Effect of particle size of activated clay on the adsorption of paraquat from aqueous solution

This paper describes the effect of particle size on the process of paraquat adsorption from aqueous solution onto an activated clay surface at 25 degrees C and initial pH 11.0. Measurements of the pore properties of the clay adsorbents with three different particle sizes (0.053-0.074 mm, 0.037-0.053 mm, and <0.037 mm) were carried out. The rates and isotherms of adsorption have been also investigated by batch methods under the controlled conditions. From the experimental results obtained, the adsorption process can be well described with the pseudo-second order model and Freundlich model for adsorption kinetics and adsorption isotherm, respectively. In addition, the effect of the particle size of the clay adsorbent on the adsorption kinetics was found to be of considerable significance; namely, the rate constant (k) of paraquat adsorption by the clay adsorbent decreased with increasing particle size. It was concluded that the pore properties (i.e., surface area and total pore volume) and particle size of the clay adsorbent played a significant role in determining adsorption capacity and adsorption rate, respectively.     

Kinetics and equilibrium studies of adsorption of chromium(VI) ion from industrial wastewater using Chrysophyllum albidum (Sapotaceae) seed shells

A new biosorbent has been prepared by coating Chrysophyllum albidum (Sapotaceae) seed shells with chitosan and/or oxidizing agents such as sulfuric acid. This study investigated the technical feasibility of activated and modified activated C. albidum seed shells carbons for the adsorption of chromium(VI) from aqueous solution. The sorption process with respect to its equilibria and kinetics as well as the effects of pH, contact time, adsorbent mass, adsorbate concentration and particle size on adsorption was also studied. The most effective pH range was found to be between 4.5 and 5 for the sorption of the metal ion. The pseudo-first-order rate equation by Lagergren and pseudo-second-order rate equation were tested on the kinetic data, the adsorption process followed pseudo-second-order rate kinetics, also, isotherm data was analyzed for possible agreement with the Langmuir and Freundlich adsorption isotherms, the Freundlich and Langmuir models for dynamics of metal ion uptake proposed in this work fitted the experimental data reasonably well. However, equilibrium sorption data were better represented by Langmuir model than Freundlich. The adsorption capacity calculated from Langmuir isotherm was 84.31, 76.23 and 59.63 mg Cr(VI)/g at initial pH of 3.0 at 30 °C for the particle size of 1.00–1.25 mm with the use of 12.5, 16.5 and 2.1 g/L of CACASC, CCASC and ACASC adsorbent mass, respectively. This readily available adsorbent is efficient in the uptake of Cr(VI) ion in aqueous solution, thus, it could be an excellent alternative for the removal of heavy metals and organic matter from water and wastewater.     

Systematic studies on adsorption of lead on sea nodule residues

Lead adsorption from aqueous solutions was studied with the aim of detoxifying industrial effluents before their safe disposal onto land or into river waters. Sea nodule residue (SNR), a waste material containing oxides and oxyhydroxides of manganese, iron, silicon, etc., was used as an effective adsorbent for lead in this study. The effect of various parameters such as contact time, initial lead concentration, pulp density, particle size of the adsorbent, pH, and temperature was studied to optimize the conditions for maximum adsorption. Adsorption followed first-order kinetics and 99% of lead adsorption was achieved at a solid:liquid ratio of 1:330, in the pH range 5.5-6.0 at a particle size of -150 microm in 8 h for solution containing 200 ppm lead. The adsorption capacity was found to be 99.0 mg of lead per gram of SNR and the adsorption isotherms followed the Langmuir and Freundlich adsorption models. The mechanism of adsorption of lead onto the sea nodule residue was also investigated. It was possible to reduce the lead level from 25-200 ppm to acceptable levels (0.1 ppm) by adsorption over this solid waste.     

Diethylenetriamine-grafted poly(glycidyl methacrylate) adsorbent for effective copper ion adsorption

Amine-functionalized adsorbents have attracted increasing interest in recent years for heavy metal removal. In this study, diethylenetriamine (DETA) was successfully grafted (through a relatively simple solution reaction) onto poly(glycidyl methacrylate) (PGMA) microgranules to obtain an adsorbent (PGMA-DETA) with a very high content of amine groups and the PGMA-DETA adsorbent was examined for copper ion removal in a series of batch adsorption experiments. It was found that the PGMA-DETA adsorbent achieved excellent adsorption performance in copper ion removal and the adsorption was most effective at pH>3 in the pH range of 1-5 examined. X-ray photoelectron spectroscopy (XPS) revealed that there were different types of amine sites on the surfaces of the PGMA-DETA adsorbent but copper ion adsorption was mainly through forming surface complexes with the neutral amine groups on the adsorbent, resulting in better adsorption performance at a higher solution pH value. The adsorption isotherm data best obeyed the Langmuir-Freundlich model and the adsorption capacity reached 1.5 mmol/g in the case of pH 5 studied. The adsorption process was fast (with adsorption equilibrium time less than 1-4 h) and closely followed the pseudo-second-order kinetic model. Desorption of copper ions from the PGMA-DETA adsorbent was most effectively achieved in a 0.1 M dilute nitric acid solution, with 80% of the desorption being completed within the first 1 min. Consecutive adsorption-desorption experiments showed that the PGMA-DETA adsorbent can be reused almost without any loss in the adsorption capacity.     

On the use of a natural peat for the removal of Cr(VI) from aqueous solutions

A natural peat has been used as an adsorbent for the removal of hexavalent chromium from aqueous solution. The peat was firstly characterized in terms of particle size and chemical composition (ash content, pH of the point of zero charge, FT-IR and thermal analysis). Next, the kinetic and equilibrium aspects of the adsorption of Cr(VI) by this adsorbent were studied. The kinetic data were satisfactorily fitted to a kinetic law of partial order in C equal to one. The specific adsorption rates are around 10(-4)s(-1), increasing as temperature does. A noticeable influence of diffusion on the global adsorption process has been demonstrated. Finally, the equilibrium isotherms were satisfactorily fitted to a previously proposed model. The adsorption capacity of Cr(VI) was similar to some other previously reported and the affinity of Cr(VI) towards the active sites of the adsorbent increases as temperature rises.     

Surface-bound humic acid increased rhodamine B adsorption on nanosized hydroxyapatite

In this study, humic acid-bound nanosized hydroxyapatite (HA-nHAP) was developed as a novel adsorbent, and the potential of using HA-nHAP for the adsorption of rhodamine B (RhB) from aqueous solution as functions of pH, adsorbent dosage, contact time, ionic strength, and temperature was investigated. The results indicated that the HA binding significantly increased the adsorption of RhB due to the introduction of abundant negatively charged functional groups. The adsorption capacity of HA-nHAP for RhB was found to be pH-dependent, and the optimal pH value was found to be 6.0. The adsorption equilibrium data obeyed Sips and Freundlich isotherms and the kinetic data were well described by the Elovich kinetic model. According to the Sips equation, the maximum adsorption capacity for RhB was 24.12 mg/g. The temperature and ionic strength experiment showed that they both had an effect on the adsorption capacity of HA-nHAP. Thermodynamic study confirmed that the adsorption was a spontaneous, endothermic, and more random arrangement process. The present investigation showed that HA-nHAP is a promising adsorbent for the removal of RhB from aqueous solution.     

Adsorption properties and mechanism of sepiolite to graphene oxide in aqueous solution

Graphene oxide (GO) is widely used in various fields such as improving the performance of cement-based materials and making composite materials due to its large specific surface area and abundant oxygen-containing functional groups. However, it has also caused water pollution. To remove GO in aqueous solution, sepiolite (SEP) was used to adsorb it. The effects of pH, adsorbent quality, GO concentration, temperature and adsorption time on the ability of SEP to adsorb GO were investigated. The materials were characterized by SAP and laser particle size analyzer, and the adsorption performance and mechanism of SEP for GO were further analyzed by XRD, FTIR, SEM, TEM, XPS, AFM, and Zeta potential microscopic tests. The results showed that: 1) Under the conditions of temperature 303 K, pH = 3, adsorbent mass 30 mg, and initial concentration of GO 100 mg/L, the adsorption effect was the best, and the adsorption rate reached 94.8 %. 2) The adsorption reached equilibrium at 2160 min, and the adsorption process was more in line with the pseudo-second-order adsorption kinetic equation, and the adsorption behavior was controlled by chemical effects. 3) The adsorption of SEP to GO is more consistent with the Langmuir and Temkin adsorption isotherm model, and the reaction is a spontaneous, endothermic, and entropy-increasing process. Experiments showed that SEP had a strong adsorption capacity for GO, which provides a reference for the treatment of toxic GO in aqueous solution and the realization of water ecological protection.     

Adsorption of Cr(III) from wastewater by wine processing waste sludge

Wine processing waste sludge has been shown to be an effective adsorbent for the adsorption of Cr(III) from aqueous solution. The sludge has been characterized by scanning electron microscopy (SEM) and energy dispersive X-rays (EDX). The effect of pH, initial concentration of Cr(III), sludge particle size, and temperature on the adsorption studied. The equilibrium data could be described well by the Langmuir and Freundlich isotherm equations. A separation factor was used to judge the favorable adsorption. The calculated thermodynamic parameters, deltaH0 and deltaS0, are 1.95 kJ/mol and 27.16 J/molK, respectively. The deltaG0 values range from -5.98 to -6.79 J/mol, which shows the physical adsorption properties of the sludge. Adsorption dynamics had been successfully studied by the Lagergren model and an intraparticle diffusion model.     

Removal of Rhodamine B,a Cationic Dye From Aqueous Solution Using Poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) Nanotubes

Poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) nanotubes were evaluated as an efficient adsorbent for the removal of Rhodamine B (RhB), a cationic dye from aqueous solution. The as-synthesized adsorbent (PZS nanotubes) were characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and N₂ adsorption/desorption isotherms. The factors influencing the adsorption efficiency and capacity had been systematically studied. Results showed that the adsorption was highly dependent on temperature, initial RhB concentration and adsorbent dose. Effects of initial solution pH indicate that the adsorption can proceed in both basic and acidic environment. The equilibrium absorption capacity at 25°C can reach up to 35.58 mg/g within 60 min implying the adsorption procedure was highly rapid. The kinetic data was better described by the pseudo-second-order model with the correlation coefficient (R² = 0.9981), and the adsorption process followed Weber's intraparticle model, indicating the adsorption process could be divided into two stages. Results also showed that the adsorption equilibrium obeyed the Langmuir isotherm, and the value of equilibrium parameter R_L suggested that the PZS nanotubes were an efficient adsorbent for the removal of RhB from aqueous solution.     

Preparation and Characterization of Activated Carbon Fiber from Paper

Activated carbon fibers (ACFS) with surface area of 1388 m²/g prepared from paper by chemical activation with KOH has been utilized as the adsorbent for the removal of methy-lene blue from aqueous solution. The experimental data were analyzed by Langmuir and Freundlich models of adsorption. The effects of pH value on the adsorption capacity of ACFS were also investigated. The rates of adsorption were found to conform to the kinetic model of Pseudo-second-order equation with high values of the correlation coefficients (R>0.998). The Langmuir isotherm was found to fit the experimental data better than the Feundlich isotherm over the whole concentration range. Maximum adsorption capacity of 520 mg/g at equilibrium was achieved. It was found that pH played a major role in the adsorption process, higher pH value favored the adsorption of MB.     

Equilibrium and kinetic studies of adsorption of phosphate onto ZnCl2 activated coir pith carbon

Phosphate removal from aqueous solution was investigated using ZnCl₂-activated carbon developed from coir pith, an agricultural solid waste. Studies were conducted to delineate the effect of contact time, adsorbent dose, phosphate concentration, pH, and temperature. The adsorption equilibrium data followed both Langmuir and Freundlich isotherms. Langmuir adsorption capacity was found to be 5.1 mg/g. Adsorption followed second-order kinetics. The removal was maximum in the pH range 3–10. pH effect and desorption studies showed that adsorption occurred by both ion exchange and chemisorption mechanisms. Adsorption was found to be spontaneous and endothermic. Effect of foreign ions on adsorption shows that perchlorate, sulfate, and selenite decreased the percent removal of phosphate.     

浮石负载壳聚糖吸附去除水中丙溴磷

通过浮石负载壳聚糖制备了吸附剂壳聚糖/浮石复合物,采用扫描电子显微镜(SEM)、热重分析(TGA)、元素分析、傅里叶红外光谱(FT-IR)、X射线衍射(XRD)和X射线荧光光谱(XRF)等技术手段表征了吸附剂性质,考察了吸附剂量、吸附时间、溶液pH值、离子强度和温度对该吸附剂吸附去除水中丙溴磷的影响,研究了再生吸附剂的吸附性能。结果表明,负载在浮石上的壳聚糖占吸附剂总量的8.69%;在p H值3.0~7.0内,壳聚糖/浮石对丙溴磷的吸附率大于90%;这种吸附剂对丙溴磷的吸附受溶液离子强度影响较小,随温度升高而稍微减小。在溶液温度25℃、pH=7.0、丙溴磷浓度40 mg/L、壳聚糖/浮石剂量为0.7 g/L和吸附平衡时间为90 min条件下,此吸附剂对丙溴磷最大吸附率为93.3%(最大吸附量为53.4 mg/g)。壳聚糖/浮石连续经过3次吸附/再生循环,每次循环对丙溴磷的吸附率下降约12%。可见壳聚糖/浮石通过吸附可有效地去除水中的农药丙溴磷。     

Enhancement of Cd2+ removal on CuMgAl-layered double hydroxide/montmorillonite nanocomposite: Kinetic,isotherm, and thermodynamic studies

In recent decades, great progress has been made in the application of adsorption processes to mitigate water pollution by hazardous metals. However, developing a highly efficient adsorbent is essential if the adsorption process is to be successfully applied in practical applications. In this study, a CuMgAl-layered double hydroxides/montmorillonite nanocomposite (CuMgAl-LDH/MMt) was prepared, characterized, and then used as a novel adsorbent for adsorption of Cd²⁺ ions from wastewater. The effects of initial pH, adsorbent dosage, agitation speed, particle size, contact time, initial Cd²⁺ concentration, and temperature on the pollutant removal efficiency were analyzed. An isotherm model reading revealed that the results of the experimental work were a good fit with the Freundlich model. The maximum adsorption capacity was reached at 174.87 mg/g under optimal conditions (pH 5, dosage of 0.02 g/l, agitation speed of 150 rpm, and particle size of 87 μm) at 50 ppm after 120 min of adsorption time. Kinetic studies showed that pseudo-second-order models were best fitted to the adsorption data, indicating heterogeneous adsorption of Cd²⁺ ions onto multilayer CuMgAl-LDH/MMt sites, and that the adsorption process is primarily chemical adsorption. Thermodynamic parameters (ΔS^o, ΔH^o, and ΔG^o) demonstrated that Cd²⁺ adsorption onto adsorbent was exothermic and spontaneous. Moreover, the synthesized adsorbent can be recovered after five consecutive cycles with a minimal reduction in the adsorption ability of 29.56 %. The study showed that specific heavy metals can be removed from aqueous solution by a newly prepared adsorbent due to its excellent morphology, high stability under a wide range of conditions, recyclability, and high adsorption capacity.     

Adsorption of Chromium (VI) on <Emphasis Type="Italic">Azadirachta Indica</Emphasis> (Neem) Leaf Powder

A novel adsorbent was developed from mature leaves of the Neem tree (Azadirachta Indica) for removing metal ions from water. The adsorbent, in the form of fine powder, was found to be very effective in removing chromium (VI) from aqueous solution. The adsorption was carried out in a batch process taking different concentrations of the metal ion in aqueous solution with variation in adsorbent amount, pH, agitation time and temperature. The suitability of the adsorbent was tested with Langmuir and Freundlich isotherms and with various equilibrium kinetic data. A small amount of the Neem Leaf Powder (NLP) (1.6 g dm^–3) could remove as much as 87% of Cr (VI) in 300 min from a solution of concentration 14.1 mg dm^–3 at 300 K. The optimum range of pH for the adsorption process was 4.5–7.5 and since the natural pH of the Cr (VI) solution was 5.5, no addition of acid or alkali was necessary for achieving maximum adsorption. The adsorption coefficients indicated a high potentiality for the NLP to be used as an adsorbent for removing Cr (VI) from water.     

Removal of Chromium(III) and Cadmium(II) Heavy Metal Ions from Aqueous Solutions Using Treated Date Seeds: An Eco-Friendly Method

The aim of the research was to prepare low-cost adsorbents, including raw date pits and chemically treated date pits, and to apply these materials to investigate the adsorption behavior of Cr(III) and Cd(II) ions from wastewater. The prepared materials were characterized using SEM, FT-IR and BET surface analysis techniques for investigating the surface morphology, particle size, pore size and surface functionalities of the materials. A series of adsorption processes was conducted in a batch system and optimized by investigating various parameters such as solution pH, contact time, initial metal concentrations and adsorbent dosage. The optimum pH for achieving maximum adsorption capacity was found to be approximately 7.8. The determination of metal ions was conducted using atomic adsorption spectrometry. The experimental results were fitted using isotherm Langmuir and Freundlich equations, and maximum monolayer adsorption capacities for Cr(III) and Cd(II) at 323 K were 1428.5 and 1302.0 mg/g (treated majdool date pits adsorbent) and 1228.5 and 1182.0 mg/g (treated sagai date pits adsorbent), respectively. It was found that the adsorption capacity of H₂O₂-treated date pits was higher than that of untreated DP. Recovery studies showed maximal metal elution with 0.1 M HCl for all the adsorbents. An 83.3–88.2% and 81.8–86.8% drop in Cr(III) and Cd(II) adsorption, respectively, were found after the five regeneration cycles. The results showed that the Langmuir model gave slightly better results than the Freundlich model for the untreated and treated date pits. Hence, the results demonstrated that the prepared materials could be a low-cost and eco-friendly choice for the remediation of Cr(III) and Cd(II) contaminants from an aqueous solution.     

Removal of uranium(VI) from aqueous solution by apricot shell activated carbon

Uranium is a toxic and radioactive heavy metal found in nuclear effluents and should be treated based on environmental considerations. The adsorption of uranyl cations (UO₂ ²⁺) by apricot shell activated carbon (ASAC) was investigated in a batch system. The effects of pH, contact time, temperature, adsorbent dosage on the adsorption kinetics and equilibrium adsorption isotherms of U(VI) were examined. The U(VI) uptake was fast within the first 60 min and reached an equilibrium state at 120 min. The adsorption process was highly pH dependent and the maximum adsorption was obtained at an initial solution pH of 6.0. Temperature over the range 25–45 °C had little effect on the U(VI) adsorption. The U(VI) removal efficiency increased concurrently with increasing ASAC dosage, whereas the U(VI) adsorption capacity decreased with increasing ASAC dosage. The adsorption process followed both Langmuir and Freundlich isotherms. On the basis of Langmuir model, the maximum adsorption capacity was found to be 59.17 mg U(VI)/g adsorbent. The adsorption kinetics can be very well defined by the pseudo-first-order rate model. The present results suggest that ASAC could be used as an adsorbent for an efficient removal of U(VI) from aqueous solution.     

聚(丙烯酸-co-丙烯酰胺)/蒙脱土/腐殖酸钠复合物对Pb2+的吸附性能

用制备的聚(丙烯酸-co-丙烯酰胺)/蒙脱土/腐殖酸钠复合吸附剂,研究了溶液pH值、吸附时间和Pb2+溶液初始浓度等因素对重金属Pb2+的吸附性能,探讨了复合吸附剂对Pb2+的吸附机理。结果表明,在pH值为6.0、吸附时间2 h、Pb2+溶液初始浓度0.01 mol/L和吸附剂用量0.10 g的条件下,复合吸附剂对Pb2+的吸附量达到364.05 mg/g,平衡所需的时间为15 min。与蒙脱土相比,复合吸附剂具有更高的吸附容量和更快的吸附速率。     

Adsorption of Cr(VI) using activated neem leaves: kinetic studies

In the present study, adsorbent is prepared from neem leaves and used for Cr(VI) removal from aqueous solutions. Neem leaves are activated by giving heat treatment and with the use of concentrated hydrochloric acid (36.5 wt%). The activated neem leaves are further treated with 100 mmol of copper solution. Batch adsorption studies demonstrate that the adsorbent prepared from neem leaves has a significant capacity for adsorption of Cr(VI) from aqueous solution. The parameters investigated in this study include pH, contact time, initial Cr(VI) concentration and adsorbent dosage. The adsorption of Cr(VI) is found to be maximum (99%) at low values of pH in the range of 1-3. A small amount of the neem leaves adsorbent (10 g/l) could remove as much as 99% of Cr(VI) from a solution of initial concentration 50 mg/l. The adsorption process of Cr(VI) is tested with Langmuir isotherm model. Application of the Langmuir isotherm to the system yielded maximum adsorption capacity of 62.97 mg/g. The dimensionless equilibrium parameter, R _L, signifies a favorable adsorption of Cr(VI) on neem leaves adsorbent and is found to be between 0.0155 and 0.888 (0<R _L<1). The adsorption process follows second order kinetics and the corresponding rate constant is found to be 0.00137 g/(mg) (min).     

Fundamental characteristics of synthetic adsorbents intended for industrial chromatographic separations

With the aim of obtaining comprehensive information on the selection of synthetic adsorbents for industrial applications, effect of pore and chemical structure of industrial-grade synthetic adsorbents on adsorption capacity of several pharmaceutical compounds was investigated. For relatively low molecular mass compounds, such as cephalexin, berberine chloride and tetracycline hydrochloride, surface area per unit volume of polystyrenic adsorbents dominated the equilibrium adsorption capacity. On the contrary, effect of pore size of the polystyrenic adsorbents on the equilibrium adsorption capacity was observed for relatively high molecular mass compounds, such as rifampicin, Vitamin B12 and insulin. Polystyrenic adsorbent with high surface area and small pore size showed small adsorption capacity for relatively high molecular mass compounds, whereas polystyrenic adsorbent with relatively small surface area but with large pore size showed large adsorption capacity. Effect of chemical structure on the equilibrium adsorption capacity of several pharmaceutical compounds was also studied among polystyrenic, modified polystyrenic and polymethacrylic adsorbents. The modified polystyrenic adsorbent showed larger adsorption capacity for all compounds tested in this study due to enhanced hydrophobicity. The polymethacrylic adsorbent possessed high adsorption capacity for rifampicin and insulin, but it showed lower adsorption capacity for the other compounds studied. This result may be attributed to hydrogen bonding playing major role for the adsorption of compounds on polymethacrylic adsorbent. Furthermore, column adsorption experiments were operated to estimate the effect of pore characteristics of the polystyrenic adsorbents on dynamic adsorption behavior, and it is found that both surface area and pore size of the polystyrenic adsorbents significantly affect the dynamic adsorption capacity as well as flow rate.     

PEI功能化秸秆生物炭对水中Cr 6+的吸附性能

选取玉米秸秆为原料, 经过缺氧炭化制备玉米秸秆生物炭, 并以聚乙烯亚胺(PEI)负载于生物炭表面, 制备PEI功能化秸秆生物炭, 研究了其对水中Cr ⁶⁺的吸附性能和机理. 结果表明, 在吸附剂添加量相等条件下, PEI碱性生物炭(PBC)对Cr ⁶⁺的吸附效率明显高于PEI酸性生物炭(HBC)和原始生物炭(CBC). PBC对水中Cr ⁶⁺的最大吸附量为386.3 mg/g, 吸附平衡时间为300 min; 当pH=2.0左右时, 对Cr ⁶⁺的吸附效率最大达到95.94%. 因此, PBC可作为一种高效去除水中Cr ⁶⁺的吸附剂.