Application of the Nernst-Planck approach to lead ion exchange in Ca-loaded Pelvetia canaliculata

Pb/As simultaneous removal from soil leachate of Pb/Zn smelting sites by magnetic biochar

Lead (Pb) and arsenic (As) contaminated soils, caused by Pb and zinc (Zn) smelting activities, pose an urgent environmental issue. Magnetic biochar (MB) has been regarded as an increasingly appealing candidate for the remediation of multi-metals in contaminated soils or their leachate. Finding economically feasible preparation methods for MB and demonstrating its remediation potential is desperately required for the remediation of such complex smelting sites. In this study, a modified MB was prepared using an optimized co-precipitation method, and its application potential for Pb/As simultaneous removal based on the basic properties of a typical Pb/Zn smelting site was evaluated. The surface modifications of MB facilitated the encapsulation of various ultrafine iron oxide particles, predominantly γ-Fe2O3 and Fe3O4, whilst notably enhancing the presence of oxygen-containing surface functional groups. The adsorption of Pb(II) and As(III) by MB was well-described using the pseudo-second-order adsorption and Langmuir models. The existence of SO42- and Ca2+ in the soil leachate competed with the adsorption sites for Pb(II) and As(III). Notably, within the pH range of 5-9, the adsorption efficiency of Pb(II) by MB increased with the rising solution pH, whereas alterations in pH minimally affected the removal rate of As(III), maintaining a consistent removal rate exceeding 95%. Furthermore, dissolved organic matter (DOM) abundant in organic functional groups, particularly CO and CC groups, significantly augmented the adsorption affinity for both Pb(II) and As(III). An application rate of 2 g/L could effectively reduce the concentration of Pb(II) and As(III) in soil leachate to <0.05 mg/L. The findings demonstrated the potential of the prepared MB for simultaneous removal of As(III) and Pb(II) in soil leachate, which should be beneficial to multi-metals polluted soil remediation in Pb/Zn smelting sites.

Enhanced microbial reduction of Cr(VI) in soil with biochar acting as an electron shuttle: Crucial role of redox-active moieties

Biochar has been proven to participate in the biotic reduction of hexavalent chromium (Cr(VI)) in environment since its involvement may accelerate the extracellular electron transfer (EET). However, roles of the redox-active moieties and the conjugated carbon structure of biochar in this EET process remain unclear. In this study, 350 °C and 700 °C were selected to produce biochar with more O-containing moieties (BC350) or more developed conjugated structures (BC700), and their performances in the microbial reduction of soil Cr(VI) were investigated. Our results showed that BC350 presented a 241% increase of Cr(VI) microbial reduction after 7-day incubation, much higher than that of BC700 (39%), suggesting that O-containing moieties might play more important roles in accelerating the EET process. Biochar, especially BC350 could serve as an electron donor for microbial anaerobic respiration, but its contribution (73.2%) as an electron shuttle for EET was dominant to the enhanced Cr(VI) reduction. The positive correlation between electron exchange capacities (EECs) of pristine and modified biochars and the corresponding maximum reduction rates of Cr(VI) evidenced the crucial role of redox-active moieties in electron shuttling. Moreover, EPR analysis suggested the nonnegligible contribution of semiquinone radicals in biochars to the accelerated EET process. This study demonstrates the crucial role of redox-active moieties, i.e., O-containing moieties in mediating the EET process during the microbial reduction of Cr(VI) in soil. Findings obtained will advance the current understanding of biochar as an electron shuttle participating in the biogeochemical processes of Cr(VI).

Surface modification of quartz sand: A review of its progress and its effect on heavy metal adsorption

Quartz sand (SiO₂) is a prevalent filtration medium, boasting wide accessibility, superior stability, and cost-effectiveness. However, its utility is often curtailed by its sleek surface, limited active sites, and swift saturation of adsorption sites. This review outlines the prevalent strategies and agents for quartz sand surface modification and provides a comprehensive analysis of the various modification reagents and their operative mechanisms. It delves into the mechanism and utility of surface-modified quartz sand for adsorbing heavy metal ions (HMIs). It is found that the reported modifiers usually form connections with the surface of quartz sand through electrostatic forces, van der Waals forces, pore filling, chemical bonding, and/or molecular entanglement. The literature suggests that these modifications effectively address issues inherent to natural quartz sand, such as its low superficial coarseness, rapid adsorption site saturation, and limited adsorption capacity. Regrettably, comprehensive investigations into the particle size, regenerative capabilities, and application costs of surface-modified quartz sand and the critical factors for its wider adoption are lacking in most reports. The adsorption mechanisms indicate that surface-modified quartz sand primarily removes HMIs from aqueous solutions through surface complexation, ion exchange, and electrostatic and gravitational forces. However, these findings were derived under controlled laboratory conditions, and practical applications for treating real wastewater necessitate overcoming further laboratory-scale obstacles. Finally, this review outlines the limitations of partially surface modified quartz sand and suggests potential venues for future developments, providing a valuable reference for the advancement of cost-effective, HMI-absorbing, surface-modified quartz sand filter media.

High capacity Pb(II) adsorption characteristics onto raw- and chemically activated waste activated sludge

The Pb(II) adsorption characteristics of chemically activated waste activated sewage sludge (WAS) were compared to raw WAS. Adsorption kinetics and equilibrium isotherm parameters were fit using classic adsorption models. HCl and H₂SO₄ activation terminated any significant sludge-based adsorption. Raw and ZnCl₂ activated WAS displayed Langmuir adsorption capacities of 307 mg/g and 274 mg/g, respectively. Surface characterization revealed that chemical activation with ZnCl₂ increased the BET surface area for raw WAS from 0.97 m²/g to 1.78 m²/g, but did not significantly change the surface structure. FTIR analyzes and XPS were used to further investigate the nature of lead binding. The relationships between equilibrium ion concentration and Pb(II) adsorption suggest cationic exchange with hydrogen, calcium, and zinc as a significant mechanism of Pb(II) removal alongside electrostatic attraction. The pH_PZC was determined as 2.58 and 2.30 for ZnCl₂ activated WAS and raw WAS respectively. HNO₃ and Ca(NO₃)₂ demonstrated sufficient elution properties for WAS recovery. For authentic industrial effluent both raw and ZnCl₂ activated WAS displayed Pb(II) removal behavior comparable to simulated Pb(II) solutions. In comparison with modified and unmodified sludges from literature, this study demonstrates the auspicious potential of raw WAS as an effective Pb(II) adsorbent independent of pyrolytic or chemical activation.

Biosorption of nickel(II) and copper(II) ions from synthetic and real effluents by alginate-based biosorbent produced from seaweed Sargassum sp

In this study, the alginate-based biosorbent produced from seaweed Sargassum sp. was used in biosorption of Ni2+ and Cu2+ ions from synthetic solutions and real electroplating effluents. Biosorption kinetics, isotherms, pH effect, thermodynamic parameters, and sorption/desorption cycles were also evaluated. Kinetic studies show the sorption equilibrium can be obtained within 180 min for Ni2+ ions and 360 min for Cu2+ ions, and the adsorption kinetics data are well described by the pseudo-second order and diffusion in spherical adsorbents. Langmuir model can be well used to describe the biosorption isotherm data. The maximum sorption capacity (qmax) and Langmuir constant (b) were up to 1.147 mmol g-1 and 1.139 L mmol-1 for Ni2+ ions and 1.640 mmol g-1 and 4.645 L mmol-1 for Cu2+ ions. The calculated thermodynamic parameters (ΔG°, ΔH°, and ΔS°) showed that the biosorption of Ni2+ and Cu2+ ions are predominantly a chemical phenomenon of endothermic nature, favorable, and spontaneous at the temperature ranges of 293-313 K. Partial desorption of the Ni2+ and Cu2+ ions on the biosorbent was achieved using acidic and saline eluents, allowing the biosorbent to be used in new sorption/desorption cycles. EDX analysis suggests an ion exchange mechanism between calcium ions on the biosorbent and target metals. Biosorption of Ni2+ and Cu2+ from real electroplating effluents with high concentrations of light metals becomes highly competitive, decreasing the amount of Ni2+ and Cu2+ ions biosorbed due to the ionic strength effect.

Brown marine macroalgae as natural cation exchangers for toxic metal removal from industrial wastewaters: A review

The discharge of inadequately treated or untreated industrial wastewaters has greatly contributed to the release of contaminants into the environment, including toxic metals. Toxic metals are persistent and bioaccumulative, being their removal from wastewaters prior to release into water bodies of great concern. Literature reports the use of brown marine macroalgae for toxic metals removal from aqueous solutions as an economic and eco-friendly technique, even when applied to diluted solutions. Minor attention has been given to the application of this technique in the treatment of real wastewaters, which present a complex composition that can compromise the biosorption performance. Therefore, the main goal of this comprehensive review is to critically outline studies that: (i) applied brown marine macroalgae as natural cation exchanger for toxic metals removal from real and complex matrices; (ii) optimised the biosorption process in a fixed-bed column, which was further scaled-up to pilot plants. An overview of toxic metals sources, chemistry and toxicity, which are relevant aspects to understand and develop treatment techniques, is initially presented. The problem of water resources pollution by toxic metals and more specifically the participation of metal finishing industries in the environmental contamination are issues also covered. The current and potential decontamination methods are presented including a discussion of their advantages and drawbacks. The literature on biosorption was reviewed in detail, considering especially the ion exchange properties of cell wall constituents, such as alginate and fucoidan, and their role in metal sequestration. Besides that, a detailed description of biosorption process design, especially in continuous mode, and the application of mechanistic models is addressed.

Efficient removal of Pb(ii) ions using manganese oxides: the role of crystal structure

The adsorption of Pb(ii) by MnO₂ depends on crystal structure; δ-MnO₂ exhibited higher adsorption capacity than α-, β-, γ- and λ-MnO₂.

Comparative study of adsorption of Pb(II) on native garlic peel and mercerized garlic peel

A comparative study using native garlic peel and mercerized garlic peel as adsorbents for the removal of Pb(2+) has been proposed. Under the optimized pH, contact time, and adsorbent dosage, the adsorption capacity of garlic peel after mercerization was increased 2.1 times and up to 109.05 mg g(-1). The equilibrium sorption data for both garlic peels fitted well with Langmuir adsorption isotherm, and the adsorbent-adsorbate kinetics followed pseudo-second-order model. These both garlic peels were characterized by elemental analysis, Fourier transform infrared spectrometry (FT-IR), and scanning electron microscopy, and the results indicated that mercerized garlic peel offers more little pores acted as adsorption sites than native garlic peel and has lower polymerization and crystalline and more accessible functional hydroxyl groups, which resulted in higher adsorption capacity than native garlic peel. The FT-IR and X-ray photoelectron spectroscopy analyses of both garlic peels before and after loaded with Pb(2+) further illustrated that lead was adsorbed on the through chelation between Pb(2+) and O atom existed on the surface of garlic peels. These results described above showed that garlic peel after mercerization can be a more attractive adsorbent due to its faster sorption uptake and higher capacity.

Combination of electroreduction with biosorption for enhancement for removal of hexavalent chromium

Hexavalent chromium is one of the most toxic heavy metals in aqueous solutions. It has been well documented that the brown seaweed can be used as a promising biosorbent for the sequestration of this heavy metal from wastewater. However, the uptake of Cr(VI) is reportedly a rather slower process; the sorption equilibrium can only be established after a few days, much slower than a few hours for the trivalent chromium ion. In this study, we developed a novel technology of electrochemically assisted biosorption (ECAB) system for the enhancement of the treatment efficiency. It was found through our study that the removal efficiencies of Cr(VI) and total chromium were greatly enhanced by 48.1% and 51.3%, respectively, with the application of -1.0 V in the ECAB system. The conversion of Cr(III) due to the electroreduction of Cr(VI) and the higher pH due to the cathodic H(2) evolution created a favorable condition for the uptake of chromium onto the modified seaweed (MSW). The reduction and adsorption of Cr(VI) by MSW was proved to play a minor role in the removal. Both direct electroreduction and indirect electroreduction by atomic H* contributed to the reduction of Cr(VI).

Characterization and lead(II), cadmium(II), nickel(II) biosorption of dried marine brown macro algae Cystoseira barbata

PURPOSE

The objectives of this research are to identify the functional groups and determine corresponding pK (a) values of the acidic sites on dried brown algae Cystoseira barbata using FTIR and potentiometric titrations, and to investigate the biosorption ability of biomass towards divalent nickel, cadmium, and lead ions. Adsorption was studied as a function of solution pH and contact time, and experimental data were evaluated by the Langmuir isotherm model.

METHODS

CaCl(2) pretreatment was applied to the sorbent for enhancing the metal uptake capacity. The effect of solution pH on biosorption equilibrium was investigated in the pH range of 1.5-5.0. Individual as well as competitive adsorption capacity of the sorbent were studied for metal cations and mixtures.

RESULTS

The retention of the tested metal ions was mostly influenced from pH in the range of 1.5-2.5, then stayed almost constant up to 5.0, while Ni(II) uptake showed the highest variation with pH. Potentiometric titrations were performed to find the number of strong and weak acidic groups and their acidity constants. The density of strong and weak acidic functional groups in the biomass were found to be 0.9 and 2.26 mmol/g, respectively. The FTIR spectra of the sorbent samples indicated various functionalities on the biomass surface including carboxyl, hydroxyl, and amino and sulphonate groups which are responsible for the binding of metal ions.

CONCLUSIONS

The capacity of the biomass for single metal ions (around 1 mmol/g) was increased to 1.3 mmol/g in competitive adsorption, Pb(II) showing the highest Langmuir intensity constant. Considering its extremely high abundance and low cost, C. barbata may be potentially important in metal ion removal from contaminated water and industrial effluents.

Relative distribution of Pb2+ sorption mechanisms by sludge-derived biochar

Lead sorption capacity and mechanisms by sludge-derived biochar (SDBC) were investigated to determine if treatment of acid mine drainage (AMD) containing metals with SDBC is feasible. It was found that the biochar derived from pyrolysis treatment of sewage sludge could effectively remove Pb(2+) from acidic solution with the capacities of 16.11, 20.11, 24.80, and 30.88mgg(-1) at initial pH 2, 3, 4 and 5, respectively. Lead sorption processes were pseudo-second order kinetic and faster at a higher pH. Furthermore, the relative contribution of both inorganic mineral composition and organic functional groups of SDBC for Pb(2+) removal mechanisms, was quantitatively studied at pH 2-5. The results showed that Pb sorption primarily involved the coordination with organic hydroxyl and carboxyl functional groups, which was 38.2-42.3% of the total sorbed Pb varying with pH, as well as the coprecipitation or complex on mineral surfaces, which accounted for 57.7-61.8% and led to a bulk of Ca(2+) and Mg(2+) release during sorption process. A new precipitate was solely observed on Pb-loaded SDBC as 5PbO·P(2)O(5)·SiO(2)(lead phosphate silicate) at initial pH 5, confirmed by XRD and SEM-EDX. The coordination of Pb(2+) with carboxyl and hydroxyl functional groups was demonstrated by FT-IR, and the contribution of free carboxyl was significant, ranging from 26.1% to 35.5%. Results from this study may suggest that the application of SDBC is a feasible strategy for removing metal contaminants from acid solutions.