Abstract:
We investigated the potential of two different types of biochars (BCs), a waste by product from a Dendro
bioenergy industry (DBC) and a steam activated rice husk derived biochar (SRBC) to remove glyphosate from
aqueous media. Equilibrium isotherms and kinetics experiments were conducted to study the adsorption behaviour
and postulate potential mechanisms. Glyphosate adsorption on both BCs was strongly pH dependent, exhibiting
maximum on DBC and SRBC at 5-6 and 2-4 pH, respectively. Isotherm data obtained for DBC adsorption was best
fitted to Freundlich and Temkin models indicating a multilayer adsorption, whereas glyphosate adsorption on SRBC
was well described by Freundlich and Langmuir models suggesting both physisorption and chemisorption
mechanisms for the adsorption process. The Langmuir maximum adsorption capacity of DBC and SRBC was 44.00
and 123.03 mg/g, respectively. The kinetics of glyphosate adsorption on DBC were best described by pseudosecond
order mode indicating that the rate limiting step can possibly be a chemical adsorption, while pseudo-first
order model described kinetics of glyphosate adsorption on SRBC indicating physisorption interactions for
glyphosate adsorption. Pore diffusion, π*-π electron donor-acceptor interactions and H-bonding were postulated to
be involved in physisorption, whereas electrophilic interactions led to chemisorption type of adsorption for both
DBC and SRBC. Overall, both DBC and SRBC could be a promising remedy of glyphosate removal from aqueous
solution.
