Sorption of Cr(III) and Cr(VI) to K 2 Mn 4 O 9 nanomaterial a study of the effect of pH, time, temperature and interferences

Abstract

A Rancieite type material (K2Mn4O9) nanomaterial was synthesized and tested for the removal of chromium (III) and chromium (VI) from aqueous solutions. The synthesized nanomaterial was characterized using powder XRD and SEM. XRD showed weak diffraction peaks at only at the angles associated with K2Mn4O9. The SEM corroborated that the nanoparticles were present; however, the nanoparticles were clustered into larger aggregates. Batch studies were performed to determine the optimum pH, capacity, time dependency, interferences, and the thermodynamics of the binding. The optimum pH for the binding of Cr(III) and Cr(VI) were determined to be pH 5 and pH 2, respectively. Isotherm studies were performed at temperatures of 4 , 25 , and 45 for Cr(III) and Cr(VI) and showed binding capacities of 21.7 mg/g, 36.5 mg/g, 41.8 mg/g for Cr(III). The Cr(VI) binding capacities were 4.22 mg/g, 4.08 mg/g, and 3.25 mg/g at the respective temperatures. The thermodynamic studies showed that the binding processes for the reactions were spontaneous and endothermic, with a ΔH was 17.54 kJ/mol for Cr(III) and 6.05 kJ/mol for Cr(VI). The of sorption for Cr(III) were determined to be −3.88 kJ/mol, −5.83 kJ/mol and −7.03 kJ/mol at the aforementioned temperatures. The ΔG values for the Cr(VI) sorption were determined to be −4.89 kJ/mol, −5.64 kJ/mol, and −6.05 kJ/mol. In addition, the ΔS values for Cr(III) and Cr(VI) were determined to be 77.92 J/mol and 39.49 J/mol, respectively. The thermodynamics indicate that the binding of Cr(III) and Cr(VI) is spontaneous and endothermic.

Chromium removal from contaminated waters using nanomaterials – A review

“…Other studies were performed approximately at 30ºC [39,48,49,51,[58][59][60][61][62][63], at 35ºC [37], and even at 40ºC [64,65] most likely ajusting to the natural conditions existing in warmer countries. Apart from the cases described by [8,9,39,66,67], efficiency of chromium sorption increases with temperature.…”

“…Numerous studies have been published on chromium sorption in aqueous phase using various materials and in particular synthetic nanomaterials [9,[35][36][37][38][39]. To select the articles For each selected article, it was extracted the information related to the parameters considered relevant in sorption [7][8][9]: name and nature of the sorbent, mass of the sorbent with respect to the water volume, type of water used in the experiment, type of experiment (single or other contaminants besides chromium), pH, temperature, contact time between the sorbent and the solution, initial concentration of chromium, chromium species initially present in solution, and removal efficiency. Table 2 lists the synthetic nanomaterials and the experimental conditions employed in the studies of the selected articles from the literature.…”

“…Among the various materials used for chromium removal, nanoparticles have been the most common, either using just the core nanoparticles [9,[40][41][42][43][44][45][46], nanoparticles with functionalization [35,[47][48][49], or modified nanoparticles incorporated on substrates [36,50]. Other type of materials have been used, such as nanocomposites [37,51,52], nanofibers [38] and carbon nanotubes [39].…”

“…Interactions with other elements. Most of the studies mentioned in Table 2 describe the chromium sorption experiments using mono-elemental systems, Cr being the only M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 9 contaminant to be treated. Only a few studies tested both mono-elemental and multielemental systems.…”

“…pH. Removal of Cr(VI) was tested at pH from 2 to 3 [9,39,[42][43][44]66,69], although some authors have been studied the removal at more realist pH interval, 5-8 [40,70], which is the pH found in actual industrial effluent. Values of optimal pH in the removal of Cr(III) were between 5 and 7 [9,38,42,48,51,71].…”