Enhanced adsorption of molybdenum(VI) from aquatic solutions by chitosan-coated zirconium–iron sulfide composite

Removal of Mo(VI), Pb(II), and Cu(II) from wastewater using electrospun cellulose acetate/chitosan biopolymer fibers

Environmentally friendly polymers such as cellulose acetate (CA) and chitosan (CS) were used to obtain electrospun fibers for Cu2+, Pb2+, and Mo6+ capture. The solvents dichloromethane (DCM) and dimethylformamide (DMF) allowed the development of a surface area of 148 m2 g-1 for CA fibers and 113 m2 g-1 for cellulose acetate/chitosan (CA/CS) fibers. The fibers were characterized by IR-DRIFT, SEM, TEM, CO2 sorption isotherms at 273 K, Hg porosimetry, TGA, stress-strain tests, and XPS. The CA/CS fibers had a higher adsorption capacity than CA fibers without affecting their physicochemical properties. The capture capacity reached 102 mg g-1 for Cu2+, 49.3 mg g-1 for Pb2+, and 13.1 mg g-1 for Mo6+. Furthermore, optimal pH, adsorption times qt, and C0 were studied for the evaluation of kinetic models and adsorption isotherms. Finally, a proposal for adsorbate-adsorbent interactions is presented as a possible capture mechanism where, in the case of Mo6+, a computational study is presented. The results demonstrate the potential to evaluate the fibers in tailings wastewater from copper mining.

Adsorption behavior of Mo(VI) from aqueous solutions using tungstate-modified magnetic nanoparticle

A new magnetic nanoparticle modified with sodium tungstate (Mnp-Si-W) was synthesized and employed for the sorption of molybdenum from aqueous solutions. The prepared nanoparticles (Mnp-Si-W) were characterized by different advanced techniques. Different parameters that influenced the adsorption percent of Mo(VI) were investigated using a batch process. Based on a systematic investigation of the adsorption isotherms and kinetics models, Mo(VI) adsorption follows the Langmuir model and pseudo-second-order kinetics. According to the Langmuir isotherm model, the Mnp-Si-W nanoparticles exhibited a maximum adsorption capacity of 182.03 mg g-1 for Mo(VI) at pH 2.0. The effect of competing ions showed that the prepared nanoparticles have a high selectivity for the sorption of molybdenum. Moreover, the effect of some interfering anions on Mo(VI) ion sorption is found in the following order: phosphate < sulfate < chromate. Finally, the nanoparticle (Mnp-Si-W) can be successfully reused five times.

Removal of toxic metals using iron sulfide particles: A brief overview of modifications and mechanisms

Growing mechanization has released higher concentrations of toxic metals in water and sediment, which is a critical concern for the environment and human health. Recent studies show that naturally occurring and synthetic iron sulfide particles are efficient at removing these hazardous pollutants. This review seeks to provide a concise summary of the evolution in the production of iron sulfide particles, specifically nanoparticles, through the years. This review presents an outline of the synthesis process for the most dominant forms of iron sulfide: mackinawite (FeS), pyrite (FeS2), pyrrhotite (Fe1-x S), and greigite (Fe3S4). The review confirms that both natural forms of iron sulfide and modified forms of iron sulfide are highly effective at removing different heavy metals and metalloids from water. Concurrently, this review reveals the interaction mechanism between toxic metals and iron sulfide, along with the impact of conditions for remedy and rectification. None the less, modifications and future investigations into the synthesis of novel iron sulfides, their use to adsorb diverse environmental pollutants, and their fate after injection into polluted aquifers, remain crucial to maximizing pollution control.

Selective adsorption of tetracycline and copper(II) on ion-imprinted porous alginate microspheres: performance and potential mechanisms

A novel epichlorohydrin and thiourea grafted porous alginate adsorbent (UA-Ca/IIP) was synthesized using ion-imprinting and direct templating to remove copper ions (Cu(II)) and tetracycline (TC) in aqueous solution. UA-Ca/IIP demonstrated great selectivity for Cu(II) and TC among different coexisting anions (CO32-, PO43- and SO42-), cations (Ca2+, Mg2+ and NH4+), and antibiotics (oxytetracycline and sulfamethoxazole). The adsorption of TC and Cu(II) by UA-Ca/IIP was significantly affected by the pH of the solution, and the quantity of TC and Cu(II) adsorbed reached a maximum at pH 5. A pseudo-second-order model better fitted the kinetic data; the Langmuir model predicted the maximum adsorption quantities 3.527 mmol TC g-1 and 4.478 mmol Cu(II) g-1 at 298 K. Thermodynamic studies indicated that the TC and Cu(II) adsorption was more rapid at a higher temperature. Antagonistic and synergistic adsorption experiments showed that the adsorption capacity of TC would increase significantly with the increase of Cu(II) concentration. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that along with the influence of pH, electrostatic interaction and complexation were the main mechanisms of TC and Cu(II) adsorption. Regeneration experiments revealed that TC and Cu(II) were removed efficiently and that UA-Ca/IIP was recyclable over the long term. These results show that the modified porous alginate microsphere is a green and recyclable adsorbent, which has good selectivity and high adsorption performance for the removal of TC and Cu(II).

Biosorption of hexavalent chromium and molybdenum ions using extremophilic cyanobacterial mats: efficiency, isothermal, and kinetic studies

Two extremophilic cyanobacterial-bacterial consortiums naturally grow in extreme habitats of high temperature and hypersaline were used to remediate hexavalent chromium and molybdenum ions. Extremophilic cyanobacterial-bacterial biomasses were collected from Zeiton and Aghormi Lakes in the Western Desert, Egypt, and were applied as novel and promising natural adsorbents for hexavalent chromium and molybdenum. Some physical characterizations of biosorbent surfaces were described using scanning electron microscope, energy-dispersive X-ray spectroscopy, Fourier transformation infrared spectroscopy, and surface area measure. The maximum removal efficiencies of both biosorbents were 15.62-22.72 mg/g for Cr(VI) and 42.15-46.29 mg/g for Mo(VI) at optimum conditions of pH 5, adsorbent biomass of 2.5-3.0 g/L, and 150 min contact time. Langmuir and Freundlich adsorption models were better fit for Cr(VI), whereas Langmuir model was better fit than the Freundlich model for Mo(VI) biosorption. The kinetic results revealed that the adsorption reaction obeyed the pseudo-second-order model confirming a chemisorption interaction between microbial films and the adsorbed metals. Zeiton biomass exhibited a relatively higher affinity for removing Cr(VI) than Aghormi biomass but a lower affinity for Mo(VI) removal. The results showed that these extremophiles are novel and promising candidates for toxic metal remediation.

Isolation and identification of the molybdenum-resistant strain Raoultella ornithinolytica A1 and its effect on MoO42- in the environment

The mining and leakage of molybdenum (Mo) can cause environmental contamination which has not been realized until recently. Bacteria that can mitigate Mo-contamination was enriched and isolated. The low temperature and different pH conditions were considered to analysis its feasibility in Northern China which suffers from a long time of low temperatures every year. The result showed that the removal rate of MoO₄^2- by Raoultella ornithinolytica A1 reached 30.46% at 25 °C and pH 7.0 in Luria-Bertani medium (LB). Meanwhile, A1 also showed some efficiency in the reduction of MoO₄^2- in low phosphate molybdate medium (LPM), which reached optimum at the MoO₄^2- concentration of 10 mM. The results of FTIR indicated that the cell wall performed an essential role in the MoO₄^2- removal process, which was illustrated by the distribution of Mo in A1 (Mo bound to cell wall accounted for 92.29% of the total MoO₄^2- removed). In addition, low temperature (10 °C) effect the removal rate of MoO₄^2- by - 8.38 to 11.66%, indicating the potential for the in-situ microbial remediation of Mo-contaminated environments in low temperature areas.

Partial Oxidation of FeS Nanoparticles Enhances Cr(VI) Sequestration

Iron sulfide nanoparticles (nano-FeS) have shown great potential for in situ remediation of Cr(VI) pollution by reducing Cr(VI) to the less soluble and toxic Cr(III). However, material oxidation that inevitably occurs during storage and application alters its reactivity. Herein, we show that partial oxidation of nanoparticulate mackinawite (FeS) significantly enhances its capability in sequestering Cr(VI). Oxidation of nano-FeS increases its binding affinity to Cr(VI), likely due to preferential inner-sphere complexation of Cr(VI) oxyanions to ferric over ferrous iron in mackinawite/lepidocrocite (FeS/γ-FeOOH) nanocomposites. A trade-off is that oxidation mitigates Cr(VI) reduction by lowering the electron-donating potential of the material and the electron transfer at a solution-material interface and consequently hinders the transformation of adsorbed Cr(VI) to Cr(III). Notably, the rate-limiting step of Cr(VI) sequestration transitions from adsorption to reduction during oxidation, as demonstrated with batch experiments coupled with kinetic modeling. Thus, an optimum oxidation degree exists, wherein the gain in the overall performance from enhanced adsorption overcompensates the loss from inhibited reduction, resulting in maximum sequestration of aqueous Cr(VI) as solid-phase Cr(III). Our findings inform better assessment and design of nanomaterials for Cr(VI) remediation and may be extended to interactions of other oxyanions with natural and engineered nanoparticles during oxidative aging.

Preparation of biochar from constructed wetland plant and its adsorption performance towards Cu2

In order to solve problems in the treatment and disposal of huge production of artificial wetland plants and heavy metal pollution, two constructed wetland plants of reed and gladiolus were selected as raw materials to prepare biochar for adsorbing heavy metals from aqueous solutions. The experimental results showed that reed biochar prepared at 600℃ and activated by KOH with an impregnation ratio of 1:3 (KRAC-3) exhibited relatively high adsorption ability towards Cu²⁺. The optimal results analyzed by Design-Expert software showed that the maximum adsorption rate of KRAC-3 towards Cu²⁺ was obtained under the optimal conditions of adsorbent dosage of 1.2 g/L, pH of 4.96, and reaction time of 137.43 min. The adsorption of Cu²⁺ followed pseudo-second-order kinetics and the Langmuir adsorption model. The theoretical maximum adsorption capacity of KRAC-3 calculated from the Langmuir isotherm model was 148.08 mg/g. Microscopic tests with the help of SEM, EDS, and XRD revealed that physical adsorption, ion exchange, electrostatic adsorption, surface complexation, and precipitation were the main adsorption mechanism of Cu²⁺ loading onto KRAC-3. This study will provide a theoretical basis for the application of biochar prepared from constructed wetland plants and the treatment of heavy metal-containing wastewater.

Polypyrrole-Bentonite composite as a highly efficient and low cost anionic adsorbent for removing hexavalent molybdenum from wastewater

The aim of current study was to develop a new material for the fast and efficient removal of hexavalent molybdenum (Mo(VI)) from contaminated water. In this work, a novel adsorbent was synthesized through the polypyrrole intercalation modification of bentonite (PPy-BT) via in-situ chemical polymerization method for effectively removal of Mo(VI) from aqueous solution. The surface morphology and chemical composition of PPy-BT composites were investigated by X-ray diffraction, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectrometer, scanning electron microscopy techniques and X-ray photoelectron spectroscopy. PPy and BT could well resist the aggregation of each other, and therefore resulted in a loose-packed structure and good exposure of active sites. Using materials for the adsorption of Mo(VI) revealed has a maximum adsorption capacity of 100.17 mg/g at 25 °C and pH 4.0 by the Langmuir model. The adsorption kinetics and isotherm data are found to be well elucidated through pseudo-second-order and Langmuir models. Moreover, high regeneration ability (>89.3%) of PPy-BT was noted for five consecutive adsorption-desorption cycles. These findings highlight the potential of PPy-BT for practical water treatment applications. The intercalation material of PPy-BT could provide a new strategy to develop cost-effective clay-based nanomaterials for wastewater treatment.