Initial Heavy Metal Concentration Research Articles

The superior adsorption capacity of biogenic α-Mn2O3 in comparison to chemogenic α-Mn2O3 for five divalent heavy metal cations and the adsorption mechanism of biogenic α-Mn2O3: Experimental and DFT investigations

Manganese oxides play a crucial role in the adsorption of heavy metals in the environment. However, there is currently a lack of information regarding the comparative adsorption efficiency of heavy metals between biogenic and chemogenic manganese oxides. In this work, we compared the adsorption performance of biogenic and chemogenic α-Mn2O3 towards Pb(II), Cd(II), Cu(II), Zn(II) and Ni(II). Mineral characterization analyses revealed that biogenic α-Mn2O3 exhibited a polycrystalline nature, whereas chemogenic α-Mn2O3 displayed a monocrystalline nature with a lower impurity content compared to biogenic α-Mn2O3. Under acidic conditions, biogenic α-Mn2O3 demonstrated a significantly higher adsorption capacity, ranging from 3 to 6 times greater than its chemogenic counterpart, within an initial heavy metal concentration range of 0.2–1.0 mM. This superiority can be attributed to the presence of more abundant functional groups and a greater content of hydroxyl O species on the surface of biogenic α-Mn2O3 in comparison to chemogenic α-Mn2O3. During the adsorption process of biogenic α-Mn2O3, there were observed ionic exchanges between Mn(II) and these cations. More importantly, biogenic α-Mn2O3 bound with these cations probably through the formation of -O/OH/S complexes. The adsorption selectivity of biogenic α-Mn2O3 towards the five heavy metals was experimentally determined to follow the order of Ni(II) > Pb(II) > Cu(II) > Zn(II) > Cd(II). The electronic interaction between biogenic α-Mn2O3 and these cations indicated that Ni(II), Pb(II) and Cu(II) were more likely to share electrons with O atoms on the surface of biogenic α-Mn2O3 compared to Zn(II) and Cd(II).

Applications of Ion Exchange in Environmental Remediation: Removal of Heavy Metals From Wastewater

ABSTRACTThe concern over heavy metal contamination and its impact on human health and the environment has led to a growing interest in cost‐effective and sustainable remediation technologies. Ion exchange is recognized as an efficient method for removing heavy metal ions from wastewater. This study focused on the removal of heavy metal ions (Ni, Cu, Zn, and Pb) from aqueous solutions using the extended batch equilibrium technique. Experimental trials were conducted using Purolite C100, a strong acid ion‐exchange resin, to assess the influence of various treatment parameters such as pH, contact time, sorbent dosages, and initial heavy metal concentrations on the removal efficiency. The results indicated that significant treatment equilibrium could be achieved within 1 h. Notably, pH levels between 5 and 6 had a significant impact on heavy metal removal, with adsorption capacities of 71, 67, 66, and 62 mg/g for Ni, Cu, Zn, and Pb, respectively. Furthermore, the equilibrium data obtained from the batch experiments were well fitted with Langmuir, Freundlich, and pseudo‐first‐order kinetic models. Statistical analysis revealed a strong correlation with the Langmuir isotherm model, highlighting its superiority over the Freundlich isotherm and pseudo‐first‐order kinetic models.

Batch adsorption studies on copper removal from an aqueous solution using natural zeolite: Process optimization

Abstract The ability of natural zeolite to remove copper ions from an aqueous solution was examined. The research aims to optimize adsorption operational variables, which include the amount of zeolite, pH, contact time, and initial heavy metal concentration for copper removal using zeolite. The research was conducted in batch experiments. The ranges of operational conditions are as follows: 0.2 - 1.0 g of zeolite, pH 4 - 8, 2 - 60 minutes of contact time, and 5 - 50 mg/L of initial concentration of copper. The outcomes indicated that the percentage removal of copper using zeolite achieved the best performance at an optimized adsorbent dosage of 1.0 g, a pH of 6, a contact time of 20 minutes with 135 rpm, and an initial copper concentration of 5 mg/L. To sum up, zeolite is an efficient adsorbent that is capable of separating copper from water-based solutions.

Investigating the possibility of using a mixture of thorium with different fissile materials as a fuel in TRISO particles for the PBMR-400 reactor

The increasing demand for nuclear reactors as a source of clean energy forced nuclear researchers to search for ways to enhance the safety operation of nuclear reactors. This paper discusses the viability of using different thorium compounds ((233U, Th)O2, (235U, Th)O2, (RGPu, Th)O2) as an accident tolerant fuel/advanced technology fuel (ATF) for Pebble Bed Modular Reactor 400 (PBMR-400). A comprehensive analysis of thorium-based fuel performance was carried out and compared with UO2 to develop a novel nuclear fuel with the capability to tolerate severe accident conditions. The neutronic characteristics such as the infinity multiplication factor, initial heavy metal concentration, RGPu concentration and fission products concentration were analyzed. In addition to, the main safety parameters have been calculated to distinguish the effect of the proposed fuels on them. The thermal spectrum and thermal output power have been visualized to give a good insight view inside the core about the distribution of the heat. In general, the neutronic analysis demonstrated good behavior of the examined thorium-based fuel in the PBMR-400 and especially in the case of (RGPu, Th)O2. PBMR-400 showed excellent performance in incinerating a large amount of reactor-grade plutonium when it was used in a kernel fuel bed.

Geospatial investigation on self-purification capacity of river Estuaries in the Caspian region: reducing heavy metals pollution

AbstractIn today’s context, the adoption of sustainable wastewater treatment methods is crucial. River estuaries have the potential to offer an economically viable and environmentally friendly solution for wastewater treatment through the flocculation of pollutants. This study investigates the role of river estuaries flowing into the southern part of the Caspian Sea in the treatment of heavy metals. Two sets of experiments were designed for this purpose. The first set involved adjusting a series of discrete aquaria in various salinity regimes, while the second set utilized only one aquarium. The results from the first set indicate the capacity of the studied estuaries to remove heavy metals through the flocculation process in the following order: Zn (70%) > Mn (60%) > Cu (49%) > Pb (24%) > Ni (19%). However, the removal rates in the second set were reduced as follows: Zn (57%) > Mn (56%) > Cu (40%) > Pb (20%) > Ni (17%). It was observed that the flocculation process exhibits an unstable nature. Furthermore, the findings reveal that heavy metals flocculation primarily occurs upstream of the estuary. However, instability in the flocculation process occurs downstream, where water parameters undergo drastic changes. Statistical analyses indicate that an increase in pH plays a significant role in the destabilization of flocs. Conversely, the initial concentration of heavy metals, dissolved oxygen, and redox potential have a positive impact on the flocculation process.

Bio-adsorption of heavy metals from aqueous solution using the ZnO-modified date pits

The bio-adsorption of heavy metals (including Cu2+, Ni2+, and Zn2+) in aqueous solution and also in an industry wastewater using the ZnO-modified date pits (MDP) as the bio-adsorbent are investigated. The fresh and used bio-adsorbents were characterized by FT-IR, SEM, BET, and XRD. The bio-adsorption parameters (including the pH of solution, the particle size of MDP, the shaking speed, the initial concentration of heavy metals, the dosing of MDP, the adsorption time, and the adsorption temperature) were screened and the data were used to optimize the bio-adsorption process and to study the bio-adsorption isotherms, kinetics, and thermodynamics. Two adsorption models (Langmuir isotherm model and Freundlich isotherm model) and three kinetic models (pseudo-first-order model, pseudo-second-order model, and intra-particle diffusion model) were applied to model the experimental data. Results show that the maximum adsorption amount of Cu2+, Ni2+, and Zn2+ on a complete monolayer of MDP are 82.4, 71.9, and 66.3 mg g−1, which are over 4 times of those of date pits-based bio-adsorbents reported in literature. The bio-adsorption of heavy metals on MDP is spontaneous and exothermic, and is regulated by chemical adsorption on the homogeneous and heterogeneous adsorption sites of MDP surface. This work demonstrates an effective modification protocol for improved bio-adsorption performance of the date pits-based bio-adsorbent, which is cheap and originally from a waste.

Effects of ultrasounds and microwaves on the morphology and adsorption capacity of calcium alginate

Three non-conventional strategies have been used to prepare calcium alginate (CaAlg) from sodium alginate (NaAlg) by a batch process: ultrasound (US); microwave (MW) and combined US-MW. The calcium alginates obtained were used to remove Pb(II) and Cd(II) from single and binary aqueous solutions. The resulting adsorption capacities were compared to those obtained by conventional synthesis of calcium alginate. Scanning electron microscopy (SEM) revealed that the use of microwave and ultrasound produced CaAlg beads with roughened surfaces and consequently with increased specific surface area. The optimum parameters for the removal of Pb(II) and Cd(II) ions from single and binary solutions were determined in terms of pH, contact time, adsorbent dose and initial heavy metal concentration. A significant increase of the maximum adsorption capacity of Cd(II) and Pb(II) ions determined from Langmuir isotherm model was recorded in the case of CaAlg particles prepared in the combined microwave and ultrasound system. These values are 1.7389 ± 0.0585 mmol/g for Cd(II) and 1.5872 ± 0.0657 mmol/g for Pb(II) compared to 0.9305 ± 0.0926 mmol/g and 0.9735 ± 0.0572 mmol/g, respectively recorded for CaAlg particles prepared and matured using the conventional method. The differences between the values of the adsorption capacity of CaAlg-C-C for Pb(II) compared to Cd(II) ions is due to the Pb(II) ions characteristics (ion radius, hydrated ion radius, electronegativity). Thus, it can be stated that use of a combination of microwave and ultrasound improved the adsorption capacity of CaAlg for the removal of heavy metal ions from polluted effluents.

Heavy Metal Remediation from Water/Wastewater Using Bioadsorbents - A Review

This paper aims to emphasize heavy metals’ impact on water and its removal mechanism with a focus on adsorption. Furthermore, factors affecting bio adsorption, such as temperature, pH, RPM, and initial heavy metal concentration, have been studied for different heavy metals and bioadsorbents. A comparison of their adsorption capacities and efficiencies has been made. This review reviewed different bioadsorbents for their suitability in removing cadmium, lead, and copper ions from water and wastewater, typically by using adsorption as a methodology. A suitable summary compares various heavy metal removal techniques and their advantages and limitations. For adsorption, the characteristics of bioadsorbents and their activation steps have been consolidated. Furthermore, the effects of operational parameters and adsorption mechanisms have been discussed in the review. Apart from assessing the suitability of bioadsorbent, a novel bioadsorbent has been suggested for copper ions removal. The findings shall be significantly useful in applying bioadsorbent in water/wastewater treatment fields to reduce heavy metal pollution. Thorough and well-planned research in this field can facilitate the creation of sustainable and durable technology for wastewater treatment, addressing the increasing demand for safe and dependable water resources, focusing on making it cost-effective and recyclable.

Sulfate-reducing bacteria-based bioelectrochemical system for heavy metal wastewater treatment: Mechanisms, operating factors, and future challenges

Heavy metal wastewater (HMW) has resulted in many adverse environmental issues. However, bioelectrochemical system (BES) has been recognized as an effective technology for HMW treatment. This technology generates electricity and removes heavy metals and high concentrations of sulfate. In the sulfate-reducing bacteria-based BES, sulfate-reducing bacteria can anaerobically reduce sulfate to produce sulfide, which reacts with heavy metal ions and forms their corresponding sulfide precipitates, or the heavy metals can be reduced by obtaining electrons at the anode or cathode of the BES. Therefore, this study comprehensively reviews the removal mechanisms of HMW at the anodes and cathodes of the BES. The effects of several key factors, such as electrode materials, biocathode, initial heavy metal concentration, external resistance, and pH, on electricity generation performance and removal efficiency were evaluated. Furthermore, the treatment effects of the microbial fuel cell-microbial electrolytic cell system and the coupled system of BES with plants, artificial wetlands, and electrolytic reactors on HMW and the recovery efficiencies of BES for sulfur and heavy (precious) metals were discussed. Therefore, this review provides a theoretical basis and technical support to broaden the prospects of BES application in HMW remediation.

Research progress on using biological cathodes in microbial fuel cells for the treatment of wastewater containing heavy metals.

Various types of electroactive microorganisms can be enriched to form biocathodes that reduce charge-transfer resistance, thereby accelerating electron transfer to heavy metal ions with high redox potentials in microbial fuel cells. Microorganisms acting as biocatalysts on a biocathode can reduce the energy required for heavy metal reduction, thereby enabling the biocathode to achieve a lower reduction onset potential. Thus, when such heavy metals replace oxygen as the electron acceptor, the valence state and morphology of the heavy metals change under the reduction effect of the biocathode, realizing the high-efficiency treatment of heavy metal wastewater. This study reviews the mechanisms, primary influencing factors (e.g., electrode material, initial concentration of heavy metals, pH, and electrode potential), and characteristics of the microbial community of biocathodes and discusses the electron distribution and competition between microbial electrodes and heavy metals (electron acceptors) in biocathodes. Biocathodes reduce the electrochemical overpotential in heavy metal reduction, permitting more electrons to be used. Our study will advance the scientific understanding of the electron transport mechanism of biocathodes and provide theoretical support for the use of biocathodes to purify heavy metal wastewater.

Urea-Functionalized mesoporous silica SBA-15 for heavy metal Adsorption: Synthesis, Characterization, and optimization

This study investigates chromium, cadmium, and lead ions adsorption on mesoporous silica SBA-15 functionalized by the urea amine group (Urea-SBA-15). Parameters affecting adsorption by Urea-SBA-15 were the initial concentration of heavy metals, contact time, pH, adsorbent concentration, and temperature. Optimum adsorption performance was achieved at pH = 2.5 for Cr(VI), pH = 5 for Cd(II), and pH = 4 for Pb(II), a contact time of 2 h for Cr(VI) and Cd(II) and 1.5 h for lead, an adsorbent concentration of 2.5 g/L, temperature equal to 45 °C, and a heavy metals concentration of 25 ppm. The obtained results were consistent with Langmuir and pseudo-second-order models. The highest adsorption capability for Cr(VI), Cd(II), and Pb(II) were 26.83, 30.53, and 43.85 mg/g, respectively. Laboratory results showed that due to an increased adsorption capacity, the Urea-SBA-15 adsorbent is promising for heavy metal ions removal from water resources.

High surface area peat moss biochar and its potential for Chromium metal adsorption from aqueous solutions

Activated carbons (ACs) have been synthesized using local peat moss biomass for adsorption of heavy metal ions. Adsorbents with different surface areas and pore sizes were obtained using a chemical activation route with different impregnation ratios (20%, 30%, and 40%) of phosphoric acid. The carbonization process was carried out in a tubular furnace under flow of nitrogen (N2) at 500 °C, and 600 °C. Physicochemical properties of developed activated carbon have been evaluated by several techniques such as; X-ray diffraction, Scanning Electron Microscopic, Energy Dispersive X-ray Spectroscopy, Nitrogen adsorption isotherm, Pore size distribution analysis, and Fourier-transform analysis. Moreover, adsorption of chromium ions (Cr+2) from an aqueous solution under different variables was carried out. Heavy metal concentration (20 - 200) ppm, the dosage of adsorbent (0.1 – 0.5) g/L, the time of contact (0 - 220) min, and initial pH (2 - 8) were studied. Results showed that a synthesis route by chemical activation with 30% H3PO4 concentration at 600 °C for 3 h gave the highest BET surface area and pore volume (1692.6 m2/g and 1.55 cm3/g) respectively, compared with other prepared samples. As well as, the removal results show that the maximum adsorption capacity was 493.3 mg/g at 200 mg/L of initial heavy metal concentration, 6.5 pH, 0.3 g/L activated carbon dosage, and 180 min contact time. The Freundlich isotherm was the better description of the adsorption equilibrium data, while the pseudo-second-order model shows the most accurately describes of adsorption kinetics, which indicates that chemisorption is dominant in the adsorption process. Temperature and thermodynamics parameters were studied. The positive value of enthalpy indicates that the adsorption was endothermic.

Lipid-extraction algal biomass for biosorption of bivalent lead and cadmium ions: Kinetics and isotherm

Residual algal biomass, which is the by-product of the extraction of value-added products such as lipids, proteins, pigments and antioxidants, represent a potentially massive and inexpensive source of biosorbents. The biosorption of heavy metal Pb(II) and Cd(II) by the residual biomass of Chlorella vulgaris after lipid extraction was investigated under varied conditions including pH, contact time and initial heavy metal concentration. That of the wet and dried biomasses of C. vulgaris were also studied for comparison. Biosorption plateaus were achieved within 10 min for Pb(II) and 30 min for Cd(II). The Pb(II) biosorption capacities of by residual, wet, and dried biomass were 262.29, 114.85 and 82.81 mg/g, respectively, and that of Cd(II) were 55.13, 33.21, and 21.41 mg/g, respectively. The biosorption capacities of the residual biomass for Pb(II) and Cd(II) were 3.18 and 2.58-fold of that of dried biomass, which can be attributed primarily to the increased specific surface area.

Optimized removal of cadmium, copper and lead from wastewater by biosorption using cabbage waste and Box-Behnken design (BBD)

In this study a Box-Behnken (BBD) design was applied to optimize biosorption of copper, cadmium, and lead using cabbage waste. The effects of operating parameters including initial pH, biosorbent dosage, contact time, and heavy metal concentration were determined by BBD. The maximum biosorption removal efficiency was achieved at pH 4, 300 min operation time, 1.5 g/250 mL biosorbent dosage, and an initial heavy metal concentration of 25 mg/L. The maximum removal efficiencies were 77.23% for Cu, 93.10% for Pb, and 67.19% for Cd at optimal conditions. The cabbage waste was found to be an effective, sustainable, locally available, and environmentally friendly biosorbent for removing heavy metals from aqueous solution.

Adsorption of Pb, Cu and Cd from Water on Coal Fly Ash-Red Mud Modified Composite Material: Characterization and Mechanism

The rational utilization of solid waste has always been a worldwide concern. In this study, coal fly ash (CFA) and red mud (RM) were used in combination to synthesize efficient heavy metal adsorbents. A new way of resource recycling was provided with the collaborative reuse of CFA and RM. To obtain the modified composite materials, CFA and RM were mixed and melted in three ratios. After modification, these materials were then utilized to adsorb Pb, Cu, and Cd in water in both single and ternary systems. The physicochemical properties of CFA, RM, and three modified composite materials were measured by X-ray diffraction analysis, energy dispersive X-ray spectroscopy, scanning electron microscope, Fourier transform infrared spectroscopy, vibrating sample magnetometer, surface area analyzer, and porosity analyzer. In the single and ternary systems, the effects of the modified composite material dosage, solution pH, initial concentration of heavy metals, and adsorption time were discussed, and the results were better fitted with the Langmuir isotherm and the pseudo-second-order kinetic. It was discovered that the modified composite materials had a greater specific surface area (63.83 m2/g) than CFA and RM alone, as well as superior adsorption capacity and magnetic characteristics. The adsorption capacities of C1R4 for Pb, Cu, and Cd were 149.81 mg/g, 135.96 mg/g, and 127.82 mg/g in the single system, while those of Cu and Cd decreased slightly in the ternary system, and the preferential adsorption order of the modified composite materials for heavy metal ions was Pb > Cu > Cd. Among the three modified composite materials, C1R4 had the best adsorption capacity.

Evaluation of Agrowaste Species for Removal of Heavy Metals from Synthetic Wastewater

This study’s goal was to learn more about how agrowaste plants tolerate, absorb, and accumulate a number of metals that are of relevance to the environment. Adsorption of lead (Pb), chromium (Cr), selenium (Se), copper (Cu), and zinc (Zn) ions from synthetic aqueous solutions and wastewater using natural waste residues (NWRs) such as moringa, Lupinus, sugarcane straw, and tea residue was evaluated. The adsorbents used for this study were prepared by washing, drying, and grinding. Fourier-transform infrared (FT-IR) spectroscopy and scanning electron microscope (SEM) analysis were used to characterize the adsorbents’ waste residues. The effect of different parameters such as pH, dose of adsorbents, and the initial concentration of heavy metals, as well as the adsorption isotherm parameters were studied. Moringa, Lupinus, sugarcane straw, or tea residue results were found to fit the Langmuir and Freundlich adsorption isotherms. The adsorption capacity reached 14.59, 16.10, 12.73, and 15.01 mg/g, respectively. The adsorption study’s overall results indicated the removal efficiency pattern as moringa > tea > Lupinus > sugarcane straw. At a dose of 0.5 g/L, the maximum removal percentages for lead, chromium, selenium, copper, and zinc ions were 90.2, 76.55, 70.55, 76.6, and 78.9, respectively. The materials might be regarded as efficient adsorbents for extracting the ions Pb, Cr, Se, Cu, and Zn from wastewater, according to the research.

Cu(II) and Cr(VI) Removal in Tandem with Electricity Generation via Dual-Chamber Microbial Fuel Cells

Microbial fuel cells (MFCs) have shown great advantages in electricity production, heavy metal removal, and energy recovery. However, the impact and mechanism of conflicting effects of numerous electron acceptors on heavy metal removal remain unknown. The effects of different initial heavy metal concentrations, cathodic dissolved oxygen, and electrode materials on the electricity generation and heavy metal removal efficiencies of Cu(II) and Cr(VI) were investigated in this study. When the initial concentration of Cr(VI) increased from 10 mg/L to 150 mg/L, the maximum voltage, coulomb efficiency, and maximum power density declined from 99 to 44 mV, 28.63% to 18.97%, and 14.29 to 0.62 mW/m2, and the removal efficiencies of Cu(II) and Cr(VI) decreased dramatically from 98.34% and 99.92% to 67.09% and 37.06%, respectively. Under anaerobic cathodic conditions, the removal efficiency and removal rate of Cu(II) and Cr(VI) were lower than those under aerobic conditions. When the cathode electrode was titanium sheet and graphite plate, the coulomb efficiency and maximum power density increased to 38.18%, 50.71%, 33.95 mW/m2, and 62.23 mW/m2. The removal efficiency and removal rates of Cu(II) and Cr(VI) were significantly increased to 98.09%, 86.13%, and 0.47, 0.50 mg/(L h) with a graphite plate, respectively. The pH of the cathode varied considerably greater as the MFC current increased. Cu(II) and Cr(VI) were removed and reduced to elemental Cu, Cu2O, and its oxides as well as Cr(OH)3 and Cr2O3 precipitates on the cathode electrode by cathodic bioelectrochemical reduction.

Multifunctional cobalt oxide nanocomposites for efficient removal of heavy metals from aqueous solutions

In this study, co-precipitation synthesis of natural clay (NC) with Co3O4 nanoparticles (NPs) is carried out to elaborate the super NC@Co3O4 nanocomposites with admirable salinity confrontation, environmental stability and reusability, to eliminate heavy metal pollution such as toxic Pb(II) and Cd(II) ions. The advantages of using the NC@Co3O4 adsorbent are easy synthesis and biocompatibility. In addition, NC@Co3O4 can keep an excellent adsorption capacity by taking into account various environmental parameters such as the pH solution, NC@Co3O4 dose, adsorption process time and the initial heavy metals concentration. Furthermore, FTIR, XRD, TGA, SEM-EDS, TEM and AFM analyses were performed to confirm NC@Co3O4 nanocomposites synthesis and characterisation. The adsorption efficiencies of Pb(II) and Cd(II) ions by NC@Co3O4 nanocomposites were demonstrated to be up to 86.89% and 82.06% respectively. Regarding the adsorption from water onto the NC@Co3O4 nanocomposites, kinetics data were well fitted with PSO kinetic model, whereas a good agreement was found between the equilibrium adsorption and theoretical Langmuir isotherm model leading to maximum adsorption capacities of 55.24 and 52.91 mg/g, for Pb(II) and Cd(II) respectively. Monte Carlo (MC) simulations confirmed the spontaneous of this adsorption based on the negative values of Eads. The MC simulations were performed to highlight the interactions occurring between heavy metal ions and the surface of NC@Co3O4 nanocomposites, these were well correlated with the experimental results. Overall the study showed that NC@Co3O4 nanoadsorbents have strongly versatile applications and are well designed for pollutant removal from wastewater due to their unique adsorptive properties.

Preparing of layered double hydroxide- alginate microspheres for Cr(VI)-contaminated soil remediation

The powdered layered double hydroxide(LDH) synthesized by hydrothermal coprecipitation was compounded with sodium alginate to form microspheres(LDH-AL). The characterizations of the LDH-AL show that the microspheres were successfully prepared. Then the immobilization experiments of hexavalent chromium(Cr(VI)) were investigated. The results have proved the effectiveness of microspheres in the immobilization of Cr(VI) in soil. Other limiting factors including LDH percentage, the effects of pH, LDH-AL dosage, interlayer ions, and initial heavy metal concentration were also explored. The LDH-AL showed advantages and its maximum adsorption capacity is 17.0 mg/g. LDH contained in the materials plays a main role in the removal process. In addition, the toxicity characteristic leaching procedure (TCLP) experiment, plant potting tests, and simulation of natural aging processes were used to verify the stability of microspheres. While a series of characterization investigated the adsorption mechanism, the interlayer ion exchange and surface adsorption are the main reasons for Cr(VI) immobilization in contaminated soil. There are also isomer substitution and complexation adsorption phenomena. This study demonstrated the potential application of LDH-AL microspheres in the immobilization of Cr(VI) from contaminated soil.

Effect of calcination temperatures on the performance of rectorite for cadmium immobilization in soil: Freeze-thaw, plant growth, and microbial diversity

The immobilization of cadmium (Cd(II)) in soil using calcined rectorite (REC) was investigated in this research. The results of immobilization show that a small amount of REC calcined at 700 °C (REC-700 °C) could effectively immobilize 90% of Cd(II) in soil, while the immobilization efficiency of REC only reached 42%. Moreover, the immobilization efficiency of REC calcined at 300 °C and 500 °C (REC-300 °C and REC-500 °C) were lower than REC. To investigate the mechanism, the materials before and after immobilization were fully analyzed by Fourier transform infrared spectroscopy (FT-IR), powdery X-ray diffraction analysis (XRD), and scanning electron microscopy (SEM). The results indicate that the structure of REC has been changed after calcination at different temperatures and Cd(II) was successfully immobilized on materials. Losing free water, structural water and OH groups respectively, the layer spacing of REC-300 °C and REC-500 °C was shrunk. However, the crystal structure of REC was destroyed after calcination at 700 °C, resulting in the generation of new phases. According to the XRD result, more cadmium hydroxide (Cd(OH)2) were produced on REC-700 °C, indicating that more OH groups were formed during immobilization. Furthermore, Tessier test demonstrates that Cd(II) in soil changed from exchangeable state and water soluble state to carbonate bound state and iron manganese oxide bound state during immobilization. The result of microbial community indicates that REC-700 °C can restore the microbial composition of Cd(II)-contaminated soil. The effects of pH, freeze-thaw, REC dosage, and initial heavy metal concentration were also evaluated to provide a theoretical basis for the subsequent application of the material in the remediation of contaminated soil.