Abstract
Continuous fixed-bed column studies were carried out, utilizing acorn shell from Quercus crassipes Humb. & Bonpl. (QCS), in order to remove total chromium and Cr(VI) from aqueous solution. Effects of various fixed-bed column parameters such as influent solution pH, influent flow rate, QCS bed height, and influent Cr(VI) concentration were investigated. Results from the fixed-bed column experiments demonstrate that total chromium biosorption and Cr(VI) removal by QCS depend strongly on the pH of influent solution. The highest capacities for Cr(VI) removal and total chromium biosorption are about 181.56 and 110.35 mg g-1 and are achieved at influent solution pH of 1.0 and 2.0, respectively. Besides this, total chromium biosorption capacities increased from 104.25 to 116.14 mg g-1, 109.07 to 117.44 mg g-1, and 85.02 to 129.87 mg g-1, as bed height, inlet flow rate, and influent Cr(VI) concentration increased from 1.7 to 6.5 cm, 0.25 to 1 mL min-1, and 50 to 400 mg L-1, respectively. The dose–response model defines the entire breakthrough curve for total chromium biosorption onto QCS, under all experimental conditions. X-ray photoelectron spectroscopy (XPS) and biosorption kinetic studies revealed that QCS is able to remove toxic Cr(VI) from acidic liquid solution by means of a complex mechanism that involves the binding of Cr(VI) oxyanions to positively charged groups present at the QCS surface, after which the Cr(VI) species are reduced to Cr(III) by adjacent electron donor groups, and the generated Cr(III) ions then become partially bound to the QCS biomass and partially released into the liquid phase. Results show that QCS can be employed as an easily accessible, abundant, eco-friendly, and inexpensive biosorbent for the removal of total chromium and Cr(VI) from Cr(VI) solutions, in continuous operation.
Highlights
Chromium [Cr] compounds are among the most common environmental contaminants because of their widespread and extensive use in industrial applications [1]
Results indicate that the breakthrough curves for the removal of total chromium and Cr(VI) are dependent on influent Cr(VI) solution pH, biosorbent bed height, influent flow rate, and influent Cr(VI) concentration
The highest total chromium biosorption capacity was 129.87 mg g-1, and this was attained at influent solution pH of 2.0, 3.5 cm bed height, 0.75 mL min-1 flow rate, and 400 mg L-1 influent Cr(VI) concentration
Summary
Chromium [Cr] compounds are among the most common environmental contaminants because of their widespread and extensive use in industrial applications [1]. Cr(VI) is highly water-soluble, highly mobile in aqueous systems, and highly toxic as it causes severe physiological and neurological ill effects on human and animal health, such as anemia; diarrhea; nausea; epigastric pain; ulcers; vomiting; eye and skin irritation; damage to nerve tissues, kidney, and liver; pulmonary congestion; internal hemorrhaging; and circulatory shutdown [1, 6]. It is highly mutagenic and can induce DNA damage and birth defects, affect gene expression, and decrease reproductive health [1, 7]. Cr(III) is an essential micronutrient for animals and humans as it plays a significant role in the normal metabolism of carbohydrates, lipids, and proteins [1, 2, 6]; at high concentrations, Cr(III) has adverse effects on cellular structure and function [7]
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