In this study, we try to find possible solutions to synchronously solving energy and environmental problems. In our design, orange peel is used as a carbon source to synthesize low-cost Fe3O4/C composites, which are employed as adsorbents to purify Cr(VI)-contaminated water. After that, these Cr(VI)-laden Fe3O4/C composites are used and tested as anodes in potassium-ion batteries. It is found that their K-storage capacity is more than 300 mAh g(-1) at a current density of 0.1 A g(-1), depending on the mass con tent of Fe3O4. The more Fe3O4 component in composite, the more adsorbed Cr(VI) species through chemisorption, and the larger K-storage capacity. The good electrical conductivity of cabon-based anodes endows them with superior rate performance. At current densities of 0.1, 0.5, 1 and 2 A g(-1), K-storage capacity amounts to 357.8, 316.3, 276.3 and 236.8 mAh g(-1), respectively. The reuse of contaminant-laden adsorbents as anodes will shed new light on the disposal of exhausted adsorbents after water treatment and development of anode materials for secondary batteries. (C) 2020 Elsevier Inc. All rights reserved.