Removal of cadmium(II) from aqueous solutions by chemically modified maize straw

Valorization of Agriculture Residues into Value-Added Products: A Comprehensive Review of Recent Studies

Global agricultural by-products usually go to waste, especially in developing countries where agricultural products are usually exported as raw products. Such waste streams, once converted to "value-added" products could be an additional source of revenue while simultaneously having positive impacts on the socio-economic well-being of local people. We highlight the utilization of thermochemical techniques to activate and convert agricultural waste streams such as rice and straw husk, coconut fiber, coffee wastes, and okara power wastes commonly found in the world into porous activated carbons and biofuels. Such activated carbons are suitable for various applications in environmental remediation, climate mitigation, energy storage, and conversions such as batteries and supercapacitors, in improving crop productivity and producing useful biofuels.

Exploring nanocellulose's role in revolutionizing the pharmaceutical and biomedical fields

The increasing global demand for eco-friendly products derived from natural resources has spurred intensive research into biomaterials. Among these materials, nanocellulose stands out as a highly efficient option, consisting of tightly packed cellulose fibrils derived from lignocellulosic biomass. Nanocellulose boasts a remarkable combination of attributes, including a high specific surface area, impressive mechanical strength, abundant hydroxyl groups for easy modification, as well as non-toxic, biodegradable, and environmentally friendly properties. Consequently, nanocellulose has been extensively studied for advanced applications. This paper provides a comprehensive overview of the various sources of nanocellulose derived from diverse natural sources and outlines the wide array of production methods available. Furthermore, it delves into the extensive utility of nanocellulose within the biomedical and pharmaceutical industries, shedding light on its potential role in these fields. Additionally, it highlights the significance of nanocellulose composites and their applications, while also addressing key challenges that must be overcome to enable widespread utilization of nanocellulose.

Adsorption of Ciprofloxacin on Clay Minerals in Argentinian Santa Rosa-Corrientes Soils

The presence of antibiotics in soils is increasing drastically in last decades due to the intensive farming industry and excessive human consumption. Clay minerals are one of the soil components with great adsorption capacity for organic pollutants. The study of interactions between antibiotics and mineral surfaces will give us scientific knowledge of these pollutants through soils. In this work, we study the adsorption of the antibiotic ciprofloxacin in the clay mineral fraction of soils from the Argentinian zone of Santa Rosa (Corrientes), in a collaborative research of experiments and atomistic modelling calculations of the intercalation of ciprofloxacin in the interlayer space of montmorillonite. Adsorption and desorption isotherms were performed and compared with different isotherm models. Additionally, enthalpy, entropy, and free energy were determined from equilibrium constants at a function of temperature. All these experiments and calculations lead to the conclusions that two adsorption types of ciprofloxacin are found on clay minerals: one weakly sorbed that is released during the desorption experiments, and other one strongly joined that remains in the soil.

Chemical modification of Aloe vera leaf hydrogel for efficient cadmium-removal from spiked high-hardness groundwater

Herein, the hydrogel from the leaf of the Aloe vera plant (ALH) was succinylated (SALH) and saponified (NaSALH). The FTIR, solid-state CP/MAS 13C NMR, and SEM-EDX spectroscopic analyses witnessed the formation of SALH and NaSALH from ALH. The pHZPC for NaSALH was found to be 4.90, indicating the presence of -ve charge on its surface. The Cd2+ sorption efficiency of NaSALH was found to be dependent on pH, NaALH dose, Cd2+ concentration, contact time, and temperature. The maximum Cd2+ removal from DW and HGW was found to be 227.27 and 212.77 mg g-1 according to the Langmuir isothermal model (>0.99) at pH of 6, NaSALH dose of 40 mg g-1, Cd2+ concentration of 90 mg L-1, contact time of 30 min, and temperature of 298 K. The kinetic analysis of Cd2+ sorption data witnessed that the Cd2+ removal by chemisorption mechanism and followed pseudo-second-order kinetics (>0.99). The -ve values of ΔG° and ΔH° assessed the spontaneous and exothermic nature of sorption of Cd2+ by NaSALH. The regeneration and sorption/desorption studies indicated that the sorbent NaSALH is regenerable.

Adsorption of Cd2+ onto apatite surface: Equilibrium, kinetics and thermodynamic studies

This study examined the application of chemically synthesized apatite (CHAp) powder as a potential adsorbent for the elimination of Cd²⁺ in aqueous medium. The synthesized hydroxyapatite (HAp) powder before and after adsorption was elucidated by XRD, EDX, FT-IR, SEM, and TEM analytical techniques. The role of time, initial Cd²⁺ concentration, amount of CHAp used, temperature and solution pH on the adsorption process were investigated. Data from the adsorption process were subjected to Dubinin-Radushkevich, Langmuir, Freundlich, and Tempkin adsorption isotherms, while pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion kinetic models were used for the kinetics investigation. Results from XRD confirmed that chief characteristic peaks of HAp powder were detected, while functional groups such as PO₄ ^3-, CO₃ ^2- and OH^- matching pure HAp were displayed in the FT-IR spectra. Round shape morphology of the CHAp was confirmed by SEM and TEM analyses. Langmuir isotherm best described the adsorption process with ceiling adsorption capacity of 195.711 mg/g, whereas, the adsorption mechanism obeys the pseudo-first-order model which suggests a physical adsorption process. The value of entropy change (ΔS) of the adsorption of Cd²⁺ onto CHAp surface was obtained to be 0.610 kJ/mol, while the value of enthalpy change obtained was 175.591 kJ/mol. Results from free energy change obtained adjudged the adsorption process to be spontaneous and endothermic in character. Thus, the chemically synthesized HAp could be an excellent adsorbent for the elimination of Cd²⁺ in bioremediation applications.

Adsorption performance and mechanism of cationic and anionic dyes by KOH activated biochar derived from medical waste pyrolysis

The massive generation of medical waste (MW) results in a series of environmental, social, and ecological problems. Pyrolysis is one such approach that has attracted more attention because of the production of value-added products with lesser environmental risk. In this study, the activated biochar (ABC600) was obtained from MW pyrolysis and activated with KOH. The adsorption mechanism of activated biochar on cationic (methylene blue) and anionic (reactive yellow) dyes were studied. The physicochemical characterization of biochar showed that increasing pyrolysis temperature and KOH activation resulted in increased surface area, a rough surface with a clear porous structure, and sufficient functional groups. MB and RYD-145 adsorption on ABC600 was more consistent with Langmuir isotherm (R² ≥ 0.996) and pseudo-second-order kinetics (R² ≥ 0.998), indicating chemisorption with monolayer characteristics. The Langmuir model fitting demonstrated that MB and RYD-145 had maximum uptake capacities of 922.2 and 343.4 mg⋅g^-1. The thermodynamics study of both dyes showed a positive change in enthalpy (ΔH°) and entropy (ΔS°), revealing the endothermic adsorption behavior and randomness in dye molecule arrangement on activated-biochar/solution surface. The activated biochar has excellent adsorption potential for cationic and anionic dyes; hence, it can be considered an economical and efficient adsorbent.

Adsorption Characteristics of Modified Eucalyptus Sawdust for Cadmium and Arsenic and Its Potential for Soil Remediation

In order to explore the utilization of Eucalyptus sawdust (C) and develop its remediation potential in cadmium and arsenic contaminated soil, Eucalyptus sawdust were modified by FeCl₃ and NaOH coprecipitation (MC). Characterization technology and pot experiment were used to explore the adsorption mechanism of cadmium and arsenic by MC and the effect of soil remediation. The results showed that iron oxide was loaded on the surface of Eucalyptus sawdust and destroyed the semi fiber structure. The adsorption mechanisms of cadmium and arsenic included electrostatic attraction, precipitation, complexation, redox. The soil pH value reduced by 0.12-0.18 units with 0.25%-1% ratio of application rates of MC to soil weight treatment; The contents of available cadmium and arsenic were reduced by 18%-25% and 12%-18%; MC could promote the transformation of Cd and As from highly active formation to low active formation and had a good application prospect for Cd and As compound pollution remediation.

Biochar derived from fruit by-products using pyrolysis process for the elimination of Pb(II) ion: An updated review

Water pollution is one of the most concerning global environmental problems in this century with the severity and complexity of the issue increases every day. One of the major contributors to water pollution is the discharge of harmful heavy metal wastes into the rivers and water bodies. Without proper treatment, the release of these harmful inorganic waste would endanger the environment by contaminating the food chains of living organisms, hence, leading to potential health risks to humans. The adsorption method has become one of the cost-effective alternative treatments to eliminate heavy metal ions. Since the type of adsorbent material is the most vital factor that determines the effectiveness of the adsorption, continuous efforts have been made in search of cheap adsorbents derived from a variety of waste materials. Fruit waste can be transformed into valuable products, such as biochar, as they are composed of many functional groups, including carboxylic groups and lignin, which is effective in metal binding. The main objective of this study was to review the potential of various types of fruit wastes as an alternative adsorbent for Pb(II) removal. Following a brief overview of the properties and effects of Pb(II), this study discussed the equilibrium isotherms and adsorption kinetic by various adsorption models. The possible adsorption mechanisms and regeneration study for Pb(II) removal were also elaborated in detail to provide a clear understanding of biochar produced using the pyrolysis technique. The future prospects of fruit waste as an adsorbent for the removal of Pb(II) was also highlighted.

Key particle properties of shells for cadmium chemisorption

Previous studies on cadmium adsorption of calcium carbonate have found that polymorph, and, crystallinity are influential factors for adsorbing cadmium ions. The predominant factor for cadmium adsorption has yet to be elucidated because these factors are linked. To overcome this, here each factor is investigated separately. First, atmospheric grinding prepared surf clam (aragonite phase) and scallop (calcite phase) shells with similar crystallite sizes and specific surface areas. Using adsorption isotherm models, kinetics, X-ray diffraction analysis, and TEM observations, both calcite and aragonite react with cadmium to form cadmium carbonate. The chemisorption follows the adsorption mechanism reported in the literature. Based on the Langmuir isotherm model fitting, the maximum adsorbed amount for the ground surf clam shells is 633.3 mg/g, while that for scallop shells is 195.8 mg/g. Then fine surf clam shell particles with a similar specific surface area, and with a relatively wide range of the aragonite ratio, and crystallite size are prepared via a combination of grinding and a subsequent calcination process. Our experiments where one explanatory variable is changed at a time demonstrate that the polymorph ratio and crystallite size of the ground shells play key roles in the chemisorption.

Efficient Removal of Cd(II) Using SiO2-Mg(OH)2 Nanocomposites Derived from Sepiolite

The pollution of Cadmium (Cd) species in natural water has attracted more and more attention due to its high cumulative toxicity. In the search for improved removal of cadmium from contaminated water, we characterized uptake on a recently identified nanomaterial (SiO₂-Mg(OH)₂) obtained by subjecting sepiolite to acid-base modification. The structural characteristics of SiO₂-Mg(OH)₂ were analyzed by means of SEM-EDS, Fourier Transform Infra-Red Spectroscopy (FTIR) and Powder X-ray Diffraction (PXRD). Static adsorption experiments were carried out to evaluate the effect of contact time, temperature, amount of adsorbent, and pH-value on the adsorption of Cd(II) by SiO₂-Mg(OH)₂. The results show that the pore structure of SiO₂-Mg(OH)₂ is well developed, with specific surface area, pore size and pore volume increased by 60.09%, 16.76%, and 43.59%, respectively, compared to natural sepiolite. After modification, the sepiolite substrate adsorbs Cd(II) following pseudo-second-order kinetics and a Langmuir surface adsorption model, suggesting both chemical and physical adsorption. At 298 K, the maximum saturated adsorption capacity fitted by Sips model of SiO₂-Mg(OH)₂ regarding Cd(II) is 121.23 mg/g. The results show that SiO₂-Mg(OH)₂ nanocomposite has efficient adsorption performance, which is expected to be a remediation agent for heavy metal cadmium polluted wastewater.

Removal of Pb (II) from aqueous solution using nanoadsorbent of Oryza sativa husk: Isotherm, kinetic and thermodynamic studies

This research focus on the removal of Pb (II) ions from aqueous solution by adsorption process using nanoadsorbent developed from agricultural waste Oryza sativa husk (OSH). Surface morphology of nanoadsorbent was analyzed by FE-SEM, elemental composition by EDX and size by AFM. Attachment of functional groups on nanoadsorbent was determined by FTIR. The effect of pH, dose, contact time, initial concentration and temperature were investigated. Optimum adsorption of lead at pH 8, contact time 70 min at 60 °C temperature with 0.6 g/50 mL nanoadsorbent dose obeyed pseudo second order kinetic model with R² 0.996. Pb (II) adsorption was analyzed by Freundlich, Langmuir and Temkin models. Freundlich isotherm model with correlation coefficient R² 0.999 was best fitted. Thermodynamic parameters anticipated the adsorption process to be endothermic and spontaneous. Post adsorption elution was carried out successfully. Results demonstrate that OSH is a low cost and eco-friendly choice for Pb (II) remediation.

Characterization and Interpretation of Cd (II) Adsorption by Different Modified Rice Straws under Contrasting Conditions

Rice straw can adsorb Cd(II) from wastewater, and modification of rice straw may improve its adsorption efficiency. The rice straw powder (Sp) from the direct pulverization of rice straw was used as the control, the rice straw ash (Sa), biochar (Sa), and modified rice straw (Ms) were prepared by ashing, pyrolysis and citric acid modification, respectively, and all of them were examined as adsorbents for Cd(II) in this study. Batch adsorption experiments were adopted to systematically compare the adsorption capacities of rice straw materials prepared with different modification methods for Cd(II) from aqueous solution under different levels of initial Cd(II) concentration (0–800 mg·L⁻¹), temperature (298, 308, and 318 K), contact time (0–1440 min), pH value (2–10), and ionic strength (0–0.6 mol·L⁻¹). The results indicated that the modification method affected the adsorption of Cd(II) by changing the specific surface area (SSA), Si content, surface morphology, and O-containing functional group of rice straw. Compared with Sp, Ms held more surface O–H, aliphatic and aromatic groups, while Sa had more phenolic, C–O (or C–O–C), and Si–O groups, and Sb held more C–O (or C–O–C) and Si–O groups; besides, Sa, Sb, and Ms had larger SSA than Sp. Adsorption capacity of the four adsorbents for Cd(II) increased and gradually became saturated with the increase in the initial Cd(II) concentration (0–800 mg·L⁻¹). The adsorption capacity of Cd(II) was significantly higher at 318 K than 298 K and 308 K, regardless of the adsorbent type. Sa had the largest SSA (192.38 m²·g⁻¹) and the largest adsorption capacity for Cd(II). When the initial Cd²⁺ concentration was at 800 mg·L⁻¹, the Cd(II) adsorption amount reached as high as 68.7 mg·g⁻¹ with Sa at 318 K. However, the SSA of Sp was only 1.83 m²·g⁻¹, and it had the least adsorption capacity for Cd(II). Only the adsorption of Cd(II) upon Sb at 298 K was spontaneous, and surprisingly, all other adsorptions were nonspontaneous. These adsorptions were all chemical, and were favorable, exothermic and order-increasing processes. The pseudo-second-order model showed a strong fit to the kinetics of Cd(II) adsorption by the four adsorbents. The adsorption capacities of Cd(II) by the adsorbents were less at low pH, and all were enhanced with the increase of initial pH value (2–10) in the solution. The inhibiting effect on Cd(II) adsorption due to the increase in ionic strength was greater with Sa, Sb, and Ms than that under Sp. The rice straw ash prepared by ashing unexpectedly had greater adsorption capacity for Cd(II) than the biochar and citric acid modified rice straw. The optimum condition for Cd(II) adsorption was established as the temperature of 318 K, initial Cd(II) concentration of 800 mg·L⁻¹, contact time of 240 min, and no Na(I) interference regardless of absorbent. In conclusion, rice straw ash shows the greatest potential of being applied to paddy fields for the remediation of Cd(II) pollution so as to reduce the risk of Cd(II) enrichment in rice grains and straws.

Adsorption of methylene blue and Cd(II) onto maleylated modified hydrochar from water

A new carboxylate-functionalized hydrochar (CFHC) was successfully prepared by reaction of hydrochar with maleic anhydride under solvent-free conditions and followed by deprotonating carboxyl group of hydrochar with NaHCO₃ solution. CFHC was characterized using X-ray photoelectron spectroscopy (XPS), elemental analysis (EA), zeta potential, Brunauer-Emmett-Teller surface area (BET) and Fourier-transform infrared spectroscopy (FTIR), and its adsorption properties and mechanisms to methylene blue (MB) and Cd(II) were investigated using the batch method. The isotherm adsorption data were accorded with Langmuir model and the maximum uptakes were 1155.57 and 90.99 mg/g for MB and Cd(II) at the temperature of 303 K, respectively. The joint analysis of batch experiments and characterizations of hydrochar confirmed the π-π interaction was accompanied by electrostatic interaction and hydrogen bond for MB adsorption, while the surface complexation and ion exchange were predominant mechanisms for Cd(II) adsorption. Therefore, a highly effective adsorbent CFHC prepared by a simple and environmentally friendly solid-phase synthesis is a promising candidate for wastewater treatment.

Characteristics and mechanisms of cadmium adsorption onto biogenic aragonite shells-derived biosorbent: Batch and column studies

Calcium carbonate (CaCO₃)-enriched biomaterial derived from freshwater mussel shells (FMS) was used as a non-porous biosorbent to explore the characteristics and mechanisms of cadmium adsorption in aqueous solution. The adsorption mechanism was proposed by comparing the FMS properties before and after adsorption alongside various adsorption studies. The FMS biosorbent was characterized using nitrogen adsorption/desorption isotherm, X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy, Fourier-transform infrared spectroscopy, and point of zero charge. The results of batch experiments indicated that FMS possessed an excellent affinity to Cd(II) ions within solutions pH higher than 4.0. An increase in ionic strength resulted in a significant decrease in the amount of Cd(II) adsorbed onto FMS. Kinetic study demonstrated that the adsorption process quickly reached equilibrium at approximately 60 min. The FMS biosorbent exhibited the Langmuir maximum adsorption capacity as follows: 18.2 mg/g at 10 °C < 26.0 mg/g at 30 °C < 28.6 mg/g at 50 °C. The Cd(II) adsorption process was irreversible, spontaneous (-ΔG°), endothermic (+ΔH°), and more random (+ΔS°). Selective order (mmol/g) of metal cations followed as Pb²⁺ > Cd²⁺ > Cu²⁺ > Cr³⁺ > Zn²⁺. For column experiments, the highest Thomas adsorption capacity (7.86 mg/g) was achieved at a flow rate (9 mL/min), initial Cd(II) concentration (10 mg/L), and bed height (5 cm). The Cd(II) removal by FMS was regarded as non-activated chemisorption that occurred very rapidly (even at a low temperature) with a low magnitude of activation energy. Primary adsorption mechanism was surface precipitation. Cadmium precipitated in the primary (Cd,Ca)CO₃ form with a calcite-type structure on the FMS surface. A crust of rhombohedral crystals on the substrate was observed by SEM. Freshwater mussel shells have the potential as a renewable adsorbent to remove cadmium from water.

Comparative adsorption of emerging contaminants in water by functional designed magnetic poly(N-isopropylacrylamide)/chitosan hydrogels

The magnetic poly(N-isopropylacrylamide)/chitosan hydrogel with interpenetrating network (IPN) structure was designed based on the functional groups of targeted emerging contaminants, represented by hydrophilic sulfamethoxazole (SMZ) and hydrophobic bisphenol A (BPA). The average particle size, specific surface area, and total pore volume of the hydrogel were turned out to be 103.7 μm, 60.70 m²/g and 0.0672 cm³/g, respectively. Adsorption results indicated that the maximum adsorption capacity occurred at the pH where SMZ was anionic and BPA was uncharged. When the adsorption temperature increased from 25 °C to 35 °C, the amount of adsorbed SMZ hardly changed, but that of BPA increased by two times. The adsorption capacity of the binary system (i.e., with both SMZ and BPA) was almost the same as that of the single system, indicating that simultaneous adsorption of SMZ and BPA was achieved. The adsorption equilibrium was reached quickly (within 5 min) for both SMZ and BPA. For adsorption isotherm, the Freundlich model fitted well for SMZ at 25, 35 and 45 °C. However, the adsorption of BPA exhibited the sigmoidally shaped isotherm at 25 °C with the Slips model fitting well, and both the Freundlich isotherm and the Slips isotherm fitted the data well at 35 °C and 45 °C, suggesting that the adsorption force was initially weak but greatly enhanced with an increase in adsorbate concentration or ambient temperature. The main adsorption mechanism was inferred to be electrostatic interactions for SMZ, and hydrophobic interactions as well as hydrogen bonding for BPA. The hydrogel adsorbent maintained favorable adsorption capacity for BPA after five adsorption-desorption cycles. These findings may provide a strategy for designing high performance adsorbents that can remove both hydrophilic and hydrophobic organic contaminants in the aquatic environment.

Evaluation of Cd(II) Ion Removal from Aqueous Solution by a Low-Cost Adsorbent Prepared from White Yam (Dioscorea rotundata) Waste Using Batch Sorption

An agricultural residue, white yam (Dioscorea rotundata) tuber peel (YTBS), was used for the removal of Cd(II) ion from an aqueous solution using a batch method. The adsorbent was characterized using FTIR, TGA, SEM, EDX, N2 BET, XRD, and XRF. The optimization of sorption variables such as pH, contact time, adsorbent dose, and initial metal ion concentration at 25 °C were also carried out. The results indicated the dependence of sorption on the adsorbate pH and adsorbent dose, while the adsorption system reached equilibrium in 180 min. The sorption kinetics was fitted to three models (pseudo first order, pseudo second order, and Elovich) to validate the kinetics, and the pseudo first order was the best model for the description of Cd(II) uptake. Equilibrium isotherm modelling was also carried out using the Langmuir, Freundlich, and Temkin models, with the Langmuir isotherm giving the best fitting to the experimental results. The maximum loading capacity (qmax) of the adsorbent for Cd(II) obtained from the Langmuir isotherm model was 22.4 mg∙g−1 with an isotherm constant (KL) of 3.46 × 10−3 L·mg−1 and r2 value of 0.99. This result indicates that the YTBS residue was a good adsorbent for the removal of Cd(II) ion from aqueous system.

Magnetic nanocellulose from olive industry solid waste for the effective removal of methylene blue from wastewater

The work shown in this article demonstrate a novel example of converting olive industry solid waste (OISW) into a magnetic cellulose nanocrystalline (MNCs) to serve as selective magnetic sorbents for methylene blue. Olive industry solid waste contains about 40% cellulose. The cellulose was extracted in a powder form from olive industry solid waste by subjecting it to a multistep pulping and bleaching process. The extracted powder cellulose was then converted to nanocrystalline cellulose (NCs) by acid hydrolysis. The NCs were then treated with a solution of FeCl₃.6H₂O, FeSO₄, and H₂O by a colloidal suspension method which produced free-flowing porous MNCs. The produced MNCs are characterized by several spectroscopic and analytical techniques such as SEM, TEM, XRD, FTIR VSM, and TGA. The efficiency of the three polymers cellulose powder, NCs, and MNCs toward extracting methylene blue (MB) from water was evaluated. Cellulose powder and NCs showed acceptable tendency for methylene blue. However, MNCs showed excellent extraction efficiency toward MB. The thermodynamic studies revealed a spontaneous adsorption of MB by MNCs at various temperatures. The spontaneous adsorption could be attributed to the electrostatic interaction and H-bonding between MNCs and MB. However, the interaction between cellulose, NCs, and MB is limited to the H-bonding.

Sandwich-like Nanosystem for Simultaneous Removal of Cr(VI) and Cd(II) from Water and Soil

In this work, a novel nanosystem with a sandwich-like structure was synthesized via face-to-face combination of two pieces of waste cotton fabrics (CFs) carrying ferrous sulfide (FeS) and carboxyl-functionalized ferroferric oxide microsphere (CFFM), respectively, and the obtained nanosystem was named as FeS/CFFM/CF. Therein, FeS has high reduction and adsorption capabilities for hexavalent chromium (Cr(VI)), CFFM possesses a high adsorption ability on cadmium ion (Cd(II)) through electrostatic attraction and chelation, and CF displays high immobilization ability for FeS and CFFM and adsorption performance on Cd(II). FeS/CFFM/CF could simultaneously remove Cr(VI) and Cd(II) from water and inhibit the uptake of Cr and Cd by fish and water spinach, ensuring the food safety. Besides, this technology could efficiently control the migration of Cr(VI) and Cd(II) in the sand-soil mixture, which was favorable to prevent their wide diffusion. Importantly, FeS/CFFM/CF possessed a high flexibility and could be conveniently produced with needed scale and shape and easily separated from water and soil, displaying a promising approach to remediate Cr(VI)-/Cd(II)-contaminated water and soil and a huge application potential.

Entrapment of ball-milled biochar in Ca-alginate beads for the removal of aqueous Cd(II)

A novel adsorbent was synthesized through the entrapment of ball-milled biochar in Ca-alginate beads for the removal of aqueous Cd(II). Batch adsorption experiments were conducted to compare Cd(II) adsorption characteristics of ball-milled biochar (BMB), Ca-alginate (CA), and Ca-alginate entrapped ball-milled biochar (CA-BMB). All the tested adsorbents showed excellent sorption ability. The maximum Cd(II) adsorption capacity estimated with Langmuir isotherm modeling was 251.8 mg g^-1 for CA, 227.1 mg g^-1 for CA-BMB, and 40.0 mg g^-1 for BMB. The results demonstrate that entrapment of ball-milled biochar in Ca-alginate provides a low-cost and high-effective way for the removal of aqueous Cd(II).

Adsorption of Cadmium(II) Ion from Aqueous Solution onto a Raw Material of Bamboo Powder and its Surface Modification

This work was focused on evaluating the potential of bamboo powder modified with manganese oxide (MnO-BP) as a low-cost byproduct adsorbent for the adsorption of cadmium(II) ion. A batch method was carried out at room temperature and the optimized conditions. The optimization of adsorption parameters including pH, equilibrium time, dosage and initial Cd(II) concentration was also systematically studied for the removal of cadmium(II) ion. The maximum monolayer adsorption capacity of MnO-BP was estimated as 8.57 mg/g that it more adsorption capacity than untreated-bamboo powder by about 5 times. The Langmuir and the Freundlich isotherms were used to describe the adsorptive mechanism and calculated the maximum monolayer adsorption capacity. It was found that the data from MnO-BP fitted well to the Freundlich isotherm with R2>0.99. It indicated that the adsorptive behavior of MnO-BP to cadmium(II) ion is preferable. In this work, MnO-BP was used for the removal of cadmium(II) ion in wastewater sample. The MnO-BP is a low-cost adsorbent that can be used to remove cadmium(II) effectively.

Mistakes and inconsistencies regarding adsorption of contaminants from aqueous solutions: A critical review

In recent years, adsorption science and technology for water and wastewater treatment has attracted substantial attention from the scientific community. However, the number of publications containing inconsistent concepts is increasing. Many publications either reiterate previously discussed mistakes or create new mistakes. The inconsistencies are reflected by the increasing publication of certain types of article in this field, including "short communications", "discussions", "critical reviews", "comments", "letters to the editor", and "correspondence (comment/rebuttal)". This article aims to discuss (1) the inaccurate use of technical terms, (2) the problem associated with quantities for measuring adsorption performance, (3) the important roles of the adsorbate and adsorbent pK_a, (4) mistakes related to the study of adsorption kinetics, isotherms, and thermodynamics, (5) several problems related to adsorption mechanisms, (6) inconsistent data points in experimental data and model fitting, (7) mistakes in measuring the specific surface area of an adsorbent, and (8) other mistakes found in the literature. Furthermore, correct expressions and original citations of the relevant models (i.e., adsorption kinetics and isotherms) are provided. The authors hope that this work will be helpful for readers, researchers, reviewers, and editors who are interested in the field of adsorption studies.

Adsorptive removal of Ni2+ and Cd2+ from wastewater using a green longan hull adsorbent

The adsorptive removal of Ni2+ and Cd2+ at concentrations of approximately 50 mg L−1 in wastewater is investigated using an agricultural adsorbent, longan hull, and the adsorptive mechanism is characterized. The maximum adsorption capacity of approximately 4.19 mg g−1 Cd2+ was obtained under the optimized conditions of room temperature, pH 5.0, and a solid-to-liquid ratio of 1:30 in approximately 15 min. For Ni2+, the maximum adsorption capacity of approximately 3.96 mg g−1 was obtained at pH 4.7 in approximately 20 min. The adsorption kinetics for both metal ions on the longan hull can be described by a pseudo second-order rate model and are well fitted to the Langmuir adsorption isotherm. The adsorption mechanism of the longan hull to Ni2+ and Cd2+ ions is shown to be a monolayer adsorption of metal ions onto the absorbent surface. Thereinto, the longan hull adsorbent contains N–H, C–H, C=O, and C=C functional groups that can form ligands when loaded with Ni2+ and Cd2+, which reduces the fluorescence of the dried longan hull material.

Biosorption of cadmium (II) from aqueous solutions by natural and modified non-living leaves of Posidonia oceanica

Natural, HCl-treated, and formaldehyde-treated non-living leaves of Posidonia oceanica, a marine plant, were investigated as potential biosorbents to remove Cd²⁺ from aqueous solutions. The studied biosorbents were characterized by elemental analysis and Fourier transform infrared spectroscopy (FTIR) and it was observed that the adsorption capacity of the biosorbents strongly depended on the pH, increasing as the pH rises. The adsorption process was fast. The adsorption kinetic was analyzed using five kinetic models: pseudo-first order, pseudo-second order, Elovich, intraparticle diffusion, and Bangham models. The adsorption isotherms were analyzed by the Langmuir, Freundlich, Dubinin-Radushkevich, Sips, Redlich-Peterson, and Toth models. The maximum biosorption capacity was attained by the biosorbent treated with HCl (1.11 mmol g^-1). The distribution equilibrium constant and the Gibbs free energy change were calculated. The effects of the presence of Na⁺, K⁺, Mg²⁺, and Ca²⁺ ions in the solution on Cd²⁺ uptake were studied. Results indicate that non-living leaves of P. oceanica, natural or treated, can be considered as effective and low-cost biosorbents for the removal of cadmium from aqueous solutions.

Effect of pyrolysis temperatures and times on the adsorption of cadmium onto orange peel derived biochar

The mechanism and capacity of adsorption of cadmium (Cd) on orange peel (OP)-derived biochar at various pyrolysis temperatures (400, 500, 600, 700 and 800°C) and heating times (2 and 6 h) were investigated. Biochar was characterized using proximate analysis, point of zero charge (PZC) analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. Equilibrium and kinetic experiments of Cd adsorption on biochar were performed. The results indicated that the pH value at PZC of biochar approached 9.5. Equilibrium can be reached rapidly (within 1 min) in kinetic experiments and a removal rate of 80.6-96.9% can be generated. The results fitted the pseudo-second-order model closely. The adsorption capacity was estimated using the Langmuir model. The adsorption capacity of Cd on biochar was independent of the pyrolysis temperature and heating time (p>0.01). The maximum adsorption capacity of Cd was 114.69 (mg g(-1)). The adsorption of Cd on biochar was regarded as chemisorption. The primary adsorption mechanisms were regarded as Cπ-cation interactions and surface precipitation. Cadmium can react with calcite to form the precipitation of (Ca,Cd)CO3 on the surface of biochar. The OP-derived biochar can be considered a favourable alternative and a new green adsorbent for removing Cd(2+) ions from an aqueous solution.

Monolithic magnetic carbonaceous beads for efficient Cr(vi) removal from water

Alginate-derived magnetic monolithic carbonaceous beads were synthesized for the first time, aiming for efficient Cr(vi) removal, easy recovery and reusability.

Separation of Cd(ii) and Ni(ii) in a binary mixture through competitive adsorption and acid leaching

Different heavy metals present simultaneously in aqueous solutions should be separated to promote environmental protection.