Cactus Potential in Heavy Metal (Pb and Cd) Removal in Water Sample Collected from Rural Area around Adigrat Town

Abstract

The main objective of this study is to investigate the heavy metals (Pb and Cd) removal capability of cactus powder from water sample using FAAS adsorption techniques by considering the influence of contact time, adsorbent dose and temperature on adsorption of Pb and Cd ions by cactus powder. The results revealed that adsorption of Pb and Cd ions increased as the dose of adsorbent increased at a certain limits. The heavy metal removal capability of cactus powder is affected by the present of NaCl salt. The heavy metal removal capability of cactus powder decreased from 65% up to 7% for Pb, and from 70% up to 14% for Cd as the dose of NaCl increased from 1g to 5g. The decrement in the removal of both Pb and Cd ions from water sample with increasing of NaCl is due to the formation of outer sphere complex with the NaCl salt which screening the functional group of cactus powder from heavy metals. The heavy metal removal capability of cactus powder also increased with contact time. The adsorption rate initially increased from 20% to 58 % for Pb ion, and 17% to 43% for Cd ion when the contact time increased from 30-120 min.  After 120 min there was no significant change in heavy metal removal of both Pb and Cd ions.  This might be due to end point at which adsorption phase reached to equilibrium. The percentage removal of Pb by cactus powder decreased from 65.05% to 29% as the temperature increased from 25 ^oC to150 ^oC.  In similar condition, the percentage removal of Cd by cactus powder also decreased from 43% to 31% as the temperature increased from 25 ^oC to150 ^oC.  This decrement in percentage removal of both Pb and Cd ions with increase temperature is due to the weak binding interaction between the active site of cactus powder and (Pb, Cd) ions which support physicosorption process.

Keywords: Cactus Powder, Heavy Metal, Adsorbent, Adsorbate, Dose, Heavy Metal Removal and Active Site.