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|contributor.author||Baral, Saroj S||-|
|contributor.author||Rath, P (Guide)||-|
|contributor.author||Das, S N (Guide)||-|
|identifier.citation||Adsorption of Hexavalent Chromium from Aqueous Solution using Various Adsorbents, Thesis submitted in partial fulfillment of the requirements for the award of the Doctor of Philosophy in Chemical Engineering, Submitted to National Institute of Technology, Rourkela||en|
|description||Copyright for the thesis belongs to National Institute of Technology Rourkela||en|
|description.abstract||The removal of Cr(VI) from aqueous solution by batch adsorption technique using different low-cost adsorbents was investigated. The objective of the study was to find out a suitable low cost, environmental friendly and highly effective adsorbent. In the present study different low cost adsorbents such as bauxite, sawdust and sweet water weed were used to determine the adsorption efficiency. All these adsorbents were used as such or after pretreatment. Among all, the pretreated materials were found to be better adsorbents as compared to untreated materials. The influence of agitation speed, pH, temperature, adsorbent dose, initial adsorbate concentration and contact time on the selectivity and sensitivity of the removal process were investigated. The physico-chemical properties of all the adsorbents were studied using different characterization techniques such as FTIR, SEM, XRD, BET surface area and porosity.
Effect of agitation speeds on the Cr(VI) adsorption capacity of the adsorbents were studied. In general, uptake capacity of the adsorbents increase with the increase of agitation speed upto certain level and thereafter, further increase in agitation speed hardly improved the kinetics. The increase of agitation speed overcomes the resistance of mass transfer from the bulk solution to adsorbent surface and hence increased the adsorption capacity of the adsorbents
Adsorption studies were carried out upto 12 h to evaluate the effect of time on adsorption efficiency. From the contact time variation experiments, it was found that the kinetics followed dual rate, i.e., an initial faster rate followed by a slower one. For calcined Bauxite, the faster kinetics was limited to an initial 10 minutes period and the equilibrium was achieved within 60 minutes. For all other adsorbents such as formaldehyde treated sawdust, weed as such, acid treated weed and carbonized weed the faster rate and equilibrium time varied between 30-60 minutes and 2-12 h respectively.
The pH of the Cr(VI) solution was varied between 1.7-6.0. Adsorption process was found to be highly pH dependent. The optimum pH for adsorption on calcined bauxite and formaldehyde treated sawdust were observed to be 3.5 and 6.0 respectively. The optimum adsorption capacity of the three forms of weed were observed to be at pH 1.7. The adsorption studies were also carried out by varying the temperature from 30-70 0C. In all the cases except calcined bauxite, the efficiency increased with the increase of temperature. Further, in all the cases the uptake capacity also increased with the increase of adsorbate concentration but it showed a reverse trend with increase of adsorbent concentration.
The basic data obtained were interpreted kinetically by using first order reversible, pseudo first order, Ritchie second order and pseudo second order rate kinetics. In all the cases the kinetics followed pseudo second order rate equation. Using the results from the temperature variation experiments, the activation energies along with other thermodynamic parameters such as ΔH, ΔG0 and ΔS0 were calculated. Experimental data for all the adsorbents were fitted to different isotherm models such as Freundlich, Langmuir and Temkin adsorption isotherms. The theoretical maximum uptake capacity of each of the adsorbents was found out by using Langmuir adsorption isotherm equation. Acid treated weed and carbonized weed were observed to be the most effective among all the selected adsorbents for the removal of Cr(VI) from aqueous solution. Therefore, all further studies were carried out using these two adsorbents only. Since all adsorbents were porous in nature, it was concluded that the adsorption process might follow surface or intraparticle diffusion or both. In both the cases, the mass transfer coefficients were evaluated from the experimental data. From the values of mass transfer coefficient it was concluded that the initial faster rate was due to surface diffusion and the latter slower part was due to intraparticle diffusion.
Adsorption studies were also carried out to evaluate the optimum parameters of the process for two most suitable adsorbents such as acid treated and carbonized weed. Scale-up experiments were performed after optimization of the adsorption parameters using the batch data of stirred tank reactors. For this purpose, adsorption studies were carried out in a fixed-bed up-flow reactor to evaluate the performance of thermally activated weed for the removal of Cr(VI) ion from the aqueous solutions. The Cr(VI) uptake capacity of the thermally activated weed was investigated as a function of different operating conditions such as flow rate, initial Cr(VI) concentration and retention time, which was supposed to be a function of bed height. In this study, breakthrough point and numbers of bed volume (BV) were used to compare and evaluate the adsorption performance of the activated weed. After saturation with Cr(VI) ions, the spent adsorbent in the column was regenerated using 0.1M NaOH solution. From the regeneration studies, it was observed that the adsorbent could be regenerated and reused over ~ 5 times for the treatment of Cr(VI) contaminated waste water. Thus, the study concluded that the fresh water weed after carbonization could serve as an inexpensive and easy to operate adsorbent to remove Cr(VI) from industrial and mine water discharges.||en|
|publisher||National Institute of Technology, Rourkela||en|
|title||Adsorption of Hexavalent Chromium from Aqueous Solution using Various Adsorbents||en|
|Appears in Collections:||Thesis (Doctor of Philosophy)|
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