Adsorption Of Cd Research Articles

Sequestration of Cd (II) utilizing biowaste-fabricated recyclable mesoporous magnetite (Fe3O4) nano-adsorbent: Process optimization, thermodynamic investigation, simulation modeling, and feasibility for electroplating effluent

The present study reports novel recyclable mesoporous magnetite (Fe3O4) nanoparticles adsorbent using Citrus limetta peels biowaste extract via a green synthesis approach. The synthesized green nano-adsorbent was carbonized at 500˚C and fully characterized using diverse techniques. Using Brunauer, Emmett, and Teller's (BET) theory, the magnetite nano-adsorbent specific surface area was determined to be 81.28 m2/g, and the average pore diameter was within the mesoporous range. Magnetite nano-adsorbent ferromagnetism was validated by the vibrating sample magnetometer (VSM), which measured magnetic saturation (Ms) at 49.40 emu/g. Mesoporous magnetite nano-adsorbent's Cd (II) adsorption applicability was thoroughly investigated in batch experiments using an aqueous solution. Further, modeling studies were carried out, and Langmuir and Pseudo-second-order models were found to be more suitable than others for Cd (II) adsorption reactions. The Langmuir isotherm revealed that the mesoporous magnetite has maximum monolayer adsorption of 48.54 mg/g. The kinetic correlation coefficient (R2=0.999 for 30 mg/L) of the Pseudo-second-order model indicates that the Cd (II) adsorption onto magnetite was dominated by chemisorption. The thermodynamics tests confirmed that adsorption was favorable and endothermic and that the adsorption capacity of Cd (II) slightly increased at higher temperatures. In addition, up to five ad-desorption cycles, the Cd (II) sequestration of magnetite was 72.09%, and eluent 0.01 M HCl desorbed 95.42% of Cd (II) from the nano-adsorbent surface, demonstrating enhanced recycling potential and cost-effectiveness. Moreover, the feasibility and cost-effectiveness study broaden their applicability as environment-friendly nano-adsorbents for Cd (II) sequestration from electroplating effluents.

Soil amendments alter cadmium distribution and bacterial community structure in paddy soils

Soil amendments play a pivotal role in ensuring the safety of food production by inhibiting the transfer of heavy metal ions from soils to crops. Nevertheless, their impact on soil characteristics and the microbial community and their role in reducing cadmium (Cd) accumulation in rice remain unclear. In this study, pot experiments were conducted to investigate the effects of three soil amendments (mineral, organic, and microbial) on the distribution of Cd speciation, organic components, iron oxides, and microbial community structure. The application of soil amendments resulted in significant reductions in the soil available Cd content (16 %–51 %) and brown rice Cd content (16 %–78 %), facilitating the transformation of Cd from unstable forms (decreasing 10 %–20 %) to stable forms (increasing 77 %–150 %) in the soil. The mineral and organic amendments increased the soil cation exchange capacity (CEC) and plant-derived organic carbon (OC), respectively, leading to reduced Cd accumulation in brown rice, while the microbial amendment enhanced OC complexity and the abundances of Firmicutes and Bacteroidota, contributing to the decreased rice Cd uptake. The synchrotron radiation–based Fourier transform infrared (SR-FTIR) spectroscopy indicated that soil amendments regulated soil Cd species by promoting iron oxides and OC coupling. Moreover, both organic and microbial amendments significantly reduced the diversity and richness of the bacterial communities and altered their compositions and structures, by increasing the relative abundances of Bacteroidota and Firmicutes and decreasing those of Acidobacteria, Actinobacteria, and Myxococcota. Soil microbiome analysis revealed that the increase of Firmicutes and Bacteroidota associated with Cd adsorption and sequestration contributed to the suppression of soil Cd reactivity. These findings offer valuable insights into the potential mechanisms by which soil amendments regulate the speciation and bioavailability of Cd, and improve the bacterial communities, thereby providing guidance for agricultural management practices.

Enhancing Cd (II) immobilization with thiol-modified low-temperature pyrolysis biochar: Efficiency, mechanism, and applications

The fixation efficiency of thiol-modified lotus seedpod biochar on Cd (II) was assessed through a comprehensive investigation involving batch experiments and sediment cultivation experiments. The influence of thiol modification on the Cd (II) adsorption performance was investigated under different pyrolysis temperatures (550°C, 700°C, and 850°C). The physicochemical properties, adsorption kinetics, isotherms, and adsorption mechanisms of the modified biochar were studied. Oxidation and thiolation significantly reduced the specific surface area and total pore volume of the biochar, augmenting its hydrophilicity. High-temperature pyrolysis biochar was more suitable for oxidation modification than thiol modification. The abundant oxygen-containing functional groups in low-temperature pyrolysis biochar can serve as active sites for thiol loading. Therefore, it exhibited the highest grafting rate, the highest affinity for Cd (II), and the maximum Cd (II) adsorption capacity of 68 mg/g. Thiol-modified biochar primarily immobilized Cd (II) through chelation. Moreover, it significantly reduced the concentration of bioavailable Cd (II) in the sediment and enhanced enzymatic activity. These findings underscore the potential role of low-temperature pyrolysis thiol-modified biochar in addressing Cd (II) pollution in water and sediments.

Respective evolution of soil and biochar on competitive adsorption mechanisms for Cd(II), Ni(II), and Cu(II) after 2-year natural ageing

To reveal the respective evolution of soil and biochar on competitive heavy metal adsorption mechanisms after natural ageing, three soils and two biochars were tested in this study. The soil-biochar interlayer samples were buried in the field for 0.5, 1, and 2 years, for which competitive adsorption characteristics and mechanisms of soils and biochars in four systems (Cd, Cd+Ni, Cd+Cu, and Cd+Ni+Cu) were investigated. Results showed that physicochemical properties, adsorption capacity and mechanisms of soils and biochars all changed the most in the first 0.5 years. The properties and adsorption capacity of biochars gradually weakened with the ageing time, meanwhile, those of soils gradually enhanced. After co-ageing with acidic soil for 0.5 years, the Cd(II) adsorption capacity of modified biochar decreased by 86.59% in the ternary system; meanwhile, that of acidic soil increased by 65.52%. The contributions of mineral mechanisms decreased significantly, while non-mineral mechanisms were slightly affected by ageing. This study highlighted that when using biochar to remediate heavy metal-contaminated soils, biochar should be applied at least half a year in advance before planting crops so that biochar can fully contact and react with the soil.

Harnessing of carboxy containing starch nanoparticles as an adsorbent for Cd (II) ions and methylene blue from waste water effluent: synthesis, metrological characterization and properties

Purpose The novelty addressed here is undertaken by using tailor-made and fully characterized starch nanoparticles (SNPs) having a particle size ranging from 80 to 100 nm with a larger surface area, biodegradability and high reactivity as a starting substrate for cadmium ions and basic dye removal from wastewater effluent. This was done via carboxylation of SNPs with citric acid via esterification reaction using the dry preparation technique, in which a simple, energy-safe and sustainable process concerning a small amount of water, energy and toxic chemicals was used. The obtained adsorbent is designated as cross-linked esterified starch nanoparticles (CESNPs). Design/methodology/approach The batch technique was used to determine the CESNPs adsorption capacity, whereas atomic adsorption spectrometry was used to determine the residual cadmium ions concentration in the filtrate before and after adsorption. Different factors affecting adsorption were examined concerning pH, contact time, adsorbent dose and degree of carboxylation. Besides, to validate the esterification reaction and existence of carboxylic groups in the adsorbent, CESNPs were characterized metrologically via analytical tools for carboxyl content estimation and instrumental tools using Fourier-transform infrared spectroscopy (FTIR) spectra and scanning electron microscopy (SEM) morphological analysis. Findings The overall adsorption potential of CESNPs was found to be 136 mg/g when a 0.1 g adsorbent dose having 190.8 meq/100 g sample carboxyl content at pH 5 for 60 min contact time was used. Besides, increasing the degree of carboxylation of the CESNPs expressed as carboxyl content would lead to the higher adsorption capacity of cadmium ions. FTIR spectroscopy analysis elucidates the esterification reaction with the appearance of a new intense peak C=O ester at 1,700 cm−1, whereas SEM observations reveal some atomic/molecules disorder after esterification. Originality/value The innovation addressed here is undertaken by studying the consequence of altering the extent of carboxylation reaction expressed as carboxyl contents on the prepared CESNPs via a simple dry technique with a small amount of water, energy and toxic chemicals that were used as a sustainable bio nano polymer for cadmium ions and basic dye removal from wastewater effluent in comparison with other counterparts published in the literature.

Competitive Adsorption of Cd(II) and Zn(II) on Biochar, Loess, and Biochar-loess Mixture

Combined heavy metal contamination in soil is a common phenomenon. Biochar amendment into the soil is considered to be an alternative for immobilization remediation of soil contaminated with heavy metals due to its adsorption and alkalization. However, much attention has been paid to the adsorption and immobilization of single heavy metals by biochar. In this paper, the competitive adsorption of Cd(II) and Zn(II) on biochar derived from cotton straw and pig manure at 500℃ (BCS500 and BPM500), loess and biochar-loess mixtures were investigated using the batch equilibrium method. The results showed that the adsorption capacities of biochars, loess, and biochar-loess mixtures to Cd(II) and Zn(II) in the mixed Cd-Zn systems increased with the increase of initial metal concentrations of Cd(II) and Zn(II). The adsorptive capacities of BCS500 and BPM500 to Cd(II) in mixed Cd-Zn system were 33% and 35% less than those in the single Cd(II)systems, while the adsorptive capacities to Zn(II) were 62% and 56% less than those in the single Zn(II) systems. The adsorptive capacities of loess to Cd(II) and Zn(II) in mixed Cd-Zn systems were 29% and 55% less than those in the single metal systems. The adsorptive capacities of loess-BCS500 (LBCS) and loess-BPM500 (LBPM) to Cd(II) in mixed Cd-Zn system were 40% and 38% less than those in the single Cd(II) systems, while the adsorptive capacities to Zn(II) were 63% and 60% less than those in the single Zn(II)systems. Moreover, the competitive adsorptive capacity of Cd(II) is greater than that of Zn(II). It can be seen that when heavy metal pollution with similar nature of multiple elements exists in soil, the amount of adsorbent should be increased to resist the possible weakened adsorption caused by competitive adsorption in order to guarantee an effective absorption treatment.

Chitosan-vermiculite composite adsorbent: Preparation, characterization, and competitive adsorption of Cu(II) and Cd(II) ions

The cost-effective removal of heavy metal ions represents a significant challenge in environmental science. In this study, we developed a straightforward and efficient reusable adsorbent by amalgamating chitosan and vermiculite (forming the CSVT composite), and comprehensively investigated its selective adsorption mechanism. Different techniques, such as Fourier-transform infrared spectroscopy (FTIR), zeta potential analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Brunauer, Emmett, Teller (BET) analysis were employed for this purpose. The prepared CSVT composite exhibited a larger surface area and higher mesoporosity increasing from 1.9 to 17.24 m2/g compared to pristine chitosan. The adsorption capabilities of the CSVT composite and pristine chitosan for Cu(II) and Cd(II) species were systematically examined. Due to its porous structure and increased surface area, the CSVT composite demonstrated superior adsorption ability when compared to pristine chitosan. The maximum adsorption capacities of Cu(II) and Cd(II), determined by Langmuir adsorption isotherms in batch experiments, were found to be 116.22 and 147.64 mg/g, respectively, under initial pH conditions of 8 and an initial concentration of 250 mg/L. The thermodynamic analysis revealed that the adsorption process for both metal ions is spontaneous, endothermic physisorption, and thermodynamically favorable. These findings collectively affirm the CSVT composite as a highly promising adsorbent for the efficient and selective removal of Cu(II) and Cd(II) from aqueous solutions.

Nanoplastics increase algal absorption and toxicity of Cd through alterations in cell wall structure and composition

Nanoplastics (NPs) may act as carriers of heavy metals and cause complex toxicity to aquatic organisms, while the exact role of NPs in the joint toxicity remains unclear. Here, we investigated the joint toxicity of polystyrene NPs (PS-NPs) and Cd to freshwater algae (Chlorella vulgaris). It was found that PS-NPs (1 mg L−1) could hardly enter algal cells and slightly inhibit algal growth (p < 0.01). The effect of PS-NPs as carriers on the joint toxicity of PS-NPs and heavy metals could be neglected because of the limited adsorption of Cd by PS-NPs, while the PS-NPs altered the cell wall structure and composition, which resulted in the increased algal absorption and toxicity of Cd. Compared to the low dose Cd (0.4 mg L−1) treatment alone, the extracellular and intracellular Cd contents in the cotreatment were significantly increased by 27.3 % and 18.0 %, respectively, due to the increased contents of cell wall polysaccharides (pectin and hemicellulose in particular) by the PS-NPs. Furthermore, after the high dose Cd (2 mg L−1) exposure, the inhibited polysaccharide biosynthesis and the loosen cell wall structure weakened the tolerance of cell wall to abiotic stress, facilitating the entry of PS-NPs into the algal cells and inducing the higher toxicity. These results elucidate the mechanism by which NPs enhance heavy metal toxicity to algae, providing a novel insight into environmental risks of NPs.

A novel oyster shell biocomposite for the efficient adsorptive removal of cadmium and lead from aqueous solution: Synthesis, process optimization, modelling and mechanism studies.

This study highlights the effectiveness of oyster shell biocomposite for the biosorption of Cd(II) and Pb(II) ions from an aqueous solution. The aim of this work was to modify a novel biocomposite derived from oyster shell for the adsorption of Cd(II) and Pb(II) ions from aqueous solution. The studied revealed the specific surface BET surface area was 9.1476 m2/g. The elemental dispersive x-ray analysis (EDS) indicated that C, O, Ag, Ca were the predominant elements on the surface of the biocomposite after which metals ions of Cd and Pb were noticed after adsorption. The Fourier transform Irradiation (FT-IR) revealed the presence of carboxyl and hydroxyl groups on the surface. The effect of process variables on the adsorption capacity of the modified biocomposite was examined using the central composite design (CCD) of the response surface methodology (RSM). The process variables which include pH, adsorbent dose, the initial concentration and temperature were the most effective parameters influencing the uptake capacity. The optimal process conditions of these parameters were found to be pH, 5.57, adsorbent dose, 2.53 g/L, initial concentration, 46.76 mg/L and temperature 28.48°C for the biosorption of Cd(II) and Pb(II) ions from aqueous solution at a desirability coefficient of 1. The analysis of variance (ANOVA) revealed a high coefficient of determination (R2 > 0.91) and low probability coefficients for the responses (P < 0.05) which indicated the validity and aptness of the model for the biosorption of the metal ions. Experimental isotherm data fitted better to the Langmuir model and the kinetic data fitted better to the pseudo-second-order model. Maximun Cd(II) and Pb(II) adsorption capacities of the oyster shell biocomposite were 97.54 and 78.99 mg/g respectively and was obtained at pH 5.56 and 28.48°C. This investigation has provided the possibility of the utilization of alternative biocomposite as a sustainable approach for the biosorption of heavy metal ions from the wastewater stream.

Adsorption Kinetics and Mechanism of Pb(II) and Cd(II) Adsorption in Water through Oxidized Multiwalled Carbon Nanotubes

Toxic heavy metals are ubiquitous in the aquatic environment and show a significant danger to human health. Carbon nanotubes have been extensively used in treating the contamination of groundwater due to their porous multi-layer nature. Batch tests revealed that oxidized multiwalled carbon nanotubes (O-MWCNTS) offer better removal of Pb(II). The removal rate of Pb(II) was 90.15% at pH 6 within 24 h, which was ~58% more than that of Cd(II). The removal rate decreased to 55.59% for Pb(II) and to 16.68% for Cd(II) when the initial concentration of Pb(II)/Cd(II) ranged from 5 to 15 mg·g−1. The removal rate in the competitive tests was about 60.46% for Pb(II) and 9.70% for Cd(II). The Langmuir model offered better description of the adsorptive data for both ions. And the Qm of Pb(II) was 5.73 mg·g−1, which was 2.39 mg·g−1 more than that of Cd(II) in a single-icon system, while Qm was 7.11 mg·g−1 with Pb(II) and 0.78 mg·g−1 with Cd(II) in competitive water. And thermodynamic tests further indicated that the activating energy of Pb(II) and Cd(II) was 83.68 and 172.88 kJ·mol−1, respectively. Lead and cadmium adsorbed on the surface of O-MWCNTS are antagonistic in the competitive system. Based on XPS analyses, it was concluded that the absorbed lead/cadmium species on O-MWCNTS were (-COO)2Pb, (-COO)Pb(-O)/(-COO)2Cd, and (-COO)Cd(-O). Additionally, they offered theoretical evidence supporting the practicality of using nanocomposite membranes as a means to remove cadmium and lead.

Adsorption of Toxic Cd(II) on an Antibacterial Biopolymeric Gel toward Fabrication of a Gel Electrolyte-Based Supercapacitor Device

Adsorption of Toxic Cd(II) on an Antibacterial Biopolymeric Gel toward Fabrication of a Gel Electrolyte-Based Supercapacitor Device

Kinetics and mechanism of Pb(II), Cd(II) and Cu(II) adsorption on ferrochrome ash from aqueous solutions

ABSTRACT There has been significant interest in the development of novel approaches and techniques that can effectively ensure the supply of safe and uncontaminated water to human communities. Among the several treatment strategies available, adsorption is particularly favourable due to its inherent versatility in terms of design and operation. Additionally, a diverse selection of cost-effective adsorbents has been successfully employed for the purpose of remediating heavy metal-contaminated wastewater. The current study employed an industrial waste ferrochrome ash (FCA), as a novel adsorbent to eliminate Pb(II) and Cd(II) ions from aqueous solutions. To accomplish this goal, the FCA underwent characterisation by XRF, XRD, and SEM-EDS analyses. Afterwards, batch adsorption experiments were carried out and the maximum adsorption capacities were obtained as 1519 and 84.5 for Pb(II) and Cd(II) mg/g, respectively which makes the FCA an applicable adsorbent for their removal from wastewater. Furthermore, it was found out that the adsorption of Pb(II) and Cd(II) on FCA fits the pseudo-second order (PSO) kinetics and Langmuir isotherm models. Based on the findings, it can be inferred that the adsorption mechanism of Pb(II) and Cd(II) followed a monolayer chemisorption process, characterised by the valency forces between the metal ions and the surface of the adsorbent. Furthermore, adsorption capacity of the WGFCA was examined at different temperatures and it was found out that the adsorption of Pb(II) and Cd(II) on WGFCA is an exothermic and spontaneous process. Additionally, an examination was conducted on the desorption characteristics and the structural integrity of the WGFCA, revealing that it may be successfully restored under acidic conditions for subsequent utilisation. Finally, competitive adsorption characteristics of Pb(II), Cd(II) and Cu(II) ions were investigated and the sequence of adsorption capacity in such multi-cationic systems was found to be Pb(II)>Cu(II)>Cd(II).

Cd(II) and Pb(II) adsorption in karst soils amended with litter extract from Ficus virens

In this study, different proportions of Le were used to amend purple, yellow, and yellow–brown soils of karst areas to investigate the effect of litter extract (Le) from Ficus virens on Cd(II) and Pb(II) adsorption in karst soils. The basic physicochemical properties of Le-amended karst soils were determined, and the microscopic morphology of Le-amended karst soils was detected. The batch method was used to study the isothermal adsorption characteristics of Cd(II) and Pb(II) adsorption on different Le-amended karst soils. Physicochemical properties and microscopic morphology results showed that Le was amended on the karst soil surface and changed the surface properties of the karst soil. The maximum adsorption capacity range of Cd(II) and Pb(II) by Le-amended karst soils was 92.10–241.61 and 108.91–262.12 mmol/kg, respectively, and the peak value was reached when the karst soils were amended with 20 % of Le. Increasing the pH and temperature were beneficial to Cd(II) and Pb(II) adsorption in each Le-amended karst soil. The adsorption amount of Cd(II) and Pb(II) initially increased and thendecreased with the increase in ionic strength. Cd(II) and Pb(II) adsorption was a spontaneous, endothermic, and entropy-increasing process, and electrostatic attraction, precipitation, complexation, and ion exchange were the main adsorption mechanisms. The adsorption amount of Cd(II) and Pb(II) by Le-amended yellow–brown soil maintained approximately 85 % of original sample after three rounds of regeneration.

Effectiveness of cork and pine bark powders as biosorbents for potentially toxic elements present in aqueous solution

Cork oak and pine bark, two of the most prolific byproducts of the European forestry sector, were assessed as biosorbents for eliminating potentially toxic elements (PTEs) from water-based solutions. Our research suggests that bioadsorption stands out as a viable and environmental eco-friendly technology, presenting a sustainable method for the extraction of PTEs from polluted water sources. This study aimed to evaluate and compare the efficiency of cork powder and pine bark powder as biosorbents. Specifically, the adsorption of Fe, Cu, Zn, Cd, Ni, Pb and Sn at equilibrium were studied through batch experiments by varying PTEs concentrations, pH, and ionic strength. Results from adsorption-desorption experiments demonstrate the remarkable capacity of both materials to retain the studied PTE. Cork powder and pine bark powder exhibited the maximum retention capacity for Fe and Cd, while they performed poorly for Pb and Sn, respectively. Nevertheless, pine bark showed a slightly lower retention capacity than cork. Increasing the pH resulted in cork showing the highest adsorption for Zn and the lowest for Sn, while for pine bark, Cd was the most adsorbed, and Sn was the least adsorbed, respectively. The highest adsorption of both materials occurred at pH 3.5–5, depending on the PTE tested. The ionic strength also influenced the adsorption of the various PTEs for both materials, with decreased adsorption as ionic strength increased. The findings suggest that both materials could be effective for capturing and eliminating the examined PTEs, albeit with different efficiencies. Remarkably, pine bark demonstrated superior adsorption capabilities, which were observed to vary based on the specific element and the experimental conditions. These findings contribute to elucidating the bio-adsorption potential of these natural materials, specifically their suitability in mitigating PTEs pollution, and favoring the recycling and revalorization of byproducts that might otherwise be considered residue.

Effects of different aging methods on the ability of biochar to adsorb heavy metal cadmium and its physical and chemical properties.

The aging process can affect the physical and chemical properties as well as adsorption capacity of biochar. This study focuses on the heavy metal cadmium (Cd) as the research object, and artificially ages biochar prepared from rice straw and corn straw through accelerated freeze-thaw cycles, alternating dry wet cycles, and ultraviolet light treatment, in order to evaluate the effects of different aging conditions on the physical and chemical properties of the two different types of biochar and on their adsorption capacities for Cd. After aging, the pH of rice and corn biochar decreased to varying degrees, respectively. The surface structure was ruptured, the average pore diameter was decreased, and the specific surface area was increased by 27.3%, 21.9%, and 9.8% (rice) and 95.4%, 27.7%, and 13.4% (corn). Ultraviolet light aging has the most significant impact on the elemental content of biochar, and the C content was decreased by 12.4% (rice) and 9.3% (corn). The O content was increased by 11.2% (rice) and 44.1% (corn), and the numbers of O/C, H/C, (O + N)/C, and oxygen-containing functional groups were increased. These results demonstrate that the aging process reduces the degree of aromatization of biochar, while enhancing its polarity and Cd adsorption capacity. Rice straw biochar (RSB) has a greater ability to adsorb Cd than corn straw biochar (CSB). In addition, ultraviolet light aging is particularly effective in increasing heavy metal adsorption.

Effects of soil water content on Cd immobilization and uptake by leek with the combined application of biochar and organic fertilizer.

This study investigated the effects of soil water content on Cd immobilization and uptake by leek with the combined application of biochar and organic fertilizer using mechanism experiment and pot experiment. Mechanism experiment was conducted with the three-layer mesh method, which can reveal the individual mechanisms and contributions of biochar and soil to Cd immobilization. The results of mechanism experiment showed that the Cd adsorption amount by biochar was very little at low soil water content (θw = 20%, w/w), and both of Cd adsorption amount and rate significantly increased at higher θw (40% and 60%). The Cd immobilization by biochar at higher θw (40% and 60%) was significantly better than that at low θw (20%) in soils because F1 (percentages of exchangeable Cd) decreased with increasing moisture. For example, the F1 percentages were 58.27%, 40.67%, and 38.46% in the soil at 4.40mg·kg-1 under M20, M40, and M60 (θw = 20%, 40%, 60%) at day 120, respectively. The results of pot experiment showed that the Cd in leek leaves and roots continuously accumulated with planting time in each batch, and biochar and organic fertilizer treatments significantly reduced the Cd enrichment in leek. Combined treatment of biochar and organic fertilizer (BO) is superior to biochar treatments (BC) and CK for Cd immobilization in soil. For example, the percentages of F1 under the treatments of CK, BC, and BO were 64.43%, 49.13%, and 43.67% at 75% field water capacity treatment, respectively. For the same treatment, with increasing water contents, the better the Cd was immobilized in the soil and the greater the leek biomass. However, the total uptake of Cd by leek were increased by promoting crop growth under water content conditions.

Utilization of oyster shell nano-hydroxyapatite modified red-brick waste as an environmentally friendly composite filler for Cd(II) and Cr(VI) adsorption: Preparation, property and mechanism

The ongoing process of urbanization in China has led to a growing concern regarding environmental contamination caused by the significant accumulation of construction demolition trash. This study employs the water thermal method to synthesize hydroxyapatite using natural waste oyster shells as the primary raw material. This study explores the use of synthesized hydroxyapatite (O-HA) on building waste red-brick fragments (RBF) for removing cadmium (Cd(II)) and chromium (Cr(VI)) from water. The RBF fillers, both before and after modification, underwent comprehensive characterization using various techniques, including automated analysis of specific surface area and porosity (BET), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). In the sixth cycle of purification experiments, the average removal rate of Cd(II) by O-HA-modified red-bricks (O-HA/RBF) could still reach 88.18 %, which was about 20.00 % higher than that of the RBF. However, the removal of Cr(VI) by O-HA/RBF was unsatisfactory at 5.33 %. The adsorption mechanisms of Cd(II) and Cr(VI) were explored by isothermal adsorption tests and adsorption kinetic tests. According to the mechanism analysis, physical adsorption and chemical adsorption were the main reasons for Cd(II) adsorption by O-HA/RBF. This involves ion exchange and surface complexation between calcium ions in O-HA and Cd(II), forming a low-solubility precipitate for effective removal. However, for Cr(VI), physisorption predominantly governs O-HA/RBF, elucidating the limited efficacy in Cr(VI) removal. The cost analysis showed that using O-HA/RBF as filler reduced overall expenses in wetland development, offering promising prospects for engineering applications.

Pb(ΙΙ), Cd(ΙΙ), and Mn(ΙΙ) adsorption onto pruning-derived biochar: physicochemical characterization, modeling and application in real landfill leachate

The aim of this study was to systemically evaluate how different pyrolysis temperatures (400, 550, and 700 °C) and particle sizes (1–2 mm and 63–75 µm) were influenced biochar evolution, made from urban pruning waste, during pyrolysis process and to establish their relationships with biochar potential for removal of lead (Pb), cadmium (Cd), and manganese (Mn) from real municipal solid waste landfill leachate. The effects of pH (2–7), contact time (30–300 min) and adsorbent dosage (0.1–5 g L−1) on heavy metals removal were also examined. The results showed that physicochemical properties of biochar were greatly influenced by pyrolysis temperature. Particle size, however, showed little influence on biochar characteristics (p > 0.05). The yield, volatile matter, hydrogen and oxygen contents, and surface functional groups decreased consistently with increasing pyrolysis temperature. An increase in the pH, electrical conductivity, ash, fixed carbon, and specific surface area values was also found. In biochar samples formed at high temperatures (i.e., 550 and 700 °C), Fourier transform infrared spectroscopy-FTIR studies confirmed the increase in aromaticity. Field emission scanning electron microscopy-FESEM images showed differences in the microporous structure and lower size pores at higher temperatures. Biochar pyrolyzed at 700 °C with a particle size of 63–75 µm (i.e., Lv700-63) showed the highest removal efficiency performance. Pb and Cd ions were completely removed (100%) by 0.2 g L−1 Lv700-63 at 7.0 pH and contact times of 120 and 90 min, respectively. The maximum percentage removal of Mn was 86.20% at optimum conditions of 0.2 g L−1 Lv700-63 dosage, 7.0 pH, and 180 min contact time. The findings suggests that the surface complexation, π-electron coordination, and cation exchange were the dominant mechanisms for the Pb, Cd, and Mn removal onto Lv700-63.

An efficient and simple approach to remove Cd(II) in aqueous solution by using rice straw biochar: performance and mechanisms.

In recent years, cadmium pollution in water environment has become an environmental problem that could not be ignored. As a porous carbon rich solid material, biochar is an environment-friendly new material because of its ultra-high adsorption capacity and strong chemical stability. In this study, rice straw biochar (RS-Biochar) was successfully prepared at different temperatures for removal of Cd(II) from aqueous solution. Through a series of characterization and adsorption experiments, the adsorption principle of Cd(II) by RS-Biochar was deeply studied. The results showed that RS-Biochar prepared at 600 °C (BioC600) has high specific surface area (232.6 m2/g) and shows high Cd(II) removal rate of 91.23% with the maximum Cd(II) adsorption capacity of 8.62 mg/g. The Langmuir model fit well to describe the adsorption process of Cd(II) on the BioC600. The mechanism analysis showed that hydroxyl and carboxyl groups on the biochar surface were concerned in the removal of Cd(II). The formation of CdCO3 in the adsorption process was also be proven. Importantly, RS-Biochar could be conveniently produced with needed scale, displaying a promising approach for remediating Cd(II)-contaminated water environment and a huge application potential.

Adsorption effect and mechanism of Cd(II) by different phosphorus-enriched biochars.

The resource utilization of agricultural and forestry waste, especially the high-value transformation of low-grade phosphate rock and derivatives, is an important way to achieve sustainable development. This study focuses on the impregnation and co-pyrolysis of rice straw (RS) with fused calcium magnesium phosphate (FMP), FMP modified with citric acid (CA-FMP), and calcium dihydrogen phosphate (MCP) to produce three phosphorous-enriched biochars (PBC). The Cd(II) removal efficiency of biochars before and after phosphorus modification was investigated, along with the adsorption mechanism and contribution of biochars modified with different phosphorus sources to Cd(II) adsorption. The result indicated that CA-FMP and MCP could be more uniformly loaded onto biochar, effectively increasing the specific surface area (SSA) and total pore volume. The adsorption of Cd(II) onto PBC followed a mono-layer chemisorption process accompanied by intraparticle diffusion. The adsorption of Cd(II) by PBC involved ion exchange, mineral precipitation, complexation with oxygen-containing functional groups (OFGs), cation-π interaction, electrostatic interaction, and physical adsorption. Ion exchange was identified as the primary adsorption mechanism for Cd(II) by BC and FBC (51.53% and 53.15% respectively), while mineral precipitation played a major role in the adsorption of Cd(II) by CBC and MBC (51.10% and 47.98% respectively). Moreover, CBC and MBC significantly enhanced the adsorption capacity of Cd(II), with maximum adsorption amounts of 128.1 and 111.5mgg-1 respectively.