The use of iron-based disposable-chemical-warmer (DCW) produces huge amount of solid wastes every year (e.g. at least 2 million tons of solid waste every year for China and Japan only), which are directly abandoned as trash now. In this work, spent DCW was recycled as adsorbent for As(V) removal from water. For the first time, we elucidated that the spent DCW was a magnetic nanocomposite consisted mainly of Fe₃O₄ nanoparticles and vermiculite with large surface area (56.6 m²/g). The detailed morphology characterization revealed the formation of Fe₃O₄ nanoparticles on vermiculite's surface, with the average crystallites’ size estimated to be ~10 nm. The adsorbent exhibited superparamagnetism with a strong saturation magnetization value 40 emu /g, which can be utilized to recollect the adsorbent after water treatment. The As(V) adsorption isotherm conformed to Langmuir isotherm model with the maximum adsorption capacity of 130 mg/g under neutral pH and room temperature. The adsorption capacity for As(V) outperformed most of the reported adsorbents, which was attributed to the hybrid structure of the adsorbent. The adsorption kinetic curve was well described by the pseudo-second order model. The favorable pH for As(V) was below 8.0, and the adsorbent had good As(V) selectivity over common co-existing anions (SO₄²⁻, H₂PO₄⁻, and SiO₃²⁻). Moreover, the adsorbent could be readily regenerated using 0.1 M NaOH aqueous solution as eluting solution. The adsorption capacity towards As(V) was still over 85% after 10 consecutive adsorption-desorption cycles. This work provided an efficient way for recycling spent DCW with minimal efforts.