Jadwiga Kaleta, Dorota Papciak, Alicja Puszkarewicz
The paper presents the results of laboratory testing of the potential use of bentonite clay from Dynowskie Foothills for removing phenol from model water solutions. Both natural clays and those treated with sodium carbonate, hydrochloric and sulfuric acids were used. The paper shows the characteristics of phenols occurring in natural water. The sources of phenols, i.e. household and industrial wastewater as well as municipal landfills and damps are given. The aim of the experiments was to determine a quantitative formulation of the adsorption process, as well as to describe the effect of various factors on the process itself. An attempt was made to solve the tasks using model experimental setups. Model phenol solution, concentration of 20,00 mg/L, prepared using distilled water was applied as an adsorptive. The phenol concentration in model solutions was determined using the linear relationship between the concentration of this compound and the absorbency value at the wavelength of 254 nm. The absorbency value was read with a SHIMADZU UV – 1601 spectophotometer using quartz cuvets with an absorbing layer 10 mm thick. The results obtained in a successive series of experiments performed under static conditions were described using basic izoterm equations i.e. those of Freundlich, Langmuir and BET. Freundlich’s equations best described the process. The adsorption capacity of the active clays tested was calculated on the basis of the isotherms. Natural clay had an adsorptive capacity of 0,74 mg/g, clay modified with hydrochloric acid 2,41 mg/g, clay modified with sulfuric acid 1,83 mg/g and clay modified with sodium carbonate 0,50 mg/g. Dynamic conditions were realised by the column filtration method. The adsorption columns were made of organic glass 32 mm in diameter, the filling height was 750 mm, filtration rate – 12 m/h. Filtration was performed from the top downwards. Filtration lasted each time until the moment of bed exhaustion, i.e. such a point where the concentration in the discharge becomes equal to that of the initial solution. The sorption effectiveness under flow conditions for bentonite clays was 100%. On the basis of the results obtained, the breakthrough curves, the so-called iso-planes, were prepared and served in turn to determine the adsorption capacities under flow conditions. The adsorptive capacities were higher than those determined through static conditions and these were 15,9 mg/g, 19,9 mg/g, 18,8 mg/g and 15,2 mg/g for natural clay, clay modified with hydrochloric acid, clay modified with sulfuric acid and clay modified with sodium carbonate, respectively. The clay modified with sodium hydrochloric acid exhibited the highest values of adsorption capacities, as determined under both static and flow conditions. Modification of samples with hydrochloric and sulfuric acids appeared advantageous for both technological and economic reasons. The exit curves (iso-planes) were used to determine the mass penetration zone (the adsorption front height), as well as to calculate the rate at which the mass-exchange zone advanced. The adsorption front height for the carbons tested was 3–5 times lower than the adsorption bed height, thus confirming the high effectiveness of clays in phenol removal. Despite this considerable superiority of active carbon as sorbent, bentonite clays may be taken into account in designing process systems, especially as insulating materials in relation to active carbon. The array of water conditioning processes to be employed for phenol polluted water should in each case be preceded by detailed and thorough technological studies.
przydatność iłołupków; usuwanie fenolu
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