Ferrihydrite transformation impacted by coprecipitation of lignin: Inhibition or facilitation?

Sulfur/zinc co-doped biochar for stabilization remediation of mercury-contaminated soil: Performance, mechanism and ecological risk

In this study, a novel sulfur/zinc co-doped biochar (SZ-BC) stabilizer was successfully developed for the remediation of mercury-contaminated soil. Results from SEM, TEM, FTIR and XRD revealed that biochar (BC) was successfully modified by sulfur and zinc. In the batch adsorption experiments, the sulfur-zinc co-pyrolysis biochar displayed excellent Hg(II) adsorption performance, with the maximum adsorption capacity of SZ-BC (261.074 mg/g) being approximately 16.5 times that of BC (15.855 mg/g). Laboratory-scale static incubation, column leaching, and plant pot experiments were conducted using biochar-based materials. At an additional dosage of 5 % mass ratio, the SZ-BC exhibits the most effective stabilization of mercury in soil, leading to a significant reduction in leaching loss compared to the control group (CK) by 51.30 %. Following 4 weeks of incubation and 2 weeks of leaching with SZ-BC, the residual mercury in the soil increased by 27.84 %. As a result, potential ecological risk index of mercury decreased by 92 % compared to the CK group. In the pot experiment, SZ-BC significantly enhanced the growth of Chinese cabbage, with biomass and root dry weight reaching 3.20 and 2.80 times that of the CK group, respectively. Additionally, the Translocation Factor (TF) and Bioconcentration Factor (BF) were reduced by 44.86 % and 74.43 %, respectively, in the SZ-BC group compared to the CK group. Moreover, SZ-BC can effectively improve enzyme activities and increase microbial communities in mercury-contaminated soils. The mechanisms of adsorption and stabilization were elucidated through electrostatic adsorption, ion exchange, surface complexation, and precipitation. These findings provide a potentially effective material for stabilizing soils contaminated with mercury.

Simultaneously inhibit cadmium and arsenic uptake in rice (Oryza sativa L.) by Selenium enhanced iron plaque: Performance and mechanism

Selenium (Se) fortification is witnessed to simultaneously inhibit absorbing Cadmium (Cd) and Arsenic (As) by rice plants, but the mechanism is unclear. Here, the effects of Se on the root morphology, iron plaque (IP) content, soil Fe2+ content, radial oxygen loss (ROL), and enzyme activities of the rice plants in the soil contaminated by Cd and As were intensively investigated through the hydroponic and soil experiments. Se effectively alleviated the toxic effects of Cd and As on the plants and the dry weight, root length, and root width were increased by 203.18%, 33.41%, and 52.81%, respectively. It also elucidated that ROL was one of the key factors to elevate IP formation by Se and the specific pathways of Se enhancing ROL were identified. ROL of the plants in the experiment group treated by Se was increased 36.76%, and correspondingly IP was magnified 50.37%, compared to the groups with Cd and As. It was owing to Se significantly increased the root porosity (62.11%), facilitating O2 transport to the roots. Additionally, Se enhanced the activities of catalase (CAT) and superoxide dismutase (SOD) to promote the catalytic degradation of ROS induced by Cd and As stress. It indirectly increased O2 release in the rhizosphere, which benefit to form more robust IP serve as stronger barrier to Cd and As. The results of our study provide a novel molecular level insight for Se promoting root IP to block Cd and As uptake by the rice plants.

Removal of Cr(vi) in wastewater by Fe-Mn oxide loaded sludge biochar

Sludge biochar loaded with Fe-Mn oxides (FMBC) was prepared and employed to remove Cr(vi) from wastewater. The influences of solution pH, co-existing ion, contact time, adsorption temperature and Cd(vi) concentrations on removing Cr(vi) by FMBC were investigated. The Cr(vi) adsorption on FMBC had strong pH dependence. Additionally, Na+, Mg2+, Ca2+, SiO32-, NO3- and Cl- ions exhibited no influence on Cr(vi) removal efficiency for FMBC, whereas there were inhibition effects of Pb2+, Cu2+, Ni2+, CO32-, SO42-, and PO43- on removing Cr(vi). The Cr(vi) adsorption from solution for FMBC was well described by models of pseudo-second-order and Langmuir, and the largest Cr(vi) removal capacity of FMBC reached 172.3 mg g-1. FMBC had good capacity for treating electroplating wastewater and mineral dissolving wastewater containing Cr(vi). After five regenerations, the 50 and 5 mg L-1 Cr(vi) removing efficiency of FMBC was 82.34% and 97.68%, respectively. The Cr(vi) removal for FMBC involved adsorption-reduction and re-adsorption of Cr(iii) generated by reduction. These results indicated that FMBC has good prospects for remediating Cr(vi)-containing wastewater.

Surface engineering of multifunctional nanostructured adsorbents for enhanced wastewater treatment: A review

Rapid urbanization and industrialization have significantly contributed to the contamination of the environment through the discharge of wastewater containing various pollutants. The development of high-performance surface functional nanostructured adsorbents is of wide interest for researchers. Therefore, we explore the significant advancements in this field, focusing on the efficiency of nanostructured materials, as well as their nanocomposites, for wastewater treatment applications. The crucial role of surface modification in enhancing the affinity of these nanostructured adsorbents towards targeted pollutants, addressing a key bottleneck in the utilization of nanomaterials for wastewater treatment, was specifically emphasized. In addition to highlighting the advantages of surface engineering in enhancing the efficiency of nanostructured adsorbents, this review also provides a comprehensive overview of the limitations and challenges associated with surface-modified nanostructured adsorbents, including high cost, low stability, poor scalability, and potential nanotoxicity. Addressing these limitations is essential for realizing the commercial viability of these state-of-the-art materials for large-scale wastewater treatment applications. This review also thoroughly discusses the potential scalability and environmental safety aspects of surface-modified nanostructured adsorbents, offering insights into their future prospects for wastewater treatment. It is believed that this review will contribute significantly to the existing body of knowledge in the field and provide valuable information for researchers and practitioners working in the area of environmental remediation and nanomaterials.

Ozone degradation of tetracycline hydrochloride enhanced by magnetic nanofluid composed of Fe3O4 nanoparticles

Magnetic Fe3O4 nanoparticles were added into the aqueous phase to form nanofluid systems, in which ozone was used for the oxidation of tetracycline hydrochloride (TC) in the solution. The nanomaterials were characterized using SEM, XRD, EDS, and FT-IR. The effects of nanoparticles size, addition ratio, and number of cycles on the process of ozone oxidation of TC were investigated. The results indicated that the addition ratio of nanoparticles have a certain impact on the performance of ozone oxidation. When the addition ratio increased from 0.02% to 0.4%, the removal rate of TC in the solution was improved significantly. Besides, the particle size of nanoparticles showed a greater impact on ozone oxidation. At the nanoscale, Fe3O4 nanoparticles exhibited significant strengthening properties, which is attributed to the construction of nanofluid systems. The removal rate of TC in solution decreased obviously with the increase of nanoparticles size. The Fe3O4 nanoparticles with particle size of 20 nm showed the most significant effect on TC degradation. The recycling experiment showed that magnetic Fe3O4 nanoparticles had stable regeneration performance. For three times of recycling treatment, with a Fe3O4 addition ratio of 0.4%, the removal rate of TC reached 98.7%, 97.21%, and 96%, respectively. Based on the characterization results, the strengthening mechanism was analyzed. The experimental results indicated that construction of nanofluids systems could improve the utilization rate of ozone, and Fe3O4 nanoparticles were reusable and easily recyclable.

Effective chromium mitigation using phosphorous doped bio carbon electrode via capacitive deionisation

Capacitive deionisation (CDI) is an emerging eco-economic water reclamation technology that can remove inorganic salts and heavy metals. Biomass-derived carbon electrodes have attracted the scientific communities in recent years due to their economic feasibility and sustainability. However, electrochemical performance needs to be improved to achieve durability and reusability. Hence, the present study develops rice straw-derived phosphorous-doped (P-doped) carbon as an electrode for mitigating Cr(VI) ions. Phosphorus doping of biocarbon electrodes enhances their electrochemical properties, including increased electrical conductivity, improved charge storage capacity, and enhanced ion adsorption capabilities. Here, Phosphoric acid plays a dual role of activation and doping that enhances the physico-electrochemical properties. The synthesised material was found to be P-doped carbon with better pore distribution, which was confirmed through FESEM-EDX analysis. Further, the physicochemical properties of the electrode material are enriched with carbon and possess an enhanced surface area of 753 m2/g. The cyclic voltammetry shows the specific capacitance of 67 F/g for the Cr(VI) ions, which was found to be 15 times more than the non-doped carbon. CDI studies were performed with optimisation of operational parameters and found that mitigation of Cr(VI) ions was efficient at pH 2 for the applied voltage of 2V. The electrode's performance with real-time chrome wash effluent confirms its potentiality and has better scope upon optimisation. The experimental data fits well with pseudo first-order kinetics, which ensures the nature of electrosorption is physisorption.

Binding capacity and co-migration potential of Pb(II), Cu(II), and Cd(II) on colloids in road runoff

To evaluate the co-migration potential between heavy metal ions and road runoff colloids, the influence of contact time, temperature, initial concentration of metal ions, pH, humic acid (HA), and polymetallic coexistence on the binding capacity of heavy metals onto runoff colloids were investigated. The adsorption of heavy metals by runoff colloids was extremely rapid, approximately 80% of the equilibrium adsorption capacity was achieved in the first 30 min. The binding capacity exhibited an increasing trend with the initial concentration of metal ions increasing, and the maximum adsorption capacities of Pb(II), Cu(II), and Cd(II) achieved 159.13, 56.06, and 78.35 mg/g at 298 K, respectively. The adsorption capacity of Cu(II) and Cd(II) by runoff colloids increased with temperature increasing, while it displayed a converse trend for Pb(II). Neutral pH facilitated the combination of metal ions and runoff colloids. The presence of humic acid increased the binding capacity of Pb(II), Cu(II), and Cd(II) onto runoff colloids by 72.19, 63.31, and 13.83mg/g, respectively. Compared to the monometallic systems, the binding capacity of Pb(II), Cu(II), and Cd(II) by runoff colloids decreased by 18.44%, 22.35%, and 56.06% in polymetallic systems, respectively. Pb(II) bounded with colloids in the road runoff should be controlled preferentially to avoid their migrations to aquatic environments.

Successful removal of fluoride from aqueous environment using Al(OH)3@AC: column studies and breakthrough curve modeling

In this study, we discuss the removal of fluoride from water through column adsorption methods using Al(OH)3@AC as a functional granular activated carbon. The height of the bed, fluoride concentration, and flow rate are the experimental factors used to obtain the breakthrough curves. As the flow rate increased, the breakthrough and saturation times decreased. The analysis of simplified column models, such as the Adams-Bohart, Thomas, and Yoon-Nelson models, revealed that the Clark model best described the adsorption process when fitting the experimental data. The obtained breakthrough curves agreed with the corresponding experimental data. The highest capacity for adsorption obtained during the column procedure was found to be 41.84 mg g-1 with a bed height of 3 cm, an initial fluoride concentration of 10 mg L-1 and a flow rate of 7.5 mL min-1.

Promotion of phosphate release from humic acid-iron hydroxide coprecipitates in the presence of citric acid

Phosphate (P) resources are expected to be depleted within a century. Therefore, promoting balanced phosphorus fertilizer use and understanding phosphorus dynamics in soils containing iron (III), organic acids, and iron (III)-organic molecule particulates is crucial. This study investigated the sorption of citric acid onto humic acid-iron hydr(o)xide coprecipitate (HAFHCP) and the reciprocal effects of citric acid and P sorption on HAFHCP with different C/Fe ratios. The results showed that the maximum sorption capacity (MSC) of citric acid on HAFHCP decreased with increasing C/Fe ratios in the HAFHCP. The P sorption on HAFHCP pre-sorbed with citric acids (denoted as C-P) decreased by 50% compared with that of the MSC on FH. However, citric acids could only reduce P sorption by 20% when P was pre-sorbed on HAFHCP (denoted as P-C). The results suggested that upon the formation of HAFHCP, citric acids might increase P availability, especially in the C-P system. Although citric acids initially inhibited P sorption on HAFHCP in the P-C system, P sorption increased with prolonged reaction time. The exposures of new sorption sites upon dissolution of Fe from HAFHCP by citric acids or/and the formations of Fe bridge between P and organic domains of HAFHCP might contribute to these results. Additionally, a number of large HAFHCP aggregates became smaller while sorbing P due to the increasing electric repulsion on the surfaces of FH, enabling the subsequent dissolutions of more Fe by citric acids from HAFHCP in the P-C system. By integrating these innovative and sustainable strategies, the recycling and reuse of P can be optimized, thereby minimizing the reliance on synthetic fertilizers and mitigating environmental impacts. This approach fosters the efficient utilization of phosphorus resources, improves soil fertility, and enhances the overall resilience of agricultural systems and ecosystems.

Fabrication of Iron-Containing Biochar by One-Step Ball Milling for Cr(VI) and Tetracycline Removal from Wastewater

Simple ball milling technology can simultaneously improve the adsorption performance of adsorbents for heavy metals and organic pollutants and has attracted increasing attention. Iron-modified biochar (Fe@MBC) was prepared by one-step ball milling, and the characterization results proved that FeCl3 was successfully loaded on biochar. The removal rates of Cr(VI) and tetracycline hydrochloride (TC) by Fe@MBC were increased by 88.27% and 82.64% compared with BC. The average pore size, oxygen-containing functional groups and graphitization degree of Fe@MBC are higher than those of BC, which is more conducive to promoting adsorption. The adsorption isotherms show that the adsorption of Cr(VI) and TC on the Fe@MBC surface conforms to the Langmuir type of single-layer adsorption and the Freundlich model of multilayer adsorption, respectively. The maximum adsorption capacities of Cr(VI) and TC are 25.46 and 66.91 mg·g-1, respectively. Kinetic experiments show that the adsorption process is more consistent with the pseudo-second-order model of chemical adsorption. The adsorption process of Cr(VI) and TC on the Fe@MBC surface is a spontaneous endothermic process that becomes more obvious as the temperature increases. The increase in solution pH has a significant impact on the removal rate of Fe@MBC. When the pH value increased from 3 to 11, the adsorption rates decreased by 53.74% and 17.16%, respectively. The presence of PO43-, CO32-, K+, and Cu2+ significantly affects the adsorption of TC by Fe@MBC, and PO43- and CO32- also affect the adsorption of Cr(VI). Mechanistic studies show that ion exchange, electrostatic interaction, pore filling, and hydrogen bonding contribute to the removal of Cr(VI) and TC by Fe@MBC. The removal mechanism of Cr(VI) also involves complexation and redox reactions, and the removal mechanism of TC involves π-π bonds and van der Waals forces. The results show that Fe@MBC is a green and efficient adsorbent.

A new solvent-free pathway for inducing quaternized lignin-derived high molecular weight polymer

In this work, kraft lignin (KL) was polymerized with vinylbenzyl chloride (VBC) in a molar ratio of 1.8:1 (KL: VBC) using sodium persulfate (Na2S2O8) as an initiator at pH 9-10 and temperature of 80-90 °C for 3 h to produce polymer kraft lignin-g-poly(4-vinylbenzyl chloride) KL-poly(VBC) 1. Then, the grafting reaction was conducted with two different imidazole-based monomers of different side-chain lengths (methyl and n-butyl), namely, 1-methylimidazole (MIM), 1-n-butylimidazole (BIM), which led to the formation of novel polymers, kraft lignin-g-poly(4-vinylbenzyl-1-methylimidazolium chloride) KL-poly(VBC-MIM) 2a and kraft lignin-g-poly(4-vinylbenzyl-1-n-butyl imidazolium chloride) KL-poly(VBC-BIM) 2b. The polymer 2a generated a larger molecular weight polymer with a higher charge density and solubility than polymer 2b since the n-butyl group would cause steric hindrance and weaker monomer to react with intermediate polymer 1 in the second stage. The contact angle analysis confirmed more hydrophilicity of polymer 2a, and elemental analysis confirmed the more successful polymerization of polymer 2a. Applying the generated polymers as flocculants for a kaolin suspension confirmed that polymer 2a had similar performance with commercial cationic polyacrylamide (CPAM) flocculants, even though polymer 2a had a smaller molecular weight. This polymerization offers a promising pathway for generating cationic polymers with excellent performance as a flocculant for suspensions.

Migration of spent grain-modified colloidal ferrihydrite: Implications for the in situ stabilization of arsenic, lead, and cadmium in co-contaminated soil

The increase of metal mining, processing, and smelting activities has precipitated a substantial escalation in the contamination of soil by heavy metals. Ferrihydrite (FH) has been commonly used as an amendment for the immobilization of heavy metals in contaminated soil. However, FH suffers from drawbacks such as agglomeration and nonmigratory characteristics, which limit its practical application in soil remediation. Herein, a novel spent grain-modified ferrihydrite (FH-SG) colloidal system was developed, and the FH-SG transport mechanisms in the soil medium were fully studied, focusing in particular on the simultaneous in situ stabilization of arsenic (As), lead (Pb), and cadmium (Cd) in co-contaminated soil. The results showed that the stabilization rates of the FH-SG material reached 94.66%, 96.12%, and 95.52% for water-soluble As, Pb, and Cd, respectively, and 72.22%, 49.39%, and 25.30% for bioavailable As, Pb, and Cd, respectively. The FH-SG material demonstrates notable migration properties in porous media. Theoretical calculation results of a single collector show that the migration deposition of FH-SG material in media is primarily governed by its inherent diffusion characteristics with minimal influence by gravitational forces and media interception. It is noteworthy that the maximum migration distance in quartz sand and soil media with different particle sizes can reach 2.07-2.92 m and 0.78-1.08 m, respectively. Altogether, our findings clearly demonstrate that FH-SG exhibits better stabilization and migration than those of FH alone and most proposed FH colloidal systems. The FH-SG colloidal system holds significant promise for the remediation of various kinds of complex polluted soil.

Magnetic nanocomposite of maize offal biomass for effective sequestration of Congo red and methyl orange dyes from contaminated water: modeling, kinetics and reusability

The current study aims to use a facile and novel method to remove Congo red (CR) and Methyl Orange (MO) dyes from contaminated water with Maize offal biomass (MOB) and its nanocomposite with magnetic nanoparticles (MOB/MNPs). The MOB and MOB/MNPs were characterized with Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), BET, XRD and point of zero charge (pHPZC). The influence of initial CR and MO levels (20-320 mg/L), adsorbent dosage (1-3 g/L), pH (3-9), co-exiting ions, temperature (25-45 °C) and time (15-180 min) was estimated. The findings demonstrated that MOB/MNPs exhibited excellent adsorption of 114.75 and 29.0 mg/g for CR and MO dyes, respectively while MOB exhibited 81.35 and 23.02 mg/g adsorption for CR and MO dyes, respectively at optimum pH-5, and dose 2 g/L. Initially, there was rapid dye removal which slowed down until equilibrium was reached. The interfering/competing ions in contaminated water and elevated temperature favored the dyes sequestration. The MOB/MNPs exhibited tremendous reusability and stability. The dyes adsorption was spontaneous, and exothermic with enhanced randomness. The adsorption effects were well explained with Freundlich model, pseudo second order and Elovich models. It is concluded that MOB/MNPs showed excellent, eco-friendly, and cost-effective potential to decontaminate the water.

Investigating the potential of structurally defective UiO-66 for Sb (V) removal from tailing wastewater

Antimony contamination of tailings from the mining process remain attracted a great amount of concern. In this study, defective UiO-66-X crystal materials are rationally constructed using trifluoroacetic acid and hydrochloric acid as modulators for the removal of Sb(V) from actual tailing sand leachates. XRD and TG characterizations reveal that the number and kind of defects in UiO-66 are influenced by the type of modulators and the addition of trifluoroacetic acid makes UiO-66-TFA contain both cluster and ligand defects. Adsorption experiments show that UiO-66 and UiO-66-HCl achieve 100% removal of Sb(V) at pH 7.5 of the tailing sand leachate, and up to 90% removal of Sb(V) by the three materials at pH 2.5. It is noteworthy that the removal rate of Sb(V) by UiO-66-HCl is still satisfactory even under strongly acidic conditions at pH 0.5, with good potential for practical applications. Four kinetic models are used to fit the adsorption data and the analysis shows that the mechanism of Sb(V) adsorption by three adsorbent is all pseudo-second order and chemisorption acts as an important role in the adsorption process. In addition, the fixed bed adsorption experiments show that the material exhibit good prospects for practical applications.

Research status of soda residue in the field of environmental pollution control

High-quality soda ash (Na2CO3) is mainly produced using the ammonia-alkaline method, generating a significant amount of industrial waste called soda residue. In China, the annual production of soda residue exceeds 10 million tons. The large-scale open-air storage of soda residue not only occupies land but also causes severe pollution to the surrounding environment. Soda residue displays characteristics such as strong alkalinity, high reactivity, and a well-developed pore structure, making it a valuable raw material for producing environmentally functional materials. This article provided an overview and summary of soda residue, including its sources and hazards, basic properties, applications in environmental management (wastewater treatment, flue gas desulfurization, and soil remediation), and associated risks. The limitations of using soda residue in "waste to waste" technologies were also analyzed. Based on this analysis, the article suggests focusing on simultaneous removal of heavy metal ions using soda residue, safely disposing of and acquiring resources from metal-laden sludge, efficiently dechlorinating soda residue, using soda residue for contaminated soil solidification, stabilization, and assisted remediation, controlling pollution via green and circular utilization approaches, and assessing long-term risk.