Heavy metals uptake from aqueous solutions and industrial wastewaters by humic acid-immobilized polymer/bentonite composite: Kinetics and equilibrium modeling

This study explored the feasibility of utilizing a novel adsorbent, humic acid-immobilized-amine-modified polyacrylamide/bentonite composite (HA-Am-PAA-B) for the adsorption of Cu(II), Zn(II) and Co(II) ions from aqueous solutions. The FTIR and XRD analyses were done to characterize the adsorbent material. The effects of pH, contact time, initial adsorbate concentration, ionic strength and adsorbent dose on adsorption of metal ions were investigated using batch adsorption experiments. The optimum pH for Cu(II), Zn(II) and Co(II) adsorption was observed at 5.0, 9.0 and 8.0, respectively. The mechanism for the removal of metal ions by HA-Am-PAA-B was based on ion exchange and complexation reactions. Metal removal by HA-Am-PAA-B followed a pseudo-second-order kinetics and equilibrium was achieved within 120 min. The suitability of Langmuir, Freundlich and Dubinin-Radushkevich adsorption models to the equilibrium data was investigated. The adsorption was well described by the Langmuir isotherm model. The maximum monolayer adsorption capacity was 106.2, 96.1 and 52.9 mg g^?1 for Cu(II), Zn(II) and Co(II) ions, respectively, at 30 °C. The efficiency of HA-Am-PAA-B in removing metal ions from different industry wastewaters was tested. Adsorbed metal ions were desorbed effectively (97.7 for Cu(II), 98.5 for Zn(II) and 99.2% for Co(II)) by 0.1 M HCl. The reusability of the HA-Am-PAA-B for several cycles was also demonstrated.     

Adsorption of anionic dyes on poly(epicholorohydrin dimethylamine) modified bentonite in single and mixed dye solutions

The performance of poly(epicholorohydrin dimethylamine) modified bentonite (EPIDMA/bentonite) as an adsorbent to remove anionic dyes, namely Direct Fast Scarlet, Eosin Y and Reactive Violet K-3R, was investigated in single, binary and ternary dye systems. In adsorption experiments in single dye solutions, the adsorption of the three dyes onto EPIDMA/bentonite was described by the Langmuir isotherm model and the pseudo-second-order kinetic model. At low dosage of EPIDMA/bentonite, preferential adsorption was observed for the dye with higher affinity to the adsorbent in mixed dye systems. The reduction in uptake of the dye with increasing equilibrium dye concentration in the isotherm and desorption in the kinetic curves were observed for the dye with lower affinity. The total amount of dyes adsorbed versus the total equilibrium dye concentrations were fitted well by the Langmuir isotherm model. The kinetics of the total adsorbed amount of dyes followed the pseudo-second-order kinetic model. The effect of the dosage of adsorbent on color removal efficiency, residual color distribution and adsorption kinetics was investigated.     

Kinetic and equilibrium modelling of Cadmium(II) ions sorption onto polymerized tamarind fruit shell

Formaldehyde polymerized tamarind fruit shell (FPTFS) having sulphonic acid groups was prepared and tested as an adsorbent for the adsorption of cadmium(II) ions from water and wastewater. Batch experiments were conducted to determine the adsorption efficiency of the adsorbent. The maximum adsorption of Cd(II) occurred at pH 7.0. The equilibrium was established in 3 h. Kinetic data were modeled using pseudo-first-order, pseudo-second-order and Ritchie modified second-order model. The equilibrium data were described using Langmuir, Freundlich, Sips and Toth isotherm equations. The results of error analysis indicated that the best parameters for kinetic and isotherm equations were obtained by hybrid fractional error function method. The kinetic data could be well described by Ritchie modified second-order expression and the adsorption capacities calculated by the model were close to those determined by experiments. The adsorption isotherm data could be well fitted to the Sips isotherm model. The efficiency of Cd(II) removal by the FPTFS decreased with an increase in ionic strength of the solution. The efficiency of FPTFS was tested using fertilizer industry wastewater. About 98.0% of the adsorbed Cd(II) ions can be released from the spent adsorbent by treatment with 0.1 M HCl solution. Consecutive adsorption/desorption (4 cycles) showed the feasibility of the FPTFS for Cd(II) adsorption.     

Chitosan modified with Reactive Blue 2 dye on adsorption equilibrium of Cu(II) and Ni(II) ions

This study aimed at immobilizing Reactive Blue 2 (RB 2) dye in chitosan microspheres through nucleophilic substitution reaction. The adsorbent chemical modification was confirmed by Raman spectroscopy and thermogravimetric analysis. This adsorption study was carried out with Cu(II) and Ni(II) ions and indicated a pH dependence, while the maximum adsorption occurred around pH 7.0 and 8.5, respectively. The pseudo second-order kinetic model resulted in the best fit with experimental data obtained from Cu(II) (R = 0.997) and Ni(II) (R = 0.995), also providing a rate constant, k₂, of 4.85 × 10⁻⁴ and 3.81 × 10⁻⁴ g (mg min)⁻¹, respectively, thus suggesting that adsorption rate of metal ions by chitosan-RB 2 depends on the concentration of ions on adsorbent surface, as well as on their concentration at equilibrium. The Langmuir and Freundlich isotherm models were employed in the analysis of the experimental data for the adsorption, in the form of linearized equations. Langmuir model resulted in the best fit for both metals and maximum adsorption was 57.0 mg g⁻¹ (0.90 mmol g⁻¹) for Cu(II) and 11.2 mg g⁻¹ (0.19 mmol g⁻¹) for Ni(II). The Cu(II) and Ni(II) ions were desorbed from chitosan-RB 2 with aqueous solutions of EDTA and H₂SO₄, respectively.     

Nano-TiO2 modified with 2-mercaptobenzimidazole as an efficient adsorbent for removal of Ag(I) from aqueous solutions

Nano-TiO₂ was modified with 2-mercaptobenzimidazole via surfactant activation and used as an adsorbent for the removal of Ag(I) under optimum conditions. The adsorbent was characterized using powder X-ray diffraction and FT-IR spectroscopy. The equilibrium data were fitted to the Langmuir, Freundlich and Temkin isotherm models. Langmuir isotherm describes the adsorption data better than Freundlich isotherm and Temkin. Kinetic studies showed that the pseudo second order kinetic model fits the adsorption kinetic processes well. Maximum adsorption capacity for Ag(I) was 128.2 mg g⁻¹ of nano-TiO₂. The method was successfully applied to the removal of silver from radiology film processing wastewater samples.     

Adsorption of Pb(II) from aqueous solution to Ni-doped bamboo charcoal

Bamboo charcoal (BC) obtained by pyrolysis of Makino bamboo in the absence of oxygen was used as support for the preparation of Ni-doped adsorbent (Ni-BC). The low-cost composite was characterized and used as an adsorbent for Pb(II) removal from water. The results showed that both BET surface area and total pore volume of Ni-BC increased. The adsorption of Pb(II) strongly depended on solution pH, temperature and ionic strength. The adsorption isotherms followed Langmuir isotherm model well, and the maximum adsorption capacities of Pb(II) at 298 K were 25.0 and 142.7 mg/g for BC and Ni-BC, respectively. The adsorption processes were well fitted by pseudo-second-order kinetic model. Thermodynamic parameters showed that the adsorptions of Pb(II) onto both adsorbents were feasible, spontaneous, and exothermic under the studied conditions. The spent Ni-BC could be readily regenerated for reuse.     

Adsorption of Cu(II) ions from aqueous solutions on modified chrysotile: Thermodynamic and kinetic studies

The adsorption of Cu(II) ions by modified chrysotile from aqueous solution was investigated under different experimental conditions. The Langmuir and Freundlich equations were introduced to describe the linear forms about the adsorption of Cu(II) ions on the surface of modified chrysotile, and it was found that the adsorption equilibrium process was well described by the Langmuir isotherm model with the maximum adsorption capacity of 1.574 mmol/g at 333 K. The thermodynamic parameters (ΔG⁰, ΔH⁰ and ΔS⁰) for adsorption on modified chrysotile were also determined from the temperature dependence. The influences of specific parameters such as temperature, pH value and initial concentration for the kinetic studies were also examined. The adsorption follows a pseudo-second order rate law.     

Adsorption of hexavalent chromium from aqueous solutions by bio-chars obtained during biomass pyrolysis

In this study, bio-chars were evaluated as a potential adsorbent for the removal of Cr (VI) ions from aqueous solutions. The effects of some important parameters including initial pH (1.5–7), adsorbent dose (0.2–5 g/L), contact time (5–900 min) and initial Cr (VI) ion concentration (5–75 mg/L) were tested on the removal of Cr (VI) ions from aqueous solution in batch experiments. Maximum adsorption capacities of the tested bio-chars under the certain experimental conditions determined as optimal were 3.53 mg/g for NCBC, 3.97 mg/g for NZCBC and 6.08 mg/g for ACBC, respectively. Results of the kinetic and isotherm modeling studies revealed that the adsorption data fitted well with a pseudo-second order and Langmuir model. In among the tested bio-chars, the bio-char (ACBC) was largely equivalent to activated carbon: AC (9.97 mg/g) in terms of adsorption capacity. All results indicated that the bio-chars had higher adsorption capacity than some chars and activated carbons reported previously, and also that these bio-chars could be used successfully as low-cost adsorbents for the removal of chromium ions from aqueous solutions under the tested experimental conditions.     

Chemically modified organic/inorganic nanoporous composite particles for the adsorption of reactive black 5 from aqueous solution

In the present work, we report a chemically modified polyacrylamide/silica nanoporous composite adsorbent for the removal of reactive black 5 (RB5) azo dye from aqueous solutions. The composite adsorbent was synthesized in a packed bed and modified by ethylenediamine (EDA). The adsorbent was characterized by Fourier transformation infrared (FT-IR), thermogravimetric analysis (TGA), thermoporometry, Brunauer, Emmett and Teller (BET) method and scanning electron microscopy (SEM). Mechanical stability of the adsorbent was examined in a packed bed by following the back-pressure of the column. Pore diameter of the composite adsorbent in dry and wet states was estimated to be about 18.71 nm and 12.61 nm, respectively. Adsorption experiments were performed in batch mode and effect of various operational parameters on the adsorption capability of the adsorbent was studied systematically. The maximum adsorption capacity of the modified composites was found to be 454.5 mg RB5/g of adsorbent. The equilibrium data were analyzed by Langmuir, Freundlich, Sips, BET and Redlich–Peterson isotherm models and found to fit well to the BET isotherm. The data kinetically followed the pseudo-second-order model. High adsorption capacity, fast removal mechanism, and good mechanical stability are three advantages of the presented composite for the removal of RB5.     

Optimised activation of bentonite for toluene adsorption

Acid-activation of bentonite was optimised to prepare an effective adsorbent of toluene. The activated bentonite was obtained with a specific surface area of 195 m²/g, a pore volume of about 0.46 cm³/g and a most frequent pore size of 62 Å. Compared to the raw bentonite, the adsorption of toluene onto acid-activated bentonite was increased from 66 mg/g to 197 mg/g. Vapor–solid adsorption isotherms of toluene were measured at 120 °C, 140 °C, 160 °C and 182 °C using an inverse gas chromatography. The experimental data were correlated with different adsorption isotherm models such as Langmuir, Freundlich, Langmuir–Freundlich and Toth models. Only the Langmuir–Freundlich equation provided good fit to the experimental data.     

The effect of polystyrene as a porogen on the fluoride ion adsorption of Zr(IV) surface-immobilized resin

A novel adsorbent, Zr(IV)-immobilized resin, was prepared by surface template polymerization. This adsorbent, prepared by adding polystyrene (PS) to resin, has a high adsorption capacity for the removal of fluoride ion from aqueous solutions. The adsorption capacity increased with rising PS concentration, since the specific surface area can be effectively increased by adding polystyrene as a porogen. The adsorption isotherm has been modeled by the Langmuir and Freundlich equations. The adsorption isotherms were well described by the Langmuir equation. The removal of fluoride was also carried out using a column method. The presence of PS in the resin exerted a remarkable influence on the uptake of fluoride ion. The fluoride adsorbed on the resin was quantitatively eluted with 0.1 M NaOH.     

Cationic polymer chain tethered on the pore-wall of 3-D ordered macroporous resin for the removal of hexavalent chromium from aqueous solution

A novel 3-D ordered macroporous (3DOM) adsorbent with a cationic polymer chain (poly(N,N-dimethylaminoethyl methacrylate), PDMAEMA) tethered on the pore wall was prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) for the removal of toxic Cr(VI) ions from aqueous solution. In comparison with recently reported adsorbents, the adsorbent remarkably stands out owing to large adsorption capacity, relatively fast kinetics, and high stability in the regeneration process. The adsorption capacity significantly depended on the solution pH and there was a wide working pH range that is much convenient in practical application. Kinetics of Cr(VI) adsorption by the 3DOM adsorbent was studied in batch experiments, in the temperature range 298–318 K. The equilibriums were arrived within 120–130 min and a pseudo-second order model can be described well. In the adsorption isotherm study, experimental data followed the Langmuir adsorption model. The maximum adsorption capacity increased with the increase of temperature, and reached the high value of 431.0 mg/g at 308 K. Thermodynamic parameters revealed spontaneous and endothermic adsorption processes. Furthermore, the 3DOM adsorbent remained high adsorption capacity (above 90% of the original Cr(VI) loading capacity) after 15 adsorption–desorption cycles by simply using sodium hydroxide solution as the desorption liquid, which ensured the reusability of 3DOM adsorbent.     

Arsenic removal from aqueous solutions with Fe-hydrotalcite supported magnetite nanoparticle

The sorptive removal of arsenic from water by synthetically-prepared magnetic Fe-hydrotalcite (M-FeHT) seeding by nano magnetite was investigated. The synthesis of M-FeHT was achieved by a co-precipitation method. M-FeHT was characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and magnetic susceptibility analysis. Batch tests were conducted to investigate the removal mechanism of As(III) and As(V) by M-FeHT. Kinetic studies revealed that uptake of As(V) (95% removal) and As(III) ions occurs rapidly within the first 15 min, and slows thereafter. The adsorption data follow a pseudo-second-order kinetic model and fit the Langmuir isotherm well. The experimental results show that stable arsenic removal efficiency, and the capability to reduce As levels, make M-FeHT a suitable adsorbent for the treatment of As-polluted waters. After adsorption, tests were conducted with magnetic separation to determine the separability of M-FeHT from solution. At magnetic field intensity of 2 T, the efficiency of M-FeHT separation was 91%. Finally, after adsorption by M-FeHT, residual arsenic concentration decreased to less than 10 μg/L (i.e., below the threshold specified by the WHO). Fe-hydrotalcite-supported magnetite nanoparticles were not only more efficient in the removal of As but also in recovery by the magnetic separator.     

Walnut shell supported nanoscale Fe0 for the removal of Cu(II) and Ni(II) ions from water

The walnut shell supported nanoscale zero‐valent iron (walnut‐nZVI) was prepared from sodium borohydride, iron(II) chloride tetrahydrate, and walnut shell by liquid phase chemical reduction and characterized by FTIR, TEM, and XRD. The composites were tested as adsorbent for the removal of Cu(II) or Ni(II) ions. The equilibrium data were analyzed by the Langmuir, Freundlich, Dubinin–Radushkevich, which revealed that Langmuir isotherm was more suitable for describing Cu(II) and Ni(II) ions adsorption than the other two isotherm models. The results indicated that the maximum adsorption capacity was higher than some other modified biomass waste adsorbents under the proposed conditions, were 458.7, 327.9 mg g^?1 for Cu(II) or Ni(II). The adsorption kinetics data indicated that the adsorption fitted well with the pseudo‐second‐order kinetic model. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43304.     

Physicochemical Parameters of Cu(II) Ions Adsorption from Aqueous Solution by Magnetic-Poly(divinylbenzene-n-vinylimidazole) Microbeads

This study is aimed at the synthesis and characterization of the mesoporous magnetic-poly(divinylbenzene-1-vinylimidazole)[m-poly(DVB-VIM))microbeads(average diameter = 53–212 µm); their application as adsorbent in the removal of Cu(II) ions from aqueous solutions was investigated. The mesoporous m-poly(DVB-VIM) microbeads were prepared by copolymerizing of divinylbenzene (DVB) with 1-vinylimidazole (VIM). The mesoporous m-poly(DVB-VIM) microbeads were characterized by N₂ adsorption/desorption isotherms, ESR, elemental analysis, scanning electron microscope (SEM), and swelling studies. At fixed solid/solution ratio the various factors affecting adsorption of Cu(II) ions from aqueous solutions such as pH, initial concentration, amount of mesoporousm-poly(DVB-VIM)) microbeads, contact time, and temperature were analyzed. Langmuir, Freundlich, and Dubinin-Radushkvich isotherms were used the model adsorption equilibrium data. The Langmuir isotherm model was the most adequate. The pseudo first-order, pseudo-second-order, Ritch-second-order, and intraparticle diffusion models were used to describe the adsorption kinetics. The experimental data fitted to pseudo second-order kinetic. The study of temperature effect was quantified by calculating various thermodynamic parameters such as Gibbs free energy, enthalpy, and entropy changes. Morever, after the use in adsorption, the mesoporous m-poly(DVB-VIM) microbeads with paramagnetic property was separated via the applied magnetic force. These features make the mesoporous m-poly(DVB-VIM) microbeads a potential candidate for support of Cu(II) ions removal under magnetic field.     

Competitive adsorption of Direct Yellow 12 and Reactive Orange 12 on ZnS:Mn nanoparticles loaded on activated carbon as novel adsorbent

A novel adsorbent (ZnS:Mn nanoparticles loaded on activated carbon) was made. The competitive adsorption of Direct Yellow 12 (DY12) and Reactive Orange 12 (RO12) dyes in binary mixture onto this adsorbent was studied. DY12 and RO12 with severe spectra overlapping were chosen and analyzed simultaneously with high accuracy by first order derivative spectrophotometric method in binary solutions. The effect of multi-solute systems on the adsorption capacity was investigated. Because of the specific characteristics of ZnS:Mn-NP-AC was found to be efficient for the removal of the dyes studied. The adsorption capacities were investigated and described by the mono- and multi-component Langmuir and Freundlich isotherm models for both single and binary dye solutions. The isotherm constants for DY12 and RO12 were calculated. For single solution of DY12 and RO12 dyes, the adsorption capacities of the applied adsorbent were found to be 90.05 mg/g and 94.52 mg/g, respectively. Equilibrium uptake amounts of DY12 and RO12 in binary solution onto the applied adsorbent were found to be considerably decreasing with increasing the concentrations of the other dye. A better agreement between the adsorption equilibrium data and mono-component Langmuir isotherm model was found. However, at concentrations within moderate ranges, the extended Freundlich isotherm model satisfactorily predicted multi-component adsorption equilibrium data. An endothermic and a spontaneous nature for the adsorption of the dyes studied were shown from thermodynamic parameters.     

Removal of Reactive Blue 21 onto magnetic chitosan microparticles functionalized with polyamidoamine dendrimers

Chitosan/poly(amidoamine) (MCS/PAMAM) microparticles were prepared as magnetic adsorbents for removal of Reactive Blue 21 (RB 21) dye from aqueous solution. Characterization of these particles was carried out using scanning electron microscopy, Fourier transform-infrared spectroscopy, X-ray diffractometry and vibrating sample magnetometry. The results indicate that the magnetic chitosan microparticles (MCS) were functionalized with PAMAM dendrimers and maintained its intrinsic magnetic properties. The effects of initial pH, adsorbent dose, initial concentration, contact time and temperature on adsorption were investigated. Kinetic studies showed that the dye adsorption process followed a pseudo-second-order kinetic model but that the adsorption rate was also influenced by intraparticle diffusion. Equilibrium adsorption isotherm data indicated a good fit to the Langmuir isotherm. The maximum adsorption capacities obtained from the Langmuir model were 555.56, 588.24, 625.00 and 666.67 mg g⁻¹ at 303, 313, 323 and 333 K, respectively. The thermodynamic parameters revealed the feasibility, spontaneity and endothermic nature of the adsorption. Recycling experiments confirmed the relative reusability of the adsorbent.     

Adsorption performance of nickel and cadmium ions onto brewer's yeast

The brewer's yeast was used as adsorbent for the removal of Ni(II) and Cd(II) metal ions from aqueous solution. The surface of the brewer's yeast had three main functional groups of sulfonate, carboxyl, and amine groups. The pH of solution played an important role on the uptake of metal ions, and optimum adsorption was obtained at pH 6. Acid solution (pH 3) was efficient for the desorption of Ni(II) and Cd(II) ions from loaded brewer's yeast and the desorption efficiency was higher than 90%. The rate of metal ions adsorption onto brewer's yeast was rapid with short contact time. The kinetics of the adsorption process was found to follow the pseudo‐second‐order kinetic model. Langmuir and Freundlich isotherm models were used to fit the experimental data with Langmuir isotherm model having a better fit. The maximum uptakes of Ni(II) and Cd(II) by brewer's yeast were estimated to be 5.34 and 10.17 mg/g, respectively.     

Removal Characteristics of Cd(II), Cu(II), Pb(II), and Zn(II) by Natural Mongolian Zeolite through Batch and Column Experiments

The removal characteristics of Cd(II), Cu(II), Pb(II), and Zn(II) from model aqueous solutions by 5 natural Mongolian zeolites were investigated. The adsorption of metals on zeolites reached a plateau value within 6 h. The adsorption kinetic data were fitted with adsorption kinetic models. The equilibrium adsorption capacity of the zeolites was measured and fitted using Langmuir and Freundlich isotherm models. The order of adsorption capacity of zeolite was Pb(II) > Zn(II) > Cu(II) > Cd(II). The maximum adsorption capacity of natural zeolite depends on its cation exchange capacity and pH. The leaching properties of metals were simulated using four leaching solutions. The results show that natural zeolite can be used as an adsorbent for metal ions from aqueous solutions or as a stabilizer for metal-contaminated soils.     

Ionic liquid based periodic mesoporous organosilica: An efficient support for removal of sunset yellow from aqueous solutions under ultrasonic conditions

The efficiency of an ionic liquid based periodic mesoporous organosilica (PMO-IL) in the removal of sunset yellow from aqueous solutions using ultrasonic assisted adsorption method was investigated. The PMO-IL was first characterized by nitrogen sorption and TEM techniques. The optimized conditions (0.013 g of adsorbent, 32 mg L⁻¹ of sunset yellow at 2 min of sonication time and pH 7) were obtained by central composite design (CCD). Fitting the equilibrium data show the suitability of the Langmuir model with second-order equation to control the kinetic of the adsorption process and good reusability (5 cycles) of PMO-IL for adsorption of dye.