Initial Cd Concentration Research Articles

Optimization of Cadmium Removal from Aqueous Solutions Using Walnut-shell Residues Biochar Supported/unsupported by Nanoscale Zero-valent Iron through Response Surface Methodology

Using various biochars to remove heavy metals (HMs) from aqueous solutions has been increased in recent years. It is believed that the use of nanocompounds in biochars surface structure may increase the efficiency of contaminants removal. Therefore, this research tries to investigate the efficiency of walnut-shell biochar (WSB) alone or supported by nanoscale zero-valent iron (WSB-nZVI) on cadmium (Cd) removal in aqueous solution controlled by four variables including initial Cd concentration, initial solution pH, contact time, and adsorbent dosage by Box Behnken design under response surface methodology. The results of present study showed that WSB-nZVI has a significant priority on WSB of Cd removal efficiency in aqueous solutions. The existence of functional groups on the surface of WSB via precipitation and adsorption processes, as well as nZVI formed on the WSB-nZVI via generating adsorption and complexation processes, have increased the ability Cd removal than WSB raw adsorbent. The maximum predicted Cd removal efficiency based on the proposed model was 99.72% with desirability of 1, in initial Cd concentration of 70.78 mg L -1 , pH of 6.92, adsorbent dose of 0.56 g L -1 and contact time of 40.42 min.

Performance of synthesized cast and electrospun PVA/chitosan/ZnO-NH2 nano-adsorbents in single and simultaneous adsorption of cadmium and nickel ions from wastewater.

The performance of synthesized cast and electrospun polyvinyl alcohol/chitosan/zinc oxide/aminopropyltriethoxylsilane (PVA/chitosan/ZnO-APTES) nano-adsorbents were compared in removal of Cd(II) and Ni(II) ions from wastewater. The adsorbents were characterized by SEM, BET, FTIR and TGA analyses. Furthermore, the swelling investigations were carried out to study the adsorbent stability in aqueous solution. The effect of several parameters such as contents of ZnO-NH2, contact time, initial Cd(II) and Ni(II) concentration and temperature on the adsorption capacity was investigated in a batch mode. In comparison with cast adsorbent, nanofiber adsorbent indicated the better adsorption performance. The experimental data well fitted the double-exponential kinetic model. In single metal ion system, the maximum adsorption capacity of nanofiber for Cd(II) and Ni(II) ions is estimated to be 1.239 and 0.851mmol/g, respectively, much higher than qm of cast adsorbent for Cd(II) (0.625mmol/g) and Ni(II) (0.474mmol/g) ions. Thermodynamic parameters were investigated to identify the nature of adsorption process. In binary system of Cd(II)-Ni(II) ions, the inhibitory effect of competitive Cd(II) ion on the Ni(II) adsorption was greater than the inhibitory effect of competitive on the Cd(II) adsorption. The selectivity adsorption of both nanofiber and cast adsorbents was in order of Cd(II) > Ni(II).

Modification of nano-clays with ionic liquids for the removal of Cd (II) ion from aqueous phase

Abstract The present study attempts to synthesize nano-modified clays of Na-bentonite (Bent) and montmorillonite (MT), using three imidazolium-based ionic liquids (ILs) including 3,3′-(hexyl)bis(3-methylimidazolium) bromide chloride ([H(mim)2[Br][Cl]), 1-hexyl-3-methylimidazolium chloride ([Hmim][Cl]) and 1-octyl-3-methylimidazolium chloride ([Omim][Cl]). X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), carbon, hydrogen and nitrogen elemental analysis (CHN), scanning electron microscope (SEM) and specific surface area (SSA) (using N2-BET) techniques provided evidence of successful modification of the guest clays. Removal of Cd (II) from aqueous phase was investigated using the modified clays under different experimental conditions of reaction time, pH and adsorbent dosage. Detailed isotherms and kinetic studies showed that the modified clays have much higher Cd (II) adsorption capacity compared to those of the starting clay minerals. The maximum Cd (II) absorption capacities of 87.46 and 94.6 mg g−1 were observed in [H(mim)2]-MT and [H(mim)2]-Bent with d-values of 35.4 A and 28.3 A respectively. The [Omim]-clays had the highest adsorption affinities of Cd (II) in initial concentrations of Cd (II). This study shows that ILs could enhance the clay capacity and tendency for Cd (II) absorption with different trends based on the ILs structures. The modified clays using ILs are green and eco-friendly adsorbents and due to substantial increase in their capacity for the removal of heavy metals, they could have positive economic and environmental impacts.

Application of Response Surface Methodology for Optimization of Cadmium Ion Removal from an Aqueous Solution by Eggshell Powder

The removal of cadmium(Cd) from synthetic solutions by batch adsorption process was performed using eggshell powder, which is mainly composed of calcite(CaCO3). In order to optimize the adsorption process, a re-sponse surface methodology(RSM) based on Central Composite Design(CCD) was applied. Developed model for Cd remo- val yields(R, %) response was statistically validated by variance analysis(ANOVA) which showed a high de-termination coefficient value(R2=0.9889). According to Minitab software, the optimal conditions were found at tem-perature of 44 °C, eggshell adsorbent dose of 2.98 g, initial Cd concentration of 36.74 mg/L and initial pH of 7. Un-der these conditions, the Cd removal yield was 98.76%. The deviation value of 1.24% confirms the validity of the model for the adsorption process optimization. The adsorption isotherm has been described by a Freundlich model. In addition, the predominant sorption mechanisms are the chemisorptions or precipitation(non-reversible) and ion ex-change(reversible).

Adsorption of Cadmium(II) Ion from Aqueous Solution onto a Raw Material of Bamboo Powder and its Surface Modification

This work was focused on evaluating the potential of bamboo powder modified with manganese oxide (MnO-BP) as a low-cost byproduct adsorbent for the adsorption of cadmium(II) ion. A batch method was carried out at room temperature and the optimized conditions. The optimization of adsorption parameters including pH, equilibrium time, dosage and initial Cd(II) concentration was also systematically studied for the removal of cadmium(II) ion. The maximum monolayer adsorption capacity of MnO-BP was estimated as 8.57 mg/g that it more adsorption capacity than untreated-bamboo powder by about 5 times. The Langmuir and the Freundlich isotherms were used to describe the adsorptive mechanism and calculated the maximum monolayer adsorption capacity. It was found that the data from MnO-BP fitted well to the Freundlich isotherm with R2>0.99. It indicated that the adsorptive behavior of MnO-BP to cadmium(II) ion is preferable. In this work, MnO-BP was used for the removal of cadmium(II) ion in wastewater sample. The MnO-BP is a low-cost adsorbent that can be used to remove cadmium(II) effectively.

Removal of Cd2+ from Aqueous Solution by Nickel Oxide/CNT Nanocomposites

The present work investigates the efficiency of the nickel oxide/carbon nanotube (NiO/CNT) nanocomposite for the removal of Cd2+ metal ions from an aqueous. The NiO/CNT nanocomposite was synthesized by the direct co-precipitation method in an aqueous media in the presence of CNTs. The resulting materials were characterized by FT-IR, XRD, SEM, N2 adsorption-desorption analysis. In order to optimize the adsorption of Cd2+ ions on NiO/CNT nanocomposite, the effects of the different parameters—namely pH, contact time, initial concentration of Cd2+, and adsorbent dosage—were also studied. Experimental data revealed that the Cd2+ ions adsorption of the NiO/CNT nanocomposite was through Langmuir and Temkin isotherm models rather than the Freundlich model. The kinetic data of adsorption of Cd2+ ions on the adsorbent was best described by a pseudo-second-order equation, indicating their chemical adsorption. Thermodynamic parameters such as ΔG°, ΔH°, and ΔS° were calculated. The obtained values showed that the adsorption was spontaneous and exothermic in nature. The reusability test showed that the Cd2+ could be easily removed from the surface site of NiO/CNT nanocomposite by a 0.1 M nitric acid solution as the adsorption capacity was maintained after 5 cycles of the adsorption/desorption process. This suggests that NiO/CNT nanocomposite can be reused through many cycles of water treatment and regeneration.

Acrylamide grafted chitosan based ion imprinted polymer for the recovery of cadmium from nickel-cadmium battery waste

Spent nickel-cadmium (Ni-Cd) batteries are classified as hazardous waste due to the presence of toxic cadmium (Cd). Sustainable solution to this problem can be adoption of resource recovery methods for the reuse of Cd. This has been attempted in the present work using the biopolymer chitosan having inherent affinity for metals. Stability of chitosan in acidic medium was improved by grafting it with a suitable grafting agent and crosslinking. Further, it was used for the synthesis of acrylamide grafted chitosan based Cd ion imprinted polymer (CdIIP) using Cd as template and epichlorohydrin (EPI) as crosslinker for the selective recovery of Cd. Density functional theory (DFT) confirmed acrylamide as the best grafting agent with ΔG of −17.98 Kcal/mol for the acrylamide grafted chitosan. FTIR confirmed the grafting of acrylamide on chitosan as well as successful synthesis of CdIIP. EPI proved to be a better crosslinking agent as compared to glutaraldehyde (GLA) for CdIIP as confirmed by EDS. Adsorption of Cd on CdIIP was influenced by pH, time, initial Cd concentration and CdIIP dose. The kinetic data fitted well to pseudo-second-order equation than first order with R2 equals to 0.997. The monolayer adsorption capacity for Cd (167 mg/g) calculated using Langmuir isotherm model was in close approximation to the experimental adsorption capacity of 152 ± 3 mg/g. The thermodynamic data confirmed exothermic and spontaneous nature of adsorption. 84.3% of Cd could be recovered by CdIIP from the acidic leachate of the Ni-Cd battery waste. CdIIP could be effectively reused for five cycles.

Acid-base properties of kaolinite, montmorillonite and illite at marine ionic strength

Abstract In marginal marine settings, understanding the role that clay minerals play in the transfer of metal cations from the water column to the seafloor is important if the composition of modern muds is to be used as a proxy for the precursors of ancient shale deposits. In this study, we conducted potentiometric titrations of three naturally abundant clay minerals (kaolinite, montmorillonite and illite) in 0.56 M NaCl electrolyte solutions to ascertain the surface reactivity of each clay mineral at seawater ionic strength. Our results demonstrate that all three clay minerals were increasingly anionic as pH increases from 3 to 9, with montmorillonite having the highest negative-charge. The potentiometric titrations and adsorption data were modeled using both non-electrostatic (NEM) and electrostatic (constant-capacitance model, CCM) surface complexation models (SCMs). A two-site surface complexation model, that included one basal siloxane surface site (≡X−) and one amphoteric edge site (≡SOH), provided an excellent fit for the protonation data of each mineral. Cd(II) adsorption experiments were conducted to quantify the magnitude of cation adsorption, which showed that 10 g montmorillonite, illite, and kaolinite powder could bind an equivalent of 4.7 × 10−4 g, 4.3 × 10−4 g, and 4.0 × 10−4 g of Cd, respectively, under conditions relevant to seawater (initial Cd concentration of 8.9 × 10−6 M, and pH = 8). To place this value into the context of modern riverine clay inputs to the ocean, 13.5 × 109 tons of total suspended sediment are deposited annually (Milliman and Meade, 1983) of which 10 to 25% is clay (Manheim et al., 1970; Schroeder et al., 2015). The total amount of Cd adsorbed to suspended clay minerals entering the modern oceans could then amount to approximately 104 to 105 tons per year. The results of this study highlight the potential role of clay minerals in transporting metals from the ocean water column to the seafloor.

Solvent extraction of zinc from synthetic Zn-Cd-Mn chloride solution using D2EHPA: Optimization and thermodynamic studies

Abstract The extraction of zinc in the presence of manganese and cadmium from chloride solution with di 2 ethyl hexyl phosphoric acid (D2EHPA) in kerosene diluent were comprehensively investigated. The extraction experiments were carried out in order to determine the influential parameters in the conditions of A:O ratio of 1:1, pH range of 1–6, temperatures of 30 °C, 40 °C and 50 °C in an aqueous solution with concentrations of 5 g/L of zinc, manganese and cadmium. The variety of influential parameters in the process such as equilibrium pH, concentration of D2EHPA, temperature, contact time, initial concentration of ions and also thermodynamic parameters of zinc extraction in chloride solution were precisely evaluated. The results showed that in the optimal condition of pH = 2.5–3, temperature 40 °C and [D2EHPA] = 10 v/v, the extraction of Zn, Mn and Cd were 97%, 14% and 3% respectively. ΔpH0.5Zn-Mn and ΔpH0.5Zn-Cd in this condition respectively equal to 2.5 and more than 5.25. Also, the study indicated that the predominant zinc species extracted by D2EHPA was ZnCl+. Based on thermodynamic studies, the values of ΔHo, ΔSo and ΔGo for zinc extraction in condition of temperature 40 °C and [D2EHPA] = 10 v/v are 25.65 kJ.mol−1, 79.20 J·K−1·mol−1 and 0.86 kJ·mol−1 respectively. Furthermore, the results showed that under constant concentration of D2EHPA, changes in the initial concentrations of Zn, Mn and Cd in the chloride solution were most effective in their separation.

Adsorption of cadmium by live and dead biomass of plant growth-promoting rhizobacteria.

Plant growth-promoting rhizobacteria (PGPR) have been extensively investigated in combination remediation with plants in heavy metal contaminated soil. However, being biosorbent, few studies of live and dead cells of PGPR have been undertaken. Meanwhile, the application of live or dead biomass for the removal of heavy metals continues to be debated. Therefore, this study uses living and non-living biosorbents of Cupriavidus necator GX_5, Sphingomonas sp. GX_15, and Curtobacterium sp. GX_31 to compare their Cd(ii) adsorption capacities by SEM-EDX, FTIR, and adsorption experiments. In the present study, whether the cells were living or dead and whatever the initial Cd(ii) concentration was, removal efficiency and adsorption capacity can be arranged as GX_31 > GX_15 > GX_5 (p < 0.05). However, removal efficiency in live and dead biosorbents was quite different and it greatly affected by the initial Cd(ii) concentrations. The dead cells exhibited a higher adsorption capacity than the live cells of GX_31. Nevertheless, for GX_5 and GX_15, the loading capacity of the non-living biomass was stronger than that of the living biomass at 20 mg L−1 of Cd(ii), but the capacity was similar at 100 mg L−1 of Cd(ii). Minor changes of spectra were found after autoclaving and it seemed that more functional groups of the dead biosorbent were involved in Cd(ii) binding by FTIR analysis, which also illustrated that the hydroxyl, amino, amide, and carboxyl groups played an important role in complexation with Cd(ii). Based on these findings, we concluded that the dead cells were more potent for Cd(ii) remediation, especially for GX_31.

HIGHLY EFFICIENT REMOVAL OF CADMIUM FROM AQUEOUS SOLUTION USING POLYMER-STABILIZED ZERO-VALENT IRON NANOPARTICLES: EQUILIBRIUM, KINETIC AND THERMODYNAMIC STUDIES

Bare zero-valent iron nanoparticles (bare-ZVIN) have a great tendency to aggregate, which drops their reactivity with pollutants. To address this issue, polyvinylpyrrolidone stabilized-ZVIN (PVP-ZVIN) was synthesized and used for the removal of Cd2+ from aqueous solution in a batch system. The effects of operation conditions such as the pH of aqueous solution (2-8), reaction time (0-120), adsorbent concentration (1-6 g L-1) and the initial Cd2+ concentration (10-60 mg L-1) on the removal efficiency of Cd2+ were studied. Furthermore, adsorption isotherm, kinetic and thermodynamic studies of Cd2+ removal were performed. Results of studies revealed that PVP could apparently enhance the colloidal stability of ZVIN and the removal efficiency of Cd2+. In addition, increasing ZVINs concentration from 1 to 6 g L-1 enhanced Cd2+ removal efficiency while a sharp decrease was observed in Cd2+ removal efficiency by increasing the initial concentration of Cd2+ from 10 to 60 mg L-1. The experimental results showed that maximum Cd2+ adsorption was obtained at pH 6 and 20 min contact time. Moreover, the experimental adsorption of isotherm and kinetic data were completely followed the Freundlich isotherm model and Pseudo first-order kinetic model with maximum coefficients of determination (R2) of >0.98 and >0.99, respectively. Also, the obtained results of thermodynamic studies implied the influence of endothermic and spontaneous nature of Cd2+ adsorption onto ZVINs surfaces, at temperature range of 293-303 K. The findings of this study demonstrated that ZVINs could be applied as applicable adsorbents to remove Cd2+ from aqueous solutions.

Non-linear Isotherm Models, Cadmium Kinetics, and Biosorption Thermodynamics of Dried Biomass of Native Aphanothece sp. in a Batch System

Dried biosorbent was prepared from Aphanothece sp. cyanobacteria harvested from a photobioreactor system fed with atmospheric carbon dioxide. Cadmium-ion biosorption of the prepared biosorbent from aqueous solution was characterized by non-linear (Langmuir, Freundlich and Dubinin"“Radushkevich) isotherms, non-linear kinetics (pseudo first-order and pseudo second-order) and thermodynamic analysis. The optimum conditions were pH 8.0, 30°C, 0.1 g/L biomass, and 60 min contact time. The biosorption efficiencies exceeded 90%. The low-range data (initial Cd concentration C0 = 1.09"“6.23 mg/L) and high-range data (C0 = 5.41"“83.07 mg/L) were best fitted to the Langmuir model, with maximum uptake capacities of 12.01 and 187.5 mg/g (R2 = 0.995 and 0.996). In the Dubinin"“Radushkevich isotherm model, the mean biosorption energy was 12.91 kJ/mol, suggesting that ion exchange was the working mechanism. The biosorption apparently followed pseudo second-order kinetics (R2 = 0.994"“0.999; k2 = 2.04 E-03 to 3.86 E-02 g/mg min). The biosorption process was energetically feasible (∆G0 = −13.47"“−8.88 kJ/mol), exothermic (∆H0 = −74.82 kJ/mol) and tended to become more ordered (∆S0 = −0.204 kJ/mol K) towards the end of the process. The biosorbent was reusable through three adsorption/desorption cycles in 1 M HCl.

Characterization of barley straw biochar produced in various temperatures and its effect on lead and cadmium removal from aqueous solutions

AbstractConversion of agricultural wastes into a carbon rich material (i.e. biochar) using pyrolysis process could be an appropriate approach for their management. This study was carried out to convert barley straw to biochar in different temperatures (300, 400 and 500°C) and to investigate the potential of the produced biochar as a sorbent of heavy metals (Pb and Cd). Considering the pretest results of Pb and Cd sorption, the biochar produced at 500°C (BS500) was selected to find effect of pH, the sorbent dose, the initial concentration of Pb and Cd and the contact time on metal removal efficiency. The results showed that the optimum conditions of adsorption were pH = 6, the sorbent dose 1 g/L and the contact time of 45 min. The adsorption kinetics and isotherms had the best fit to the pseudo‐second order and Langmuir models, respectively.

Adsorption of cadmium ions using the bioadsorbent of Pichia kudriavzevii YB5 immobilized by polyurethane foam and alginate gels.

Pichia kudriavzevii YB5, mutated from Pichia kudriavzevii A16 with a strong ability to remove cadmium ions, was immobilized by polyurethane foam and alginate gels in this work. The immobilization conditions were optimized as follows: sodium alginate concentration of 2% (w/v), calcium chloride concentration of 2% (w/v), biomass dose of 1 × 109 cell/mL, and cross-linking time for 4h. Then, the results of batch adsorption experiments showed that the removal capacity of prepared bioadsorbent was significantly affected by the pH of media, contact time, and the initial Cd(II) concentration, and a suitable adsorption conditions of Cd(II) could be achieved with a pH value of 6.0 at 20°C for 90min. Kinetic and isothermal results indicated the behavior of Cd(II) adsorption onto immobilized P. kudriavzevii YB5 fitted to the pseudo-second-order kinetic equation and the Langmuir adsorption model. Thermodynamic results showed that the Cd(II) adsorption process was endothermic and spontaneous in nature. Besides, the Cd(II) removing capacity of the prepared bioadsorbent was also tested in the oyster hydrolysates, showing an average removal rate of 54.35%. Thus, the immobilized P. kudriavzevii YB5 adsorbent had great potential for application in aquatic products to ensure the food safety.

How Does Oyster Shell Immobilize Cadmium?

The exact mechanism of cadmium (Cd) immobilization by oyster shell (OS) has not been reported. The effect of OS on Cd immobilization and the exact mechanism should be known before applying remediation technology using OS to Cd contaminated soils. Therefore, the objective of this study was to elucidate the mechanism of Cd immobilization by OS. Three grams of OS (<0.84mm) was reacted with 30mL of 0-3.56mgCdL-1 solution at 25°C for 48h. Cadmium adsorption increased with increasing initial concentration of Cd in solution. The X-ray diffraction patterns clearly demonstrated that precipitation of CdCO3 did not take place in suspensions of OS after reacting with up to 3.56molCdL-1. Interestingly, we found formation of Ca0.67Cd0.33CO3 crystalline in suspension of OS after reacting with maximum initial Cd concentrations. Precipitation and chemisorption might contribute to Cd immobilization together. However, we feel confident that chemisorption is the major mechanism by which Cd immobilization occurs with OS. In conclusion, OS could be an effective bioadsorbent to immobilize Cd through formation of geochemically stable Cd mineral.

Synthesis and sorption properties of bridged polysilsesquioxane microparticles containing 3-mercaptopropyl groups in the surface layer

In this paper the technique of obtaining mercapto-containing spherical particles based on 1,2-bis(triethoxysilyl)ethane (BTESE) and 3-mercaptopropyltrimethoxysilane (MPTMS) using the modified Stöber method was developed. The hydrolytic polycondensation reaction of alkoxysilanes was carried out in ethanol solution and catalyzed by fluoride ions. The influence of various factors (ratio of reacting components, the amount of solvent and water) on the morphology, particle size, porosity, and content of SH-groups was studied.The synthesized materials were investigated by scanning electron microscopy, photon cross-correlation spectroscopy, Fourier-transform infrared and Raman spectroscopies, X-ray photoelectron spectroscopy, N2 adsorption–desorption isotherms, elemental analysis. Using these methods, it was determined that such silica particles feature mesoporous spheres of about ∼250–300nm in size with 3.4-7.3mmol/g of sulfur-containing groups, both thiol and disulfide. The effects of the contact time and the initial concentrations of Ag(I), Pb(II), and Cd(II) ions were analyzed by conventional static mode adsorption test. The obtained materials remove metal ions from the wastewater.

Enrichment of Cd2+ from water with a calcium alginate hydrogel filtration membrane

A new method was developed for effective enrichment of Cd2+ ions from water with a calcium alginate (CaAlg) hydrogel filtration membrane. First, the CaAlg hydrogel filtration membrane was prepared without a pore-forming agent. This membrane was used to remove Cd2+ via ion exchange with Ca2+, and the Cd2+ was preserved in the CaAlg hydrogel. Then, the CaAlg hydrogel containing Cd2+ was soaked in a sodium citrate solution, and the hydrogel was fully dissolved. The removal rate of the CaAlg filtration membrane reached almost 100% within 120 min when the Cd2+ concentration was under 1 mg/L. Factors affecting the removal rate were investigated, such as NaAlg concentration, operating pressure, operating time and the initial concentration of Cd2+. The effects of initial Cd2+ concentration, pressure and filtration time on the enrichment factor were also investigated. The results show that the enrichment factor reached 87.3 when the pressure was 0.18 MPa and the filtration time was 240 min. Different enrichment factors could be achieved by adjusting the operating pressure and filtration time.

The Adsorption of Cd(II) on Manganese Oxide Investigated by Batch and Modeling Techniques

Manganese (Mn) oxide is a ubiquitous metal oxide in sub-environments. The adsorption of Cd(II) on Mn oxide as function of adsorption time, pH, ionic strength, temperature, and initial Cd(II) concentration was investigated by batch techniques. The adsorption kinetics showed that the adsorption of Cd(II) on Mn oxide can be satisfactorily simulated by pseudo-second-order kinetic model with high correlation coefficients (R2 > 0.999). The adsorption of Cd(II) on Mn oxide significantly decreased with increasing ionic strength at pH < 5.0, whereas Cd(II) adsorption was independent of ionic strength at pH > 6.0, which indicated that outer-sphere and inner-sphere surface complexation dominated the adsorption of Cd(II) on Mn oxide at pH < 5.0 and pH > 6.0, respectively. The maximum adsorption capacity of Mn oxide for Cd(II) calculated from Langmuir model was 104.17 mg/g at pH 6.0 and 298 K. The thermodynamic parameters showed that the adsorption of Cd(II) on Mn oxide was an endothermic and spontaneous process. According to the results of surface complexation modeling, the adsorption of Cd(II) on Mn oxide can be satisfactorily simulated by ion exchange sites (X2Cd) at low pH and inner-sphere surface complexation sites (SOCd+ and (SO)2CdOH− species) at high pH conditions. The finding presented herein plays an important role in understanding the fate and transport of heavy metals at the water–mineral interface.

Chemometrics optimization for simultaneous adsorptive removal of ternary mixture of Cu(II), Cd(II), and Pb(II) by Fraxinus tree leaves

Fraxinus tree leaves were successfully used to remove ternary mixture of Cu(II), Cd(II), and Pb(II) from an aqueous solution in a batch system. The simplex‐centroid mixture design was used for optimization of the biosorption process. The effective factors on biosorption process, such as pH, s (amount of biosorbent), and Ci initial concentrations of metal ions, were considered via a crossed mixture–process design. Optimal conditions were found to be as follows: pH = 5, s (sorbent mass) = 0.05 g, CCu (initial Cu(II) concentration) = 100.0 mg/L, CCd (Initial Cd(II) concentration) = 129.1 mg/L, and CPb (Initial Pb(II) concentration) = 70.9 mg/L. The results clearly show competitive effects between mixture ingredients in favor of Pb(II), and also an interaction between process and mixture variables was observed. It was found that, with increasing Pb(II) contribution, the removal efficiency increases to its highest value. The pH has a positive effect and sorbent mass a negative effect on the response. To characterize the biosorption, Fourier transform infrared analysis was performed and, according to the results, the main functional groups of sorbent were involved in the biosorption process.

Microalgal-biochar immobilized complex: A novel efficient biosorbent for cadmium removal from aqueous solution

The feasibility of the bioremediation of cadmium (Cd) using microalgal-biochar immobilized complex (MBIC) was investigated. Major operating parameters (e.g., pH, biosorbent dosage, initial Cd(II) concentration and microalgal-biochar ratio) were varied to compare the treatability of viable algae (Chlorella sp.), biochar and MBIC. The biosorption isotherms obtained by using algae or biochar were found to have satisfactory Langmuir predictions, while the best fitting adsorption isotherm model for MBIC was the Sips model. The maximum Cd(II) adsorption capacity of MBIC with a Chlorella sp.: biochar ratio of 2:3 (217.41mgg−1) was higher than that of Chlorella sp. (169.92mgg−1) or biochar (95.82mgg−1) alone. The pseudo-second-order model fitted the biosorption process of MBIC well (R2>0.999). Moreover, zeta potential, SEM and FTIR studies revealed that electrostatic attraction, ion exchange and surface complexation were the main mechanisms responsible for Cd removal when using MBIC.