New technology to remove toxic metal ions using hop biomass: Use of chemical modification and x -ray absorption spectroscopy to determine the mechanism(s) of metal removal
The agricultural by-products of the hop plant (Humulus lupulus ) were investigated to determine their potential use for the removal of lead(II), copper(II), cadmium(II), zinc(II) chromium(VI) and chromium(III) ions from contaminated aqueous solutions. Results have shown a pH dependent binding trend from pH 2 to 6, with the maximum binding taking place around pH 5.0. Time dependency experiments showed a rapid adsorption of lead(II), copper(II), cadmium(II), zinc(II), and chromium(III) ion within the first five to fifteen minutes. Binding capacity experiments produced a significant binding for lead(II) and measurable amounts for copper(II), cadmium(II), zinc(II) and chromium(III), calculated as milligram of metals per gram of the biomass. Results showed that after 3 cycles of metal binding and stripping with 0.5M sodium citrate, the binding ability of the immobilized hop biomass for Pb(II), Cr(III), Cu(II), Cd(II) and Zn(II) did not decrease. Comparison studies were performed with ion-exchange resins, including carboxylic, sulfonic and phosphate functional groups. Studies performed with hop leaves and stems showed that this biomass is potentially useful for removing heavy metals from aqueous waste solutions. However, there is no information about the functional groups involved in the biosorption of Cu(II), Cd(II), Zn(II) and Cr(III) to hop biomass. Thus, experiments were performed to establish how the modification of chemical groups possessed by hop biomass changes the binding ability. The treatments included native, esterified, and hydrolyzed hop leaves and stems biomasses. It was observed that the hydrolization of the biomass significantly increased the binding ability to the metals, while esterification of carboxyl functional group significantly decreased the biosorption of Cu(II), Cd(II), Zn(II) and Cr(III). Fourier Transformation Infrared Spectroscopy (FTIR) studies were utilized in order to understand and validate of the mechanisms by which these metals bind to the hop biomass. X-ray absorption spectroscopy (XAS) including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) were used to investigate the binding mechanism of heavy metals to hop biomass. Overall, these studies indicated that carboxyl functional groups play a critical role in the biosorption of lead(II), copper(II), cadmium(II), zinc(II) and chromium(III) by hop leaves and stems biomass. (Abstract shortened by UMI.)
Environmental engineering|Chemical engineering
Hejazi, Michael, "New technology to remove toxic metal ions using hop biomass: Use of chemical modification and x -ray absorption spectroscopy to determine the mechanism(s) of metal removal" (2001). ETD Collection for University of Texas, El Paso. AAI3035098.