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Résumé:
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Experiments were conducted to precipitate dissolved copper, zinc, and lead from simulated wastewater solutions as solids which could then be separated by filtration. The precipitants used were hydrated lime, as a slurry and in powdered form, aqueous ammonium hydroxide, ferrous sulphide sludge, and carbon dioxide gas. These five different chemicals, singly or in combination, were used; at least one of which was highly successful in precipitating each of the metals, removing at least 99% of that originally present. Copper and zinc were very effectively precipitated as the hydroxides with lime, whereas lead was not. Considering lead to be the most difficult metal to remove, four other chemical conditions were attempted for lead; these were ferrous sulphide alone, lime with ferrous sulphide, lime with carbon dioxide, and lime with ozone. The precipitation of lead with ferrous sulphide alone, was only partially successful with only 95% removal. The other three combinations of chemicals precipitated more than 99% of the soluble lead, giving excellent results. Furthermore, because lead is usually difficult to remove from solution, it is considered that the three new chemical combinations show strong promise for the removal of other heavy metals from wastewater solutions. Experiments were also conducted to decompose the organic compounds, formaldehyde and pyridine, in simulated wastewater solutions in a mixed reactor, using ozone and UV radiation as oxidants. Although 200 ppm Total Organic Carbon content of each of those chemicals, and a mixture of both, were completely decomposed by ozone-UV oxidation, the time taken for these decompositions ranged from about three to four hours. Such prolonged reaction times are considered too long for most wastewater treating processes. However, low concentrations of organic matter might be successfully treated using ozone/UV processes. |
