Experiments were also established in order to understand the kinetics of Cr(III) removal by both zeolites from two different initial concentrations. The kinetics of sorption describing the solute uptake rate which in turn governs the residence time of sorption reaction is one of the important characteristics defining the efficiency of sorption. Mathematical models that are used most frequently to describe kinetics of sorption in a free suspension in a well agitated batch system are pseudo first and pseudo second order equations . The kinetics of Cr(III) uptake by both zeolites followed the pseudo second order kinetic model since the plotting of the graphs fitted well with this model.
Liet al. studied the kinetics and equilibrium of Cr(III) removal from aqueous solution by IRN-77 cation-exchange . Gando-Ferreira et al. studied the application of ion exchange resins in the selective separation of Cr(III) from electroplating effluents using Diaion CR11-containing iminodiacetic acid groups . Petruzzelli et al. studied Purolite C160 and Duolite A-7 for metal ion separation of Cr(III), Fe(III), and Al(III) . Kocaoba et al. performed kinetic experiments with Amberlite IR 120 a strong cation exchange resin, for chromium removal,and they found that the system is controlled byboth particle and film diffusion . Alguacil et al. studied Cr(III) removal using Amberlite 200 resin in batch and column tests, and they found that the Langmuir isotherm described the adsorption process well .
element for humans and is much less toxic than Cr (VI), it is required to potentiate insulin and for normal glu- cose metabolism  . Cr (III) is poorly adsorbed by any route so the toxicity of chromium is attributed to the Cr (VI) form . Cr (VI) can be absorbed by the lung and gastrointestinal tract, and even to a certain extent by intact skin. If Cr (VI) is reduced to Cr (III) extracellularly, the toxicity is not observed. Cr (VI) can be reduced intracellularly by hydrogen peroxide, glutathione reductase and ascorbic acid to produce reactive intermediates. Any of these species could attack DNA, proteins and membrane lipids thereby disrupting cellular integrity and functions. Exposure to chromium (VI) can cause respiratory, renal, hepatic, gastrointestinal, cardiovascular and hematological problems. Also Cr (VI) is considered to be carcinogenic  . Cr (VI) is introduced into natural waters by a variety of industrial processes including textile, dyes and pigment production, film and photography, galvanometry, leather tanning, electroplating and metal finishing industries . A number of treatment methods for the removal of metal ions from aqueous solutions have been reported. These include reduction, ion exchange, electro dialysis, electrochemical precipitation, evaporation, solvent extraction, reverse osmosis, chemical preci- pitation and adsorption. Most of these methods have a lot of disadvantages including high operational cost . Recently, adsorption processes utilizing natural low cost adsorbents were employed in order to remove chro- mium from aqueous solutions. Some of these processes were also able to reduce Cr (VI) to Cr (III)  -. On the other hand, specific sorbents consisting of polymer microspheres containing metal chelating ligands were employed for heavy metal ion removal .
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carbon as a function of time. Initial Cr(VI) concentration 5 mg/l and absorbents dose of 2 g/100ml were used. Fig. 1 shows rapid adsorption in the initial 15 min for all biosorbent. Basically, the removal of Cr(VI) is rapid, but it gradually decreases with time until it reaches equilibrium. The necessary time to reach this equilibrium is about 15 min. Further increase in contact time did not show an increase in biosorption.
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A new modified chitosan resin with pendent amidoxime moieties (CACR) was prepared by reaction of cross-linked chitosan beads with acrylonitrile to support the polymer with nitrile group that facilities the reaction of beads with hydroxylamine hydrochloride. Synthesized CACR is characterized using FTIR, thermal gravimetric analysis, SEM, surface area. This resin have high sorption capacity for Co(II) and Cr(III) from their aqueous medium. The sorption of metal ions onto CACR is influenced by several factors such as the solution pH, concentration of metal ions, contact time and solution temperature. In batch equilibrium adsorption method, the optimum sorption pH for Co(II) and Cr(III) were 7.3 and 4.9 respectively. The maximum adsorption capacity of CACR followed the order Cr (III) > Co(II). For Chromium and Cobalt ions, Langmuir isotherm model was the best to indicate the adsorption process also the kinetic experiments showed that adsorption well presented by pseudo-second order model. Thermodynamic parameters also showed that adsorption of metal ions on CACR is spontaneous and endothermic in nature. CACR isn’t only efficient for Cr(III) and Co(II) removal by batch but also by column methods, and the best condition for adsorption process at 0.5ml/min and 1.7 cm bed height. Adams-Bohart, Thomas and Yoon Nelson models are suitable models to describe fixed bed column operations.
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stretching of alkane, and the band appearing at 1731, 1724, and 1640 cm −1 was referenced to the C=O bond of carboxylic acids, 1610 and 1641 cm − 1 to C–O stretches of ester or ether. Aromatic C–O stretching vibrations of the lignin component and –C–O–C– stretching appear- ing at 1025, 1027, and 1033 cm − 1 , respectively (Noeline et al. 2005; Kumar et al. 2010). The weak band in the re- gion of 885 and 889 cm −1 was attributed to N–H de- formation of amino groups. Looking at the spectrum, it shows carboxylic acid, and hydroxyl groups showed a dominant role in the removal of Cr(VI) ions. Some clear shifts from the matrix of the adsorbents were seen after the adsorption of Cr(VI). These were a changing of wavenumber from 3343 cm −1 (CKS) to 3323 cm −1 (Cr(VI)-loaded CKS), from 3351 cm − 1 (RSS) to 3320 cm −1 (Cr(VI)-loaded RSS), and from 3294 cm −1 (BP) to 3324 cm −1 (Cr(VI)-loaded BP). The number of –OH groups in the dominant form in the structure of the ad- sorbents was decreased by interaction with Cr(VI). This caused the decrease in the intensity of the band and changed the existing band to a narrow band spectrum. FT-IR analysis of the adsorbents displayed that some bands shifted after Cr(VI) adsorption. The following are for CKS: the band in 1724 cm − 1 to 1741 cm − 1 , the band in 1610 cm −1 to 1597 cm −1 , and the band in 1224 cm −1 to 1226 cm −1 ; the following are for RSS: the band in 2924 cm − 1 to 2933 cm − 1 , the band in 1729 cm − 1 to 1731 cm −1 , the band in 1560 cm −1 to 1641 cm −1 , the band in 1224 cm −1 to 1226 cm −1 , and the band in 1074 cm −1 to 1033 cm − 1 ; and the following are for BS: the band in 2919 cm −1 to 2915 cm −1 , the band in 1670 cm −1 to 1637 cm −1 , the band in 1592 cm −1 to 1614 cm −1 , and the band in 1025 cm − 1 to 1022 cm − 1 . Changes in the band fre- quencies in the FT-IR spectrum correspond to the
In this work we investigated the optimization conditions for removal of Cr(III) ions by MnO 2 / MWCNT nanocomposite that we reach to a fairly good results. We investigated the adsorption in a wide range of pH to identify the best range. So we found that the pH = 5 is better. Therefore we did our measurements in this pH. We also investigated the best dosage of adsorbent, contact time, and also various concentrations have been studied. In lower concentration we got better results, and then we estimated thermodynamic parameters. As we found the studied adsorption was exothermic and spontaneously. Also we compare our experimental results with our calculation results. We concluded, the our results are better comparable with Freundlich isotherm.
The removal of Cr(III) by the beans peel powder is examined at different time intervals as shown in Figure 1.As can be seen ,during first 2 minutes ,the Cr(III) % removal increase extremely with prolonged time and reaches value of 99%. Above first 2 minutes, no significant change of Cr(III) %removal is observed and a maximum value was 99.4% at 30 min. Depending on the results, it can be concluded that the adsorption equilibrium is reached after 30 minutes.
In this work we investigated the optimization conditions for removal of Cr(III) ions by MnO 2 /MWCNT nanocomposite that we reach to a fairly good results. We investigated the adsorption in a wide range of pH to identify the best range. So we found that the pH = 5 is better. Therefore we did our measurements in this pH. We also investigated the best dosage of adsorbent, contact time, and also various concentrations have been studied. In lower concentration we got better results, and then we estimated thermodynamic parameters. As we found the studied adsorption was exothermic and spontaneously. Also we compare our experimental results with our calculation results. We concluded, the our results are better comparable with Freundlich isotherm.
was found to depend on the initial metal ion concentration, pH and contact time. Sugarcane bagasse an agricultural residue from sugar refining industries had been shown to have a great potential as a low cost adsorbent for Cd(II) removal and could be applied for waste water management strategies. Both Langmuir and Freundlich adsorption isotherms describe the sorption behaviour. The adsorption data followed pseudo- second order kinetics 5 .Hamadi et al. studied the adsorption kinetics for the removal of Cr(VI) from aqueous solution by using tyre and saw dust. They found that the removal was favourable at low pH, with maximum removal at pH 2. They found both adsorbents were effective to remove Cr(VI) from solution. The sorption kinetics was found to follow pseudo- second order model 6 .Basyal and Ozdin studied the biosorption of Cr(VI) and Al(III) on Chrysemonas Luteola TEM05. They found the greatest capacity for Al(III) 55.2 mg/g and for Cr(VI) 3.0 mg/g at pH 5 and pH 4 respectively. The biosorption equilibrium was described by Langmuir and Freundlich isotherm. Freundlich isotherm fitted well for both ions. The kinetic data followed pseudo-second order model 7 .
This work is focused on the removal of Cr(VI) ions from aqueous solution using water-soluble poly(diallyldimethylammonium chloride), PDDA, coupled to an ultrafiltration membrane of regenerated cellulose and subsequent electrochemical reduction of Cr(VI) to Cr(III). The removal of Cr(VI), using the washing mode, was studied as a function of pH, the molar ratio of polymer:Cr(VI), and the presence of interfering ions. The enrichment mode was used to determine the maximum retention capacity of the polymer, and the release of Cr(VI) and regeneration of the polymer were analysed by sorption-desorption process. Subsequently, the electroanalysis of Cr(VI) was conducted by linear sweep voltammetry and full electrolysis at controlled-potential in acidic media and in the presence of PDDA.
ABSTRACT: Duckweeds are of special interest, as they are naturally growing weeds that have the capacity to tolerate and remove toxic pollutants, including heavy metals from the environment. Studies have revealed that duckweed (Lemna minor) can tolerate and remove heavy metals from aqueous solutions. In the present study, the efficiency of L. minor in the removal of Ni and Cr individually from aqueous solutions was investigated at concentrations of 3.05, 3.98 and 4.9 mg/L for Ni and 1.91, 2.98, and 4.2 mg/L for Cr. Experiments were run for 22 days, after which the metal content in the plant was estimated by atomic absorption spectrophotometer (AAS). The duckweed showed higher percentage of Ni removal than Cr. Specific Growth Rate (SGR) was found to be reduced at high concentrations of both Ni and Cr. Statistical analysis suggested that the growth of the plant was affected by the toxic effect of both Ni and Cr. Bioaccumulation of Ni was higher than Cr in L. minor. The mechanism of removal of both Ni and Cr followed second order kinetics. It is suggested that these duckweeds can remove Ni and Cr from aqueous solution and can also accumulate the same in considerable concentrations, at low initial metal concentrations.
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FT-IR spectra of banana peel were obtained in order to understand the nature of the functional groups present in banana peel. FT-IR spectra (Fig. 1a) displayed a number of peaks, indicating the complex nature of the adsorbent. Bands appearing at 3313.4, 2920.3, 2850.6, 1734, 1613.6, 1317.4, 1035.2 and 884.6 cm -1 in Fig. 1a were assigned to OH stretching, C-H stretching of alkane, C-H and C=O stretching of carboxylic acid or ester, COO - anion stretching, OH bending, C-O stretching of ester or ether and N-H deformation of amines respectively . Out of these, carboxylic and hydroxyl groups played a major role in the removal of Cr(III) ions. As expected a significant reduction in the intensity of other groups especially OH and COOH group peak (absorbance intensity reduced from 0.0447 and 0.0659 to 0.0266 and 0.0314) along with peak shifting from 3336 and 1613.6 to 3313.4 and 1622.9 cm -1 were recorded in the spectra of esterified banana peel (Fig. 1b) .
The adsorption capacity for a given initial concentration was fully depend on biosorbent dosage. The variation of biosorbent dosage ranged from 0.1 to 1.0 g have been investigated. The results in Figure 4.a and 4.b showed that the optimum dose was achieved at 0.25 g for both type of biosorbent. The percent removal of longan`s seed and skin at optimum dosage were 74.36 % and 67.52 % respectively.Interestingly, the adsorption capacity and percent removal of Cr (VI) ions were significantly decreased at 0.5 g. In case of percent removal, it may slightly increased at biosorbent dosage > 0.5 g for both type of biosorbent. Furthermore this result may suggest that addition of biosorbent was relativelyineffective at higher dose due to the powder formed of biosorbent may caused saturation and particle interaction such as aggregation [27-28].
Various natural sorbents such as coconut husk, coconut shell, rice husk, hazelnut shell, husk of Bengal gram, sugarcane bagasse, rice bran, wheat residue, wheat bran, sunflower stalks, eucalyptus bark, maize bran, waste tea, tea factory waste, maple sawdust, walnut husk, peanut husk, bael fruit shell, orange waste, apple waste, orange peel, carrot residue have potentially been used for the removal of toxic metals      - . Biosorbents are cheapest, most abundant and environmentally friendly  . They provide a large sur- face area and adsorption on them is possible under the broad range of environmental conditions. Agricultural waste materials contain proteins, polysaccharides and lignin, which are associated with functional groups re- sponsible for metal ion adsorption  . The presence of large amounts of various natural biosorbents pro- vides a good alternative to expensive synthetic adsorbents. Metals are attached with sorbent either by physically (London-Van der Waals forces) or by chemically (ionic or covalent bonds).
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take major part in porosity of adsorbent. Imaging of adsorbents was done by Scanning Electron Microscope (SEM - JEOL, JSM 6480 LV). Adsorption experiments were carried out in shake flask system. The stock solutions were diluted as required to obtain standard solutions of concentration ranging between 2 and 10 mg/l. Batch adsorption studies were performed in Erlenmeyer flasks of 250 ml by contacting the selected activated carbon of different doses (0.5 – 2 g/l) with 50 ml of solution containing different metal concentrations (2 – 10 mg/l) at solution pH (2 – 11) and for different contact times (1 – 4 h). All the flasks were maintained at room temperature and provided continuous shaking of 110 rpm by Environmental Orbital Shaker Incubator (DENEB Instruments). Concentration of Cr(III) and Cr(VI) species in the aqueous solutions were determined by standard procedure 25 using UV/VIS spectrophotometer (Jasco, V-530). The percentage removal of Cr(III) and Cr(VI) were calculated according to
For example, the adsorption capacities of Ni (II) were 10.11 at hazelnut shell and coir-pith activated carbon. Moreover, rice husk and hazelnut shell activated carbon could be used to other heavy metal removal including Cr(VI), Cu(II), Hg(II) and Zn(II). Further these activated methods to enhance sorption capacity or selectivity. They were respectively treated by inorganic acid for Cr(III), Cu(II), Ni(II) and Cd(II) removal, ethylenediamine and triethylenetetramine for Cd(II), Cr(III), Fe(III) and Pb(II) adsorption, amine for Cu(II) uptake, sulfurized steam for Pb(II) and Hg(II) removal. From above facts, it always is significant to develop low-cost and high effective activated carbon materials in terms of the heavy metal ions removal. In this work, PFR resin grafted nFe 2 O 3
The physicochemical parameters of the effluent from a typical electroplating industry are presented in Table 1. The value of each parameter is the mean of three replicate analyses. In a typical study 10 mL of the sample was treated with FeCNB maintaining the optimum condition of FeCNB dose and contact time in batch operation. It is observed that 86% of chromium removal takes place lowering to the level recommended by the WHO. The simple operation, low amount of adsorbent and sufficient quick operation makes the synthesized adsorbent a good one for removal of chromium from effluent.
In this study, the removal of several heavy metal ions of Pb(II), Cd(II), Hg(II) and Cr(III) from aqueous medium via sorption process onto calixresorcinarene derivative was investigated. The used adsorbent was highly oxygenated calixresorcinarene namely C-4-hydroxyphenylcalix resorcinarene. Several adsorption parameters were studied including pH, adsorbent dosage, interaction time as well as the kinetic studies. While the maximum removals of Pb(II), Cd(II) and Hg(II) were observed in pH 5, the removal of Cr(III) reached the maximum value at pH 6. The optimum adsorbent dosages for Pb(II), Hg(II) and Cr(III) were 0.025 g, whereas that for Cd(II) was 0.05 g. The kinetic data were evaluated by using three kinetic models of first order model of Santosa, pseudo- first order of Lagergren and pseudo-second order of Ho. The results showed that the adsorption of these metal ions could be well described with Ho’s pseudo-first order model.
The removal of toxic metal ions from aqueous streams requires the use and implementation of new environment friendly materials. Due to its high toxicity ,  and threat to public health and to the environment, chromium is set as of high priority for removal. In the environment, this metal is established as one of the most toxic metals –. In nature, chromium is present in two oxidation states, Cr(III) and Cr(VI). Cr(VI) shows more toxicity than Cr(III); it is carcinogenic and mutagenic. However, Cr(III) shows toxicity to plants at elevated concentrations and presents less toxicity to animals, but trace levels of this element affect sugar and lipid metabolism in humans. Despite the fact that Cr(III) presents less toxicity compared to Cr(VI), elevated levels can be present in the environment as a consequence of non-treated discharges or badly treated streams from industries or the disposal of chromium-containing sludges –. The World Health Organization (WHO) sets the maximum allowable concentration in drinking water for total Cr should be 0.05 mg/L , , whereas the United States Environmental Protection Agency (USEPA) sets the limit to 0.01 mg L -1 .
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