Ca-Mg-Al LDH-modified wheat straw biochar for efficient lead chemisorption from aqueous solution: Insights from isotherm and kinetic analyses

This study reports layered double hydroxides (LDHs) modified wheat straw biochar (W-B), denoted as (LDH/W-B), asan efficient adsorbent material for removal oflead (Pb2+) ions from aqueous solution. This study also juxtaposes the adsorptive performance ofLDH/W-B with W-B for Pb2+ removal. W-B was prepared via pyrolysis ofwheat straw inamuffle furnace, using acontrolled heating rate of5C per min toreach 600C over aduration ofthree hours. Subsequently, LDH/W-B was synthesised using the co-precipitation method. Both resulting adsorbents were characterised for surface morphology and functional groups bymeans ofscanning electron microscope (SEM) and Fourier transform infrared (FTIR), respectively. The influence ofkey adsorption parameters onthe adsorption efficiency ofW-B and LDH/W-B was systematically evaluated. At60min, the maximum Pb2+ removal efficiency was observed tobe 78.21% for W-B and 92.4% for LDH/W-B. Anincrease inadsorbent dosage from 0.05 to0.7g and atacontact time of1h further enhanced Pb2+ removal, achieving efficiencies of97% for W-B and 99% for LDH/W-B. The optimal conditions for maximum Pb2+ removal were determined tobe 0.3g ofadsorbent (W-B and LDH/W-B), aninitial heavy metal concentration of10mg/L, and acontact time of1h. Pb2+ removal data ofW-B and LDH/W-B best fitted tothe Langmuir isotherm and pseudo-second order kinetic model, which confirmed the dominance ofchemisorption ofPb2+ ions. Additionally, the maximum theoretical adsorption capacity for Pb2+ isclose tothe experimentally obtained values, suggesting that the adsorption ofPb2+ primarily occurs through monolayer formation onthe surface ofboth adsorbents. Overall, this study demonstrates that LDH/W-B isahighly promising adsorbent for Pb2+ removal in wastewater treatment applications.