Production and characterization of adsorbents from a hydrothermal char by pyrolysis, carbon dioxide and steam activation

Adsorbents for wastewater treatment were produced from industrially obtained hydrochars using pyrolysis, CO 2 , and steam activation. Both pyrolysis and CO2 activation were studied between 400 to 900 °C, with a holding time of 1 or 2 h. Steam activation was carried out between 600 to 900 °C for a holding time of 2 h. Pyrolysis, CO 2, and steam activation yields were in the ranges of 44–72, 26–51, and 14–59 wt.%, respectively. The best performing adsorbents based on phenol and methylene blue removal were obtained at 800 °C and a 2-h holding time with the three gases (N 2 , CO 2 , steam). Steam activation of hydrochar provided the best adsorbent with maximum capacities of 179 and 167 mg g −1 toward methylene blue and phenol. The maximum Brunauer–Emmett–Teller (BET) surface area of the product was 593 m 2 g −1 with an average pore size diameter of 4.38 nm and a total pore volume of 0.651 cm 3 g −1 . This study shows that adsorbents derived from hydrochar can be used for wastewater remediation, offering a valorization pathway of a waste stream from hydrothermal processes.