Application of KOH modified seaweed hydrochar as a biosorbent of Vanadium from aqueous solution: Characterisations, mechanisms and regeneration capacity

Highlights

• KOH modified Ascophyllum nodosum seaweed hydrochar is an effective V(V) adsorbent;

• Weak binding of V(V) to the hydrochar indicates a reversible adsorption process;

• The impact of co-existing cations had negligible impact on uptake of V(V);

• Desorption and re-adsorption results indicate reusable potential for V(V) recovery.

Abstract

Vanadium exists as a mobile and toxic trace metal in many alkaline residue leachates. Its removal and recovery not only reduces a global environmental risk but is also critical to the emergence of innovative technologies and the circular economy. In parallel, the use of treated biomass feedstock is receiving increased attention as a low cost adsorbent for toxic metals in wastewater. This study investigated the adsorption of Vanadium (V) from aqueous solution by KOH modified seaweed (Ascophyllum nodosum) hydrochar (HC_KOH). The results showed that HC_KOH is an effective V(V) adsorbent, achieving maximum uptake of 12.3 mg g⁻¹ at solution pH 4, 60 min contact time and temperature 293 K. The kinetics followed a pseudo second order model with film diffusion controlling the overall adsorption rate. The type I adsorption isotherm was well fitted to a Langmuir model (q_m = 12.3 mg g^-1, R² = 0.970, RMSE = 0.66) and a thermodynamic study indicated that the V(V) adsorption was both exothermic and spontaneous. The low enthalpy change (-10.97 kJ mol⁻¹) indicated a weak binding of V(V) to HC_KOH pointing to the possibility of V recovery. The impact of co-existing cations on V(V) uptake was negligible for Na(I) and Ga (III) but was reduced slightly for Al(III). Desorption and re-adsorption results (3 cycles) indicated that HC_KOH has reusable potential to remove and recover V(V) from waste leachates.