Heavy Metals In Aqueous Solutions Research Articles

Calculations of mean ionic activity coefficients of copper and manganese salts in aqueous solutions

Accurately predicting the activity coefficients of copper and manganese salts in aqueous solutions is crucial for treating industrial wastewater, and it is of practical interest to calculate the activity coefficients of heavy metals in aqueous solutions using the Equation of State because of its high flexibility and wide range of applicability. This work conducts a modeling study on the mean ionic activity coefficients of copper and manganese salts in aqueous solutions. The thermodynamic framework used in this work is an electrolyte version of the Cubic Plus Association Equation of State (e-CPA). The model's ion-water binary interaction parameters are obtained by regressing the osmotic coefficients and mean ionic activity coefficients in aqueous solutions. The modeling results indicate that the electrolyte Equation of State can satisfactorily correlate the water activity, osmotic coefficients, and mean ionic activity coefficients of copper and manganese salts in aqueous solutions over a wide range of salt concentrations. Among all the systems at 298.15 K, the biggest average relative deviation between calculated and experimental values is within 6.7 % and 2.3 % for the mean ionic activity coefficients and water activity, respectively. Furthermore, this work discusses the impact of ion pairs on the phase equilibrium of aqueous systems from a microscopic mechanism perspective and analyzes and discusses the model's adaptability. The model used in this work can accurately predict the activity coefficients of a variety of copper and manganese salts in aqueous solutions over wide concentration ranges and provides an improved interface for improving the calculation accuracy of the model under high concentration or other complex conditions.

Cyperus longus to bioremediate heavy metals in aqueous solutions

Finding environmentally friendly methods for the bioremediation of the environment, including water, contaminated with heavy metals is of utmost significance. The ability of 50 Cyperus longus species, harvested from Shadegan International Wetland, Iran, for the phytoremediation of heavy metals in contaminated water was investigated. The plants were transplanted in the aquariums contaminated with one of the heavy metals (0–20 mgL-1) at the pHs of 4 and 7 for 30 days. Plant removal of heavy metals was determined. The single and double interactions of plant tissue, heavy metal type and concentration, and pH significantly affected the absorption of plant heavy metals. The highest removal of heavy metals including Pb (45.9 %) > Zn (36.1 %) > Cr (32.8 %) > Cd (27.5 %) > Ni (25.9 %) was related to the 20 mgL-1 and pH4 treatments by the order of root> stem> leaf> flower. The 5–10 mgL-1 concentration resulted in the highest removal efficiency by stems (Ni, 44.12 %), flowers (Zn, 44.00 %), leaves (Cr, 44.14 %) and roots (Cr, 44.36 %). The highest bioconcentration (BCF) and translocation factors (TF) of 4.106 and 2 (Zn), 2.124 and 1.461 (Cd), 1.815 and 1.289 (Ni), 5.291 and 2.460 (Pb), and 2.811 and 1.885 (Cr) were resulted. Although with increasing heavy metal concentrations, the plant absorbed higher heavy metals, its removal efficiency decreased as it was the highest at the heavy metal concentration of 5–10 mgL-1. According to plant removal efficiency and the BCF and TF factors, it is possible to efficiently bioremediate water contaminated with heavy metals using C. longus.

Heavy metals immobilization of LDH@biochar-containing cementitious materials: Effectiveness and mechanisms

The utilization of tailings for producing solid waste-based concrete can effectively mitigate the environmental consequences stemming from tailings accumulation. However, the presence of high concentrations of heavy metal ions in certain tailings can deleteriously affect the microstructure of the cement matrix. This study investigated the in-situ immobilization performance of Pb2+ and Mn2+ by calcium-aluminum layered double hydroxides (CaAl-LDH) and LDH@biochar blended in cement-based materials. The equilibrium adsorption capacity of CaAl-LDH/LDH@biochar for heavy metals in aqueous solution was assessed by adsorption kinetics, while the effect of pH value on the removal rate of heavy metals was also studied. The workability and mechanical properties of cement mortar are significantly improved with the addition of 4 % LDH@biochar. LDHs@biochar can effectively reduce the deteriorating effects of heavy metal ions on the fundamental properties of cement materials. Compared with CaAl-LDH, the leaching concentrations for Pb2+ and Mn2+ in LDH@biochar at 28 d is decreased by 59 % and 39 %, respectively. The stable adsorption of Pb2+ and Mn2+ by LDH@biochar is attributed to multiple mechanisms, including interlayer anion exchange effect, chemical adsorption of surface functional groups and electrostatic attraction. This study provide valuable insights for enhancing the efficiency of heavy metal immobilization in cement-based materials.

STUDY OF NON-FUEL APPLICATION OF BROWN COAL DERIVATIVES IN THE PRODUCTION OF MEMBRANES BASED ON HYBRID BIODEGRADABLE MATERIALS

The article shows research into the non-fuel use of brown coal derivatives in the production of membranes based on hybrid biodegradable materials. The work used polylactide brand Terramac TP-4000, humic substances obtained from brown coals. Membranes for water purification from heavy metals were obtained from hybrid biopolymer materials based on pol- ylactide and humic substances in the form of polymer porous films with a pore size of 20 microns and a working surface area of the membrane of 28.26∙10-4 m2 with a circle diameter of 6 cm. Used in our The work of humic substances belonged to the group of well-hummified, more aromatic with a high content of acidic functional groups, which leads to their high com- plexing ability to form stable metal-humic complexes. The developed hybrid biodegradable materials based on polylactide and humic substances were used as highly effective sorption membrane materials to reduce the content of heavy metals in aqueous solutions. Obtaining membranes of hybrid biodegradable materials based on polylactide and humic substances have maximum selectivity for the extraction of metal ions in relation to Cu2+ – 95 % and Pb2+ – 94 %; and for metals such as Cd2+, Hg2+, Zn2+ and Co2+, it ranges from 82 to 89 %. Comparing the percentage of metal ions adsorbed, it can be seen that the easiest adsorbed metal was lead, copper and zinc adsorbed similarly, with cadmium showing the lowest percentage, but its adsorption was slightly worse than in the case of copper and zinc. The highest value was obtained for single adsorption of Cu2+ ions; in the case of adsorption from a mixture, this metal also had the highest distribution coefficient, and strong adsorption was also found for Pb2+. On the other hand, the adsorption of Zn2+ was, according to the “partition coefficient,” relatively weak. Strong and residual phases were highest for copper and lead, these two metals were largely bound into strong complexes by humic substances and only a very small amount could be washed out under normal conditions. It was found that the leaching of metal ions from mem- brane hybrid biodegradable materials based on polylactide and humic substances into water was very low, in most cases it was about 10 % and did not exceed 20 %. Most of the metal ions (≥60 %) were very tightly bound and were partially leached out under strongly acidic conditions. The obtained results of adsorption resistance vary significantly and correlate well with the age and degree of humification of humic substances.

Highly nanocrystalline Mg doped ZnFe2O4 powders for rapid and simultaneous adsorption of Lead, Copper, and Cadmium heavy metals ions in synthetic / sea waters

This research aims to investigate the effect of Mg doping on individual and simultaneous adsorption of Pb+2, Cu+2, and Cd+2 heavy metals in aqueous solution and in seawater samples, by Zinc ferrite nanoparticles. The Mg-doped Zinc ferrite nanoparticles are synthesized successfully by the sol-gel route and varying Mg concentrations. TEM, XRD, FTIR, Raman, and XPS characterizations confirm the cubic spinel structure of Zinc ferrite with a semi-spherical shaped nanosized particles (10-15nm) irrespective of Mg doping content. The BET surface area manifests a significant increase within Mg doping (39.3 m2/g) compared with the pure zinc ferrite (28.4 m2/g). Accordingly, Mg-doped Zinc ferrite powders demonstrate considerable adsorption capacities for Pb+2 (143.5mg/g), Cu+2 (117mg/g), and Cd+2 (77mg/g) within 2h under optimized experimental conditions. The prepared nanopowders exhibit high selectivity towards Pb+2 in simultaneous adsorption in aqueous solutions (85mg/g) and real seawater samples. Nonetheless, the selectivity of Pb+2 ions drops dramatically to 25mg/g within real seawater samples due to the strong ionic strength of high-salinity seawater. This study provides insights into the importance of doped spinel ferrite nanoparticles in highly efficient, rapid, and simultaneous adsorption of heavy metals. Besides, it reveals the challenge of performing the adsorption process in real seawater.

Performances Study of Polyvinylidene Fluoride (PVDF)/Waste Eggshell (WES) Mixed-Matrix Membrane for Copper Removal

The presence of heavy metals in water resources brings hazard to health and the environment considering that most of these cannot be degraded and may result in bioaccumulation in the food chain. This study investigated the applicability and efficiency of waste eggshells for the removal of Copper (Cu) heavy metal in aqueous solution. The mixed-matrix membrane with polyvinylidene fluoride (PVDF) as membrane material, N-Methyl-2-pyrrolidone (NMP) as solvent and waste eggshell as additive with ratio of (a) 15:85:0, (b) 14.9:85:0.1, (c) 14.7:85:0.3, (d) 14.5:85:0.5 and (e) 14:85:1 is fabricated using phase inversion method. Phase inversion is a well-studied immersion precipitation technique for membrane synthesis. Using this common method, polymer is dissolved in an organic solvent and the solution cast upon a glass surface with 0.40 knife gap. The resulting membrane morphologies were analysed by using Scanning Electron Microscopy (SEM) and the significant functional group of the resulting membranes were identified using Fourier Transform Infrared Spectroscopy (FTIR). The addition of waste eggshell to the casting solution improved the morphology and structure of the membrane significantly. The appearance of waste eggshell on membrane surface demonstrated in SEM and FTIR analysis. Furthermore, the result of the study showed that the waste eggshells as an adsorbent could remove Cu in an aqueous solution up to 99% with water permeability of 56.52 Lm-2h-1bar-1. Overall, the study demonstrated that the waste eggshell that is generally considered as wastes in large quantities could become an economically advantageous for Cu removal.

Efficient extraction performance and mechanisms of Cd2+ and Pb2+ in water by novel dicationic ionic liquids

Ten novel hydrophobic dicationic ionic liquids (DILs) were synthesized and applied for the extraction of heavy metals in aqueous solutions. Their physicochemical properties were measured at ambient temperature, and the leaching behaviors of the as-prepared DILs in water were assessed by TOC analysis. Metal extraction experiments were carried out to evaluate the extraction performances of the DILs. It was found that the extraction rates of up to 0.45 and 0.53 mg·(g·min)−1 were achieved with 100 mg DILs for 5 mL of 5 mg/L Cd2+ and Pb2+ solutions. Besides, the extraction efficiencies of Cd2+ and Pb2+ were respectively up to 95.48% and 98.46%, when the volumes of the simulated wastewater were expanded by a factor of 20 at a constant extraction phase ratio (1000 mg DILs for 50 mL of 5 mg/L Cd2+ or Pb2+ solutions). The reusability of the novel DILs was successfully proved by the back-extraction experiments with 0.5 M HNO3. Finally, taking Cd2+ extraction as an example, the extraction mechanism based on FTIR analysis and quantum chemical calculations showed that both S and O atoms in the anions of DILs had physical and quasi-chemical interactions with Cd2+, which were stronger than the electrostatic attraction.

Green Synthesis of Stable and Reusable Zinc Nanoparticle Adsorbents for the Removal of Carcinogenic Heavy Metals in Aqueous Solution

industrial applications led to an alarming rise in their presence, heightening the potential for contamination in various environmental mediums. In order to mitigate the adverse impacts of these heavy metals, it is imperative to reduce their concentrations in environmental samples. Therefore, this study aimed to produce zinc nanoparticles employing Diospyros chloroxylon (Roxb.) to effectively eliminate carcinogenic metals from water. The produced nanoparticles were subjected to comprehensive characterization using FT-IR, XRD, SEM, and EDX techniques. The XRD data indicated the emergence of a hexagonal wurtzite structure. SEM images illustrated the spherical morphology of the synthesized particles, with an average diameter measuring 53 nm and having elemental zinc accounting for 69.4% of the composition. The subsequent heavy metal sorption experiments encompassed a range of variables, remarkably, the nanoparticles displayed exceptional adsorption capabilities, achieving maximum removal rates of 95.81%, 90.13%, and 91.25% within an equilibrium time of 90 minutes for Cr, Pb, and Cd, respectively. The adsorption process adhered to a pseudo-first-order reaction kinetics model, with high correlation coefficients of 0.9561, 0.99058, and 0.98481, along with respective rate constants (K) of 0.483, 0.233, and 0.328 for Cr, Pb, and Cd. The outcomes highlight that the synthesized zinc nanoparticles exhibit biocompatibility, stability, and reusability, making them a promising tool for effectively removing carcinogenic heavy metals from polluted water sources.

A novel approach to modify Stenotrophomonas sp. D6 by regulating the salt composition in the growth medium: Enhanced removal performance of Cr(VI)

In this study, a novel and effective modified microbial reducing agent was developed to detoxify Cr(VI) from aqueous solutions. This was achieved by carefully controlling specific salt components in the growth medium. Based on the single-salt modification, several effective modified salts were selected and added to the medium for synergistic modification. The results showed that the synergistic modification with NH4Cl and KH2PO4 had the best detoxification effect on Cr(VI), reaching 98.5% at 100 mg/L Cr(VI), which was much higher than the 43.7% of the control (original Luria-Bertani medium). This enhancement was ascribed to the ability of NH4Cl and KH2PO4 to stimulate the growth of Stenotrophomonas sp. D6 promoted chromate reductase secretion. The protein content of the modified medium supernatant was significantly increased by 10.76% compared to that before modification. Based on the micro-characterization, the main process for the elimination of Cr(VI) is microbial reduction rather than biosorption. Most of the reduced Cr was found in the extracellular suspension, thereby suggesting that the primary reduction occurred outside the cells, whereas only a small fraction was detected intracellularly. Overall, this study provides a simple and effective method for microbial treatment of heavy metals in aqueous solutions.

Combination of magnetic activated carbon and activated sludge for methylene blue and nickel(II) ions removal in aerobic biological treatment

AbstractThe treatment of dyes and heavy metals in aqueous solutions is a major environmental concern, and many methods have been developed to address this problem. However, most of these methods focus on treating either dyes or heavy metals and have their own limitations. Therefore, treatment process that can simultaneously remove both dyes and heavy metals on large scale is essentially required. In this study, we synthesized magnetic activated carbon (MAC) derived from Litsea glutinosa seeds, which was applied to eliminate methylene blue and nickel ions in the aeration tank of the biological treatment system. Structural characteristics and adsorption properties of MAC were studied. The obtained results revealed that the removal efficiency of these pollutants significantly improved as a combination of MAC and activated sludge, especially in the case of nickel ions removal. Furthermore, using MAC in the biological treatment system markedly enhanced the COD removal in compared with that treated without MAC or activated sludge. The advantage of treatment process with MAC addition was also clearly observed by accelerating the settling of activated sludge. Moreover, the obtained results confirmed that wastewater after being treated was assessed as non‐toxic to living organisms by using bioassay.

Hindered diffusion of heavy metal cations in the adsorption rate on activated carbon fiber

Water resource pollution caused by heavy metals represents a risk to the environment because of their toxicity. Adsorption on activated carbon materials can be applied to remove heavy metals in aqueous solutions. Activated carbon fiber (ACF) is a microporous material successfully used for adsorbing heavy metals from water solutions; however, the adsorption rate on ACF has yet to be investigated in detail. The adsorption equilibrium and rate of Cd(II), Ni(II) and Zn(II) on ACF were analyzed in this study, and the experimental data were procured in a differential packed bed batch adsorber. The Radke-Prausnitz isotherm successfully interpreted the experimental adsorption equilibrium data. The adsorption rate was analyzed employing a diffusional model, supposing that the external mass transfer along with intraparticle or intrafiber diffusion affect the overall adsorption rate. Besides, the metal intrafiber diffusion was attributed exclusively to diffusion in the pores volume, excluding surface diffusion. The results revealed that intrafiber diffusion is significantly affected by hindered diffusion caused by frictional effects on pore walls (Kr), steric exclusion (Kp), and blocking provoked by metal cations adsorbed onto pore walls (Ka). The hindrance factors Kr and Kp were estimated using literature correlations, and Ka was related to the mass of metal adsorbed.

Experimental investigation of fibroin content in polymethyl methacrylate‐based membranes for removal of heavy metals in aqueous solutions

AbstractMembrane technology has recently been given extensive consideration for the treatment of effluent to remove suspended solids, organic compounds and inorganic contaminants such as heavy metals. The aim of this study was to prepare, characterize, and test membranes made of silk fibroin (SF) and polymethyl methacrylate (PMMA) blend with different wt% ratios (5%, 10%, and 15%), respectively. The membranes were prepared by phase inversion scheme using water as non‐solvent. Fourier transform infrared spectroscopy (FTIR) was performed to find chemical interactions between polymer matrix and fibroin. The mechanical property of synthesized membranes was also carried out. The surface roughness, and finger‐like pore geometry developed by impregnation of fibroin filler in membrane matrix were depicted by atomic force microscopy (AFM) and scanning electron microscope (SEM), respectively. Surface porosity improved from 4.5% ± 1.9% to 30.0% ± 2.8%, water contact angle reduced from 68° ± 3.0° to 38° ± 1.2°, and highest pure water permeation value (31 L m−2 h−1) was obtained with the addition of fibroin loading. The membrane showed a greater affinity for Cr(VI) in comparison with Pb(II). The highest % rejection was evaluated to be 83% and 56% for Cr(VI), and Pb(II) by utilizing 1.70 wt% fibroin filler in membrane composition, respectively.

An investigation of Pseudomonas marincola to determine Pb(II) biosensor potential

Biosensors are strong alternatives to conventional analytical techniques such as HPLC and spectroscopic techniques for water quality and heavy metal detection. Heavy metal contaminated waters can monitor by microbial biosensors efficiently. For this purpose, newly isolated Pseudomonas sp. is used to develop a highly sensitive low-cost microbial biosensor for water quality monitoring. The objective of the study is the invention of new high sensitive low-cost microbial biosensors to determine heavy metals in aqueous solutions and optimise the working conditions Pseudomonas marincola cells were embedded onto the Screen Printed Electrode (SPE) carbon surface and dried for 30 minutes at laminar flow cabinet. Developed microbial sensors were immersed into the Pb(II) solution for electrochemical analysis. After the exposure time, cyclic voltammetry (CV) and differential pulse voltammetry (DPV) analyses were carried out. The study shows that the sensor was found in a linear range between 1x10−8 M and 8x10−8 M, with the lowest detection limit 10−9 M. The optimum pre-concentration time and scan rate were measured as 10 minutes and 10 mV/s, respectively. The results support that the new isolated Pseudomonas sp. has significant potential to determine the trace amount of lead in aqueous solutions.

Effective Azo-functionalized metal-organic framework colorimetric and ratiometric sensor for detection of heavy metals in aqueous solution by the naked eye

In this work, azo-functionalized zirconium metal organic framework grafted on carboxymethlated cellulose membrane (UiO-66-Azo-Im@CCM) was synthesized by solvothermal method. The developed sensor was systematically characterized and their sensitivity, selectivity and ratiometric properties were investigated. The effect of pH on the sensing performance of the fabricated sensor was also studied. The findings show that developed sensor exhibited excellent sensitivity, selectivity and ratiometric property toward copper, cobalt and nickel heavy metal ions. The calculated limit of detection (LOD) these heavy metals ions were lower than the world health organization permissible concentration that reveals its potential candidacy in monitoring these heavy metals. This work confirms that the developed UiO-66-Azo-Im@CCM can used as powerful tool for the monitoring of Cu2+, Ni2+, and Co2+ without need of the sophisticated instrument. Therefore, we anticipate that it will play its role in environmental remediation in general wastewater treatment in particular.

Preparation of recycled poly s tyrene derivatives to remove heavy metal ions from contaminated water

In recent years, numerous researchers have concentrated on the process of turning waste into usable materials. Polystyrene and its modifications have received great attention over the past few decades due to their outstanding ion exchange behavior toward various toxic heavy metals in aqueous solutions. Therefore, this study is concerned with the preparation of three different cationic polymeric resins for the removal of Pb2+, Cd2+, and Fe3+ heavy metal ions from their contaminated water samples based on the sulfonated single-used polystyrene teacup waste (SPS), which was used to prepare sulfonated polystyrene-g-acrylamide monomer (SPS-g-Acryl) and sulfonated polystyrene-g-chitosan (SPS-g-Chit) using commercial chitosan (DD=85%) originally extracted from shrimp cortex. The concentrations of the selected heavy metal ions were measured before and after each experiment with a flame atomic absorption spectrometer (F-AAS). The analytical studies started by exploring the influence of pH (2, 4, 6, and 8) on removing the heavy metal ions Pb2+, Cd2+, and Fe3+ from their aqueous solutions. The obtained results revealed that as the pH of the analyzed ion solution is increased, the removal efficiency for ions increases. All three resins (SPS, SPS-g-Acryl, and SPS-g-Chit) had different removal efficiencies for the investigated ions, with SPS-g-Chit resin.

Low-cost modified adsorbents derived from the solid residue of Rosmarinus officinalis L. for heavy metal uptake

The current study investigates for the first time the potential of using solid residues collected from the hydrodistillation of R. officinalis, after their modification with Fe, as low-cost adsorbents to alleviate the heavy metals in aqueous solutions. Physicochemical properties and adsorptive performances of R. officinalis solid residue (RO-SR) and Fe-modified R. officinalis solid residue (Fe-RO-SR) were investigated. The Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) revealed that the iron was successfully fixed to the surface of RO-SR. Furthermore, after iron modification, the specific surface area of ROSR was increased from 36.2 to 50.4 m2/g. Kinetics and isotherms of adsorption of Co onto RO-SR and Fe-RO-SR were fitted by applying different models, though the pseudo-second-order (Adj. R2 > 0.9985) and Langmuir (Adj. R2 > 0.9532) models fitted the experimental results better, respectively. The adsorption performances of RO-SR and Fe-RO-SR for Co were 37.31 and 50.25 mg.g−1, respectively. The equilibrium adsorption capacity was reduced from 22.56 g/L to 10.67 g/L when the temperature was raised from 25 °C to 45 °C. Furthermore, after four successful cycles of adsorption-desorption, the adsorbent's adsorptive performance remained above 83.04%, and the adsorbent selectivity revealed interesting heavy metal uptake. Selectivity tests revealed that the adsorption capacities are different for the heavy metal species at the same concentrations, and the series is Fe2+ > Co2+> Cu2+ > Cr3+. Fe-RO-SR could be an interesting, inexpensive ($4.56/Kg), and attractive potential adsorbent for heavy metal removal from aqueous solutions.

Synthesis, Characterization and Application of Karak Bentonite Clay-Graft-Poly (Acrylamide/Co- Acrylic Acid) Superabsorbent Composite and its Adsorption Study for Selected Heavy Metals

A novel superabsorbent composite (SAC) based on bentonite, acrylamide and acrylic acid was synthesized. The effects of bentonite quantity, initiator content on the grafting degree and on the water absorbency for the samples were studied. Synthesis mechanism, morphology and thermal properties of the SAC were characterized. FTIR results confirmed the presence of acrylamide/ acrylic acid onto bentonite backbone while TGA showed that introduction of 70 % bentonite to polymer increases thermal stability. The SAC was also tested in the removal of heavy metal in aqueous solution where kinetics analyses were performed using Langmuir adsorption isotherm. The optimum adsorption capability of heavy metal ions onto bentonite-based SAC from solution was 92, 48 and 91 % for Pb++, Ni++, and Cu++ respectively. The unique characteristics of these SAC such as its slow-release and water-retention capability, nontoxicity in soil, environmentally friendly and high capacity for the removal of heavy metals might be very valuable in agriculture and environmental studies

Development of a magnetic calcium-alginate hydrogel-sphere encapsulated with Fe–Mn–Zr ternary metal composite for heavy metal adsorption

Heavy metal contamination has become one of the greatest global environmental problems. In this study, a magnetic calcium-alginate hydrogel-sphere encapsulated with Fe–Mn–Zr ternary-metal composite (MCHETC) was prepared through a combined co-precipitation and extrusion approach and used for the adsorption of heavy metals in aqueous solutions. The active sites were dispersed in the MCHETC, which can be separated by the magnetic force for the ease in operation. Above 80% of ultimate adsorption was completed at a contact time of 5 h. The copper uptake history was well described by the intraparticle surface diffusion model, suggesting a multi-step process for the adsorption. The optimum pH for adsorption was 4; the maximum adsorption capacity was 103.1 mg-Cu/g. The adsorption capability well remained after the 5 adsorption–desorption cycles and the copper could be recovered. Furthermore, the adsorbent performed well in the nature water spiked with copper ions. The mechanism studies illustrated that the adsorption was mainly controlled by the ion-exchange reaction. This study demonstrated that the MCHETC adsorption technology may be used for heavy metal removal and recovery with higher efficacy.

N-Doped Biochar from Lignocellulosic Biomass for Preparation of Adsorbent: Characterization, Kinetics and Application.

Medulla tetrapanacis is composed of a lignocellulosic biopolymer and has a regular porous structure, which makes it a potential biomass material for preparing porous N-doped biochar. Herewith, N-doped Medulla tetrapanacis biochar (UBC) was successfully prepared by modification with urea and NaHCO3 under pyrolysis at 700 °C. The nitrogen-containing groups were efficiently introduced into biochar, and the micro-pore structures of the UBC were developed with sizeable specific surface area, which was loaded with massive adsorption sites. The adsorption kinetics and isotherms of the UBC conformed to pseudo-second-order and Langmuir model. The superior adsorption capacities of the UBC for methylene blue (MB) and congo red (CR) were 923.0 mg/g and 728.0 mg/g, and the capacities for Cu2+ and Pb2+ were 468.5 mg/g and 1466.5 mg/g, respectively. Moreover, the UBC had a stronger affinity for Cr3+ and Fe3+ in multiple metal ions and retained at a preferable adsorption performance for dyes and heavy metals after five cycles. Precipitation, complexation, and physical adsorption were the main mechanisms of the UBC-adsorbing metal ions and dyes. Thus, lignocellulosic biochar has great potential for removing dyes and heavy metals in aqueous solutions.

Effect of Pyrolysis Temperature on Removal Efficiency and Mechanisms of Hg(II), Cd(II), and Pb (II) by Maize Straw Biochar

Pyrolysis temperature significantly affects the properties of biochar, which in turn can affect the removal of heavy metal ions and the underlying mechanism. In this work, biochars from the pyrolysis of maize straw at 300, 400, and 500 °C (BC300, BC400, and BC500, respectively) and wheat straw at 400 °C (WBC400) were investigated. The influence of production temperature on the adsorption of Hg2+, Cd2+, and Pb2+ by maize straw biochar was investigated by the characterization of the biochars and by adsorption tests. The adsorption capacities of maize and wheat straw biochar were compared in an adsorption experiment. Biochar BC400 showed the best physical and chemical properties and had the largest number of surface functional groups. The pseudo-second-order kinetic model was more suitable for describing the adsorption behavior of metal ions to biochar. The Langmuir model better fit the experimental data. Biochar BC400 had a higher adsorption speed and a stronger adsorption capacity than WBC400. The sorption of Pb2+ and Hg2+ to maize straw biochar followed the mechanisms of surface precipitation of carbonates and phosphates and complexation with oxygenated functional groups and delocalized π electrons. The adsorption mechanism for Cd2+ was similar to those of Hg2+ and Pb2+, but precipitation mainly occurred through the formation of phosphate. In the multi-heavy-metal system, the adsorption of Cd2+ by BC400 was inhibited by Pb2+ and Hg2+. In summary, BC400 biochar was most suitable for the adsorption effect of heavy metals in aqueous solution.