Encapsulation of a powdery spinel-type Li⁺ ion sieve derived from biogenic manganese oxide in alginate beads

A powdery lithium ion sieve (HMO) derived from biogenic birnessite was homogeneously integrated in sodium alginate (AL) beads. The composite beads were then characterized and their Li⁺ adsorption properties were investigated. Scanning electron microscopy–energy dispersive spectroscopy analysis showed that the HMO particles were homogeneously dispersed in the AL beads even after drying. The adsorption isotherm of Li⁺ adsorption to HMO encapsulated in AL beads (HMO–AL) was well fitted by the linear Langmuir model, and the beads showed a maximum adsorption capacity of 3.61 mmol/g based on HMO, which is comparable with the value of the original powdery HMO. Kinetic studies revealed that adsorption of Li⁺ follows a pseudo-second-order model with rate constant k₂ = 2.8–11.9 × 10^− 3 g/(mmol min) for the initial Li⁺ concentration range 2.56–4.23 mM. Diffusion of Li⁺ from aqueous solution to the HMO particle through the Ca–AL network is the rate-limiting step for Li⁺ adsorption to HMO–AL beads. The HMO-AL beads enhanced the handling efficiency for Li⁺ adsorption and reused without significant reduction of Li⁺ adsorption efficacy.