Vanadium removal and recovery from aqueous solution with repeated use of a KOH modified seaweed biochar adsorbent: characterisation and removal mechanisms.

BACKGROUND: Vanadium (V) is a critical raw material which is extensively used in metallurgical, aerospace and chemical industries. However, V-enriched wastewaters pose risks to human and environmental health due to their tendency to persist and bioaccumulate. Active V treatment processes generate significant quantities of byproducts with associated high operating costs and there is a need therefore to investigate novel passive technologies such as biosorption. This study investigates the capacity and reusability of KOH-modified seaweed biochar (BC_KOH) to (re-)adsorb, desorb and recover V, and evaluates the influences of initial V concentration, contact time, solution temperature and pH. RESULTS: The maximum uptake of 48.8 mg V g⁻¹ BC_KOH occurred within 75 min and followed an exothermic adsorption process best described by the Langmuir isotherm model. The magnitude of enthalpy change suggested a physisorption binding interaction with optimum uptake in the range pH 3.5–4.5. Introduction of a saline content (100–400 mg Na⁺ L⁻¹) into the adsorption solution resulted in a modest reduction in the V adsorption level by BC_KOH but further increases in saline concentration thereafter had only limited impact. Successive V(V) adsorption/desorption cycles indicated that V(V) binding to BC_KOH displays effective reversibility with the adsorbent material demonstrating good regeneration characteristics. CONCLUSION: BC_KOH offers clear potential to be used as a cost-effective passive and robust adsorbent of V within a range of acidic industrial waste streams. The capacity of the biochar to desorb and re-adsorb demonstrates high V recovery potential and excellent biochar regeneration capability.