Cellulose Based Bio-Adsorbents for Removal of Chromium (Cr)

Increased use of heavy metals in production has caused a rise in pollution due to metal-based industries such as mining metal, smelting, and foundries. Chromium specifically has been found to have adverse health effects such as DNA damage, neurotoxicity, and cancer. Our goal is to remove chromium from water by using an environmentally friendly adsorbent based on biochar. All the biochar adsorbents prepared are cellulose based. First, cellulose is converted to biochar using hydrothermal carbonization which uses water as a green solvent. Biochar is then impregnated with potassium hydroxide (KOH) at varying concentrations. This impregnated biochar is then activated at 700, 750, 800, 850 Celsius and is labeled as one-step activation. A two-step activation is also prepared, by first taking the cellulose biochar and activating it at 1000 Celsius in an inert atmosphere (nitrogen). Once thermally activated, chemical activation of this biochar then follows the same procedure as the one step activation The adsorption capacity of each one of these different bio-adsorbents was then tested by setting up adsorptions at a concentration of 1.5g/L of the bio-adsorbent in chromium solutions (50, 100 and 200 ppm) both with an adjusted pH of 2 (the experimentally determined point of zero charge, PZC where theoretically adsorption should work best) and a non-adjusted pH (at neutral pH). Once the adsorption is complete after 24 hours, the solution was analyzed with a flame atomic adsorption spectrometer (FAAS). It was observed that as activation temperature increased, adsorption capacity of all bio-adsorbents increased. Comparison between the one step and two step activation, it was seen that at neutral unadjusted pH, two step activation produced better results than 1-step. However, at the PZC (pH 2), the reverse was true: 1-step activation did significantly better than the two step activation. When comparing the two methods at pH2, one-step activation fares better than 2-step at all chromium concentrations.