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1.
《分离科学与技术》2012,47(15):1363-1375
Abstract

Adsorption of microamounts of silver on manganese dioxide from nitric and perchloric acid solutions has been studied and optimized with respect to shaking time, concentrations of electrolyte, adsorbent, and adsorbate. Maximum adsorp- tion (>99.5%) has been achieved from 0.01 mol/dm3 acid solution using 50 mg oxide at 10?5 mol/dm3 silver concentration after 30 min shaking. The adsorption decreases with increasing concentration of acid and adsorbate from both the acids. The presence of a 104-fold greater concentration of cyanide, thiocyanate, thiosulfate, and Pb(II) than silver reduces the adsorption drastically. The adsorption of silver follows the Freundlich adsorption isotherm over the entire concentration range investigated from 9.27 × 10?6 to 2.92 × 10?3 mol/dm3 with a value of A = 49 mmol/g and 1/n = 0.93. Moreover, the Langmuir adsorption isotherm is also valid except at the lowest and highest concentrations. The values of the limiting adsorption concentrtion (Cm ) have been found to be 1 mmol/g and of the equilibrium constant for adsorption 87 dm3/mol at 23 ± 2°C.  相似文献   

2.
This work reports the viability and modelling of the removal of Cr(VI) from polluted groundwaters by means of ion exchange using the resin Lewatit MP‐64. Feed groundwaters that contained Cr(VI) at an average concentration of 2431 mg dm?3 and 1187 mg dm?3 of chloride and 1735 mg dm?3 of sulfate as main anions were acidified to a pH of 2.0 prior to the removal process. Dynamic experiments were carried out in a fixed bed column with feed waters at flow rates in the range of 2.78 × 10?7 m3 s?1 to 5.55 × 10?7 m3 s?1. Regeneration was achieved with NaOH (2 mol dm?3). From the experimental results, the equilibrium of the ion exchange reaction was successfully modelled, obtaining an equilibrium constant (KAB) = 44.90. Finally, a mass balance that included mass transfer resistances in the liquid and solid phases was developed and from the comparison between simulated and experimental data the value of the effective intraparticle diffusivity (Ds) was determined as 1.43 × 10?12 m2 s?1. Copyright © 2004 Society of Chemical Industry  相似文献   

3.
The adsorption of chlorophyll-a on bentonite desiccated at 110°C, untreated and acid-treated with H2SO4 solutions over a concentration range between 0·25 and 2·50 mol dm?3, from acetone solution at 25°C has been studied. The adsorption isotherms may be classified as using Giles' classification, as type S (untreated sample and 0·25 mol dm?3 H2SO4-treated sample), type H (0·50 mol dm?3 H2SO4-treated sample) and type L (1·00 and 2·50 mol dm?3 H2SO4-treated samples). This fact suggests that the bentonite surfaces (low, high and medium affinity, respectively) behave in differently relation to the adsorption of the chlorophyll-a molecules. The experimental data points have been fitted to the Freundlich equation in order to calculate the adsorption capacities (Kf) of the samples; Kf values range from 0·43 mg kg?1 for the untreated bentonite up to 108·89 mg kg?1 for the 0·50 M H2SO4-treated bentonite. The removal efficiencies (R) have also been calculated and range from 5·71% for the untreated bentonite up to 85·18% for the 0·50 M H2SO4-treated bentonite.  相似文献   

4.
This study addresses the removal of humic acid (HA) dissolved in an aqueous medium by a photoelectrocatalytic process. UV254 removal and the degradation of color (Vis400) followed pseudo‐first order kinetics. Rate constants were 1.1 × 10?1 min?1, 8.3 × 10?2 min?1 and 2.49 × 10?2 min?1 (R2 > 0.97) for UV254 degradation and 1.7 × 10?1 min?1, 6.5 × 10?2 min?1 and 2.0 × 10?2 min?1 for color removal from 5 mg dm?3, 10 mg dm?3 and 25 mg dm?3 HA respectively. Following a 2 h irradiation time, 96% of the color, 98% of the humic acid and 85% of the total organic carbon (TOC) was removed from an initial 25 mg dm?3 HA solution in the photoanode cell. Photocatalytic removal on the same photoanode was also studied in order to compare the two methods of degradation. Results showed that the photoelectrocatalytic method was much more effective than the photocatalytic method especially at high pH values and with respect to UV254 removal. The effect of other important reaction variables, eg pH, external potential and electrolyte concentration, on the photoelectrocatalytic HA degradation was also studied. Copyright © 2003 Society of Chemical Industry  相似文献   

5.
The aim of this study was to examine the synthesis of a graft copolymer of chitosan and methacrylic acid (MAA) by free‐radical polymerization with a potassium peroxymonosulfate/cyclohexanone (CY) redox system in an inert atmosphere. The optimum reaction conditions affording maximum grafting ratio (%G), grafting efficiency (%E), add on (%A), and conversion (%C) were determined. The grafting parameters were found to increase with increasing concentration of MAA up to 24 × 10?2 mol/dm3, but thereafter, these parameters decreased. With increasing concentration of peroxymonosulfate from 0.6 × 10?2 to 1.2 × 10?2 mol/dm3, %G, %A, and %E increased continuously. All of these grafting parameters increased with increasing concentration of CY up to 1.2 × 10?2 mol/dm3, but beyond this concentration, the grafting parameters decreased. With various concentrations of chitosan from 0.6 to 1.4 g/dm3, the maximum %G, %A, and %E were obtained at 1.4 g/dm3. %G, %A, and %C decreased continuously with various concentrations of hydrogen ions from 2 × 10?3 to 6 × 10?3 mol/dm3. The grafting parameters increased with increasing temperature up to 35°C, but thereafter, these parameters decreased. With increasing time period of reaction from 60 to 180 min, %G, %A, and %E increased up to 120 min, but thereafter, these parameters decreased. The graft copolymer was characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009  相似文献   

6.
The adsorption of cadmium and zinc ions on natural bentonite heat-treated at 110°C or at 200°C and on bentonite acid-treated with H2SO4 (concentrations: 0·5 mol dm?3 and 2·5 mol dm?3), from aqueous solution at 30°C has been studied. The adsorption isotherms corresponding to cadmium and zinc may be classified respectively as H and L types of the Giles classification which suggests the samples have respectively a high and a medium affinity for cadmium and zinc ions. The experimental data points have been fitted to the Langmuir equation in order to calcualte the adsorption capacities (Xm) and the apparent equilibrium constants (Ka) of the samples; Xm and Ka values range respectively for 4·11 mg g?1 and 1·90 dm3 g?1 for the sample acid-treated with 2·5 mol dm?3 H2SO4 [(B)-A(2·5)] up to 16·50 mg g?1 and 30·67 dm3 g?1 for the natural sample heat-treated at 200°C [B-N-200], for the adsorption process of cadmium, and from 2·39 mg g?1 and 0·07 dm3 g?1, also for B-A(2·5), up to 4·54 mg g?1 and 0·45 dm3 g?1 [B-N-200], for the adsorption process of zinc. Xm and Ka values for the heat-treated natural samples were higher than those corresponding to the acid-treated ones. The removal efficiency (R) has also been calculated for every sample; R values ranging respectively from 65·9% and 8·2% [B-A(2·5)] up to 100% and 19·9% [B-N-200], for adsorption of cadmium and zinc.  相似文献   

7.
Unreported graft copolymer of N,N′‐dimethylacrylamide (DMA) with partially carboxymethylated guar gum (CmgOH) has been synthesized and the reaction conditions have been optimized for affording maximum grafting using a potassium peroxymonosulphate (PMS)/thiourea (TU) redox initiators under nitrogen atmosphere. The study of graft copolymerization has been performed to observe maximum value of grafting parameters except percentage of homopolymer by varying the concentrations of DMA, PMS, and TU. The grafting parameters increase continuously on increasing the concentration of DMA from 8 × 10?2 to 24 × 10?2 mol dm?3, PMS from 5 × 10?3 to 21 × 10?3 mol dm?3, and TU from 1.6 × 10?3 to 4.8 × 10?3 mol dm?3. The optimum temperature and time for grafting of DMA onto CmgOH were found to be 35°C and 120 min, respectively. The water‐swelling capacity of graft copolymer is investigated. Flocculation property for both coking and noncoking coals is studied for the treatment of coal mine waste water. The graft copolymer is characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010  相似文献   

8.
Van der Sluis et al.'s model was used to determine the rate of the partial dissolution of a Tunisian phosphate rock with dilute phosphoric acid (1.5 mass% P2O5). When the temperature rises from 25 to 90°C, for a given particle size, the mass-transfer coefficients, kL°, vary from 3 × 10?3 to 8 × 10?3 m ·s?1. The corresponding diffusion coefficients, D, lies between 6 × 10?7 and 27 × 10?7 m2·s?1. Activation energy is equal to 14 kJ·mol?1 and values of kL°, at 25°C, are in the range of 0.28 × 10?3 and 4 × 10?3 m·s?1 when the agitation speed goes from 220 to 1030 rpm, showing that the leaching process is controlled by diffusion rather than by chemical reaction.  相似文献   

9.
The optimum conditions for grafting N‐vinyl‐2‐pyrrolidone onto dextran initiated by a peroxydiphosphate/thiourea redox system were determined through the variation of the concentrations of N‐vinyl‐2‐pyrrolidone, hydrogen ion, potassium peroxydiphosphate, thiourea, and dextran along with the time and temperature. The grafting ratio increased as the concentration of N‐vinyl‐2‐pyrrolidone increased and reached the maximum value at 24 × 10?2 mol/dm3. Similarly, when the concentration of hydrogen ion increased, the grafting parameters increased from 3 × 10?3 to 5 × 10?3 mol/dm3 and attained the maximum value at 5 × 10?3 mol/dm3. The grafting ratio, add‐on, and efficiency increased continuously with the concentration of peroxydiphosphate increasing from 0.8 × 10?2 to 2.4 × 10?2 mol/dm3. When the concentration of thiourea increased from 0.4 × 10?2 to 2.0 × 10?2 mol/dm3, the grafting ratio attained the maximum value at 1.2 × 10?2 mol/dm3. The grafting parameters decreased continuously as the concentration of dextran increased from 0.6 to 1.4 g/dm3. An attempt was made to study some physicochemical properties in terms of metal‐ion sorption, swelling, and flocculation. Dextran‐gN‐vinyl‐2‐pyrrolidone was characterized with infrared spectroscopy and thermogravimetric analysis. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   

10.
The ZnO/ZnMn2O4 nanocomposite (ZnMn) was used as adsorbent for the removal of cationic dye Basic Yellow 28 (BY28) from aqueous solutions. The adsorbent was characterized by X-ray diffraction, scanning electron microscope, TEM, Fourier transform infrared ray, BET, particle size distribution and zeta potential measurements. The adsorption parameters, such as temperature, pH and initial dye concentration, were studied. Kinetic adsorption data were analyzed using the pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models. The Langmuir and Freundlich isotherm models were applied to fit the equilibrium data. The maximum adsorption capacity of BY28 was 48.8 mg g?1. Various thermodynamic parameters, such as ΔG°, ΔH° and ΔS°, were calculated.  相似文献   

11.
Glucose oxidase was immobilized onto poly(2-hydroxyethyl methacrylate) (pHEMA) membranes by two methods: by covalent bonding through epichlorohydrin and by entrapment between pHEMA membranes. The highest immobilization efficiency was found to be 17.4% and 93.7% for the covalent bonding and entrapment, respectively. The Km values were 5.9 mmol dm?3, 8.8 mmol dm?3 and 12.4 mmol dm?3 for free, bound and entrapped enzyme, respectively. The Vmax values were 0.071 mmol dm?3 min?1, 0.067 mmol dm?3 min?1 and 0.056 mmol dm?3 min?1 for free, bound and entrapped enzyme. When the medium was saturated with oxygen, Km was not significantly altered but Vmax was. The optimum pH values for the free, covalently-bound and entrapped enzyme were determined to be 5, 6, and 7, respectively. The optimum temperature was 30°C for free or covalently-bound enzyme but 35°C for entrapped enzyme. The deactivation constant for bound enzyme was determined as 1.7 × 10?4 min?1 and 6.9 × 10?4 min?1 for the entrapped enzyme.  相似文献   

12.
The removal of trivalent chromium from solutions using biosorption in cork powder is described. The adsorption isotherm was determined, along with the effect of different variables, such as biomass particle size, solid–liquid ratio, reaction time, metal concentration and pH, on the efficiency of chromium removal. It was concluded that the adsorption is slow and favoured by an increase in pH. Therefore, using a solid–liquid ratio of 4 g dm?3 it is possible to reduce the chromium concentration in the solution from 10 mg dm?3 to less than 1.5 mg dm?3 in 2 h at 22 °C. The kinetic studies verified that the sorption of chromium by cork was described by a second‐order model. The elution results showed that 50% of the chromium bound to the cork was eluted using 0.5 mol dm?3 H2SO4 and that cork maintains its binding capacity over four cycles of biosorption/elution. © 2002 Society of Chemical Industry  相似文献   

13.
BACKGROUND: Owing to the rapid depletion of petroleum fuel, the production of bio‐butanol has attracted much attention. However, low butanol productivity severely limits its potential industrial application. It is important to establish an approach for recovering low‐concentration butanol from fermentation broth. Experiments were conducted using batch adsorption mode under different conditions of initial butanol concentration and temperature. Batch adsorption data were fitted to Langmuir and Freundlich isotherms and the macropore diffusion, pseudo‐first‐ and second‐order models for kinetic study. RESULTS: The maximum adsorption capacity of butanol onto KA‐I resin increase with increasing temperature, ranged from 139.836 to 304.397 mg g?1. The equilibrium adsorption data were well fitted by the Langmuir isotherm. The adsorption kinetics was more accurately represented by the macropore diffusion model, which also clearly predicted the intraparticle distribution of the concentration. The effective pore diffusivity (Dp) was dependent upon temperature, but independent of initial butanol concentration, and was 0.251 × 10?10, 0.73 × 10?10, 1.32 × 10?10 and 4.31 × 10?10 m2 s?1 at 283.13, 293.13, 303.13 and 310.13 K, respectively. CONCLUSION: This work demonstrates that KA‐I resin is an efficient adsorbent for the removal of butanol from aqueous solutions and available for practical applications for future in situ product recovery of butanol from ABE fermentation broth. Copyright © 2012 Society of Chemical Industry  相似文献   

14.
In this article, graft copolymerization of N‐vinyl‐2‐pyrrolidone onto xanthan gum initiated by potassium peroxydiphosphate/Ag+ system in an aqueous medium has been studied under oxygen free nitrogen atmosphere. Grafting ratio, grafting efficiency, and add on increase on increasing the concentration of potassium peroxydiphosphate (2.0 × 10?3 to 12 × 10?3 mol dm?3), Ag+(0.4 × 10?3 to 2.8 × 10?3 mol dm?3), and hydrogen ion concentration from 2 × 10?3 to 14.0 × 10?3 mol dm?3. Maximum grafting has been obtained when xanthan gum and monomer concentration were 0.4 g dm?3 and 16 × 10?2 mol dm?3, respectively, at 35°C and 120 min. Water swelling capacity, swelling ratio, metal ion uptake, and metal retention capacity have also been studied, and it has been found that graft copolymer shows enhancement in these properties than pure xanthan gum. The graft copolymer has been characterized by FTIR and thermal analysis. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009  相似文献   

15.
Zirconium pillared clay (PILC) was prepared using montmorillonite as the base clay. Adsorption of tannic acid (tannin) was studied by a batch equilibrium technique, as a function of adsorbate concentration, temperature, pH, agitation speed, particle size of the adsorbent and ionic strength. The process of uptake is governed by diffusion controlled first‐order reversible rate kinetics. The higher uptake for the pH range 4.0–6.0 was attributed to external hydrogen bonding between phenolic‐OH groups of tannin molecules and the hydrogen bonding sites on the clay. The removal of tannin by adsorption was found to be >99.0% depending on the initial concentration in the pH range of 4.0–6.0. The process involves both film and pore diffusion to different extents. The effects of solute concentration, temperature, agitation speed and particle size on the diffusion rate were investigated. Tannin uptake was found to increase with ionic strength due to the compression of diffuse double layers. The applicability of Langmuir and Freundlich isotherm models has been tested. The maximum adsorption capacity of PILC was found to be 45.8 µmol g?1 of clay and the affinity constant is 2.9 × 10?2 dm3 µmol?1 at 30 °C. Thermodynamic parameters such as ΔG °,ΔH ° and ΔS ° were calculated to predict the nature of adsorption. The isosteric enthalpies of adsorption were also determined and found to decrease with increasing surface coverage. Regeneration with hot water (60 °C) has been investigated for several cycles with a view to recovering the adsorbed tannin and also restoring the sorbent to its original state. Copyright © 2001 Society of Chemical Industry  相似文献   

16.
Carbon nanotubes (CNTs) were used as adsorbent to remove fulvic acids (FA) from aqueous solutions. The adsorption capacity of CNTs for FA can reach 24 mg g?1 at 5 °C and equilibrium concentration of 18 mg dm?3. The kinetic and thermodynamic parameters, such as rate of adsorption, standard free energy changes (ΔG0), standard enthalpy change (ΔH0) and standard entropy change (ΔS0), have been obtained. Acidic conditions (pH = 2–5) favor FA removal. An increase in the ionic strength or the addition of divalent cations increase the adsorption of FA dramatically (FA = 60 mg dm?3). An increase in the maximum adsorbed amount of FA was observed when treating FA in synthetic seawater. Desorption studies reveal that FA can be easily and quickly removed from CNTs by altering the pH values of the solution. Good adsorption capacity and quick desorption indicate that CNTs are a promising adsorbent to remove FA from aqueous solutions. Copyright © 2007 Society of Chemical Industry  相似文献   

17.
The graft copolymerization of acrylamide (AAm) and ethylmethacrylate (EMA) monomers onto cellulose has been carried out using ceric ammonium nitrate (CAN) as initiator in presence of nitric acid at (25 ± 1)°C and varying feed molarity from 7.5 × 10?2 mol dm?3 to 60.0 × 10?2 mol dm?3 at fixed feed composition (fAAm = 0.6). The graft yield (%GY) has shown a linear increasing trend upto a feed molarity of 37.5 × 10?2 mol dm?3. The composition of grafted copolymer chains was found to be constant (FAAm = 0.56) during feed molarity variation but shown variations with feed composition (fAAm) and reaction temperature. The grafting parameters have shown increasing trends up to 7.5 × 10?3 mol dm?3 concentration of ceric (IV) ions and decreased on further increasing the concentration of ceric (IV) ions beyond 7.5 × 10?3 mol dm?3. The IR and elemental analysis data were used to determine the composition of grafted chains (FAAm) and reactivity ratio of acrylamide (r1) and ethylmethacrylate (r2) comonomers. The reactivity ratio for acrylamide (r1) and ethylmethacrylate (r2) has been found to be 0.7 and 1.0 respectively, which suggested for an alternate arrangement of average sequence length of acrylamide (mM?1) and ethylmethacrylate (mM?2) in grafted chains. The rate of graft copolymerization of comonomers onto cellulose was found to be proportional to square concentration of comonomers and square root to the concentration of ceric (IV) ions. The energy of activation (ΔEa) of graft copolymerization was found to be 9.57 kJ mol?1 within the temperature range of 20–50°C. On the basis of experimental findings, suitable reaction steps have been proposed for graft copolymerization of selected comonomers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2546–2558, 2006  相似文献   

18.
Pseudomonas aeruginosa AT10 produced a mixture of surface‐active rhamnolipids when cultivated on mineral medium with waste free fatty acids as carbon source. The development of the production process to an industrial scale included the design of the culture medium. A 24 full factorial, central composite rotational design and response surface modelling method (RSM) was used to enhance rhamnolipid production by Pseudomonas aeruginosa AT10. The components that are critical for the process medium were the carbon source, the nitrogen source (NaNO3), the phosphate content (K2 HPO4/KH2PO4 2:1) and the iron content (FeSO4·7H2O). Two responses were measured, biomass and rhamnolipid production. The maximum biomass obtained was 12.06 g dm?3 DCW, when the medium contained 50 g dm?3 carbon source, 9 g dm?3 NaNO3, 7 g dm?3 phosphate and 13.7 mg dm?3 FeSO4·7H2O. The maximum concentration of rhamnolipid, 18.7 g dm?3, was attained in medium that contained 50 g dm?3 carbon source, 4.6 g dm?3 NaNO3, 1 g dm?3 phosphate and 7.4 mg dm?3 FeSO4·7H2O. © 2002 Society of Chemical Industry  相似文献   

19.
The purpose of the present investigation was to develop an electrochemical process to obtain simultaneously cuprous oxide powder and metallic nickel in a two-compartment cell. Nafion® 901 bimembrane (Dupont, USA) was employed to separate the compartments to avoid the diffusion of nickel ions from the catholyte to the anolyte. A continuous addition of sodium hydroxide solution to the anodic compartment was necessary to form in situ the cuprous oxide by chemical reaction with the cuprous chlorocomplexes generated at the anode. As an anode system, a titanium basket filled with copper scrap wire was utilized. The anodic operating conditions were: NaCl 250 g dm?3, pH 10, 80°C, c.d. 6 A dm?2 and current concentration 0.4 A dm?3, The cathodic parameters were: Ni2i 74 g dm?3, H3B0330 g dm?3, sodium lauryl sulphate 0.5 g dm?3, coumarin 0.15 g dm?3, pH2, 50°C, c.d. 6 A dm?2 Good quality red-violet cuprous oxide powder, meeting ASTM specifications D912-65 to be used in antifouling paints and metallic nickel (> 99.96% Ni) was obtained.  相似文献   

20.
《分离科学与技术》2012,47(1):203-222
Abstract

The decontamination of lead ions from aqueous media has been investigated using styrene‐divinylbenzene copolymer beads (St‐DVB) as an adsorbent. Various physico‐chemical parameters such as selection of appropriate electrolyte, contact time, amount of adsorbent, concentration of adsorbate, effect of foreign ions, and temperature were optimized to simulate the best conditions which can be used to decontaminate lead from aqueous media using St‐DVB beads as an adsorbent. The atomic absorption spectrometric technique was used to determine the distribution of lead. Maximum adsorption was observed at 0.001 mol L?1 acid solutions (HNO3, HCl, H2SO4 and HClO4) using 0.2 g of adsorbent for 4.83×10?5 mol L?1 lead concentration in two minutes equilibration time. The adsorption data followed the Freundlich, Langmuir, and Dubinin‐Radushkevich (D‐R) isotherms over the lead concentration range of 1.207×10?3 to 2.413×10?2 mol L?1. The characteristic Freundlich constants i.e. 1/n=0.164±0.012 and A=2.345×10?3±4.480×10?5 mol g?1 have been computed for the sorption system. Langmuir isotherm gave a saturated capacity of 0.971±0.011 mmol g?1, which suggests monolayer coverage of the surface. The sorption mean free energy from D‐R isotherm was found to be 18.26±0.75 kJ mol?1 indicating chemisorption involving chemical bonding for the adsorption process. The uptake of lead increases with the rise in temperature. Thermodynamic parameters i.e. ΔG, ΔH, and ΔS have also been calculated for the system. The sorption process was found to be exothermic. The developed procedure was successfully applied for the removal of lead ions from real battery wastewater samples.  相似文献   

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