Initial Pb2 Research Articles

Sodium bicarbonate-hydroxyapatite used for removal of lead ions from aqueous solution

This study reports the development of a novel biocomposite for potential applications in the environmental remediation. The hydroxyapatite/sodium bicarbonate (HAp-SB) biocomposite obtained by a cheap method could offer promising characteristics to be used in environmental applications. The obtaining of HAp-SB ceramic composites was studied with the aim of increasing the adsorption efficiency of lead ions from contaminated waters. A composite material (HAp-SB) with good crystallinity that preserves the hexagonal structure of pure hydroxyapatite was obtained. For the powder recovered after decontamination of the lead solution (PbHAp-SB), the XRD model highlighted additional maxima belonging to Ca10(PO4)5(OH)2, Ca0.805Pb4.195(PO4)(OH) and PbH2P2O7. The FTIR spectra of PbHAp-SB are similar to those of HAp-SB composites showing a broadening of the vibration peaks and a slight shift. The XPS and EDS studies illustrated the purity of the HAp-SB sample. Moreover, the presence of lead in the powder recovered after decontamination was also highlighted by XPS and EDS studies. The efficiency of HAp-SB in the adsorption of Pb2+ ions from the contaminated solution was also highlighted by ultrasound studies using double-distilled water as the reference liquid. The adsorption kinetics were investigated with the aid of Langmuir and Freundlich theoretical models. The results demonstrated that the HAp-SB ceramic composite has a strong affinity for the adsorption of Pb2+ ions from contaminated solutions. The removal efficiency of Pb2+ ions was about 92% for the initial Pb2+ concentration above 50 mg/L. The results of the cell viability and cytotoxicity studies demonstrated that HAp-SB nanoparticles did not influence negatively the HeLa cell's viability and did not induce any significant changes of the morphological features of HeLa cells after 24 h of incubation. The batch adsorption results as well as the cytotoxicity assay results suggested that the HAp-SB powder could be successfully used for the removal of Pb2+ from contaminated water.

Performance of cross-linked chitosan-zeolite composite adsorbent for removal of Pb2+ ions from aqueous solutions: Experimental and Monte Carlo simulations studies

In this study, we investigated the performance of a cross-linked chitosan (Ch)-zeolite (Z) composite (Ch-Z) adsorbent for the removal of Pb2+ ions from water. The results revealed that the Ch-Z composite exhibited excellent adsorption performance for Pb2+ ions. The maximum adsorption capacity was found to be 275 mg g−1 at pH 4.5, Ch-Z composite dose of 5 g/L and an initial Pb2+ concentration of 1000 mg/L for 24 h. The adsorption equilibrium data and its kinetics followed a Langmuir and PSO models. Furthermore, thermodynamic parameters were determined, indicating that adsorption was spontaneous and endothermic. MC simulations were used to investigate the interaction between Pb2+ ions and the modeled composite. The considerable negative adsorption energy values confirm the strong affinity between the adsorbate molecules and the adsorbent surface. Overall, the Ch-Z composite adsorbent exhibited remarkable potential to remove Pb2+ ions from wastewater.

Performance and mechanisms of active attapulgite-supported sulfidated nanoscale zero-valent iron materials for Pb(II) removal from aqueous solution

To inhibit the oxidation, passivation, and agglomeration of nano-zero-valent iron (nZVI), a liquid phase reduction method was used to load sulfurized nZVI onto acid-modified ATP with attapulgite (ATP) as the carrier (S-nZVI@ATP). The performance and mechanism of this material were studied for Pb2+ removal in water. The S-nZVI@ATP preparation prevents the agglomeration of nZVI particles and reduces nZVI oxidation. Pb2+ removal proceeds efficiently and stably when using S-nZVI@ATP at pH values ranging from 2.5–5.5. According to the electron sharing and transfer-based pseudo-second-order kinetic model, the Pb2+ is adsorbed onto S-nZVI@ATP, and the speed control step is completed by liquid film diffusion and intraparticle diffusion. The S-nZVI@ATP mediated Pb2+ adsorption is well-described by Freundlich’s isothermal adsorption model, which is a multilayer chemical adsorption process. The temperature and initial Pb2+ concentration were varied, and it was determined that Pb2+ adsorbs on S-nZVI@ATP in an endothermic reaction. This S-nZVI@ATP composite material has high reducibility, high surface activity, and good adsorption properties for Pb2+. Tests were performed for 24 h using adsorbent (1 g l−1) in Pb2+ solution (30 ml). For an initial Pb2+ concentration of 700 mg l−1, S−1-nZVI@ATP removes 57.37% of the Pb2+ and has an adsorption capacity of 401.60 mg g−1. In addition to forming PbS and Pb(OH)2 precipitates, Pb2+ also complexes with the Fe/H oxide shell of S-nZVI@ATP, and Fe0 reduces some Pb2+ on the nZVI to Pb0. The results exhibited that S-nZVI@ATP has excellent potential as an adsorbent for the removal of Pb2+ from the industrial wastewater.

Magnetic sepiolite/iron(III) oxide composite for the adsorption of lead(II) ions from aqueous solutions

AbstractClay minerals are effective adsorbents used for the remediation of toxic heavy metals from wastewater due to their large surface areas and great cation-exchange capacities. In this study, the removal of lead ions from aqueous solutions via adsorption was investigated using raw and iron-modified Turkish sepiolite. The aim of this study was to examine the effects of modification and environmental conditions on the sorptive properties of sepiolite samples. Initially, the raw sepiolite (Sep) and magnetic sepiolite/Fe2O3 composite (MagSep) prepared using the co-precipitation method were characterized via mineralogical and petrographical means and the physicochemical properties were determined. Then, the batch adsorption of lead (Pb2+) ions on the sepiolite samples was examined under various conditions (solution pH, adsorbent dosage, contact time, initial Pb2+ ion concentration, temperature, shaking rate). The adsorption capacity of MagSep was found to be greater than that of Sep under all experimental conditions. The results showed that the adsorption process followed a pseudo-second-order kinetic model, and the Langmuir isotherm best correlated with the experimental data. The maximum adsorption capacities were found to be 60.6 and 90.1 mg g–1 for Sep and MagSep, respectively. The characterization of the Pb-adsorbed sepiolite samples showed that lead formed covalent bonds with the sepiolite samples and attached to the sepiolite surface mainly through ion exchange. MagSep can be used efficiently in the field of wastewater treatment for the removal of Pb2+ ions as it does not release any toxic pollutants and can be separated easily with the use of a magnetic field.

Mechanistic insight into lead immobilization on bone-derived carbon/hydroxyapatite composite at low and high initial lead concentration

The contamination of heavy metal lead has a serious impact on the natural environment and organisms. Among various materials for lead removal, animal bone derived hydroxyapatite has received extensive attention. However, there are different opinions among researchers regarding the mechanism of lead removal by hydroxyapatite, possibly due to varying initial lead concentrations used in different studies and lack of accuracy in the study of lead removal mechanisms. In present work, we synthesized a carbon-containing hydroxyapatite (CHAP) through pyrolysis of bovine bone with excellent lead removal efficiency, and further investigated the lead removal mechanism of CHAP under high and low initial lead concentrations by combining XRD Rietveld refinement, FTIR, XPS, HRTEM etc. methods. The results showed that under low initial Pb2+ concentration condition, the main mechanism of lead removal by CHAP was chemical precipitation (94.1 %), with small contributions of lead complexation with carbon functional groups and cation-π interactions on the amorphous carbon in CHAP, and surface adsorption on the precipitates. Under high initial Pb2+ concentration condition, chemical precipitation remained the main mechanism (74.68 %), but the contributions of the other three mechanisms increased, and ion exchange appeared in the later stage of the removal process. This study provides new insights on the lead immobilization mechanism by CHAP at different initial Pb2+ concentrations in water.

Exploring the Potential of Aerated Concrete and Clay Bricks from Construction and Demolition Waste as Adsorbents for Pb(II) Removal from Aqueous Solutions

This study aimed to evaluate the potential of utilizing aerated concrete (AC) and clay bricks (CB) sourced from construction and demotion waste (CDW) as low-cost adsorbents for the removal of Pb2+ from aqueous solutions. The effects of various parameters, including particle size, solution pH, contact time, adsorbent dosage, and initial Pb2+ concentration, were analyzed through batch experiments. The results indicated that AC performed more efficiently in removing lead ions than CB under all the tested conditions. The highest removal efficiency of Pb2+ with AC was 99.0%, which was achieved at a pH of 5.0, contact time of 1 h, an adsorbent dosage of 5 g/L, and an initial Pb2+ concentration of 100 mg/L. The maximum adsorption capacities of AC and CB were 201.6 mg/g and 56.3 mg/g, respectively. The adsorption isotherm data of the adsorbents were successfully modeled using both the Langmuir and Freundlich models. The removal of lead ions from aqueous solutions by both adsorbents is primarily achieved through adsorption and microprecipitation. Compared to CB, AC exhibited superior performance, attributed to its larger specific surface area, pore volume, and alkalinity. The cost-effectiveness and availability of AC make it a promising candidate for treating of Pb-contaminated wastewater, providing a new way for resource utilization of CDW.

Fabrication of hyperbranched polyamidoamine immobilized mesocellular siliceous foam for rapid decontamination of lead(II) from aqueous solution

Developing of adsorbents with merits of higher adsorption capacity and quicker adsorption equilibrium through facile method merits more attention. Generally, large specific surface area porous adsorbent coupled with multi functional groups is a wise option. In the current work, a feasible protocol of preparing efficient adsorbent toward Pb2+ was established via integrating amino abundant hyperbranched polyamidoamine and bimodal pore structured mesocellular siliceous foam. The polyamidoamine was synthesized through a vacuum thermo polymerization method by gradually elevating temperature. The uniform spherical mesocellular siliceous foam substrate was prepared via inorganic salt-assisted soft-template method, and the pore structure and particle morphology were adjusted through post hydrothermal treatment. The obtained hyperbranched polyamidoamine immobilized mesocellular siliceous foam was characterized using FT-IR, SAXS, BET, SEM, TEM, TGA and zeta potential measurement techniques. Large specific surface area, unique bimodal pore structure with interconnected spherical and window pore and ultra large pore diameter rendered the adsorbent high adsorption capacity and efficient elimination. Batch experiment results elucidated that various operating parameters including pH, contact time, initial Pb2+ concentration, temperature and ionic strength deemed to be at play in adsorption behavior. The measured experimental maximum adsorption capacity at 298.15 K was 142.87 mg·g−1. The equilibrium data fitted well by pseudo second order kinetic model unveiled that the rate determining step might be chemical adsorption. The adsorption behavior was found to more suitable described with Langmuir isotherm model, implying the formation of adsorbate monolayer, and thus a maximum adsorption capacity of 315.46 mg·g−1 at 298.15 K was estimated. An underlying spontaneous entropy increased endothermic nature of adsorption of Pb2+ by the as-prepared adsorbent was conceived through adsorption thermodynamics study. Furthermore, a possible adsorption mechanism of comprehensive interaction of chemical chelation and ion exchange was proposed. This study supports the prospect that hyperbranched polyamidoamine immobilized mesocellular siliceous foam can serve as a candidate for efficiently removing Pb2+ from aqueous solution.

Adsorptive removal of stable and radioactive Pb(II) isotopes from aqueous solution using bentonite, zeolite and perlite: characterization, isotherm and thermodynamic studies

AbstractIn this study, stable and radioactive lead removal from aqueous solution by adsorption using bentonite, zeolite and perlite minerals obtained from various locations in Türkiye was studied in batch experiments. The adsorbents were first characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS), and then the physicochemical properties were determined. The effects of various factors that influence adsorption, such as solution pH, adsorbent dosage, contact time, initial Pb2+ ion concentration, temperature and shaking rate, were studied. The adsorption of Pb2+ was modelled using the Langmuir, Freundlich and Dubinin–Radushkevich isotherms. The adsorption capacities of the minerals for Pb2+ followed the order: bentonite > zeolite > perlite, and the maximum adsorption capacities were 131.6, 36.1 and 21.5 mg g–1, respectively. The adsorption data fit well with the Langmuir isotherm. The bonding of lead ions on the adsorbents was confirmed by XRF and FTIR analyses after the adsorption process. The adsorption of Pb2+ ions on the adsorbents was spontaneous and endothermic. The adsorption process took place by cation exchange in addition to electrostatic interaction. Furthermore, radioactive 210Pb2+ adsorption on bentonite, zeolite and perlite was studied, with the analyte being analysed using a liquid scintillation counter. It was seen that in addition to Pb(II) ions, these minerals also adsorbed the radioactive decay products of 210Pb, which were 210Po and 210Bi. The removal percentages of 210Pb were 95%, 38% and 30% and those of 210Po were 75%, 60% and 74% for bentonite, zeolite and perlite, respectively.

Adsorption of lead ions by magnetic carbon: Comparison of magnetic carbon properties and modification methods

Magnetic biochar (MBC) is extensively used to remove contaminants from environmental media because of being easy to recover and separate. However, magnetic modification generally decreases the surface area of Biochar (BC), leading to an insignificant improvement in adsorption performance. In the present study, research was conducted on the changes in the physicochemical characteristics of the modified MBC in terms of elemental distribution, morphological characteristics, and surface functional groups based on magnetic carbon. Magnetic carbon was prepared using pine cone material and modified by four methods (ball milling, acid and oxidant modifications as well as metal impregnation). The role of contact time (0.25–8 h), initial Pb2+ concentration (5–200 mg/L), solution pH (2-7), and other process parameters in removing Pb2+ from the contaminated water was evaluated. The results showed that the maximum adsorption of Pb2+ by MBC reached up to 123.38 mg/g when time varied from 0.25 to 8 h. The proposed secondary kinetic and Langmuir isotherm models better proved the results of adsorption. The adsorption performance of ball milling modified MBC (BMBC) was evenly enhanced to varying degrees by several modification methods, especially ball milling with green and low-cost, a simple mechanical process to enhance the number and surface area of functional groups of MBC.

Efficient and selective removal of Pb2+ from aqueous solutions by modified metal-organic frame materials

The broad application of lead in various industries has caused it to accumulate in the environment, with severe implications for human health. There is an urgent need to develop efficient separation materials for treating lead-containing wastewater. In this study, a novel metal-organic framework material (UIO-66-TETA) was prepared using triethylenetetramine (TETA) as a modifier and applied to remove Pb2+ from water. The material was characterized by SEM, EDS, BET, XRD, FTIR, XPS, and other analytical methods. The results indicated that TETA was successfully introduced into the material surface, and the original crystal structure and morphology were maintained. The effects of pH, contact time, initial Pb2+ concentration, and temperature on Pb2+ removal were systematically investigated. Adsorption experimental data were consistent with the pseudo-second-order kinetic model and the Langmuir adsorption isotherm model. The adsorption thermodynamic analysis revealed that the adsorption process was endothermic and spontaneous. UIO-66-TETA had excellent adsorption selectivity for Pb2+ even in a mixed solution containing many other heavy metal ions. Regeneration experiments showed that UIO-66-TETA has good regeneration performance. Based on the results obtained in this work, it can be concluded that UIO-66-TETA can be used as an ideal adsorbent for the removal of Pb2+.

Chitosan Polymer Functionalized-Activated Carbon/Montmorillonite Composite for the Potential Removal of Lead Ions from Wastewater.

A simple approach for synthesizing a highly adsorbent composite was described for the uptake of heavy metal ions from wastewater. A simple approach for synthesizing a highly adsorbent composite was also described for the elimination of heavy metal ions from contaminated water. The nanocomposite was synthesized via a polymer grafting of chitosan on the activated carbon surface, followed by a stacking process with the layers of montmorillonite clay. The spectroscopic analyses were exploited to confirm the composite structure of the prepared materials. Various adsorption parameters, such as pH, initial concentration, and adsorption time, were assessed. The results showed that the adsorption capacity of the composite for Pb2+ ions increased as the pH increased until it reached pH 5.5. The maximum adsorption capacity was observed at an initial Pb2+ level of 20 mg/L and a contact time of 150 min. Kinetic models were evaluated, and the pseudo second-order model showed the best match. The adsorption isotherm data were processed by fitting the model with different isotherm behaviors, and the Langmuir isotherm was found to be the most suitable for the system. The maximum adsorption capacity for Pb2+ ion on the MMT/CS/AC composite was found to be 50 mg/g at pH 5.5. Furthermore, the composite maintained a high adsorption capability of 85% for five adsorption-desorption cycles. Overall, this composite is envisioned as an addition to the market of wastewater remediation technology due to its chemical structure, which provides influential functional groups for wastewater treatment.

Experimental study on evaluation and optimization of heavy metals adsorption on a novel amidoximated silane functionalized Luffa cylindrica

This study aimed to synthesize an amidoximated Luffa cylindrica (AO-LC) bioadsorbent, and evaluate its efficiency in the adsorption of heavy metals from the aqueous solutions. For this purpose, NaOH solution was used to alkaline treatment of Luffa cylindrica (LC) fibers. The silane modification of LC was performed using 3-(trimethoxysilyl)propyl methacrylate (MPS). Polyacrylonitrile (PAN)/LC biocomposite (PAN-LC) was synthesized by PAN grafting onto the MPS-modified LC (MPS-LC). Finally, the AO-LC was obtained by the amidoximation of PAN-LC. The chemical structures, morphology, and thermal properties of biocomposites were characterized by the infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and field emission scanning electron microscopy. The results showed a successful grafting of MPS and PAN on the surface of LC. The order of heavy metals adsorption on AO-LC was: Pb2+ > Ag+ > Cu2+ > Cd2+ > Co2+ > Ni2+. The effects of operational parameters on the Pb2+ adsorption were studied using Taguchi experimental design method. Statistical analysis of the results showed that the initial Pb2+ concentration and the bioadsorbent dosage significantly affect the adsorption efficiency. The adsorption capacity and removal percentage of Pb2+ ions were obtained as 18.88 mg/g and 99.07%, respectively. The Langmuir isotherm and Pseudo-second order kinetics models were found to be better compatible with experimental data as a consequence of the isotherm and kinetics analysis.

Utilization of Enterobacter cloacae WW1 Biomass for Biosorption of Lead(II) from Aqueous Solution

The present study evaluated lead biosorption by Enterobacter cloacae WW1 isolated from tannery wastewaters under different initial Pb2+ concentrations, biomass concentrations, and contact times. The results showed that at an initial Pb2+ concentration of 80 mg.L-1, the optimal conditions for living cells were a biomass concentration of 7 g.L-1 and a contact time of 120 min. For non-living cells, biomass was a biomass concentration of 4 g.L-1 and contact time of 45 min, which provided removal efficiencies of 92.03 ± 0.10% and 99.51 ± 0.01%, respectively. The maximum biosorption capacity obtained for non-living cells using an initial Pb2+ concentration of 640 mg.L-1 was 76.65 ± 0.05 mg.g-1. The equilibrium data followed the Langmuir and Freundlich models for living cells, and the data for non-living cell biosorbents fit the Langmuir model. The biosorption kinetics for living and non-living cells fit well with a pseudo-second-order kinetic equation. SEM-EDX analysis clearly showed the morphology and presence of Pb2+ particles on non-living cell surfaces after biosorption. In addition, the results revealed that functional groups such as hydroxyl, amino, carboxyl, amide, and phosphate groups on the bacterial cell surface detected by FTIR were associated with the binding of Pb2+ ions. The results indicated that E. cloacae WW1, a lead-resistant bacterium, can be used as an alternative biosorbent for lead removal from wastewater.

Efficient lead immobilization by bio-beads containing Pseudomonas rhodesiae and bone char

Mineralization of lead ions (Pb2+) to pyromorphite using phosphorus-containing materials is an effective way to remediate lead (Pb) contamination. Bone char is rich in phosphorus, but its immobilization of Pb2+ is limited by poor phosphate release. To utilize the phosphorus in bone char and provide a suitable growth environment for phosphate-solubilizing bacteria, bone char and Pseudomonas rhodesiae HP-7 were encapsulated into bio-beads, and the immobilization performance and mechanism of Pb in solution and soil by bio-beads were investigated. The results showed that 137 mg/g of phosphorus was released from bone char in the presence of the HP-7 strain. Pb2+ removal efficiency reached 100 % with an initial Pb2+ concentration of 1 mM, bone char content of 6 g/L, and bio-bead dosage of 1 %. Most Pb2+ was immobilized on the surface of the bio-beads as Pb5(PO4)3Cl. The soil remediation experiments showed a 34 % reduction in the acid-soluble fraction of Pb. The bio-beads showed good stability in long-term (30 d) soil remediation. The present study shows that bone char can be turned into an efficient Pb immobilization material in the presence of phosphate-solubilizing bacteria. Thus, bio-beads are expected to be used in the remediation of Pb-contaminated environments.

Artificial neural network approach for lead removal from aqueous solution by agricultural waste derived biochars

Lead (Pb2+) which is one of the most important heavy metals found in water sources, has a toxic effect on living things in aquatic environment. Therefore, the removal of Pb2+ ions from wastewater is very important if its concentration is above the determined discharge limits. Due to its advantage such as high efficiency, the adsorption process is a widely used successful technique for heavy metals removal from an aqueous solutions. On the other hand, determining the adsorption efficiencies of different adsorbents experimentally is both costly, and time-consuming considering that there are large number of process variables. Therefore, ANN can be used to make theoretical predictions with high efficiency in this treatment process. In this study, modeling of Pb2+ removal from an aqueous solution by using biochars that produced by pyrolyzing of hazelnut, and walnut shell was studied at different adsorption conditions; pH (2.5-5), temperature (25-45oC), initial Pb2+ concentration (15-45 mg/L), adsorbent amount (1-3 g/L), and mixing speed (200-600 rpm). The purpose of modeling studies with ANN approach was to estimate lead ions removal (%) as an output. Inputs for ANN modeling approach were selected as pH, initial Pb2+ concentration, temperature, adsorbent dosage, and mixing speed. Experimental data were categorized 50:25:25 for two adsorption systems. Levenberg-Marquardt (LM) was preferred as a training function, and tansig was used as an activation function. The number of hidden neurons in the hidden layer was found by trial, and error. Values of correlation coefficient (R2), and Mean Square Error (MSE) were taken to be performance criteria of the ANN modeling. R2 values were found to be 97%, and 98% for biochars derived from walnut, and hazelnut shells, respectively. Results showed that ANN is an effective tool for modeling of adsorption system for the removal of lead ions from an aqueous solution. Additionally, different training algorithms such as Bayesian Regularization (BR), and Scaled Conjugate Gradient (SCG) were used to compare the prediction capability.

Effective Adsorption of Pb2+ on Porous Carbon Derived from Functional Octadecahedron ZIF-8

An adsorbent ZO (oxidized ZIF-8-derived carbon) was prepared on the ZIF-8-derived carbon (ZC) by modified Hummer’s method. The removal rate and adsorption amount of Pb2+ were measured on the different molar ratios of 2-Hmim to 2, 2′-bipyridine in ZO, including 1:1 (1:1 ZO) and 1:2 (1:2 ZO). The adsorption experiments show that the best condition to adsorb Pb2+ in Pb2+ solution for 1:1 ZO is an adsorbent dosage of 20 mg, adsorption time of 16 h, initial Pb2+concentration of 15 mg/L, and pH = 3; that for 1:2 ZO is the adsorbent dosage of 15 mg, adsorption time of 18 h, initial Pb2+ concentration of 15 mg/L, and pH = 4. The adsorption data fits the quasi-second-order kinetics (R2 = 0.99998), indicating that chemical adsorption plays a leading role. The fitted isotherm adsorption curve is more consistent with the Langmuir adsorption model (1:1 ZO, R2 = 0.95058; 1:2 ZO, R2 = 0.97488). The competitive adsorption results show that the removal rate of Pb2+ by 1:1 ZO and 1:2 ZO is more than 98%, indicating that 1:1 ZO and 1:2 ZO have a superior selectivity for Pb2+ competing with Cu2+ and Fe2+. The maximum adsorption amount of Pb2+ is 15.52 mg/g by 1:1 ZO and 18.09 mg/g by 1:2 ZO. This study shows that 1:2 ZO is more helpful for the removal of Pb2+ than 1:1 ZO.

Effect of Butyl Xanthate on Pb2+ and Cd2+ Adsorption by Soil Around a Dressing Plant

Flotation agents can enter the soil and water environment around mining areas through beneficiation wastewater discharge and overflow from tailings ponds. The adsorption of Pb2+ and Cd2+ on soil around a lead-zinc dressing plant was investigated in the presence of potassium butyl xanthate (PBX). Batch experiments were conducted with different initial pH, PBX, Pb2+, and Cd2+solution concentrations. The fractions of lead and cadmium were altered after treatment with different concentrations of PBX. The results showed that adsorption of Pb2+and Cd2+ on soil was seriously inhibited by PBX. When PBX concentration was 40 mg·L-1, the adsorption capacity of Pb2+ and Cd2+ decreased from 3540 mg·kg-1 and 387 mg·kg-1 to 3085 mg·kg-1 and 100 mg·kg-1, respectively. The Pb2+ and Cd2+ adsorption kinetic process was best fitted by the quasi-second-order kinetic model, which indicated that the adsorption process of Pb2+ and Cd2+ on soil was mainly chemical adsorption. The formation of a hydrophobic and insoluble complex and competitive adsorption between PBX, Pb2+, and Cd2+ on the soil surface was the main reason for reducing the adsorption capacity. The results showed that PBX could increase the mobility of Pb2+ and Cd2+ on soil. The degree of impact improved with increasing initial concentration of PBX and pH but decreased with increasing initial concentration of Pb2+ and Cd2+, and the adsorption isotherms conformed to the Freundlich isotherm. Under low PBX content (100 mg·kg-1), exchangeable and reducible cadmium contents in the soil increased, which could lead to the activation of cadmium in soil. However, the addition of PBX to the treated soil could reduce the content of exchangeable and reducible lead. As the concentration of PBX increased, the reduction effect also increased, which was related to the stronger complex stability of Pb(C4H9OCS2)2 than that of Cd(C4H9OCS2)2. The results showed that residual flotation reagents in beneficiation wastewater may increase the potential ecological risk of heavy metals such as Pb and Cd in soil, and the prevention and control of the potential ecological risk should be strengthened.

Sodium modification of low quality natural bentonite as enhanced lead ion adsorbent

Developing efficient and low-cost adsorbent for removing heavy metal ions from aqueous solution is of great significance for environmental protection. Herein, low quality natural bentonite was purified and sodium-modified to adsorb Pb2+ from the aqueous phase. The effects of initial pH value of the solution, type and amount of the adsorbent, contact time and initial Pb2+ concentration on the adsorption performance of sodium bentonite were systematically studied. The adsorption efficiency of sodium bentonite was significantly better than that of purified bentonite and natural bentonite toward Pb2+. Under the optimum adsorption conditions of pH = 5, adsorbent dosage of 0.2 g, initial Pb2+ concentration of 400 mg/L, and adsorption time of 120 min, sodium bentonite can remove more than 99.94% of Pb2+. Adsorption behavior fitted well with Freundlich isotherm and pseudo-second-order kinetics adsorption equations. Adsorption process was endothermic and feasible. The adsorption pathways of Pb2+ on sodium bentonite are mainly including ion exchange, surface hydroxyl functional group capture, electrostatic attraction and chemical precipitation by CO32- in the pore channel to form PbCO3. This research is anticipated to give technical support for prompting the wider application of bentonite as an adsorbent material.

Magnetically functionalized alunite as a recyclable and ecofriendly adsorbent for efficient removal of Pb2+

Alunite (KAl3(SO4)2(OH)6) was evaluated for Pb2+ removal after magnetically functionalization (MagA) which led to a considerable improvement in the natural mineral's characteristics and adsorption capability. Pb2+ adsorption was investigated in both batch and column systems concerning the influence of pH, MagA amounts, contact time, initial Pb2+ concentration, ionic strength, flow rate, and bed height. The maximum Pb2+ adsorption performance was obtained at pH 5.0. The pseudo–second–order kinetic and Langmuir isotherm models were found to characterize the adsorption process. MagA had a monolayer Pb2+ adsorption capacity of 158.73 mg g−1. Application tests with real wastewater have shown that MagA has satisfactory adsorption performance (>90%) for practical applications as well. Furthermore, the adsorption efficiency of Pb2+ ions in dynamic flow mode was still around 80% after 10 consecutive cycles. MagA was characterized by infrared (IR), Brunauer–Emmett–Teller (BET), scanning electron microscope (SEM), energy dispersive X-ray (EDX), isoelectric point (IEP), and vibrating sample magnetometer (VSM) analysis. Thermodynamic analysis indicated that the binding of Pb2+ ions to MagA was endothermic. The maximum breakthrough capacity calculated from the breakthrough curve at the exhausted point was 31.1 mg g–1. The estimated cost of preparing MagA was calculated to be 6.70 USD/kg. Overall, the findings clearly showed that the MagA seems to be an eco-friendly, economic, and recyclable adsorbent for the removal of toxic Pb2+ from wastewaters.

High lead ion removal in a single synthetic solution utilising plant-based Tacca leontopetaloides biopolymer flocculant (TBPF)

The present study aimed to remove lead ions (Pb2+) in a single synthetic solution by employing a plant-based Tacca leontopetaloides biopolymer flocculant (TBPF). The ions were eliminated through the flocculation process via the Jar test experiment. The maximum Pb2+ removal was determined based on one-factor-at-a-time (OFAT) and central composite design (CCD). Based on the OFAT, the maximum Pb2+ eliminated, 83%, was achieved at pH 6 synthetic solution, 2.5 mg/L initial Pb2+ concentration, and 3% initial TBPF concentration at 192 mg/L dosage. The highest Pb2+ removal of 73% was recorded at pH 6.4 synthetic solution with 11.8 mg/L initial Pb2+ concentration at a constant 3% initial TBPF concentration and 192 mg/L TBPF dosage when the CCD was employed. The excellent Pb2+ removal with the environmentally friendly plant-based TBPF utilised in the current study demonstrated outstanding potential in industrial heavy metal treatments, particularly at the primary stages.