Kinetic Study of the Effect of pH on Hexavalent and Trivalent Chromium Removal from Aqueous Solution by Cupressus lusitanica Bark

Abstract

Solution pH is among the most important parameters that influence heavy metal biosorption. This work presents a kinetic study of the effects of pH on chromium biosorption onto Cupressus lusitanica Mill bark from aqueous Cr(VI) or Cr(III) solutions and proposes a mechanism of adsorption. At all assayed contact times, the optimum pH for chromium biosorption from the Cr(III) solution was 5.0; in contrast, optimum pH for chromium biosorption from the Cr(VI) solution varied depending on contact time. The kinetic models that satisfactorily described the chromium biosorption processes from the Cr(III) and Cr (VI) solutions were the Elovich and pseudo secondorder models, respectively. Diffuse reflectance infrared Fourier transform spectroscopy studies suggest that phenolic compounds present on C. lusitanica Mill bark play an important role in chromium biosorption from the Cr(III) solution. On the other hand, chromium biosorption from the Cr(VI) solution involved carboxyl groups produced on the bark by redox reactions between oxygen-containing groups and Cr(VI), and these were in turn responsible for the biosorption of Cr (III) produced by Cr(VI) reduction.

Removal of Cr(VI) from Model Solutions by a Combined Electrocoagulation Sorption Process

“…10). As previously stated [35], this result can assign the responsibility of the Cr(III) biosorption obtained from Cr(VI) reduction to the carboxyl groups. 3 a) identified the disappearance of the band at 1739 cm -1 .…”

“…The absence of this vibration, after the use of the hybrid process, indicates the involvement of this vibration in the adsorption process. As previously stated [35], this result can assign the responsibility of the Cr(III) biosorption obtained from Cr(VI) reduction to the carboxyl groups. Moreover, the presence of Cr(OH) on the ROS can be considered as an explanation for the appearance of the band at 529 cm -1 [45].…”

“…At low pH, functional groups of the biosorbent become protonated and easily attract negatively charged chromium. Moreover, it has been observed that during the process of Cr(VI) removal by ROS the solution pH remains constant, revealing that Cr(VI) is not reduced to Cr(III) [35]. Though in principle there is a possibility of reduction of Cr(VI) ion into Cr(III) at low pH, earlier studies reported that at low pH the amount of total Cr corresponds nearly to that of Cr(VI), indicating that the presence of Cr(III) in the final solution is insignificant [34].…”

“…Though in principle there is a possibility of reduction of Cr(VI) ion into Cr(III) at low pH, earlier studies reported that at low pH the amount of total Cr corresponds nearly to that of Cr(VI), indicating that the presence of Cr(III) in the final solution is insignificant [34]. Moreover, it has been observed that during the process of Cr(VI) removal by ROS the solution pH remains constant, revealing that Cr(VI) is not reduced to Cr(III) [35].…”

Efficacy of unmodified and chemically modified Swietenia mahagoni shells for the removal of hexavalent chromium from simulated wastewater

“…Such adsorbents can be used for the production of activated carbon with high adsorption capacity, considerable mechanical strength, considerable renewability as a resource, considerable reusability and eco-friendly nature [12][13][14]. Various biomasses like sugar beet pulp [15], rice husk [16], corn stalk [17], Ficus glomerata [18], persimmon [19], Daucus carota [20], Cupressus lusitanica bark [21], Citrus limetta peel [22], neen saw dust [23], peanut husk [24], longan seed [25], Fucus vesiculosus [26], etc. have been used for the removal of hexavalent chromium.…”