Kinetic Intraparticle Diffusion Research Articles

Immobilization of cobalt ions using hierarchically porous 4A zeolite-based carbon composites: Ion-exchange and solidification

The efficacy of the synthesized 4A zeolite and the 4A zeolite-based carbon composites were examined for the removal of cobalt ions from an aqueous solution by ion-exchange. Two types of agricultural waste were chosen as precursors to prepare the porous supports for composites synthesized at hydrothermal conditions. The maximum exchange capacity of zeolite portions present in 4A zeolite/Almond shells carbon (AAS) and 4A zeolite/Walnut shells carbon (AWS) reached to 235.175 and 202.887 mg ion/g zeolite; but it reached to 99.525 mg ion/g zeolite for 4A zeolite (A) at same conditions. Removal of cobalt ions by ion-exchange process enhanced when the temperature and pH of the cobalt solution increased. The equilibrium data are precisely fitted by the Freundlich model with a correlation factor (R2) of 0.9807, 0.9859 and 0.9857 for A, AAS and AWS. The cobalt uptake by zeolite-based carbon composites process is controlled by ion-exchange. The Weber and Morris intra-particle diffusion kinetics and Boyd model equations confirmed enhancement of cobalt removal using the composites. The seepage of cobalt ions from the solidified ion-exchangers encapsulating ions reduced to 0.01 ppm in H2O and to 0.05-0.25 ppm in 0.5 N NaCl solution.

Eucalyptus leaf powder as an efficient scavenger for Congo red from water: Comprehensive batch and column investigation

ABSTRACT Abundantly available Eucalyptus leaf (Eucalyptus globulus) was investigated as promising bio-sorbent for removal of Congo red by batch and column method. Material was characterized by proximate analysis, SEM-EDS, FT-IR, BET, XRD, and chemical analysis. Physico-chemical parameters like contact time, dose, and pH were optimized. Maximum adsorption capacity is 29.68 mg/g. Adsorption follows intraparticle diffusion kinetics (K = 0.211 mg/g/min0.5, R2 = 0.996) and Freundlich isotherm model (R2 = 0.996). Thermodynamic study revealed a spontaneous and feasible process (ΔG = – 13.06 kJ/mol). Regeneration (82%) with dilute alkali enables multicycle use. Column breakthrough follows Thomas and BDST model. Cost-benefit analysis suggests economically sustainable material for dye decolorization.

The investigation on Fe3O4 magnetic flocculation for high efficiency treatment of oily micro-polluted water

For the low-concentration oily micro-polluted water formed by the leakage of refined oil products, an unexpensive and high-efficiency magnetic enhanced flocculation method was introduced in this study. First, the performance of magnetic flocculation(MF) to remove oily contaminants was discussed. The results indicated that it achieved more than 95% removal in only 1min with 50mg/L-Polyaluminum chloride(PAC), 50mg/L-Fe3O4 and10mg/L- Polyacrylamide (PAM). The novel indexs Rδand Si were proposed to evaluate the oil removal with UV-Abs in-situ method. According to the adsorption kinetics of oil contaminants, the adsorption kinetics changed from pseudo-first-order to pseudo-second-order kinetics after the addition of Fe3O4 on the basis of conventional coagulation (CF). It was transformed into intraparticle diffusion kinetics when the PAM continued to be added. Combined with the Fe–O–Al bond in the FTIR spectrum of flocs, the main mechanism of MF is enhanced charge neutralization and hydrogen bond adsorption. In addition, it was shown that satisfactory oil removal after recover, which indicated the great potential of a sustainable way by reusing low-cost magnetic seeds.

Combined Minimum-Run Resolution IV and Central Composite Design for Optimized Removal of the Tetracycline Drug Over Metal⁻Organic Framework-Templated Porous Carbon.

In this study, a minimum-run resolution IV and central composite design have been developed to optimize tetracycline removal efficiency over mesoporous carbon derived from the metal-organic framework MIL-53 (Fe) as a self-sacrificial template. Firstly, minimum-run resolution IV, powered by the Design–Expert program, was used as an efficient and reliable screening study for investigating a set of seven factors, these were: tetracycline concentration (A: 5–15 mg/g), dose of mesoporous carbons (MPC) (B: 0.05–0.15 g/L), initial pH level (C: 2–10), contact time (D: 1–3 h), temperature (E: 20–40 °C), shaking speed (F: 150–250 rpm), and Na+ ionic strength (G: 10–90 mM) at both low (−1) and high (+1) levels, for investigation of the data ranges. The 20-trial model was analyzed and assessed by Analysis of Variance (ANOVA) data, and diagnostic plots (e.g., the Pareto chart, and half-normal and normal probability plots). Based on minimum-run resolution IV, three factors, including tetracycline concentration (A), dose of MPC (B), and initial pH (C), were selected to carry out the optimization study using a central composite design. The proposed quadratic model was found to be statistically significant at the 95% confidence level due to a low P-value (<0.05), high R2 (0.9078), and the AP ratio (11.4), along with an abundance of diagnostic plots (3D response surfaces, Cook’s distance, Box-Cox, DFFITS, Leverage versus run, residuals versus runs, and actual versus predicted). Under response surface methodology-optimized conditions (e.g., tetracycline concentration of 1.9 mg/g, MPC dose of 0.15 g/L, and pH level of 3.9), the highest tetracycline removal efficiency via confirmation tests reached up to 98.0%–99.7%. Also, kinetic intraparticle diffusion and isotherm models were systematically studied to interpret how tetracycline molecules were absorbed on an MPC structure. In particular, the adsorption mechanisms including “electrostatic attraction” and “π–π interaction” were proposed.

Preparation and characterization of imprinted zeolite-Y for p-cresol removal in haemodialysis

In this work, the novel imprinted zeolite (IZ) was synthesized, and its properties and performance in terms of adsorption of p-Cresol, which represent the protein-bounded uremic toxins in aqueous phase under phosphate buffer saline, were studied and compared with the synthesized zeolite-Y (ZeoY-S) and commercial CBV 100 zeolite-Y (ZeoY-C). The ZeoY-S was synthesized from sodium aluminate, NaOH, H2O and SiO2 under aging for 24 h at room temperature and hydrothermal condition for 24 h at 100 °C, with an initial composition of 10SiO2:Al2O3:4Na2O:180H2O. The ZeoY-S has been modified by using the imprinting technology to produce the IZ via the use of p-Cresol as a template. The p-Cresol successfully imprinted on the zeolite-Y was proved through the multipoint Brunauer-Emmett-Teller (BET) and the performance of IZ that was compared to ZeoY-S and ZeoY-C. Based on the BET results, it proves that the pore size of IZ is in accordance with the target compound, which is p-Cresol at 0.79 nm. This modification was able to adsorb p-Cresol 2.5 and 3.5 times higher than ZeoY-S and ZeoY-C can, respectively. Langmuir and Freundlich adsorption isotherm models, together with the pseudo-first and -second order and intra-particle diffusion kinetics models, were used to investigate the adsorption behavior of p-Cresol on the zeolites. The IZ has 4.30 times greater competitive molecules than ZeoY-S and the properties of IZ were not influenced by the content of other phenolic group uremic toxins as competitive molecules. It can be concluded that the micropores of zeolite as adsorbent can be modified using the imprinting technology in order to increase its sensitivity and selectivity towards p-Cresol.

Adsorption Performance of Methyl Blue onto Magnetic Ni(1−x−y)CuyZnxFe2O4 Nanoparticles Prepared by A Novel Alcohol-Assisted Combustion Method

In this work, magnetic Ni(1−x−y)CuyZnxFe2O4 nanoparticles were prepared by an alcohol-assisted combustion method, and they were characterized by XRD, SEM, TEM, SAED and EDX techniques. For larger adsorption capacity, the preparation conditions of absolute alcohol volume and the calcination temperature were optimized. The magnetic Ni0.4Cu0.4Zn0.2Fe2O4 nanoparticles were employed to research the adsorption performance of methyl blue (MB) onto them, and they revealed very large adsorption capacity of MB. The adsorption kinetics data were evaluated with the pseudo first-order, the pseudo second-order and the intraparticle diffusion models, and the results showed that the intraparticle diffusion kinetics model was best fitted for the adsorption of MB onto magnetic Ni0.4Cu0.4Zn0.2Fe2O4 nanoparticles. While, the adsorption isotherm experiments were carried out at room temperature, and the experimental data conformed to the Langmuir model, which suggested that the adsorption of MB onto magnetic Ni0.4Cu0.4Zn0.2Fe2O4 nanoparticles was the monolayer adsorption process. Additionally, the effect of pH on the adsorption of MB was studied, the adsorbed materials reached the maximum adsorption capacity at pH value of 3. The magnetic adsorbents showed good reusability, and the adsorption capacity was maintained over 87% of the initial capacity after being used for five cycles. Magnetic Ni(1−x−y)CuyZnxFe2O4 nanoparticles were prepared by an alcohol-assisted combustion method, the experimental data of the adsorption kinetics and the adsorption isotherm was fitted for the adsorption of methyl blue (MB) onto magnetic Ni0.4Cu0.4Zn0.2Fe2O4 nanoparticles, and the adsorption mechanism was discussed

Kinetic Study of Garlic and Ginger Particles in Adsorption of Heavy Metals in Aqueous Solution

This study involved investigation and comparison of the capacity of garlic and ginger particles in adsorption of lead, cadmium and chromium ions from contaminated water. This was motivated by the perennial contamination of well water by crude oil, which carried alongside heavy metals from earth surface and other sources in contact with it while discharging from oil facilities to the subsurface region. Heavy metal analysis on the well water and crude oil from the polluted site showed high level of heavy contamination. Effect of initial concentration of heavy metals, adsorbents dosage and contact time on adsorption of the lead, cadmium and chromium ions in aqueous solution by garlic and ginger particles were studied. Garlic and ginger particles adsorption process was studied using Langmuir and Temkin isotherms. Also, to describe the kinetics of the adsorption process, the Pseudo first and second order kinetics as well as the intra-particle diffusion kinetics were used to study the experimental data. The analysis showed that the percentage of lead, cadmium and chromium ions adsorbed by garlic and ginger particles decreased as the initial concentration of metals in solution and contact time were increased. Similarly, the percentage of lead, cadmium or chromium ions adsorbed by the garlic and ginger particles at equilibrium increased as adsorbent dosages was increased due to increased effective surface area of the adsorbent. Equilibrium was attained at about 60 minutes with either garlic or ginger particles. However, garlic particles adsorbed the heavy metals more than the particles of ginger at all conditions. Also, it was observed that lead ion has more affinity to both garlic and ginger particles followed by cadmium ion. The adsorption of lead, cadmium and chromium ions were better explained by the Langmuir isotherm model than the Temkin’s isotherm model. The maximum adsorption capacity for lead, cadmium and chromium ions with garlic particles were 3.9308 mg/g, 3.3223 mg/g and 1.992 mg/g while that of ginger particles were 2.9011 mg/g, 2.3121 mg/g and 1.9543 mg/g respectively. The adsorption of lead, cadmium and chromium ions in the solution of both adsorbents revealed that diffusion and chemisorptions occurred in the adsorption process, which was best fitted in the Pseudo second order kinetics. Indicating that the Pseudo second order kinetics was the rate controlling step, and thus, will predict accurately the concentration of metal ions adsorbed. Conclusively, the garlic and ginger particles showed capacity for the removal of lead, cadmium and chromium in aqueous solution, and therefore are recommended for use in adsorption of heavy metals in wastewater. Keywords : Garlic, Ginger, Heavy metals, Adsorption Isotherm, Kinetics DOI : 10.7176/CPER/60-04 Publication date :March 31 st 2019

Arsenic(V) adsorption on ferric oxyhydroxide gel at high alkalinity for securely recycling of arsenic-bearing copper slag

Arsenic contamination has raised great concern around the world as the cause of many severe health issues, including internal and external cancers. Discharging arsenic waste into the environment before proper handling is strictly forbidden. In order to treat the arsenic-bearing wastes in a safe way, we used the oxidation alkali leaching to dissolve arsenic in the low-risk state arsenate (AsO43−) firstly, followed by recycling of the alkali solution after arsenate removal. In this paper, we synthesized high-concentrated ferric oxyhydroxide gels (HFGs) with different supersaturation in a hydrothermal system to adsorb arsenate anions at high alkali without consuming the hydroxyls. The arsenate adsorption onto HFGs followed the pseudo second-order and intra-particle diffusion kinetics and fitted Langmuir isotherms model well. Through characterization of the synthesized HFGs particles by XRD, Raman spectra, SEM and TGA, it was confirmed that the surface hydroxyl sites on the ferric oxyhydroxide reacted with arsenates to form the bidentate surface complexation. In addition, the synthesized HFG at lower supersaturation had lower crystallinity and more surface hydroxyl sites, resulting in higher adsorption capacity for arsenate. Using HFG as the adsorbent, the arsenic (V) concentration in the copper slag alkali leaching solution can be reduced from 2084 mg/L to 71.8 mg/L, which can realize stabilization of the high-concentrated arsenate at high alkali and alkali solution recycling.

The applicability of evaluable wastes for the adsorption of Reactive Black 5

In this study, it is proposed that pumpkin seed hulls and eggshells that are household wastes are low-cost materials to remove the Reactive Black 5 from water media. Through a number of experiments, the influences of the contact time, adsorption quantity, temperature, and pH of the solution were studied. Characterization of pumpkin seed hulls and eggshells was done by using Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Adsorption of the experimental data well fitted with both the models called Langmuir and Freundlich isotherm. The maximum experimental capacities of adsorption related to pumpkin seed hulls and eggshells were 9.18 and 18.46 mg g−1, respectively. The optimum conditions were determined as adsorbent amount = 0.5 g L−1, pH = 6, and contact time = 15 min for the eggshells adsorption process and adsorbent dosage = 1 g L−1, pH = 2, and contact time = 30 min for the pumpkin seed hulls adsorption system. In addition, pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics were used to study the adsorbing dynamics of Reactive Black 5 onto pumpkin seed hulls and eggshells. In this study, it was observed that the pseudo-second-order kinetic was appropriate. Calculation of the thermodynamic parameters, such as changes in the free energy, enthalpy, and entropy of adsorption, was performed. According to the thermodynamic parameters, these processes were less spontaneous, practicable, and exothermic. To remove the dye from aqueous solutions, the pumpkin seed hulls and eggshells can be used as an alternative cheap adsorbent.

Adsorption of UV-quenching substances (UVQS) from landfill leachate with activated carbon

Co-treatment of landfill leachate with sewage at publicly owned treatment works (POTWs) is a common leachate management practice. However, the UV absorbing property of UV-quenching substances (UVQS) present in municipal landfill leachate may significantly reduce the efficiency of disinfection at POTWs that adopt ultraviolet irradiation for disinfection. The UVQS represents an emerging concern in the solid waste and wastewater treatment industries. This study aimed to evaluate the performance of activated carbon (AC) for removal of UVQS from landfill leachate in order to address the leachate UV-quenching issue. Results showed that the abatement of leachate UV254 absorbance with AC followed a pseudo-2nd-order reaction or intra-particle diffusion kinetics model. The adsorption isotherm patterns for leachate UV254 absorbance, dissolved organic carbon (DOC), and chemical oxygen demand (COD) well fit the Freundlich models. AC was capable of effectively adsorbing UV-quenching organic matter, regardless of humic acid (HA), fulvic acid (FA), and hydrophilic (HPI) isolates, via both chemisorption and physical adsorption mechanisms. Of note, after the AC adsorption, the residual UV254 absorbance was linearly correlated with COD remaining in leachate and exponentially correlated with residual DOC in leachate, separately. Furthermore, fluorescence excitation-emission matrix (EEM) analyses could indicate the removal of hydrophobic UVQS during AC adsorption, but could not reflect the presence or variation of hydrophilic UVQS. Findings of this study demonstrate that AC adsorption provides an effective treatment option for mitigation of the leachate-induced UV transmittance impacts on POTWs.

Synthesis of nano alumina for defluoridation of drinking water

In the present study, nano alumina was synthesized via sol–gel technique with and without a surfactant as a template. The synthesized adsorbents were first characterized to determine the morphology and surface composition. TEM images showed the formation of nano lathes and nano rods in the size range of 50–100 nm. The sharp, high intensity peaks obtained from XRD analysis confirmed the formation of highly crystalline alumina. Pure and modified nano alumina were then tested for defluoridation of water under different experimental conditions such as agitation time, solute concentration and pH. Defluoridation using pure nano alumina was achieved in 120 min using an adsorbent dose of 10 mg/L in a solution of pH 7. With modified nano alumina, defluoridation was achieved within 30 min with an adsorbent dose of 8mg/L at near neutral solution pH. From Langmuir adsorption isotherm, the maximum solute capacity was found to be 2.55 mg/g and 5.66 mg/g for pure and modified nano alumina respectively. The kinetics of the process was explained using both pseudo-second order and intra-particle diffusion kinetics. The water quality post treatment adhered to the norms of drinking water thus indicating the feasibility of using nano alumina for defluoridation of drinking water. To the best of the authors’ knowledge, the study has demonstrated successful water defluoridation using synthesized nano alumina in the crystalline phase hence emphasizing its role in drinking water defluoridation in the future.

Keratin-Nylon 6 engineered microbeads for adsorption of Th (IV) ions from liquid effluents

The applicability of novel porous microbeads (average diameter of about 2.0mm) of α-keratin engineered with Nylon 6, have been investigated for the adsorption of radioactive and non-biodegradable Th (IV) ions from the effluents. Thorium ion uptake on the intrinsically compatible adsorbent system was investigated using experimental analysis and kinetic studies. The developed system demonstrates maximum adsorption efficiency of 66.26% under ecologically optimal conditions i.e. pH=7, with 1000ppm initial Th (IV) concentration at 303K for 120min. The experimental results reveal that the adsorption kinetics study best fits with the Dubinin–Radushkevich isotherm model (R2=0.993) and Intra-particle diffusion kinetics model (R2=0.995). The kinetic models namely Pseudo-first order, Pseudo-second order, particle diffusion, & Elovich were used for the adsorption study, and were compared and calculated using linear & nonlinear regression methods thermodynamic analysis revealed the spontaneity, viability and exothermic nature of the adsorption process with free energy change (ΔG0) of −11.48kJ/mol. Further, the inter-polymer miscibility and compatibility was explored by atomistic molecular modelling and extended Flory-Huggins theory via Materials Studio software on geometrically minimized repeat units of Cysteine (functional group of α-keratin) and Nylon 6, employing Discover, Amorphous Cell, Forcite and Blends modules, which showed results to be consistent with FT-IR studies, revealing strong hydrogen bonding.

Recycling of eggshell waste into low-cost adsorbent for Ni removal from wastewater

The disposal of about 8 million ton/year of eggshell waste produced worldwide is an environmentally challenging issue. However, this waste can be converted to new materials useful for several industrial applications. In this study, hydroxyapatite was synthesized from eggshell waste and used as adsorbent for Ni2+ removal from aqueous solutions. Eggshell-derived hydroxyapatite was characterized using X-ray diffraction, scanning electron microscopy with the energy dispersion spectrum analysis and Fourier transform infrared spectroscopy. Batch experiments were conducted to investigate the effects of contact time and initial Ni2+ concentration on the adsorption process. Adsorption equilibrium was achieved within 80 min. The kinetics of the adsorption process was studied applying pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetics models. The kinetics study showed that the pseudo-second-order kinetic model described well the adsorption process with high correlation coefficient. The maximum Ni2+ adsorption capacity was found to be 109 mg g−1 which is generally higher than other waste-derived adsorbents. The adsorption of Ni2+ on eggshell-derived hydroxyapatite was well fitted by the Langmuir equation as compared to Freundlich, Temkin and Dubinin-Radushkevic isotherm models. The removal mechanism of Ni2+ by eggshell-derived hydroxyapatite could involve ion exchange with Ca2+ and dissolution/precipitation of the starting hydroxyapatite resulting in the formation of a Ni-bearing phosphate. The results of the present study showed that hydroxyapatite synthesized from eggshell waste represents an excellent low-cost adsorbent for treatment of Ni2+ contaminated waters.

Single-Step Room-Temperature in Situ Syntheses of Sulfonic Acid Functionalized SBA-16 with Ordered Large Pores: Potential Applications in Dye Adsorption and Heterogeneous Catalysis

A single-step in situ synthetic method of sulfonic acid functionalized SBA-16 material with ordered large pores has been fabricated involving ammonium fluoride (NH4F), tetraethylorthosilicate (TEOS) in heptane, and 3-mercaptopropyltrimethoxysilane (MPTMS) in the presence of hydrogen peroxide (H2O2) and Pluronic F127 (block copolymer) under mild acidic condition at room temperature. Due to the presence of numerous sulfonic acid groups on the surface, these materials show proficient adsorption capacities for dyes (qm = 365.46 mg g–1 for fuchsine basic, FB; qm = 217.87 mg g–1 for rhodamine 6G, R6G). Pseudo-second-order and intraparticle diffusion kinetics model as well as Langmuir isotherm model provided the best correlation with the obtained kinetic and isotherm data, respectively. Besides this, these materials prove to be efficient heterogeneous catalysts and show great catalytic activity toward Beckmann rearrangement of some oximes and esterification reaction. Moreover, these can be well regenerated in di...

Optimization of adsorption process parameters by response surface methodology for hexavalent chromium removal from aqueous solutions using Annona reticulata Linn peel microparticles.

Fruit peel microparticles of Annona reticulata Linn were used as biosorbent for the sequestration of hexavalent chromium (CR(VI)). Characterization of the biosorbent was done using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDXS), Fourier transfer infrared spectroscopy (FTIR), gas chromatography-mass spectrometry (GCMS), carbon, hydrogen, nitrogen and sulphur (CHNS) elemental analysis, mercury intrusion porosimetry and point of zero charge. Influential parameters were optimized using response surface methodology (RSM) with a total of 17 experimental runs based on the Box-Behnken design and found to be pH 1.0, temperature 25 °C and 100 mg/L initial chromium concentration. pH and concentration were found to be more influential than temperature. The analysis of variance indicated that a second-order polynomial regression equation was the most suitable for fitting the experimental data. The experimental runs showed a good correlation with the predicted responses (R2 = 0.9956). The biosorption process fitted well with the Langmuir isotherm with an adsorption capacity of 108. 32 mg/g out of the other isotherms such as Freundlich and Dubinin-Radushkevich that were analyzed. Non linear pseudo first order, pseudo second order, and intraparticle diffusion kinetics were applied to describe the interaction between the biosorbent and Cr(VI). Desorption and regeneration performances showed that fruit peels of Annona reticulata Linn can be an environmental friendly option for hexavalent chromium removal from aqueous solutions.

Purification of quercetin-3- O -sophoroside and isoquercitrin from Poacynum hendersonii leaves using macroporous resins followed by Sephadex LH-20 column chromatography

In China, Poacynum hendersonii is frequently used as a substitute for Apoacynum venetum L (Luobuma), which is a famous traditional Chinese medicine. Quercetin-3-O-sophoroside and isoquercitrin are two major flavonoids in Poacynum hendersonii leaves. In this work, a suitable method was established for the large-scale preparation of quercetin-3-O-sophoroside (QOS) and isoquercitrin (ISO) from Poacynum hendersonii leaves using macroporous resin combined with Sephadex LH-20 column chromatography. The adsorption/desorption capacities and desorption ratios of six macroporous resins were evaluated using static experiments. The HPD-300 resin had the best adsorption performance because it had the largest surface area, and was selected for further study. Compared with pseudo-first-order and intraparticle diffusion kinetics models, the pseudo-second-order model could better fit the adsorption kinetics of both QOS and ISO on the HPD-300 resin. In addition, the adsorption isotherms of the two compounds on the HPD-300 resin were fitted well to the Langmuir model. Under optimal conditions, the purities of QOS and ISO in the product were increased from 2.16% and 1.26% to 21.34% and 10.70% with recovery yields of 82.1% and 77.3%, respectively. Subsequently, Sephadex LH-20 column chromatography was employed for improving the purities of the two compounds. After separation by Sephadex LH-20 column chromatography, the purities of QOS and ISO achieved 93.5% and 95.6%, respectively.

Characterization and adsorption capacity of raw pomegranate peel biosorbent for copper removal

This study investigates the adsorption potential of natural materials waste. The biosorbent used is an untreated pomegranate peel (PGP) derived from local agricultural activities to remove copper Cu(II) ions. Natural PGP biosorbent has given, for the first time in literature, high removal efficiency for copper ions removal. The characterization of the biosorbent have been made by means Fourier Transform Infrared Spectroscopy (FTIR), TG/DTA analysis, Boehm titration and point of zero charge (pHpzc). Studied parameters are: the initial metal concentration, the pH of the solution, the particle size, the temperature and contact time. The highest Cu(II) adsorption capacity is obtained at pH = 5.8, for a particle size of 630 μm, a temperature of 313 K, a contact time of 2 h, and by increasing the initial concentration of Cu(II) solution. Langmuir, Freundlich, Dubinin Radushkevich and Temkin isotherm models have been used. Langmuir maximum adsorption capacity is 30.12 mg/g. Experimental data have been fitted to Pseudo-first order, Pseudo-second order, Intra-particle diffusion and Elovich kinetics models. Thermodynamic analysis has indicated a spontaneous endothermic adsorption of Cu(II) on pomegranate peel. The results of this study suggest that copper could be removed through an environmentally friendly process using a low cost biosorbent from an agricultural waste i.e. PGP.

Application of chitosan/poly(vinyl alcohol)/CuO (CS/PVA/CuO) beads as an adsorbent material for the removal of Pb(II) from aqueous environment

The utilization of CS/PVA/CuO as a novel adsorbent for the removal of Pb(II) from aqueous solution has been examined in a batch adsorption process with several experimental conditions including initial solution pH, dose, contact time, initial metal ion concentration, and temperature. The new and novel material was characterized by structural (XRD), spectral (FTIR), morphological with elemental (SEM with EDS), and size of the nanoparticles (TEM) analyses. The pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetics equations were used to analyze the kinetic data of the adsorption process and the data was fitted well with the pseudo-second-order kinetic model with R2 values (close to the unity). Equilibrium isotherms for the adsorption of Pb(II) were analyzed by the Langmuir, Freundlich, and D-R isotherm models. The best interpretation for the equilibrium data was given by Langmuir isotherm, and the maximum adsorption capacity was 116.84mg/g at pH 5, and adsorbent dose of 100mg at 323K. Different thermodynamic parameters namely, Gibbs free energy change (-8.436, −9.167 and −9.723kJ/mol for 303, 313 and 323K respectively), enthalpy change (11.61, 11.52 and 11.62kJ/mol), and entropy change (0.0661J/mol k), were also evaluated from the temperature dependence, and the results suggest that the adsorption reaction is spontaneous and endothermic in nature.

Batch and column studies for the adsorption of chromium(VI) on low-cost Hibiscus Cannabinus kenaf, a green adsorbent

Adsorption is one of the excellent ways for heavy metal removal from aqueous solution because of advantages like the low cost, availability, profitability, ease of operation and efficiency. In this study, adsorption potential of a low cost adsorbent Hibiscus Cannabinus kenaf was investigated for Cr(VI) removal from water using batch and continuous mode experiments. Optimum removal of Cr(VI) ions was occurred at pH 7. The kinetic results showed that the Cr(VI) removal followed intraparticle diffusion kinetics with a correlation coefficient greater than 0.94. The adsorption isotherms of Cr(VI) could be described very well by both the Langmuir and Freundlich equations (R2=0.997). The maximum Cr(VI) uptake was found to be 582µg/g in Langmuir model. Column studies have been carried out to compare these with batch capacities. The Yoon–Nelson and Thomas models were found appropriate for description of the breakthrough curve, whereas the Bohart–Adams model was not match very well. The recovery of Cr(VI) and chemical regeneration of the spent kenaf have also been studied. The high Cr(VI) adsorption capacity and regeneration efficiency of kenaf suggests it as a promising alternative for heavy metal removal specially at near circumneutral pH.

Thiol-functionalized Fe3O4/SiO2 microspheres with superparamagnetism and their adsorption properties for Au(III) ion separation

Thiol-functionalized Fe3O4/SiO2 microspheres (Fe3O4/SiO2-SH) with high saturation magnetization (69.3 emu g–1), superparamagnetism, and good dispersibility have been prepared by an ethylene glycol reduction method in combination with a modified Stober method. The as-prepared composite magnetic spheres are characterized with fourier transform infrared spectroscopy (FT-IR), zeta potential, X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and superconducting quantum interference magnetometer, and tested in separation of Au(III) ions from aqueous solutions. The data for Au(III) adsorption on Fe3O4/SiO2-SH are analyzed with the Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models, and the pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics models. The adsorption behaviors of Au(III) on Fe3O4/SiO2-SH follow the Langmuir isotherm model, and the adsorption process conforms to the pseudo-second-order kinetic model. The maximum adsorption capacity of Au(III) on Fe3O4/SiO2-SH is 43.7 mg g–1. Acetate anions play an important role yet Cu(II) ions have little interference in the adsorption of Au(III) on the adsorbent. A satisfactory recovery percentage of 89.5% is acquired by using an eluent with 1 M thiourea and 5% HCl, although thiols have a high affinity to Au(III) ions based on the hard-soft acid-base (HSAB) theory by Pearson.