Phenol removal from wastewater by adsorption on zeolitic composite

It is well known that adsorption is an efficient method of removal of various pollutants from wastewater. The present study examines the phenol removal from water by adsorption on a new material, based on zeolitic volcanic tuff. This compound contains zeolitic tuff and cellulose, another known adsorbent, in a mass ratio of 4 to 1. The performances of the new adsorbent composite were compared with those of a widely used adsorbent material, zeolitic volcanic tuff. The adsorbent properties were tested on batch synthetic solutions containing 1–10 mg L^?1 (1–10 ppm) phenol, at room temperature without pH adjustment. The influence of the adsorbent dose, pH and contact time on the removal degree of phenol from water was investigated. The experimental data were modeled using the Langmuir, Freundlich, and Temkin adsorption isotherms. The Langmuir model was found to best represent our data revealing a monolayer adsorption with a maximum adsorption capacity between 0.12 and 0.53 mg g^?1 at 25 °C, for 2.00 g of adsorbent, depending on the initial phenol concentration. The adsorption kinetic study was performed using a pseudo-first- and pseudo-second-order kinetic models illustrating that phenol adsorption on zeolite composite is well described by pseudo-first kinetic equations. Our results indicated that phenol adsorption on the new adsorbent composite is superior to that on the classic zeolite.     

Arsenic sorption by red mud-modified biochar produced from rice straw

Red mud-modified biochar (RM-BC) has been produced to be utilized as a novel adsorbent to remove As because it can effectively combine the beneficial features of red mud (rich metal oxide composition and porous structure) and biochar (large surface area and porous structure properties). SEM-EDS and XRD analyses demonstrated that red mud had loaded successfully on the surface of biochar. With the increasing of pH in solution, arsenate (As(V)) adsorption on RM-BC decreased while arsenite (As(III)) increased. Arsenate adsorption kinetics process on RM-BC fitted the pseudo-second-order model, while that of As(III) favored the Elovich model. All sorption isotherms produced superior fits with the Langmuir model. RM-BC exhibited improved As removal capabilities, with a maximum adsorption capacity (Q_max) for As(V) of 5923 μg g^?1, approximately ten times greater than that of the untreated BC (552.0 μg g^?1). Furthermore, it has been indicated that the adsorption of As(V) on RM-BC may be strongly associated with iron oxides (hematite and magnetite) and aluminum oxides (gibbsite) by X-ray absorption near-edge spectroscopy (XANES), which was possibly because of surface complexation and electrostatic interactions. RM-BC may be used as a valuable adsorbent for removing As in the environment due to the waste materials being relatively abundant.     

Modelling the adsorption of mercury onto natural and aluminium pillared clays

Introduction

The removal of heavy metals by natural adsorbent has become one of the most attractive solutions for environmental remediation. Natural clay collected from the Late Cretaceous Aleg formation, Tunisia was used as a natural adsorbent for the removal of Hg(II) in aqueous system.

Methods

Physicochemical characterization of the adsorbent was carried out with the aid of various techniques, including chemical analysis, X-ray diffraction, Fourier transform infrared and scanning electron micrograph. Batch sorption technique was selected as an appropriate technique in the current study. Method parameters, including pH, temperature, initial metal concentration and contact time, were varied in order to quantitatively evaluate their effects on Hg(II) adsorption onto the original and pillared clay samples. Adsorption kinetic was studied by fitting the experimental results to the pseudo-first-order and pseudo-second-order kinetic models. The adsorption data were also simulated with Langmuir, Freundlich and Temkin isotherms.

Results

Results showed that the natural clay samples are mainly composed of silica, alumina, iron, calcium and magnesium oxides. The sorbents are mainly mesoporous materials with specific surface area of <250 m² g^?1. From the adsorption of Hg(II) studies, experimental data demonstrated a high degree of fitness to the pseudo-second-order kinetics with an equilibration time of 240 min. The equilibrium data showed the best model fit to Langmuir model with the maximum adsorption capacities of 9.70 and 49.75 mg g^?1 for the original and aluminium pillared clays, respectively. The maximum adsorption of Hg(II) on the aluminium pillared clay was observed to occur at pH 3.2. The calculated thermodynamic parameters (?G°, ?H° and ?S°) showed an exothermic adsorption process. The entropy values varied between 60.77 and 117.59 J?mol^?1 K^?1, and those of enthalpy ranged from 16.31 to 30.77 kJ mol^?1. The equilibrium parameter (R _L) indicated that the adsorption of Hg(II) on Tunisian smectitic clays was favourable under the experimental conditions of this study.

Conclusion

The clay of the Aleg formation, Tunisia was found to be an efficient adsorbent for Hg(II) removal in aqueous systems.     

Preparation of carbonaceous adsorbent from straw and its adsorption performance for H2S removal

ABSTRACT

Activated carbonaceous were prepared from high-carbon, abandoned straw biomass. With hydrogen sulfide gas as the target pollutant, single factor experiments were employed to assess the effects of activator type, activation temperature, activation time, and liquid-material ratio on the adsorption performance of the prepared carbonaceous adsorbent. The materials were characterized using elemental analysis, SEM, FTIR, and BET. The results showed -OH, -CH-, and -C = O groups exist on the surface of the prepared adsorbent, specific surface area can reach 1104.84 m²?g^?1, total pore volume can reach 0.261 cm³?g^?1 and, where the pore volume is greater than 80%, well-developed pore structures were present that facilitated adsorption. The experimental results showed the adsorption time could reach 198 min with optimal ZnCl₂ activator concentration (30%), carbonization temperature (550°C), and liquid-to-material ratio (3:1). Compared with the existing activated carbon adsorbents, the adsorption effects and preparation cost of this absorbent are advantageous, and the absorbent has prospects for broad market application.     

Preparation of activated carbon from dried pods of Prosopis cineraria with zinc chloride activation for the removal of phenol

Utilization of agrowaste materials for the production of activated carbon, as an excellent adsorbent with large surface area, is well established industrially, for dephenolation of wastewater. In the present work, dried pods of Prosopis cineraria—a novel and low-cost agrowaste material—were used to prepare activated carbons by zinc chloride activation. Batch adsorption experiments were carried out to study the effects of various physicochemical parameters such as initial phenol concentration, adsorbent dose, initial solution pH, and temperature. Pseudo-first-order second-order and diffusion kinetic models were used to identify the possible mechanisms of such adsorption process. The Langmuir and Freundlich equations were used to analyze the adsorption equilibrium. Maximum removal efficiency of 86 % was obtained with 25 mg?L^?1 of initial phenol concentration. The favorable pH for maximum phenol adsorption was 4.0. Freundlich equation represented the adsorption equilibrium data more ideally than the Langmuir. The maximum adsorption capacity obtained was 78.32 mg?g^?1 at a temperature of 30 °C and 25 mg?L^?1 initial phenol concentration. The adsorption was spontaneous and endothermic. The pseudo-second-order model, an indication of chemisorption mechanism, fitted the experimental data better than the pseudo-first-order Lagergren model. Regeneration of spent activated carbon was carried out using Pseudomonas putida MTCC 2252 as the phenol-degrading microorganism. Maximum regeneration up to 57.5 % was recorded, when loaded phenol concentration was 25 mg?L^?1. The data obtained in this study would be useful in designing and fabricating an efficient treatment plant for phenol-rich effluents.     

Novel insights in Al-MCM-41 precursor as adsorbent for regulated haloacetic acids and nitrate from water

High concentration of NO ₃ ^? in groundwater has raised concern over possible contamination of drinking water supplies. In addition, the formation of haloacetic acids (HAAs) as by-products during disinfection with chlorine-based agents is still a relevant issue, since HAAs pose serious health hazard. In this work, we investigated the affinity of a precursor of Al-MCM-41 (a mesostructured hexagonal aluminosilicate containing the template surfactant) towards nitrate and HAAs, for its possible application in the removal of these pollutants from natural and drinking waters. Additionally, adsorption kinetics and isotherms were studied. The adsorbent was synthesized using cetyltrimethylammonium bromide as surfactant and characterized by physico?Cchemical techniques. Simulated drinking water was spiked with the EPA-regulated HAAs (monochloroacetic (MCAA), monobromoacetic (MBAA), dichloroacetic (DCAA), dibromoacetic (DBAA), and trichloroacetic (TCAA) acids) and placed in contact with the adsorbent. The effect of matrix composition was studied. Adsorption kinetic studies were performed testing three kinetics models. For the adsorption studies, three adsorption isotherm approaches have been tested to experimental data. The pollutant recoveries were evaluated by suppressed ion chromatography. The affinity of the adsorbent was TCAA = DBAA = DCAA > MBAA > MCAA with DCAA, DBAA, and TCAA completely removed. A removal as high as 77?% was achieved for 13?mg/L nitrate. The adsorption isotherms of NO ₃ ^? and monochloroacetic acid can be modeled by the Freundlich equation, while their adsorption kinetics follow a pseudo-second-order rate mechanism. The adsorbent exhibited high affinity towards HAAs in simulated drinking water even at relevant matrix concentrations, suggesting its potential application for water remediation technologies.     

Removal and recovery of copper and nickel ions from aqueous solution by poly(methacrylamide-co-acrylic acid)/montmorillonite nanocomposites

Nanocomposite hydrogels based on poly(methacrylamide-co-acrylic acid) and nano-sized montmorillonite were prepared by aqueous dispersion and in situ radical polymerization. Optimum sorption conditions were determined as a function of montmorillonite content, contact time, pH, and temperature. The equilibrium data of Cu²⁺ and Ni²⁺ conformed to the Freundlich and Langmuir isotherms in terms of relatively high regression values. The maximum monolayer adsorption capacity of the nanocomposite hydrogel (with 3 wt% montmorillonite content), as obtained from the Langmuir adsorption isotherm, was found to be 49.26 and 46.94 mg g^?1 for Cu²⁺ and Ni²⁺, respectively, at contact time?=?60 min, pH?=?6.8, adsorbent dose?=?100 mg/ml, and temperature?=?318 K. Kinetic studies of single system indicated that the pseudo-second order is the best fit with a high correlation coefficient (R ²?=?0.97–0.99). The result of five times sequential adsorption–desorption cycle shows a good degree of desorption and a high adsorption efficiency.     

磷在磁铁矿-针铁矿混合相上的吸附

首次采用使用后贴式取暖物（商业名：热力贴）为原料制备吸附剂,元素分析、XRD、红外图谱综合鉴定为磁铁矿-针铁矿混合相（magnetite-goethite mix phase,MGM）,其比表面积为98.3 m2/g,平均粒径为510 nm,零电荷点在pH=5.7附近;磷在MGM上的吸附等温线符合Langmuir方程,其吸附历时曲线遵循准二级动力学模型,升温能促进磷的吸附;在实际废水磷浓度为51.8 mg/L、初始溶液pH=2的条件下,当MGM投加量为10 g/L时,磷的去除率为94.16%。     

Sorption kinetics and isotherm modelling of imidacloprid on bentonite and organobentonites

Bentonite was modified by quaternary ammonium cations viz. cetytrimethylammonium (CTA), cetylpyridinium (CP), rioctylmethylammonium (TOM) and pcholine (PTC) at 100% cation exchange capacity of bentonite and was characterized by X-ray diffraction, CHNS elemental analyser and Fourier transform infrared spectroscopy. The sorption of imidacloprid on organobentonites/bentonite was studied by batch method. Normal bentonite could adsorb imidacloprid only upto 19.31–22.18% while all organobentonites except PTC bentonite (PTCB), enhanced its adsorption by three to four times. Highest adsorption was observed in case of TOM bentonite (TOMB) (76.94–83.16%). Adsorption kinetic data were fitted to pseudo-first-order, pseudo-second-order and intraparticle diffusion models. For normal bentonite data were best fitted to pseudo-first-order kinetic, while for organobentonites fitted to pseudo-second-order kinetics. Sorption data were analysed using Freundlich, Langmuir, Temkin and Dubinin–Radushkevich isotherm models. Data were well fitted to Freundlich adsorption isotherm. Product of Freundlich adsorption constant and heterogeneity parameter (K_f.1/n) was in following order: TOMB (301.87) > CTA bentonite (CTAB) (152.12) > CP bentonite (CPB) (92.58) > bentonite (27.25). Desorption study confirmed hysteresis and concentration dependence. The present study showed that the organobentonite could be a good sorbent for removal of imidacloprid from natural water sample also. Percentage adsorption and Distribution coefficient (mL g^?1) value of different adsorbent was in following order: TOMB (74.85% and 297.54) > CTAB (55.78% and 126.15) > CPB (45.81% and 84.55) > bentonite (10.65% and 11.92).     

Comparative study of adsorption of Pb(II) on native garlic peel and mercerized garlic peel

A comparative study using native garlic peel and mercerized garlic peel as adsorbents for the removal of Pb²⁺ has been proposed. Under the optimized pH, contact time, and adsorbent dosage, the adsorption capacity of garlic peel after mercerization was increased 2.1 times and up to 109.05 mg g^?1. The equilibrium sorption data for both garlic peels fitted well with Langmuir adsorption isotherm, and the adsorbent–adsorbate kinetics followed pseudo-second-order model. These both garlic peels were characterized by elemental analysis, Fourier transform infrared spectrometry (FT-IR), and scanning electron microscopy, and the results indicated that mercerized garlic peel offers more little pores acted as adsorption sites than native garlic peel and has lower polymerization and crystalline and more accessible functional hydroxyl groups, which resulted in higher adsorption capacity than native garlic peel. The FT-IR and X-ray photoelectron spectroscopy analyses of both garlic peels before and after loaded with Pb²⁺ further illustrated that lead was adsorbed on the through chelation between Pb²⁺ and O atom existed on the surface of garlic peels. These results described above showed that garlic peel after mercerization can be a more attractive adsorbent due to its faster sorption uptake and higher capacity.     

Kinetic and equilibrium studies of adsorptive removal of phenol onto eggshell waste

The aim of the present research is to develop economic, fast, and versatile method for the removal of toxic organic pollutant phenol from wastewater using eggshell. The batch experiments are conducted to evaluate the effect of pH, phenol concentration, dosage of adsorbent, and contact time on the removal of phenol. The paper includes in-depth kinetic studies of the ongoing adsorption process. Attempts have also been made to verify Langmuir and Freundlich adsorption isotherms. The morphology and characteristics of eggshell have also been studied using scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray fluorescence analysis. At ambient temperature, the maximum adsorption of phenol onto eggshells has been achieved at pH 9 and the contact time, 90 min. The experimental data give best-fitted straight lines for pseudo-first-order as well as pseudo-second-order kinetic models. Furthermore, the adsorption process verifies Freundlich and Langmuir adsorption isotherms, and on the basis of mathematical expressions of these models, various necessary adsorption constants have been calculated. Using adsorption data, various thermodynamic parameters like change in enthalpy (?H ⁰), change in entropy (?S ⁰), and change in free energy ?G ⁰ have also been evaluated. Results clearly reveal that the solid waste material eggshell acts as an effective adsorbent for the removal of phenol from aqueous solutions.     

The removal of uranium (VI) from aqueous solutions onto activated carbon developed from grinded used tire

In this study, activated carbon was prepared from waste tire by KOH chemical activation. The pore properties including the BET surface area, pore volume, pore size distribution, and average pore diameter were characterized. BET surface area of the activated carbon was determined as 558 m²/g. The adsorption of uranium ions from the aqueous solution using this activated carbon has been investigated. Various physico-chemical parameters such as pH, initial metal ion concentration, and adsorbent dosage level and equilibrium contact time were studied by a batch method. The optimum pH for adsorption was found to be 3. The removal efficiency has also been determined for the adsorption system as a function of initial concentration. The experimental results were fitted to Langmuir, Freundlich, and Dubinin–Radushkevich (D-R) isotherm models. A comparison of best-fitting was performed using the coefficient of correlation and the Langmuir isotherm was found to well represent the measured sorption data. According to the evaluation using the Langmuir equation, the saturated monolayer sorption capacity of uranium ions onto waste tire activated carbon was 158.73 mg/g. The thermodynamic equilibrium constant and the Gibbs free energy were determined and results indicated the spontaneous nature of the adsorption process. Kinetics data were best described by pseudo-second-order model.     

Temperature-responsive graphene oxide/N-isopropylacrylamide/2-allylphenol nanocomposite for the removal of phenol and 2,4-dichlorophenol from aqueous solution

In this study, a novel thermo-responsive polymer was synthesized with efficient grafting of N-isopropylacrylamide as a thermosensitive polymer onto the graphene oxide surface for the efficient removal of phenol and 2,4-dichlorophenol from aqueous solutions. The synthesized polymer was conjugated with 2-allylphenol. Phenol and 2,4-dichlorophenol were monitored by ultra-performance liquid chromatography system equipped with a photodiode array detector. The nanoadsorbent was characterized by different techniques. The nanoadsorbent revealed high adsorption capacity where the removal percentages of 91 and 99% were found under optimal conditions for phenol and 2,4-dichlorophenol, respectively (for phenol; adsorbent dosage = 0.005 g, pH = 8, temperature= 25 °C, contact time = 60 min; for 2,4-dichlorophenol; adsorbent dosage = 0.005 g, pH = 5, temperature = 25 °C, contact time = 10 min). Adsorption of phenol and 2,4-dichlorophenol onto nanoadsorbent followed pseudo-second-order kinetic and Langmuir isotherm models, respectively. The values of ΔG (average value = ? 11.39 kJ mol^?1 for phenol and 13.42 kJ mol^?1 for 2,4-dichlorophenol), ΔH (? 431.72 J mol^?1 for phenol and ? 15,721.8 J mol^?1 for 2,4-dichlorophenol), and ΔS (35.39 J mol^?1 K^?1 for phenol and ? 7.40 J mol^?1 K^?1 for 2,4-dichlorophenol) confirmed spontaneous and exothermic adsorption. The reusability study indicated that the adsorbent can be reused in the wastewater treatment application. Thermosensitive nanoadsorbent could be used as a low-cost and efficient sorbent for phenol and 2,4-dichlorophenol removal from wastewater samples.

     

Development of an activated carbon impregnation process with iron oxide nanoparticles by green synthesis for diclofenac adsorption

The objective of this study was to impregnate the surface of palm coconut activated carbon with nanoparticles of iron compounds using Moringa oleifera leaf extracts and pomegranate leaf by a green synthesis method and to evaluate its adsorption capacity for sodium diclofenac. The adsorbent material was characterized by zeta potential, X-ray diffraction (XRD), N₂ adsorption/desorption (BET method), transmission electronic microscopy (TEM), and scanning electronic microscopy (SEM) coupled to dispersive energy spectrometry X-ray (EDX) methods. To evaluate the adsorption capacity of sodium diclofenac, the influence of pH, kinetics, isotherms, and thermodynamic properties were analysed. The impregnated adsorbents showed efficiency in the adsorption of sodium diclofenac. The kinetic model that best fit the experimental data was the pseudo-second-order model, and the equilibrium model was the Langmuir model. As for the thermodynamic study, it was verified that the adsorption reaction for all adsorbents occurs in a spontaneous, favourable way, and it is endothermic by physisorption. Therefore, this process is promising because it is a clean and non-toxic method when compared with chemical methods for the synthesis of nanoparticles.

     

Biosorption of chromium (VI) from aqueous solutions and ANN modelling

The use of sustainable, green and biodegradable natural wastes for Cr(VI) detoxification from the contaminated wastewater is considered as a challenging issue. The present research is aimed to assess the effectiveness of seven different natural biomaterials, such as jackfruit leaf, mango leaf, onion peel, garlic peel, bamboo leaf, acid treated rubber leaf and coconut shell powder, for Cr(VI) eradication from aqueous solution by biosorption process. Characterizations were conducted using SEM, BET and FTIR spectroscopy. The effects of operating parameters, viz., pH, initial Cr(VI) ion concentration, adsorbent dosages, contact time and temperature on metal removal efficiency, were studied. The biosorption mechanism was described by the pseudo-second-order model and Langmuir isotherm model. The biosorption process was exothermic, spontaneous and chemical (except garlic peel) in nature. The sequence of adsorption capacity was mango leaf > jackfruit leaf > acid treated rubber leaf > onion peel > bamboo leaf > garlic peel > coconut shell with maximum Langmuir adsorption capacity of 35.7 mg g^?1 for mango leaf. The treated effluent can be reused. Desorption study suggested effective reuse of the adsorbents up to three cycles, and safe disposal method of the used adsorbents suggested biodegradability and sustainability of the process by reapplication of the spent adsorbent and ultimately leading towards zero wastages. The performances of the adsorbents were verified with wastewater from electroplating industry. The scale-up study reported for industrial applications. ANN modelling using multilayer perception with gradient descent (GD) and Levenberg-Marquart (LM) algorithm had been successfully used for prediction of Cr(VI) removal efficiency. The study explores the undiscovered potential of the natural waste materials for sustainable existence of small and medium sector industries, especially in the third world countries by protecting the environment by eco-innovation.     

Adsorptive removal of Pb2+ form aqueous solution by macrocyclic calix[4]naphthalene: kinetic, thermodynamic, and isotherm analysis

Background

The adsorption characteristics of Pb²⁺ ions from aqueous solutions onto calix[4]naphthalene have been investigated.

Method

Calix[4]naphthalene was prepared by the condensation of 1-naphthol and formaldehyde (1:2) in presence of hydrochloric acid at 80°C. The effect of various operation parameters, such as solution pH, initial metal ion concentration, contact time, and temperature, on the adsorption capacity of calix[4]naphthalene for Pb²⁺ have been investigated.

Result

Experimental results showed that the adsorption of Pb²⁺ ions increased with the increase in solution pH and temperature. Langmuir and Freundlich isotherms models were used to describe the adsorption behavior of Pb²⁺ by calix[4]naphthalene. Equilibrium data fitted well with the Langmuir isotherm model and the maximum adsorption capacity of calix[4]naphthalene for Pb²⁺ at 30°C was found to be 29.15 mg g^?1. Kinetic studies indicated that the adsorption followed pseudo-second order model and the thermodynamic studies revealed that the adsorption process was spontaneous and endothermic in nature. The obtained results demonstrated that calix[4]naphthalene can be used as an effective adsorbent for Pb²⁺ ions removal from water.     

Equilibrium and kinetics of adsorption of phosphate onto iron-doped activated carbon

Purpose

Two series of activated carbons modified by Fe (II) and Fe (III) (denoted as AC/N-Fe^II and AC/N-Fe^III), respectively, were used as adsorbents for the removal of phosphate in aqueous solutions.

Method

The synthesized adsorbent materials were investigated by different experimental analysis means. The adsorption of phosphate on activated carbons has been studied in kinetic and equilibrium conditions taking into account the adsorbate concentration, temperature, and solution pH as major influential factors.

Results

Maximum removals of phosphate are obtained in the pH range of 3.78?C6.84 for both adsorbents. Langmuir isotherm adsorption equation well describes the experimental adsorption isotherms. Kinetic studies revealed that the adsorption process followed a pseudo-second order kinetic model. Results suggest that the main phase formed in AC/N-Fe^II and AC/N-Fe^III is goethite and akaganeite, respectively; the presence of iron oxides significantly affected the surface area and the pore structure of the activated carbon.

Conclusions

Studies revealed that iron-doped activated carbons were effective in removing phosphate. AC/N-Fe^II has a higher phosphate removal capacity than AC/N-Fe^III, which could be attributed to its better intra-particle diffusion and higher binding energy. The activation energy for adsorption was calculated to be 22.23 and 10.89 kJ mol^?1 for AC/N-Fe^II and AC/N-Fe^III, respectively. The adsorption process was complex; both surface adsorption and intra-particle diffusion were simultaneously occurring during the process and contribute to the adsorption mechanism.     

Determination of the Adsorption Isotherm of Vapor-Phase Mercury Chloride on Powdered Activated Carbon Using Thermogravimetric Analysis

Abstract

This study investigated the use of thermogravimetric analysis (TGA) to determine the adsorptive capacity and adsorption isotherm of vapor-phase mercury chloride on powdered activated carbon (PAC). The technique is commonly applied to remove mercury-containing air pollutants from gas streams emitted from municipal solid waste incinerators. An alternative form of powdered activated carbon derived from a pyrolyzed tire char was prepared for use herein. The capacity of waste tire-derived PAC to adsorb vapor-phase HgCl₂ was successfully measured using a self-designed TGA adsorption system. Experimental results showed that the maximum adsorptive capacities of HgCl₂ were 1.75, 0.688, and 0.230 mg of HgCl₂ per gram of powdered activated carbon derived from carbon black at 30, 70, and 150 °C for 500 µg/m³ of HgCl₂, respectively. Four adsorption isotherms obtained using the Langmuir, Freundlich, Redlich-Peterson, and Brunauer–Emmett–Teller (BET) models were used to simulate the adsorption of HgCl₂. The comparison of experimental data associated with the four adsorption isotherms indicated that BET fit the experimental results better than did the other isotherms at 30 °C, whereas the Freundlich isotherm fit the experimental results better at 70 and 150 °C. Furthermore, the calculations of the parameters associated with Langmuir and Freundlich isotherms revealed that the adsorption of HgCl₂ by PAC-derived carbon black favored adsorption at various HgCl₂ concentrations and temperatures.     

改性荞麦壳对水溶液中Cu~(2+)离子吸附效果及机理

以柠檬酸对荞麦壳进行化学改性,改性后荞麦壳吸附剂对Cu2+的吸附量增加。研究了不同pH、吸附剂投入量、浓度和时间对吸附效果的影响。在pH值为5.5,Cu2+初始浓度50 mg/L,吸附剂投入量为1 g,吸附时间为120 min的条件下,Cu2+的吸附量达到较大值。通过用改性荞麦壳吸附剂对Cu2+的热力学吸附过程的分析,结果表明,改性荞麦壳吸附剂符合Langmuir吸附等温模式,改性荞麦壳吸附剂对Cu2+的吸附存在化学吸附,改性荞麦壳的最大吸附量可以达2.26 mg/g。研究改性荞麦壳吸附剂吸附Cu2+的动力学特性,吸附动力学行为可用准二级速率方程进行很好的描述,准二级吸附速率常数随温度升高而增大。准一级速率方程和颗粒扩散模型可以较好地描述吸附初始阶段,Cu2+浓度较高,颗粒内扩散;吸附后期,Cu2+浓度较低,受到颗粒外扩散的控制。总之,整个吸附过程可能是多种动力学机理共同作用的结果。