*Corresponding author: Department of Applied Chemistry and Chemical Engineering, University of Rajshahi, Bangladesh E-mail addresses:[email protected] (Md. Rakib-uz-Zaman)
45
Removal of Hexavalent Chromium from Aqueous Solution Using Date Palm and Shimul Sawdust as Adsorbent
Nazia Nasrin
1, Jewel Hossen
2, Md. Rakib-uz-Zaman
1,*1
Department of Applied Chemistry and Chemical Engineering, University of Rajshahi, Bangladesh
2
Department of Chemistry, Rajshahi University of Engineering & Technology, Bangladesh
ARTICLE INFORMATION ABSTRACT
Received date: 15 Jan 2019 Revised date: 24 May 2019 Accepted date: 29 June 2019
Adsorption characteristics of Cr (VI) ion from aqueous solution is studied using date palm and shimul sawdusts. Different sawdusts viz. date palm (phoenix dactylityfera), sissoo (dalbergia sissoo), neem (azadirachta indica), shimul (cotton tree, bombax ceiba) and jackfruit (artocarpus heterophyllus) were subjected to adsorption. Among them date palm and shimul sawdusts exhibit maximum efficiency at same conditions. The process was optimized by studying different parameters such as contact time, adsorbent dose, initial Cr (VI) concentration and pH. It is observed that, 82-83% removal of Cr (VI) was attained at 60 minutes contact time, with adsorbent dose 20 g/L, at initial Cr (VI) concentration of 50 ppm and pH 4.0. In all cases, removal efficiency of date palm sawdust was higher than that of shimul. Adsorbent regeneration was also studied and NaOH solution exhibited the best result. This study is considered as utilization of waste materials in contribution for making green environment.
Keywords
Hexavalent chromium removal Adsorption
Electron beam evaporation Surface roughness
1. Introduction
Water pollution from heavy metal ions has drawn substantial attention in recent years because of their carcinogenicity, mutagenicity, genotoxicity and bioaccumulation through the food chain, causing serious health and environmental hazards [1]. Compounds of hexavalent chromium, Cr (VI), has been being used for decades in industrial sectors for various purpose. Hexavalent chromium is known to be very toxic and carcinogenic. In most cases, more toxic hexavalent Cr (VI) compounds are chemically treated to form less toxic trivalent chromium [2]. Chromium forms compounds of several oxidation states, but most common forms are trivalent and hexavalent. Hexavalent chromium is more hazardous, carcinogenic, and mutagenic and more water soluble which easily come in to living cells [3].
Hexavalent chromium is listed by the Environmental Protection Agency (EPA) as a harmful heavy metal ion. The chromium (VI) compounds are being extensively used and/or produced as wastage in electroplating, tanning, corrosion inhibition, and pigment production industries. The effluents of these industries get mixed with the nearest water stream and contaminate groundwater this way [4]. Other heavy metals such as copper, nickel, chromium, zinc, etc. present in wastewater are harmful too. Recently, electrochemical approaches has been applied for the treatment of such wastewaters [5].
Journal of Engineering and Applied Science
Contents are available at www.jeas-ruet.ac.bd
46 Nanocomposite, micro spherical carbon loaded with nanoscale zero valent iron was made-up to remove hexavalent chromium Cr (VI) from aqueous system [6]. A continuous fixed bed experiment was studied using pistachio shell as a green as well as eco-friendly adsorbent for removal of Cr (VI) by adsorption [7]. Low cost Corncob based activated carbon (CAC) was examined for the removal of Cr (VI) from electroplating wastewater [8]. Chemical Coagulation (CC) and Electrocoagulation (EC) processes were compared using iron as coagulating agent while treating aquifer water loaded with relatively higher concentration of total chromium [9]. Coconut coir and shell, rice husk, sugar cane bagasse, tulsi leaf and branches, fly ash were applied for removal of chromium from aqueous solution and highest 81% removal efficiency was reported for coconut shell [10].
The methods are either complicated, costly or less economically effective. In this study, date palm and shimul sawdust were used as adsorbent for the removal of hexavalent chromium from aqueous solution. This method is easily adaptable and equally efficient.
2. Materials and methods
2.1 Collection and preparation of adsorbent
The date palm sawdust and cotton tree sawdust were collected from Katakhali sawmill, Rajshahi, Bangladesh. The collected sawdusts were dried in sunlight and then passes through 30 mesh sieve (USA Standard Testing Sieve ASTM E-11, USA). The processed sawdusts were finally dried at 100 oC for 12 hours in an oven (Gallen Kamp REGD, Model: OV, England) and preserve into two different air-tight jars.
All reagents utilized were AR grade. All glassware utilized were pre-washed with detergent water solution and washed with tap water and rinsed with deionized distilled water. All the solutions were prepared in deionized water. The stock standard solution of chromium (VI) of 1000 ppm was prepared dissolving 2.8287 g of K2Cr2O7 in deionized water in a 1000 ml volumetric flask. The solution were preserved in refrigerator. The working standard solutions of different ppm were prepared by appropriate dilution of the stock standard solution with deionized water and used within 1 day.
2.2 Preparation of calibration curve
For preparation of calibration curve, several solutions of Cr (VI) of different concentrations (0.10 to 1.00 ppm) were prepared by proper dilution of the standard stock solution. Then the solutions were passed through the flame of computer interfaced atomic absorption spectrophotometer (Model: AA-6800, Shimadzu Corporation, Japan). The calibration curve was plotted as absorbance versus concentration of Cr (VI).
Figure 1: Standard calibration curve
For the removal of Cr (VI) from aqueous solution, particular amount of adsorbents were added to 100 ml Cr (VI) solution in a 250 conical flask. They were shaken for a certain period in a rotary shaker (Model: SH-N110, China).
After that (adsorption) the solution was filtered through Whatman 42 filter paper. Equilibrium Cr (VI) concentration y = 0.1579x - 0.0006
R² = 0.9972
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18
0 0.2 0.4 0.6 0.8 1 1.2
Absorbance
Concentration of Cr (VI), ppm
47 was determined by atomic absorption spectrophotometer. The removal of Cr (VI) is expressed in percentage by the following equation (1).
% Removal =Co−Ca
Co × 100 (1) Where, Co = initial centration of Cr (VI) and Ca = concentration of Cr (VI) after adsorption.
Five types of sawdust were primarily used individually to check their performance as adsorbent in removing Cr (VI) from aqueous solution. These were date palm (phoenix dactylityfera), sissoo (dalbergia sissoo), neem (azadirachta indica), shimul (cotton tree, bombax ceiba) and jackfruit (artocarpus heterophyllus). Among them, date palm and shimul sawdust were the best and were selected for the next experiments. The effects of various parameters such as contact time, dose of adsorbent, initial concentration and pH were studied. Batch experiments were carried out for adsorption and desorption of Cr (VI) from adsorbents.
3. Results and discussion 3.1 Adsorbent selection
Five different sawdusts were applied for removal of Cr (VI) from aqueous solution under same conditions. They were date palm, sissoo, neem, shimul and jackfruit. Among them date palm sawdust and shimul sawdust showed higher removal efficiencies which were more than 82% (cf. figure 2). The other adsorbents had removal efficiencies less than 50%. Bio-sorbents prepared from agricultural wastes have insoluble organic compounds and poly functional groups such as -NH2, -COO-, =C=O, -OH- and PO42-. These ions interact with Cr (VI) ions through the electrostatic force of attraction due to which the bio-sorbent have effective potential for the removal of Cr (VI) and other pollutants from water [11].
Figure 2: Hexavalent chromium adsorption efficiency of different sawdust.
3.2 Effect of contact time
The contact time is observed to be an important parameter for adsorption of Cr (VI) on sawdust. The figure 3 (a) depicts the effect of contact time on the adsorption of chromium on sawdust from aqueous solution. It is revealed that, increasing contact time increases the removal efficiency but at a certain time the percentage removal becomes almost constant. As shown in figure 3 the percentages removal at a contact time of 30 min were 70.7% and 68.4% for date and shimul sawdusts respectively. These were increased to 83.9% and 80.0% as time passed to 60 min. Therefore, the equilibrium time for the removal of hexavalent chromium from aqueous solution by sawdust is taken as 60 min.
Similar result was reported using activated coffee husk [3].
3.3 Effect of adsorbent dose
Different doses of adsorbent (5, 10, 15, 20, 40, 60 and 80 g/L) were introduced in different solutions of chromium of same volume and same initial concentration. The amount of adsorption increases with the dose of adsorbent and after a certain dose (20 g/L), adsorption does not increase significantly (figure 3 (b)). The increase of adsorption seems that,
0 20 40 60 80 100
Date sawdust
Sisso sawdust
Neem sawdust
Shimul sawdust
Jackfruit sawdust
% Removal of Cr (VI)
48 there are still active sites on the surface of the adsorbent that are unsaturated [12]. The rate of increment is significantly high up to (20 g/L) after which it decreases.
Figure 3: Effect of (a) contact time, (b) adsorbent dose on the removal of Cr (VI) 3.4 Effect of initial concentration
It has been observed that the percentage of adsorption decreases with the increase of initial concentration of adsorbate (figure 4). But the uptake capacity increases with initial concentration of adsorbate. This may be due to the higher availability of Cr (VI) in the solution. Moreover, higher initial adsorbate concentration provides higher driving force to overcome all mass transfer resistance of metal ion from the aqueous solution to the solid phase resulting in higher probability of collision between Cr (VI) ions and the active sites. Removal capacity slightly decreases up to 50 ppm initial adsorbate concentration for both date and shimul sawdust and after that decreases significantly. It is noticeable that the uptake of date sawdust becomes less than that of shimul sawdust after 50 ppm chromium concentration.
Figure 4: Effect of (a) initial concentration of hexavalent chromium and (b) pH on the removal of Cr (VI)
3.5 Effect of pH
The pH of aqueous solution is an important parameter in the adsorption process. pH affects the surface charge of the adsorbent, and degree of ionization and specification of the adsorbed species [13]. In order to study the effect of pH on the adsorption of Cr (VI) using date and shimul sawdusts as adsorbent, different batch processes were carried out in the range of pH 1.0 to 11.0. The figure 4 (b) shows that the removal of chromium is more or less similar up to pH 4.0 and after that the value decreases rapidly for date sawdust but for shimul sawdust after 5.0.The removal of Cr (VI) were 85% and 83% for date and shimul sawdusts at pH 4.0. At pH 8.0 and then up to 11.0 the adsorption for both sawdusts is less than 40%.
0 20 40 60 80 100
0 25 50 75 100 125 150 175 200
% Removal of Cr (VI)
Contact time, min Date sawdust Shimul sawdust
0 20 40 60 80 100
0 10 20 30 40 50 60 70 80 90
% Removal of Cr (VI)
Adsorbent dose, g/100ml Date sawdust Shimul sawdust
0 20 40 60 80 100
0 25 50 75 100 125
% Removal of Cr (VI)
Initial concentration, ppm Date sawdust Shimul sawdust
0 20 40 60 80 100
0 3 6 9 12
% Removal of Cr (VI)
pH
Date sawdust Shimul sawdust
(a) (b)
(a) (b)
49 Figure 5: Desorption of adsorbed Cr (VI) with (a) desorbing agents and (b) concentration of NaOH solution.
3.6 Desorption
Regeneration of adsorbent for repeated use is of crucial importance in industrial practice. Experiments were conducted for regenerating sawdust using various desorbing agents such as HCl, HNO3, NaOH and Na2CO3 solution. The elution efficiency of these desorbing agents is shown in the figure 5.
The result obtained indicates that, the desorbing capacity of acid solution is very less than that of basic solution. Here NaOH solution shows highest elution efficiency, 76% for date sawdust and 81% for shimul sawdust. The elution efficiency of NaOH solution increases with increasing its concentration and it becomes maximum at 2.0 N. This indicates the possibility of reusing the spent adsorbent.
4. Conclusion
In this work, date sawdust and shimul sawdust were applied for the removal of Cr (VI) from water. It is concluded from this work that: the date sawdust and shimul sawdust can be effective adsorbents for the removal of Cr (VI) from aqueous solutions. Here date sawdust exhibits higher activity than shimul sawdust. Date sawdust and shimul sawdust as adsorbent can be compared with well-recognized adsorbent activated carbon as well as others in economical respect.
This adsorbent can be regenerated and reused. Moreover, sawdust is sawmill as well as industrial waste that has been directed as a wealth in the treatment of waste water. In the context of present environmental situation, new pathway might be opened in the whole range of contaminant removal from waste water.
Acknowledgements
Authors wish to acknowledge to the Department of Applied Chemistry and Chemical Engineering, University of Rajshahi, Bangladesh for providing analytical facilities and logistic supports during the working periods.
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0 20 40 60 80 100
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