Abstract
Over the years, water pollution due primarily to the discharge of toxic heavy metals from industrial activities has served as a major challenge in our quest to provide clean drinking water to millions of people across the world. Numerous cheap and environmentally friendly methods and technologies have been developed for the treatment of wastewater contaminated with heavy metals. Key among these technologies is the use of adsorbent as it is the most economical and efficient. In this present study, coconut shells were used to develop microporous adsorbent (activated carbon) through chemical activation by phosphoric acid (H3PO4). An analysis of the effect of various process parameters such as pH, temperature, initial metal ion concentration, adsorbent dose and contact time was conducted through batch adsorption of hexavalent chromium [Cr (VI)] on prepared AC sample. Initial Cr (VI) concentration was investigated through a range of 10 – 50 mg/L with the study showing an optimum concentration for AC of 20 mg/L for percentage removal (93.3%) but adsorption capacity (Qe) was highest for 50 mg/L (4.512 mg/g). The optimum conditions for adsorbent dose, contact time and temperature were determined as 6 g/L, 100 minutes and 30°C respectively for the prepared AC. Maximum adsorption was recorded for pH (2) at 88.2 5% (removal) and 4.41 mg/g (adsorption capacity) for AC. The experimental data obtained were modelled using various isotherms, including adsorption equilibrium isotherms, adsorption kinetic study and adsorption mechanisms with positive correlations (better fit) obtained for Freundlich isotherm, D-R isotherm (slightly), pseudo-second-order kinetic and Boyd models.
Highlights
The presence of hazardous heavy metals and metalloids, especially in aqueous media is an important environmental and social problem
The purpose of this study is to evaluate the suitability of prepared acidimpregnated activated carbon derived from locally sourced coconut shell waste as an adsorbent in the removal of heavy metal ions and evaluate the various mechanisms that control the adsorption process whilst determining the effect of various process parameters such as pH, adsorbent dose, initial metal ion concentration, contact time and temperature on the removal efficiency of the prepared Activated carbons (AC)
The N2 adsorption capacity of the AC400 was determined as 501.5 cc/g
Summary
The presence of hazardous heavy metals and metalloids, especially in aqueous media is an important environmental and social problem. Huge amounts of coconut shells are generated as agricultural wastes in Ghana, which when analyzed show significant lignin (macropores yielding) and cellulose (micropores yielding) dominance. Regardless of these vast quantities of such resources, a significant amount of AC used in the country for both industrial and wastewater treatment is imported from Japan and Germany. The utilization of these low-cost agricultural wastes as carbon precursor is very promising, but their use as metal ion scavenger is rare [3]. The purpose of this study is to evaluate the suitability of prepared acidimpregnated activated carbon derived from locally sourced coconut shell waste as an adsorbent in the removal of heavy metal ions and evaluate the various mechanisms (equilibrium, kinetic and adsorption) that control the adsorption process whilst determining the effect of various process parameters such as pH, adsorbent dose, initial metal ion concentration, contact time and temperature on the removal efficiency of the prepared AC
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