The removal of heavy metals from aqueous solutions by sawdust adsorption--removal of lead and comparison of its adsorption with copper

Adsorptive removal of lead, copper, and nickel using natural and activated Egyptian calcium bentonite clay

This study evaluates the efficiency of alkali-activated Egyptian calcium bentonite, obtained from the El Alamein region in northern Egypt, for the removal of copper (Cu2⁺), lead (Pb2⁺), and nickel (Ni2⁺) from synthetic wastewater. The bentonite samples underwent a series of preparation steps, including crushing, ball milling, magnetic separation, acid treatment with 0.1N acetic acid, and alkali activation using 5% sodium carbonate (Na2CO3). Various analytical techniques, such as X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), cation exchange capacity (CEC) measurements, scanning electron microscopy (SEM), and free swelling analysis, were employed to characterize the materials. Absorption experiments were performed to examine the effects of pH, temperature, starting metal concentration, bentonite dose, and contact duration on heavy metal removal. The characterization results confirmed that montmorillonite was the predominant mineral in both the natural and activated bentonite samples. Adsorption studies indicated a significant improvement in heavy metal removal efficiency after activation. Under optimal conditions (pH 7, 1 g/L adsorbent dose, 120 min contact time, 20 mg/L initial metal concentration, and 20 °C), the maximum adsorption capacities of the activated bentonite were determined as 14 ± 0.03 mg/g for Cu2+, 13 ± 0.04 mg/g for Pb2+, and 12.2 ± 0.05 mg/g for Ni2+, exceeding those of the natural bentonite, which recorded capacities of 9.2 ± 0.04 mg/g, 9 ± 0.03 mg/g, and 8 ± 0.02 mg/g, respectively. Adsorption equilibrium data according to the Langmuir isotherm model, exhibiting high correlation values (R2 = 0.9979 for Cu2+, 0.9972 for Pb2+, and 0.9973 for Ni2+). Moreover, kinetic modeling demonstrated that the adsorption followed a pseudo-second-order mechanism, suggesting an intense chemisorption process. The thermodynamic analysis indicated that the adsorption process was spontaneous and endothermic, demonstrating enhanced adsorption at higher temperatures.

Thermodynamic, kinetic, and equilibrium studies of Cu(II), Cd(II), Ni(II), and Pb(II) ion biosorption onto treated Ageratum conyzoid biomass

The issue of environmental contamination, particularly caused by the existence of heavy metal particles, is a major and widely recognized subject that receives substantial global attention. The remediation of Cu(II), Cd(II), Ni(II), and Pb(II) ionic metal particles from synthetic wastewater using chemically treated plant leaves of Ageratum conyzoides (TAC) as a biosorbent was investigated. The biosorption process was implemented utilizing a batch system, wherein several operational parameters were considered, including temperature, pH, agitation time, biosorbent dosage, and initial concentration of the metal ion. Langmuir, Freundlich, Temkin, and D-R isotherm models were used to evaluate equilibrium data. The analyzed parameter exhibits characteristics that were best fitted with the Langmuir isotherm. The observed biosorption capacities (qm) of Cu(II), Pb(II), Ni(II), and Cd(II) ions on the TAC were measured as 51.573, 30.49, 33.53, and 35.91 mg/g, respectively, at a temperature of 22 °C. The affinity sequence of these metal ions follows the order Cu(II) > Pb(II) > Ni(II) > Cd(II). The measured values for the biosorption free energy change (ΔG) of Cu(II), Pb(II), Cd(II), and Ni(II) metal ions ranged from -1.017 to -4.723, -1.368 to -3.612, -2.785 to -5.21, and -1.047 to -5.135 kJ/mol, respectively. The enthalpy (ΔH) for Cu(II), Pb(II), Cd(II), and Ni(II) were determined to be +19.33, +6.82, +14.83, and +38.07 kJ/mol, respectively. Similarly, the corresponding entropy changes (ΔS) for the same series of metal ions were recorded as +0.075, +0.064, +0.063, and +0.135 kJ/mol.K. The pseudo-second-order kinetic models yielded superior outcomes in comparison to the pseudo-first-order kinetic models. The findings of the experiment indicated that the TAC demonstrates favorable efficacy in extracting all four metal ions. Hence, the utilization of biomass derived from Ageratum conyzoides leaves has proven to be a viable and economically feasible approach for biosorption of all four metals.

Optimization of fenugreek seed mucilage extraction for the synthesis of a novel bio-nano composite for efficient removal of cadmium ions from aqueous environments

This research investigates the application of an innovative bio-nanocomposite, Fenugreek seed mucilage/silicon carbide (FSM/SiC), as an exceptionally effective adsorbent for eliminating cadmium ions from aqueous solutions. Optimization of fenugreek mucilage extraction involved ultrasonic methods, establishing ideal conditions with a solid-to-solvent ratio of 1:55, 50 °C temperature, 37 kHz frequency, 100 % power, and 30 min processing time. Comprehensive characterization through FTIR spectroscopy, XRD, imaging, DLS, and SEM confirmed the preservation of crucial adsorption-related characteristics. Enhanced adsorption efficiency was achieved by systematically adjusting pH, temperature, adsorbent concentration, pollutant concentration, and contact time, identifying optimal conditions at pH 6, 0.03 g adsorbent dosage, 35 min contact time, and 30 mg/L initial cadmium concentration at 30 °C. Adsorption kinetics followed a pseudo-second-order model, while the Langmuir isotherm fit suggested monolayered adsorption. Thermodynamic analysis indicated exothermic and spontaneous Cd2+ ion adsorption onto FSM/SiC. Remarkably, FSM/SiC demonstrated exceptional regeneration potential, positioning it as a promising solution for water decontamination and environmental remediation. This research showcases FSM/SiC's potential with a maximum adsorption capacity of 41.6 mg/g for cadmium ions, highlighting its significance in addressing cadmium contamination.

Modeling Cu removal from aqueous solution using sawdust based on response surface methodology

Copper (Cu), as one of the heavy metals widely used in industrial and agricultural activities, has a fundamental role in the pollution of water resources. Therefore, removing Cu from the aqueous solutions is considered an important challenge in the purification of water resources. Thus, in this study, sawdust with a diameter of 260-600 μm was used to remove Cu from the aqueous solutions. At first, sawdust was washed using distilled water and dried at laboratory temperature. Cu absorption experiments in closed conditions were performed based on the central composite design (CCD) model and with a range of initial Cu concentrations equal to 1-25 mgl-1. The amount of changes for other variables, including pH, time, and amount of sawdust, was equal to 2-10, 5-185 (min), and 5-25 (gl-1), respectively. After the completion of each test, the remaining Cu concentration in the solution was measured using atomic absorption, and the percentage of Cu removed was determined from the difference between the initial and final concentrations. The results showed that the CCD model has a favorable ability to predict Cu removal from the aqueous solutions (R2=0.90 and RSME=3.34%). Based on the Pareto analysis, contact time, the amount of sawdust, pH, and the Cu concentration had the most significant effect on removing Cu from the solution. Contact time, amount of sawdust, and pH were directly related, and the amount of dissolved Cu was proportional to the removal of Cu from the solution. Therefore, sawdust is desirable as a natural adsorbent, and the removal efficiency of Cu from solutions with low Cu concentration is very high (94%). In this regard, it is advised to use sawdust in the process of targeting Cu and heavy metals due to its low cost and availability.

“Gamma Irradiation Synthesis of Carboxymethyl Chitosan-Nanoclay Hydrogel for the Removal of Cr(VI) and Pb(II) from Aqueous Media”

Hydrogel composites comprised of N,O carboxymethyl chitosan crosslinked with different weight ratios of acrylic acid and fabricated with nanoclay particle were prepared via gamma irradiation at 25 kGy irradiation dose. The prepared composites were coded as CsAA1Cl, CsAA2Cl and CsAA3Cl based on the weight ratio of acrylic acid to the chitosan derivative. The claimed hydrogels were characterized by FTIR, TGA and XRD. The TGA data implied that the incorporation of clay nanoparticles enhanced the thermal stability of the composites; the decomposition temperature increased up to 500 °C for CsAA3Cl. Three AFM outcomes were used to compare the surface features of the samples; topography, height and surface roughness. The topography data reveals that the nanoclay particles incorporated in CsAA3Cl are intercalated and exfoliated. Then, the optimized sorbent (CsAA3Cl) was investigated as green sorbents for chromium (VI) and lead (II). The data revealed that CsAA3Cl displayed maximum removal performance towards both lead and chromium with removal efficiencies 125 mg/g and 205 mg/g respectively at the optimum application conditions within 90 min only. Also, it was found that the optimum pH value was 9 for chromium and 8 for lead. The data proved that the adsorption of both cations followed pseudo-first order kinetic model. The prepared composites showed acceptable metal uptake capacity at three successive cycles.

Graphical Abstract

Thermal plasma processing of Moringa oleifera biochars: adsorbents for fluoride removal from water

Anthropogenic activities accelerate fluoride contamination in groundwater, which largely affects public health. Though biochars have been explored for defluoridation, the plasma technology-based production of biochars has not received as considerable attention as other methods and it is also important that biochars be tested on groundwater samples. In the present study, for the first time, we report the preparation of biochars from different parts of Moringa oleifera using thermal plasma processing and demonstrate fluoride adsorption in both synthetic and contaminated groundwater. Water samples were collected from different locations in Nuapada district of Odisha such as Kotamal-Makardampada (20°24'46''N 82°37'19''E), Pandrapathar (20°34'41''N 82°39'25''E), Karlakot-Kadobhata (20°22'52''N 82°37'24''E), Kotamal-Jhakarpada (20°24'35''N 82°37'20''E), and Dohelpada (20°33'50''N 82°38'57''E). The Moringa leaf samples are processed at 1600 °C for 3 min in an inert atmosphere under a continuous flow of argon to get suitable biochars. The plasma-synthesized biochars contain larger exposed surfaces, which are efficient for the adsorption of fluoride. The prepared biochars were highly porous, amorphous, and contain > 72% carbon, which increases the efficiency of defluoridation due to the surface adsorbate site exposed. XRD of the samples showed the presence of calcium hydroxide, magnesium oxide, and calcium oxide, and large peaks of carbon. Raman data showed the double bond of carbon with oxygen in the form of carbonyl bonds, thioether, and sulfhydryl bonds, which contribute to the protonated site for the adsorption of fluoride, and assist in water penetration and swelling of biochars. The biochar of Moringa oleifera is very efficient for the adsorption of fluoride from standard samples as well as groundwater samples up to a concentration of 6 ppm. Conclusively, the present investigation shows that Moringa oleifera leaves are a good alternative adsorbent that could be used for the removal of fluoride from groundwater samples with > 85% removal in 18 h using 1 g biochar for 100 mL or 10 g biochar for 1 L water containing 4 ppm fluoride. To our knowledge, this is the first report on the thermal plasma-based production of Moringa biochars for the removal of fluoride from drinking water.

Design of a Novel Nanosensors Based on Green Synthesized CoFe2O4/Ca-Alginate Nanocomposite-Coated QCM for Rapid Detection of Pb(II) Ions

Pb(II) is a significant contaminant that is known to have negative effects on both humans and animals. Recent industrial operations have exacerbated these consequences, and their release of several contaminants, including lead ions, has drawn attention to the potential effects on human health. Therefore, there is a lot of interest in the rapid, accurate, and selective detection of lead ions in various environmental samples. Sensors-based nanomaterials are a significant class among the many tools and methods developed and applied for such purposes. Therefore, a novel green synthesized cobalt ferrite (CoFe₂O₄) nanoparticles and functionalized CoFe₂O₄/Ca-alginate nanocomposite was designed and successfully synthesized for the fabrication of nanoparticles and nanocomposite-coated quartz crystal microbalance (QCM) nanosensors to detect the low concentrations of Pb(II) ions in the aqueous solutions at different temperatures. The structural and morphological properties of synthesized nanoparticles and nanocomposite were characterized using different tools such as X-ray diffraction (XRD), N₂ adsorption-desorption isotherm, dynamic light scattering (DLS), zeta potential analyzer (ζ-potential), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The QCM results revealed that the green synthesized CoFe₂O₄ nanoparticles and functionalized CoFe₂O₄/Ca-alginate nanocomposite-coated QCM nanosensors exhibited high sensitivity, stability, and rapid detection of Pb(II) ions in the aqueous solutions at different temperature. The lowest detection limit for Pb(II) ions in the aqueous solutions could reach 125 ng, which resulted in a frequency shift of 27.49 ± 0.81, 23.63 ± 0.90, and 19.57 ± 0.86 Hz (Δf) for the QCM detector coated with green synthesized CoFe₂O₄ nanoparticles thin films, and 25.85 ± 0.85, 33.87 ± 0.73, and 6.87 ± 0.08 Hz (Δf) for the QCM detector coated with CoFe₂O₄/Ca-Alg nanocomposite thin films in a real-time of about 11, 13, and 13 min at 25 °C, 35 °C, and 45 °C, respectively. In addition, the resonance frequency change results showed the superiority of functionalized CoFe₂O₄/Ca-alginate nanocomposite coated QCM nanosensor over CoFe₂O₄ nanoparticles towards Pb(II) ions detecting, which attributed to the beneficial properties of alginate biopolymer.

Fabrication and application of nanosized stannic oxide for sorption of some hazardous metal ions from aqueous solutions

A batch equilibrium method was utilized to evaluate the retention of Fe(III) and Pb(II) onto stannic oxide (SnO2) nanomaterial. SnO2 was prepared by a simple precipitation method and characterized by different analytical apparatuses like FT-IR, SEM, TEM, and XRD. Scherrer’s formula and Williamson-Hall (WH) analysis were utilized to detect the crystallite size and lattice strain. The XRD and TEM data revealed that SnO2 has a nanoscale and crystalline nature. The retention study for Fe(III) and Pb(II) includes the influence of shaking time, batch factor, pH, initial concentrations, capacity, and applications. The data reveal that the maximum uptake of SnO2 was achieved at pH 2.5 and 3.7 for Fe(III) and Pb(II), respectively. SnO2 has a fast kinetic (60 min) and the reaction kinetic data obey the pseudo–second-order model. The capacity has values of 50.4 and 48.8 mg/g for Fe(III) and Pb(II), respectively. The real sample applications proved that SnO2 is an excellent sorbent for the capture of Pb(II) and Fe(III) from industrial wastewater and low-grade monazite (LGM) respectively, in addition to the capture of 59Fe radionuclide from low-level radioactive waste (LLRW).

Removal of lead ions (Pb2+) from water and wastewater: a review on the low-cost adsorbents

The presence of lead compounds in the environment is an issue. In particular, supply water consumption has been reported to be a significant source of human exposure to lead compounds, which can pose an elevated risk to humans. Due to its toxicity, the International Agency for Research on Cancer and the US Environmental Protection Agency (USEPA) have classified lead (Pb) and its compounds as probable human carcinogens. The European Community Directive and World Health Organization have set the maximum acceptable lead limits in tap water as 10 µg/L. The USEPA has a guideline value of 15 µg/L in drinking water. Removal of lead ions from water and wastewater is of great importance from regulatory and health perspectives. To date, several hundred publications have been reported on the removal of lead ions from an aqueous solution. This study reviewed the research findings on the low-cost removal of lead ions using different types of adsorbents. The research achievements to date and the limitations were investigated. Different types of adsorbents were compared with respect to adsorption capacity, removal performances, sorbent dose, optimum pH, temperature, initial concentration, and contact time. The best adsorbents and the scopes of improvements were identified. The adsorption capacity of natural materials, industrial byproducts, agricultural waste, forest waste, and biotechnology-based adsorbents were in the ranges of 0.8-333.3 mg/g, 2.5-524.0 mg/g, 0.7-2079 mg/g, 0.4-769.2 mg/g, and 7.6-526.0 mg/g, respectively. The removal efficiency for these adsorbents was in the range of 13.6-100%. Future research to improve these adsorbents might assist in developing low-cost adsorbents for mass-scale applications.

Helping plants to deal with heavy metal stress: the role of nanotechnology and plant growth promoting rhizobacteria in the process of phytoremediation

Heavy metals (HMs) are not destroyable or degradable and persist in the environment for a long duration. Thus, eliminating and counteracting the HMs pollution of the soil environment is an urgent task to develop a safe and sustainable environment. Plants are in close contact with the soil and can play an important role in soil clean-up, and the process is known as phytoremediation. However, under HM contaminated conditions, plants suffer from several complications, like nutrient and mineral deficiencies, alteration of various physiological and biological processes, which reduces the plant's growth rate. On the other hand, the bioavailability of HMs is another factor for reduced phytoremediation, as most of the HMs are not bioavailable to plants for efficient phytoremediation. The altered plant growth and reduced bioavailability of HMs could be overcome and enhance the phytoremediation efficiency by incorporating either nanotechnology, i.e., nanoparticles (NPs) or plant growth promoting rhizobacteria (PGPR) along with phytoremediation. Single incorporation of NPs and PGPR might improve the growth rate in plants by enhancing nutrient availability and uptake and also by regulating plant growth regulators under HM contaminated conditions. However, there are certain limitations, like a high dose of NPs that might have toxic effects on plants. Thus, the combination of two techniques such as PGPR and NPs-based remediation can conquer the limitations of individual techniques and consequently enhance phytoremediation efficiency. Considering the negative impacts of HMs on the environment and living organisms, this review is aimed at highlighting the concept of phytoremediation, the single or combined integration of NPs and PGPR to help plants deal with HMs and their basic mechanisms involved in the process of phytoremediation. Additionally, the complications of using NPs and PGPR in the phytoremediation process are discussed to determine future research questions and this will assist to stimulate further research in this field and increase its effectiveness in practical application.

Assessing the efficiency and mechanism of zinc adsorption onto biochars from poultry litter and softwood feedstocks

The efficiency and adsorption mechanism of zinc removal was assessed in aqueous solution using four biochars from multiple biomass residues (poultry litter and three tree species). The effect of pH, kinetic effects, and isotherm fittings were investigated, as well as zinc-laden biochar using x-ray diffraction and absorption near edge structure. Sorbent load results showed softwood biochar exhibited the greatest zinc removal from both deionized (15 mg_Zn/L) and mining influenced river water (10 mg_Zn/L). The Langmuir isotherm was the best fit for the majority of the biochars. Exchangeable cations contributed most for the adsorption mechanism from the softwood biochars, while precipitation was greatest contribution for the poultry litter biochar. Overall, our results suggest that biochars from Douglas Fir trees are more efficient at removing zinc from aqueous solutions (up to 19.80 mg_Zn/g) compared to previously studied biochars (0.61 to 11.0 mg_Zn/g) and should be used for future remediation efforts.

Microbial application in remediation of heavy metals: an overview

Heavy metal contamination poses a menacing threat to all living forms in the natural world due to its catastrophic consequences, contributing to environmental pollution. The need for human beings increasing each day along with anthropological activity is contributing directly to the destruction of the environment with the release of a large number of heavy metals into the food chain. These metals can be accumulated in the food chains and are very extremely toxic even at low concentrations. Heavy metals aggregation can deteriorate the healthy ecosystem of the water bodies as well. One of the major concerns is the diminution and administration of the heavy metals aggregating in marine water bodies and lakes. Heavy metals are not degradable and thus tend to remain in the environment for a prolonged time period. Heavy metal aggregation can demonstrate immediate repercussions such as DNA damage, inhibition of respiration and photosynthesis, and rapid reactive oxygen species generation. Conventional or standard chemical and physical methods for remediation of heavy metals are uneconomical and lead to the production of a large magnitude of chemical waste. This shifts the focus and interest towards the utilization of microbes in remediation of heavy metals from the environment which is eco-friendly and economical. To contend with heavy metals, microorganisms have a specific mechanism such as biotransformation, biosorption, and homeostasis. The microbial system is responsive to the toxicity that is created by the heavy metals which are easily water-soluble and available in the environment. The current review article describes the sources and effects of metal ions in the environment followed by bioremediation strategies followed in their remediation. Microbial approaches in remediation of metal ions from extraterrestrial materials are depicted in the paper.

Removal of hexavalent chromium ions using micellar modified adsorbent: isothermal and kinetic investigations

Hexavalent chromium is a very poisonous oxyanion and has had a negative impact on human health. This study assessed the viability of removing chromium(vi) using micellar modified adsorbents. In this study, chromium(vi) was removed from locally accessible wheat bran using separate applications of anionic sodium dodecyl sulfate (SDS) and cationic cetyltrimethylammonium bromide (CTAB) surfactants. The initial chromium content (5–12 ppm), pH (2–12), adsorbent dose (1–6 g/100 mL), agitation time (15–240 min), agitation speed (50–300 rpm), and temperature (15–50 °C) were all varied in the adsorption investigation. Pseudo first-order and second-order kinetic models were utilized to analyze the kinetic investigation. To determine thermodynamic parameters, the van't Hoff relationship was used. The maximum result for chromium(vi) uptake was obtained as 87.7%, 83.5% and 98.9% for WB, SDS-mWB, and CTAB-mWB, respectively, at an agitation time of 240 min (i.e., 4 h), temperature (i.e., 25–30 °C), agitation speed (150 rpm). However, both WB and CTAB-mWB derives metal ion removal at lower pH levels (2–4), whereas SDS-mWB requires a pH between 4 and 6 for maximum percentage removal of Cr(vi). The equilibrium data of WB and SDS-mWB were modeled by the Langmuir adsorption isotherm, while the data of CTAB-mWB fitted well in the Freundlich isotherm model. The kinetic analysis of WB, SDS-mWB, and CTAB-mWB revealed that the pseudo-second-order kinetic model provides a thorough explanation for each of these adsorbents. It was found that CTAB-mWB can preferably be used for the removal of chromium(vi) due to its high affinity with adsorbate molecules and adsorption capacity.

In this investigation, anionic sodium dodecyl (SDS) and cationic cetyltrimethylammonium bromide (CTAB) surfactants were separately applied to locally accessible wheat bran to remove chromium(vi).

Leaching Performance and Zinc Ions Removal from Industrial Slag Leachate Using Natural and Biochar Walnut Shell

This study aims to investigate leaching characteristics of zinc slag according to leaching tests, including; TCLP (Toxicity Characteristic Leaching Procedure), SPLP (Synthetic Precipitation Leaching Procedure), ASTM-D3987 (American Society for Testing and Materials), and TS EN-12457-4 (Turkish Standards Institute) tests methods. The present study describes the adsorption potential of natural and biochar walnut shells for removing ions from the zinc leachate. TCLP leachate, with a value of 38.575 mg/L, has a high zinc (Zn⁺²) concentration compared to other methods. Therefore, TCLP leachate was used in the adsorption experiments. Adsorption experiments were carried out at different adsorbent dosages, pH values, and contact time conditions. In the dosage study, the highest removal efficiency was obtained as 84% and 92% in natural and biochar walnut shell adsorbents, respectively. As a result of pH study, it was observed that adsorption under alkaline conditions had a much higher removal efficiency. Moreover, adsorption studies performed against contact time were applied to four different kinetic models and both adsorbents were found to be fit with the pseudo-second-order model. This kinetic model showed that the Zn⁺² adsorption mechanism of natural and biochar walnut shells is chemical adsorption. With this study, it was shown that a very high 96% zinc removal can be achieved under optimum adsorption conditions. This may be the first study of zinc removal after leaching from industrial slag in the literature. This study has shown that high removal efficiencies can be obtained by an economical adsorbent.

Competitive and non-competitive zinc, copper and lead biosorption from aqueous solutions onto flax fibers

Competitive and non-competitive batch experiments were conducted on flax fibers to study Zn²⁺, Cu²⁺, and Pb²⁺ ions biosorption performance. Biosorption efficiency was dependent on contact time, pH, and biosorbent concentration. The results under competitive conditions were different from those obtained in non-competitive form. A high affinity of lead, with a selectivity sequence in general of Pb > Cu > Zn was observed. The biosorption data fitted very well the Langmuir model for lead in both types of solutions and for zinc and copper in the monometal form. The fit with the Freundlich model was not as successful, except for copper in the ternary system. Regarding zinc under competitive conditions, the sorption process was quite difficult and thus the equilibrium data could not fit well the adsorption models. The maximum adsorption capacities (mmol.kg^-1) were respectively 112, 122 and 71, for Pb, Cu and Zn in the single metal ion solution and 82, 57 and 8 only in the ternary, showing thus a high competition between metal ions when added simultaneously. Overall, lead could still be efficiently removed in spite of the presence of other ions while zinc would be overcome in the presence of lead and copper.

Inexpensive Organic Materials and Their Applications towards Heavy Metal Attenuation in Waters from Southern Peru

There is interest in using locally available, low cost organic materials to attenuate heavy metals such as Cd, Cr, Cu, Hg, Ni, Pb, and Zn found in surface waters in Peru and other developing regions. Here we mesh Spanish language publications, archived theses, and prior globally available literature to provide a tabulated synthesis of organic materials that hold promise for this application in the developing world. In total, nearly 200 materials were grouped into source categories such as algae and seashells, bacteria and fungi, terrestrial plant-derived materials, and other agricultural and processing materials. This curation was complemented by an assessment of removal potential that can serve as a resource for future studies. We also identified a subset of Peruvian materials that hold particular promise for further investigation, including seashell-based mixed media, fungal blends, lignocellulose-based substrates including sawdust, corn and rice husks, and food residuals including peels from potatoes and avocadoes. Many studies reported percent removal and/or lacked consistent protocols for solid to liquid ratios and defined aqueous concentrations, which limits direct application. However, they hold value as an initial screening methodology informed by local knowledge and insights that could enable adoption for agriculture and other non-potable water reuse applications. While underlying removal mechanisms were presumed to rely on sorptive processes, this should be confirmed in promising materials with subsequent experimentation to quantify active sites and capacities by generating sorption isotherms with a focus on environmental conditions and specific contaminated water properties (pH, temperature, ionic strength, etc.). These organics also hold promise for the pairing of sorption to indirect microbial respiratory processes such as biogenic sulfide complexation. Conversely, there is a need to quantify unwanted contaminant release that could include soluble organic matter and nutrients. In addition to local availability and treatment efficacy, social, technical, economic, and environmental applicability of those materials for large-scale application must be considered to further refine material selection.

Construction of a sensitive and specific lead biosensor using a genetically engineered bacterial system with a luciferase gene reporter controlled by pbr and cadA promoters

BACKGROUND

A bacterial biosensor refers to genetically engineered bacteria that produce an assessable signal in the presence of a physical or chemical agent in the environment.

METHODS

We have designed and evaluated a bacterial biosensor expressing a luciferase reporter gene controlled by pbr and cadA promoters in Cupriavidus metallidurans (previously termed Ralstonia metallidurans) containing the CH34 and pI258 plasmids of Staphylococcus aureus, respectively, and that can be used for the detection of heavy metals. In the present study, we have produced and evaluated biosensor plasmids designated pGL3-luc/pbr biosensor and pGL3-luc/cad biosensor, that were based on the expression of luc+ and under the control of the cad promoter and the cadC gene of S. aureus plasmid pI258 and pbr promoter and pbrR gene from plasmid pMOL30 of Cupriavidus metallidurans.

RESULTS

We found that the pGL3-luc/pbr biosensor may be used to measure lead concentrations between 1-100 μM in the presence of other metals, including zinc, cadmium, tin and nickel. The latter metals did not result in any significant signal. The pGL3-luc/cad biosensor could detect lead concentrations between 10 nM to 10 μM.

CONCLUSIONS

This biosensor was found to be specific for measuring lead ions in both environmental and biological samples.

Removal of Pb2+ from Aqueous Solutions Using K-Type Zeolite Synthesized from Coal Fly Ash

In this study, a novel zeolite (K-type zeolite) was synthesized from coal fly ash (FA), and adsorption capacity on Pb2+ was assessed. Six types of zeolite (FA1, FA3, FA6, FA12, FA24, and FA48) were prepared, and their physicochemical properties, such as surface functional groups, cation exchange capacity, pHpzc, specific surface area, and pore volume, were evaluated. The quantity of Pb2+ adsorbed by the prepared zeolites followed the order FA < FA1 < FA3 < FA6 < FA12 < FA24 < FA48. Current results indicate that the level of Pb2+ adsorbed was strongly related to the surface characteristics of the adsorbent. Additionally, the correlation coefficient between the amounts of Pb2+ adsorbed and K+ released from FA48 was 0.958. Thus, ion exchange with K+ in the interlayer of FA48 is critical for the removal of Pb2+ from aqueous media. The new binding energies of Pb(4f) at 135 and 140 eV were detected after adsorption. Moreover, FA48 showed selectivity for Pb2+ adsorption in binary solution systems containing cations. The results revealed that FA48 could be useful for removing Pb2+ from aqueous media.

Adsorptive removal of trivalent and pentavalent arsenic from aqueous solutions using iron and copper impregnated melanin extracted from the marine bacterium Pseudomonas stutzeri

The metalloid arsenic is one of the most conspicuous groundwater contaminants in the Indian subcontinent and its removal from aqueous medium is the main focus of this study. The study aims at functionalising melanin using iron and copper for the efficient removal of arsenic and rendering water fit for consumption. Melanin obtained from the marine bacteria Pseudomonas stutzeri was functionalised by iron impregnation (Fe-melanin) and copper impregnation (Cu-melanin). Morphological studies using FESEM portrayed the impregnated iron and copper granules on the surface of melanin, while XRD analysis confirmed the presence of Fe₂O₃ and CuO on melanin. Adsorption studies on As (V) and As (III) were conducted using Fe-melanin and Cu-melanin for different operating variables like pH, temperature and contact time. More than 99% per cent of As (III) and As (V) from water was removed at a pH range between 4 and 6 within 50 min in the case of Fe-melanin and 80 min for Cu-melanin. Adsorption equilibrium studies showed better fit with Langmuir adsorption isotherm and had good agreement with Redlich-Peterson's three-parameter model. The maximum adsorption capacities of Fe-melanin and Cu-melanin obtained from Langmuir adsorption model are 50.12 and 20.39 mg/g, respectively, for As (V) and similarly 39.98 and 19.52 mg/g, respectively, for As (III). Arsenic-binding to the functionalised melanin was confirmed using FT-IR and the XPS analysis. Reuse of the adsorbent was effectively done by desorbing the iron and copper together with the bound As (III) and As (V) and further re-impregnation of iron and copper in melanin. Re-functionalised melanin showed 99% adsorption efficiency up to four cycles of adsorption/desorption.

Adsorption characteristics and mechanism of Pb(II) by agricultural waste-derived biochars produced from a pilot-scale pyrolysis system

The objective of this study was to investigate the feasibility of removing Pb²⁺ by pilot-scale fluidized bed biochar, and then to put forward an industrial-scale fluidized bed pyrolysis progress of cogeneration of biochar and high-temperature gas. Corn stalk biochars (CSBs) were prepared at 400-600 °C, in which the maximum Pb²⁺adsorption capacity (Q_m) of CSB450 is 49.70 mg⋅g^-1 at the optimal condition. Adsorption isotherms, kinetics, and thermodynamics were determined, and Pb²⁺-loaded biochar was analyzed by fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD) and scanning electron microscope with energy dispersive spectrometer (SEM-EDS). Ion exchange, complexation and mineral precipitation together contributed to Pb²⁺ adsorption on CSBs. For high-temperature CSBs with fewer oxygen functional groups (OFGs) and stronger aromatization, Pb²⁺ adsorption by ion exchange and functional group complexation was reduced. The mineral precipitationwas formed during the adsorption process. Using the pilot-scale fluidized bed in this study, the carbon yield per year would achieve 31.79 t, and about 1.58 t of Pb²⁺ would be adsorbed according to the adsorption capacity at the pyrolytic temperature of 450 °C.The results are beneficial to screen for effective biochar as a cost-effective industrial adsorbent to remove Pb²⁺ in contaminated water.

Lead and cadmium adsorption by electrospun PVA/PAA nanofibers: Batch, spectroscopic, and modeling study

Water-stable PVA/PAA nanofibers were fabricated through electrospinning and evaluated for their performance in lead (Pb(II)) and cadmium (Cd(II)) removal from water in a batch experiment. The adsorption mechanism of Pb(II) was explored using the extended X-ray absorption fine structure (EXAFS) spectroscopic analysis. The PVA/PAA nanofibers showed a pH-dependent behavior for heavy metal removal, and its adsorption capacities for Pb(II) and Cd(II) could reach as high as 159 and 102 mg/g, respectively. The calcium ion (Ca(II)) had no effect on Pb(II) removal at pH 5.0 whereas it significantly reduced Cd(II) removal at pH 7.0. The adsorption of Pb(II) and Cd(II) was spontaneous and exothermic in nature with a decrease in randomness. The saturated PVA/PAA nanofibers could be regenerated using acidic solutions for reuse. The Fourier-transform infrared (FTIR) spectroscopic analysis indicated the formation of surface complexes between adsorbed Pb(II) and Cd(II) and carboxyl groups on PVA/PAA nanofibers. Moreover, EXAFS analysis suggested that a Pb(II) cation was chelated with three carboxyl groups on the nanofibers. This molecular-level adsorption structure was successfully implemented into a surface complexation model for the prediction of the macroscopic Pb(II) and Cd(II) adsorption behaviors. The results gained from this study provided complementary information on heavy metal removal by a new generation of adsorbents and improved the fundamental understanding for the removal process.

Tannins: Prospectives and Actual Industrial Applications

The origin of tannins, their historical evolution, their different types, and their applications are described. Old and established applications are described, as well as the future applications which are being developed at present and that promise to have an industrial impact in the future. The chemistry of some of these applications is discussed where it is essential to understand the tannins and their derivates role. The essential points of each application, their drawbacks, and their chance of industrial application are briefly discussed. The article presents historical applications of tannins, such as leather, or traditional medicine, and more recent applications.

Data on the removal of heavy metals from aqueous solution by adsorption using melanin nanopigment obtained from marine source: Pseudomonas stutzeri

Heavy metals are one of deadly contaminants in ground water across the globe. Thus, herein, this data set comprises experimental and modelled data on the removal of heavy metals from ground water using melanin synthesized by the marine bacteria Pseudomonas stutzeri. Characterization of biosynthesized melanin and modelling of the kinetic and the thermodynamic study on adsorption of heavy metals such as mercury (Hg(II)), lead (Pb(II)), chromium (Cr(VI)), and copper (Cu(II)) are included in this article. Apart from the study of parameters involved in adsorption such as pH, temperature, concentration and time; the data from these studies are modelled to analyze the nature and characteristic of heavy metals adsorbing to melanin nanoparticles. The figures from models, results from models as tables, characterization and analytical figures are depicted in this work.

Natural adsorbent based on sawdust for removing impurities in waste lubricants

Sawdust was expected to remove impurities in waste lubricant, and was modified with sodium hydroxide and triethanolamine, which can ameliorate its surface properties and improve its adsorption capacity. The increase of hydroxyl groups, the decrease of carbonyl groups and grafting new azyl after modification were beneficial for the adsorption of impurities. The surface area of modified sawdust is 0.969 m² g^-1, which is nearly 1.39 times as much as raw sawdust. The point of zero charge for modified sawdust decreased from 6.75 to 5.68 while the crystallinity of modified sawdust increased from 40.35 to 56.16. This research discovered that compared with raw sawdust and filter paper, modified sawdust possessed superior adsorption performances. The removal percentages for Si, Al, Fe, Cu was enhanced from 2.54%, 20.34%, 16.55%, 0.26% to 15.37%, 21.99%, 45.37%, 4.88%, respectively, while that for oxidation, aromatics, sulphation, soot and water was improved by 4.33, 4.69, 0.76, 1.20, 1.28 times at 80 °C with 1000 rpm for 12 h. The research has also explored the optimum adsorption conditions (adsorption temperature, adsorption time and rotation rate). The modified sawdust showed a stable adsorption capacity for impurities under different adsorption conditions.

Application of treated eggplant peel as a low-cost adsorbent for water treatment toward elimination of Pb2+: Kinetic modeling and isotherm study

In this study, treated eggplant peel was used as an adsorbent to remove Pb2+ from aqueous solution. For this purpose batch adsorption experiments were performed for investigating the effect of contact time, pH, adsorbent dose, solute concentrations, and temperature. In order to assess adsorbent’s physical and chemical properties, Fourier transform infrared spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy were used. The results showed that the adsorption parameters for reaching maximum removal were found to be contact time of 110 min, adsorbent dose of 0.01 g/ml, initial lead(II) concentration of 70 ppm, pH of 4, and temperature of 25°C. Moreover, for the experiments carried out at pH > 4 the removal occurred by means of significant precipitation as well as adsorption. Furthermore, these results indicated that the adsorption followed pseudo-second-order kinetics model implying that during the adsorption process strong bond between lead(II) and chemical functional groups of adsorbent surface took place. The process was described by Langmuir model (R2 = 0.99; maximum adsorption capacity 88.33 mg/g). Also thermodynamics of adsorption was studied at various temperatures and the thermodynamic parameters including equilibrium constant (K), standard enthalpy change, standard entropy change, and standard free energy changes were obtained from experimental data.

Wastewater treatment from ions of heavy and non-ferrous metals by ion-exchange adsorption

This article presents the results of experimental research on wastewater treatment from ions of heavy and non-ferrous metals by ion exchange adsorption. The object of investigation was a model solution containing ions of heavy and non-ferrous metals and prepared of wastewater from Turkestan locomotive depot. As a sorbent, phosphorus–acidic cationite KRF-10P was used. The impact of the cation exchanger mass, reaction time of cationite and temperature of the solution on the degree of wastewater treatment from ions of heavy and non-ferrous metals (Zn2+, Pb2+, Cd2+) were studied. On the basis of experiments, optimal conditions of wastewater treatment from ions of heavy and non-ferrous metals were established: mKRF-10P = 2.0 g, t = 1.0 h, T = 55°C. At the optimized conditions, the degree of wastewater treatment from zinc ions reached 96.1%, the degree of removal of lead ions reached 89%, the degree of removal of cadmium ions reached 95%. Experimental results showed the possibility of wastewater treatment from ions of heavy and nonferrous metals by ion exchange adsorption using phosphorus–acidic cationite KRF-10P.

Adsorption of Heavy Metal Ions on Virgin and Chemically-Modified Lignocellulosic Materials

Amidoximated wood sawdust (Am-WS) and wood flour (Am-WF) were prepared using the same procedure as described recently for amidoximated cellulose (Am-Cell). The modified supports thus obtained were characterized by IR, TGA and DSC methods. In comparison to the untreated material, such treatment led to a considerable increase in adsorption capacity towards heavy metal ions from aqueous solution. The quantity adsorbed increased with pH, initial metal ion concentration and immersion time. The formation of a 1:1 complex between the amidoxime group and Cu(II), Cr(III) and Cd(II) ions and a 2:1 complex with the Ni(II) ion was demonstrated by the adsorption limit values. Overall, Am-WS and Am-WF exhibited similar behaviour to Am-Cell and are suitable for the treatment of wastewaters containing heavy metal ions.

Removal of Cu2+ Ions from Aqueous Solutions by Carbon Nanotubes

Carbon nanotubes (CNTs), a new crystalline form in the carbon family, have been shown to be an effective adsorbent for Cu2+ ion removal from aqueous solution. After oxidation with nitric acid, the adsorption capacity of the oxidized CNTs towards Cu2+ ions at a pH of 5.2 reached 27.6 mg/g, compared to a value of only 14.4 mg/g for the as-grown CNTs under the same circumstances. Increasing the pH to 5.4 led to 95% removal of Cu2+ ions with the oxidized CNTs, whereas with the as-grown CNTs it was necessary to increase the pH to 8.6 to achieve the same extent of removal. The Cu2+ ion adsorption capacity increased with increasing CNT dosage for the different initial Cu2+ ion concentrations. The kinetic curve for adsorption of the Cu2+ ions suggested that not only the outer surfaces but also inner cavities and inter-layers in the structures of the CNTs were responsible for the removal of the ion from aqueous solutions.

Removal of Cu (II) and Pb (II) from Aqueous Solution using engineered Iron Oxide Nanoparticles

Nano-sized Fe₃O₄ and Fe₂O₃ were synthesized using a precipitation method. The nanomaterials were tested as adsorbents for the removal of both Cu²⁺ and Pb²⁺ ions. The nanomaterials were characterized using X-ray powder diffraction to determine both the phase and the average grain size of the synthesized nanomaterials. Batch pH studies were performed to determine the optimum binding pH for both the Cu²⁺ and Pb²⁺ to the synthesized nanomaterials. The optimum binding was observed to occur at pH 4 and above. Time dependency studies for Cu²⁺ and Pb²⁺ showed the binding occurred within the first five minutes of contact and remained constant up to 2 hours of contact. Isotherm studies were utilized to determine the binding capacity of each of the nanomaterials for Cu²⁺ and Pb²⁺. The binding capacity of Fe₃O₄ with Cu²⁺ and Pb²⁺ were 37.04 mg/g and 166.67 mg/g, respectively. The binding capacities of the Fe₂O₃ nanomaterials with Cu²⁺ and Pb²⁺ were determined to be 19.61 mg/g and 47.62 mg/g, respectively. In addition, interference studies showed no significant reduction in the binding of either Cu²⁺ or Pb²⁺ to the Fe₃O₄ or Fe₂O₃ nanomaterials in the presence of solutions containing the individual ions Na⁺, K⁺, Mg²⁺ and Ca²⁺ or a solution consisting of a combination of all the aforementioned cations in one solution.

Synthesis of a functionalized fibrous adsorbent of high uptake capacity: a study on Pb(ii) uptake and simple acidic site model development

Development and exposure of acidic functional groups on lignocellulose biomaterials through destruction of lignin barrier by acid treatment.

Competitive Adsorption of Cadmium(II) and Mercury(II) Ions from Aqueous Solutions by Activated Carbon from Xanthoceras sorbifolia Bunge Hull

This paper presents low-cost and recyclable activated carbon (XLAC) derived from Xanthoceras sorbifolia Bunge hull for high-efficiency adsorption of Cd(II) and Hg(II) ions in industrial wastewater. XLAC was prepared through H3PO4 activation and was characterized using N2 adsorption-desorption, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX), and Fourier transform infrared (FTIR) spectroscopy. In single-metal-system adsorption experiments, the maximum adsorption capacities for Cd(II) and Hg(II) obtained under different experimental conditions were 388.7 and 235.6 mg·g−1, respectively. All adsorption equilibrium data fit perfectly with the Langmuir isotherm model. In a binary metal system, competitive studies demonstrated that the presence of Cd(II) significantly decreased the adsorption of Hg(II), but the adsorption of Cd(II) showed a little change in the presence of Hg(II). In addition, XLAC can be regenerated with a 0.01 mol·L−1 HNO3 solution and reused at least four times. The FTIR spectra revealed that a chemical interaction occurs between functional groups containing lone electron pairs in XLAC and metal ions. Overall, these results suggest that XLAC may be suitable as an adsorbent for heavy metal removal from wastewater streams.

A review on progress of heavy metal removal using adsorbents of microbial and plant origin

Heavy metals released into the water bodies and on land surfaces by industries are highly toxic and carcinogenic in nature. These heavy metals create serious threats to all the flora and fauna due to their bioaccumulatory and biomagnifying nature at various levels of food chain. Existing conventional technologies for heavy metal removal are witnessing a downfall due to high operational cost and generation of huge quantity of chemical sludge. Adsorption by various adsorbents appears to be a potential alternative of conventional technologies. Its low cost, high efficiency, and possibility of adsorbent regeneration for reuse and recovery of metal ions for various purposes have allured the scientists to work on this technique. The present review compiles the exhaustive information available on the utilization of bacteria, algae, fungi, endophytes, aquatic plants, and agrowastes as source of adsorbent in adsorption process for removal of heavy metals from aquatic medium. During the last few years, a lot of work has been conducted on development of adsorbents after modification with various chemical and physical techniques. Adsorption of heavy metal ions is a complex process affected by operating conditions. As evident from the literature, Langmuir and Freundlich are the most widely used isotherm models, while pseudo first and second order are popularly studied kinetic models. Further, more researches are required in continuous column system and its practical application in wastewater treatment.