Adsorption of Cu2+, Pb2+, and Cd2+ onto oiltea shell from water

Recovery of vanadium with melamine in acidic medium

Many hydro-metallurgical methods are developed to recover vanadium, while ammonium salt precipitation possesses the final step and it has threatened the environment. The key point is to find a new compound to replace ammonium salts without reducing vanadium recovery efficiency. Some compounds with -NH2 function groups have attracted our attention as they have similar function groups with ammonium salts. In this paper, the adsorption of vanadium with melamine is conducted. The results show that high adsorption efficiency can be achieved in a short time and melamine displays great performance in the recovery of all concentrations of vanadium. Response surface methodology (RSM) is used to optimize the reaction conditions and order the parameters: reaction temperature > concentration of vanadium > dosage of melamine > reaction time. 99.63% vanadium is adsorbed under optimized conditions: n(melamine)/n(V) = 0.6, reaction time of 60 min, 10 g/L vanadium solution and reaction temperature of 60°C. The successful application of melamine in the recovery of vanadium provides a new way for the utilization of melamine and also a glorious future for -NH2 compounds in the recovery heavy metals.

A comprehensive study of artificial neural network for sensitivity analysis and hazardous elements sorption predictions via bone char for wastewater treatment

Using bone char for contaminated wastewater treatment and soil remediation is an intriguing approach to environmental management and an environmentally friendly way of recycling waste. The bone char remediation strategy for heavy metal-polluted wastewater was primarily affected by bone char characteristics, factors of solution, and heavy metal (HM) chemistry. Therefore, the optimal parameters of HM sorption by bone char depend on the research being performed. Regarding enhancing HM immobilization by bone char, a generic strategy for determining optimal parameters and predicting outcomes is crucial. The primary objective of this research was to employ artificial neural network (ANN) technology to determine the optimal parameters via sensitivity analysis and to predict objective function through simulation. Sensitivity analysis found that for multi-metals sorption (Cd, Ni, and Zn), the order of significance for pyrolysis parameters was reaction temperature > heating rate > residence time. The primary variables for single metal sorption were solution pH, HM concentration, and pyrolysis temperature. Regarding binary sorption, the incubation parameters were evaluated in the following order: HM concentrations > solution pH > bone char mass > incubation duration. This approach can be used for further experiment design and improve the immobilization of HM by bone char for water remediation.

A novel double-network hydrogel made from electrolytic manganese slag and polyacrylic acid-polyacrylamide for removal of heavy metals in wastewater

Electrolytic manganese slag (EMS), a bulk waste generated in industrial electrolytic manganese production, can be a cost-effective adsorbent for heavy metals removal after appropriate modification. In this study, EMS was activated by NaOH and then used to make the EMS-based double-network hydrogel (an EMS/PAA hydrogel) via a one-pot method. The results showed that the EMS/PAA hydrogel exhibits a high selective adsorption capacity of 153.85, 113.63 and 54.35 mg·g-1 for Pb (II), Cd (II) and Cu (II), respectively. In addition, Density Functional Theory (DFT) suggests that the adsorption energies (Ead) of Pb, Cd and Cu on SiO2/PAA of the EMS/PAA gels are - 4.15, - 1.96, and - 2.83 eV, respectively, and SiO2/PAA, with a strong affinity to Pb2+, is one of the reasons for the selective adsorption capacity of EMS/PAA gel for Pb2+. The removal efficiency of the EMS/PAA gel for Pb2+, Cd2+, Cu2+ decreased after four adsorption-desorption cycles by 20.00 %, 24.56 % and 46.56 %, respectively. Mechanism studies suggested that the elimination of the heavy metals by EMS/PAA gels mainly involves electrostatic attraction, inner-sphere complexation, and coordination interactions. The EMS/PAA hydrogels not only have high adsorption capacity, but are also easy to prepare and circulate, making them ideal for practical applications.

Plants, animals, and fisheries waste-mediated bioremediation of contaminants of environmental and emerging concern (CEECs)-a circular bioresource utilization approach

The release of contaminants of environmental concern including heavy metals and metalloids, and contaminants of emerging concern including organic micropollutants from processing industries, pharmaceuticals, personal care, and anthropogenic sources, is a growing threat worldwide. Mitigating inorganic and organic contaminants, which can be coined as contaminants of environmental and emerging concern (CEECs), is a big challenge as traditional physicochemical processes are not economically viable for managing mixed contaminants of low concentrations. As a result, low-cost materials must be designed to provide high CEEC removal efficiency. One of the environmentally viable and energy-efficient approaches is biosorption, which involves using biomass or biopolymers isolated from plants or animals to decontaminate heavy metals in contaminated environments using inherent biological mechanisms. Among chemical constituents in plant biomass, cellulose, lignin, hemicellulose, proteins, polysaccharides, phenolic compounds, and animal biomass include polysaccharides and other compounds to bind heavy metals covalently and non-covalently. These functional groups include carboxyl, hydroxyl, carbonyl, amide, amine, and sulfhydryl. Cation-exchange capacities of these bioadsorbents can be improved by applying chemical modifications. The relevance of chemical constituents and bioactives in biosorbents derived from agricultural production such as food and fodder crops, bioenergy and cash crops, fruit and vegetable crops, medicinal and aromatic plants, plantation trees, aquatic and terrestrial weeds, and animal production such as dairy, goatery, poultry, duckery, and fisheries is highlighted in this comprehensive review for sequestering and bioremediation of CEECs, including as many as ten different heavy metals and metalloids co-contaminated with other organic micropollutants in circular bioresource utilization and one-health concepts.

Adsorption and Removal of Cr6+, Cu2+, Pb2+, and Zn2+ from Aqueous Solution by Magnetic Nano-Chitosan

Magnetic nano-chitosan (MNC) was prepared and characterized. The kinetics, thermodynamics, and influencing factors of the adsorption of Cr6+, Cu2+, Pb2+, and Zn2+, as well as their competitive adsorption onto MNC in aqueous solution, were studied. The results showed that the adsorption kinetics and thermodynamics of Cr6+, Cu2+, Pb2+, and Zn2+ were well described by the pseudo-second-order kinetic model and Langmuir isothermal adsorption model, indicating that the adsorption was mainly chemical adsorption and endothermic. Increasing the dosage of MNC, the equilibrium adsorption capacity (qe) of Cr6+, Cu2+, Pb2+, and Zn2+ decreased; their removal rate (η) increased. With the increase in the solution’s pH, the qe and η of Cr6+ first increased and then decreased; the qe and η of Cu2+, Pb2+, and Zn2+ increased. With the increase in the metal ion initial concentration, the qe increased; the η of Cr6+, Cu2+, and Zn2+ decreased, while the η of Pb2+ increased first and then decreased. Temperature had a weak influence on the qe of Cr6+ and Pb2+, while it had a strong influence on Cu2+ and Zn2+, the qe and η were greater when the temperature was higher, and the adsorption was spontaneous and endothermic. The qe and η of Cu2+, Pb2+, and Zn2+ decreased in the presence of co-existing ions. The influences among metal ions existed in a binary and ternary ion system. The current study’s results provide a theoretical support for the simultaneous treatment of harmful metal ions in wastewater by MNC.

Adsorptive removal of beryllium by Fe-modified activated carbon prepared from lotus leaf

Lotus leaf was used as raw material to prepare HNO₃-activated carbon with 1.5:1 (HNO₃:lotus leaf) (wt:wt) impregnation. Then, the activated carbon was modified by Fe(NO₃)₃ to obtain Fe-activated carbon (Fe-AC). The adsorption test results show that Fe-AC maximum saturated adsorption capacity (Q_m) is 45.68 mg/g when the Fe(NO₃)₃ loading is 5% of the total activated carbon, pH = 6, and the temperature is 35 ℃. The adsorption effect of Fe-AC under neutral conditions is better than that under alkaline and acidic conditions. The modified activated carbon has better adsorption selectivity. The obtained material (Fe-AC) was characterized by N₂ adsorption-desorption isotherm, SEM, FT-IR, BET, XRD, XPS, and pH_pzc. The total pore volume, specific surface area, and zero charges of modified activated carbon were increased. The types of modified functional groups were reduced, and the iron reacted with the functional groups, providing ion exchange sites for the adsorption of beryllium. The adsorption thermodynamics showed that the adsorption process was spontaneous and endothermic. The adsorption mechanism of Fe-AC to beryllium is mainly chemical adsorption.

Cost-effective microwave-assisted hydrothermal rapid synthesis of analcime-activated carbon composite from coal gangue used for Pb2+ adsorption

Heavy metal contamination of water has brought about serious harm to the ecological environment and also threatens human health to a certain extent. In this study, a composite structure comprised of analcime-activated carbon (ANA-AC) was synthesized in situ via a microwave-assisted hydrothermal method using coal gangue (CG) for the potential treatment of Pb²⁺ from aqueous solution. The products were systematically characterized using XRD, SEM, BET, FTIR, and XPS. The results showed that activated carbon was successfully integrated with the structure of the analcime and the BET surface area of the ANA-AC (20.82 m²/g) was much greater than that of the CG (9.33 m²/g) and ANA (10.04 m²/g) independently. The relationship between Pb²⁺ adsorption capacity and the initial solution concentration, adsorbent dosages, contact time, pH, and temperature was studied. Under optimal conditions (Pb²⁺  = 100 mg/L, dosage = 0.1 g, contact time = 6 h, pH = 5.4-6, temperature = 298 K), the maximum adsorption capacity of ANA-AC can reach 100%, which was higher than that of CG and ANA. The Langmuir isotherm model was in good agreement with the data obtained for Pb²⁺ adsorption, and the pseudo-second-order kinetic model was more suitable for describing the experimental data, showing that chemical adsorption was the controlling step during the adsorption process. In summary, analcime-activated carbon composite prepared from coal gangue could be used as an appropriate adsorbent for Pb²⁺ adsorption from an aqueous solution.

Simultaneous Removal of Cu2+, Cd2+ and Pb2+ by Modified Wheat Straw Biochar from Aqueous Solution: Preparation, Characterization and Adsorption Mechanism

As an eco-friendly and efficient adsorbent for removal of potential toxic metals from aqueous solution, biochar has received widespread attention. In the present study, wheat straw biochar (BC) and corresponding modified biochar (HNC) were used to remove Cu²⁺, Cd²⁺ and Pb²⁺ from an aqueous solution. The influence of the environment factors on metals adsorption and adsorption mechanism were discussed in detail. The results showed that the HNC had porous structures and owned ample functional groups (-OH, -COOH and C-N groups) compared with the BC. In the single system, the adsorption capacities of HNC for Cu²⁺, Cd²⁺ and Pb²⁺ at a pH of 5.5 were 18.36, 22.83 and 49.38 mg/g, which were 76.89%, 164.36% and 22.75% higher than that of the BC, respectively. In addition, the adsorption process of Cu²⁺ and Cd²⁺ on BC and HNC fitted to the Langmuir isotherm model and pseudo-second-order kinetics, but the adsorption of Pb²⁺ on BC and HNC fitted to the Langmuir isotherm model and pseudo-first-order kinetics. Adsorption isotherms indicated that the adsorption of Cu²⁺, Cd²⁺ and Pb²⁺ by BC and HNC was a spontaneous endothermic process. The competitive adsorption of mixed metal ions (Cu²⁺, Cd²⁺ and Pb²⁺) revealed that HNC was more preferential to adsorb Cu²⁺ compared with Cd²⁺ and Pb²⁺. Furthermore, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses revealed that the main adsorption mechanisms were surface complexation and precipitation, and the adsorbed Cu²⁺, Cd²⁺ and Pb²⁺ on HNC mainly exist as CuO, Cd(OH)₂, Pb₃O₄ and Pb(OH)₂.

Sorption of Cd2+ on Bone Chars with or without Hydrogen Peroxide Treatment under Various Pyrolysis Temperatures: Comparison of Mechanisms and Performance

In this study, bone char pretreated with hydrogen peroxide and traditional pyrolysis was applied to remove Cd2+ from aqueous solutions. After hydrogen peroxide pretreatment, the organic matter content of the bone char significantly decreased, while the surface area, the negative charge and the number of oxygen-containing functional groups on the bone char surface increased. After being pyrolyzed, the specific surface area and the negative charge of the material were further improved. The adsorption kinetics and isotherms of Cd2+ adsorption were studied, and the influence of solution pH and the presence of ionic species were investigated. The experimental results showed that the samples with lower crystallinity exhibited less organic matter content and more surface oxygen-containing functional groups, resulting in stronger adsorption capacity. After being treated with hydrogen peroxide and pyrolyzed at 300 °C, the maximum adsorption capacity of bone char was 228.73 mg/g. The bone char sample with the lowest adsorption capacity(47.71 mg/g) was pyrolyzed at 900 °C without hydrogen peroxide pretreatment. Ion exchange, surface complexation, and electrostatic interactions were responsible for the elimination of Cd2+ by the bone char samples. Overall, this work indicates that hydrogen peroxide-treated pyrolytic bone char is a promising material for the immobilization of Cd2+.

Experimental and modeling studies of competitive Pb (II) and Cd (II) bioaccumulation by Aspergillus niger

Co-existence of toxic metals causes complex toxicity to microorganisms during bioremediation in water and soil. This study investigated the immobilization of Pb²⁺ and Cd²⁺ by fungus Aspergillus niger, which has been widely applied to environmental remediation. Five treatments were set, i.e., CK (no toxic metals), Pb²⁺ only, Cd²⁺ only, Pb²⁺/Cd²⁺ = 1:1(molar ratio), and Pb²⁺/Cd²⁺ = 2:1. Cadmium induced strong toxicity to the fungus, and maintained the high toxicity during incubation. However, as Pb/Cd ratio increased from 0 to 2, the removal rates of Cd²⁺ by A. niger were raised from 30 to 50%. The elevated activities of pyruvate dehydrogenase (PDH) and citrate synthetase (CS) enzymes confirmed that Pb addition could stimulate the growth of A. niger. For instance, citric acid concentrations and CS activities were 463.22 mg/L and 78.37 nmol/min/g, respectively, during 3-day incubation as Pb/Cd = 1. However, these two values were as low as ~ 50 with addition of only Cd. It was hence assumed that appropriate co-existence of Pb²⁺ enhanced microbial activity by promoting TCA cycle of the fungus. Moreover, the SEM analysis and geochemical modeling demonstrated that Pb²⁺ cations were more easily adsorbed and mineralized on A. niger with respect to Cd²⁺. Therefore, instead of intensifying metal toxicity, the addition of appropriate Pb actually weakened Cd toxicity to the fungus. This study sheds a bright future on application of A. niger to the remediation of polluted water with co-existence of Pb and Cd. KEY POINTS: • Cd²⁺ significantly inhibited P consumption, suggesting its high toxicity to A. niger. • Pb²⁺ stimulated the growth of A. niger by promoting TCA cycle in the cells. • Cd²⁺ removal by A. niger were improved with co-existence of Pb²⁺.

Possibility of Removing Pb and Cd from Polluted Water by Modified Fly Ash

In this study, fly ash (FA) was modified by sodium hydroxide to prepare a new adsorption material (IP) and treat Pb2+- and Cd2+-polluted wastewater. The effect of preparation parameters (mass ratio of FA/NaOH and modification temperature) on IP adsorption performance was investigated. The results indicated that the IP4 showed the highest adsorption capacity prepared at the FA/NaOH mass ratio of 1 : 2 and the roasting temperature of 250°C. The IP4 was characterized by SEM, EDX, XRD, and FTIR analyses. The results showed that the surface morphology and microstructure of FA were significantly changed. Furthermore, in order to study the adsorption performance of Pb2+ and Cd2+ on IP4, the different initial concentrations of Pb2+ and Cd2+, pH, and contact time were analyzed, and the results indicated that IP4 has excellent adsorption capacity for heavy metals. In addition, kinetic model results demonstrated that the adsorption behavior of Pb2+ and Cd2+ on IP4 was better described by a pseudo-second-order model.

A Highly Expanded Polycarboxylate Gel and New Environmental Response Effects for Efficiently Adsorbing and Recovering Cu(II) from Water

A new highly expanded polycarboxylate gel (EPCG) was accidentally formed in a facile cross-linking copolymerization system. When used as an adsorbent material, the EPCG could be quickly expanded 29.44 times in water to have a high permeability inside for realizing the efficient adsorption toward Cu(II) from water. The adsorption capacity of EPCG toward Cu(II) was 261.70 mg/g, which was higher than that of all the selected existing adsorbents reported in recent years. The adsorption rate of expanded EPCG was 3.61 times higher than that of the previous polyantionic gel. Similarly, due to the high expansion and high permeability of EPCG, the EPCG skeleton could be further coated with an alkaline NaOH, forming a novel NaOH-coated EPCG material, and its adsorption capacity toward Cu(II) was further improved to 333.21 mg/g compared to that of pure EPCG adsorbent. Moreover, the EPCG wastes after adsorbing Cu(II) could be fully desorbed to be regenerated for reuse. A total of 99.39% of the adsorbed Cu(II) was desorbed from EPCG wastes to be recovered. The adsorption capacity of regenerated EPCG reused for adsorbing Cu(II) was 259.05 mg/g, which was very near that of the original EPCG. In addition, a series of simulation experiments and instrumental analysis were adopted to confirm the new environmental response effects as the key factors in the purification of Cu(II)-containing wastewater, including "expansion-shrink," "alkali-coating," and "acid-desorption" responses.

Polyethyleneimine-impregnated alkali treated waste bamboo powder for effective dye removal

In this study, the polyethyleneimine (PEI) modified waste bamboo powder (WBP-Na-PEI) was successfully prepared and applied to adsorbing Congo red (CR) dye from aqueous solution. The obtained materials were characterized by field emission scanning electron microscope, X-ray diffraction, Fourier transform-infrared, and thermogravimetric analysis. The results showed that WBP-Na-PEI(1.8 K-5) was synthesized successfully and PEI uniformly covered the WBP-Na-PEI(1.8 K-5) surface. In the process of adsorption, four kinds of influencing factors were discussed, and the adsorption mechanisms such as kinetics, isotherm, thermodynamics were explored. The maximum adsorption capacity of WBP-Na-PEI(1.8 K-5) was 992.94 mg·g^-1 at 298 ± 1 K, and the removal efficiency was over 98%. Pseudo-first-order, pseudo-second-order and intra-particle diffusion models were studied, the results showed that the adsorption process conformed to the pseudo-second-order model, and the rate of this process was controlled by many steps. Furthermore, the removal efficiency of the adsorption kinetics reached 85% within 10 minutes. The results of the isotherm model and thermodynamics showed that the adsorption process was consistent with the Langmuir model and was mainly a spontaneous chemical endothermic process of monolayer. And the removal efficiency of the adsorbent reached 93% at the concentration of 400 mg/L, which can be expected to have a broad prospect in the treatment of CR industrial wastewater.

Heavy metals biosorption mechanism of partially delignified products derived from mango (Mangifera indica) and guava (Psidium guiag) barks

This paper evaluates the biosorption of toxic metal ions onto the bioadsorbents derived from mango (Mangifera indica) and guava (Psidium guiag) barks and their metal fixation mechanisms. Maximum metal biosorption capacities of the mango bioadsorbent were found in the following increasing order (mg/g): Hg (16.24) < Cu (22.24) < Cd (25.86) < Pb (60.85). Maximum metal biosorption capacities of guava bioadsorbent follow similar order (mg/g): Hg (21.48) < Cu (30.36) < Cd (32.54) < Pb (70.25), but with slightly higher adsorption capacities. The removal mechanisms of heavy metals using bioadsorbents have been ascertained by studying their surface properties and functional groups using various spectrometric, spectroscopic, and microscopic methods. Whewellite (C2CaO4·H2O) has been identified in bioadsorbents based on the characterization of their surface properties using X-ray techniques (XPS and XRD), facilitating the ion exchange of metal ions with Ca2+ bonded with carboxylate moieties. For both the bioadsorbents, the Pb2+, Cu2+, and Cd2+ are biosorbed completely by ion exchange with Ca2+ (89-94%) and Mg2+ (7-12%), whereas Hg2+ is biosorbed partially (57-66%) by ion exchange with Ca2+ (38-42%) and Mg2+ (19-24%) due to involvement of other cations in the ion exchange processes. Bioadsorbents contain lignin which act as electron donor and reduced Cr(VI) into Cr(III) (29.87 and 37.25 mg/g) in acidic medium. Anionic Cr(VI) was not adsorbed onto bioadsorbents at higher pH due to their electrostatic repulsion with negatively charged carboxylic functional groups.

Efficient removal of Hg2+ from aqueous solution by a novel composite of nano humboldtine decorated almandine (NHDA): Ion exchange, reducing-oxidation and adsorption

Efficient removal of Hg²⁺ from aqueous solution is key for environmental protection and human health. Herein, a novel composite of nano humboldtine decorated almandine was synthesized from almandine for the removal of Hg²⁺. Results showed that the Hg²⁺ removal process followed pseudo-second-order kinetic model and Langmuir equation, and the maximum adsorption capacity was 575.17 mg/g. Furthermore, Hg²⁺ removal by the composite was pH-dependent and low pH value facilitated the removal of Hg²⁺. SEM and HADDF-STEM results suggested a new rod morphology was generated and the adsorbed mercury was mainly enriched into this structure after reaction with Hg²⁺ solution. The removal mechanisms of Hg²⁺ by the composite was pH dependent, and included ion exchange, surface complexation, reduction and oxidation. Our results demonstrated that the composite was an ideal material for Hg²⁺ removal and the transformation ways of mercury related species could be a significant but currently underestimated pathway in natural and engineered systems.

Adsorptive removal of heavy metals from battery industry effluent using MOF incorporated polymeric beads: A combined experimental and modeling approach

In this study, the metal organic framework (MOF) ZIF-8 was investigated as potential adsorbent for heavy metal ions. The MOF powder was used further to prepare mixed matrix beads (MMBs) using polysulfone as the base material. Both the MOF powder and the MMBs were characterized using Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller (BET) analyzer and zetasizer. Adsorption capacity of the MMBs were 164-220 mg/g for Pb and 92-161 mg/g for Cd. A fundamental pore diffusion-adsorption model was used to predict the batch kinetics for both single and multicomponent cases and effective pore diffusivities and mass transfer coefficients were determined. Mutual interactions among heavy metals were quantified using interaction parameters. ZIF-8, incorporated in the PSF matrix, plays the predominant role in capturing the metal ions through surface complexation with the NH and metal-OH groups. A first principle-based model involving convection, diffusion and adsorption was used to quantify the breakthrough behavior for the continuous fixed bed column using the MMBs. The column performance was tested with battery industry effluent. The saturated beads were suitably regenerated using 0.1(M) HCl solution. Finally, the model parameters were used for scaling up of the columns.

Fabrication of novel amine-functionalized magnetic silica nanoparticles for toxic metals: kinetic and isotherm modeling

In this research, an amine-functionalized magnetic silica nanosorbent was prepared using the co-precipitation technique, and this nanosorbent can be effortlessly detached using an external magnetic field. FTIR and SEM analyses identified that the nanosorbent holds extraordinary adsorption characteristics for toxic metals' (copper, cadmium, zinc, and nickel) removal. The adsorption-affecting parameters were optimized, and the thermodynamic studies assessed that the adsorption process seemed to be spontaneous, feasible, and exothermic. The pseudo-first-order and Freundlich models perfectly fit the kinetic and equilibrium data, respectively. Langmuir monolayer capacity of the nanosorbent was analyzed using nonlinear evaluation methods such as 419.9 mg/g for copper, 321.9 mg/g for nickel, 217.3 mg/g for cadmium, and 137.6 mg/g for zinc. The used adsorbent was simply rejuvenated using the 0.2 N HCl solution subsequently with intense agitation. The result of the present research confirms that the produced nanosorbent can be effectively utilized for industrial wastewater management.

Simultaneous removal of Pb2+, Cu2+ and Cd2+ ions from wastewater using hierarchical porous polyacrylic acid grafted with lignin

In PAA-g-lignin, phase separation, caused by the difference in expansion properties between lignin and polyacrylic acid, is used to build a porous hydrogel. In this study, PAA-g-APL was produced by grafting polyacrylic acid with acid-pretreated alkali lignin. Acid-pretreated alkali lignin acts as a hierarchical pore-forming agent that enhances the simultaneous adsorption capacities for Pb²⁺, Cu²⁺ and Cd²⁺ ions from wastewater. Notably, PAA-g-APL acted as a selective adsorbent for Pb²⁺ ions has an excellent selective removal coefficient α (20.22) in contaminated wastewater contained Cu²⁺ ions. Its molar partition coefficient for Pb²⁺ ions (68 %) is higher than that for either Cu²⁺ ions (28.6 %) or Cd²⁺ ions (3.4 %). At equilibrium, the total adsorption capacities of PAA-g-APL for Pb²⁺, Cu²⁺ and Cd²⁺ were 1.076 mmol g^-1, 0.3233 mmol g^-1 and 0.059 mmol g^-1, respectively. The experimental kinetic data fitted well to a pseudo-second order model and to an intra-particle-diffusion model. The Freundlich isotherm model gave the best fit with the experimental equilibrium data. The ΔG° for PAA-g-APL is < 0, indicating that the adsorption of heavy metal ions is a spontaneous process. This study provides a highly promising candidate for the treatment of wastewater contaminated with a mixture of heavy metals.

Microwave-assisted urea modified crop residue in Cu2+ scavenging

Raphia hookeri fruit epicarp (RHFE) was used in a novel adsorbent preparation via a combination of urea modification and microwave irradiation. The prepared adsorbent (URHFE) was characterized physicochemically, spectroscopically and microscopically characterized. URHFE efficiency in Cu²⁺ scavenging was tested with focus on operational parameters such as pH, dosage, concentration, contact time, ionic strength and temperature. Adsorption data were tested with isotherms and kinetics models. Optimum adsorption occurred at pH of 5.5. The presence of competing ion decreased Cu²⁺ removal and this varied with competing ion concentration. Cu²⁺ uptake decreased with increase in temperature. Percentage desorption was found generally low. The Langmuir monolayer adsorption capacity (q_max) was obtained to be 144.93 mg/g, this compared well in effectiveness with other adsorbent previously reported. Dubinin Radushkevich (D-R) isotherm model suggests that adsorption mechanism was chemical in nature. Pseudo second order kinetics best described the adsorption kinetics while multilinear adsorption was observed from the intraparticle diffusion model.

Megamerger of biosorbents and catalytic technologies for the removal of heavy metals from wastewater: Preparation, final disposal, mechanism and influencing factors

Heavy metal pollution, because of its high toxicity, non-biodegradability and biological enrichment, has been identified as a global aquatic ecosystems threat in recent decades. Due to the high efficiency, low cost, satisfactory recyclability, easy storage and separation, biosorbents have exhibited a promising prospect for heavy metals treatment in aqueous phase. This article comprehensively summarized different types of biosorbents derived from available low-cost raw materials such as agricultural and forestry wastes. The raw materials obtained are treated with conventional pretreatment or novel methods, which can greatly enhance the adsorption performance of the biosorbents. The suitable immobilization methods can not only further enhance the adsorption performance of the biosorbents, but also facilitate the process of separating the biosorbents from the wastewater. In addition, once biosorbents are put into large-scale use, the final disposal problems cannot be avoided. Therefore, it is necessary to review the currently accepted final disposal methods of biosorbents. Moreover, through the analysis of the adsorption and desorption mechanisms of biosorbents, it is not only beneficial to find the better methods to improve the adsorption performance of the biosorbents, but also better to explain the influencing factors of adsorption effect for biosorbents. Especially, different from many researches focused on biosorbents, this work highlighted the combination of biosorbents with catalytic technologies, which provided new ideas for the follow-up research direction of biosorbents. Finally, the purpose of this paper is to inject new impetus into the future development of biosorbents.

Micro-nano-engineered nitrogenous bone biochar developed with a ball-milling technique for high-efficiency removal of aquatic Cd(II), Cu(II) and Pb(II)

A cost-effective and eco-friendly engineering method to improve biochar's physicochemical and sorption performance is critical in various environmental applications. In this study, micro-nano-engineered nitrogenous biochars derived from cow bone meal pyrolyzed at different temperatures and were engineered with the assistance of a ball-milling technique. The ball-milled bone biochars were natural composites combined with plant biochars and hydroxyapatite components on the micro-nanoscale. Both the micropore area and the external specific surface area of the bone biochars were significantly improved after ball-milling. The sorption capacities for heavy metal ions were heavy metal ions were MBC-600 > MBC-450 > BC-600 > MBC-300 > BC-450 > BC-300, consistent with the variation tendency in the specific surface areas of the bone biochars. The adsorption capacities of MBC-600 for Cd(II), Cu(II) and Pb(II) were 165.77, 287.58 and 558.88 mg/g, respectively (T 298K, pH 5.0), representing increases of 93.91.%, 75.56% and 64.61% compared with the un-milled preparation. Surface complexation, cation exchange, chemical precipitation, electrostatic interaction and cation-π bonding were responsible for the removal of heavy metal ions by bone biochar materials. Taken together, the results show that micro-nano-engineered nitrogenous bone biochar prepared using ball-milling technology is a promising material for the remediation of heavy metals-bearing aquatic environments.

Adsorption of Ni2+ and Pb2+ from water using diethylenetriamine-grafted Spirodela polyrhiza: behavior and mechanism studies

Novel adsorbent, diethylenetriamine-grafted Spirodela polyrhiza (DSP), was synthesized via modifying natural S. polyrhiza (SP) with diethylenetriamine by cross-linking with epichlorohydrin and applied to adsorb Ni²⁺ and Pb²⁺ from water. The effecting parameters on adsorption of Ni²⁺ and Pb²⁺ such as adsorbent dosage, pH, contact time, temperature, and initial concentration were studied through equilibrium experiments. The adsorption of Ni²⁺ and Pb²⁺ followed the pseudo-second-order model and the Langmuir isotherm adsorption model. The study discusses thermodynamic parameters, including changes in Gibbs free energy, entropy, and enthalpy, for the adsorption of Ni²⁺ and Pb²⁺ on DSP, and revealed that the adsorption process was spontaneous and exothermic under natural conditions. The maximum Ni²⁺ and Pb²⁺ adsorption capacities of DSP were 33.02 and 36.50 mg/g, respectively. The newly prepared materials were characterized through scanning electron microscopy (SEM), mapping analysis, and zeta potential analysis. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses indicated that functional groups (-OH and N-H) were involved in Ni²⁺ and Pb²⁺ adsorption. Notably, DSP can be easily regenerated and reused for multiple cycles. Therefore, DSP is a promising adsorbent for effective Ni²⁺ and Pb²⁺ removal.

Contrasting the Pb (II) and Cd (II) tolerance of Enterobacter sp. via its cellular stress responses

Successful application of microorganisms to heavy metal remediation depends on their resistance to toxic metals. This study contrasted the differences of tolerant mechanisms between Pb²⁺ and Cd²⁺ in Enterobacter sp. Microbial respiration and production of formic acid showed that Enterobacter sp. had a higher tolerant concentration of Pb (>1000 mg l^-1 ) than Cd (about 200 mg l^-1 ). Additionally, SEM confirmed that most of Pb and Cd nanoparticles (NPs) were adsorbed onto cell membrane. The Cd stress, even at low concentration (50 mg l^-1 ), significantly enlarged the sizes of cells. The cellular size raised from 0.4 × 1.0 to 0.9 × 1.6 μm on average, inducing a platelet-like shape. In contrast, Pb cations did not stimulate such enlargement even up to 1000 mg l^-1 . Moreover, Cd NPs were adsorbed homogeneously by almost all the bacterial cells under TEM. However, only a few cells work as 'hot spots' on the sorption of Pb NPs. The heterogeneous sorption might result from a 'self-sacrifice' mechanism, i.e., some cells at a special life stage contributed mostly to Pb sorption. This mechanism, together with the lower mobility of Pb cations, caused higher microbial tolerance and removal efficiency towards Pb²⁺ . This study sheds evident contrasts of bacterial resistance to the two most common heavy metals.

Sustainable and scalable in-situ synthesis of hydrochar-wrapped Ti3AlC2-derived nanofibers as adsorbents to remove heavy metals

To ensure a sustainable future, it is imperative to efficiently utilize abundant biomass to produce such as platform chemicals, transport fuels, and other raw materials; hydrochar is one of the promising candidates derived by hydrothermal carbonization of biomass in pressurized hot water. The synthesis of "hydrochar-wrapped Ti₃AlC₂-derived nanofibers" was successfully achieved by a facile one-pot hydrothermal reaction using glucose as the hydrochar precursor. Meanwhile, cellulose and pinewood sawdust as raw materials were also investigated. Products were characterized by XRD, N₂ adsorption-desorption isotherms, SEM, TEM and FT-IR to investigate their crystal structures, textural properties, morphologies, and surface species. In the adsorption test to remove Cd(II) and Cu(II) in aqueous solution, hydrochar-wrapped nanofibers outperformed pure nanofibers derived from Ti₃AlC₂, hydrothermal carbon derived from glucose and commercial activated carbon. Finally, the regeneration, sorption kinetics, and possible adsorption mechanism were also explored.

Sewage biogas efficient purification by means of lignocellulosic waste-based activated carbons

The present paper evaluates the efficiency of sustainable activated carbons obtained from the valorization of lignocellulosic waste in removing siloxanes and volatile organic compounds for the purification of anaerobic digester biogas. Pyrolized and non-pyrolized lignocellulosic residues generated in food and wood industries were used as precursor materials to obtain experimental adsorbents by a chemical activation process using several activating agents. The highest porosity was obtained by non-pyrolized residue activated by K₂CO₃ at 900 °C. The performance of the experimental materials was compared with that of commercial activated carbons in gas adsorption tests of siloxanes (octamethylcyclotetrasiloxane and hexamethyldisiloxane) and volatile organic compounds (toluene and limonene). The waste-based activated carbons developed in this work proved to be more efficient for the removal of both siloxanes and VOCs than the commercial samples in most of the conditions tested. Adsorption capacities correlated with porosity, while the more relevant pore size depends on the adsorbate.