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Based on a study of the German Ministry of Research and Technology in 1990 every year about 2.5 t of heavy metals are released per hectare of landfill by aqueous leaching. This leachate contains approximately 2000 t of heavy metals per year. Their decontaminations in accordance with the legal requirements represent an enormous potential for easing the burden on the environment. On the other hand, this potential opens new possibilities in the production and recycling of selected compounds. The composition of a given model solution corresponds to a landfill leachate resulting from a municipal dump leachate produced by an average German city. Actually, in most cases, a decontamination of such solutions occurs by the transfer of the problematic cations into insoluble compounds usually done by precipitation. The result of the procedure is an unspecific separation of all liquid components - and the "cycle of waste" (landfill- leaching-deposition) begins anew, certainly on a higher level. The objective of our work is the simultaneous separation of heavy metals from alkaline earth metals and iron in order to obtain a leachate which we can lead back to the landfill. The reactive extraction as a separation process offers the possibility of a selective separation of cations that is the separation of toxic - from unproblematic components and includes also the possibility of electrolysis or further winning processes to obtain the wished metals. For the realisation of extraction processes, several commercial extractants and technical equipments are available. Apart from iron, LIX 54 could be used advantageously for an extraction process - unfortunately without any considerable extraction of cadmium. But it is favourable to separate non toxic alkaline earth metals from problematic heavy metals. Such a complex task as the separation of cations from natural solutions cannot be solved easily in a one-step-extraction process. Better results should be obtained by the combination of different procedures, e.g. extraction, ion-exchange and precipitation.
Quinoxalines X : a new and convenient synthesis of 1H-Pyrazolo[3,4-b] quinoxalines (Flavazoles)
(2001)
A model system of tanning of a protein matrix within a fibrous structure, such as most commonly found in insect cuticle, was developed, using the cellulose of paper in place of chitin. The paper was impregnated with a tripeptide, DOPA-Gly-Gly, or a protein (BSA) plus catechol and treated with tyrosinase to oxidize the catechol. The resulting material was waterproof and had very high wet strength. If the material was wetted and dried repeatedly its water retention decreased by a factor of at least two.
Toxic heavy metals are extracted simultaneously by reactive liquid-liquid-extraction from a model landfill leachate. This is taken as an example to generate an unproblematic waste water. Alkylphosphoric acids (commercial D2EHPA and D2EHTPA), ß-diketones, 4-Acyl-5-pyrazolones and a novel commercial alkyl-methyl-phosphonic acid are used as extractants. By means of the functions E%=f (pH, t) and lg D=f (pH, cL) some thermodynamic parameters of the extraction are determined. In the case of the alkylthiophosphoric acid the thiophilic cations are extracted advantageously in contrast to chromium, magnesium or calcium. There is no significant separation between the heavy metals and the alkaline earth metals. The complexes are extracted with the composition ML(HL)n. According to their ligand force, the presence of complexing agents in the aqueous phase (for example cyanide, tartrate, ammonia or chloride) hinders the extraction. The influence of humic acid is comparable to that of tartaric acid. Because of the formation of less soluble compounds, sulphate ions make the extraction of calcium more difficult. The extraction data points out that aromatic or chloric solvents are not advantageous in contrast to the non toxic aliphatic hydrocarbons. With the novel aminomethylphosphonic acid (ironex, BASF) the extraction of iron, indium and gallium is possible at a pH > 1.5 as ML2(HL) and ML(HL)2 resp. Copper and zinc were extracted quantitatively as 1:2 complexes only in a small pH-range between 4 to 6. Generally, the best results were found for the ß-diketones (LIX 54 included) and 4-acyl-5-pyrazolones. In these cases the toxic heavy metals could be separated quantitatively. Only 6% of calcium and 23% of magnesium are coextracted by the ligands. The extraction process can further be optimized by synergistic effects.