Sorpcja metali ciężkich na utlenionych węglach aktywnych

Przeprowadzono sorpcję z roztworów wodnych następujących metali ciężkich: ołowiu, kadmu, niklu, kobaltu. Modyfikację węgla WG-12 prowadzono w piecu obrotowym w temperaturach 400 i 800°C z udziałem pary wodnej, powietrza lub dwutlenku węgla oraz na stanowisku wykorzystującym nagrzewanie węgla ciepłem Joule'a do temperatury 400°C. Użyte sposoby modyfikacji pozwoliły na uzyskanie węgli o zwiększonych możliwościach sorpcyjnych w stosunku do wszystkich użytych w badaniach metali ciężkich. Nie można wybrać sposobu modyfikacji, który byłby jednocześnie optymalny dla wszystkich usuwanych metali. Najlepsze efekty uzyskano dla węgla modyfikowanego powietrzem w piecu obrotowym w 400°C oraz parą wodną i dwutlenkiem węgla w 800°C. Uzyskane wyniki sorpcji na węglach modyfikowanych z udziałem ciepła Joule'a są porównywalne z rezultatami na węglach utlenionych w piecu obrotowym z udziałem pary wodnej oraz dwutlenku węgla. W przypadku wyjściowego węgla aktywnego metale te sorbowały się w następującej kolejności: Pb > Ni ≈ Cd > Co.

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There has been conducted the adsorption from water solutions in static conditions of the following heavy metals: lead, cadmium, nickel and cobalt. The research was made on initial and modified carbon WG-12. In the case of initial, activated carbon, these metals adsorbed in the following order: Pb > Ni ≈ Cd > Co. The modification of WG-12 carbon was conducted in rotary furnace at the temperatures: 400 and 800°C with the usage of water vapour, air and carbon dioxide. It was carried out at the experimental stand using the heating of carbon by means of Joule heat up to the temperature of 400°C. The presented ways of modification allowed to obtain carbons of greater adsorption abilities in relation to all used heavy metals used in the research. There cannot be chosen one way of modification which would be optimum for all removed metals. In the case of lead, the efficiency of Pb2+ removing from solution of 0.1 mmol/dm³ concentration on initial carbon was: 23% and on carbon modified in rotary furnace at the temperature of 400°C with the usage of air (WG/400/AIR) was about 90%. Similar results were obtained on carbon modified at 800°C with the usage of carbon dioxide (WG/800/CO2). Much lower efficiency of removing was obtained for cadmium ions. On initial carbon, this efficiency was equal: 7.7%; and on WG/400/AIR was equal: 49%. Similar results were obtained during nickel adsorption, however, in this case the best results were obtained for modified carbon: WG/800/H2O (the degree of Ni2+ ions removal increased from 7.1% to about 60%). The degree of cobalt removal on modified carbon WG/800/H2O increased from 4.2 to 54%. The obtained adsorption results on carbons modified with the usage of Joule heat are comparable to the results observed on carbons oxidized in rotary furnace with the usage of water vapour and carbon dioxide. The best results are obtained on carbons modified in one heating-cooling down cycle. While analysing the adsorption results of the used heavy metals and the number of units of acidic and basic character, which are denoted by means of Boehm method, there can be observed that the greatest amount of acid units are on the surface of carbon WG/400/AIR which characterizes of great capacities in relation to other examined carbons. Nevertheless, high adsorption abilities in relation to: lead, nickel and cobalt were observed in the case of carbons, modified at 800°C in the atmosphere of both carbon dioxide and water vapour, when the amount of oxides of acidic character lowered a bit in relation to non-modified carbon. Such results can suggest the coexistence of other processes, not only the ion exchange processes on acidic oxides.