93, and for Ni, a quadratic model was the best fit with an R-square of 0.92. Both these models were validated experimentally. The efficiency variation followed an optimum curve concerning GSD, contamination level, and the nZVI dosage. For multimetal contamination, the immobilization efficiency gradually decreased from 10% finer to 90% finer soil, both in the case of Cd and Ni. It was observed that for both single metal and multimetal contamination, the interaction between soil and the nZVI plays a vital role in immobilization along with the factors considered.

Simultaneous immobilization of heavy metals and nutrient elements in contaminated sediment using a novel composite agent product.

In this research, an innovative type of sediment resource treatment agent (SRA) was synthesized successfully, which could immobilize ammonia nitrogen (NH3-N), total phosphorus (TP), potassium (K), and simultaneously stabilize cadmium (Cd), lead (Pb), chromium (Cr), copper (Cu), nickel (Ni), and zinc (Zn) in dredged sediment. The effects of SRA dosage on stabilizing the nutrient elements and heavy metals were investigated. The results demonstrated that the increase of SRA dosage significantly enhanced the stabilization of nutrients and heavy metals. The 14-day rainwater infiltration and rainwater scouring experiments were carried out. With the simulation test of rainwater infiltration, the stabilization ratios of Cr, Cu, Ni, Pb, Zn, Cd, NH3-N, TP, and K with 2% SRA addition reached 80.8%, 76.8%, 80.3%, 77.5%, 78.0%, 72.7%, 64.3%, 73.9%, and 73.9%, respectively. Under the action of rainwater scouring, the stabilization ratios of Cr, Cu, Ni, Pb, Zn, Cd, NH3-N, TP, and K with 6.4% SRA addition reached 84.6%, 84.0%, 77.6%, 87.3%, 80.0%, 61.5%, 76.2%, 77.8%, and 91.7%, respectively. Therefore, the results demonstrate that SRA is an excellent composite material in stabilizing heavy metals while reserving the nutrients in dredged sediment, thus showing great potential in the application for dredged sediment resource treatment.

Reduction of bioavailability and phytotoxicity effect of cadmium in soil by microbial-induced carbonate precipitation using metabolites of ureolytic bacterium Ochrobactrum sp. POC9.

The application of ureolytic bacteria for bioremediation of soil contaminated with heavy metals, including cadmium (Cd), allows for the efficient immobilization of heavy metals by precipitation or coprecipitation with carbonates. Microbially-induced carbonate precipitation process may be useful also in the case of the cultivation of crop plants in various agricultural soils with trace but legally permissible Cd concentrations, which may be still uptaken by plants. This study aimed to investigate the influence of soil supplementation with metabolites containing carbonates (MCC) produced by the ureolytic bacterium Ochrobactrum sp. POC9 on the Cd mobility in the soil as well as on the Cd uptake efficiency and general condition of crop plants (Petroselinum crispum). In the frame of the conducted studies (i) carbonate productivity of the POC9 strain, (ii) the efficiency of Cd immobilization in soil supplemented with MCC, (iii) crystallization of cadmium carbonate in the soil enriched with MCC, (iv) the effect of MCC on the physico-chemical and microbiological properties of soil, and (v) the effect of changes in soil properties on the morphology, growth rate, and Cd-uptake efficiency of crop plants were investigated. The experiments were conducted in soil contaminated with a low concentration of Cd to simulate the natural environmental conditions. Soil supplementation with MCC significantly reduced the bioavailability of Cd in soil with regard to control variants by about 27-65% (depending on the volume of MCC) and reduced the Cd uptake by plants by about 86% and 74% in shoots and roots, respectively. Furthermore, due to the decrease in soil toxicity and improvement of soil nutrition with other metabolites produced during the urea degradation (MCC), some microbiological properties of soil (quantity and activity of soil microorganisms), as well as the general condition of plants, were also significantly improved. Soil supplementation with MCC enabled efficient Cd stabilization and significantly reduced its toxicity for soil microbiota and plants. Thus, MCC produced by POC9 strain may be used not only as an effective Cd immobilizer in soil but also as a microbe and plant stimulators.

Modified Natural Diatomite with Various Additives and Its Environmental Potential.

Diatomite has recently been the subject of intensive scientific research aimed at its extensive use in industry, breeding and agriculture. The only active diatomite mine is in Jawornik Ruski, in the Podkarpacie region of Poland. Chemical pollution in the environment, including that from heavy metals, poses a threat to living organisms. Reducing the mobility of heavy metals in the environment through the use of diatomite (DT) has recently gained much interest. More effective immobilisation of heavy metals in the environment with DT, mainly through the modification of its physical and chemical properties by various methods, should be applied. The aim of this research was to develop a simple and inexpensive material showing more favourable chemical and physical properties compared with unenriched DT in terms of metal immobilisation. Diatomite (DT), after calcination, was used in the study, considering three grain fractions, i.e., 0-1 mm (DT1); 0-0.5 mm (DT2) and 5-100 µm (DT3). Biochar (BC), dolomite (DL) and bentonite (BN) were used as additives. The proportion of DTs in the mixtures amounted to 75%, and of the additive, 25%. The use of unenriched DTs after calcination poses the risk of releasing heavy metals into the environment. Enrichment of the DTs with BC and DL resulted in a reduction or absence of Cd, Zn, Pb and Ni in aqueous extracts. It was found that for the specific surface area values obtained, the additive used for the DTs was of crucial importance. The reduction in DT toxicity has been proven under the influence of various additives. The mixtures of the DTs with DL and BN had the least toxicity. The obtained results have economic importance, as the production of the best quality sorbents from locally available raw materials reduces transport costs and thus the environmental impact. In addition, the production of highly efficient sorbents reduces the consumption of critical raw materials. It is estimated that the savings from producing sorbents with the parameters described in the article can be significant in comparison with popular competitive materials of other origins.

Utilization of size-fractionated pozzolanic bottom ash to immobilize heavy metals in MSW incinerator fly ash

Fly ash (FA) from Municipal solid waste incineration (MSWI) is disposed of in landfills after the immobilization of hazardous heavy metals. Pozzolans found in the fine-fraction of MSWI bottom ash (BA) have the potential to immobilize heavy metals. The aim of this study was to examine the effect of size-fractionated BA in immobilizing heavy metals in FA, in order to enhance the effective utilization of resources. BA was applied at two distinct fractions (d<0.25 and d<2.0 mm) when considerable amorphous reactive pozzolans (i.e., siliceous and aluminous) were present. In order to conduct the experiments, FA, BA, and water were mixed in a ratio of 10:1:10, dried at room temperature and in an oven at 120 °C for 4 h, and settled for 4, 8, 16, 30, and 60 days. The results showed that under the air-dried conditions, both BA fractions significantly immobilized Pb and Zn. Pb and Zn leaching stabilized at about 99.9% and 95.6%, respectively, over 16 days with a BA fraction of d< 0.25 mm in an air-dry environment. The pH reduction, the calcite, C-S-H gel, and several new secondary minerals formation demonstrated that the carbonation and pozzolanic reactions were the immobilization mechanisms. Despite the method's simplicity, the findings suggested a potential approach of utilizing residual BA fractions that can be reused directly in the incineration facility. Therefore, this technique can minimize the amount of raw materials required as a metal stabilizer, reduce the amount of waste sent to landfills, and create a new material that can be reused as fillers.

Synergistic optimization of bio–oil quality and heavy metal solidification during microwave co–pyrolysis of cow dung and red mud

To decrease the environmental risks caused by heavy metals (HMs) in red mud (RM) and improve the quality of pyrolysis oil from biomass, high–temperature pretreated RM and cow dung (CD) were microwave co–pyrolyzed. Then, the optimization potential of energy consumption was evaluated and the interaction mechanism between RM and CD was explored. The results showed that the increase in transition metal oxides and specific surface area improved the microwave–absorption and catalytic capacity of the pretreated RM. By optimizing the parameters, a pretreatment temperature of 650 °C resulted in a 21.65% reduction in acid content of bio–oil, higher HMs immobilization rates (>91%) and a 7.44% reduction in energy consumption. The synergistic optimization of bio–oil quality, HMs immobilization and energy consumption was achieved. After microwave co–pyrolysis with cow dung, the larger specific surface area (92.90 m2 g−1) and higher carbon crystallinity (ID/IG = 1.02) of pyrolysis residues enhanced the physical adsorption to HMs. The complexation of HMs with –OH could further enhance the solidification of HMs. This work will provide support to efficient resource utilization of solid waste, and demonstrate the great potential of microwave co–pyrolysis in HMs immobilization.

Co-pyrolysis of industrial sludge with phytoremediation residue: Improving immobilization of heavy metals at high temperature

Phytoremediation as an attractive technology for the degradation or removal of pollutants from the environment inevitably produces large amounts of heavy metal-accumulated plants. Although pyrolysis is effective in treating the generated biomass, the problem of considerable emissions of heavy metals into the atmosphere has not received deserved attention. In this study, industrial sludge (IS) was attempted as an additive to improve the immobilization performance of pyrolysis for heavy metals at high temperature. Based on the separate pyrolysis and co-pyrolysis experiments of IS and the phytoremediation residue (PR) rich in Cd, Pb and Zn at 350–750 °C, the results showed that, compare to separate pyrolysis, introducing IS to PR pyrolysis system could reduce the emission of heavy metals while enhancing their stability in resultant biochar. It was also found that the complexation of heavy metals with functional groups, the combination of heavy metals with π electrons and the formation of heavy metal crystalline compounds could be the main reasons improving the immobilization of heavy metals during co-pyrolysis. Correspondingly, the heavy metal ecological risk evaluation indicated that the biochar obtained from feedstocks containing IS was at no risk or low risk while other biochar possessed a higher risk. This study demonstrated that IS additive was able to optimize the migration and transformation behavior of heavy metals in hyperaccumulator biomass during pyrolysis, which provides new insights into the environmentally sound treatment of heavy metal-rich biomass.

Simultaneous immobilization of multiple heavy metals in polluted soils amended with mechanical activation waste slag

Heavy metal soil contamination has become an increasingly serious problem in industrial development. However, industrial byproducts used for remediation are one aspect of green remediation that can contribute to sustainable practices in waste recycling. In this study, electrolytic manganese slags (EMS) were mechanically activated and modified into a passivator (M-EMS), and the heavy metal adsorption performance of M-EMS, heavy metal passivation ability in soil, dissolved organic matter (DOM) change and its effect on the microbial community structure of soil were investigated. The findings revealed that the maximum adsorption capacities of As(V), Cd2+, Cu2+ and Pb2+ were 76.32 mg/g, 301.41 mg/g, 306.83 mg/g and 826.81 mg/g, respectively, indicating that M-EMS demonstrated remarkable removal performance for different heavy metals. The Langmuir model fits Cd2+, Cu2+ and Pb2+ better than the Freundlich model, and monolayer adsorption is the main process. Surface complexation played a major role in the As(V) adsorption's on the surface of metal oxides in M-EMS.The passivation effect was ranked as Pb > Cr > As>Ni > Cd > Cu, with the highest passivation rate of 97.59 % for Pb, followed by Cr (94.76 %), then As (71.99 %), Ni (65.17 %), Cd (61.44 %), and the worst one was Cu (25.17 %). In conclusion, the passivator has the effect of passivation for each heavy metal. The addition of passivating agent can enhance the diversity of microorganisms. Then it can change the dominant flora and induce the passivation of heavy metals through microorganisms. XRD, FTIR, XPS and the microbial community structure of soil indicated that M-EMS can stabilize heavy metals in contaminated soils through four main mechanisms: ion exchange, electrostatic adsorption, complex precipitation and the microbially induced stabilization. The results of this study may provide new insights into the ecological remediation of multiple heavy-metal-contaminated soils and water bodies and research on the strategy of waste reduction and harmlessness by using EMS-based composites in combination with heavy metals in soil.

Encapsulation of red mud with ultra-high performance concrete (UHPC) for immobilization of alkaline and heavy metals: Experiments and simulations

To alleviate the storage of red mud (RM) and the resulting pollution, this study presented an encapsulation-based strategy for the safe management of RM, and adopted ultra-high performance concrete (UHPC) as an encapsulating material due to its superior impermeability and chemisorption properties. It is noteworthy to find that encapsulated material suffered from a selective chemisorption and density functional theory (DFT) calculations were innovatively employed to investigate the selective chemisorption mechanism. The simulation results suggested that distinct bonding forms lead to the selective chemisorption of heavy metals, with Pb being adsorbed by Si–O–Pb chemical bonds and a strong Si–O–Pb–O–Si long chain, while As and Cr only form relatively weak As–O and Cr–O bonds through their attraction to O atoms. With the thickness of the encapsulating material increases, the synergistic effect of chemical solidification and physical package is provided to achieve a stronger stabilization effect. The leaching results indicated that the encapsulated RM exhibited exceptionally low concentrations of hazardous components (i.e., Na at 1.580 mg/L, As at 0.003 mg/L, Cr at 0.027 mg/L, and undetected levels of Pb in encapsulated RM with a thickness of 1.5 mm), far below the limits set by the United States Environmental Protection Agency (EPA). This study opening a new window for the sustainable and efficient management of hazardous solid waste.

Utilization of municipal solid waste incineration fly ash as construction materials based on geopolymerization

Incineration has been widely used to dispose municipal solid wastes (MSWs) with heat recovery. The generation of fly ash (FA, around 3∼5 wt% of the fed amount) that is normally defined as hazardous wastes remains a serious problem. It is ideal to work out a way to reutilize FA for valuable use instead of landfilling. As a novel utilization technology for municipal solid waste incineration (MSWI) fly ash, geopolymerization can produce geopolymer as construction materials with the advantages of low energy consumption, low pollution and high utilization rate. In this paper, metakaolin (MK) and washed fly ash (WFA) were used to prepare MSWI fly ash-based geopolymer (FAG) with alkali activator. Besides, the strength, heavy metals immobilization and acid resistance of FAG were in detail studied. Under the proper formulation, all the prepared FAGs exhibited strength higher than MU15 level (≥15 MPa) and the maximized one reached MU30 (≥30 MPa). Heavy metals including Cr, Mn, Cu, As, Pb, Zn and Cd had a immobilization rate of more than 92%, and others like As, Pb and Zn were nearly fully immobilized. As for the simulated testing for acid rain scenario, FAG could still fix up the heavy metals well indicating a controllable risk for the environment, which could be ascribed be its high acid neutralization capacity. In a word, this work reports a feasible method for treatment and resource reutilization of MSWI fly ash.

Evaluating the Impact of Crushing Process on Strength Characteristics and Leachability of Cement-Stabilized Dredged Sediment

Stabilization of dredged sediment and reusing the mixture as a construction material is an effective way to reduce environmental problems and save natural resources. However, the crushing process that occurs during construction may affect the mechanical properties and leachability of the reused stabilized soil, an issue that is less reported. Therefore, consolidated undrained triaxial tests and semi-dynamic leaching tests were conducted on stabilized sediments and recompacted crushed stabilized sediment grains (SG) to evaluate the influence of the crushing process. The results of the triaxial tests showed that the stabilized sediment exhibited strain-softening and brittle behaviors under various confining pressures (100, 200, and 400 kPa), while strain-hardening and ductile behaviors were more obvious in the SG. The reduction in cohesion between stabilized sediment and the SG reflected a loss of cementation bonding during the crushing process. The overall leaching behaviors versus curing time of heavy metals (As, Cr, Cu, Zn, Pb, Ni, and Hg) in stabilized sediment was similar to that of SG. The leaching mechanism indicated a good immobilization of heavy metals in stabilized sediment, while their stability in SG was poorer. The reason for the differences in triaxial strength properties and leachability were mainly attributed to the fact that the strong cementation bonding was destroyed by the crushing process, weakening the soil structure and raising the potential for release of elements.

Manufacture of alkali-activated cementitious materials using municipal solid waste incineration (MSWI) ash: Immobilization of heavy metals in MSWI fly ash by MSWI bottom ash

Based on the purpose of safe solid waste recycling, this work proposed a new method of co-treatment of municipal solid waste incineration fly ash (MSWIFA) and municipal solid waste incineration bottom ash (MSWIBA). The alkali-activated binder was synthesized from MSWIFA and MSIWBA by Ca/Si ratio design. The results showed that the maximum compressive strength of the samples at 56 d reached 8.8 MPa. A low concentration of alkali (6% Na2O dosage) favors the development of compressive strength when more MSWIFA is used in the binder system. The C-S-H gel is the main gel product in this case. In contrast, a high concentration of alkali (8% Na2O dosage) is required in the MSWIBA-based binder system. And C-(A)-S-H gels and N-A-S-H gels coexist under this condition. The results of leaching tests showed that after 56 d of curing, the reaction products limited the migration and leaching of potentially toxic elements from MSWIFA by physical encapsulation or chemical bonding. The immobilization efficiency of heavy metals such as Cd, Cr, Cu, Ni, Pb and Zn were above 98%, and their leaching concentrations were below the limits of the relevant Chinese standards.

Thermochemical heat storage utilization of MSWI fly ash after carbonation enhancement with ammonia water regulation: Carbon sequestration efficiency, heavy metal immobilization, and heat storage characteristics analysis

Accelerated carbonation is an effective method of treating municipal solid waste incineration fly ash (FA). However, the efficiency of CO2 sequestration is limited and the usage of products is uncertain. This study proposed a method for enhancing carbonation by ammonia water (NH4OH) regulation and thermochemical heat storage of its products. The influences of NH4OH on CO2 sequestration and heavy metals immobilization were investigated. The results demonstrated that the carbon sequestration efficiency improved from 65.2% to 98.3%, with the NH4OH addition increasing (0–20%). NH4OH promoted the conversion of calcium chloride (CaCl2) and calcium sulfate (CaSO4), which were not originally involved in the carbonation reaction, to calcium carbonate (CaCO3). Excess NH4OH increased the release of heavy metals into the liquid phase due to the chelation of heavy metals by ammonia ions (NH4+) and the effect of high pH. The appropriate amount of NH4OH (8%) offered a high-efficient immobilization of heavy metals. The energy density of FA samples increased from 226.6 kJ/kg to 1207.8 kJ/kg with the NH4OH addition increasing, positively correlating with the content of CaCO3. After the thermal cycle treatment, the non-ammonia carbonated FA had a serious sintering phenomenon with chlorellestadite (Ca5(P,Si,S)3O12(Cl,OH,F)), which was produced from the reaction between CaSO4 and other compounds; while the carbonated FA with NH4OH addition (8%) showed good thermal cycle stability with fine particles and single component (calcium oxide). Therefore, the carbonation treatment in this study is a novel and highly-efficient method, with the final products providing an alternative material for thermochemical heat storage.

Determination of Heavy Metals Immobilization by Chemical Fractions in Contaminated Soil Amended with Biochar

Biochar is a promising tool to immobilize heavy metals (HMs) in the soil. Biochar’s effect on HMs immobilization into acidic soil (pH &lt; 5) and the interaction of plants have been investigated. Three types of feedstocks were used for biochar development via pyrolysis at two temperatures and then applied as soil amendments. A vegetative experiment has been carried out with buckwheat and white mustard to determine the effect of biochar as an HMs immobilizing agent in the presence of sewage sludge. The results show promising biochar properties to immobilize heavy metals and reduce their availability for plants. Biochar incorporation increased soil pH and reduced heavy metal forms available to plants. A sequential extraction procedure was applied to investigate five different forms of six heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) and evaluate their distribution after plants’ cultivation. The proportion of the residual fraction (RES) of HMs varied widely and differed from metal to metal and from plant species. RES in the soil after treatment with biochar and buckwheat harvest varied between 68.14 and 96.40% for Zn, 42.39 and 59.48% (Cu), 75.89 and 93.11% (Cr), 81.85 and 92.83% (Ni), and 98.94 and 99.20% (Pb). In comparison, a slightly opposite trend was found in the soil after white mustard cultivation. The proportion of RES was: 0.82–53.44% for Zn, 0.99–52.93% (Cu), 48.87–76.41% (Cr), 10.22–72.63% (Ni), and 98.31–99.32% (Pb). HMs immobilization efficiency in the soil after biochar treatment followed the order Ni &gt; Cr &gt; Pb &gt; Cu &gt; Zn and Ni &gt; Pb &gt; Zn &gt; Cr &gt; Cu after buckwheat and white mustard cultivation, respectively.

Soil quality index as a tool to assess biochars soil quality improvement in a heavy metal-contaminated soil.

The assessment of soil quality improvement provided by biochars is complex and rarely examined. In this work, soil quality indices (SQIs) were produced to evaluate coffee industry feedstock biochars improvement on soil quality samples of a heavy metal-multicontaminated soil. Therefore, a 90-day incubation experiment was carried out with the following treatments: contaminated soil (CT), contaminated soil with pH raised to 7.0 (CaCO3), contaminated soil + 5% (m/m) coffee ground biochar, and contaminated soil + 5% (m/m) coffee parchment biochar (PCM). After incubation, chemical and biological attributes were analyzed, and the data were subjected to principal component analysis and Pearson correlation to obtain a minimum dataset (MDS), which explain the majority of the variance of the data. The MDS-selected attributes were dehydrogenase and protease activity, exchangeable Ca content, phytoavailable content of Cu, and organic carbon, which composed the SQI. The resulting SQI ranged from 0.50 to 0.56, with the highest SQI obtained for the PCM treatment and the lowest for the CT. The phytoavailable content Cu was the determining factor for differentiating PCM from the other treatments, which was a biochar original attribute and helped to improve soil quality based on the SQI evaluation, further than heavy metal immobilization due to the soil sample pH increase. Longer-term experiments may illustrate clearer advantages of using biochar to improve heavy metal-contaminated soil quality, as physical attributes may also respond, and more significant contributions to biological attributes could be obtained as biochar ages.

Rare Earth Elements (REEs) Adsorption and Detoxification Mechanisms in Cell Wall Polysaccharides of Phytolacca americana L.

The cell wall (CW) is critical for the accumulation of heavy metals in metal-tolerant plants. Polysaccharides, the main component of the CW, contribute significantly to the immobilization of heavy metals. However, the mechanisms of rare earth elements (REEs) adsorption and detoxification by polysaccharides in the cell walls of Phytolacca americana L. (P. americana) remain unclear. In this work, we explored the binding sites of REEs and the modifications to polysaccharides in the cell walls of roots and leaves in P. americana, in order to elucidate the adsorption and fixation mechanism of REEs by the cell wall. Our findings indicated that up to 40.7% and 48.1% of cell-wall-bound REEs were present in the root and leaf pectin, respectively. The removal of pectin led to a 39.8% and 23.6% decrease in the maximum adsorption of REEs in the CW, suggesting that pectin was the main binding site for REEs in the cell walls of P. americana. Hydroxyl (-OH) and carboxyl (-COOH) groups in the cell wall interacted mainly with REEs ions under stress conditions, which played a key role in REEs binding. An obvious REEs fractionation was found during the various fractions of the CW, and all fractions of the root cell wall were enriched with HREEs, whereas all fractions of the leaf cell wall were enriched with LREEs. Moreover, P. americana modulated cell wall composition in reaction to REEs stress. In conclusion, cell wall pectin is the main binding site of REEs, and the functional groups on the cell wall play a significant role in the binding of REEs. At the same time, plants can control the selective adsorption and fixation of REEs by adjusting the composition of cell walls. This study offers valuable insights into the mechanisms of REEs adsorption and fixation in cell walls of P. americana, contributing to a theoretical basis for the bioremediation of REEs pollution.