Facile Synthesis of Calcite-Impregnated Hydrochar with High Sorption Capacity for Cu(II) from Aqueous Solution

Calcite-impregnated hydrochar (Ca-HC) was successfully synthesized by a one-step hydrothermal method and used as an adsorbent for Cu(II) remediation. Characterization techniques showed that Ca-HC contained calcite and oxygen-containing functional groups. A series of Cu(II) sorption experiments onto Ca-HC showed that the initial Cu(II) concentration, contact time, sorption temperature, and initial pH of the solution influenced the sorption of Cu(II). The actual achievable sorption capacity of Ca-HC for Cu(II) was 130.57 mg g^-1 at 303 K, and the sorption process obeyed the Langmuir model and pseudo-second-order kinetic equation. The precipitation and surface complexation rather than ion exchange were mainly ascribed to the removal of Cu(II) onto Ca-HC. The calcite provided the active site to produce posnjakite precipitation during the sorption process and enhance the sorption capacity of the hydrochar. Therefore, these results demonstrated that Ca-HC is an effective sorbent that can remove Cu(II) from water.