Hydrothermal carbonization method was used to produce different hydrochars from chestnut outer shell at various temperatures while resolving the environmental issues of agricultural bio-waste. Hydrochars were adopted as adsorbents to remove heavy metal ions (copper and zinc ions) from aqueous solution. Hydrochar samples were characterized by Scanning Electron Microscope (SEM), Fourier Transform Infrared (FTIR), and Brunauer–Emmett–Teller (BET) nitrogen adsorption–desorption isotherm. An increase in the hydrothermal temperature from 160 °C to 220 °C results in higher BET surface area (18.81 m² g⁻¹) and the porosity of the samples. The resultant hydrochar at 220 °C exhibited a more excellent adsorption performance (8.13 mg g⁻¹ for copper nitrate) than the other two hydrochars at low hydrothermal temperature. The current study addressed the influence of interfering anions of nitrates, sulfates and chlorides on the adsorption performance. The result shows that the hydrochar possesses larger removal efficiency for heavy metal nitrates that that of chlorides and sulfates.