Assessment of Cactus Biosorption Potential in The Removal of Hexachromium Ions from Synthetic and Tannery Waste Water

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Addis Ababa University


Chromium (VI) is environmentally mobile owing to its high solubility in water. Its pollution is largely attributed by discharge of inadequately treated effluents of chrome utilizing industries. Discharges of such effluents pose a potential threat to human health unless are treated properly before its disposal. Adsorption using activated carbon prepared from biomaterials is a new technology for the treatment of heavy metals rich industrial effluents. Opuntia Ficus Indicus (OFI) activated with H3PO4 (45%) was evaluated for Cr (VI) removal capability from both synthetic and tannery waste water. The present work was aimed at assessing the biosorbent capability of OFI in removal of Cr (VI) from synthetic aqueous solution and tannery waste water. OFI was activated with H3PO4 (45%) and carbonized at 450 o C in muffle furnace for 1hr and its different physical properties such as bulk density and moisture content was determined. Besides; the sorbent characterized by FTIR spectroscopy test analysis before and after adsorption processes, suggested possible key contributions of hydroxyls and carboxyls in the sequestering of Cr(VI) on OFI. Maximum Cr(VI) removal efficiency of 99.5% was achieved by OFI under different study parameters. The percentage removal of Cr (VI) ions increased with increase of the amount of sorbent concentration for which the Optimum removal of Cr (VI) was observed at sorbent dose of 125 mg. The adsorption efficiency of Cr (VI) on OFI was increased at low pH values between 2 and 3, attending its optimum at pH of 2. Percentage removal was observed to increase, while decreasing the initial concentration of Cr (VI) to which 6mg/l was the minimum of adsorption system. Whereas; the removal was increased with increasing the agitating speed and its corresponding contact time, whereby; the optimal adsorption reached at 60 minutes at 150rpm agitating speed. Both Langmuir and Freundlich models and followed adsorption process with high regression correlation coefficient (R 2 ) values of 0.999 and 0.956 respectively. But, Langmuir isotherm with higher R 2 was best fitted to the experimental values, with monolayer adsorption capacity of 4.587mg/l. Besides; the RL values were obtained in range of 0 < RL < 1 that confirmed the favorability of adsorption process. The optimized parameters were applied to the real waste water resulted in 88.7% of optimal adsorption removal efficiency. The reduction in percentage of removal might be due the matrix effect of the competing ions present the chrome liquor spent. Adsorbent used in present study was prepared at laboratory scale and observed to hold distinct position for its efficient removal of Cr (VI) both from synthetic aqueous solution and tannery waste water and could be an alternative promising plant based biosorbent in field.



Adsorption, Sorbent, Opuntia- Ficus Indicus, Langmuir-Freundlich Isotherm Models