Removal of heavy metals from aqueous solutions using activated carbon prepared from Cicer arietinum

Removal of Cu²⁺, Cd²⁺, Pb²⁺, and Zn²⁺ from aqueous solutions by activated carbon prepared from stems and seed hulls of Cicer arietinum, an agricultural solid waste, has been studied. The influence of various parameters, such as pH, contact time, adsorbent dose, and initial concentration of metal ions on removal was evaluated. The activated carbon was characterized by FT-IR spectroscopy, X-ray diffraction, and elemental analysis. Sorption isotherms were studied using Langmuir and Freundlich isotherm models. All experimental sorption data were fitted to the sorption models using nonlinear least-squares regression. The maximum adsorption capacity values for activated carbon prepared from Cicer arietinum waste for metal ions were 18 mg g^?1 (Cu²⁺), 18 mg g^?1 (Cd²⁺), 20 mg g^?1 (Pb²⁺), and 20 mg g^?1 (Zn²⁺), respectively. The Freundlich isotherm model fit was best, followed by the pseudo-second-order kinetic model. Desorption studies were carried out with dilute hydrochloric acid for quantitative recovery of the metal ions and for regeneration of the adsorbent.     

Low-cost and efficient adsorbent derived from pyrolysis of Jatropha curcas seeds for the removal of Cu2+ from aqueous solutions

Biochar, is a low-cost material that can be used as an alternative adsorbent for the removal of heavy metals. In this study, a low-cost and efficient adsorbent synthesised from Jatropha curcas seeds was used for the uptake of Cu²⁺ from aqueous solutions. The as-prepared adsorbent was characterised by scanning electron microscopy and Brunauer–Emmett–Teller analysis post calcination at 500 °C, its BET surface area and total pore volume were 39.62?m²?g^?1 and 0.049?m³?g^?1, respectively. Subsequently, the effects of initial pH of the solution, contact time, and adsorbent material dosage on the adsorption of Cu²⁺ by the prepared adsorbent were investigated. The as-prepared adsorbent exhibited a high performance, with a maximum adsorption amount of 32.895?mg?g^?1 for Cu²⁺ at pH 5.0 and 25 °C, owing to the presence of ?OH, C=O, C–O, Si-O-Si, and O-Si-O on its surface. The predominant Cu²⁺ adsorption mechanism was assumed to be ion exchange. Notably, the Cu²⁺ adsorption could attain equilibrium within 90?min. In addition, the fact that the Langmuir model was a better fit than the Freundlich model for the isotherm data of Cu²⁺ adsorption by the as-prepared adsorbent suggested that the adsorption of Cu²⁺ was a monolayer adsorption process.     

Metal removal with two biochars made from municipal organic waste: adsorptive characterization and surface complexation modeling

The adsorptive characteristics of biochar produced from garden green waste (S-char) and a mixture of food waste and garden green waste (FS-char) were investigated. Adsorption of Cu²⁺, Zn²⁺, and Mn²⁺ onto the two biochars reached equilibrium within 48 hours. The metal adsorption was effectively described by the pseudo-second-order kinetic and Freundlich isotherm models which suggest heterogeneous chemisorption. The initial solution pH influenced adsorption of Zn²⁺ and Mn²⁺ but not of Cu²⁺. Simulation via a surface complexation model showed that the fraction of XOCu⁺ adsorbed onto biochar was increased with increasing pH until it reached the adsorption maximum at pH 8.5, while the endpoint for the maximum of XOMn⁺ was higher than pH 12.     

Removal of Mo(VI) from aqueous solutions using sulfuric acid-modified cinder: kinetic and thermodynamic studies

Removal of Mo(VI) from aqueous solutions was investigated using cinder modified by sulfuric acid. Various parameters such as pH, agitation time, Mo(VI) concentration, and temperature have been studied. The maximum adsorption of Mo(VI) occurred at pH between 4.0 and 6.0. Kinetic studies showed that the adsorption generally obeyed a pseudo second-order model. The activation energy was 31.4?kJ?mol^?1, indicating that the adsorption process was governed mainly by interactions of physical nature. Furthermore, application of Langmuir and Freundlich isotherm models to the adsorption equilibrium data showed that the adsorption behavior obeyed the Langmuir model. The adsorption capacity was found to be 10.8?g Mo(VI)?kg^?1 adsorbent. Finally, thermodynamic parameters such as ΔH ⁰, ΔS ⁰, and ΔG ⁰ were also evaluated, which showed that the adsorption of Mo(VI) on the treated cinder was endothermic, entropy increasing, and spontaneous. In conclusion, the sulfuric acid-modified cinder was shown to be an inexpensive, effective, and simple adsorbent for the removal of Mo(VI) from water.     

First determination of Cu adsorption on soil humin

Humic substances are heterogeneous mixtures of organic compounds occurring in huge amounts mainly in waters, soils, sediments and organic wastes. They are formed during the decay of living organisms. They play a very important role in many environmental processes including carbon sequestration, water cleaning and retention, soil erosion, fertility and pollutant retention. However, due to their complex nature, humic substances are still poorly characterized and much less known than living matter. Humin is the most insoluble and, in turn, the least understood fraction of humic substances. To our knowledge, no information is currently available on the adsorption and desorption behaviors of metal ions on soil humin. Here, we report the adsorption and desorption properties of Cu(II) on humin and humic acids isolated from a forest soil in northeast China using the batch equilibration method. Solid-state ¹³C cross-polarization magic angle spinning nuclear magnetic resonance (¹³C CPMAS NMR) spectroscopy was used to characterize and compare the chemical structures of humin and humic acid. The batch experiments’ results show that humin has a lower adsorption capacity and higher adsorption reversibility for Cu(II) than humic acid. The adsorption isotherms well fitted both the Langmuir and Freundlich equations. Humin, therefore, plays an important role in controlling the fate, transport and bioavailability of Cu(II) in the environment. The ¹³C CPMAS NMR spectra showed that compared with humic acid, humin was higher in alkyl C, carbohydrate C and phenolic C and was lower in methoxyl C, aryl C and carbonyl C. These findings mean that humin was less alkylated, more aliphatic and more hydrophobic.     

Sorption of cadmium(II) and copper(II) by soil humic acids: temperature effects and sorption heterogeneity

Sorption by humic acids is known to modify the bioavailability and toxicity of metals in soils and aquatic systems. The sorption of cadmium(II) and copper(II) to two soil humic acids was measured at pH 6.0 using ion-selective electrode potentiometric titration at different temperatures. Sorption reactions were studied with all components in aqueous solution, or with the humates in suspension. Adsorption reactions were described using a multiple site-binding model, and a model assuming a continuous log-normal distribution of adsorption constants. Adsorption of Cu²⁺ was more favourable than adsorption of Cd²⁺. The log-normal distribution model provided the closest fit to observations and allowed parameterisation of adsorption data using a mean adsorption constant (log K _μ). Sorption of Cd²⁺ to dissolved humic acids increased slightly in extent and sorption affinity with increasing temperature, but the effect was small (log K _μ 2.96–3.15). A slightly greater temperature effect occurred for sorption of Cd²⁺ to solid-phase humic acids (log K _μ 1.30–2.08). Sorption of copper(II) to both aqueous- and colloidal-phase humates showed more pronounced temperature dependence, with extent of sorption, and sorption affinity, increasing with increasing temperature (log K _μ 3.4–4.9 in solution and 1.4–4.5 in suspension). The weaker adsorption of Cd²⁺ than Cu²⁺, and smaller temperature effects for dissolved humates than suspended humates, suggested that the observed temperature effects had a kinetic, rather than thermodynamic, origin. For any metal-to-ligand ratio, free metal ion concentration, and by inference metal bioavailability, decreased with increasing temperature. The consistency of the data with kinetic rather than thermodynamic control of metal bioavailability suggests that equilibrium modelling approaches to estimating bioavailability may be insufficient.     

Steam activation,characterisation and adsorption studies of activated carbon from maize tassels

In this paper, steam-produced activated carbon (STAC) from maize tassel (MT) was evaluated for its ability to remove basic dye (methylene blue MB) from aqueous solution in a batch adsorption process. The equilibrium experiments were conducted in the range of 50–300 mg/L initial MB concentrations at 30°C, for effect of pH, adsorbent dosage and contact time. The experimental data were analysed by Langmuir, Freundlich and Temkin isotherm models of adsorption. Freundlich adsorption isotherm was found to have highest value of R²(R²=0.97) compared to other models of Langmuir and Temkin having (0.96 and 0.95 respectively). STAC has a high adsorptive capacity for MB dye (200 mg/g) and also showed favourable adsorption for the dye with the separation factor (R_L<1) for the dye-activated carbon system. The kinetic data obtained were analysed using pseudo first-order kinetic equation and pseudo second-order kinetic equation. The experimental data fitted well into pseudo second-order kinetic equation, as demonstrated by the high value of R².     

Kinetic,equilibrium and thermodynamic studies for the sorption of metribuzin from aqueous solution using banana peels,an agro-based biomass

Banana peels were employed for the removal of metribuzin from aqueous solution. Sorption in the batch mode was optimized regarding pH, contact time, sorbent dose, initial pesticide concentrations, and temperature. The sorption data were fitted to pseudo-first-order, pseudo-second-order, intraparticle diffusion, Elovich, and liquid film diffusion model, the pseudo-second-order exhibiting best fit (R² = 0.9803). Of the four most common sorption isotherm models (Langmuir, Freundlich, Tempkin, and Dubinin–Radushkevich), the data followed the Langmuir isotherm with highest correlation. The maximum adsorption capacity was found to be 167 mg g^?1. Gibbs free energy, enthalpy, and entropy showed that the sorption was exothermic and spontaneous.     

Cd2+ adsorption on alkaline-pretreated diatomaceous earth: equilibrium and thermodynamic studies

Naturally occurring diatomaceous earth was modified by alkaline pretreatment, and its effectiveness for Cd²⁺ removal from contaminated water was investigated. Batch experiments were carried out to determine Cd²⁺ adsorption capacity and the efficiency of the sorption process under different experimental conditions. Experimental data showed good fitting to Langmuir and Freundlich isotherms models. The Cd²⁺ maximum adsorption capacity was 0.058 mmol g⁻¹ for raw diatomite and increased to 0.195 mmol g⁻¹ for alkaline-pretreated diatomite with efficiency higher than 96% (diatomite dose 2.5 g L⁻¹, pH 6). Adsorption of Cd²⁺ to alkaline-pretreated diatomite increased as the temperature increased. Thermodynamic parameters were calculated to evaluate the feasibility of the adsorption process at different temperatures. The adsorption process was spontaneous and endothermic. The interaction between Cd²⁺ ions and diatomite surface was weak enough to be considered as physical sorption, confirmed by the low value of activation energy.     

Removal of cadmium(II), lead(II), and chromium(VI) ions from aqueous solution using clay

Removal of cadmium(II), lead(II), and chromium(VI) from aqueous solution using clay, a naturally occurring low-cost adsorbent, under various conditions, such as contact time, initial concentration, temperature, and pH has been investigated. The sorption of these metals follows both Langmuir and Freundlich adsorption isotherms. The magnitude of Langmuir and Freundlich constants at 30°C for cadmium, lead, and chromium indicate good adsorption capacity. The kinetic rate constants (K _ad) indicate that the adsorption follows first order. The thermodynamic parameters: free energy change (ΔG ^o), enthalpy change (ΔH ^o), and entropy change (ΔS ^o) show that adsorption is an endothermic process and that adsorption is favored at high temperature. The results reveal that clay is a good adsorbent for the removal of these metals from wastewater.     

Pomegranate husk as an adsorbent in the removal of toxic chromium from wastewater

The use of a new sorbent developed from the husk of pomegranate, a famous fruit in Egypt, for the removal of toxic chromium from aqueous solution has been investigated. The batch experiment was conducted to determine the adsorption capacity of the pomegranate husk. The effects of initial metal concentration (25 and 50 mg l^?1), pH, contact time, and sorbent concentration (2–6 g l^?1) have been studied at room temperature. A strong dependence of the adsorption capacity on pH was observed, the capacity increased as the pH decreased, and the optimum pH value was pH 1.0. Adsorption equilibrium and kinetics were studied with different sorbent and metal concentrations. The adsorption process was fast, and equilibrium was reached within 3 h. The maximum removal was 100% for 25 mg l^?1 of Cr⁶⁺ concentration on 5 g l^?1 pomegranate husk concentration, and the maximum adsorption capacity was 10.59 mg g^?1. The kinetic data were analysed using various kinetic models—pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion equations—and the equilibrium data were tested using several isotherm models, Langmuir, Freundlich, Tempkin, Dubinin–Radushkevich, and Generalized isotherm equations. The Elovich and pseudo-second-order equations provided the greatest accuracy for the kinetic data, while Langmuir and Generalized isotherm models were the closest fit for the equilibrium data. The activation energy of sorption has also been evaluated as 0.236 and 0.707 kJ mol^?1 for 25 and 50 mg l^?1 chromium concentration, respectively.     

Magnetic particles precipitated onto wheat husk for removal of methyl blue from aqueous solution

Magnetic particles prepared via co-precipitation and impregnated onto wheat husk (MN-WH) were used for the removal of methyl blue (MB) from aqueous solution. Experiments were conducted in a batch mode for optimization regarding pH, contact time, adsorbent dose, initial dye concentrations, and temperature. Maximum adsorption (98%) was achieved at pH 5. The adsorption data were fitted into pseudo-first, pseudo-second, intraparticle diffusion, and Elovich equation revealing that adsorption followed pseudo-second-order kinetics. The four most common isotherm models, i.e. the Langmuir, Freundlich, Tempkin, and Dubinin–Radushkevich (D–R), were used to evaluate the data, with the best fit to a Langmuir isotherm (R² = 0.996), followed by a Freundlich isotherm (R² = 0.995), indicating monolayer adsorption of MB on the surface of MN-WH. Thermodynamic parameters calculated from the Van't Hoff equation revealed that the adsorption is exothermic (ΔHº = ?19.7 kJ mol^?1).     

Adsorptive features of banana (Musa paradisiaca) stalk-based activated carbon for malachite green dye removal

Chemically prepared activated carbon derived from banana stalk (BSAC) was used as an adsorbent to remove malachite green (MG) dye from aqueous solution. BSAC was characterised using thermogravimetric analyser, Brunauer Emmett Teller, Fourier transform infrared spectrometry, scanning electron microscopy, pH_pzc, elemental analysis and Boehm titration. The effectiveness of BSAC in adsorbing MG dye was studied as a function of pH, contact time, temperature, initial dye concentration and repeated desorption–adsorption processes. pH_pzc of BSAC was 4.5 and maximum dye adsorption occurred at pH 8.0. The rate of dye adsorption by BSAC was very fast initially, attaining equilibrium within 120 min following a pseudo-second-order kinetic model. Experimental data were analysed by Langmuir, Freundlich and Dubinin–Raduschevich isotherms. Equilibrium data fitted best into the Langmuir model, with a maximum adsorption capacity of 141.76 mg·g^?1. Δ G ⁰ values were negative, indicating that the process of MG dye adsorption onto BSAC was spontaneous. The positive values of Δ H ⁰ and Δ S ⁰ suggests that the process of dye adsorption was endothermic. The regeneration efficiency of spent BSAC was studied using 0.5 M HCl, and was found to be in the range of 90.22–95.16% after four cycles. This adsorbent was found to be both effective and viable for the removal of MG dye from aqueous solution.     

Preparation and characterization of calcium alginate-based composite adsorbents for the removal of Cd,Hg, and Pb ions from aqueous solution

Composite adsorbent materials containing calcium alginate, clinoptilolite, and coal-derived humic acid were prepared. Humic acid (HA), clinoptilolite (CL), alginate (AL), alginate-entrapped humic acid (AL/HA), clinoptilolite (AL/CL), and humic acid/clinoptilolite (AL/HA/CL) samples were characterized. The effectiveness of the samples as adsorbents for the removal of cadmium (Cd), mercury (Hg), and lead (Pb) were studied in a series of batch-adsorption experiments. For the AL, AL/HA, AL/CL, and AL/HA/CL adsorbents, uptake versus time data were evaluated using two kinetic models, a linear and a non-linear pseudo-first-order and a pseudo-second-order model. The data for each metal ion on all adsorbents showed good correspondence with the pseudo-second-order kinetic model. The equilibrium data were fitted to Langmuir, Freundlich, Dubinin–Radushkevich, and Temkin isotherm models. The results show that a non-linear method seems more appropriate for obtaining isotherm parameters. The non-linear Freundlich and Langmuir models for Pb and Hg produced a best fit with high R ² value (0.99). For HA adsorbent, the equilibrium data for Cd removal better fit to the non-linear Dubinin–Radushkevich isotherm.     

The cadmium adsorption capacity of contaminated marine sediments from Hong Kong

The binding capacity of Cd to the sediment particles determines the potential of Cd release from the sediments. An experiment was performed to evaluate the adsorption of Cd by contaminated sediments collected from three different locations in Hong Kong, i.e. Kwun Tong, North Point and Nam Tam Wan, having different degrees of pollution. Langmuir and Freundlich equations were used to evaluate the adsorption of Cd by the sediments. Adsorption isotherms obtained from the Freudlich and Langmuir equations were generally linear and the adsorption of Cd by the sediments was significantly correlated with the adsorption maximum and binding energy constant of the Langmuir equation, and equilibrium partition constant of the Freundlich equation. All sediments had a high Cd adsorption capacity and the highly organic contaminated sediments from Kwun Tong had the highest adsorption capacity of 24,272 mg kg^‐1 at pH8. The adsorption of Cd for all sediments increased with a rise in pH of the equilibrium solution and the total organic carbon content of the sediments. Therefore, a change in the sediment chemical equilibrium is likely to reduce the binding capacity.     

Adsorptive behaviors of humic acid onto freshly prepared hydrous manganese dioxides

This study focused on the adsorptive behaviors of humic acid onto freshly prepared hydrous MnO₂(s) (δMnO₂), and investigated the feasibility of employing δMnO₂ for humic acid removal from drinking water. Effects of such parameters as molecular mass of humic acid, kinds of divalent cations on adsorptive behaviors and possible mechanisms involved were investigated. This study indicated that humic acid with higher molecular mass exhibited more tendency of adsorbing onto δMnO₂ than that with lower molecular mass. Ca²⁺ facilitated more humic acid adsorption than Mg²⁺; UV-Vis spectra analysis indicated higher capabilities of Ca²⁺ coordinating with acidic functional groups of humic acid than that of Mg²⁺. Additionally, ζ potential characterization indicated that Ca²⁺ showed higher potential of increasing gz potential of δMnO₂ than Mg²⁺. Ca²⁺ of 1.0 mmol/L increased ζ potential of δMnO₂ from ?37 mV (pH 7.9) to +7 mV (pH 7.2), while 1.0 mmol/L Mg²⁺ increased to lower value as ?9 mV (pH 6.5), correspondingly. Fourier transform infrared (FTIR) spectra demonstrated the adsorption of humic acid onto δMnO₂, showing the important roles of-COO^? functional groups and surface Mn-OH in the adsorption of humic acid onto δMnO₂.     

Removal of chromium(VI) by ZnCl2 activated coir pith carbon

The adsorption of chromium(VI) onto ZnCl₂ activated carbon developed from coir pith was investigated to assess the possible use of this adsorbent. The influence of contact time, adsorbent dose, Cr(VI) concentration, pH and temperature were investigated. The two theoretical adsorption isotherms, namely, Langmuir and Freundlich were used to describe the experimental results. The Langmuir adsorption capacity (Q ₀) was found to be 120.5?mg Cr(VI) per g of the adsorbent. The adsorption followed the second-order kinetics and was found to be maximum at pH 2.0. The pH effect and the desorption studies showed that ion exchange mechanism might be involved in the adsorption process. The effects of foreign ions such as chloride, sulphate, phosphate, selenite, molybdate, nitrate and perchlorate on the removal of Cr(VI) have been investigated. The removal of Cr(VI) from synthetic ground water was also tested. The results show that ZnCl₂ activated coir pith carbon is effective for the removal of Cr(VI) from water.     

Removal of C.I. acid brown 75 from aqueous solution by kaolinite

The adsorption of acid brown 75 onto kaolinite in aqueous solution was studied with respect to the pH, adsorbent dosage, contact time, initial concentration, and operating temperature. Desorption of dye from dye-saturated kaolinite was observed. Experimental data indicated that the adsorption capacity of kaolinite for the dye was higher in acidic rather than in basic solution. The maximum adsorption capacity of kaolinite towards the dye was found to be 96.5 mg g^?1 (pH 1.0). At the optimal adsorption condition, the dye removal ratio was 95.5%. Dye-saturated kaolinite could desorb at aqueous NaOH, the desorption ratio of dye was 78.8%. The linear Langmuir and Freundlich isotherm models are well fitting to represent the experimental data.     

Adsorption of cationic and anionic surfactants onto organic polymer resin Lewatit VPOC 1064 MD PH

The adsorption of a cationic (CTAB, cetyl trimethylammonium bromide) and an anionic surfactant (SLES, sodium dodecylethersulfate) from aqueous solution onto organic polymer resin (Lewatit VPOC 1064 MD PH) was studied. A series of batch experiments were performed to determine the sorption isotherms of surfactants to organic polymer resin. The experimental studies were analyzed by Langmuir and Freundlich isotherms. Furthermore, the isotherm parameters, average percentage errors (ε) of model data, and separation factor (R _L) were calculated. Other factors influencing the adsorption capacity (contact time, adsorbent amount, and initial surfactant concentration) were also discussed. The experimental data fitted very well to the Langmuir equilibrium model in the studied concentration range. The calculated R _L values showed that the adsorption of both surfactants were favorable. Among the surfactants, CTAB showed higher adsorption capacity onto organic polymer resin compared to SLES (Q ⁰ = 250 and 34.36 mg g⁻¹, respectively).     

Suitability of various chemically prepared activated carbons for the removal of copper(II) ions

Studies on the suitability of various chemically prepared activated carbons (CPACs) like straw carbon (SC), sawdust carbon (SDC), dates nut carbon (DNC) and commercial activated carbon (CAC) for the removal of copper(II) ions by adsorption from simulated wastewater have been carried out under batch mode at 30?±?1°C and the results are compared. The percentage removal of Cu(II) ions increased with a decrease in initial concentration, particle size and added electrolytes (ionic strength) and increased with an increase in contact time, dose of adsorbent and initial pH of the solution. The adsorption data were fitted with the Langmuir isotherm. The applicability of the first order kinetic equation viz. Lagergren equation was tested by correlation analysis. The adsorption process is concluded to be a spontaneous, first order reaction, occurring with increased randomness at the solid–liquid interface. Studies on the desorption of Cu²⁺-loaded activated carbons (ACs) were carried out with nitric acid (0.2–1?N). The possibility of reuse of the regenerated ACs in cycle (in cue-one after another) was tested. SC was found to be a suitable adsorbent alternative to CAC among CPACs for the removal of metal ions, in general, and Cu²⁺ ions, in particular.