Removal of hexavalent and total chromium from aqueous solution by avocado shell

The main aim of this work was to evaluate the potential of Hass avocado (Persea americana Mill var. 'Hass') shell to remove hexavalent chromium [Cr(VI)] and total chromium from aqueous solutions. Results showed that avocado shell removed Cr(VI) by two different mechanisms: chromium biosorption and bioreduction of Cr(VI) to Cr(III). The capacity for removing Cr(VI) and total chromium gradually increased as the contact time proceeded, reaching values of 101.81 and 61.67 mg g^-1 respectively, after 120 h. The opposite behavior was observed concerning the volumetric rates of Cr(VI) and total chromium removal. The pseudo-second order model adequately described the kinetic process of chromium biosorption by avocado shell, which suggests that this process chiefly occurs as a result of chemisorption.