Membrane-Filtered Kraft Lignin–Silica Hybrids as Bio-Based Sorbents for Cobalt(II) Ion Recycling

Efficient and sustainable recycling of cobalt­(II) is of increasing importance to support technological development in energy storage and electric vehicle industries. A composite material based on membrane-filtered lignin deposited on nanoporous silica microparticles was found to be an effective and sustainable sorbent for cobalt­(II) removal. This bio-based sorbent exhibited a high sorption capacity, fast kinetics toward cobalt­(II) adsorption, and good reusability. The adsorption capacity was 18 mg Co­(II) per gram of dry adsorbent at room temperature (22 °C) at near-neutral pH, three times higher than that of the summarized capacity of lignin or silica starting materials. The kinetics study showed that 90 min is sufficient for effective cobalt­(II) extraction by the composite sorbent. The pseudo-second-order kinetics and Freundlich isotherm models fitted well with experimentally obtained data and confirmed heterogeneity of adsorption sites. The promising potential of the lignin–silica composites for industrial applications in the cobalt recovering process was confirmed by high values of desorption in mildly acidic solutions.