In order to obtain hydrophobic material, the surface of natural limestone with the high content of calcite (>95%), was treated with 0.5, 1, 1.5, 2, 3 and 4% of stearic acid. Two methods were used for modification: the solution method and the dry coating. The obtained products were characterized using the thermal analysis (DT/TG), X-ray powder diffraction analysis (XRPD), scanning electron microscopy (SEM) and by the evaluation of floating test. Results of floating test showed that when the solution method was applied, the hydrophobicity arrived at above 99% when the amount of stearic acid was 1.5%, while with the dry coating the same hydrophobicity was achieved with 3% of stearic acid. From the position of the principal exothermic peak (> 310 °C) at DTA curves, for calcites modified with dry coating and with the solution method, it can be concluded that with both modification processes, the same active sites exist at the calcite surface onto which stearic acid may be chemisorbed. However, the position and the intensity of the other exothermic peaks, indicate the differences in bonding of stearic acid at the calcite surface during the solution method and the dry coating

k o v i 6 , J T u r k u l o v andE. D i m i C 'This paper contains the results of the investigation of oils got by extraction with supercritical CO1. The extraction was done on a Nova-Swiss pilot plant. The following oils were investigated: soybean, sunflower and rapeseed oils. The results were compared with the liquid hexane extraction results.

In this paper, the results of the surface modification of natural zeolite with different amounts (2, 5 and 10 mmol M+/100g) of octadecyldimethylbenzyl ammonium ions (ODMBA) are presented. The obtained organozeolites were denoted as OZ-2, OZ-5 and OZ-10. The degree of ion exchange was followed by determination of amounts of inorganic cations released from zeolite. Results confirmed that reaction between ODMBA and starting zeolite has occurred via ion exchange mechanism. The obtained value for point of zero charge, pHpzc, of natural zeolite was 6.8±0.1, while for OZ-2, OZ-5 and OZ-10 pHpzc was 7.0±0.1. Below the pHpzc, the surfaces of materials are positive while at pH values higher than pHpzc their surfaces are negative. Compared to the pHpzc of natural zeolite, no significant differences in pHpzc was observed for all three organozeolites indicating that obtained products have similar functional groups with similar acid and basic characteristics as starting zeolite. The pHpzc was not dependent on the amount of ODMBA ions at the zeolitic surface and the value of pHpzc for all investigated sorbents is the same for all three electrolyte concentrations indicating that the pHpzc of each material is independent of the ionic strength of KNO3

This paper presents results of investigations of the quality of the natural zeolite as well as the quality of particular particle size classes of the natural zeolite. The aim of the investigations was to determine if the different classes possess different qualitys. The starting material used in experiements was the natural zeolite from Zlatokop deposit (Vranjska Banja, Serbia).. The classes -0.2+0.8 mm; -0.8+0.6 mm; -0.6+0.4 mm; -0.4+0.1 mm were obtained by wet sieving of the natural zeolite. Grinding processes of the natural zeolite gave classes -0.3+0.63 mm; -0.63+0 mm; -0,43+0 mm. Chemical composition , mineralogical XRPD analysis and cation exchange capacity (CEC) were performed on the starting sample and the obtained particle size classes. It was determined that all particle size classes possess similar quality. The highest cation exchange capacity was observed in classes -0,043+0mm (166,5 meq/100g) and -0,063+0mm (158, 8 meq/100g). [Projekat Ministarstva nauke Republike Srbije, br. TR 34013

In this paper, the results of adsorption of uranyl ion on acid-modified zeolitic mineral clinoptilolite are presented. Adsorption was investigated at different amounts of solid phase in suspension, as well as at different pH values. The modified clinoptilolite samples were obtained by treatment of clinoptilolite with acids: hydrochloric, oxalyc and citric. Starting and modified clinoptilolites were characterized by chemical analysis, thermal (DT/TG) analysis and by determination of cation exchange capacity, while starting and nonadsorbed amounts of uranyl ion were determined by fluorometric method. Uranyl ion adsorption experiments on natural unmodified zeolitic mineral showed that uranyl ion adsorption was low (29.2%) and that treatment of clinoptilolite with acids significantly increases the adsorption of uranyl ion (>90%). In the case of acid treated clinoptilolites, the highest adsorption of uranyl ion was achieved on clinoptilolite modified with hydrochloric acid. Kinetics of adsorption showed that adsorption of uranyl ion begins very fast and that the most of uranyl ion was adsorbed in first 30 min. Practically, there were no changes in uranyl ion adsorption within next 72 h