The action of atmospheric carbon dioxide is one of the agents which substantially reduce the durability of concrete structures. Th is so called carbonation is one of the corrosive processes ...influencing properties of mature concrete. It is caused by a chemical reaction of carbon dioxide infiltrating into the surface of a concrete construction with the minerals of cementing compound. The eff ect of carbonation can be evaluated by means of the "accelerated carbonation depth test in 98% CO
2
". The principle of this method consists in finding a correlation dependence of "depth (or time) of carbonation in the natural environment / depth (or time) of carbonation in the accelerated test". The theoretical carbonation depth of common concrete placed in the natural environment of 0.03% CO
2
for a long time can be determined from the Fick's law. The actual carbonation depth of common concrete placed in 98% CO
2
can be determined by a simple phenolphthalein test on fresh fragments of standard concrete samples. The correlation dependence found in the so-called "accelerated test" enables us to determine intervals of real time in the natural environment of 0.03% CO
2
corresponding to the intervals of accelerated exposition in 98% CO
2
.
There are 18 species belonging to the genus of Campylobacter (rRNK group I), of which thermophilic ones are the following: Campylobacter jejuni, Campylobacter coli, Campylobacter lari and ...Campylobacter upsaliensis. The aim of our research was to determine the sensitivity of Campylobacter species, isolated from human feces, to antibiotics being used in practice. The study involved 50 human strains of C. jejuni/coli isolated from feces in the Center for Microbiology in the Public Health Institute Nis. Sensitivity was tested by applying the disk diffusion method on seven antibiotics (erythromycin, gentamicin, tetracycline, ciprofloxacin, hloramphenicol, cephalexin and nalidixic acid). Our results showed low resistance to erythromycin, gentamicin and tetracycline (2%), which corresponds to the studies conducted in the world. Moreover, these findings indicate that erythromycin may be considered the drug of choice in the treatment of Campylobacter diarrhea in this region. Resistance to fluoroquinolone and nalidixic acid was 44%, and C. coli showed higher resistance compared to C. jejuni, though statistical significance was not proved.
The ingress of various gases, liquids and ions from the environment is responsible for the deterioration of concrete structures. A large number and variety of protective surface treatments and ...coatings on the base of polymers have been developed for application to concrete surfaces in those instances, where special protection against aggressive attack is necessary. At the same time, new protective systems are continually appearing, whose adaptability to specific environments must in every case be proved. Semi-empirical predictive models for the deterioration over time are presented enabling design of coatings with required barrier properties. This paper describes the performance of a system based on inden-coumarone resins over a wide variety of exposures and application conditions and presents recommendations for design of such protective coatings.
Spektroskopija NMR danas je metoda odabira za izučavanje interakcija biomolekula s potencijalnim ligandima, što predstavlja jedan od glavnih preduvjeta za dizajn lijekova na racionalnim osnovama. ...Najvažniji doprinos spektroskopije NMR dizajnu lijekova do prije nekoliko godina bilo je rješavanje 3D strukture proteina. Uz to što nam spektroskopija NMR daje podatke o 3D strukturi slobodnih proteina kao sirove podatke za molekulsko modeliranje vezanja liganada, NMR nam izravno može dati važne eksperimentalne informacije o samim biološki važnim kompleksima. Za razliku od rendgenske strukturne analize spektroskopijom NMR može se proučavati dinamika kako samih velikih biomolekula tako i dinamika kompleksa biomolekula i potencijalnih liganda. Tako je moguće proučavanjem promjena u NMR parametrima prilikom vezanja kvalitativno (npr. "SAR by NMR") i kvantitativno (promjene kemijskih pomaka i vremena relaksacije, difuzijski NMR eksperimenti itd.) odrediti sklonosti vezanja liganada. Također je moguće i uporabom metoda kao što su npr. tr-NOESY, STD, WaterLOGSY i dr. odrediti i mjesto vezanja, odnosno dobiti informacije o konformaciji proteina, liganda ili njihovog kompleksa te epitope, tj. skupine na ligandu koje su u neposrednoj blizini mjesta vezanja. U posljednje vrijeme razvijen je velik broj tehnika NMR za izučavanje interakcija ligand-receptor, no u ovome radu opisane su samo neke od njih te su pokazane njihove prednosti i nedostaci.
The aim of this paper is improving, development and application of pulsed
thermography as experimental method for detection of defect in material. To
accomplish this, the paper has 3 aspects: 1. ...Experimental research including
оf development and improving conditions for measuring and data acquisition.
2. Theoretical research containing of analytical and numerical solving the
system of partial differential equations for heat convection by conduction,
with corresponding initial and boundary conditions. 3. Theoretical research
considering method and procedure application in pulsed infrared thermography
for given theoretical and experimental conditions. During the first part of
research, specific samples were prepared for experiment where at one side of
the plate equally spaced slots are forming the periodical structure of
defects with defined spatial frequency and depth. The other side of plate was
irradiated with short light pulse and temperature distribution on that side
was analyzed by pulsed infrared thermography. The second part of the
research, considers different models describing twodimensional heat
conduction through planparallel plate with defect in form of flat-bottom
slot, with general and specific initial and boundary conditions. In the third
part of research, comparison of experimental results and results of
simulation was made to determine the conditions and limits of method
applicability for periodically structured defects. The theoretical analysis
and experimental testing of the method was done for the defects in aluminum
plate.
Cilj ovog rada je poboljšanje, razvoj i primena impulsne termografije kao
eksperimentalnog metoda za otkrivanje defekata u materijalu. Da bi se
ostvario taj zadatak, rad je usmeren ka tri sledeća pravca: 1.
Eksperimentalna istraživanja koja obuhvataju razvoj i poboljšanja uslova za
merenje i akviziciju podataka. 2. Teorijska istraživanja koja obuhvataju
analitičko i numeričko rešavanje sistema parcijalnih diferencijalnih
jednačina provođenja toplote kondukcijom uz odgovarajuće početne i granične
uslove. 3. Teorijska istraživanja koja podrazumevaju primenu metode i
procedure u impulsnoj infracrvenoj termografiji za date teorijske i
eksperimentalne uslove. U toku prvog dela istraživanja, izrađeni su posebni
uzorci pripremljeni za eksperiment, gde su na jednoj strani ploče podjednako
razmaknuti žljebovi praveći periodičnu defektnu strukturu sa određenom
prostornom frekfencijom i određenom dubinom. Druga strana ploče bila je
ozračena kratkim svetlosnim impulsom i temperaturna raspodela na istoj strani
bila je analizirana impulsnom infracrvenom termografijom. U drugom delu
testirani su različiti modeli koji opisuju dvodimenzionalnu kondukciju
toplote kroz planparalelnu ploču sa defektom u obliku žljeba sa ravnim dnom
sa opštim i posebnim početnim i graničnim uslovima. U trećem delu izvršeno je
poređenje eksperimentalnih rezultata i rezultata simulacije u cilju
utvrđivanja uslova i granica primenljivosti metoda za periodičnu strukturu
defekata. Izvršena je teorijska analiza i eksperimentalna provera metoda u
slučaju defekata u aluminijumskoj ploči.
The motivation of the research presented in this thesis was to investigate thermomechanical processes that appears during the convective drying of food materials in systems with air recirculation. ...The mathematical model was formed to describe the change of moisture ratio of the material during the time, by taking into account the influence of all relevant thermomechanical properties of drying air (temperature, relative humidity and velocity) on the drying process. Convective laboratory scale dryer with possibility of full drying air recirculation was designed and built in order to achieve and measure all relevant drying process parameters. Apples, potatoes and bananas were used in the experiments. The chosen materials were dried under the same drying conditions. Drying air temperature was in range 35-55°C, relative humidity in range 10-30% and velocity in range 1-2 m/s. The apples were cut into cubes with 10 mm and 13 mm side dimension, potatoes were sliced into chips of 2 mm and 3 mm thickness and bananas were sliced into the cylinders with 6 mm and 7 mm thickness. Analysis of error appearance probability was performed. The effective moisture diffusivity was used to describe drying process efficiency. The experimental results confirmed that thermomechanical properties of drying air have significant influence on drying process. It was discovered that drying air, relative humidity could be ignored in some occasions. The performance of heat pump drying system was analyzed in order to discover system efficiency. The system energy and mass flows, air circulation behavior, drying air properties and system components behavior were monitored in order to calculate the main parameters of system performance. It was discovered that appropriate system performance optimization could increase system energy efficiency and reduce specific energy consumption. The results of mathematical model equation were compared with the experimental results and with the models and with the experimental results of the other authors, in order to be verified.
Predmet rada u ovoj disertaciji je istraživanje termomehančkih procesa pri konvektivnom sušenju prehrambenih materijala vlažnim vazduhom kao agensom sušenja u sistemima sa recirkulacijom. Matematičko-numeričkim metodama i regresionom analizom definisan je fizičko-matematički model koji omogućava simulaciju promene vlažnosti materijala u bezdimenzionom obliku tokom procesa sušenja, a koji uzima u obzir uticaj termomehaničkih osobina vlažnog vazduha (temperature, relativne vlažnosti i brzine strujanja) na proces sušenja. U cilju verifikacije postavljenog modela, osmišljena je i izrađena laboratorijska instalacija za konvektivno sušenje prehrambenih materijala u tankom sloju, koja radi sa potpunom recirkulacijom vazduha. Odabrani materijali (jabuka, krompir i banana) su sušeni pod istim režimima, sa temperaturom sušenja u opsegu 35 - 55°C , relativnom vlažnošću u opsegu 10 ÷ 30% i brzinom strujanja vlažnog vazduha u opsegu 1-2 m/s. Jabuke su sušene u komadićima oblika kocke dimenzija 10 mm i 13 mm, krompir u listovima debljina 2 mm i 3 mm, a banana u kolutovima debljina 6 mm i 7 mm. Analiziran je uticaj termomehaničkih osobina vlažnog vazduha na kinetiku procesa sušenja, na osnovu dobijenih vrednosti efektivnog koeficijenta difuzije. Rezultati istraživanja su potvrdili da termomehaničke osobine vlažnog vazduha značajno utiču na proces sušenja, pri čemu se u slučajevima slabijeg uticaja na proces sušenja pojedine veličine mogu zanemariti. Analiziran je rad sistema sušenja koji je podržan radom toplotne pumpe, na osnovu izračunatih vrednosti osnovnih pokazatelja efikasnosti rada sistema. Ustanovljeno je da se pravilno utvrđenim parametrima rada instalacije može uticati na povećanje energetske efikasnosti sistema i smanjenje specifične potrošnje energije po količini izdvojene vlage. Verifikacija dobijenih rezultata izvršena je poređenjem rezultata sopstvenog modela sa rezultatima sprovedenog eksperimentalnog istraživanja, a potom i sa modelima i eksperimentalnim istraživanjima drugih autora.
Nesuicidalno samoozljeđivanje (NSSO) je značajan problem mentalnog zdravlja adolescenata. Pretpostavlja se da problemi u formiranju identiteta imaju važnu ulogu u nastanku samoozljeđujućeg ponašanja ...kod mladih. Ciljevi istraživanja su bili ispitati klinička obilježja u adolescenata s NSSO te istražiti razlike u razvoju identiteta između opće
(školske) populacije adolescenata i adolescenata s NSSO.
U istraživanju su sudjelovali adolescenti u dobi od 11 do 18 godina oba spola. Kliničku skupinu (n=31) činili su adolescenti prvi puta psihijatrijski hospitalizirani kod kojih je kliničkom procjenom utvrđena prisutnost NSSO unutar 6 mjeseci prije hospitalizacije. Školsku populaciju (n=294) činili su učenici osnovnih i srednjih škola Grada Zagreba. Svi adolescenti su popunjavali upitnik Procjena razvoja identiteta u adolescenciji (AIDA), dok su pacijenti ispunjavali
i Inventar namjernog samoozljeđivanja (DSHI). U kliničkoj populaciji adolescenata utvrđena je visoka učestalost i multipli tipovi NSSO. Pacijenti s NSSO su imali značajno više rezultate difuzije identiteta u odnosu na učenike, što upućuje na veće poteškoće u razvoju identiteta kod adolescenata s NSSO. Bolje razumijevanje odnosa između oštećenja u razvoju identiteta i NSSO moglo bi unaprijediti procjenu i liječenje adolescenata s ovim značajnim psihijatrijskim problemom.
This study is about the origin and genesis of regulation of one segment of media system – broadcasting, which has been operating in The Republic of Serbia in different socio-economic conditions. ...Analyzing the development of broadcasting regulation in Serbia, we have tried to systematize our view on the origin, historical phases and, finally, characteristics of modern regulation processes of that segment of domestic media system. Taking into account the up-to-date transformation of media system in Serbia and the adoption of new laws which regulate it and which are aimed for the implementation of democratic models of developed countries and for approaching European economic and political integration in Serbia, the analytical consideration of the results of implementation of contemporary European regulatory practice in broadcasting in domestic media legislative has been of great importance. Using analytical and descriptive approach to the largest extent, the study presents different periods of broadcasting regulation in Serbia in which its development has been determined by specific historical, political and socioeconomic conditions. Thus we analyze the development of broadcasting regulation in Serbia through several historical phases, from its origin until The Second World War, during socialism, as well as in the last decade of the twentieth century and after democratic changes in 2000. We have shown that since the beginning of broadcasting in Serbia (1924-1941), in the earliest phases of regulation process, national legislation in this area relied on European regulatory framework and principles of international law then in force, which secured monopolistic position to the State and adhering to highly restrictive media policy. In this period, state interventionism was justified with practical and moral reasons. Period after The Second World War (1944-1991) was marked with dominant influence of ideological matrix of Communist Party on media system. Public media were treated as information-propaganda tools and it was expected that media experts would act as socio-political workers. Legal regulation based ownership relations on state, later social property thus preventing the existence of media market and securing direct influence of the State on the foundation, organization, financing and selection of staff who were required to implement a unique editorial policy of media. In the 1990s, so-called self management model of media system was dismantled and the largest broadcasting systems in Serbia were fully nationalized. Repressive control mechanisms have used the media for propaganda purposes. Undemocratic media laws have produced chaos in air enabling the establishment of large number of private broadcasters, while the independent media suffered a lot of pressure and irregular conditions of quasi-democratic system which articulated only formally many legal provisions as democratic. In modern times (2000-2012), media system in transition in Serbia calls for democratic transformation. This transformation has been partly realized through the adoption and implementation of the principles of European regulatory framework. However, despite normatively founded principles of democratic transformation of broadcasting system in Serbia, inconsistent implementation of the legislation in practice points out to unprincipled attitude of Government towards the key issues considering the media independence. It turned out that in transitional Serbia there is still not enough political willingness for dispossessing governing structures in broadcasting area, and the influence of government on media is dispersed on all levels of the state, from local to central. State interventionism is reflected primarily in government efforts to penetrate in public sphere and broadcasting area with help of non-media laws.
Predmet ovog rada je nastanak i geneza regulacije jednog dela medijskog sistema – radio-difuzije, koji funkcioniše u okviru Republike Srbije, posmatran u različitim društveno-istorijskim uslovima. Analizirajući dosadašnji razvoj regulacije radio-difuzije u Srbiji, nastojali smo da sistematizujemo jedan pogled na nastanak, istorijske faze i konačno, savremene osobenosti procesa regulacije tog dela domaćeg medijskog sistema. S obzirom na aktuelnost transformacije medijskog sistema u Srbiji i donošenje novih zakona koji regulišu ovu oblast a kojima Srbija nastoji da usvoji i primeni demokratske modele razvijenih zemalja i približi se evropskim ekonomsko-političkim integracijama, značajno je analitičko razmatranje rezultata primene savremene evropske regulatorne prakse u oblasti radio-difuzije u domaćem medijskom zakonodavstvu. Rad prikazuje, pretežno analitičkim i deskriptivnim pristupom, različita razdoblja regulacije radio-difuzije u Srbiji, u kojima su njen razvoj determinisale specifične istorijske, političke, društveno-ekonomske, i druge okolnosti. Stoga razvoj regulacije radio-difuzije u Srbiji posmatramo kroz nekoliko istorijskih faza: od nastanka, do Drugog svetskog rata, u periodu socijalizma, u poslednjoj deceniji 20. veka i posle demokratskih promena 2000. godine. Počev od uspostavljanja radio-difuzije u Srbiji (1924–1941), pokazano je da se u najranijim fazama razvoja regulacije nacionalno zakonodavstvo u ovoj oblasti oslanjalo na evropski regulatorni okvir i principe tada važećeg međunarodnog zakonodavstva, koje je državi obezbeđivalo neprikosnovenu monopolsku poziciju i vođenje izrazito restriktivne medijske politike. Državni intervencionizam u ovom periodu opravdavan je praktičnim i moralnim razlozima. Period posle Drugog svetskog rata (1944–1991) obeležio je dominantan uticaj ideološke matrice Komunističke partije nad medijskim sistemom. Javna glasila su tretirana kao informativno-propagandna sredstva, a od medijskih stručnjaka očekivalo se da deluju kao društveno-politički radnici. Zakonska regulativa temeljila je vlasničke odnose na državnoj odnosno društvenoj svojini, čime je onemogućeno postojanje medijskog tržišta, a državi osiguran direktan uticaj na osnivanje, organizaciju, finansiranje i izbor kadrova koji su bili dužni da sprovode jedinstvenu uređivačku koncepciju svih medija. U periodu devedesetih godina prošlog veka (1991–2000), razrušen je takozvani samoupravni model medijskog sistema i nastupilo potpuno podržavljenje najvećih radiodifuznih sistema u Srbiji. Represivni regulacioni mehanizmi instrumentalizovali su medije u propagandne svrhe. Nedemokratski medijski zakoni proizveli su haos u etru, omogućivši osnivanje velikog broja privatnih elektronskih medija, dok su nezavisni mediji trpeli snažan pritisak i neregularne uslove kvazidemokratskog sistema, koji je mnoge zakonske odredbe artikulisao samo deklarativno demokratski. U savremeno doba (2000–2012), tranzicioni medijski sistem u Srbiji pretežno karakteriše nužnost demokratske transformacije, koja se realizuje kroz usvajanje i primenu principa evropskog regulatornog okvira. Međutim, uprkos normativno utemeljenim načelima demokratske transformacije radiodifuznog sistema Srbije, nedosledna primena zakona u praksi ukazuje na neprincipijelan odnos vlasti prema ključnim pitanjima ostvarenja medijske nezavisnosti. Pokazalo se da u tranzicionoj Srbiji još uvek nema dovoljno političke volje da se razvlaste vladajuće strukture u oblasti radio-difuzije, odnosno da se produžava uticaj vlasti na medije od lokalnog do nivoa države. Državni intervencionizam ogleda se prevashodno u zalaganju vlasti da se nemedijskim zakonima zadire u javnu sferu i oblast radio-difuzije.
Obilježja infracrvenog sušenja i sušenja vrućim zrakom tankih lamela drva jasena (Fraxinus excelsior L.) i drva hrasta (Quercus robur L.) utvrđene su eksperimentalno uz pomoć laboratorijskih uređaja ...za infracrveno sušenje i sušenje vrućim zrakom. Krivulje sušenja lamela debljine 2 mm utvrđene su u rasponu temperatura između 60 i 90 °C te su prilagođene Fickovu difuzijskome modelu. Učinkovitost i brzina sušenja te efektivna difuznost procijenjene su i uspoređene unutar primijenjenih tehnika sušenja. Omjer sadržaja vode eksponencijalno se smanjuje s trajanjem procesa pri svim temperaturama primijenjenima u eksperimentu. Efektivna je difuznost drva jasena bila veća nego drva hrasta, a tehnike sušenja nisu znatnije utjecale na nju. Za obje vrste drva potvrđena je veća difuznost vezane vode s povećanjem temperature sušenja, što je uzrokovalo skraćenje procesa sušenja. Slična je energija aktivacije utvrđena za obje vrste drva, a niža je zabilježena pri IC tehnikama sušenja.
The subject of the work presented in this dissertation was to investigate the sorption of Cu (II)- ions onto synthetic hydroxyapatite (HAP)-and natural sorbents: zeolite, clay and diatomite, in order ...to define process equilibrium and kinetics under different conditions. Physico-chemical characterization showed that synthetic HAP was consisted of pure non-stoichiometric, calcium deficient, calcium hydroxyapatite, zeolite of clinoptilolite, while clay was the composite of illite, kaolinite and montmorillonite. The main phase of diatomite was amorphous silicon dioxide. Also, HAP and zeolite were characterized as a mesoporous sorbents with specific surface areas of 58 m2 / g and 23 m2 / g, respectively, while the clay and diatomite were non-porous, with low specific surface areas of 8 m2/g and 5 m2 / g. pHPZC of 6.6 was defined for HAP, clay and diatomite, while higher value of 7.5 was obtained for zeolite. Obtained results for pHPZC for HAP, clay and zeolite are in good agrement with literature, while pHPZC of diatomite has not been published. The investigation of influence of initial solution pH in the range of 2 - 10 on equilibrium showed that the final pH values varied depending on the tested sorbent. In general, final pH values increased the most in pH range 2 – 4. Areas of the plateau, where the final pH values were independent on the initial pH indicating the buffering properties of sorbents, were dependent on the sorbent and the concentration of metal ions in solution. Further increase of initial pH caused increase of final pH values. The plots of sorbed amounts vs. initial pH were of the same shape as plots pH final vs. pH initial, which can be explained with higher solubility of sorbents and their components and competition between Cu(II) and H+ ions in the strong acidic media. The final pH increase above 6 caused copper hydroxide precipitation and 100 % removal of metal ions from solution. The maximal sorption capacities at room temperature decreased in the order: HAP (0,585 mmol/g) > zeolite (0,128 mmol/g) > clay (0,098 mmol/g) > diatomite (0,047 mmol/g). In these experiments pH drop was observed, signifying the existence of specific cation sorption mechanism which was the most dominant during the sorption onto diatomite. Also, ion-exchange mechanism between Cu(II)- ions and Ca2+ ions from HAP surface was responsible for metal bonding, as well as ion-exchange with Na+, K+, Ca2+, Mg2+ from surfaces of natural mineral sorbents. The stability of system sorbent/ metal was investigated in acidic leaching solution and it was dependant on sorbent type, as well as on the previously loaded amounts. With increase of loaded metal amounts onto HAP and diatomite, the percentages of desorption also increased, while the opposite was observed for desorption from zeolite and clay- the samples with higher loadings were more stable in the acidic media. The desorbed amounts expressed in mmol/g or mg/g were higher for the more saturated samples, independent of sorbent type. The process kinetics was investigated as a function of initial metal concentration in batch system, on horizontal shaker. It was shown that the sorption onto non-porous sorbents, clay and diatomite was limited with diffusion film resistance. Contrary, the film diffusion was significant only during the first 15 minutes of process onto HAP and zeolite. The values of volumetric mass transfer coefficient kf•a were calculated using Boyd model. The values of kf•a were independent on initial concentration, and varied around averaged value of: 0,046 1/min for HAP, 0,023 1/min for zeolite, 0,017 1/min for clay and 0,031 1/min for diatomite. According to this it can be concluded that kf•a was a function of particle size for nonporous sorbents, i.e. it was highest for the smallest particles because specific surface area was higher. The obtained values for kf•a decreased in the order: HAP>diatomite>zeolite>clay, but probably this order would be different if the zeolite particles were smaller, where value for kf•a onto zeolite would be higher. Using pore diffusion models, it was shown that the effective diffusivities slightly decreased with c0 increase, while for sorption onto zeolite Deff was independent on c0. Dependence of Deff on c0 and independence of kfa on c0 can be explained by counter diffusion of cations released from sorbent surface, as well as with electrostatic repulsion of positive charged particles. These phenomena can be neglected in the fluid mass, but not inside the pores. From the analysis of results obtained for sorption onto HAP in the agitated vessel, it was observed that kf•a calculated for the first 10 minutes of the process was independent on sorbent mass and agitation speed, but slightly decreased with initial metal concentration increase, which was probably caused by the existence of pore diffusion resistance. Contrary, kf•a calculated for zeolite was independent on metal concentration and sorbent mass, but increased with agitation speed increase and particle size decrease. Effective diffusivities for sorption onto HAP and zeolite were independent on sorbent mass and agitation speed. Deff decreased with c0 increase because of counter diffusion inside the pores, but increased with particle size increase. Finally, it can be concluded that for the first 15 minutes of the sorption onto HAP and zeolite using shaker, the limiting step was film diffusion, and after that the pore diffusion, where sorption occurred inside the mesopores. Also, the mixing using shaker was not good enough, thus the obtained values for kfa and Deff were significantly lower than the values obtained for the sorption in the agitated vessel. The sorption onto HAP in the agitated vessel was limited only by pore diffusion because the film diffusion and surface saturation occurred almost instantaneously. The sorption onto zeolite in agitated vessel was governed by film diffusion during the first 10 minutes, whereas after that by diffusion inside the pores.
Predmet rada ove doktorske disertacije je bio ispitivanje sorpcije Cu (II)- jona sintetičkim HAP-om i prirodnim sorbentima zeolitom, glinom i dijatomitom, u cilju definisanja ravnoteže i kinetike procesa pri različitim uslovima. Fizičko-hemijska karakterizacija je pokazala da se sintetički HAP sastoji od čistog nestehiometrijskog, kalcijum deficitarnog, kalcijum-hidroksiapatita, zeolit od klinoptilolita, dok je glina kompozit ilita, kaolinita i montmorilonita. Glavna faza u dijatomitu je amorfni silicijum-dioksid. Takođe, HAP i zeolit su okarakterisani kao mezoporozni sorbenti specifičnih površina 58 m2/g i 23 m2/g, redom, dok su se glina i dijatomit pokazali neporozni, nižih specifičnih površina od 8 m2/g i 5 m2/g. Definisana je pHPZC koja iznosi 6,6 za HAP, glinu i dijatomit, dok je kod zeolita nešto viša i iznosi 7,5. Dobijene vrednosti pHPZC HAP-a, gline i zeolita su u dobroj saglasnosti sa literaturom, dok pHPZC dijatomita do sada nije objavljena. Ispitivanjem uticaja inicijalne pH vrednosti rastvora na ravnotežu, pokazano je da se finalne pH vrednosti razlikuju u zavisnosti od ispitivanog sorbenta. Generalno, ravnotežne pH vrednosti najviše rastu sa porastom inicijalnih pH rastvora u oblasti 2 - 4. Oblast platoa, u kome su finalne pH vrednosti nezavisne od inicijalnih i koja ukazuje na puferska svojstva sorbenata, zavisi od vrste sorbenta i koncentracije jona metala u rastvoru. Dalje povećanje polaznih pH prouzrokuje porast i finalnih. Krive zavisnosti sorbovane količine od inicijalnih pH su istog oblika kao i krive pH finalno-pH inicijalno, što se objašnjava povećanom rastvorljivoću sorbenata ili njihovih komponenti i kompeticijom Cu(II) i H+ jona u jako kiselim rastvorima. Porast finalnih pH iznad 6 dovodi do precipitacije bakar – hidroksida što rezultira 100% uklanjanjem jona metala iz rastvora. Maksimalni sorpcioni kapaciteti prema Cu(II)- jonima, na sobnoj temperaturi, opadaju u nizu: HAP (0,585 mmol/g) > zeolit (0,128 mmol/g) > glina (0,098 mmol/g) > dijatomit (0,047 mmol/g). U datim eksperimentima je utvrđen pad pH vrednosti rastvora u odnosu na početnu, što ukazuje na postojanje mehanizma specifične sorpcije, koji je najdominantniji tokom sorpcije na dijatomitu. Za vezivanje jona metala ispitivanim materijalima, odgovoran je i mehanizam jonske izmene, gde se Cu(II)- joni izmenjuju sa Ca2+ jonima sa površine HAP-a, odnosno sa jonima Na+, K+, Ca2+, Mg2+ sa površine prirodnih sorbenata. Stabilnost sistema sorbent/jon metala je ispitana u kiselom rastvoru za izluživanje i zavisi od vrste sorbenta, kao i prethodno sorbovane količine Cu(II)- jona. Sa porastom sorbovane količine na uzorcima HAP-a i dijatomejske zemlje, raste i procenat desorbovane količine, dok desorpcija sa zeolita i gline pokazuje suprotan trend - u kiseloj sredini su stabilniji uzorci sa većom sorbovanom količinom jona metala. Ako posmatramo desorbovanu količinu izraženu u mmol/g ili mg/g, ona je veća na uzorcima koji su više zasićeni, nezavisno od vrste sorbenta. Kinetika procesa je ispitana u različitim šaržnim sistemima. Prvi sistem su pojedinačne šarže sa mešanjem na horizontalnom šejkeru, gde je proces sorpcije ispitan u funkciji od početne koncentracije Cu(II)- jona na svim ispitanim sorbentima. Drugi šaržni sistem je sud sa mešalicom u kom je ispitana kinetika procesa sorpcije HAP-om i zeolitom u funkciji od koncentracije sorbata, mase sorbenta, brzine mešanja, a za zeolit i od granulacije sorbenta. Pokazano je da je sorpcija glinom i dijatomitom, kao neporoznim sorbentima, limitirana otporom u filmu fluida. Nasuprot tome, difuzija u filmu fluida tokom sorpcije na šejkeru HAP-om i zeolitom je značajna na početku procesa, tokom prvih 15 minuta. Vrednosti zapreminskog koeficijenta prenosa mase su izračunate Boyd-ovim modelom. Dobijene vrednosti kf•a su nezavisne od početne koncentracije Cu(II)- jona u rastvoru i variraju oko srednje vrednosti 0,046 1/min za HAP, 0,023 1/min za zeolit, 0,017 1/min za glinu i 0,031 1/min za dijatomit. Iz preth
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