Alginate-modified biochar derived from Ca(II)-impregnated biomass: Excellent anti-interference ability for Pb(II) removal

Plant extract mediated in-situ synthesis of iron/manganese alginate hydrosphere and its excellent recovery of rare earth elements in mine wastewater

The recovery of rare earth elements (REEs) is a major issue based on environmental governance and sustainable resource utilization. In this study, we developed a novel hydrogel material (Fe/Mn@ALG) by anchoring Fe/Mn NPs on alginate spheres, where Fe/Mn NPs were in-situ synthesized using Euphorbia cochinchensi leaf extract as reduced and protection agents. The Fe/Mn@ALG was applied directly to real mine wastewater, generating efficient and selective recovery of REEs with the coexistence of numerous competing metal ions. As results have shown, Fe/Mn@ALG was a useful adsorbent for REEs with an adsorption efficiency 78.62 % achieved, which was also confirmed by distribution coefficients (Kd), up to 2451.66 mL·g-1. Furthermore, Fe/Mn@ALG exhibited preferential response to REEs over other metal ions with the separation factor (SF) being up to 240. This great adsorption performance and selectivity toward REEs were attributed to its specific surface area, oxygen-rich functional groups and negatively charged surface in acid wastewater. Furthermore, REEs could be greatly desorbed from Fe/Mn@ALG with output concentration being three times higher than the initial concentration. Additionally, Fe/Mn@ALG maintained its good adsorption performance with efficiency reaching 72.24 % after five reuses. Overall, Fe/Mn@ALG can be considered as a promising candidate for wastewater remediation and sustainable management of resources.

Removal of Pb pollution using alginate-coupled magnetic sludge biochar: Solidification and stabilization behavior and electron promotion mechanisms

Environmental and human health problems caused by Pb pollution have attracted much attention, and solidification and stabilization are effective means for its remediation. Improving the ability of biochar to remediate heavy metals through modification is the focus of current biochar research. This study used calcium-alginate gel (GB) and Fe3+ (magnetic) to encapsulate and improve sludge biochar (SB), and explored the adsorption behavior and passivation mechanism of Pb2+ on it from outside to inside. The magnetic-biochar (MB) in magnetic-biochar-gel microspheres (MBGB) showed a homogeneous dispersion and part of the Fe ion was detached from the MB into the three-dimensional pores of the gel. The results of kinetic, isothermal and pH adsorption experiments showed that the MBGB has 108.4 % and 200 % higher Pb2+ adsorption capacity and rate than SB and can be applied to pH 3-9. The adsorption of Pb2+ by MBGB is a multilayer adsorption with both physical and chemical mechanisms. Mineralogical and electrochemical results demonstrate that the cross-linking of the gel with magnetic-biochar (MB) can provide a directional diffusion channel for Pb2+ from the outside to the inside. The electron transfer rate of MBGB was significantly higher than that of SB (222.2 %) after the reaction. The dissolved cations and electrons on the MB guide Pb2+ from the MBGB surface to the internal MB quickly via accelerating the electron transfer and migration rate between Pb2+ and MB. Subsequently, the abundance of PO43- on the MB ensures stable mineral precipitation (Pyromorphite). Moreover, four-step extraction analysis confirmed that most of Pb2+ in MBGB was stable (36.2 % acid-soluble and 47.6 % non-bioavailable). Meanwhile, the Pb adsorption efficiency of MBGB was still >93.0 % after three cycles of adsorption-desorption. Excellent reuse performance and stability guarantee the environmental security of MBGB. The results of the study provide theoretical support for the efficient treatment of Pb2+ polluted water assisted by gel materials.

Alginate-encapsulated biochar as an effective soil ameliorant for reducing Pb phytoavailability to lettuce (Lactuca sativa L.)

The alginate-biochar formulation for metal removal from aquatic environments has been widely tried but its use for lowering phytoavailability of metals in the soil-crop continuum is limited. Biochar has been increasingly used as a soil amendment due to its potential for soil carbon sequestration and sorption capacity. Handling of powdery biochar as a soil top-dressing material is, however, cumbersome and vulnerable to loss by water and wind. In this experiment, biochar powder, which was pyrolyzed from oak trees, was encapsulated into beads with alginate, which is a naturally occurring polysaccharide found in brown algae. Both batch and pot experiments were conducted to examine the effects of the alginate-encapsulated biochar beads (BB), as compared to its original biochar powdery form (BP), on the Pb adsorption capacity and phytoavailability of soil Pb to lettuce (Lactuca sativa L.). The BB treatment improved reactivity about six times due to a higher surface area (287 m2 g-1) and five times due to a higher cation exchange capacity (50 cmolc kg-1) as compared to the BP treatment. The maximum sorption capacity of Pb was increased to 152 from 81 mg g-1 because of surface chemosorption. Adsorption of Pb onto BB followed multiple first-order kinetics and comprised fast and slow steps. More than 60% of the Pb was adsorbed in the fast step, i.e., within 3 h. Also, the BB treatment, up to the 5% level (w/w), increased soil pH from 5.4 to 6.5 and lowered the phytoavailable fraction of Pb in soil from 5.7 to 0.3 mg kg-1. The Pb concentrations in lettuce cultivated at 5% for the BP and BB treatments were similar but 63 and 66% lower, respectively, than those of the control soil. The results showed that the encapsulation of biochar with alginate enhanced adsorption by the biochar.

Insights into adsorption behavior and mechanism of Cu(II) onto biodegradable and conventional microplastics: Effect of aging process and environmental factors

The widespread promotion attempt of biodegradable plastics is considered as an effective solution to address conventional plastic pollution. However, the interaction of microplastics (MPs) easily broken down from biodegradable plastics with the coexisting pollutants in aquatic environments has gained less attention. Herein, we investigated the effects of the aging process and environmental factors on copper (Cu(II)) adsorption behavior by biodegradable polylactic acid and conventional polystyrene MPs. Results demonstrated that the aging process significantly altered physicochemical properties of both types of MPs, and PLA showed less resistance to aging. The aged polylactic acid MPs (aged-PLA) exhibited the far highest Cu(II) maximum adsorption capacity (7.13 mg/g) mainly due to its abundant oxygen-containing functional groups (OCFGs), followed by pristine polylactic acid (PLA, 6.08 mg/g), aged polystyrene (aged-PS, 0.489 mg/g) and pristine polystyrene (PS, 0.365 mg/g). The adsorption kinetics of Cu(II) on PLA MPs were controlled by film and intraparticle diffusion, while film diffusion governed the Cu(II) adsorption onto PS MPs. In addition to roles of rougher surface structure, greater surface area and pore filling, the complexation of OCFGs and electrostatic interaction were critical to the adsorption mechanism of aged-PLA and aged-PS, and cation-π interaction was associated with adsorption of aged-PS. Moreover, the adsorption capacity of Cu(II) on aged MPs gradually grew with the increasing pH from 4 to 7. Besides, humic acid significantly promoted the adsorption of Cu(II) at a low concentration (0-20 mg/L) due to the formation of binary mixtures of MPs-HA but inhibited the adsorption at a high concentration (50 mg/L) because of its competitive effect, suggesting the dual roles of humic acid in the adsorption process. Overall, our findings provide a better understanding of the adsorption behavior of metals on biodegradable MPs and emphasize their non-negligible risk as carriers of contaminant.

Modified kaolin hydrogel for Cu2+ adsorption

Removal of Cu2+ ions from contaminated water is an important but challenging task. This study reports the synthesis of a composite hydrogel from two natural polysaccharides, namely, sodium alginate and chitosan, using inexpensive kaolin as a raw material and polyacrylamide as a modifier. The hydrogel had a high adsorption capacity and selectivity for Cu2+. The composite hydrogel was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The pseudo-second-order kinetic model was the most suitable model for the kinetic results, and the Langmuir isotherm model was the most representative of the sorption system. The results revealed that the adsorption process was mainly controlled by chemisorption. The maximum adsorption capacity of the adsorbent was 106.4 mg·g−1. Therefore, this study presents a new perspective on the application of composite hydrogels as Cu2+ adsorbents.

Effect of pyrolysis temperature of biochar on Cd, Pb and As bioavailability and bacterial community composition in contaminated paddy soil

To further investigate the effect of pyrolysis temperature on bioavailable Cd, Pb and As, as well as the bacterial community structure in multi-metal(loid) contaminated paddy soil, six types of biochar derived from wood sawdust and peanut shell at 300 °C, 500 °C and 700 °C were prepared and incubated with Cd, Pb and As contaminated paddy soil for 45 days. The results showed that adding biochar decreased bioavailable Cd by 31.3%- 42.9%, Pb by 0.61-56.1%, while bioavailable As changed from 9.68 mg kg^-1 to 9.55-10.84 mg kg^-1. We found that pyrolysis temperature of biochar had no significant effect on Cd bioavailability while Pb bioavailability decreased obviously with pyrolysis temperature raising. Biochar reduced the proportion of soluble and exchangeable Cd from 45.0% to 11.2-15.4% in comparison with the control, while no significant effect on the speciation of Pb and As. Wood sawdust biochar (WSBs) had more potential in decreasing bioavailable Cd and Pb than peanut shell biochar (PSBs). Although high-temperature biochar resulted a larger increase in bacterial species than low-and mid- temperature biochar, feedstock played a more important role in altering soil bacterial diversity and community composition than pyrolysis temperature. PSBs increased the diversity of soil bacteria through elevating soil dissolved carbon (DOC). Biochar altered soil bacterial community structure mainly by altering the level of soil electricity conductivity, DOC and bioavailable Cd. In addition, applying high-temperature PSBs increased the genus of bacteria that relevant to nitrogen cycling, such as Nitrospira, Nitrosotaleaceae and Candidatus_Nitrosotalea.

Application of chitosan- and alginate-modified biochars in promoting the resistance to paddy soil acidification and immobilization of soil cadmium

To develop more green, practical and efficient biochar amendments for acidic soils, chitosan-modified biochar (CRB) and alginate-modified biochar (ARB) were prepared, and their effects on promoting soil pH buffering capacity (pHBC) and immobilizing cadmium (Cd) in the paddy soils were investigated through indoor incubation experiments. The results of Fourier transform infrared spectroscopy and Boehm titration indicated that the introduction of chitosan and sodium alginate effectively amplified the functional groups of the biochar, and improved acid buffering capacity of the biochar. Since there was a plateau region between pH 4.5 and 5.5 in acid-base titration curve of the CRB, adding this biochar to acidic paddy soils apparently improved the pHBC and enhanced the acidification resistance of the paddy soils. The addition of ARB enhanced the reduction reactions during submerging and weakened the oxidation reactions during draining, thus retarded the decline of paddy soil pH during drainage. Furthermore, the pH of the paddy soils with ARB addition was higher at the end of draining, which reduced the activity of soil Cd. Considering the environmental sustainability of chitosan and sodium alginate and convenience of preparation method, biochars modified with these two materials provided alternatives for acidic paddy soil amelioration and heavy metal immobilization. However, the additional experiments should be conducted under field conditions to confirm practical application effects in the future.

Physical-Chemical Characterization of Different Carbon-Based Sorbents for Environmental Applications

Biochar has been used in various applications, e.g., as a soil conditioner and in remediation of contaminated water, wastewater, and gaseous emissions. In the latter application, biochar was shown to be a suitable alternative to activated carbon, providing high treatment efficiency. Since biochar is a by-product of waste pyrolysis, its use allows for compliance with circular economics. Thus, this research aims to obtain a detailed characterization of three carbonaceous materials: an activated carbon (CARBOSORB NC 1240^®) and two biochars (RE-CHAR^® and AMBIOTON^®). In particular, the objective of this work is to compare the properties of three carbonaceous materials to evaluate whether the application of the two biochars is the same as that of activated carbon. The characterization included, among others, particle size distribution, elemental analysis, pH, scanning electron microscope, pore volume, specific surface area, and ionic exchange capacity. The results showed that CARBOSORB NC 1240^® presented a higher specific surface (1126.64 m²/g) than AMBIOTON^® (256.23 m²/g) and RE-CHAR^® (280.25 m²/g). Both biochar and activated carbon belong to the category of mesoporous media, showing a pore size between 2 and 50 nm (20-500 Å). Moreover, the chemical composition analysis shows similar C, H, and N composition in the three carbonaceous materials while a higher O composition in RE-CHAR^® (9.9%) than in CARBOSORB NC 1240 ^® (2.67%) and AMBIOTON^® (1.10%). Differences in physical and chemical properties are determined by the feedstock and pyrolysis or gasification temperature. The results obtained allowed to compare the selected materials among each other and with other carbonaceous adsorbents.

Resource utilization of rice husk biomass: Preparation of MgO flake-modified biochar for simultaneous removal of heavy metals from aqueous solution and polluted soil

In general, the remediation performance of heavy metals can be further improved by metal-oxide modified biochar. This work used MgO-modified rice husk biochar (MgO-5%@RHB-450 and MgO-5%@RHB-600) with high surface activity for simultaneous remediation and removal of heavy metals in soil and wastewater. The adsorption of MgO-5%@RHB-450/MgO-5%@RHB-600 for Cd(II), Cu(II), Zn(II) and Cr(VI) followed the pseudo-second order, with the adsorption capacities reaching 91.13/104.68, 166.68/173.22, 80.12/104.38 and 38.88/47.02 mg g^-1, respectively. The addition of 1.0% MgO-5%@RHB-450 and MgO-5%@RHB-600 could effectively decrease the CaCl₂-extractable Cd concentration (CaCl₂-Cd) by 66.2% and 70.0%, respectively. Moreover, MgO-5%@RHB-450 and MgO-5%@RHB-600 facilitated the transformation of exchangeable fractions to carbonate-bound and residual fractions, and reduced the exchangeable fractions by 8.1% and 9.6%, respectively. The mechanisms for the removal of heavy metals from wastewater by MgO-5%@RHB-450 and MgO-5%@RHB-600 mainly included complexation, ion exchange and precipitation, and the immobilization mechanisms in soil may be precipitation, complexation and pore filling. In general, this study provides high-efficiency functional materials for the remediation of heavy metal pollution.

Optimization of target biochar for the adsorption of target heavy metal ion

The purpose of this work is to study the pyrolysis conditions of target biochar suitable for target heavy metal ion, to characterize the optimized target biochar, and to study the adsorption performance of biochar. With Cu²⁺ and Zn²⁺ as the target pollutants, the pyrolysis conditions involved in the preparation process as pyrolysis temperature, pyrolysis time, and heating rate were evaluated and optimized from Box–Behnken Design (BBD), response surface methodology (RSM) and desirability function, the optimized pyrolysis conditions of target biochar for Cu²⁺ (Cu-BC) and Zn²⁺ (Zn-BC) were obtained. The optimum pyrolysis parameters for Cu-BC and Zn-BC were pyrolysis time of 3.09 and 2.19 h, pyrolysis temperature of 425.27 and 421.97 °C, and heating rate of 19.65 and 15.88 °C/min. The pseudo-second-order kinetic and Langmuir isotherm model proved to be the best fit for the equilibrium data, with a maximum adsorption capacity (Q_max) fitted by Langmuir model were 210.56 mg/g for Cu²⁺ by Cu-BC and 223.32 mg/g for Zn²⁺ by Zn-BC, which were both higher than the Q_max of unoptimized biochar (BC) for Cu²⁺ (177.66 mg/g) and Zn²⁺ (146.14 mg/g). The physical properties, chemical structure, surface chemistry properties of Cu-BC and Zn-BC were characterized by Zeta potential meter, Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). This study puts forward a new perspective for optimizing target biochar production for special environmental application.

Engineered biochar: A multifunctional material for energy and environment

Biochar is a stable carbon-rich product loaded with upgraded properties obtained by thermal cracking of biomasses in an oxygen-free atmosphere. The pristine biochar is further modified to produce engineered biochar via various physical, mechanical, and chemical methods. The hasty advancement in engineered biochar synthesis via different technologies and their application in the field of energy and environment is a topical issue that required an up-to-date review. Therefore, this review deals with comprehensive and recent mechanistic approaches of engineered biochar synthesis and its further application in the field of energy and the environment. Synthesis and activation of engineered biochar via various methods has been deliberated in brief. Furthermore, this review systematically covered the impacts of engineered biochar amendment in the composting process, anaerobic digestion (AD), soil microbial community encouragement, and their enzymatic activities. Finally, this review provided a glimpse of the knowledge gaps and challenges associated with application of engineered biochar in various fields, which needs urgent attention in future research.

Adsorption of copper, and zinc onto novel Ca-alginate-biochar composite prepared by biochars produced from pyrolysis of groundnut husk

Alginate-based composites have been studied for adsorption technology as adsorbents due to their biocompatible, non-toxic, and cost-effective properties. In this work, groundnut husk biochar (GHB), calcium alginate (CA), and groundnut husk biochar/calcium alginate novel composites (%10) (CA-GHB1) and (% 20) (CA-GHB2) are synthesized and characterized using BET, SEM, EDX, FTIR, TGA. Adsorption performance is compared among GHB, CA, CA-GHB1, and CA-GHB2 composites to remove Cu(II), Zn (II) from aqueous solutions. Factors affecting adsorption, as well as kinetics, equilibrium, and thermal properties of adsorption, were studied using conventional equations. Adsorption isotherm models were used for two and three-parameter isotherm models to understand the interaction between the adsorbent and the adsorbate. 24.3, 44.6, 45.6, and 40.73 mg g^-1 for removal of Cu(II) on GHB, CA, CA-GHB1, and CA-GHB2 and 32.16, 25.07, 36.09, and 40.55 mg g^-1 for removal of Zn(II) on GHB, CA, CA-GHB1, and CA-GHB2 found maximum adsorption capacity (Qm) calculated from Langmuir isotherm. According to D-R isotherm data, the adsorption process is classified as physical adsorption. Thermodynamically, the adsorption process is non-spontaneous and endothermic.

Efficient reclaiming phosphate from aqueous solution using waste limestone modified sludge biochar: Mechanism and application as soil amendments

A novel limestone-modified biochar derived from sewage sludge was prepared to reclaim phosphorus (P) from aqueous solution, and the potential application of P-laden biochar as soil amendments was also investigated. The limestone-modified biochar demonstrated excellent performance on phosphate recovery from aqueous solution in a wide range of pH (2.0-11.0), with maximum adsorption capacity of the biochar (Limestone/sludge mass ratio of 3:1) up to 231.28 mg P/g, which was 10.7 times that of the original sludge biochar. The adsorption was well described by the pseudo second-order model and Langmuir isotherm model. According to the adsorption thermodynamic parameters, the phosphate adsorption was spontaneous (ΔG⁰ < 0) and endothermic (ΔH⁰ > 0) so that increasing the temperature was beneficial to adsorption. Characterization analysis by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscope-energy dispersive spectrometer (SEM-EDS) proved that electrostatic attraction, surface complexation and brushite (CaHPO₄^.2H₂O) precipitation were the dominant mechanism. The P-laden biochar exhibited an excellent ability to be reused as a new slow-release P fertilizer for soil. Pot experiment results showed that the treatment of P-laden LB 3:1 (P content of 22.8%) addition (1 wt%) significantly promoted Indian Lettuce germination (increasing by 14.4%), plant height (increasing by 18.6%), and dry biomass (53.0%) compared with the control, though it underperformed compared to commercial fertilizer.

Batch study for Pb2+ removal by polyvinyl alcohol-biochar macroporous hydrogel bead

In this paper, a novel adsorbent which used polyvinyl alcohol, alginate and biochar was successfully made and been used to remove lead from aqueous solutions. Batch experiments were carried out to evaluate the adsorption capacities of Pb (II) on this bead. Experimental data were analysed by the model equations like Langmuir and Freundlich and adsorption kinetic constants were determined using pseudo-first-order (PFO) and pseudo-second-order (PSO). In this study, the adsorption characteristics of Pb (II) were well fitted by the Langmuir isotherm model and pseudo-second-order (PSO) kinetic model. The adsorption of Pb (II) onto PVA-biochar beads are spontaneous and exothermic at 303-333 K by the evidence of the changes in standard Gibbs free energy, standard enthalpy and standard entropy. The maximum adsorption capacity for Pb (II) was estimated to be 176.40 mg/g, which is comparable with other adsorbents. While the maximum adsorption increased varying the pH of initial solution from 2 to 6, the effect on the adsorption amount by the sodium ion concentration is not very large. The results of EDS spectra indicated that the existence of lead in polyvinyl alcohol (PVA)-biochar bead after adsorption, which proving the adsorption of lead. In XPS spectrum, the observed Pb elements also demonstrated that the lead was adsorbed by PVA-biochar bead.

Evaluation of Lead (Pb(II)) Removal Potential of Biochar in a Fixed-bed Continuous Flow Adsorption System

BACKGROUND

Lead (Pb(II)) exposure from drinking water consumption is a serious concern due to its negative health effect on human physiology. A commercially available filter uses the adsorption potential of activated carbon for removing heavy metals like Pb(II). However, it has some constraints since it uses only surface area for the adsorption of these contaminants. Biochar produced via slow pyrolysis of biomass shows the presence of oxygen-containing functional groups on its surface that take part in the adsorption process, with higher removal potential compared to activated carbon.

OBJECTIVES

The current study examined the adsorption kinetics and mechanisms of Pb(II) removing potential of biochar from water using a fixed-bed continuous flow adsorption system.

METHODS

The effect of initial Pb(II) concentration, mass of adsorbent (bed depth), and flow rate on adsorption potential were evaluated. The Adams-Bohart model, Thomas model, and Yoon-Nelson model were applied to the adsorption data.

RESULTS

The maximum removal efficiency of Pb(II) was 88.86 mg/g. The result illustrated that the Yoon-Nelson model is the best fit to analyze the adsorption phenomena of Pb(II) in a fixed-bed biochar column.

CONCLUSIONS

The breakthrough data obtained from this study can be utilized to design a point of use filter that would be able to effectively remove Pb(II) from drinking water.

COMPETING INTERESTS

The authors declare no competing financial interests.

Removal of high-molecular-weight polycyclic aromatic hydrocarbons by a microbial consortium immobilized in magnetic floating biochar gel beads

A bacterial consortium immobilized in magnetic floating biochar gel beads is proposed to remove high-molecular-weight polycyclic aromatic hydrocarbons. The microbial consortium performed better than single strains and consisted of four strains of marine bacteria for degrading pyrene (PYR), two strains for benzo(a)pyrene (BAP), and three strains for indeno(1,2,3-cd)pyrene (INP), which were isolated from oil-contaminated seawater. The immobilized cells could biodegrade 89.8%, 66.9% and 78.2% of PYR, BAP and INP, respectively, and had better tolerance to pH, temperature and salinity than free cells. The Andrews model was used to explore the biodegradation kinetics, and when the initial concentrations of PYR, BAP, and INP were 7.80, 3.05, and 3.41 mg/L, the specific biodegradation rates reached maximum values of 0.2507, 0.1286, and 0.1930 d^-1, respectively. The immobilized microbial consortium had a high HMW-PAH removal ability and good floatability and magnetic properties and could be collected by an external magnetic field.

Different adsorption behaviors and mechanisms of a novel amino-functionalized hydrothermal biochar for hexavalent chromium and pentavalent antimony

A novel amino-functionalized hydrothermal biochar modified with nitric acid and nicotinamide (NMSH) was prepared and applied to remove heavy metal in different systems. The study of batch adsorption found that NMSH had different adsorption behaviors for Cr(VI) and Sb(V), and different concentrations of heavy metal ions exhibited different coadsorption behaviors in mixed system. NMSH had great anti-interference ability to coexisting inorganic ion and humic substance. The maximum adsorption capacity of NMSH was 132.74 mg/g for Cr(VI), and 241.92 mg/g for Sb(V). Moreover, different interfering ions and matter had different effects on adsorption. The mechanism study found that the adsorption mechanism of NMSH involved multiple interactions, and the mechanisms were different. Some O-containing functional groups of NMSH could reduce Cr(VI) to Cr(III), but not Sb(V). NMSH had great removal efficiency and reusability performance, which suggested that NMSH had prospects for practical wastewater treatment.

Adsorption of Lead (II) from Aqueous Solution with High Efficiency by Hydrothermal Biochar Derived from Honey

A novel natural honey hydrothermal biochar (HHTB) was prepared using natural honey as raw material. The as-prepared adsorbent was applied to adsorb Pb²⁺ from aqueous solution and characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy to investigate the structure and morphology change of the adsorbent before and after Pb²⁺ adsorption. The influence of the pH, initial Pb²⁺ concentration, temperature, and contact time on the adsorption of Pb²⁺ was systematically investigated. The results revealed that the adsorption capacity for Pb²⁺ is up to 133.2 mg·g⁻¹ at initial pH of 5.0 and adsorption temperature of 298 K. Meanwhile, the adsorption of Pb²⁺ on HHTB can be well fitted by the pseudo-second-order model and Langmuir isotherm model. The adsorbent had great selectivity for Pb²⁺ from the aqueous solution containing coexisting ions including Cd²⁺, Co²⁺, Cr³⁺, Cu²⁺, Ni²⁺ and Zn²⁺. Furthermore, the adsorption of Pb²⁺ on HHTB was attributed to complexation coordination, where it involved hydroxyl and carboxylic groups on HHTB in the process of adsorption of Pb²⁺.

Shewanella oneidensis MR-1 impregnated Ca-alginate capsule for efficient Cr(VI) reduction and Cr(III) adsorption

Shewanella oneidensis MR-1 (MR-1)-impregnated alginate capsules with 3D porous structure were prepared through cation crossing-linking and was used for the Cr(VI) reduction and removal. After being encapsulated by alginate, the endurance of the MR-1 was largely enhanced under conditions of high Cr(VI) concentrations (up to 4 mM) and low pH (pH 5). The Cr(VI) reduction over the MR-1-impregnated alginate capsules could be fitted by pseudo first-order kinetic model. With the Cr(VI) initial concentration increasing from 1 to 4 mM, the first-order rate constant for the encapsulated MR-1 (k_capsules) and free cells (k_cells) fell by 26.3% and 82.4%, respectively. At pH 5, the k_capsules value was 0.19 h^{- 1}, which was about 3.7 times higher than k_cells. Moreover, the encapsulated MR-1 held 90.5% of the Cr(VI) reduction ability after 15 days of resting time, while the free MR-1 held 19.7%. After bioreduction, 73.6% of total chromium was adsorbed on the MR-1 impregnated Ca-alginate capsules. XPS results showed 85% of the adsorbed chromium was Cr(III). The mechanism for chromium removal over the MR-1-impregnated Ca-alginate capsules was proposed with the following steps: (1) Cr(VI) was bioreduced via the encapsulated MR-1; (2) the reduced soluble Cr(III) was adsorbed by alginate selectively. In the study, the Ca-alginate shell of the cabbage-like MR-1 impregnated capsules could be a shelter for encapsulated MR-1 to endure unfavorable conditions (e.g., low pH and high concentration of Cr(VI)) and immobilize the soluble chromium. Considering the obtained capsules derived from biomolecules were environment-friendly, the MR-1-impregnated Ca-alginate capsules were potential for the application in the remediation of environmental pollution. Graphical abstract.

Electrochemical recovery of cobalt using nanoparticles film of copper hexacyanoferrates from aqueous solution

Nanoparticles film of copper metal hexacyanoferrates (CuHCF) was fabricated to electrochemically separate Co²⁺ in aqueous solutions under various conditions such as applied potential, solution pHs, initial concentrations, contact time and coexisting ions. Results showed that the removal efficiency conducted in reduction potential was obviously higher than that in oxidation potential. The optimal pH for Co²⁺ adsorption occurred at 8.0. Coexisting ions studies revealed that Co²⁺ could be removed from aqueous solutions containing Li⁺, Cu²⁺ and Al³⁺. Considering that cobalt and lithium are the main metallic elements in LiCoO₂, the effect of different ionic strengths (IS) of LiNO₃ (0.5, 1, 2, 5, 10) on adsorption was further investigated. Results showed that IS of LiNO₃ had little impact on the removal efficiency of Co²⁺, which indicated the potential of selective recovery of cobalt from LiCoO₂ in spent lithium-ion batteries. X-ray energy-dispersion spectroscopy (EDS) confirmed that the Co²⁺ could be adsorbed effectively onto CuHCF film. The adsorption was well described by Langmuir isotherm and the maximum sorption capacity is 218.82 mg/g. The kinetic rate of Co²⁺ adsorption was rapid initially and attained equilibrium within 60 min, and the data well fitted the Redlich-Peterson and the Elovich model, implying a chemisorption dominated process.

Risk Evaluation of Pyrolyzed Biochar from Multiple Wastes

This paper aims at demonstrating the significance of biochar risk evaluation and reviewing risk evaluation from the aspects of pyrolysis process, feedstock, and sources of hazards in biochar and their potential effects and the methods used in risk evaluation. Feedstock properties and the resultant biochar produced at different pyrolysis process influence their chemical, physical, and structural properties, which are vital in understanding the functionality of biochar. Biochar use has been linked to some risks in soil application such as biochar being toxic, facilitating GHGs emission, suppression of the effectiveness of pesticides, and effects on soil microbes. These potential risks originate from feedstock, contaminated feedstock, and pyrolysis conditions that favor the creation of characteristics and functional groups of this nature. These toxic compounds formed pose a threat to human health through the food chain. Determination of toxicity levels is a first step in the risk management of toxic biochar. Various sorption methods of biochar utilized low-cost adsorbents, engineered surface functional groups, and nZVI modified biochars. The mechanisms of organic compound removal was through sorption, enhanced sorption, modified biochar, postpyrolysis thermal air oxidation and that of PFRs degradation was through activation, photoactive functional groups, magnetization, and hydrothermal synthesis. Emissions of GHGs in soils amended with biochar emanated through physical and biotic mediated mechanisms. BCNs have a significance in reducing the health quotient indices for PTEs risk contamination by suppressing cancer risk arising from consumption of contaminated food. The degree of environmental risk assessment of HM pollution in biomass and biochars has been determined by using potential ecological risk index and RAC while organic contaminant degradation by EPFRs was considered when assessing the environmental roles of biochar in regulating the fate of contaminants removal. The magnitude of technologies’ net benefit must be considered in relation to the associated risks.

Removal of Mercury (II) by EDTA-Functionalized Magnetic CoFe2O4@SiO2 Nanomaterial with Core-Shell Structure

In order to reduce the difficulty and risk of operation, decrease the preparation time and improve the adsorption performance of magnetic nano-silicon adsorbent with core-shell structure, a carboxylated CoFe₂O₄@SiO₂ was prepared by EDTA-functionalized method using a safe, mild and simple hydrothermal method. The results show that the prepared material of CoFe₂O₄@SiO₂-EDTA has a maximum adsorption capacity of 103.3 mg/g for mercury ions (Hg(II)) at pH = 7. The adsorption process of Hg(II) is a chemical reaction involving chelation and single-layer adsorption, and follows the pseudo-second-order kinetic and Langmuir adsorption isotherm models. Moreover, the removal of Hg(II) is a spontaneous and exothermic reaction. The material characterization, before and after adsorption, shows that CoFe₂O₄@SiO₂-EDTA has excellent recyclability, hydrothermal stability and fully biodegradable properties. To summarize, it is a potential adsorption material for removing heavy metals from aqueous solutions in practical applications.

Sulfamic acid modified hydrochar derived from sawdust for removal of benzotriazole and Cu(II) from aqueous solution: Adsorption behavior and mechanism

A novel hydrochar adsorbent derived from sawdust (SAHC) was prepared for highly efficient simultaneous removal of benzotriazole (BTA) and Cu(II) from aqueous solution. The prepared adsorbent was characterized by several methods such as SEM, FTIR, and XPS. Batch adsorption experiments showed that the maximum adsorption capacity of SAHC for BTA and Cu(II) was 159.91 and 298.86 mg/g, respectively. Additionally, the study of competitive adsorption showed that the adsorption of Cu(II) was barely affected by the existence of BTA while the BTA adsorption was significantly improved with the coexistence of Cu(II). The study of adsorption mechanism found that Cu(II) could chelate with BTA to form complex, and the complexing-bridging interaction improved BTA adsorption. SAHC exhibited high adsorption ability after six adsorption cycles, which indicated excellent stability and regeneration performance of SAHC. All the results suggested that SAHC could be a promising adsorbent for simultaneous removal of BTA and Cu(II) from wastewater.

Preparation, characterization and application in cobalt ion adsorption using nanoparticle films of hybrid copper-nickel hexacyanoferrate

Different mole ratios (n Cu : n Ni = x : y) of hybrid copper-nickel metal hexacyanoferrates (Cu x Ni y HCFs) were prepared to explore their morphologies, structure, electrochemical properties and the feasibility of electrochemical adsorption of cobalt ions. Cyclic voltammetry (CV), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) indicated that the x : y ratio of Cu x Ni y HCF nanoparticles can be easily controlled as designed using a wet chemical coprecipitation method. The crystallite size and formal potential of Cu x Ni y HCF films showed an insignificant change when 0 ≤ x : y < 0.3. Given the shape of the CV curves, this might be due to Cu2+ ions being inserted into the NiHCF framework as countercations to maintain the electrical neutrality of the structure. On the other hand, crystallite size depended linearly on the x : y ratio when x : y > 0.3. This is because Cu tended to replace Ni sites in the lattice structure at higher molar ratios of x : y. Cu x Ni y HCF films inherited good electrochemical reversibility from the CuHCFs, in view of the cyclic voltammograms; in particular, Cu1Ni2HCF exhibited long-term cycling stability and high surface coverage. The adsorption of Co2+ fitted the Langmuir isotherm model well, and the kinetic data can be well described by a pseudo-second order model, which may imply that Co2+ adsorption is controlled by chemical adsorption. The diffusion process was dominated by both intraparticle diffusion and surface diffusion.