Adsorption Of Heavy Metals Research Articles

Synthesis and characterization of novel β-CD-Xanthate and its application in the treatment of heavy metal containing wastewater and lignin enriched paper industry wastewater

ABSTRACT Three grades of β-cyclodextrin xanthates (β-CDXs) have been synthesized by the reaction of β-cyclodextrin (β-CD) with CS2 in alkaline medium (NaOH), through xanthation process. The synthesized β-CDXs has been characterized by UV-visible (UV-Vis) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, Proton Nuclear Magnetic Resonance (1HNMR) spectroscopy, Thermogravimetric (TG) analysis, Differential Scanning Calorimetry (DSC) analysis, scanning electron microscopy (SEM) analysis and point of zero charge (ΔpHPZC) analysis. Further, β-CDXs and raw β-CD has been used for the heavy metals removal (Cu2+ and Ni2+) and also used for the treatment of lignin enriched paper industry wastewater (LEPIW). The maximum % removal by β-CDX3 for Cu2+ ion at optimum dosage of 2 g/L, optimum pH of 6.5, temperature of 45°C, initial concentration of 1000 mg/L and at contact time of 80 min was 95.8%. For Ni2+ ion the maximum % removal by β-CDX3 at optimum dosage of 2.5 g/L, optimum pH of 5.8, initial concentration of 1000 mg/L, temperature of 55°C and contact time of 100 min was 94.1%. While LEPIW treatment efficacy of 86% has been observed with β-CDX3. The calculated data fitted well in Langmuir isotherm model confirming that the adsorption of Cu2+ & Ni2+ ions onto the β-CDXs adsorbent is monolayer. The rate of adsorption of heavy metals (Cu2+ and Ni2+) on the β-CDXs adsorbent has been controlled by Pseudo second order kinetic model indicating the chemisorption process. The optimal adsorption capacity of β-CDX3 has been found to be 534.75 mg/g for Cu2+ and 423.72 mg/g for Ni2+ ions, respectively.

Effect of Crosslinking on the Properties of Membrane Formulated from Quaternized Chitosan

Heavy metals are easily absorbed by living things because of their high-water solubility. Adsorption is a popular separation technique that is used to remove heavy metals from water since it is inexpensive, widely available, and ecologically benign. Chitosan's structure includes hydroxyl and amino groups, which make it a popular adsorbent for heavy metals. In this study, quaternization was used to change chitosan and improve its adsorption capacity. As the quaternizing agent, hexadecyltrimethylammonium bromide (TMAB) was employed. After blending the quaternized chitosan with polyvinyl alcohol and polysulfone, a membrane was created, and tetraethyl orthosilicate (TEOS) was used to crosslink it. Tetraethyl orthosilicate loadings of 1, 2, and 4 weight percent were added to the membrane formulation as a crosslinker. The surface morphology and surface charge of the prepared membranes were then described. Antifouling analysis and water permeation were used to test the performances. According to the results, membrane M4 with 4 weight percent TEOS exhibited the best characteristics, especially in terms of surface charge and surface morphology with strong antifouling capabilities. Furthermore, it has the highest water flux attributed to good surface hydrophilicity. The developed membranes may find application in the heavy metal removal phase of water treatment.

Natural hydroxyapatite powder from pig-bone waste (pHAP) for the rapid adsorption of heavy metals (Cu) in aqueous solution

Natural hydroxyapatite powder from pig-bone waste (pHAP) for the rapid adsorption of heavy metals (Cu) in aqueous solution

Heavy Metal Removal from Wastewater Using Poly(Gamma-Glutamic Acid)-Based Hydrogel.

The removal of toxic heavy metal ions from wastewater is of great significance in the protection of the environment and human health. Poly(gamma-glutamic acid) (PGA) is a non-toxic, biodegradable, and highly water-soluble polymer possessing carboxyl and imino functional groups. Herein, water-insoluble PGA-based hydrogels were prepared, characterized, and investigated as heavy metal adsorbents. The prepared hydrogels were recyclable and exhibited good adsorption effects on heavy metal ions including Cu2+, Cr6+, and Zn2+. The effects of adsorption parameters including temperature, solution pH, initial concentration of metal ions, and contact time on the adsorption capacity of the hydrogel for Cu2+ were investigated. The adsorption was a spontaneous and exothermic process. The process followed the pseudo-first-order kinetic model and Langmuir isotherm model, implying a physical and monolayer adsorption. The adsorption mechanisms investigation exhibited that Cu2+ adsorbed on the hydrogel via electrostatic interactions with anionic carboxylate groups of PGA in addition to the coordination interactions with the -NH groups. Importantly, the PGA hydrogel exhibited good reusability and the adsorption capability for Cu2+ remained high after five consecutive cycles. The properties of PGA hydrogel make it a potential candidate material for heavy metal ion removal in wastewater treatment.

Measurement of elements by portable x-ray fluorescence spectrometry for the study of adsorption processes: the case of Pb2+ adsorption on soybean straw biochar

This study evaluated the reliability of portable X-ray fluorescence (pXRF) in Pb2+ adsorption kinetics and isotherm experiments using soybean straw biochar. The research aimed to compare pXRF results with those obtained through traditional atomic absorption spectrometry (AAS). Soybean straw biochar, produced at 400 °C, was employed as the adsorbent for Pb2+. The efficiency of adsorption was assessed using Langmuir and Freundlich models. The kinetics of Pb2+ adsorption was analysed through pseudo-first-order and pseudo-second-order models. The pseudo-second-order model described the kinetics of Pb2+ adsorption on biochar better than the pseudo-first order model. Importantly, the pXRF technique demonstrated comparable results to those of AAS, making it a reliable and resource-efficient method for studying Pb2+ kinetics. The results of the isotherm analyses fit the Langmuir model, indicating a desirable and irreversible adsorption of Pb2+ on biochar. PXRF measurements on biochar allowed simultaneous observations of Pb2+ adsorption and K+ and Ca2+ desorption, highlighting ionic exchange as the primary adsorption mechanism. In conclusion, our results showcased the applicability of pXRF for Pb+2 adsorption studies in biochars, offering a valuable alternative to traditional methods. The findings contribute to the understanding of biochar as an effective adsorbent for heavy metals, emphasizing the potential of pXRF for cost-effective and efficient environmental research. In this study, we present a novel and detailed procedure that will allow other researchers to continue their studies on Pb2+ adsorption on biochar or similar matrices, significantly reducing the resources and time used and enabling the simultaneous study of the behavior of other ions participating in the process.

Improving Pb(II) Removal via Ascorbic Acid-Enhanced Red Mud Adsorption: Kinetics and Isotherm Analysis

This study explored the efficacy of red mud, an aluminum production by-product, as an adsorbent for Pb(II) ion removal from contaminated water and assessed the adsorption isothermal model and kinetics. Red mud, characterized by its richness in oxide minerals with reactive surfaces, has potential for heavy metal adsorption, but its capacity for larger ions like Pb(II) is limited. This research aimed to enhance red mud’s adsorption properties through modification with ascorbic acid. The modification process involved heating a mixture of red mud and ascorbic acid to its boiling point, followed by the formation of adsorbent beads using red mud and Na-alginate mixture dropped into a 2 % CaCl2 solution at −2 °C. The beads were tested over varying durations ranging from 30 to 210 min. The results indicated that ascorbic acid modification led to the transformation of minerals in red mud, improving its pore diameter, pore volume, and specific surface area of the adsorbent. The modified and unmodified red mud adhered to both Langmuir and Freundlich isotherms, with R² values converging to one, and displayed pseudo-second-order kinetics. Notably, the introduction of ascorbic acid augments the adsorption efficacy of red mud for Pb(II) ions from 84.8 % to a compelling 99.3 %. This underscores the augmented capability of ascorbic acid-modified red mud, highlighting its prospective applicability as a potent adsorbent in the remediation of heavy metal-contaminated water. HIGHLIGHTS Innovative Use of Red Mud: Explored the potential of red mud, a by-product of aluminum production, as an adsorbent for removing Pb(II) ions from contaminated water Ascorbic Acid Modification: Developed a novel modification process using ascorbic acid, including heating the red mud and ascorbic acid, enhancing the adsorption properties of red mud as pore diameter, pore volume, and specific surface area of the adsorbent Adsorption Isotherms and Kinetics: Conducted a comprehensive assessment of adsorption isothermal models and kinetics, with modified and unmodified red mud adhering to Langmuir and Freundlich isotherms and displaying pseudo-second-order kinetics Enhanced Adsorption Efficacy: the adsorption effectiveness is enhanced from 84.8 to 99.3 %, emphasizing its potential applicability for Pb(II) GRAPHICAL ABSTRACT

Superior performance of N-doped carbon Nanoonions/Nafion based microfluidic electrochemical Cd2+ sensor when compared to Screen-Printed Carbon-Based electrode devices

The sensing of cadmium is important due to its highly toxic effects on various organs of humans and animals. Commonly employed are screen-printed carbon-based electrodes (SPCE) as suitable low-cost sensing platform. Microfluidic electrochemical sensor (μCS) can also be portable, highly sensitive, and low-cost but are up to now only seldom studied and applied. Here we demonstrate the superior performance of μCS over SPCE arrangements for sensing ultra-trace of Cd2+. Additionally, N-doped carbon nanoonions (N-CNOs) are introduced as sustainable non-metallic modifier and employed for both sensing arrangements. The study depicted that employing the modifier the electrochemically active surface area and the electron transfer rate in both arrangements is improved together with improve sensitivity. Both arrangements were compared using cyclic voltammetry and electrochemical impedance spectroscopy in [Fe(CN)6]3−/4−, and also square-wave anodic stripping voltammetry (SWASV) for Cd2+ sensing. The µCS arrangement clearly outperforms the SPCE arrangement in signal strength. For the final device (μCS modified with N-CNOs) a linear concentration range from 1.0 to 100 μg L−1 was achieved. The limit of detection and sensitivity resulted to 0.25 μg L−1 and 1.02 μA µg−1 L cm−2, respectively. Besides this excellent sensitivity combines with high stability, which was tested for 8 repetitive measurements with a single device resulting in high reproducibility. Additionally, this procedure was favorably employed for measurements of Cd2+ in different real samples, which demonstrated the excellent applicability of the device for the adsorption and detection of heavy metal ions.

Cellulose nanocrystals intercalated clay biocomposite for rapid Cr(VI) removal.

The application of bentonite (Bt) as an adsorbent for heavy metals has been limited due to its hydrophobicity and insufficient surface area. Herein, we present cellulose nanocrystal (CNC) modified Bt composite (CNC@Bt) with enhanced efficiency for Cr(VI) removal. CNC@Bt exhibited an increased specific surface area and a porous structure, while maintaining the original crystal structure of Bt. This was achieved through a synergistic function of ion exchange, hydrogen bonding, electrostatic interactions, and steric hindrance. The adsorption of Cr(VI) by CNC@Bt followed the pseudo-second-order kinetic and Langmuir isotherm adsorption model. Moreover, the process was endothermic and spontaneous. At an initial Cr(VI) concentration of 20mg/L and pH = 4.0, 10g/L CNC@Bt achieved a removal rate of 92.7%, and the adsorption capacity was 1.85mg/g, significantly higher than bare Bt (37.9% and 0.76mg/g). The removal efficiency remained consistently above 80% over a wide pH range, indicating the potential practical applicability of CNC@Bt. With its fast adsorption rate, pH adaptability, and stable performance, CNC@Bt presents promising prospects for the rapid treatment of Cr-contaminated wastewater.

Efficient isolation and characterization of functional melanin from various plant sources

SummaryIn recent years, natural pigments in living organisms have attracted increased interest as an excellent biological material for the development of new biotechnological approaches. Melanin, a large polymeric pigment, has important functions in cells, including free radical scavenging and radiation protection, making this molecule attractive for medical and nutritional purposes. The variety of forms of melanin in organisms requires the use of various approaches to its purification. In this study, we have developed a simple yet unique and effective method for extracting melanin from six plant sources. The melanin yield was in the range of 6.7–21.5% for the plant sources used. The advantage of using grape skin waste as a raw material is shown, which is of great importance for obtaining cheap and functional melanin. The activity of purified melanin in scavenging 2, 2‐diphenyl‐1‐picrylhydrazyl radical is IC50 3.2–99.0 mg L−1. This remarkable feature highlights the attractiveness of grape melanin for further use as a natural antioxidant in medicine. The ability of grape melanin to adsorb heavy metal ions highlights its attractiveness for the food industry and for the development of other biotechnological applications. Smoke, after passing through a cigarette filter charged with melanin, is significantly enriched with reducing agents, which is a phenomenon for the health of smokers.

Porous sulfur polymers for effective aqueous-phase organic contaminant removal

Sulfur polymers produced through 'inverse vulcanization' exhibit various attributes, such as photocatalytic activity and a high capacity to adsorb heavy metals. Nevertheless, there is a lack of research investigating the use of sulfur polymers as materials for the removal of organic contaminants. In this work, porous sulfur polymers (PSPs) were synthesized from elemental sulfur and 1,3-diisopropenylbenzene, with porosity introduced via salt templating. The result is a material that can strongly adsorb and chemically neutralize a model organic contaminant (caffeine). PSPs show adsorption up to 5 times higher than a leading adsorption material (activated carbon). Furthermore, either the adsorption or degradation processes can govern the removal efficiency depending on the synthesis parameters of PSPs. This is the first-ever report demonstrating sulfur polymers as effective materials for removing emerging contaminants from water. The versatile synthesis of sulfur polymers offers variation, which means that there is much more to explore in this exciting research area.

Reduction of heavy metal emissions by adding modified attapulgite to sludge in bubbling fluidized bed incineration process

The utilization of natural mineral adsorbents to adsorb heavy metals generated from sludge incineration was currently a research hotspot. To enhance the adsorption capacity of the adsorbent, a combination of thermal activation and acid-washing modification methods was designed to modify natural attapulgite. The effects of adding the adsorbent on the distribution of heavy metals (Cr, Cu, Ni, Zn, Pb, and Cd) were tested in a laboratory-scale bubbling fluidized bed reactor. The results indicated that increasing the incineration temperature could promote the transformation of heavy metals into the stable state in the incineration ash (bottom slag and fly ash), while facilitating the volatilization and enrichment of semi-volatile heavy metals (Zn, Pb, and Cd) in the fly ash. The addition of modified attapulgite during the sludge incineration process was superior to raw attapulgite, as it enhanced the capacity of unit adsorbents to adsorb and immobilize heavy metals in flue gaseous, thus reducing the emission of heavy metals. BCR and TCLP experiments indicated that a greater proportion of heavy metals in the incineration ash were transformed into the residual fraction, thereby reducing environmental risks. Characterization revealed that the composite modification approach promoted the adsorbent to expose more active sites and increase the active amorphous components, which improved the adsorption and immobilization of heavy metals.

A review on agrowaste based activated carbons for pollutant removal in wastewater systems

Environmental pollution from chemicals utilized in manufacturing, pharmaceuticals, and chemical process industries is of serious concern nowadays due to the contamination that ensues when these chemicals are discharged into water bodies. Activated carbon adsorption provides an efficient and economically viable means for mitigation of toxic chemicals (i.e., heavy metals, dyes, pharmaceutics, and antibiotics). However, the exorbitant cost of commercial activated carbons has resulted in the search for low-cost alternatives for the treatment of contaminated effluents. An exhaustive literature survey in this area is necessary to know the extent of work done in this area and seek out the gaps that future research will provide answers to. In this review, various works on activated carbon utilization, batch adsorption, fixed-bed adsorption (experimental and numerical studies) are summarized. This review elucidates the different kinetic and isotherm models of agrowastes-derived activated carbon materials in context with pollutants (dyes, heavy metals, pharmaceuticals, miscellaneous adsorbates) removal through batch and column methods. In addition, fixed-bed column adsorption/regeneration methods using various activated carbons derived from agrowastes are discussed. Among these methods, heavy metal adsorption from aqueous solutions by the activated carbons is the most efficient. The deployment of mathematical and machine learning approaches (ANN and novel GMDH algorithms) in optimization of batch and continuous adsorption processes are also highlighted. Numerical simulation of fixed-column adsorption systems for more improved industrial-scale column designs is described. Conclusions and future challenges of chemicals removal from polluted wastewater utilizing agrowaste-derived activated carbons are also presented.

Competitive adsorption of heavy metals onto xanthate-modified sludge hydrochar and its solidification as secondary minerals

In this study, a sulfur-modified magnetic hydrochar was synthesized by grafting thiol-containing groups onto the sludge-derived hydrochar. The modified hydrochar exhibited effective adsorption of Cu2+, Pb2+, Zn2+, and Cd2+ over a wide pH range and in the presence of coexisting ions, and showed almost no secondary leaching in three acidic solutions. In the mult-metal ion system, the modified hydrochar exhibited maximum adsorption capacities were 39.38, 105.74, 26.53, and 38.11 mg g−1 for Cu2+, Pb2+, Zn2+, and Cd2+, respectively. However, the binding capacity and adsorption amount of modified hydrochar for metal ions were lower in the mult-metal ion system compared to the unit-metal ion system. Notably, Pb2+ showed a strong inhibitory effect on the adsorption of other heavy metal ions by modified hydrochar due to strong competition for xanthate functional groups. The Pb2+ occupied the xanthate and native functional groups (–OH, –NH2, and Fe–O etc.), leaving only a small amount of adsorption sites for Cu2+, Zn2+ and Cd2+. Simulation results further supported these findings, indicating that Pb2+ had the highest density profiles near the four functional groups, and the density profiles of the four heavy metals near the xanthate functional groups were greater compared to the other three functional groups. Furthermore, the SEM-EDS, TOF-SIMI, and XPS results indicated that modified hydrochar achieved excellent mineral binding mainly through electrostatic interaction, ion exchange, and chelation. Overall, these results highlight the sulfur-modified magnetic hydrochar as a highly efficient adsorbent for heavy metals in environmental applications.

Functionalization Mesoporous Silica using Aminopropyltriethoxysilane (APTES) as Adsorbent for Removal Ni (II) from Aqueous Solution

<p>This study successfully synthesized mesoporous silica using the template methyl ester ricinoleate (MS-TMR) and further functionalized the MS-TMR surface with 3-aminopropyltriethoxysilane (APTES). The functionalization of MS-TMR with APTES was achieved through a 48-hour grafting method. For the adsorption experiments, 20 mg of both MS-TMR and MS-TMR-APTES adsorbents were employed to remove Ni(II) from aqueous solutions at a concentration of 30 mg/L and pH 6. The objective was to assess the adsorption capacity and to characterize the synthesized adsorbents. Characterization was conducted using Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD). FTIR analysis revealed that the MS-TMR adsorbent possessed silanol (Si-OH) and siloxane (Si-O-Si) groups. Conversely, the MS-TMR-APTES adsorbent exhibited additional amine (N-H) and C-H groups after the APTES grafting. XRD results indicated that both samples were amorphous. The concentration of Ni(II) ions was determined using Atomic Absorption Spectroscopy (AAS), which facilitated the calculation of removal percentages and adsorption capacities. MS-TMR achieved a mere 3.54% removal of Ni(II) ions, corresponding to an adsorption capacity of 3.21 mg/g. In contrast, MS-TMR-APTES demonstrated significantly enhanced performance, removing 54.23% of Ni(II) ions with an adsorption capacity of 48.81 mg/g. The findings suggest that APTES-functionalized MS-TMR has considerable potential for removing Ni(II) ions and could be explored further for the adsorption of other heavy metal ions.</p>

Synthesis of biochar-ZnAl-layered double hydroxide composite for effective heavy metal adsorption: Exploring mechanisms and structural transformations

Rapid industrialization has increased the extent of heavy metal contamination in water sources, demanding effective wastewater treatment methods. To mitigate this issue, adsorption techniques play a crucial role in wastewater treatment. Layered double hydroxides (LDHs) are commonly employed in such processes; however, they exhibit limitations in effectively adsorbing contaminants. Here, biochar (BC) was incorporated into LDHs using a simple hydrothermal method and subsequently used for Cd2+ and Pb2+ adsorption. Additionally, the physicochemical characteristics of BC and ZnAl-LDH-BC were assessed utilizing various instruments. The obtained ZnAl-LDH-BC400 and ZnAl-LDH-BC600 had surface areas of 52.55 and 102.56 m²/g, respectively, several times greater than those of the original BC. Adsorption performance was investigated using different kinetic and isothermal models. The Langmuir–Freundlich and pseudo-second-order kinetic models demonstrated the adsorption of single-layer chemicals. Furthermore, the highest observed adsorption capacities for Cd2+ and Pb2+ were 99.8 mg g−1 and 128.4 mg g−1, respectively, when using ZnAl-LDH–BC600. In contrast, BC600 demonstrated adsorption capacities of 42.1 mg g−1 for Cd2+ and 51.7 mg g−1 for Pb2+. Cd2+ and Pb2+ adsorption by ZnAl-LDH-BC was primarily governed by surface precipitation and cation exchange processes. These findings highlight the mechanisms underlying the removal of heavy metals using ZnAl-LDH-BC and provide valuable theoretical and applied insights into the management of agricultural waste and control of water pollution.

Adsorption Potential and Mechanism of Sludge-Based Activated Carbon Modified with Fly Ash for Removal of Heavy Metals

The treatment of sludge has received a lot of attention due to its intractable status and potential resource value. In order to explore methods of sludge resource utilization and to reduce the harm of heavy metals in municipal sewage, this study analyzed the preparation method of a modified sludge adsorbent (MSA). Another common waste (fly ash) was added to raw domestic sludge (RDS) in a certain proportion and developed to have the ability to adsorb heavy metals through multiple steps such as drying, mixing, activation and carbonization. The adsorption performance of the modified sludge adsorbent (MSA) was verified by simulating wastewater containing Cu2+ and Cd2+, and the surface and structural properties were studied from a microscopic perspective with the aid of SEM and XRD. This study showed that the MSA was characterized by increased microporosity, an enlarged surface area and enhanced activity of functional groups, and the best performance for heavy metal adsorption was found when the RDS was mixed with fly ash at a ratio of 4:3 and a pH of 8. The highest removal rates for the heavy metals Cu2+ and Cd2+ were 99.6% and 99.7%, respectively. The adsorption kinetics and adsorption isotherms indicated that the adsorption behavior of the MSA was controlled by both physical and chemical adsorption, and the best fit of the Langmuir adsorption isotherm model revealed the predominance of monolayer adsorption. The present study is a meaningful exploration of the resource utilization of sludge and fly ash and can provide a cheaper and more effective material for addressing heavy metal pollution in domestic sewage.

Chitosan-based materials for heavy metal adsorption: Recent advancements, challenges and limitations

The advancement of industrialization has put the environment at risk of getting saturated with different contaminants. Heavy metals (HMs) emerging from industries, reaching the water bodies expose marine biota to these stressors, leading to negative effects on growth and development. Thus, it is imperative to detoxify the environment from these HM contaminants through degradation, and adsorption. Several mechanical and chemical methods have been developed and implied for the purpose of minimizing HM contamination, but they often give rise to certain by-products that are toxic in nature. Over the years, chitosan has emerged as a potent adsorption material for reducing HM contamination. Chitosan is obtained from multiple natural sources, and owing to its versatile nature, it shows significant capacity for adsorbing different HMs and HM ions. Chitosan is used in synergy with some of the agents to increase its adsorption efficiency. The preparation of graft, beads, functionalized chitosan, crosslinkers, nanoparticles, and nanotubes are some of the potential methods that have been used in modifying chitosan. This paper gives an overview of the ecotoxicological effects of HMs, besides mentioning the fundamental sources of chitosan. The individual role of chitosan and its synergistic role have been discussed in greater detail. Moreover, the limitations associated with chitosan as an HM adsorbent have been delineated.

Effect of chitosan and sodium alginate on heavy metal adsorption by natural plant extracts

To investigate the effects of chitosan (CS) and sodium alginate (SA) on heavy metal ions adsorption by natural plant extract (Pe), different proportions (0%, 10%, 20%, and 50%) of CS and SA were used to modify Pe to prepare CS- and SA-modified Pe (CS-Pe and SA-Pe). The different CS-Pes and SA-Pes were analyzed by different spectroscopic test instruments. The adsorption properties and differences of Cu2+, Pb2+, and Cd2+ under various temperatures, pH, and ionic strengths were studied. Results displayed that (1) characterization showed that CS and SA attached to the Pe surface and altered the morphology of Pe surface. The adsorption of Cu2+, Pb2+, and Cd2+ by different CS-Pes and SA-Pes was better suited to Langmuir model than that to Freundlich model, maintaining the maximum adsorption capacity at 378.01–833.83 (Cu2+), 218.66–531.04 (Pb2+), and 221.46–384.93 (Cd2+) mmol/kg. (2) Higher pH and temperature facilitated the pollutants adsorption by CS-Pes and SA-Pes, which followed a chemisorption mechanism. Heavy metal ions adsorption rose initially and then reduced with increasing ionic strength (peak value at 0.1 mol/L). Thermodynamic parameters presented that the pollutants adsorption was a spontaneous, primarily chemical, and multi-mechanism reaction. (3) Heavy metal ions adsorption by SA-Pes maintained approximately 60–72% of the raw material by triple regeneration. The economy (qm/price) of different modified Pes for heavy metal ions adsorption ranged from 0.97 to 6.41 mmol/¥, and SA-Pe showed the highest economy.

Scallop shells as biosorbents for water remediation from heavy metals: Contributions and mechanism of shell components in the adsorption of cadmium from aqueous matrix

To ascertain their potential for heavy metal pollution remedy, we studied the adsorption mechanism of cadmium onto scallop shells and the interactions between the heavy metal and the shell matrix. Intact shells were used to investigate the uptake and diffusion of the metal contaminant onto the shell carbonatic layers, as well as to evaluate the distribution of major and trace elements in the matrix. LA-ICPMS measurements demonstrate that Cd is adsorbed on a very thin layer on the inner and outer surfaces of the shell. Structural and thermal analyses showed the presence of 9 wt.-% of a CdCO3 phase indicating that the adsorption is mainly a superficial process which involves different processes, including ion exchange of Ca by Cd. In addition, organic components of the shell could contribute to adsorption as highlighted by different metal uptake observed for shells with different colours. In particular, darker shells appeared to adsorb more contaminant than the white ones. The contribution of the organic shell components on the adsorption of heavy metals was also highlighted by the element bulk content which showed higher concentrations of different metals in the darker specimen. Raman spectroscopy allowed to identify the pigments as carotenoids, confirmed by XRD measurements which highlighted the presence of astaxanthin phases. The results presented here provide new insights into the Cd adsorption mechanism highlighting the important contribution given by the organic components present in the biogenic carbonate matrix. Furthermore, the high efficiency of Cd removal from water by scallop shells, supported by adsorption kinetic and isotherm studies, has been demonstrated.

Adsorption mechanism of Cs+ and Pb2+ on the N-A-S-H surface under the different Si/Al ratio and temperature

The application of low-calcium alkali-activated geopolymers has significantly enhanced the removal of Pb2+ and Cs+ from the contaminated soils and water. However, the adsorption mechanisms of Pb2+ and Cs+ influenced by the temperature and Si/Al at the molecular scale remain unclear, which were the two critical factors influencing the adsorption capacity. This study employed molecular dynamics simulation to elucidate the effects of temperature and Si/Al ratio on the adsorption mechanism and behavior of Pb2+ and Cs+ on the N-A-S-H surface. Research findings demonstrate that the adsorption of Pb2+ and Cs+ on the N-A-S-H surface is attributed to chemical adsorption. Increasing temperature can regulate the removal ratio of heavy metal ions by enhancing the quantity of cation exchange (correlation coefficient of 0.88). Temperature also influences the removal ratio by changing in adsorption energy, potential of mean force, and controlling the maximum adsorption capacity, hydration, and diffusion ability of the heavy metals (correlation coefficient of 0.67, 0.55, 0.6, and 0.57). While the Si/Al ratio influences the adsorption of heavy metals by enhancing the negative charge density of N-A-S-H gel and strengthening the interaction between heavy metals and oxygen atoms on the N-A-S-H surface (correlation coefficient of 0.96 and 0.52). Additionally, temperature exhibits a more pronounced effect on enhancing in the removal ratio of heavy metals. The heavy metal removal was maximally increased by 435 % (for Cs+) and 439 % (for Pb2+) via elevated temperature, while it was increased by 63 % (for Cs+) and 98 % (for Pb2+) via decreased Si/Al ratio. This study can not only provide a new perspective on the removal of heavy metals by N-A-S-H gel, but also can contribute to the achievement of green and sustainable development goals.