Magnetic bio-activated carbon production from lignin via a streamlined process and its use in phosphate removal from aqueous solutions

Abstract

Lignin and ferrous salt were mechanically mixed, melted, carbonized and steam activated to produce magnetic bio-activated carbons (MBACs). Phosphate adsorption capacity measurement was conducted on representative MBAC, which has a high surface iron oxide proportion and mesoporous volume. The results indicate that iron species are embedded into the carbon matrix by lignin melting. Steam is not only an activation agent for pore generation and widening but is also effective for the oxidization of Hagg iron carbide produced via ferrous salt decomposition and subsequent reduction during the carbonization process to form magnetite. The porous and magnetic properties and surface iron oxide content of the produced MBACs can be modified by controlling the steam/magnetic biochar (MBC) ratio. The MBAC production process is streamlined and novel, compared with conventional coprecipitation or impregnation methods. The maximum phosphate adsorption onto the representative MBAC product using the best fitting model, i.e., the Langmuir-Freundlich model, is estimated to be 21.18 mg/g, suggesting that the representative MBAC product has a comparable phosphate adsorption capacity to most of the reported MBCs and MBACs.

Keywords: Lignin; Magnetic bio-activated carbon; Melting; Phosphate adsorption; Steam activation.