Mogućnost primene zeolita u tehnologijama vezanim za unapređenje i zaštitu životne sredine

Abstract

Ovaj rad ukazuje na moguće pravce upotrebe prirodnih mineralnih sirovina - zeolita, u tehnologijama vezanim za zaštiti i očuvanju životne sredine. Zeoliti su tektoalumosilikati u kojima (Si,Al)4O4 tetraedri izgrađuju kostur ili skelet, stvarajući šupljine u kojima se nalaze veliki katjoni i molekuli vode, koji imaju značajan stepen pokretljivosti što dopušta katjonsku izmenjivost i reverzibilnu dehidrataciju, što je jedno od najvažnijih svojstava zeolita, na kome se i zasniva njegova višestruka primena. Ovi minerali bez prethodne modifikacije se koriste za uklanjanje metala, amonijaka i drugih katjonskih zagađivača iz vode, vazduha i zemljišta. Ispitivanja efikasnosti adsorpcije Pb, Cu, Zn iz otpadnih voda rađena su na prirodnom klinoptilolitu i klinoptilolitu prethodno prevedenom u Na-oblik. Rezultati pokazuju da je visok stepen adsorpcije Pb postignut na oba ispitana mineralna adsorbenta (99%), dok je adsorpcija Cu i Zn efikasnija na Na-klinoptilolitu, i za Cu iznosi 95%, a za Zn 96%. Zeoliti takođe mogu imati značajnu ulogu u uklanjanju amonijum jona iz kontaminiranih voda. Ispitivanja pokazuju da se umanjenje koncentracije amonijum jona kreće od oko 74% do čak 98% u zavisnosti od količine dodatog adsorbenta. U vodama u kojima je prisutan uglavnom amonijačni jon kao zagađivač, zeoliti se nakon upotrebe mogu koristiti za proizvodnju amonijačnih đubriva. Kontrolisanim procesom modifikacije organskim površinski aktivnim supstancama, dobijaju se modifikovani alumosilikatni minerali koji imaju veću efikasnost adsorpcije, kako prema slabije polarnim organskim zagađivačima, tako i prema neorganskim anjonima. Izmenjivi katjoni na površini minerala mogu biti zamenjeni velikim dugolančanim molekulima kvaternarnih amina, pri čemu se dobijaju pogodni adsorbenti za fenol, benzen, ksilen, toluen i druge organske kontaminente. Osim značajne uloge u prečišćavanju voda, u poslednje vreme se dosta govori i o upotrebi zeolita u adsorpciji gasovitih polutanata. Vršena su istraživanja uklanjanje NOx iz industrijskih gasnih tokova upotrebom zeolita aktiviranog amonijumovim jonima. Proces se zasniva na tome da joni amonijuma vezani za mikroporozne alumosilikate redukuju NOx u N2 na temperaturama manjim od 373 K u suvim uslovima. Različiti autori su uporedo ispitivali adsorpciju isparljivih organskih jedinjenja na zeolitu i aktivnom uglju, i istaknuta je prednost zeolita u odnosu na aktivni ugalj u svim aspektima osim u ceni. Na osnovu svega prikazanog, a dat je samo deo širokog spektra moguće primene ovih minerala, može se konstatovati da zeoliti zaista predstavljaju prirodne resurse izuzetnih sposobnosti, i da će dalja ispitivanja njihove upotreba doprineti održivoj budućnosti, s obzirom na trenutnu i projektovanu sliku stanja životne sredine.

This article points out some possible applications and uses of natural mineral raw materials - zeolites in environmental and remediation technologies. Zeolites are tecto-alumosilicates, in which (Si, Al)4O4 thetraeders form skeleton structures with voids which large cations and water molecules can enter. Within the zeolite structure they remain highly movable which allows cation-exchange and reversible dehydratation. This is one of the main properties of zeolites on which their multiple use is based on. These minerals are often used without any prior modification for removal of metal ions, ammonia and other cationic water, soil and air pollutants. Determinations of adsorption efficiencies for Pb, Cu, Zn from wastewaters were performed with natural clinoptilolite, and modified clinoptilolite in Na-form. Results show high degree of adsorption for Pb on both analyzed mineral adsorbents (99%), while adsorption of Cu and Zn is much more efficient on Na-clinoptilolite and equals 95% for Cu and 96% for Zn. Zeolites can also have significant role in wastewater treatment for ammonia removal processes. Studies show reductions in ammonia concentration (removal efficiency) from 74 to even 98%, depending on quantity of added adsorbent. Furthermore spent adsorbent from treatment processes, where mainly ammonia is present as a pollutant, can be used for production of ammonia fertilizers. Through controlled process of modification with organic surfactants, modified alumosilicate minerals with higher adsorption affinity towards weak polar organic pollutants as well as inorganic anions are obtained. Exchangeable cations on the surface of the mineral can be substituted with large long-chained molecules of quaternary amines and efficient adsorbents for phenol, xylene, toluene, and other organic pollutants are produced. Besides significant role in wastewater treatment processes, lots of potential uses in adsorption of gaseous pollutants are investigated lately. Use of ammonia activated zeolites in NOx removal processes from industrial flue gases, is an example of such research activities. NOx is reduced to N2 on temperatures less than 373 K in dry conditions by the ammonia ions bonded to the microporous alumosilicates. Different authors have analyzed and compared adsorption of volatile organic pollutants on zeolite and charcoal. Results of these studies favor zeolite in all aspects apart from the price. With all mentioned above it is safe to say that zeolites are natural materials with outstanding properties and that further investigations of their use could be beneficial to sustainable future regarding current and projected state of the environment.