Adsorption Capacity Of Cd Research Articles

Adsorption Characteristics of Arsenic and Cadmium by FeMnNi-LDH Composite Modified by Fulvic Acid and Its Mechanisms

Toxic As(Ⅲ) and Cd(Ⅱ) ions in water can be transferred and enriched into human bodies through the food chain, causing serious health damage at excessive levels. In this study, fulvic acid (FA) was selected as the modifier of iron-manganese-nickel layered double hydroxide (FeMnNi-LDH), and a stable layered composite (FA@FeMnNi-LDH) was prepared using the co-precipitation method, which could adsorb As(Ⅲ) anions and Cd(Ⅱ) cations simultaneously, especially with the higher adsorption capacity of the cation Cd(Ⅱ). Its structure was characterized by XRD, TEM, FT-IR, and XPS, and the adsorption capacity and mechanisms of As(Ⅲ) and Cd(Ⅱ) in water by the composite were also investigated. The results showed that with typical characteristic peaks of layered double hydroxides, the synthesized composite possessed a stable structure, maximum FA loading capacity, and optimal adsorption performance. The adsorption kinetics of As(Ⅲ) and Cd(Ⅱ) conformed to the pseudo-second-order kinetic model, and the adsorption isotherms well-followed the Langmuir model, with the maximum adsorption capacity at 25℃ being 249.60 mg·g-1 for As(Ⅲ) and 156.50 mg·g-1 for Cd(Ⅱ), respectively. The composite exhibited a good adsorption performance on As(Ⅲ) and Cd(Ⅱ) in the range of pH 2-7 and pH 4-7, respectively. The competitive adsorption effect of co-existed anions on As(Ⅲ) showed a sequence of PO43->CO32->NO3-, and that of co-existed cations on Cd(Ⅱ) was Pb2+>Cu2+>K+. The adsorption capacity of As(Ⅲ) and Cd(Ⅱ) decreased with the increase in the concentration of competing ions. The main adsorption mechanism for As(Ⅲ) was ion-exchange occurring in the interlayers of LDH, and that for Cd(Ⅱ) was coordination complexation occurring with the loaded FA, respectively. In conclusion, the prepared FA@FeMnNi-LDH composite material posed a good application prospect for adsorption removal of As(Ⅲ) and Cd(Ⅱ) in water and their toxicity control.

Study on the mechanism of removing Pb (II) and Cd (II) from industrial wastewater by copper based MOF modified with ethylenediamine

In this study, we synthesized ethylenediamine modified copper-based organometallic framework by hydrothermal method. The materials were characterized by SEM, XRD, FTIR, XPS and BET. The adsorption properties of the materials for Cu (II) and Pb (II) were studied in depth by varying the adsorbate concentration, ionic strength, contact time, adsorption temperature and pH of the solutions. At a pH value of 5.2, the maximum adsorption capacities for Cd (II) and Pb (II) were 909.09 and 12.85 mg·g−1 within 20 min, respectively. The adsorption process was fitted with pseudo second order kinetics and Langmuir isotherm model. Thermodynamic experiments showed that an appropriate temperature reduction was helpful to promote Cd (II) and Pb (II) removal. Given that the underlying chemical properties of the materials are unknown, the factors leading to affecting the selectivity of heavy metals remain unclear. To reveal key molecular level factors, we performed state-of-the-art computational simulations combining high-density functional theory (DFT), semi empirical calculations, and configurational sampling of metal ion MOF binding modes in aqueous solution. And the intermolecular interactions, absorption patterns, and most remarkable structural features were determined to improve the selectivity against heavy metals. The mechanism of heavy metals separation by ethylenediamine grafted MOFs was rationalized using quantum mechanical and electrostatic principles. Density functional theory calculations showed that the chelating effect of amino groups, ion-exchange effect and electrostatic interaction of hydroxyl groups were the main factors to improve the removal efficiency of Cd (II) and Pb (II). These results provide a new method for the preparation of MOF based adsorbents and demonstrate the great potential of ethylenediamine modified copper based metal organic frameworks for high-performance environmental remediation.

Sorption and mobility of cadmium in soil impacted by irrigation waters

Soil contamination by Cd has drawn global attention, while how irrigation waters modulate Cd sorption and mobility in soil remains obscure. We address this by investigating how cropped sandy soil irrigated with different waters altered Cd sorption and mobility using a rhizobox experiment followed by a batch experiment. Maize were planted in the rhizoboxes and irrigated by reclaimed water (RW), livestock wastewater (LW) and deionized water (CK), respectively. The bulk soil sampled from each treatment after 60 days of growth was employed to measure the Cd sorption and mobility using the isothermal adsorption and desorption experiments. The results showed that, in a small rhizobox experiment, the adsorption rate of Cd by the bulk soil in the adsorption phase was much faster than the desorption rate in desorption phase. Irrigation with RW and LW both reduced the Cd adsorption capacity of soil, and the reducing degree brought by LW was more obvious. Cd desorption rate was very low but keep increasing in the desorption stage, and pre-RW irrigation had the potential to increase Cd desorption from soil. Although the results were obtained based on the bulk soil sampled from a rhizobox experiment, our study strongly suggests that the altered Cd adsorption and desorption behavior in the soil caused by the RW and LW irrigation may risk the farmland ecosystem and deserve more concern.

Co-adsorption mechanisms of Cd(II) and As(III) by an Fe-Mn binary oxide biochar in aqueous solution

Biochar can remove oppositely charged ionic species of Cd(II) and As(III)/As(V) from water but the co-adsorption mechanisms of the metal(loid)s are poorly understood. This study aims to unravel the co-absorption mechanisms of Cd(II) and As(III) by a Pennisetum sp. straw biochar (BC) modified with Fe-Mn oxide (FMBC). The maximum adsorption capacity of Cd(II) and As(III) by FMBC was 141.1 and 31.8 mg/g, respectively, which was 2.71 and 3.89 times higher than that of BC. The adsorption of Cd(II) by FMBC demonstrated a homogeneous monolayer chemical process, while the As(III) adsorption presented a heterogeneous multilayer process. In the dual-adsorbate system, Cd(II) increased the adsorption of As(III) on FMBC by 5.1–123.9%, while As(III) reduced the adsorption of Cd(II) by 0.7–24.8%, indicating respective synergism and competition effect. Systematic co-adsorption experiments and adsorbent characterization results suggested that the synergistic mechanism occurred via electrostatic attraction and ternary surface complexation, whereas the competitive effect emerged due to complexing reaction with oxygen-containing functional groups of FMBC. The FMBC could be a potential adsorbent to adsorb Cd(II) and As(III) simultaneously.

Effect of iron impregnation ratio on the properties and adsorption of KOH activated biochar for removal of tetracycline and heavy metals

The effect of iron impregnation ratio on magnetic biochars (MBCs) prepared by biomass pyrolysis accompanied by KOH activation has been less reported. In this study, MBCs were produced by one-step pyrolysis/KOH-activation of walnut shell, rice husk and cornstalk with different impregnation ratios (0.3–0.6). The properties, adsorption capacity and cycling performance for Pb(II), Cd(II) and tetracycline of MBCs were determined. MBCs prepared with low impregnation ratio (0.3) showed stronger adsorption capacity on tetracycline. The adsorption capacity of WS-0.3 toward tetracycline was up to 405.01 mg g−1, while that of WS-0.6 was only 213.81 mg g−1. It is noteworthy that rice husk and cornstalk biochar with an impregnation ratio of 0.6 were more effective in removing Pb(II) and Cd(II), and the content of Fe0 crystals on surface strengthened the ion exchange and chemical precipitation. This work highlights that the impregnation ratio should be changed according to the actual application scenarios of MBC.

The importance of presoaking to improve the efficiency of MgCl2-modified and non-modified biochar in the adsorption of cadmium

Investigating the effect of presoaking, as one of the most important physical factors affecting the adsorption behavior of biochar, on the adsorption of heavy metals by modified or non-modified biochar and presoaking mechanism is still an open issue. In this study, the water presoaking effect on the kinetics of cadmium (Cd) adsorption by rice husk biochar (produced at 450 °C, B1, and at 600 °C, B2) and the rice husk biochar modified with magnesium chloride (B1 modified with MgCl2, MB1, and B2 modified with MgCl2, MB2) was investigated. Furthermore, the effect of pH (2, 5, and 6), temperature (15, 25, and 35 °C), and biochar particle size (100 and 500 µm) on the kinetics of Cd adsorption was also investigated. Results revealed that the content of Cd adsorbed by the presoaked biochar was significantly higher than that by the non-presoaked biochar. The highest Cd adsorption capacity of MB2 and MB1 was 98.4 and 97.6 mg g−1, respectively, which was much better than that of B1 (7.6 mg g−1) and B2 (7.5 mg g−1). The modeling of kinetics results showed that in all cases pseudo-second-order model was well-fitted (R2>0.99) with Cd adsorption data. The results also indicated that the highest Cd adsorption values were observed at pH 6 in presoaked MB1 with size of 100 µm as well as at the temperature of 35 °C in presoaked MB2, indicating the optimum conditions for this process. The presoaking process was not affected by biochar size and pH, and the difference in adsorbed Cd content between presoaked biochars and non-presoaked ones was also similar. However, the temperature had a negative effect on presoaking. The presoaking process decreased micropores (<10 µm) in the biochars but had no effect on biochar hydrophobicity. Therefore, presoaking, which could significantly increase Cd adsorption and reduce equilibrium time by reducing the micropores of biochars, is suggested as an effective strategy for improving the efficiency of modified biochars or non-modified ones in the adsorption of contaminants (Cd) from aquatic media.

Mechanism of aniline aerofloat and Cd2+ elimination from mining wastewater by customized S-scheme Halloysite@MoS2/goethite nanotube: Synergy of photo-Fenton decomplexation and adsorption

Aniline aerofloat (AAF) and Cd2+ have caused severe pollution near the mine site, simultaneous remediation technologies are facing enormous challenges due to different reaction conditions of these two pollutants. Herein, a surface optimized Halloysite@MoS2/goethite was established to simultaneously remove AAF-Cd2+ pollution in a photo-Fenton reaction system. The spatial confinement of halloysite nanotube, special surface modulated particle size, acid-base property, and Zeta potential efficiently enhanced photo-Fenton degradation activity and adsorption for cations. 94.2 % of AAF and 94.1 % of Cd2+ were eliminated within 60 min and the adsorption capacity for Cd2+ reached 68.14 mg g−1. The built-in electric field between MoS2 and goethite promoted separation of photogenerated carrier via an S-Scheme separation strategy, which maintained high potential electrons in CB and holes in VB for generating reactive oxidation species (ROS). The photocatalysis of MoS2 facilitate to regulate valence of iron species for sustainable activation of H2O2. Combined with HPLC-MS analysis, theoretical calculation of frontier molecular orbital and adsorption energy, the removal mechanism of AAF-Cd2+ was proposed. This study provides novel insights into simultaneous removal of beneficiation reagents-heavy metals combined pollutants and may contribute to remediation of water pollution near the mine sites.

Efficient cadmium immobilization by organic loaded Na-montmorillonite in a contaminated soil

Clay minerals are effective sorbents for toxic metal immobilization in contaminated soils and waters. However, their Cd immobilization efficiency is unclear when they are loaded with organics. In this study, sodium montmorillonite (Na-M) was successfully loaded with potassium humate, chitosan, and glycine to adsorb Cd(II) in solution. Potassium humate loaded Na-M (Na-M-HA), which had the highest specific surface area and cation exchange capacity (CEC), showed the highest Cd(II) adsorption capacity (73.7 mg g−1), 22.5 % and 81.8 % higher than that of chitosan loaded Na-M (Na-M-CTS) and glycine loaded Na-M (Na-M-G), respectively. The pseudo-second-order kinetic model best described (R2 > 0.98) the adsorption kinetics of Cd(II) on the three Na-Ms, indicating that the adsorption processes were of chemisorption nature. The adsorption isotherm of Cd(II) on Na-M-HA was of the Freundlich type, suggesting multilayer adsorption. In contrast, the isothermal adsorption of Cd(II) on Na-M-CTS (R2 = 0.99) and Na-M-G (R2 = 0.89) was better described by the Langmuir model, suggesting the dominance of monolayer adsorption in the adsorption process. High temperature, high pH, low background ionic strength, and low valence competing cations favored Cd(II) adsorption on Na-M-HA. The underlying mechanisms of Cd(II) sorption on Na-M-HA were electrostatic attraction, ion exchange and complexation. Na-M-HA was applied to a Cd polluted soil planted with lettuce (Lactuca sativa L.). in a pot experiment. Compared to the control with no adsorbent application, Na-M-HA application at 2 % effectively reduced the available Cd content in soil and Cd accumulation in plant by 36.0 % and 56.8 %, respectively. This work demonstrated that Na-M-HA is a green, low-cost and excellent adsorbent for Cd stabilization, and that its application in Cd-polluted soils can efficiently reduce Cd bioavailability and thereby Cd transfer along the food chain and eventually reduce the threat of Cd pollution to human health.

Aminated Polyacrylonitrile Nanofiber Membrane for Effective In Situ Bivalent Cadmium Contaminated Kaolin Remediation

AbstractCadmium is a harmful pollutant in soil. Here, an aminated polyacrylonitrile (PAN) nanofiber membrane is obtained by electrospinning and amination modification for effective in situ remediation of bivalent cadmium (Cd(II)) contaminated kaolin. The aminated PAN (APAN) nanofiber membrane has the potential to be used as permeable reactive barrier (PRB) combined with electrokinetics (EK) for the remediation of potentially toxic metal contaminated soil. Morphology and chemical characterizations of the nanofibers are analyzed by scanning electron microscopy and attenuated total reflectance Fourier transform infrared spectroscopy. The maximal adsorption capacities of Cd(II) on APAN nanofiber membrane, as calculated from the Langmuir model, are 51.8 mg g−1. In addition, the obtained APAN nanofiber membrane can also be facilely regenerated through the adsorption/desorption experiments (5 cycles). The APAN‐15 nanofiber membrane is used for the remediation of Cd(II) contaminated kaolin. The pH, water content, conductivity, and Cd(II) concentration of kaolin are detected after EK process. These results show that the APAN‐15 nanofiber membrane works as adsorption medium and can accelerate the migration rate of Cd(II) in kaolin, stabilize the pH, and water content. The APAN nanofiber membrane as PRB material can remove Cd(II) in soil effectively and remediate the soil via the EK/APAN process.

Remarkable performance of GO/ZnO nanocomposites under optimized parameters for remediation of Cd (II) from water

The rapid increase in toxic Cd (II) levels in water demand urgent steps toward its remediation. Here, we synthesized graphene oxide/zinc oxide (GO/ZnO) nanocomposites for Cd(II) ion removal from water, using modified Hummers and chemical precipitation methods to synthesize GO and ZnO nanoparticles, respectively. Nanocomposites were synthesized with 0.1, 0.5, and 1 wt% GO and 2.5 wt% ZnO by solution mixing in ethanol followed by characterization of its morphology, surface chemistry, crystal structure, and specific surface area. Adsorption studies were carried out at room temperature and parameters such as pH, initial metal ion concentration, and contact time were optimized for maximizing Cd(II) removal. Adsorption process followed Langmuir isotherm and pseudo-second-order kinetics. Nanocomposites with GO: ZnO in the weight ratio of 2:98 had the highest adsorption capacity for Cd(II) ions of 4125 ± 796 mg/g. Post-adsorption studies confirmed Cd(II) in the X-ray photoelectron spectra of the composite due to chemisorption of Cd(II) on the GO/ZnO surface. The synergistic effect of enhancement functional groups and the increase in the specific surface area made the GO/ZnO nanocomposite a promising material for effective removal of excess Cd(II) from water and maintaining it within WHO limit.

High-efficiency electrochemical removal of Cd(II) from wastewater using birnessite-biochar composites: Performance and mechanism.

Birnessite has been widely used for electrochemical removal of heavy metals due to its high pseudocapacitance. Incorporation of carbon-based materials into birnessite can enhance its conductivity and stability, and synergistically improve the electrochemical adsorption capacity due to the double-layer capacitor reaction derived from carbon-based materials. In this study, biochar was successfully incorporated with birnessite at various ratios to synthesize composites (BC-Mn) for effective electrochemical removal of cadmium (Cd(II)) from water. The effects of cell voltage, initial pH, and recycling performance of BC-Mn were evaluated. As a result, the electrosorption capacity of BC-Mn for Cd(II) exhibited gradual increases with increasing birnessite content and reached equilibrium at a Mn content of 20% (BC-Mn20). The Cd(II) adsorption capacity of BC-Mn20 rose at higher cell voltage, and reached the maximum at 1.2V. At pH 3.0-6.0, the electrosorption capacity initially rose until pH 5.0 and then approached equilibrium with a further increase in pH value. The Cd(II) electrochemical adsorption capacity of BC-Mn20 in the solution could reach 104.5mgg-1 at pH 5.0 for 8h at 1.2V. Moreover, BC-Mn20 exhibited excellent reusability with a stability of 95.4% (99.7mgg-1) after five cycles of reuse. Due to its superior heavy metal adsorption capacity and reusability, BC-Mn20 may have a promising prospect in the remediation of heavy metal polluted water.

Binding of Cd(II) to birnessite and fulvic acid organo-mineral composites and controls on Cd(II) availability

Manganese oxide minerals (MnOs) are major controls on cadmium (Cd) mobility and fate in the environment. However, MnOs are commonly coated with natural organic matter (OM), and the role of this coating in the retention and availability of harmful metals remains unclear. Herein, organo-mineral composites were synthesized using birnessite (BS) and fulvic acid (FA), during coprecipitation with BS and adsorption to preformed BS with two organic carbon (OC) loadings. The performance and underlying mechanism of Cd(II) adsorption by resulting BS-FA composites were explored. Consequently, FA interactions with BS at environmentally representative (5 wt% OC) increase Cd(II) adsorption capacity by 15.05–37.39% (qm = 156.5–186.9 mg g−1), attributing to the enhanced dispersion of BS particles by coexisting FA led to significant increases in specific surface area (219.1–254.8 m2 g−1). Nevertheless, Cd(II) adsorption was notably inhibited at a high OC level (15 wt%). This might have derived from the supplementation of FA decreased pore diffusion rate and generated Mn(II/III) competition for vacancy sites. The dominant Cd(II) adsorption mechanism was precipitation with minerals (Cd(OH)2), and complexation with Mn–O groups and acid oxygen-containing functional groups of FA. In organic ligand extractions, the exchange Cd content decreased by 5.63–7.93% with low OC coating (5 wt%), but increased to 33.13–38.97% at a high OC level (15 wt%). These findings help better understand the environmental behavior of Cd under the interactions of OM and Mn minerals, and provide a theoretical basis for organo-mineral composite remediation of Cd-contaminated water and soil.

Single and Ternary Removal of Heavy Metals from Aqueous Solution Using Fe3O4 Magnetic Nano-particles

This research aims to investigate the use of magnetic iron nano-particles (FeN) for the removal of heavy metals under single and ternary scenarios. The methodology includes synthesis of FeN using chemical precipitation approach, batch experiments for single and ternary metals removal, isotherm and kinetic studies, thermos-dynamic study and assessing the effect of different parameters on the adsorption process. The results showed that the maximum removal for As and Hg was achieved at a pH of 7, while a pH of 6 provided a slightly higher removal of Cd than a pH of 7 at an optimum mixing time of 120 minutes. The optimum adsorption capacities of As, Cd and Hg at the initial concentration of 200 ppm were 260, 280 and 75.0 mg/g in the case of single metal removal against 91.5, 237.8 and 341.5 mg/g in the case of ternary combination, respectively. The removal of all metals increased with increasing the FeN dose and the mixing time, while it decreased with the increase of the initial concentration. The removal efficiency was affected strongly by the presence of multiple metals, while As removal decreased sharply and Hg removal increased significantly. Adsorption selectivity is affected negatively by the increase in atomic weight and atomic radius. In the case of single-metal removal, fitting of isotherm models can be ranked as Langmuir&gt;Freundlich&gt;Temkin&gt;D-R for As and Cd and Temkin&gt;Freundlich&gt;D-R&gt;Langmuir for Hg, while contradictory results were obtained in the case of ternary combination. Kinetic studies found that the adsorption follows the pseudo-second-order model with R2=0.99. For all metals, the adsorption process is highly favourable at higher temperatures and is endothermic in nature with (ΔHo) of 10.91, 23.86 and 0.163 for As, Cd and Hg, respectively. Coating of FeN with silica resulted in lower removal efficiency for all metals up to 50%. It can be concluded that FeN can be successfully used for the removal of heavy metals either through the single or ternary approach, but the single approach provides a higher performance. KEYWORDS: Nano-materials, Magnetite iron, Adsorption, Arsenic, Cadmium, Mercury, Lead.

The use of various magnetic adsorbents for cadmium uptake from dyes-containing wastewater

Simultaneous presence of organic dyes with Cd(II) is possible and may affect Cd(II) removal from wastewater. This study involved various magnetic adsorbents for Cd(II) removal in the presence of various organic dyes (Tartrazine, Allura red, Rhodamine). Magnetic carbon nanotubes (MCNT), magnetic graphene oxide (MGO) and magnetic olive wood (MOW) were involved as adsorbents. The following adsorption issues were considered at various pHs: Effect of magnetic adsorbent type on Cd(II) uptake in presence and absence of Tartrazine; Effect of dye type on Cd(II) uptake by MCNT; Adsorption of organic dyes’ onto MCNT; Effect of other adsorption factors [“magnetite:CNT” mass ratio; “Cd: Rhodamine” molar ratio]. It was found that the presence of dyes caused an enhanced uptake of Cd(II) uptake by MCNT, which was attributed to suraface-dye-Cd ternary complex formation, in which Rhodamine caused the maximum Cd(II) uptake at pH 8. The maximum Cd(II) uptake conditions [using MCNT at pH 8 in (1:3) “Cd:Rhoadamine” molar ratio] gave Cd(II) adsorption capacity of 23 mg g−1. The method was re-useable, applicable on environmental waters and selective with a 20% decrease in its performance in presence of competing ions.

A Novel Chitosan/Nano-Hydroxyapatite Composite for the Adsorptive Removal of Cd(II) from Aqueous Solution.

A novel polymer bio-composite based on nano-hydroxyapatite (n-Hap) and chitosan (CS) (CS/n-Hap) was synthesized to effectively address toxic cadmium ions removal from water. The composition and structure of CS/n-Hap bio-composite were analyzed through different characterization techniques. XRD patterns affirmed that the crystalline structure of n-Hap remained unaltered during CS/n-Hap synthesis, while FT-IR spectrum sustained all the characteristic peaks of both CS and n-Hap, affirming the successful synthesis of CS/n-Hap. Adsorption studies, including pH, adsorbent dosage, contact time, initial Cd(II) concentration, and temperature, were carried out to explain and understand the adsorption mechanism. Comparatively, CS/n-Hap bio-composite exhibited better Cd(II) adsorption capacity than pristine CS, with an experimental maximum uptake of 126.65 mg/g under optimized conditions. In addition, the kinetic data were well fitted to the pseudo-second-order model, indicating the formation of chemical bonds between Cd(II) and CS/n-Hap during adsorption. Furthermore, the thermodynamic study suggested that Cd(II) adsorption onto CS/n-Hap was endothermic and spontaneous. The regeneration study showed only about a 3% loss in Cd(II) uptake by CS/n-Hap after five consecutive cycles. Thus, a simple and facile approach was here developed to synthesize an eco-friendly and cost-effective material that can be successfully employed for the removal of toxic heavy metal ions from water.

Characterization and Co-Adsorption Mechanism of Magnetic Clay-Biochar Composite for De-Risking Cd(II) and Methyl Orange Contaminated Water.

The application of the adsorption method in sewage treatment has recently become a hot spot. A novel magnetic clay-biochar composite (BNT-MBC) was fabricated by co-pyrolysis of bentonite and biomass after being impregnated with Fe (NO3)3·9H2O. Its adsorption capacity for Cd(II) and methyl orange was approximately doubled, reaching a maximum of 26.22 and 63.34 mg/g, and could be easily separated from the solution by using external magnets with its saturation magnetization of 9.71 emu/g. A series of characterizations including surface morphology and pore structure, elemental analysis, functional group analysis and graphitization were carried out, showing that the specific surface area was increased 50 times by loading 20 wt.% bentonite, while its graphitization and oxygen-containing functional groups were also enhanced. The isotherm fitting indicated that Cd(II) was adsorbed in multiple layers, while methyl orange was in both monolayer and multilayer adsorptions. The kinetic fitting indicated that chemisorption was the rate-limiting step of both, and it was also a complex process controlled by two steps with the fitting of intra-particle diffusion. In the binary system of Cd(II) and methyl orange, the co-existing pollutants facilitated the adsorption of the original one, and there was no competition between adsorption sites of Cd(II) and methyl orange. BNT-MBC also exhibited good reusability and can be magnetically recovered for recycling. Thus, the magnetic clay-biochar composite BNT-MBC is a cost-effective and promising adsorbent for simultaneous removing Cd(II) and methyl orange from wastewater.

Effect of natural soil nanocolloids on the fate and toxicity of cadmium to rice (Oryza sativa L.) roots

Toxic heavy metals are common contaminants and will most likely interact with ubiquitous natural nanocolloids (Ncs) in the soil environment. However, the effect of soil Ncs on the fate and health risk of cadmium (Cd) have not been well addressed. Here, the interaction between Ncs and Cd is investigated using two-dimensional correlation spectroscopy (2DCOS) combined with synchronous fluorescence and Fourier transform infrared spectroscopy. Our results reveal that Cd binding to the soil Ncs surface is mainly driven through strong hydrophilic effects and π − π interactions, which contribute to a high adsorption capacity (366–612 mg/g) and strong affinity (KL = 4.3–9.7 L/mg) of Cd to soil Ncs. Interestingly, soil Ncs and Cd coexposure can significantly mediate the phytotoxicity (e.g., uptake, root growth, and oxidative stress) of Cd to rice (Oryza sativa L.) roots after 7 days of exposure. At the molecular level, metabolomic analysis reveals that the downregulated metabolic pathways (e.g., isoquinoline alkaloid and aminoacyl-tRNA biosynthesis, glycine, serine and threonine metabolism) may contribute to the above adverse phytotoxicity. This study provides new insight into the effect of natural Ncs on the fate and health risks of toxic heavy metals in soil environments.

Study on the Adsorption Characteristics of Calcareous Sand for Pb(II), Cu(II) and Cd(II) in Aqueous Solution

The adsorption characteristics of calcareous sand for heavy metals Pb(II), Cu(II) and Cd(II) have been studied by batch testing in this study. The influence of the solid–liquid ratio, initial pH0 value, ionic strength, reaction time, temperature and initial concentration on adsorption has been investigated. Test results indicate that the initial pH and the solid–liquid ratio have a significant influence on the removal efficiency. At T = 30 °C, r = 1.0 g/L, and C0 = 1000 mg/L and for 12 h of reaction, the removal efficiencies of Pb(II), Cu(II) and Cd(II) are 97.6%, 88.15% and 65.72%, respectively. The adsorption quantity is more than 80% of the maximum adsorption quantity within 60 min, and the equilibrium adsorption can be reached within 120 min. The pseudo-second-order kinetic model is suitable to simulate the dynamic adsorption process of calcareous sand, and the isothermal process is found to obey the Langmuir model. Calcareous sand has a very high adsorption capacity for Pb(II), Cu(II) and Cd(II), with a maximum adsorption quantity Qm reached 1052.95 mg/g, 1329.84 mg/g and 1050.56 mg/g, respectively. Thermodynamic test results indicate that the adsorption process is spontaneously exothermic and that low temperature is favorable to the adsorption reaction.

Natural organic matter changed the capacity and mechanism of Pb and Cd adsorptions on iron oxide modified biochars

Employing Fe-oxide loaded biochars (FBCs) to remediate heavy metal (HM) pollution has been regarded as a promising alternative. However, the removal performance and mechanism of FBCs to compound Pb and Cd in both systems with and without natural organic matter were poorly examined. Here, a series of FBCs were prepared and their adsorption capacity and mechanism for Pb and Cd in dual metal systems affected by humic acid (HA) were studied. The results demonstrated that the pyrolysis temperatures during the FBC preparation significantly affected the physico-chemical properties of FBCs and the specie of Fe-oxides it supported. The FBC300-300 showed the best adsorption performance, with maximum adsorption capacities up to 96.8–151 and 29.1–82.3 mg g−1 for Pb and Cd, respectively. Integrating the findings from adsorption kinetics and isotherm experiments and surface characteristics of the FBCs before and after reaction, the underlying dominated adsorption mechanisms were discussed. The dominant mechanisms and their degrees of action for HM adsorption were significantly different among the FBCs, controlling by the specie of loaded Fe-oxides and other physico-chemical properties of the FBCs (e.g., pH, specific surface area, and functional group). The presence of HA was found that it can distinctly alter HM adsorption process on FBCs, and the alterations depended on the interactions of HM and FBC type. Overall, the findings presented in our study could provide a systematic understanding of the remediation of Pb and Cd compound pollution by the FBCs in a natural environment where natural organic matter were widespread.

Biofuel Ash Aging in Acidic Environment and Its Influence on Cd Immobilization.

Biofuel ash (BFA), which is the ash generated by biomass combustion in a biomass power plant, can be prepared as a heavy metal immobilizer and have a good immobilization effect on Cd in the soil environment of southern China, but the long-term effects of BFA on Cd immobilization remained unclear. Therefore, research about BFA aging and its influence on Cd immobilization was conducted in the paper. BFA was naturally aged into BFA-Natural aging (BFA-N) in the soil environment of southern China, and to simulate BFA-N, BFA was also artificially acid aged into BFA-Acid aging (BFA-A). The result indicated that BFA-A could partially simulate BFA-N in physicochemical properties. The Cd adsorption capacity of BFA reduced after natural aging and the decrease was more obvious in BFA-A according to Qm in Langmuir equation and qe from the pseudo-second-order kinetic model. The adsorption processes of BFA before and after aging were mainly controlled by chemical action rather than physical transport. The immobilization of Cd included adsorption and precipitation, and adsorption was the dominant factor; the precipitation proportion was only 12.3%, 18.8%, and 1.7% of BFA, BFA-N, and BFA-A, respectively. Compared with BFA, both BFA-N and BFA-A showed Ca loss, and BFA-A was more obvious than BFA-N. Ca content level was consistent with Cd adsorption level among BFA, BFA-N, and BFA-A. It could be inferred that the main immobilization mechanism of Cd by BFA before and after aging was consistent and closely related to Ca. However, the adsorption mechanism of electrostatic interaction, ion exchange, and hydroxyl complexation changed to varying degrees in BFA-N and BFA-A.