Heavy Metal Adsorption Capacity Research Articles

Aging behavior of microplastics accelerated by mechanical fragmentation: alteration of intrinsic and extrinsic properties.

Microplastics (MPs) inevitably undergo multiple aging processes during their life cycle in the environment. However, the information regarding the mechanical fragmentation behavior of MPs remained unclear, including the changes in the intrinsic properties of aged MPs, the measurement of aging degree, the underlying mechanism, and the interaction with heavy metals. Here, MPs (PS, PP, PET) were aged by crushing (-CR) and ball-milling (-BM) to simulate mild and severe mechanical fragmentation, respectively. Our results indicated that mechanical fragmentation significantly affected the morphology of MPs. The aging degree of MP-BM was deeper compared to MP-CR owing to smaller particle size, larger specific surface area, poorer heat resistance, better hydrophilicity, and richer oxygen-containing functional groups. The carbonyl index (CI) and O/C ratio were used to measure the aging degree of the two mechanical aging treatments. Besides, the mechanism was proposed and the discrepancy between the two treatments was elaborated from three aspects including the excitation energy source, reaction interface, and reaction dynamics. Furthermore, the extrinsic properties of MPs altered with the increase of aging degree; specifically, the adsorption capacities of heavy metals were enhanced. Meanwhile, it was unveiled that the CI value and O/C ratio played a vital role in estimating the adsorption ability of heavy metals. The findings not only reveal the mechanical fragmentation behavior of MPs but also provide new insights into the assessment of the potential risks of the aged MPs via chemical indexes.

Response of Heavy Metals to Microseism in Coal Mining Subsidence Water of Huainan, China

Coal mining causes surface subsidence, and the accumulated water body is constantly affected by the mining microseism in this process. Understanding the relationship between the subsided water quality and microseism plays a special role in assessing the environmental impact of mining activities. Based on sampling and monitoring, analyzing, and evaluating the Pansan subsided water area of Huainan, the influence of microseism activity on heavy metal elements in subsided water was verified. We found that the microseism effects decreased the contents of Zn, Pb, and Cu in the subsided water by 43.76%, 35.88%, and 28.83%, respectively, and Cd was not detected. The mechanism of heavy metal evolution in the water–sediment system under microseism factors was further explored by simulating experiments with similar materials. The results showed that the mining microseism increases the heavy metal adsorption capacity of suspended solids, and the dissolved heavy metals in water were transformed into suspended heavy metals. The heavy metals of subsided water eventually accumulate in the sediment, and the purpose of controlling heavy metal pollution can be achieved through regular cleaning of the bottom sediment.

Protein/Polysaccharide Composite toward Multi-in-One Toxin Removal in Blood with Self-Anticoagulation and Biocompatibility.

Biocompatible adsorbents play an essential role in hemoperfusion. Nevertheless, there are no hemoperfusion adsorbents that can simultaneously remove small and medium toxins, including bilirubin, urea, phosphor, heavy metals, and antibiotics. This bottleneck significantly impedes the miniaturization and portability of hemoperfusion materials and devices. Herein, a biocompatible protein-polysaccharide complex is reported that exhibits "multi-in-one" removal efficacy for liver and kidney metabolism wastes, toxic metal ions, and antibiotics. Through electrostatic interactions and polysaccharide-mediated coacervation, adsorbents can be prepared by simply mixing lysozyme (LZ) and sodium alginate (SA) together in seconds. The LZ/SA absorbent presented high adsorption capacities for bilirubin, urea, and Hg2+ of up to 468, 331, and 497mgg-1 , respectively, and the excellent anti-protein adsorption endowed LZ/SA with a record-high adsorption capacity for bilirubin in the interference of serum albumin to simulate the physiological environment. The LZ/SA adsorbent also has effective adsorption capacity for heavy metals (Pb2+ , Cu2+ , Cr3+ , and Cd2+ ) and multiple antibiotics (terramycin, tetracycline, enrofloxacin, norfloxacin, roxithromycin, erythromycin, sulfapyrimidine, and sulfamethoxazole). Various adsorption functional groups exposed on the adsorbent surface significantly contribute to the excellent adsorption capacity. This fully bio-derived protein/alginate-based hemoperfusion adsorbent has great application prospects in the treatment of blood-related diseases.

Bioinspired and dual-functional nanocellulose aerogels for water disinfection and heavy metal removal

Treating water resources contaminated by pathogenic microorganisms and heavy metals is a great challenge because of the difficulties in developing efficient strategies for water treatment. Traditional adsorbent materials have the drawbacks of high cost, low adsorption efficiency, secondary pollution creation, and a lack of adaptability in removing a wide variety of pollutants. In this study, inspired by the hierarchical fibrous structure and antibacterial property of the natural silkworm cocoon, we developed a guanidine-functionalized sericin/nanocellulose aerogel (GSNA) with a biomimetic skeletal architecture, which holds great promise for achieving hybrid water disinfection and heavy metal removal. The nanocellulose (CNC) fibers integrated into a robust building block with an interconnected structure and mechanical stability. The grafted polyhexamethylene biguanide (PHMB) endows the biomimetic aerogel with exceptional bactericidal activity (7 log reduction against Escherichia coli within 30 min). Benefiting from the abundant surface functional groups on sericin and CNC-PHMB, the obtained aerogel also exhibits superior heavy metal adsorption capacity (571.5 mg/g for Cu). These compelling merits enable the aerogel to disinfect water and remove heavy metal ions simultaneously as a membrane filter. The synthesized GSNA can be a promising candidate for water disinfection and purification because of its facile preparation, cost-effectiveness, and environmentally friendly characteristics.

Equilibrium isotherm and kinetic study of biosorption of cadmium from synthetic water using wastes leaves of Averrhoa carambola

Globally, the discharge of heavy metals into the water bodies is a matter of serious concern. Heavy metals like cadmium are considered as toxic even at very low concentration. Several conventional methods are available to remove heavy metals from the wastewater. They bear high costs, generate high sludge, and consume high energy. Biosorbents provides many beneficial properties due to their good adsorption capacity for heavy metals. The present work focuses on the potential of waste leaves of Averrhoa carambola (WACLP) as an adsorbent for its ability to remove Cd (II) ions from synthetic water by batch experimental process. The adsorbent was characterized by using elemental analysis, Energy Dispersive X-ray or EDAX and Scanning Electron Micrograph (SEM). The batch experiment was carried out considering various parameters such as pH, initial metal ion concentration, contact time and dose of the adsorbent. The fitting of the experimental data was done by Langmuir, Freundlich and Temkin isothermal models. The study on isothermal models revealed that the experimental parameters were best fitted to the Langmuir isothermal model with R2 value of 0. 976.The Kinetic studies showed pseudo second order depicting chemisorption. The results showed that Averrhoa carambola is a good adsorbent for cadmium and hence it can widen the scope and prospects for future studies on heavy metal removal from the aqueous solution.

Insights into interactions of biodegradable and non-biodegradable microplastics with heavy metals.

Biodegradable microplastics (BMPs) are considered to be environmentally friendly compared to non-biodegradable plastics (NMPs). However, BMPs are likely to become toxic during their transport because of the adsorption of pollutants (e.g., heavy metals) onto them. This study investigated the uptake of six heavy metals (Cd2+, Cu2+, Cr3+, Ni2+, Pb2+, and Zn2+) by a common BMPs (polylactic acid (PLA)) and compared their adsorption characteristics to those of three types of NMPs (polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC)) for the first time. The order of heavy metal adsorption capacity among the four MPs was PE > PLA > PVC > PP. The findings suggest that BMPs contained more toxic heavy metals than some NMPs. Among the six heavy metals, Cr3+ showed considerably stronger adsorption than other heavy metals in both BMPS and NMPs. The adsorption of heavy metals on MPs can be well explained using the Langmuir isotherm model, while the adsorption kinetic curves showed the best fit to the pseudo-second-order kinetic equation. Desorption experiments revealed that BMPs released a higher percentage of heavy metals (54.6-62.6%) in the acidic environment in a shorter time (~ 6h) compared to NMPs. Overall, this study provides insights into interactions of BMPs and NMPs with heavy metals and their removal mechanisms in aquatic environment.

Modifying Natural Zeolites to Improve Heavy Metal Adsorption

Problems with increasing heavy metal contents in natural waters are becoming a global issue. At the same time, improved methods for water treatment are becoming increasingly important. In this context, natural zeolites can be used to purify polluted water. In this paper, we investigated how the adsorption capacity of natural zeolites can be improved. Natural zeolites from the Shankanay district, Almaty, Kazakhstan, were used as adsorbent material for experiments on improving the water treatment of heavy metals. We found that the adsorption capacity for heavy metals was increased greatly by thermal activation using furnace treatment. The optimal thermal activation condition was about 550 °C for a duration of 2 h. However, the improved adsorption capacity for different heavy metals varied depending on the heat treatment temperature. Adsorption by the heat-treated zeolites at a temperature of 550 °C was 87% for nickel, 99% for copper and cadmium, and 100% for lead. Adsorption by heat-treated zeolites at a temperature of 500 °C was 78% for nickel, 98% for copper, 83% for cadmium, and 88% for lead. The residual concentration of heavy metals in the filtered water did not exceed the maximum permissible concentrations for drinking purposes. In all experiments, intense adsorption took place during the first 10 min representing 35 to 61% of the metal ions in the water. Adsorption properties were verified using adsorption capacity (BET), IR spectroscopy, and scanning electron microscopy. The study shows that modified Shankanay natural zeolites have great potential as a low-cost adsorbent material for purifying water from heavy metals.

The types of microplastics, heavy metals, and adsorption environments control the microplastic adsorption capacity of heavy metals.

Anthropogenic development has released large amounts of microplastics (MPs), which are carriers of migratory heavy metals, into the environment, and heavy metal adsorption by MPs may have strong combined toxic effects on ecosystems. However, until now, a comprehensive understanding of the factors influencing these adsorption capacities of MPs has been lacking. Thus, we used 4984 experimental data points to systematically assess the factors influencing the adsorption strength of 8 types of MPs on 13 types of heavy metals. We found that (1) the types of MPs, heavy metals, and adsorption environments significantly impacted the heavy metal adsorption capacities of MPs; (2) polyvinyl alcohol (PVA) showed a higher adsorption capacity for lead (Pb) and cadmium (Cd) than did other MPs, by 2810.62mg/kg and 2732.84mg/kg, respectively; (3) the adsorption capacities of MPs for heavy metal were regulated by multiple variables, with heavy metal concentration, MP quality, solution amount, adsorption time, and pH being the most important; and (4) MPs had a higher adsorption capacity in aquatic environments (except for seawater) than which in soil environments. Overall, our study clearly showed that the types of heavy metals, adsorption environments, and MPs influenced the heavy metal adsorption capacities of MPs and may exacerbate their combined environmental toxicity, which would help better characterize the severity of MP pollution.

Multifunctional fully biobased aerogels for water remediation: Applications for dye and heavy metal adsorption and oil/water separation

Water ecosystem contamination from industrial pollutants is an emerging threat to both humans and native species, making it a point of global concern. In this work, fully biobased aerogels (FBAs) were developed by using low-cost cellulose filament (CF), chitosan (CS), citric acid (CA), and a simple and scalable approach, for water remediation applications. The FBAs displayed superior mechanical properties (up to ∼65 kPa m3 kg−1 specific Young’s modulus and ∼111 kJ/m3 energy absorption) due to CA acting as a covalent crosslinker in addition to the natural hydrogen bonding and electrostatic interactions between CF and CS. The addition of CS and CA increased the variety of functional groups (carboxylic acid, hydroxyl and amines) on the materials’ surface, resulting in super-high dye and heavy metal adsorption capacities (619 mg/g and 206 mg/g for methylene blue and copper, respectively). Further modification of FBAs with a simple approach using methyltrimethoxysilane endowed aerogel oleophilic and hydrophobic properties. The developed FBAs showed a fast performance in water and oil/organic solvents separation with more than 96% efficiency. Besides, the FBA sorbents could be regenerated and reused for multiple cycles without any significant impact on their performance. Moreover, thanks to the presence of amine groups by addition of CS, FBAs also displayed antibacterial properties by preventing the growth of Escherichia coli on their surface. This work demonstrates the preparation of FBAs from abundant, sustainable, and inexpensive natural resources for applications in wastewater purification.

Comparison of the adsorption capacity and mechanisms of mixed heavy metals in wastewater by sheep manure biochar and Robinia pseudoacacia biochar.

Under various pyrolysis temperatures, the characteristics and heavy metal adsorption capabilities of biochar obtained from sheep manure (SMB) and Robinia pseudoacacia (RPB) were studied. The results indicated that SMB had higher yields, pH values, and ash contents than RPB. SMB3 and RPB3 have more oxygen-containing functional groups, whereas SMB8 and RPB8 have higher aromaticity and polarity. The maximum adsorption capacities of SMB for Pb2+ (20.2 mg·g-1), Cu2+ (13.9 mg·g-1), Cd2+ (3.2 mg·g-1), and total heavy metals (37.3 mg·g-1) were obtained by SMB3. However, the maximum adsorption capacities of RPB for Pb2+ (7.4 mg·g-1) and Cu2+ (10.5 mg·g-1) were obtained by RPB8. Furthermore, SMB and RPB had relatively higher adsorption capacities for Pb2+ and Cu2+ than for Cd2+. The pseudo-second-order model and the Freundlich Langmuir model provided a good fit to the adsorption kinetics and isotherms, indicating that chemical adsorption was dominant in the heavy metal adsorption by SMB and RPB. According to the contribution of various mechanisms, ion exchange and mineral precipitation were the primary mechanisms responsible for RPB8, while functional group complexation was the dominant mechanism for SMB3. This study provided important information on the comprehensive recycling utilization of SMB and RPB and promoted sustainable development.

Calcium-doped magnetic humic acid nano particles for the efficient removal of heavy metals from wastewater: the role of Ca

ABSTRACT Ca doping is an effective method for improving the adsorption capacity of HA–Fe aggregates and regulating their structures. Understanding the structural characteristics of Ca–HA–Fe aggregates can help explore their microscopic adsorption effect on heavy metals. However, the heterogeneity of HA results in an incomplete understanding of the structural characteristics of the ternary system of Ca–HA–Fe aggregates and adsorption of the quaternary system of Ca–HA–Fe–Pb/Cu/Cd. In this study, interactions between Ca–HA–Fe ternary and Ca–HA–Fe–Pb/Cu/Cd quaternary systems were discussed from a molecular perspective. The structures of the basic structural units of HA were identified. Density functional theory (DFT) was employed to calculate the stable states of basic structural units of HA and Ca2+. The results showed that hydroxyl and carboxyl groups exhibited the highest capacity to bind with Ca2+. The interactions among Ca, HA, and Fe led to the formation of network aggregates. The binding energies of functional groups for heavy metals and the feasibility of ion exchange were calculated by the method of experiment and DFT. According to the contribution of functional group complexation and ion exchange, the ion exchange values for Pb2+, Cu2+, and Cd2+ were 66.71%, 62.87%, and 60.79%, respectively, which indicated that Ca2+ ion exchange showed considerable potential in enhancing the adsorption capacity of heavy metals.

Adsorption and desorption characteristics of heavy metals onto conventional and biodegradable plastics

Biodegradable plastics have been widely used to replace conventional plastics to minimize environmental impacts of plastic packaging. However, before biodegradable plastics decompose in the environment, they could pose a threat to terrestrial and aquatic creatures by acting as vectors of contaminants in the food chain. In this study, conventional plastic bags (CPBs) made of polyethylene and biodegradable plastic bags (BPBs) made of polylactic acid were examined for their heavy metal adsorption. Effects of solution pHs and temperatures on adsorption reactions were investigated. Because of a larger BET surface area, presence of oxygen-containing function groups, and smaller crystallinity, the heavy metal adsorption capacities of BPBs are significantly larger than those of CPBs. Among Cu (up to 791.48 mg⋅kg−1), Ni (up to 60.88 mg⋅kg−1), Pb (up to 1414.58 mg⋅kg−1), and Zn (up to 295.17 mg⋅kg−1), Pb and Ni show the largest and the lowest extents of adsorption onto the plastic bags, respectively. In the different waterbodies in nature, Pb adsorption on the CPBs and the BPBs were 318.09–379.91 and 528.41–764.22 mg⋅kg−1, respectively. Consequently, Pb was selected as the target contaminant in the desorption experiments. After Pb was adsorbed onto the CPBs and the BPBs, Pb could be completely desorbed and released into simulated digestive systems in 10 h. In conclusion, BPBs could be potential vectors of heavy metals, and their suitability as a substitute for CPBs must be thoroughly investigated and confirmed.

Delamination of multilayer Ti3C2Tx MXene alters its adsorpiton and reduction of heavy metals in water

MXenes are considered as an emerging class of two-dimensional (2D) adsorbent for various environmental applications. In this work, two different morphologies of Ti3C2Tx MXene (multilayer (ML-Ti3C2Tx) and delaminated titanium carbide (DL-Ti3C2Tx)) were prepared through mild in situ HF etching and further delamination. The structural differences between the two were explored with a focus on their effects on the performance and mechanism of removing heavy metals from water. In comparison to ML-Ti3C2Tx, DL-Ti3C2Tx had more oxygen-containing functional groups, higher specific surface area (19.713 vs. 8.243 m2/g), larger pore volume (0.135 vs. 0.040 cm3/g), higher maximum Pb(II) adsorption capacity (77.0 vs. 56.68 mg/g), but lower maximum Cu(II) adsorption capacity (23.08 vs. 55.46 mg/g). Further investigation revealed that the removal of Pb(II) by the MXenes was mainly controlled through electrostatic attraction and surface complexation mechanisms, while Cu(II) was removed mainly through surface reduction by Ti-related groups. Because delamination of ML-Ti3C2Tx increased the surface area and surface functional groups, DL-Ti3C2Tx became a better sorbent for Pb(II) in water. During sonication, however, delamination inevitably led to partial oxidation of Ti3C2Tx nanosheets and thus weakened the reducing ability of DL-Ti3C2Tx for Cu(II) in water. Nevertheless, both ML- and DL-Ti3C2Tx not only exhibited excellent heavy metal adsorption capacity under different solution conditions, but also showed good reusability. Findings of this study indicate that Ti3C2Tx MXenes are promising adsorbents for treating heavy metal pollutants in water.

Effects of winter warming on the migration characteristics and pollution risk assessment of Zn, Cu, and Pb in the snow-soil continuum in seasonal snow cover area

The response of snow to climate warming is extremely sensitive. Climate warming will affect the melting rate of snow and its adsorption capacity for heavy metals, thereby affecting soil heavy metal content and pollution risk. This study regards snow and soil as a continuum, and two different warming treatments and one control treatment were set up with infrared radiometer to simulate the changing characteristics of this process under the background of future climate warming. In controlled experiments, the content of Zn, Cu and Pb in snow decreased significantly due to climate warming. Compared with the warming treatments, the concentrations of Zn, Cu, and Pb in the control treatment were increased by 6μg L−1, 4.9μg L−1, and 1μg L−1 and 8.3μg L−1, 1.75μg L−1, and 2.85μg L−1, respectively. The positive response of snow to climate warming directly affected the spatio-temporal distribution pattern of Zn, Cu, and Pb in soil, as a result, the Igeo of soil Zn increased by 0.221 and 0.165, the Igeo of soil Cu decreased by 0.076 and 0.080, and the Igeo of soil Pb decreased by 0.018 and 0.073, respectively. Thus, the living environment of soil microorganisms was changed, and the ecological environment of soil was significantly affected. Our results highlighted the importance of snow cover in assessing the risk of soil heavy metal pollution in the context of future warming, meanwhile, the results had important reference value for pollution prevention and sustainable development of farmland ecosystem in seasonal snow cover area.

High-efficiency electrochemical removal of Cd(II) from wastewater using birnessite-biochar composites: Performance and mechanism.

Birnessite has been widely used for electrochemical removal of heavy metals due to its high pseudocapacitance. Incorporation of carbon-based materials into birnessite can enhance its conductivity and stability, and synergistically improve the electrochemical adsorption capacity due to the double-layer capacitor reaction derived from carbon-based materials. In this study, biochar was successfully incorporated with birnessite at various ratios to synthesize composites (BC-Mn) for effective electrochemical removal of cadmium (Cd(II)) from water. The effects of cell voltage, initial pH, and recycling performance of BC-Mn were evaluated. As a result, the electrosorption capacity of BC-Mn for Cd(II) exhibited gradual increases with increasing birnessite content and reached equilibrium at a Mn content of 20% (BC-Mn20). The Cd(II) adsorption capacity of BC-Mn20 rose at higher cell voltage, and reached the maximum at 1.2V. At pH 3.0-6.0, the electrosorption capacity initially rose until pH 5.0 and then approached equilibrium with a further increase in pH value. The Cd(II) electrochemical adsorption capacity of BC-Mn20 in the solution could reach 104.5mgg-1 at pH 5.0 for 8h at 1.2V. Moreover, BC-Mn20 exhibited excellent reusability with a stability of 95.4% (99.7mgg-1) after five cycles of reuse. Due to its superior heavy metal adsorption capacity and reusability, BC-Mn20 may have a promising prospect in the remediation of heavy metal polluted water.

Feasible synthesis of magnetic zeolite from red mud and coal gangue: Preparation, transformation and application

A feasible synthesis of magnetic zeolite from the mixture of industrial solid wastes (red mud and coal gangue) was proposed. The preparation conditions, formation mechanism and adsorption performance of magnetic zeolite were investigated. Magnetic zeolite with uniform distribution of zeolite and magnetite could be successfully synthesized at the alkali reducing calcination conditions of n(Na:Al:Si) = 3.6:1:1, 600 °C, 1.5 h and the hydrothermal conditions of n(Na:H2O) = 2.8:1, 90 °C, 9 h. During this process, aluminosilicates in the mixture of red mud and coal gangue could be transformed into sodium-containing phases and zeolite A in turn; meanwhile, hematite in red mud could be reduced by carbon in coal gangue to transform into magnetite. The prepared magnetic zeolite showed excellent adsorption capacity and reusability for heavy metals. The maximum adsorption capacity for Cu2+, Cd2+ and Pb2+ reached 76.2, 92.2 and 178.4 mg/g, respectively, which could be attributed to the different ionic radius of heavy metals.

Competitive adsorption of heavy metals between Ca–P and Mg–P products from wastewater during struvite crystallization

Wastewater usually contains high concentration of calcium (Ca), posing a competitive reaction with magnesium (Mg) on phosphorus (P) recovery during the struvite crystallization. The differences in the adsorption of heavy metals by Ca–P and Mg–P (struvite) generated are still unclear. Herein, we analyzed the residues of four kinds of common heavy metals (Cu, Zn, Cd, Pb) in Ca–P and Mg–P (struvite) under varying conditions (solution pH, N/P ratio, Mg/Ca ratio) in the swine wastewater and explored their possible competitive adsorption mechanisms. The experiments using synthetic wastewater and real wastewater have similar experimental patterns. However, under the same conditions, the metal (Pb) content of struvite recovered from the synthetic wastewater (16.58 mg/g) was higher than that of the real wastewater (11.02 mg/g), as predicted by the Box-Behnken Design of Response Surface Methodology (BBD-RSM). The results demonstrated that Cu was the least abundant in the precipitates compared to Zn, Cd, and Pb of almost all experimental groups with an N/P ratio greater than or equal to 10. The fact might be mainly attributed to the its stronger binding capacity of Cu ion with NH3 and other ligands. Compared with struvite, the Ca–P product had a higher adsorption capacity for heavy metals and a lower P recovery rate. In addition, the higher solution pH and N/P ratio were favorable to obtain qualified struvite with lower heavy metal content. It can be applied to reduce the incorporation of heavy metals by modulating pH and N/P ratio through RSM, which is suitable for different Mg/Ca ratios. It is anticipated that the results obtained would offer support for the safe utility of struvite from wastewater containing Ca and heavy metals.

Adsorption of heavy metals from mine wastewater using amino-acid modified Montmorillonite

This study was conducted to identify the ability of a modern developed amino-acid modified montmorillonite clay (AA-Mont) to adsorb Cu2+, Pb2+ and Ni2+ cations from a multi-aqueous wastewater. This experimental was conducted to identify the potential of clay-based adsorbents to remediate pollutants from the PRA river basin. Experimental wastewater was prepared using a range of the lowest and highest recorded upstream and downstream heavy metal concentrations of u2+(10.84 mg/L-108.48 mg/g), Ni2+(7.99 mg/g–79.92 mg/g), and Pb2+(33.538 mg/L—335.38 mg/L). The variants of the designed clay-based adsorbents were L-Cysteine montmorillonites (Cys-Mont), Glycine montmorillonite (Gly-Mont), and L-lysine Montmorillonites (Lys-Mont) prepared at pH 4, 5, and 6 respectively. The experimental conditions were; Adsorbent dosages range = 25 mg–400 mg, pH = 6.0, Contact time = 24 hrs, Temperature = 25°C and Shaker speed = 180 rmp. After the adsorption experiments, it was identified that the maximum average removal efficiency obtained for Cu2+, Ni2+, and Pb2+ were all attained at adsorbent dosage 400 mg/L and in the order Lys-Mont (99.82%)>Cys-Mont (99.28%)>Gly-Mont (95.8%). Thus, the modified Lys-Mont clay exhibited the highest heavy metal adsorption capacity amongst the above three studied. The highest and lowest adsorbed metal pollutants amounts recorded for Lys-Mont were Cu2+ (86.49 and 8.65) mg/g, Ni2+ (44.51 and 5.99) mg/g, and Pb2+ (267.85 and 26.67) mg/g respectively. The number of metal ions adsorbed per unit mass for each metal cation tested decreased with increasing adsorbent dosage. The general order of selectivity documented for all the AA-Monts in this study was Pb>Cu>Ni which is similar to the levels in the prepared wastewater solution (Pb>Cu>Ni). The findings of this study have shown that heavy metal polluted river basins can remediated given the right conditions of temperature, adsorbent dosage, pH and agitation speed.

Modified Shrimp-Based Chitosan as an Emerging Adsorbent Removing Heavy Metals (Chromium, Nickel, Arsenic, and Cobalt) from Polluted Water

Water quality is under constant threat worldwide due to the discharge of heavy metals into the water from industrial waste. In this report, we introduce a potential candidate, chitosan, extracted and isolated from shrimp shells, that can adsorb heavy metals from polluted water. The waste shrimp shell chitosan was characterized via Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS). The adsorption capacity of heavy metals on the modified shrimp shell was measured using an inductively coupled plasma mass spectrometry before and after adsorption. The highest adsorption of arsenic, nickel, and cobalt was 98.50, 74.50, and 47.82%, respectively, at neutral pH, whereas the highest adsorption of chromium was 97.40% at pH 3. Correspondingly, the maximum adsorption capacities of MSS for As, Cr, Ni, and Co were observed to be 15.92, 20.37, 7.00, and 6.27 mg/g, respectively. The application of Langmuir and Freundlich isotherm models revealed that the adsorption processes for the heavy metals were statistically significant (r2 > 0.98). The kinetic studies of metal adsorption, using modified shrimp shell, were well explained by the pseudo-second-order kinetic model with linear coefficients (r2) of >0.97. The presence of a greater number of functional groups on the adsorbent, such as N–H coupled with H–O, –COO−, C–H, N–N, and C–O–C, was confirmed by FTIR analyses. Furthermore, SEM-EDX analysis detected the presence of elements on the surface of modified shrimp shell chitosan. This noteworthy adsorption capacity suggests that MSS could serve as a promising, eco-friendly, and low-cost adsorbent for removing toxic heavy metals including Cr, Ni, As, and Co and can be used in many broad-scale applications to clean wastewater.

Waste to resource: Utilization of waste bagasse as an alternative adsorbent to remove heavy metals from wastewaters in sub-Saharan Africa: A review

AbstractHeavy metals pollution of both surface and groundwater sources of sub-Saharan Africa is alarmingly increased due to unplanned urban populations. Inadequate policies for water management, political commitment, and financial resources forced 65% of rural communities of sub-Saharan Africa to live in economic water stress areas. Sugarcane bagasse (SCB) shows high heavy metals (HMs) adsorption capacity (20–700 mg/g) through chemical entrapments to carbon-oxygen containing functional group and interior pore filling of porous surface. Various modifications like a physical/thermal, chemical, and composite form of bagasse show better adsorption performance for HMs removal. Kinetic and isotherm studies of HMs adsorption equilibrium data over SCB show that both Langmuir and Freundlich adsorption isotherms (cooperative adsorption) as the main adsorption mechanism. In addition, SCB shows potential bio-adsorbent properties for the selective adsorption of target HMs based on their physicochemical properties and shows good repeatability in acid environments. It is believed that information on this review will shed light on the current and future prospects of raw and modified SCB for HMs adsorption removal capacity. Sugarcane bagasse shows a remarkable selectivity for HMs adsorption removals based on their physicochemical properties and shows good potential capability for future utilizations in real wastewaters of developing countries.