Almond Shell-Derived Biochar for Lead Adsorption: Comparative Study of Pyrolysis Techniques and Sorption Capacities

Area of Science:

• Environmental Science
• Materials Science
• Water Treatment

Background:

• Lead (Pb(II)) contamination in water presents significant environmental and health hazards.
• Biochar derived from agricultural waste is a promising adsorbent for heavy metal removal.

Purpose of the Study:

• To compare the structural properties and Pb(II) adsorption performance of almond shell biochars produced via slow pyrolysis (SP) and microwave pyrolysis (MW).
• To evaluate the impact of KOH activation on biochar characteristics and lead adsorption efficiency.

Main Methods:

• Biochar production using slow pyrolysis (SP) and microwave pyrolysis (MW), with and without KOH activation.
• Characterization of biochars using proximate analysis, elemental analysis, BET surface area, and FTIR spectroscopy.
• Adsorption experiments including pH dependence, kinetics, and equilibrium isotherms for Pb(II) removal.

Main Results:

• Non-activated SP biochar exhibited the highest surface area (693 m²·g^-1) and mesoporosity, leading to superior Pb(II) adsorption capacities.
• KOH activation degraded textural properties and led to pore collapse in MW biochars, while increasing surface hydroxyl content.
• Adsorption followed Freundlich and Redlich-Peterson models, indicating heterogeneous adsorption sites. Optimal Pb(II) removal occurred at pH 4.

Conclusions:

• Non-activated almond shell biochar produced by slow pyrolysis is the most effective, sustainable, and low-cost material for Pb(II) removal from water.
• Avoiding aggressive chemical activation maximizes adsorption performance and avoids issues like high post-adsorption pH.
• This biochar presents a viable solution for mitigating lead contamination in aquatic environments.