Abstract
Hexavalent chromium is a widespread pollutant that threatens ecological and human health. However, its removal from the environment is limited by the high cost and energy consumption rate of current technologies. In this study, the Cr(vi) biosorption mechanism of Aspergillus niger spores pretreated by freezing/thawing was studied by batch experiments and surface chemistry analyses. The results indicated that pretreatment enhanced the spores' Cr(vi) removal efficiency. The cell surface, internal functional groups, and morphology of the freezing/thawing-pretreated spores (FTPS) before and after Cr(vi) loading were characterized by advanced spectroscopy techniques such as SEM-EDAX, XPS, FTIR, and FETEM analyses. The SEM and BET data showed that the surface of FTPS was rougher than that of untreated spores. The XPS data showed that FTPS bio-transformed Cr(vi) into Cr(iii). The intracellular localization of chromium was visualized by FETEM, and both surface and intracellular structures removed Cr(vi) following pseudo-second-order biosorption kinetics. The biosorption dynamics of Cr(vi) fit the Langmuir isotherm model describing a monolayer. These results suggest that freezing/thawing pretreatment of A. niger spores could lead to the development of a novel, efficient biomaterial for the removal of Cr(vi).
Highlights
Hexavalent chromium is widely used in electroplating, textile dyeing, stainless steel, leather, wood treatment, and other industries
To identify the conditions that would achieve the maximum removal efficiency, experiments were conducted at temperatures of 193 and 253 K and one to four cycles (Fig. 1), with the US as a control
The biosorption capacities of the freezing/thawing-pretreated spores (FTPS) held under 193 K were 50.2, 48.0, 46.8, and 39.0 mg gÀ1, respectively, as the number of cycles increased from one to four, while those held under 253 K were 46.0, 48.2, 47.4, and 48.3 mg gÀ1, respectively
Summary
Hexavalent chromium is widely used in electroplating, textile dyeing, stainless steel, leather, wood treatment, and other industries. The effects of pH (2–7), contact time (15–300 min), initial concentration (25–250 mg LÀ1), and temperature (293–313 K) on the biosorption of Cr(VI) by FTPS biomass were studied. The biosorption experiments were conducted at a Cr(VI) concentration of 100 mg LÀ1 and with 0.1 g of FTPS or US in 100 mL of the solution. The initial concentration ranged from 25–250 mg LÀ1 in the adsorption capacity experiments. The US and FTPS (0.1 g) were added to a 100 mL solution containing Cr(VI) at 100 mg LÀ1, with a pH of 2.0 and temperature of 303 K These experiments were conducted for 4 h. Qeq is the metal biosorption capacity at equilibrium (mg gÀ1), ceq is the metal ion concentration at equilibrium (mg LÀ1), and KF and n are the Freundlich constants.
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