Removal of Cr(VI) from synthetic wastewater by adsorption onto coffee ground and mixed waste tea

We attempted to recycle mixed waste tea and coffee ground as alternative low-cost adsorbents for Cr(Vl) removal. The adsorption parameters optimized were: initial Cr(VI) concentration (10-30 mg L-1), contact time (180 min), adsorbent dose (2.0 g L-1), initial pH (2.0), temperature (30-50 degrees C), and agitation speed (250 rpm). Freundlich isotherm was found better fitted with a high correlation coefficient (R-2 = 0.97 for mixed waste tea and 0.92 for coffee ground) than to Langmuir model (R-2 = 0.89 for mixed waste tea and 0.86 for coffee ground) for the 10-250 mg L-1 concentration range. Analysis of kinetic studies indicated that Cr(VI) adsorption by both adsorbents was consistent with the pseudo-second-order kinetic model with a good R-2 and Marquardt's present standard deviation (MPSD) values. Experimental data demonstrated a sorption capacity of 94.34 mg g(-1) of mixed waste tea and 87.72 mg g(-1) of coffee ground. Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Energy dispersive Xray spectroscopy (EDS) revealed the noticeable chromium accumulation on the adsorbent surfaces after adsorption. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) studies showed that carbon and oxygen functional groups on the surface of both adsorbents involved in Cr(VI) adsorption. The adsorbents could be reused four times. Large-scale operation using 100 L of packed-bed reactor showed the breakthrough time of adsorption for mixed waste tea of 30 min in 100 mg L-1 Cr(VI) concentration. These results suggested that mixed waste tea and coffee ground be considered as alternative adsorbent for Cr(VI) removal. (C) 2019 Elsevier Ltd. All rights reserved.