High adsorption capacity and super selectivity for Pb(Ⅱ) by a novel adsorbent: Nano humboldtine/almandine composite prepared from natural almandine

Application of positively charged red mud-based carriers for anaerobic ammonium oxidizing bacteria biofilm formation

Enrichment of anaerobic ammonium oxidizing bacteria (AnAOB) in the anaerobic ammonium oxidation (anammox) process remains a challenge in engineering applications. In this study, for faster enrichment of AnAOB, red mud-based carriers were positively charged with FeCl3 and microbial promoters. The experimental results showed that the average nitrogen removal rates of the red mud-based carriers (RMGA), FeCl3-modified red mud-based carriers (RMGA-Fe), and microbial promoter-modified red mud-based carriers (RMGA-MA) increased by 24.4%-175% compared with the commercially available K3 carriers. Combining the results of SEM and laser confocal microscope, electrostatic attraction played a leading role on loading AnAOB. The increase in the surface roughness and specific area of the carriers after the attachment and the presence of Fe2+, Ca2+, and Mg2+ plasma were necessary for the subsequent growth of AnAOB, while the leaching of Cr(VI) promoted the nitrogen removal effect of AnAOB.

Adsorption of Pb(II) from wastewater using a red mud modified rice-straw biochar: Influencing factors and reusability

Efficient environmental remediation of toxic chemicals using effective sorbents has received considerable attention recently. For the present study, the synthesis of a red mud/biochar (RM/BC) composite was performed from rice straw with the aim of achieving Pb(II) removal from wastewater. Characterization was performed by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), Zeta potential analysis, elemental mapping, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Results showed that RM/BC had higher specific surface area (S_BET = 75.37 m² g^-1) than raw biochar (S_BET = 35.38 m² g^-1). The Pb(II) removal capacity (q_e) of RM/BC was 426.84 mg g^-1 at pH 5.0, and the adsorption data well fitted pseudo second order kinetics (R² = 0.93 and R² = 0.98), as well as the Langmuir isotherm model (R² = 0.97 and R² = 0.98) for both BC and RM/BC. Pb(II) removal was slightly hindered with the increasing strength of co-existing cations (Na⁺, Cu²⁺, Fe³⁺, Ni²⁺, Cd²⁺). The increase in temperatures (298 K, 308 K, 318 K) favored Pb(II) removal by RM/BC. Thermodynamic study indicated that Pb(II) adsorption onto BC and RM/BC was spontaneous and primarily governed by chemisorption and surface complexation. A regeneration study revealed the high reusability (>90%) and acceptable stability of RM/BC even after five successive cycles. These findings indicate that RM/BC evidenced special combined characteristics of red mud and biochar, hence its use for Pb removal from wastewater offers a green and environmentally sustainable approach fitting the "waste treating waste" concept.

Periplasmic space is the key location for Pb(II) biomineralization by Burkholderia cepacia

Phosphate solubilizing bacteria (PSB) induced phosphate precipitation is considered as an effective method for Pb(II) removal through the formation of stable Pb(II)-phosphate compound, but the location of end-products is still unclear. Herein, the PSB strain of Burkholderia cepacia (B. cepacia) coupled with the hydroxyapatite (HAP) was used in this study to investigate the Pb(II) removal mechanism and the biomineralization location. The dissolving phosphate of three particle sizes of HAP and Pb(II) resistant capabilities, and the effect factors such as HAP dosage, initial concentrations of Pb(II), pH, temperature, and different treatments were determined. The results indicated that the highest soluble phosphate could reach 224.85 mg/L in a 200 nm HAP medium and the highest removal efficiency of Pb(II) was about 96.32 %. Additionally, it was interesting that Pb(II) was mainly located in the periplasmic space through the cellular distribution experiment, which was further demonstrated by scanning electron microscope (SEM) and transmission electron microscopy (TEM). Besides, the characterization results showed that the functional groups such as amide, hydroxy, carboxy and phosphate played an important role in Pb(II) biomineralization, and the free Pb(II) in aqueous solution could be transformed into pyromorphite through phosphate dissolution, extracellular adsorption/complexation, and intracellular precipitation.

Simultaneous adsorption of As(III) and Pb(II) by the iron-sulfur codoped biochar composite: Competitive and synergistic effects

Simultaneous elimination of As(III) and Pb(II) from wastewater is still a great challenge. In this work, an iron-sulfur codoped biochar (Fe/S-BC) was successfully fabricated in a simplified way and was applied to the remediate the co-pollution of As(III) and Pb(II). The positive enthalpy indicated that the adsorption in As-Pb co-pollution was an endothermic reaction. The mechanism of As(III) removal could be illustrated by surface complexation, oxidation and precipitation. In addition to precipitation and complexation, the elimination mechanism of Pb(II) also contained ion exchange and electrostatic interactions. Competitive and synergistic effects existed simultaneously in the co-contamination system. The suppression of As(III) was ascribed to competitive complexation of the two metals on Fe/S-BC, while the synergy of Pb(II) was attributed to the formation of the PbFe₂(AsO₄)₂(OH)₂. Batch experiments revealed that Fe/S-BC had outstanding ability to remove As(III) and Pb(II), regardless of pH dependency and interference by various coexisting ions. The maximum adsorption capacities of the Fe/S-BC for As(III) and Pb(II) were 91.2 mg/g and 631.7 mg/g, respectively. Fe/S-BC could be treated as a novel candidate for the elimination of As(III)-Pb(II) combined pollution.

Zirconium-modified attapulgite was used for removing of Cr(vi) in aqueous solution

This work fabricated the zirconium-modified attapulgite (Zr@ATP) for removing Cr(vi) ions in aqueous solutions. According to X-ray diffraction, scanning electron microscopy, TEM, Fourier transform infrared, and X-ray photoelectron spectroscopy analyses, Zr was successfully grafted onto the attapulgite rod surface. Cr(vi) adsorption onto Zr@ATP surface fitted well with the Langmuir isotherm and pseudo-second-order kinetic models, which suggested that the adsorption is primarily chemisorption. When the pH of the aqueous solution is 3, Zr@ATP achieved the highest Cr(vi) absorption, of about 32.84 mg/g. Density functional theory studies revealed that the hydroxyl functional group introduced through the modification process supplies more active sites to form the hydrogen bond with CrO 4 2 − {\text{CrO}}_{4}^{2-} and HCrO 4 − {\text{HCrO}}_{4}^{-} .

Remediation of chromium, zinc, arsenic, lead and antimony contaminated acidic mine soil based on Phanerochaete chrysosporium induced phosphate precipitation

Microbial induced phosphate precipitation (MIPP) is an advanced bioremediation technology to reduce the mobility and bioavailability of heavy metals (HMs), but the high level of HMs would inhibit the growth of phosphate solubilizing microbes. This study proposed a new combination system for the remediation of multiple HMs contaminated acidic mine soil, which included hydroxyapatite (HAP) and Phanerochaete chrysosporium (P. chrysosporium, PC) that had high phosphate solubilizing ability and HMs tolerance. Experimental data suggested that in HAP/PC treatment after 35 d of remediation, labile Cr, Zn and As could be transformed into the stable fraction with the maximum immobilization efficiencies increased by 53.01 %, 22.43 %, and 35.65 %, respectively. The secretion of organic acids by P. chrysosporium was proved to promote the dissolution of HAP. Besides, the pH value, available phosphorus (AP) and organic matter (OM) increased in treated soil than in original soil, which also indicated the related dissolution-precipitation mechanism of HMs immobilization. Additionally, characterization results revealed that adsorption and ion exchange also played an important role in the remediation process. The overall results suggested that applying P. chrysosporium coupled with HAP could be considered as an efficient strategy for the remediation of multiple HMs contaminated mine soil and laid a foundation for the future exploration of soil microenvironment response during the remediation process.

Elevated Adsorption of Lead and Arsenic over Silver Nanoparticles Deposited on Poly(amidoamine) Grafted Carbon Nanotubes

An efficient adsorbent, CNTs-PAMAM-Ag, was prepared by grafting fourth-generation aromatic poly(amidoamine) (PAMAM) to carbon nanotubes (CNTs) and successive deposition of Ag nanoparticles. The FT-IR, XRD, TEM and XPS results confirmed the successful grafting of PAMAM onto CNTs and deposition of Ag nanoparticles. The absorption efficiency of CNTs-PAMAM-Ag was evaluated by estimating the adsorption of two toxic contaminants in water, viz., Pb(II) and As(III). Using CNTs-PAMAM-Ag, about 99 and 76% of Pb(II) and As(III) adsorption, respectively, were attained within 15 min. The controlling mechanisms for Pb(II) and As(III) adsorption dynamics were revealed by applying pseudo-first and second-order kinetic models. The pseudo-second-order kinetic model followed the adsorption of Pb(II) and As(III). Therefore, the incidence of chemisorption through sharing or exchanging electrons between Pb(II) or As(III) ions and CNTs-PAMAM-Ag could be the rate-controlling step in the adsorption process. Further, the Weber-Morris intraparticle pore diffusion model was employed to find the reaction pathways and the rate-controlling step in the adsorption. It revealed that intraparticle diffusion was not a rate-controlling step in the adsorption of Pb(II) and As(III); instead, it was controlled by both intraparticle diffusion and the boundary layer effect. The adsorption equilibrium was evaluated using the Langmuir, Freundlich, and Temkin isotherm models. The kinetic data of Pb(II) and As(III) adsorption was adequately fitted to the Langmuir isotherm model compared to the Freundlich and Temkin models.

The highly efficient simultaneous removal of Pb2+ and methylene blue induced by the release of endogenous active sites of montmorillonite

The inherent periodic structure of montmorillonite limits the adsorption capacity of its endogenous active units such as Si-O tetrahedron and Al-O octahedron for pollutants. The high-intensity ultrasound method was used to release these active units and the layer-by-layer assembly was adopted to prepare carbon@chitosan@montmorillointe microsphere adsorbent (C@CS@Mt) to give full play to the adsorption capacity of montmorillonite. The montmorillonite nanosheet exhibited good hole-making ability, resulting in high surface area, pore volume and pore diameter of microspheres. Benefitting from the release of active sites in Si-O tetrahedron and Al-O octahedron of montmorillonite nanosheets, the adsorption capacity of C@CS@Mt was significantly improved. The maximum adsorption capacities of Pb²⁺ and methylene blue (MB) reached 884.19 mg·g^-1 and 326.21 mg·g^-1, respectively. The simultaneous adsorption experiments indicated that the occupation of active sites by Pb²⁺ caused the observed decrease of MB adsorption capacity. The theoretical calculations indicated that Pb was preferentially adsorbed by active adsorption units due to strong electron donating ability in comparison to MB. As an active unit, Si-O tetrahedron exhibited stronger adsorption capacity for cationic dyes than Al-O octahedron due to both the large electronegativity and lower adsorption binding energy.

Experimental Study of Salicylic Acid as a Calcium Sulfate Dihydrate Scale Inhibitor, Analyzed from Surface Properties and Crystal Growth

Static and dynamic experiments were carried out to study the antiscale performance of salicylic acid (SA) to calcium sulfate dihydrate (CSD) scale. The CSD scale formed in the reuse of processing of wastewater of phosphorite flotation. The scale surface physicochemical properties have been investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ζ potential, and contact angle measurements. The antiscale mechanisms of SA to CSD were studied from surface properties and crystal growth. The results showed that the scale inhibition efficiency of SA to CSD reached 98.9% (6 mg/L) under static conditions. Under dynamic conditions, the faster the fluid velocity, the less CSD formed. The order of scaling capability on different material surfaces was 20#CS > 304SS > PC > PE. The growth of CSD was inhibited by SA resulting in the surface becoming porous. The deprotonated SA could easily interact with the Ca²⁺ to make the CSD surface potential negative. The wettability properties of the CSD are greatly improved when the contact angle is reduced. The surface tension values of CSD without and with 6 mg/L SA are 19.06 and 240.69 mN/m², respectively. SA as a scale inhibitor can significantly inhibit crystallization of CSD.

Design of nitrogen-phosphorus-doped biochar and its lead adsorption performance

The surface properties of the adsorbents and the acidic environment have an influence effect on Pb adsorption. In order to further improve the adsorption performance of biochar, we herein reported an effective method to synthesize high-adsorbed biochar by co-doping with nitrogen and phosphorus. After atom doping, the N/P co-doped biochar (NP-BC) showed the enhanced adsorption capacity for lead ion (Pb²⁺). The adsorption kinetics, isotherm, pH value, and influencing factors were studied. The results show that the synthesized NP-BC has high Pb²⁺ adsorption capacity in aqueous solution, and can be maintained with various environmental interference factors including pH, natural organic matter, and other metal ions. High adsorption performance shows that the material may be well used to remove Pb²⁺ in various water bodies. Various characterization experiments prove that surface properties contribute to Pb²⁺ adsorption, and the high performance of NP-BC is mainly due to the surface complexation between functional groups and Pb²⁺. This work demonstrates that the surface functional groups of biochar are critical to the development of high-performance heavy metal adsorbents.

Single and binary adsorption of lead and cadmium ions in aqueous solutions and river water by butylamine functionalized vermiculite: performance and mechanism

Lead and cadmium are toxic to human, animal, and plant health; they enhance oxidative stress indirectly while simultaneously acting through other toxicodynamic mechanisms. In this study, pristine vermiculite (VER) was functionalized with butylamine (BUT) and a novel organoclay (BUT-VER) adsorbent material was produced for simultaneous removal of Pb(II) and Cd(II) in aquatic medium. The adsorbents were characterized by spectroscopic, microscopic, spectrometric, and potentiometric techniques. The adsorption affecting parameters, including pH, time, initial concentration, temperature, and co-existing cations were investigated and optimized. The kinetic data results were in better agreement with pseudo-second-order (PSO) model (R² > 0.992). Multiple isotherm models were used to study the adsorption system and results showed that adsorption was monolayer. The BUT-VER showed an improvement in adsorption capacity in a single system (Pb(II): from 134.2 to 160.6 mg g^-1) and (Cd(II): from 51.1 to 58.9 mg g^-1) while in binary system (Pb(II): from 107.3 to 114.5 mg g^-1) and (Cd(II): from 33.7 to 39.7 mg g^-1), respectively. Furthermore, BUT-VER was tested in real river water and removed efficiency of >99% was achieved in just 1 h. The dominant mechanisms were electrostatic attraction and complexation. BUT-VER was regenerated for five consecutive cycles and showed >90% removal efficiency. These findings suggest that the proposed inexpensive adsorbent has the potential for practical applications of toxic metals removal from water.

Efficient removal of Cd2+ from aqueous solution with a novel composite of silicon supported nano iron/aluminum/magnesium (hydr)oxides prepared from biotite

Taking low cost silicate minerals to develop efficient Cd²⁺ adsorption materials was favorable to the comprehensive utilization of minerals and remediation of environmental pollution. In this study, a composite of silicon supported nano iron/aluminum/magnesium (hydr)oxides was prepared with biotite by combining acid leaching and base precipitation process, which was used to remove Cd²⁺. Cd²⁺ adsorption behaviors were in accordance of pseudo-second order kinetic model and Langmuir model, and the obtained maximal Cd²⁺ adsorption capacity was 78.37 mg/g. Increasing pH and temperature could accelerate the removal of Cd²⁺. The activation energy was calculated as 66.05 kJ/mol, meaning that Cd²⁺ removal process was mainly depended on chemical adsorption. XRD and SEM results showed that this composite was a micro-nano structure of layered silica supported nano iron/aluminum/magnesium (hydr)oxides. Cd²⁺ removal mechanisms were consisted of surface complexation and ion exchange between Cd²⁺ and other metal ions, and the ion exchange interaction played the major role. These results indicated that a novel efficient utilization way for silicate minerals was developed.

Mineralization of lead by Phanerochaete chrysosporium microcapsules loaded with hydroxyapatite

In this study, microcapsules assembled with Phanerochaete chrysosporium (P. chrysosporium, PC) and hydroxyapatite (HAP) were successfully prepared and applied for Pb(II) immobilization in aqueous solution. The effect of different conditions on Pb(II) removal was investigated, such as pH, temperature, dosages of microcapsules and HAP, and initial concentrations of Pb(II). The removal efficiency of Pb(II) was in order of HAP+PC > HAP > PC > CK (control check) at the Pb(II) initial concentration of 100 mg L^-1, which were 87.7%, 82.82%, 63.67% and 2.06%, respectively. Under HAP+PC treatment, P. chrysosporium secreted plentiful organic acids like formic, oxalic and citric acids, when the addition dose of HAP increased from 5 g L^-1 to 15 g L^-1, the production of formic acid increased remarkably from 32.37 g L^-1 to 66.02 g L^-1. After reaction, P. chrysosporium kept a good biological activity evidenced by the live/dead stain test. The characterization results indicated that the insoluble apatite could transform to soluble phosphate due to the secreted organic acids, then reacted with Pb(II) to form pyromorphite [Pb₁₀(PO₄)₆Cl₂] and lead phosphate hydroxide [Pb₁₀(PO₄)₆(OH)₂]. The overall results clearly demonstrated that combining P. chrysosporium with HAP could be used as a promising technology to accelerate lead immobilization.

Recyclable nitrogen-doped biochar via low-temperature pyrolysis for enhanced lead(II) removal

Facile and low-cost preparation are essential in the conversation of agricultural waste into biochar. In this work, nitrogen-doped biochar (NBC-350-0.1) was prepared by thermal decomposition of urea (urea/biochar = 0.1:1 mass ratio) at a low temperature of 350 °C. NBC-350-0.1 showed good performance for Pb(II) removal with the maximum adsorption capacity of 130.87 mg g^-1 at 25 °C, which was five times that of pristine biochar (BC). Adsorption kinetics, isotherms and thermodynamics studies indicated that the adsorption of Pb(II) by NBC-350-0.1 or BC was the homogeneous monolayer adsorption with chemical action as the rate-limiting step, and was accompanied by spontaneous endothermic. Further analysis showed that the removal of Pb(II) on NBC-350-0.1 and BC depended on the complexation with unsaturated carbon bonds and ion exchange with Ca(II). Moreover, graphitic- and pyridinic-N in NBC-350-0.1 exerted a key part in the adsorption of Pb(II). NBC-350-0.1 regenerated by NaOH exhibited excellent recycling performance keeping the original removal efficiency at 84% after five cycles. In addition, this N doping method is suitable for improving the performance of coffee grounds, sawdust, and bagasse biochar. These results would provide an idea for obtaining recyclable N-doped biochar to treat the Pb(II) polluted wastewater.

Optimized synthesis of lignin sulfonate nanoparticles by solvent shifting method and their application for adsorptive removal of dye pollutant

Synthesis of value added products from wastes is of importance from different perspectives. Wood and paper industry produces tons of wastewaters that contains lignin. In this paper, we report a new approach, called solvent-shifting method, to synthesize lignin sulfonate nanoparticles (LS-NPs). The effective parameters on size of LS-NPs were carefully tuned and the size of LS-NPs was minimized by response surface methodology. The results suggested that LS-NPs with size of 53 nm can be synthesized at low lignin sulfonate concentration (0.28 g/mL), moderate surfactant concentration (0.32 g/mL) but relatively high anti-solvent content (92 mL of ethanol for 40 mL of the aqueous phase). The as-synthesized LS-NPs were characterized by different analytical techniques, where presence of various negatively charged functional groups on surface of LS-NPs was conformed. To investigate the potential of LS-NPs for adsorptive removal of pollutant molecules, basic red 2 (known as Safranin-O) was used as a model pollutant dye. The results suggested that the maximum removal occurs at alkaline pH, where there is strong electrostatic interactions between LS-NPs and cationic Safranin-O molecules. The adsorption capacity was 85.14 mg/gr, where the isotherm data was best described by Redlich-Peterson isotherm model. The kinetic data also revealed that the adsorption is very fast in the first 20 min, where there is three diffusional steps to complete the adsorption in 90 min. The results of this study could open up new window to the field of value-added products to synthesize waste-driven nanomaterials for environmental applications.

Synthesis and adsorption properties of gelatin-conjugated hematite (α-Fe2O3) nanoparticles for lead removal from wastewater

Gelatin-conjugated hematite nanoparticles (HT NPs) are prepared through the solid-state phase transformation in the presence of phosphate. Their adsorption capacity and kinetics are investigated for Pb removal in wastewater. The gelatin-conjugated HT NPs with a size of 4-6 nm exhibit an excellent Pb removal performance, with a high adsorption capacity of 169.49 mg g^-1 and a fast equilibrium adsorption kinetics, attributed to the large number of active sites and highly negative charge on the surface of HT NPs. Moreover, the magnetic property of HT NPs enables to selectively collect NPs in the wastewater by using a permanent magnet, leading to its high reusability.

Coal Fly Ash Decorated with Graphene Oxide-Tungsten Oxide Nanocomposite for Rapid Removal of Pb2+ Ions and Reuse of Spent Adsorbent for Photocatalytic Degradation of Acetaminophen

Coal fly ash was decorated with a graphene oxide-tungsten oxide nanorods nanocomposite (CFA/GO/WO3NRs nanocomposite) via a hydrothermal method and applied for the remediation of lead (Pb2+ ions). The Pb2+ ion-loaded spent adsorbent (CFA/GO/WO3NRs + Pb2+ nanocomposite) was reused for the photodegradation of acetaminophen. CFA/GO/WO3NRs + Pb2+ nanocomposite displayed rapid removal of Pb2+ ions. Pseudo-second-order kinetics and the Langmuir isotherm model described the adsorption data. The adsorption capacity of the CFA/GO/WO3NRs nanocomposite was 41.51 mg/g for the removal of Pb2+ ions. Additionally, the Pb2+ ion-loaded spent adsorbent significantly influenced the degradation of acetaminophen by photocatalysis where 93% degradation was observed. It is worthy to note the reuse application of Pb2+ ion-loaded spent adsorbent as a photocatalyst, which will significantly reduce the secondary waste obtained from conventional adsorption methods.

Efficient removal of Pb(II) ions from aqueous solution by modified red mud

In the work, we employed a hydrothermal method for modification of red mud using colloidal silica and sodium hydroxide under mild conditions, and applied it into adsorbing Pb(II) ions in aqueous solutions. In the modification, zeolite structure was formed. The adsorption experiments found that the adsorption capacity of the modified red mud for Pb(II) ions was significantly improved, almost 10 times as much as that of the original red mud. Both the pseudo-first-order and pseudo-second-order kinetic equation can describe the adsorption process, indicating it a more complicated interaction. Langmuir and Dubinin-Radushkevich models well fit the adsorption isotherm, indicating that the modified red mud mainly removes lead ions from aqueous solution by monolayer physical adsorption. According to the fitting results, the saturated adsorption capacity of Pb (II) by the modified red mud is 551.11 mg/g, confirming its high efficiency adsorption performance. XRD, FTIR, XPS and SEM-EDS all detected the formation of PbCO₃ and Pb₃(CO₃)₂(OH)₂. It was speculated that the adsorption mechanism should be attributed to the joint contribution of ion exchange and precipitation. The excellent performance of the modified red mud on Pb(II) ions adsorption makes it a promising candidate for the treatment of wastewater contaminated by heavy metal ions.