外文翻译--蓝色膨润土经微波和酸处理后作为吸附剂从模拟染料废水吸附甲基蓝(含word版） .pdf

f. banat s. al-asheh s. al-anbar s. al-refaie microwave- and acid-treated bentonite as adsorbents of methylene blue from a simulated dye wastewater received: 9 february 2006 accepted: 28 april 2006 published online: 10 june 2006 ? springer-verlag 2006 abstract batch adsorption tests for removal of methylene blue dye (mbd) from aqueous solutions onto bentonite was investigated using natural chemically treated (sulphuric acid) and physically treated (micro- waved) bentonite. in batch sorption tests for mbd removal by the developed sorbents, the time needed to reach equilibrium was less than 30 min. the uptake of mbd by the microwave-treated bentonite was the highest, followed by the acid-treated and fi nally the untreated bentonite. the uptake of mbd increased with an increase in the dye concentration or the solution temperature. three kinetic models were used for eluci- dation of the probable mechanisms of mbd uptake by the three sor- bents. the rates of mbd uptake followed the pseudo second-order model with a high correlation. in- traparticle diff usion was involved in the sorption process but was not the rate-controlling factor. the freund- lich and langmuir isotherm models were employed and well represented the experimental data. keywords bentonite adsorption mbd microwave natural kinetics isotherm re sume des tests dadsorption en se rie, destine s a enlever des colora- tions au bleu de me thyle ne (mbd) de solutions aqueuses, a laide de bentonite, ont e te re alise s. la ben- tonite utilise e e tait naturelle, traite e chimiquement a lacide sulfurique ou traite e physiquement par micro- ondes. dans les tests dadsorption pour enle vement de mbd par les agents de sorption mis en oeuvre, le temps ne cessaire pour atteindre le quilibre est infe rieur a 30 mn. le pre le vement de mbd par la ben- tonite traite e par micro-ondes a e te le plus important, suivi par la ben- tonite traite e a lacide et fi nalement la bentonite naturelle. le pre le ve- ment de mbd augmente avec la concentration du colorant ainsi quavec la tempe rature de la solu- tion. trois mode les cine tiques ont e te conside re s pour comprendre les processus vraisemblables de pre le v- ement de mbd par les trois agents de sorption. les taux de pre le ve- ment de mbd suivent un mode le de second ordre, de tre s pre s. la dif- fusion intra-particulaire est con- cerne e par le processus de sorption, mais nest pas le facteur contro lant le taux de pre le vement. les mode les des isothermes de freundlich et de langmuir rendent bien compte des donne es expe rimentales. mots cle s bentonite adsorption mbd micro-ondes naturel cine tique isotherme bull eng geol env (2007) 66: 5358 doi 10.1007/s10064-006-0054-1 original paper f. banat s. al-anbar s. al-refaie department of chemical engineering, jordan university of science and technology, irbid 22110, jordan s. al-asheh ( however, a broader understanding of the problem can be found in the works of brown and devito (1993). removal of dyes from wastewater effl uents is an important issue in environmental engineering. in many cases, destruction of these wastes is not feasible for eco- nomic, technical or political reasons. chemical treatment is one of the techniques used by textile companies to remove excess colour from wastewater. for example, the coagulationfl occulation process was employed for the treatment of reactive dye wastewater, using ferric chlo- ride as a coagulant (papic et al. 2000). dyes can also be removed by biological processes using anaerobic diges- tion (talarposhti et al. 2001; sirianuntapiboon and saengow 2004). membrane separation and ion exchange processes are also used for the removal of colour from dye wastewater. the cost and/or ineff ectiveness is the main drawback of these techniques (mishra and tripa- thy 1993). adsorption is one of the most eff ective methods of decolourization of wastewater (mckay 1980; yeh et al. 1993; mckay and al-duri 1990). in adsorp- tion, activated carbon is the most commonly used adsorbent (mckay and al-duri 1990), however, other materials such as activated clay, wood and diff erent types of cellulose-based materials have also been used (yeh et al. 1993; nassar and geundi 1990; yeh and thomas 1995). fly ash (viraraghavan and ramakrishna 1999) and low-cost adsorbents, such as shells of almond and hazelnut, and poplar and walnut sawdust (aydin et al. 2004) have also been investigated as potential adsorbents for removing dyes from textile water. the use of diff erent natural clays for the removal of toxic and other organic materials from wastewaters has been increasing lately (boyd et al. 1988). one of these clay minerals is bentonite, which previously been used for removal of basic red dye (hu et al. 2005). al-asheh et al. (2003) tried to enhance the adsorption capacity for methylene blue (mb) by placing a suitable surfactant on bentonite or by thermal treatment in an oven at 850?c. they found the capacity of bentonite to absorb mb was signifi cantly improved. in this work, natural, acid-treated and microwave- treated bentonite are used for the removal of methylene blue dye (mbd) from aqueous solutions. the main objectives of this work are: (1) to determine the ability of physically and chemically treated bentonite to adsorb dye, (2) to compare the adsorption capacity of treated bentonite with that of natural (untreated) bentonite and (3) to study the eff ect of diff erent parameters such as temperature, concentration and contact time on the adsorption process. materials and methods materials the pure powder form of bentonite was obtained from suppilco chemicals (england). the mesh size, average particle diameter, total surface area and cation exchange capacity of this material were 200300, 40 lm, 400 m2/g and 90 mequiv/100 g, respectively. mb powder and distilled water were used for the preparation of the stock solution. for acid treatment, sulphuric acid (h2so4) 50/ 50 (v/v), of analytical grade was used (aldrich com- pany, milwaukee, wi, usa). acid-treated bentonite fifteen grams of natural bentonite were activated by refl uxing, using 50/50 (v/v) h2so4solution at 60?c for 2 h in a round-bottom fl ask. the suspension was left to cool in air. bentonite was then separated from the sus- pension by sedimentation, washed several times with distilled water and placed in an oven at 120?c until dry. the dried bentonite was in the form of clumps, thus crushing by mortar and pestle was required before the sample was passed through a 0.125 mm mesh analysis. microwave-treated bentonite ten grams of natural bentonite were placed in a porce- lain dish which was placed in a microwave oven for 3 h. the samples were then kept in dark closed bottles for storage. batch sorption test sorption tests on the treated and untreated bentonite were performed in order to determine the time needed to reach equilibrium and the pattern of the kinetics. for this purpose, samples of 0.15 g of natural, or acid- treated or heat-treated bentonite were transferred into dark bottles containing 30 ml of 100-ppm mbd 54f. banat et al. solution. the bottles were placed in a temperature- controlled shaker (gfl, hanover, germany) to agitate the mixture at 30?c. samples from the solution were taken at pre-determined time intervals. the sorbent was separated from the samples by centrifugation (300 g, 10 min) and the supernatant was analysed spectropho- tometrically at a wavelength of 610 nm (al-asheh et al. 2003) for the residual concentration of mbd. distilled water was used as a control. another set of tests were performed to study the ef- fect of temperature on the sorption of mbd. for this purpose, thermally (microwave) treated bentonite was used as a model sorbent. the procedure was similar to that mentioned above but in this case, the mbd solution concentrations employed were in the range of 60 1,000 mg/l. the temperature-controlled shaker was used to agitate the mixture at the desired temperatures, namely 25, 30 and 40?c. in this case, the bottles were left in the shaker till equilibrium, without any sampling during the course of the experiment. results and discussion kinetics of the adsorption process the eff ect of contact time on the uptake of mbd by natural bentonite, chemically and thermally treated bentonite has been considered using 100 mg/l initial dye concentration. the results (fig. 1) showed that all three types of bentonite have the ability to adsorb mb from aqueous solution. it can also be seen from the results in fig. 1 that the time needed to reach equi- librium does not exceed 30 min, although to ensure that equilibrium was reached experiments were carried out for 60 min. a comparison between the adsorption rate of mbd on the three used sorbents shows that the mbd adsorption on microwave-treated ben- tonite is much faster than on acid-treated bentonite followed by natural bentonite. such behaviour can be attributedtothetreatmentofbentoniteinthe microwave which takes place at a high temperature, thus volatile matter could have been released in a larger fraction than the acid-treated bentonite, hence creating more porous sites. the kinetic data for the three tested sorbents indicate that the initial decrease in the concentration of dye with time is governed by diff usion in the boundary, and the remainder of the curve where the rate of adsorption is diminished has an infl uence on internal diff usion. the fi rst mechanism is relatively fast, followed by diff usion of dye in the pores and capillaries of the structure of the bentonite (banerjee et al. 1997; mckay et al. 1980). to verify the possible controlling mechanism during this sorption process by the diff erent sorbents, the following kinetic models were used and applied on the experi- mental data in fig. 1: (1) lagergren pseudo fi rst-order model: logqe? qt log qe? k1t 2:303 1 where k1 is the fi rst-order rate constant, qtand qe(mg mbd/g bentonite) represent the amount of dye ad- sorbed at time t (min) and equilibrium time, respectively. (2) the pseudo second-order model: t qt 1 k2qe t qe 2 where k2is the rate constant of the pseudo second-order adsorption. (3) weber and morris intraparticle diff usion model: qt kdt1=2 c3 where kd is the intraparticle diff usion rate constant and c is an empirical constant; c=0 if intraparticle diff usion is the rate-controlling step. the validity of the above-mentioned three models was checked using linear plots of log(qe- qt) versus t, t/qt versus t and qtversus t1/2, respectively. best linearity of the plots indicates the applicability of the models to the experimental data. such plots (not shown) showed that the adsorption kinetics data for the three sorbents used in this work obey the pseudo second-order model. it was also found that intraparticle diff usion is obvious in the adsorption process but it is not the rate-controlling step (i.e. c 0). table 1 displays the rate constant for the pseudo second-order model and the correlation coeffi - cients (r2) for the three kinetic models applied to the three types of bentonite considered in this work. time (min) mbd uptake (mg/g) 19.700 10203040506070 19.75 19.80 19.85 19.90 19.95 20.00 natural bentonite acid-treated bentonite microwave-treated bentonite fig. 1 kinetics of the mbd sorption by natural and treated bentonite. initial mbd concentration100 mg/l; bentonite con- centration5 mg/l treated bentonite as adsorbents of methylene blue55 eff ect of temperature: equilibrium isotherms the experiments were performed to measure the iso- therms of adsorption of mbd on microwave-activated bentonite at 25, 30 and 40?c. the increase in tempera- ture led to an increase in mb uptake (fig. 2). this indicates that adsorption of mbd on bentonite is an endothermic process. this trend has been reported by some authors when studying the adsorption of diff erent types of dyes and other organic compounds on several adsorbents (mckay et al. 1980, 1982; nakhla et al. 1994; asfour et al. 1985; gayle 1994). it has been suggested (mckay et al. 1980) that this behaviour is due to the possibility of an increase in the porosity and in the total pore volume of the adsorbent with the increase of the temperature. achife and ibemesi (1989) also suggested the possibility of the increase in the number of active sites for the adsorption with the increase of the tem- perature. the equilibrium isotherms for the adsorption of mbd by microwave-treated bentonite were obtained at diff erent temperatures. the experimental data were well represented by the linearized forms of the langmuir and the freundlich isotherm models. one of its linearized forms, the langmuir model can be expressed as: ce qe ce qmax 1 klqmax 4 where qeis the equilibrium dye concentration on the adsorbent (mg/g), ceis the equilibrium dye concentra- tion in the solution (mg/l), qmaxis the monolayer capacity of the adsorbent (mg/g) and klis the langmuir adsorption constant (l/mg mbd). the linearized form of the freundlich model is nor- mally expressed as: ln qe ln kf 1 n ln cf5 where kfis the freundlich constant related to the sorp- tion capacity and 1/n is the other freundlich constant which is called heterogeneity factor. the langmuir and freundlich isotherm represen- tation of the equilibrium experimental data obtained from this work are shown in figs. 3 and 4, respec- tively. both models fi t the data very well; however, the langmuir model showed a better fi t of the data than thefreundlichmodel.themaximumadsorption capacity of microwave-treated bentonite for mbd at diff erent temperatures, qmaxas obtained from the langmuir model is given in table 2, as well as values of the same parameter for the other adsorbents. it is seen that the adsorption capacity, at diff erent tem- peratures, of the microwave-treated sorbent for mbd developed in this work is much higher than the other potential sorbents. table 1 rate constant for the pseudo second-order model and r2 values for other models adsorbentk2(min)1)r2pseudo fi rst-order kinetic model r2 pseudo second-order kinetic model r2 intraparticle diff usion model microwave- treated bentonite 3.130.96641.000.8268 acid-treated bentonite 4.180.99541.000.9476 natural bentonite 2.230.99321.000.7548 equilibrium mbd concentration, ce (mg/l) mbd uptake (mg/g) 00 100200300400500600700 20 40 60 80 100 120 40c 30c 25c fig. 2 eff ect of temperature and mbd concentration on the uptake of mbd by microwave-activated bentonite. bentonite concentration5 mg/l equilibrium mbd concentration, ce (mg/l) 0200400600 ce/qe 0 2 4 6 8 10 40c 30c 25c fig. 3 langmuir isotherms at diff erent temperatures for sorption of mbd by microwave-treated bentonite. bentonite concentra- tion5 mg/l 56f. banat et al. conclusions natural bentonite, acid-treated bentonite and micro- waveheat-treatedbentoniteremoveappreciable amounts of mbd from aqueous solutions. the level of uptake of mbd by these three potential sorbents follows thefollowingranking:microwave-treatedbenton- ite acid-treated bentonite natural bentonite. the kinetics studies showed that the uptake of mbd by the three sorbents increases with time up to 30 min, after which no more uptake was observed. the kinetic data are best accommodated by the pseudo second-order model. the intraparticle diff usion was involved in the adsorption of mbd but was not the rate-controlling step. the uptake of heat-treated bentonite increased with increasing temperature and initial concentration of mbd. the langmuir and the freundlich isotherm models followed the experimental data reasonably, but the langmuir model gave the better representation. ln(ce) 234567 ln(qe) 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 40c 30c 25c fig. 4 freundlich isotherms at diff erent temperatures for sorption of mbd by microwave-treated bentonite. bentonite concentra- tion5 mg/l table 2 adsorption capacity of potential sorbents for mb adsorbentsorption capacity (mg/g) reference wood84mckay and poots (1986) cotton waste24mckay and poots (1986) activated tyres130saniz-diaz and griffi ths (2000) pyrolysed furniture80saniz-diaz and griffi ths (2000) orange peel18.6annadurai et al. (2002) raw date pits80.3banat et al. (2003) activated date pits12.9banat et al. 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