Rare earth elements are strategic resources with diverse applications. However, during mining, wastewater rich in these elements is generated, leading to the loss of valuable rare-earth resources and poses a significant environmental threat. Therefore, a sustainable strategy for recycling rare earth elements from secondary sources is essential. This study developed a carboxymethylcellulose-based porous hydrogel adsorbent, termed ACMN, functionalized with an amidoxime group using a Pickering emulsion stabilized by waste oyster shell powder. The ability of ACMN to adsorb Gd