Spectroscopic Characterization of Organic Structures and Organic‐Inorganic Interactions in Paper Mill Sludge

The organic composition and organic‐inorganic interaction in paper mill sludge (PS) solvent extracts (hexane, ethyl acetate, acetone and ethanol) and humic fractions, humic acid (HA) and humin (HU) were studied by electron paramagnetic resonance spectroscopy (EPR), proton and carbon‐13 nuclear magnetic resonance spectroscopy (¹H NMR; ¹³C NMR), Fourier‐transformed infrared spectroscopy (FTIR), and ultraviolet‐visible spectroscopy (UV‐vis). The strategy of fractionating the PS, sequentially, with organic solvents of increasing polarity is a reliable analytical procedure for humic substance sample separation because it results in more purified fractions. FTIR, ¹H NMR and ¹³C NMR results showed that hexane extract consisted mainly of aliphatic hydrocarbon structures. Their contents in the extracts decreased as the polarity of the extracting solvent increased and the content of oxygen functional groups increased. Carboxylic and carboxylate functional groups were found in the acetone extract, and ester and ether functions were predominantly found in the ethanol extract. EPR spectra revealed some Fe³⁺ complexes with rhombic structure (g₁ = 4.3; g₂ = 9.0) in the humic fractions and in all solvent extracts, except hexane. Quasi‐octahedral Fe³⁺ complexes (g = 2.3; ΔH_pp ≤ 400 G) were found in the HU fraction and in the acetone extract. The organic free radical content in the HA fraction was higher than the non‐fractionated PS sample and HU fraction.     

Applicability of Single and Sequential Extractions for Assessing the Potential Mobility of Heavy Metals in Contaminated Soils

Heavy metal polluted sites are bearing an acute hazardous risk for the groundwater, but also a potential one. While the acute risk can be assessed directly via seepage water measurements, determination of the potential risk is much more complex. It results from the sum of all reactions that are capable to mobilize heavy metals under worst case environ-mental conditions. Using a fourfold sequential extraction (SE₄) such a worst case was simulated for four soils highly contaminated with Pb, Zn, and Cu. The resulting potential mobilizable amounts ϕ_pm have been compared with those derived from 6 single extractions. By means of variance analyses, it is shown that ϕ_pm of lead can be represented by a single extraction with NH₂OH. In contrary, ϕ_pm of zinc can be represented using the pH_stat test or an extraction with aqua regia, while ϕ_pm of copper can be represented only by aqua regia extraction. The water-soluble amounts deriving from the DEV-S4 test do not correlate with the potential mobilizable amounts of any metal. Therefore, an assessment of contaminated sites should include an aqua regia extraction additionally to the seepage water analysis.     

Simplification of a Sequential Extraction Scheme To Determine the Mobilisable Heavy Metal Pool in Soils

This investigation had the purpose of evaluating the reliability of a sequential extraction procedure according to Zeien and Brümmer (1989) which is performed routinely to analyse the distribution of heavy metals to different soil phases. Reliability was tested by two hypotheses. According to the first hypothesis an error propagation increased during a morefold extraction of heavy metals from a single soil sample to such an extend that it does not allow a statistical comparison of different analyses. This assumption was confirmed in an interlaboratory study of five participants applying the sequential extraction scheme on two different soils. The heavy metal amounts extracted by the different partners were of the same magnitude, but from the results no statistical correspondence at the 95% confidence level could be observed. The second hypothesis stated that also weak extraction agents were able to release metals from the more immobile soil fractions, especially if the amount of easily soluble metals was comparatively small. To answer this question the sequential extraction was modified by carrying out selected weak extraction steps several times. As expected the intensified extraction conditions caused a decrease of the element content within the more resistant phases. However, the additional release in the first four extraction steps of Pb, Mn, Fe, and Zn was only in the range of 5 to 10%. Furthermore, it was observed that a single EDTA extraction (step four within the sequential extraction scheme) was capable to extract the same amount of metals as the first four extraction steps of the original scheme at a variation of about 15%. From these results it was concluded that the EDTA step alone already represents a reliable pool of mobilisable metals. Thus it can be maintained that such a simple single EDTA extraction can be used to assess the environmental risk from heavy metal contaminated soils or to predict the potential heavy metal release of soil remediation processes.