Band 41, Heft 3

This paper focuses on the graphite flotation from Bent Um Qureia ore at Eastern desert of Egypt. Minerals in ore were evaluated by XRD. The sample was crushed in jaw crushing. The sample was ground minus 74 μm and the product was then sieved +45 and −45 μm. The conventional and column flotation were used to float the graphite. In two flotation techniques, kerosene was used as a collector. Factor affecting the graphite grade was investigated. The rougher concentrate was cleaned in both conventional cell and column to compare the performance. The effects of different variables were evaluated in both cases and the conditioned were optimized to achieve better grade and recovery. The results indicate that column can give superior performance compared to conventional cell by either reducing the number of stages of operation or by improving grade and recovery.

Alkyl polyglucosides (APGs) and polyethylene glycol glycosides (PEGG) were applied as coatings on fresh pineapple to extend their postharvest shelf-life and to prevent Black Heart (BH). The pineapples were coated with solutions of APGs and PEGG, and the tissue firmness, total soluble solids (TSS), grade of freshness, incidence and grade of BH were measured. The APGs and PEGG were obviously able to reduce the decay incidence, firmness and flavor loss as well as retard color change and ripening rate of pineapples during storage. C 12/14 -APGs could not only improve quality and shelf-life characteristics, but also markedly reduce incidence of BH. The combination of APGs with PEGG showed the obvious synergism for preventing BH.

An analytical method has been developed for the determination of alcohol ethoxylate (AE) components in sewage sludge. The method has been extensively ring tested in several industrial laboratories and concentrations in sludge samples from a number of EU countries have been obtained. The method is based on a methanol soxhlet extraction of centrifuged sludge, which is then cleaned up using an alumina column, followed by derivatisation with naphthoyl chloride and a further alumina column clean-up. The extract is analysed using high performance liquid chromatography (HPLC) with fluorescence detection. The method is capable of determining alcohol ethoxylate components in the range of C12–C18 alkyl chain lengths with an ethoxylate chain of EO4 up to approximately EO20 in sludge samples. The detection limit is approximately 20–30 mg kg −1 of total AEs in dry weight of sludge. Using the method, sludges from several European Sewage Treatment Plants (STP) were analysed. The concentration of the AEs, which are primarily linear, in digestor inlet averaged 1164 mg kg −1 (550–2947 mg kg −1 ) and in outlet sludges the mean value obtained was 167 mg kg −1 (<22–468 mg kg −1 ). At those plants in which concentrations were monitored in both inlet and outlet sludges, removal of the AEs by anaerobic digestion at the STP averaged 82% (range 61–93%). The interlaboratory relative standard deviation of the procedure was around 40% for the digester sludges analysed. The method developed provides a more accurate estimate of the environmental level of AE components compared to existing colorimetric approaches, but the method will over-estimate the concentration of alcohol ethoxylates in sludges due to the non-specific nature of the detection. However, it is sufficiently robust and accurate to estimate alcohol ethoxylates in sludges and hence concentrations that could be applied to soil.

Molecular clips and tweezers tend to bind selectively electron deficient aromatic and aliphatic substrates. These interesting processes of molecular recognition are usually investigated in dilute solutions of organic or aqueous solvents. Due to discrepancy between polar and hydrophobic groups, molecular clips and tweezers are surface-active chemical compounds which can form monomolecular films at the surface of water. In this publication, we have systematically investigated the self-association and phase-behavior of these artificial receptors by means of pressure-area-isotherms and Brewster-Angle-Microscopy (BAM). We observed spherical and rod-shaped two-dimensional aggregates in the liquid condensed phase. The size and shape of these domains are similar to corresponding structures of classical surfactants.

Sugar-based surfactants have recently attracted considerable interest. In this work, the surface tension and critical micelle concentration (CMC) of alkyl polyglucosides (APGs) with differences in both alkyl chain lengths and average degree of polymerization (DP) were measured, and the effects of sodium chloride and sodium hydroxide on the surface tension and CMC of aqueous solutions of APGs were investigated. The alkyl chain length has a far stronger influence on the CMC than the degree of headgroup polymerization. The addition of sodium chloride to solutions of APGs has a relatively small effect compared with ionic surfactants. The observed effects of sodium hydroxide were explained in terms of the salting out of the hydrocarbon chains of APGs and the hydrotropic effect due to a negative charge on APGs micelles resulting in the deprotonation of the glucose fraction in strong alkaline system.

The profile of pressure change and the product composition were used to model oxyethylation of fatty acid methyl esters, carried out in a semi-batch reactor with successive dosing of ethylene oxide. It was found that the model fitted well with the experimental data obtained in the presence of a calcium-based catalyst. The introduction of the first and second oxyethylene groups are the slowest and the quickest step, respectively. The pseudo-rate constants of the successive steps are lower than the constant of the second step but approximately twice as high as the first rate constant. The modeling also demonstrates that the oxyethylation cannot proceed via oxyethylation of calcium alkoxylate and transesterification with fatty acid methyl esters.