Investigating the effect of activating agents on removal of lead ions from water using activated rice husk carbon

Abstract

Activated carbon is very important in treating polluted water. Carbon can be produced from locally sourced agricultural waste. This helps in reducing the amount of agricultural waste in the environment. This study investigated the effect of activating agents on removal of Pb2+ ions from water using activated rice husk carbon. Chemical activation method was used where rice husk carbon (RHC) was impregnated with chemical activating agents before heating. Three distinct activating agents were used namely; potassium hydroxide (KOH), phosphoric acid (H3PO4) and zinc chloride (ZnCl2). RHC activated with a 7.5% concentration of KOH using 5g/L adsorbent showed 99.9% efficiency in removing lead ions, almost achieving complete elimination. RHC activated with 1% ZnCl2 while using 20g/L adsorbent demonstrated 98.5% removal efficiency, just 1.36% less than the RHC activated with 7.5% KOH. RHC activated with 2.5% H3PO4 while using 20g/L adsorbent showed 84.1% removal efficiency, making it least effective among the three agents tested at their optimal levels. Despite achieving removal efficiencies of 98.5% and 84.1%, RHC activated with ZnCl2 and H3PO4, respectively, required a higher adsorbent dosage (20 g/L), indicating lower effectiveness compared to KOH-activated carbon. KOH activation created a highly porous and rough surface with a well-developed network of interconnected pores. On the other hand, ZnCl2 and H3PO4 resulted in less aggressive pore formation and different surface morphologies, leading to less interconnected and less rough porous structures. It was observed that the uptake of Pb²⁺ ions by activated RHC aligns more accurately with the Langmuir isotherm model.