Hana Šillerová

Evaluating the potential of three Fe- and Mn-(nano)oxides for the stabilization of Cd, Cu and Pb in contaminated soils.

The potential of three Fe- and Mn-(nano)oxides for stabilizing Cd, Cu and Pb in contaminated soils was investigated using batch and column experiments, adsorption tests and tests of soil microbial activity. A novel synthetic amorphous Mn oxide (AMO), which was recently proposed as a stabilizing amendment, proved to be the most efficient in decreasing the mobility of the studied metals compared to nano-maghemite and nano-magnetite. Its application resulted in significant decreases of exchangeable metal fractions (92%, 92% and 93% decreases of Cd, Cu and Pb concentrations, respectively). The adsorption capacity of the AMO was an order of magnitude higher than those recorded for the other amendments. It was also the most efficient treatment for reducing Cu concentrations in the soil solution. No negative effects on soil microorganisms were recorded. On the other hand, the AMO was able to dissolve soil organic matter to some extent.

Brewers draff as a new low-cost sorbent for chromium (VI): Comparison with other biosorbents

In this study, used brewers draff was investigated as a novel sorbent for Cr(VI) and compared with other biosorbents (grape waste, peat moss, and sawdust). FTIR-ATR, BET analysis, and pHPZC determination were used to characterize the sorbents. Kinetic and equilibrium experiments were performed, and two empirical models, Langmuir and Freundlich, were used to describe Cr adsorption. Additionally, packed bed column experiments were also performed. In order to identify possible reduction processes, ion exchange separation on the AG1-X8 resin was used to separate the anionic Cr(VI) and the reduced cationic Cr(III) from the aqueous phase after biosorption. Cr(VI) removal was pH-dependent and fitted well both the Langmuir and the Freundlich isotherm models. The ion exchange separation showed that Cr(VI) reduction had occurred in the solution during biosorption. The efficiency of draff as a biosorbent was comparable (or even higher) to highly organic materials (e.g., composted peat), showing its potential application for Cr(VI) decontamination.

Isotope fractionation and spectroscopic analysis as an evidence of Cr(VI) reduction during biosorption.

This work investigates the mechanisms behind Cr(VI) biosorption/reduction on three biomaterials (brewers draff, grape waste and synthetic humic acid). Coupled Cr isotope analysis with ICP-OES, XPS and SEM was tested as a novel approach to study the reduction of Cr(VI) by the biomaterials. The Cr(VI) biosorption process was accompanied with heavier Cr isotopes enrichment in the remaining Cr(VI) fraction. A significant fractionation of Cr stable isotopes was observed with no significant pH effect; δ(53)Cr of the remaining fraction ranged from 0.2‰ to 1.9‰ while δ(53)Cr of the product (sorbed Cr) ranged from -1.2‰ to -2.8‰. The Rayleigh fractionation model fitted well the measured data and Cr isotope analysis provides thus an efficient tool to quantify Cr(VI) reduction by different biomaterials. In general, the sorption/reduction potential of the three studied biomaterials decreased in the following order: grape waste>humic acids>brewers draff.

Interactions of nano-oxides with low-molecular-weight organic acids in a contaminated soil

Various low-molecular-weight organic acids (LMWOAs) play an important role in the mobilisation of contaminants and their subsequent uptake by plants. Nano-maghemite (NM) and an amorphous Mn oxide (AMO) were investigated for their stabilisation potential under simulated rhizosphere conditions in terms of their use during chemical stabilisation and aided phytostabilisation of metal(loid)s in contaminated soils. In order to understand the reactivity of these potential sorbents of contaminants in soils and subsequent mobility of metal(loid)s, a set of time-dependent batch leaching experiments was performed using a mix of acetic, lactic, citric, malic and formic acids simulating root exudates. Despite being relatively unstable under given conditions, the AMO proved to be an efficient amendment for rapid stabilisation of both metals and As compared to NM. Generally, low pH (∼ 4) and the presence of citrate complexes resulted in higher mobility of metals in the non- and NM-amended soil. In contrast, the presence of AMO in the soil accelerated the neutralisation reactions related to pH increase and (co-) precipitation of secondary Fe/Mn/Al oxyhydroxides. Mineralogical transformations of the AMO showed to be crucial for contaminant immobilisation.

Biosorbent encapsulation in calcium alginate: Effects of process variables on Cr(VI) removal from solutions.

Selected biosorbents, brewers draff and grape waste, have been encapsulated in calcium alginate beads and used for the removal of Cr(VI) from aqueous solutions. The effects of encapsulation variables, including the type of waste, the percentage of waste in the beads and the curing time of the beads in CaCl2, on the diameters of the beads and Cr(VI) sorption kinetics have been evaluated. In total, 21 different types of beads were produced. The diameters of the beads increased with increasing amounts of encapsulated biomaterial. Beads that contained grape waste were larger than those containing brewers draff. The most efficient beads for Cr(VI) removal were beads that contained 4% (w/w) of grape waste. No significant differences in the kinetics of Cr(VI) sorption were found with respect to the curing time variable in the case of grape waste calcium alginate beads. Statistical analysis confirmed that the type and percentage of waste are the critical parameters influencing the diameters of the beads and Cr(VI) removal. It was proven that the sorption efficiencies of the beads containing draff and grape waste encapsulated under the optimum conditions were much higher than the efficiencies obtained when using both wastes in their native states.