Adsorption Capacity Of Cd Research Articles

Iron and silicon modified biochar for enhancing cadmium removal from water: Unveiling the crucial role of iron-induced silicon dissolution

The interaction mechanisms of silicon (Si) and active ingredient iron (Fe) on cadmium (Cd) removal are still unknown. Herein, the Fe/Si modified biochar (Fe/Si-BC) was synthesized to enhance Cd removal by pre-immersion of Fe and ball milling loading of Si. Detailed characterizations indicated that Fe and Si were successfully introduced into Fe/Si-BC, resulting in the formation of a new metallic silicate (Ca2.87Fe0.13(SiO3)2). The maximum Cd adsorption capacity of Fe/Si-BC (31.66 mg g−1) was 3.6 times and 2.5 times higher than that of Fe-BC (8.89 mg g−1) and Si-BC (11.03 mg g−1), respectively, deriving from an enhancement of Si dissolution induced by Fe introduction. The dissolved Si could capture and combine Cd to form CdSiO3 precipitation, which was strongly supported by the random forest regression and correlation between dissolved Si content and Cd adsorption capacity. This study advances the mechanistic insights into synergistic functions of Si and Fe in Cd removal.

Using solid waste to treat wastewater: Preparation of flowerlike calcium silicate hydrate from coal fly ash for cadmium removal

Efficient utilization of Coal fly ash (CFA) and ingenious treatment of cadmium (Cd (II)) in the water environment are interesting topics. In this paper, a mesoporous floral calcium silicate hydrate (MCSH) for removal of Cd (II) was prepared by low temperature hydrothermal synthesis using CFA desilication solution. Different synthesis parameters (molar ratio of Ca to Si (Ca/Si), temperature, time) of MCSH were investigated and optimized. All synthesized MCSH showed good adsorption properties for Cd (II), and MCSH synthesized at Ca/Si molar ratio of 1.0, temperature of 363 K and time of 120 min had the optimum Cd (II) adsorption capacity of 357.43 mg/g. The effects of solution pH, MCSH dosage, coexisting cations and ionic strength on the Cd (II) adsorption performance by MCSH were further considered systematically. The adsorption process was a spontaneous and endothermic process, conformed to the pseudo-second-order kinetic and Langmuir isothermal model. The main mechanism of Cd (II) removal by MCSH was the precipitation between Cd (II) and OH– released by MCSH, accompanied by ion exchange, surface complexation and electrostatic adsorption. The mesoporous flowery MCSH prepared from CFA provides an satisfactory solution for the utilization of solid waste resources and the purification of heavy metal wastewater.

Development of suitable magnetite–diatomite nanocomposite for Cd (II) adsorptive removal from wastewater

A magnetite-diatomite nanocomposite (MDM) adsorbent was synthesized using the co-precipitation method, wherein a magnetite precursor was intercalated into diatomite clay minerals sourced from the Ethiopian Rift Valley. Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy energy dispersive x-ray (SEM-EDX), Brunauer-Emmett-Teller (BET) and magnetometry measurements were used to look into the structure and magnetic properties of the adsorbent. Batch experiments were conducted to study the remarkable Cd (II) adsorption capacity of MDM and the ease of separating the used adsorbent with a bar magnet. The most important adsorption parameters, namely, initial pH, adsorbent dose (g), initial (Cd (II) concentration (mg), and contact time (min), were optimized using Box-Behnken design (BBD). The MDM has shown exceptional Cd (II) removal under optimum conditions, with a maximum adsorption capacity of 31.4 mg/g from aqueous solution. Based on the results of isotherm and kinetic studies, the Temkin and pseudo-second-order models were found to provide the most accurate fit for adsorption equilibrium when compared to the alternative models. The thermodynamic studies, under standard conditions revealed that, Cd (II) uptake is exothermic and spontaneous. The finding of this study confirms that the MDM adsorbent is easily reusable, extractable from the solution using an external magnet, and capable of recovering around 80 % of Cd (II) when HNO3 is used as a desorbing agent. The study demonstrates a cost-effective and environmentally friendly approach to remediate Cd (II) pollution in wastewater. Furthermore, the superior Cd (II) adsorption capacity, combined with the ease of separating using a bar magnet and high reusability, highlights the potential of this novel adsorbent as a sustainable and efficient solution for addressing Cd (II) contamination in various wastewater treatment applications.Thereby contributing significantly to advancements in the field of heavy metal removal from aqueous solutions.

Birnessite-Type MnO2 Modified Sustainable Biomass Fiber toward Adsorption Removal Heavy Metal Ion from Actual River Aquatic Environment.

In this work, a novel birnessite-type MnO2 modified corn husk sustainable biomass fiber (MnO2@CHF) adsorbent was fabricated for efficient cadmium (Cd) removal from aquatic environments. MnO2@CHF was designed from KMnO4 hydrothermally treated with corn husk fibers. Various characterization revealed that MnO2@CHF possessed the hierarchical structure nanosheets, large specific surface area, and multiple oxygen-containing functional groups. Batch adsorption experimental results indicated that the highest Cd (II) removal rate could be obtained at the optimal conditions of adsorbent amount of 0.200 g/L, adsorption time of 600 min, pH 6.00, and temperature of 40.0 °C. Adsorption isotherm and kinetics results showed that Cd (II) adsorption behavior on MnO2@CHF was a monolayer adsorption process and dominated by chemisorption and intraparticle diffusion. The optimum adsorption capacity (Langmuir model) of Cd (II) on MnO2@CHF was 23.0 mg/g, which was higher than those of other reported common biomass adsorbent materials. Further investigation indicated that the adsorption of Cd (II) on MnO2@CHF involved mainly ion exchange, surface complexation, redox reaction, and electrostatic attraction. Moreover, the maximum Cd (II) removal rate on MnO2@CHF from natural river samples (Xicheng Canal) could reach 59.2% during the first cycle test. This study showed that MnO2@CHF was an ideal candidate in Cd (II) practical application treatment, providing references for resource utilization of agricultural wastes for heavy metal removal.

Humic-like components in dissolved organic matter inhibit cadmium sequestration by sediment

China's lakes are plagued by cadmium (Cd) pollution. Dissolved organic matter (DOM) significantly regulates Cd(II) transport properties at the sediment-water interface. Understanding the effects of different DOM components on the transportation properties of Cd(II) at the sediment-water interface is essential. In this study, typical DOM from different sources was selected to study Cd(II) mobility at the sediment-water interface. Results showed that terrestrial-derived DOM (fulvic acids, FA) and autochthonous-derived DOM (α-amylase, B1) inhibit Cd(II) sequestration by sediments (42.5% and 5.8%, respectively), while anthropogenic-derived DOM (sodium dodecyl benzene sulfonate, SDBS) increased the Cd(II) adsorption capacity by sediments by 2.8%. Fluorescence quenching coupling with parallel factor analysis (EEM-PARAFAC) was used to characterize different DOM components. The results showed that FA contains three kinds of components (C1, C3: protein-like components, C2: humic-like components); SDBS contains two kinds of components (C1, C2: protein-like components); B1 contains three kinds of components (C1, C2: protein-like components, C3: humic-like components).Three complex reaction models were used to characterize the ability of Cd(II) complex with DOM, and it was found that the humic-like component could hardly be complex with Cd(II). Accordingly, humic-like components compete for Cd(II) adsorption sites on the sediment surface and inhibit Cd(II) adsorption from sediments. Fourier transform infrared spectroscopy (FTIR) of the sediment surface before and after Cd(II) addition was analyzed and proved the competitive adsorption theory. This study provides a better understanding of the Cd(II) mobilization behavior at the sediment-water interface and indicates that the input of humic-like DOM will increase the bioavailability of Cd.

Urease-producing bacteria enhance the adsorption of Cd on organo-Fe hydroxide coprecipitates

Microorganisms, organic carbon, and iron oxides are important active components in soil that control the availability of heavy metals. In the extensive cultivation areas based on wheat–maize rotation, returning corn straw to the field increases the content of dissolved organic carbon (DOC) in the soil, affecting heavy metal adsorption by iron oxides and thereby threatening the safety of wheat. However, the effects and underlying mechanisms of maize straw-derived DOC on Cd adsorption by ferrihydrite (Fh) are unclear, and the effects of functional strains on Cd adsorption by organo-Fe hydroxide coprecipitates (OFCs) need further study. The effect of DOC on the adsorption of Cd by Fh was studied through batch solution adsorption experiments. Moreover, the mechanisms underlying the synergistic adsorption of Cd by the urease-producing bacterium Enterobacter sp. TJ6 and OFC were studied in adsorption experiments via scanning electron microscopy and X-ray photoelectron spectroscopy. The results showed that DOC inhibited the adsorption of Cd by OFC, while strain TJ6 enhanced the adsorption of Cd by OFC. Fe-OH and Fe-O bonds on the surface of Fh were important Cd adsorption sites. DOC affected the adsorption of Cd by Fe-OH and Fe-O, thereby inhibiting the adsorption of Cd by OFC. DOC also served as a reducing agent, reducing Fe2O3 on the surface of OFC to FeO and thus inhibiting OFC adsorption of Cd. The mechanisms by which strain TJ6 enhanced Cd adsorption by OFC included the following: 1) strain TJ6 utilized its own oxidation ability to oxidize FeO on the surface of OFC to Fe2O3, promoting the secondary precipitation of Cd during the redox process and enhancing the Cd adsorption capacity of OFC; and 2) strain TJ6 immobilized Cd2+ through ion exchange between Cd2+ and H+ in surface amino groups. In conclusion, this study has revealed the mechanism by which urease-producing bacteria regulate the adsorption of Cd by OFC and provides a theoretical basis for safe straw return to Cd-polluted farmland. This study also provides technical approaches and bacterial resources for the remediation of heavy metal-contaminated soil under straw return.

Facile synthesis of novel hexagonal strontium ferrites for promising adsorption of cadmium from aqueous solutions

Cadmium (Cd(II)) contamination in both the surface and ground water is threatening the lives of millions of people across the world. In this work, we have hydrothermally synthesized the novel multiphase (MP) and single phase (SP) M-type hexagonal strontium ferrites (SF, SrFe12O19) for removing Cd(II) from contaminated water. The as-synthesized materials were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform Infrared spectroscopy (FTIR) and X-ray photoelectron spectrometry (XPS). The MP-SF and SP-SF demonstrated excellent Cd(II) adsorption capacities over wide pH range. The pseudo-first and second-order kinetics models as well as the Langmuir and Freundlich isotherms models were used for fitting the experimental data for adsorption of Cd(II) on both the MP-SF and SP-SF. The maximum adsorption capacities reached to 57.5 and 78.9 mg/g for the MP-SF and SP-SF, respectively, at pH 7, which were better than many recently reported magnetic adsorbents. The effects of common co-existing ions on the adsorption capacities of both the MP-SF and SP-SF were also evaluated. FTIR and XPS spectroscopic analyses further confirmed that Cd(II) was adsorbed on to the surface of SP-SF through the formation of an inner-sphere complex between the Cd(II) and surface metal centers.Furthermore, the as-synthesized materials were employed for the treatment of simulated real Cd(II) contaminated water. The experimental results suggested that the SP-SF could be a strong candidate for practical applications of Cd(II) removal from aqueous solutions.

A novel nanocomposite-based zeolite for efficient remediation of Cd-contaminated industrial wastewater

Novel nanocomposite sorbent was produced by depositing nanostructured water treatment residual (nWTR) onto zeolite (Ze) using high-energy ball milling process. The physicochemical properties of nanocomposite (Ze-nWTR) prior and after Cd adsorption were analyzed by SEM–EDX, FTIR, BET and XRD. A batch study of cadmium adsorption (Ze-nWTR) was performed at various process parameters (sorbent dose, contact time, solution pH, competing ions, initial concentration and temperature). The obtained data were fitted to various equilibrium and kinetics models. The Langmuir and power function models successfully described Cd adsorption equilibrium and kinetic processes, respectively. The maximum adsorption capacity (qmax) value of Cd by Ze-nWTR nanocomposite (147 mgg−1) was 3 and 5.9 times higher than those of nWTR and zeolite sorbents, respectively. Increasing temperature from 287 to 307 K has resulted in increasing the maximum Cd adsorption capacity (qmax) of the nanocomposite from 147.9 to 270 mgg−1. The calculated thermodynamics parameters suggested physical and chemical attraction between Cd and Ze-nWTR and the association of dissociative mechanism in Cd(II) sorption process. The excellent reusability and Cd removal ability of Ze-nWTR nanocomposite (98%) from industrial wastewater confirm its potential as promising adsorbent for wastewater treatment applications.

Application of machine learning and statistical approaches for optimization of heavy metals (Cd2+, Pb2+, Cu2+, and Zn2+) adsorption onto carbonized char prepared from PET plastic bottle waste

ABSTRACT This study focuses on the probable use of carbonized char prepared from PET plastic bottles for heavy metals (HMs) adsorption (Cd2+, Pb2+, Cu2+, and Zn2+). The prepared adsorbent is characterized by field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), and Fourier-transform infrared spectroscopy (FTIR). Batch adsorption experiments were conducted with the influencing of different operational conditions: contact time (1–180 min), adsorbate concentration (25–300 mg/L), adsorbent dose (0.5–6 g/L), pH (3–7), and temperature (25–60 ºC). High coefficient value [Cd2+ (R2 = 0.99), Pb2+ (R2 = 0.97), Cu2+ (R2 = 0.94), and Zn2+ (R2 = 0.98)] of process optimization model suggest that this model was significant, where pH and adsorbent dose expressively stimulus removal efficiency including 86.68, 73.66, 67.10, and 57.04% for Cd2+, Pb2+, Cu2+, and Zn2+ at pH (7), respectively. Furthermore, ANN and BB-RSM revealed a good association between the tested and projected values. The maximum monolayer adsorption capacity of Cd2+, Pb2+, Cu2+, and Zn2+ was 263.157, 78.740, 196.078, and 84.745 mg/g, respectively. Pseudo-second-order was the well-suited kinetics, where Langmuir and Freundlich isotherm could explain better for equilibrium adsorption data. Thermodynamic study shows HMs adsorption is favorable, exothermic, and spontaneous.

Enhanced cadmium absorption and tolerance of rice epiphytic microbes by iron oxide nanoparticles

Nanoparticles present a promising approach for mitigating cadmium (Cd) uptake in crops. Nevertheless, limited research has been focused on the application nanoparticles to mitigate plant Cd stress through increasing Cd absorption and tolerance of epiphytic microbes. Herein, Methylobacterium currus DSD (Meb) was isolated and identified as the type strain. The application of iron oxide nanoparticles (200 mg L−1 IONPs, including Fe2O3NPs and Fe3O4NPs) resulted in considerably enhanced adsorption capacity for Cd by Meb, accompanied by increased surface functional groups, particularly carboxyl and hydroxyl groups. The extracellular polymeric substances (EPS) of Meb-Fe3O4NPs exhibited the higher contents of proteins and polysaccharides. The introduction of Fe3O4NPs increased the mole% of ribose, arabinose, and glucose, as well as the contents of most amino acids. Fe3O4NPs might drive the glycolytic process of converting glucose to amino acids. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analyses further confirmed the involvement of CO and C–N groups in proteins, and C–O groups in polysaccharides. Moreover, the presence of IONPs enhanced Meb tolerance to Cd, which was a highlight. This study provides a novel perspective from epiphytic microbes for nanoparticles to reduce the toxicity and accumulation of Cd in crops.

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.

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.

Soil Cd increased the leaf litter Cd remains of Solanum nigrum and Solanum lycopersicum

Plant litter decomposition is a natural pathway of heavy metal cycling in soil ecosystems, but the dynamics of heavy metal release during litter decomposition are relatively poorly understood. The purpose of this study was to investigate the effects of species, soil fauna and soil Cd addition on litter decomposition and Cd release dynamics. Therefore, we selected two plants, Solanum nigrum and S. lycopersicum with large differences in Cd accumulation capacity. First, they were enriched with Cd during the growing period and leaf litter was harvested after 6 months of pretreatment. Then, the decomposition of leaf litter was conducted with or without soil Cd and Eisenia fetida through lab pot tests. Our results showed that leaf litter Cd led to a significant decrease in litter decomposition rate (K value), with a maximum decrease of 32.1% in S. nigrum and 30.1% in S. lycopersicum. We observed that the presence of E. fetida significantly increased K value, but the effect was similar in the +leaf Cd treatment and the -leaf Cd treatment, both for S. nigrum and S. lycopersicum. Interestingly, the litter Cd concentration did not decrease during decomposition, but showed an increasing trend, especially for S. nigrum in the +soil Cd treatment. Moreover, the litter Cd remains was higher in the +soil Cd treatment compared to the -soil Cd treatment for both S. nigrum and S. lycopersicum, no matter whether with or without E. fetida. This result suggests that the Cd may be transferred from soil to litter, thus increasing the litter Cd remains. Overall, our study shows that leaf litter Cd slowed down the carbon cycling in ecosystems. In addition, the release of litter Cd has a lag, and the litter has a certain adsorption capacity for soil Cd, which intensifies the harm to the ecology during litter transfer.

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.

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.

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.

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.

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.

Nanoscale Insights into the Interaction Mechanism Underlying the Adsorption and Retention of Heavy Metal Ions by Humic Acid.

The mobility and distribution of heavy metal ions (HMs) in aquatic environments are significantly influenced by humic acid (HA), which is ubiquitous. A quantitative understanding of the interaction mechanism underlying the adsorption and retention of HMs by HA is of vital significance but remains elusive. Herein, the interaction mechanism between HA and different types of HMs (i.e., Cd(II), Pb(II), arsenate, and chromate) was quantitatively investigated at the nanoscale. Based on quartz crystal microbalance with dissipation tests, the adsorption capacities of Pb(II), Cd(II), As(V), and Cr(VI) ionic species on the HA surface were measured as ∼0.40, ∼0.25, ∼0.12, and ∼0.02 nmol cm-2, respectively. Atomic force microscopy force results showed that the presence of Pb(II)/Cd(II) cations suppressed the electrostatic double-layer repulsion during the approach of two HA surfaces and the adhesion energy during separation was considerably enhanced from ∼2.18 to ∼5.05/∼4.18 mJ m-2. Such strong adhesion stems from the synergistic metal-HA complexation and cation-π interaction, as evidenced by spectroscopic analysis and theoretical simulation. In contrast, As(V)/Cr(VI) oxo-anions could form only weak hydrogen bonds with HA, resulting in similar adhesion energies for HA-HA (∼2.18 mJ m-2) and HA-As(V)/Cr(VI)-HA systems (∼2.26/∼1.96 mJ m-2). This work provides nanoscale insights into quantitative HM-HA interactions, improving the understanding of HMs biogeochemical cycling.