Removal of hexavalent chromium from water using hydrochar obtained with different types of feedstock

Hydrochar (HC) was obtained through the hydrothermal digestion of beetroot, carrot, or spent coffee grounds. The yield (i.e., mass of HC produced per mass of feedstock used) was [approximately equal to]80%, [approximately equal to]20%, and [approximately equal to]50% with spent coffee, carrot, and beetroot, respectively. The surface area determined with the Brunauer-Emmett-Teller method was 3.06 [m.sup.2] * [g.sup.-1] for HC from beetroot, 1.19 [m.sup.2] * [g.sup.-1] for HC from carrot, 2.84 [m.sup.2] * [g.sup.-1] for HC from dark roast coffee, and 3.22 [m.sup.2] * [g.sup.-1] for HC from original roast coffee. Fourier transform infrared spectroscopy experiments showed that amine groups had a significantly higher density in HC produced with spent coffee grounds than that produced using either beetroot or carrot. HC could sorb hexavalent chromium (Cr(VI)) from water. The concentration of Cr(VI) in water decreased from 0.3 ppm to [approximately equal to]0.07 ppm and to [approximately equal to]0.1 ppm within 90 min using 20 g * [L.sup.-1] of HC made from spent coffee grounds and from beetroot and carrot, respectively. Key words: hydrochar, sorption, hexavalent chromium (Cr(VI)), water treatment. L'hydrochar (HC) a ete produit par digestion hydrothermale de betteraves, de carottes ou de grains de cafe uses. Le rendement (c.-a-d. la masse d'HC produite par poids de matiere premiere utilisee) etait de [approximately equal to]80, [approximately equal to]20 et [approximately equal to]50 % avec le cafe use, la carotte et la betterave, respectivement. La superficie determinee selon la methode Brunauer-Emmett-Teller etait de 3,06 [m.sup.2] * [g.sup.-1] pour l'HC obtenu a partir de betteraves, de 1,19 [m.sup.2]-g_1 pour l'HC a partir de carottes, de 2,84 [m.sup.2] * [g.sup.-1] pour l'HC a partir de cafe torrefie fonce et de 3,22 [m.sup.2] * [g.sup.-1] pour l'HC a partir de cafe torrefie original. Les experiences de spectroscopie infrarouge a transformee de Fourier ont montre que les groupes d'amines avaient une densite significativement plus elevee dans l'HC produit avec des grains de cafe uses que dans l'HC produit avec de la betterave ou de la carotte. L'HC pouvait sorber le chrome hexavalent (Cr(VI)) present dans l'eau. La concentration de Cr(VI) dans l'eau a diminue de 0,3 ppm a 0,07 ppm et a 0,1 ppm en 90 min, en utilisant 20 g * [L.sup.-1] d'HC a base de grains de cafe uses et de betterave et de carotte, respectivement. [Traduit par la Redaction] Mots-cles: hydrochar, sorption, chrome hexavalent (Cr(VI)), traitement de l'eau.
1. Introduction Hexavalent chromium (Cr(VI)) is highly toxic. If inhaled, Cr(VI) can cause acute toxic effects, including ulceration of the nasal septum and asthma. If ingested, Cr(VI) may adversely affect [...]