Effect of bentonite-mineral co-pyrolysis with macroalgae on physicochemical property and dye uptake capacity of bentonite/biochar composite

The effect of bentonite-mineral co-pyrolysis in amounts of 5%, 10%, and 20% with macroalgae (Saccharina japonica; kelp) on the physicochemical property changes and dye adsorption of the bentonite/biochar composite was investigated. Mathematical relations to assess the contribution of mineral and biochar components of the bentonite/biochar composite on cationic, crystal violet (CV) and anionic, Congo red (CR) dye uptake were first developed via comparison with bentonite/biochar blends from stand-alone pyrolysis of kelp and bentonite. Results demonstrated that bentonite was successfully loaded into the biochar matrix, increased mesoporosity (2.67–12.7 nm), and simultaneously enhanced bio-oil (by 7.4%–35%) and biochar yields (by 6.0%–13.6%). The carbon sequestration potential increased by 27% on co-pyrolysis with 5% bentonite with an adsorption capacity value amongst the highest for CV (1275 mg/g); dominated by chemisorption. Mathematical derivations and calculations showed that co-pyrolysis enhanced adsorption capacity contribution of bentonite (f_q,PyB,co > 0) on both dyes. Synergy comparison (r_q,co/sp) between bentonite/biochar composites from the co-pyrolysis and stand-alone pyrolysis were comparable on CR and CV with 20% bentonite but superior for co-pyrolysis (r_q,co/sp=1.79), on CR adsorption with 10% bentonite. Bentonite/biochar composite thus harbor potential as an effective wastewater treatment and carbon sequestration tool.