Unraveling sorption of lead in aqueous solutions by chemically modified biochar derived from coconut fiber: A microscopic and spectroscopic investigation.

In this study, we examined the efficacy of nine different types of coconut-fiber derived biochars (CFBs), prepared at different temperatures and chemically modified with ammonia, hydrogen peroxide and nitric acid, to remove lead (Pb 2 + ) from aqueous solutions. Langmuir- q m values of the biochars pyrolyzed at 300 °C and modified with ammonia and nitric acid increased from 49.5 to 105.5 and 85.2 mg g − 1 , respectively, compared to control (unmodified), whereas hydrogen peroxide treatment had no effect. The maximum amount of Pb adsorbed on biochars was in the order of CFB-700 > MCFB-300-NH 3 ·H 2 O > CFB-500 > MCFB-300-HNO 3 > CFB-300. X-ray absorption fine structure (XAFS) spectroscopy results revealed that Pb-montmorillonite, Pb(C 2 H 3 O 2 ) 2 , PbSO 4 , Pb-Al 2 O 3 and Pb 3 (PO 4 ) 2 were the five most important Pb species observed in Pb-loaded biochars, and as such, favoring Pb immobilization in aqueous solutions. Overall, the sorption capacity of CFBs pyrolyzed at 300 °C substantially increased for Pb 2 + with ammonia and nitric acid modification. However, these chemical modifications did not improve the sorption of Pb on CFBs pyrolyzed at temperatures ≥ 500 °C, thereby highlighting a temperature dependent response of chemically modified biochars to Pb sorption in this study. [ABSTRACT FROM AUTHOR]