Environmental Zeolites and Aqueous Media: Examples of Practical Solutions

The word “zeolite” has Greek roots and means “boiling stones” (zein = to boil and lithos = stone), derived from the visible loss of water, noted when natural zeolite was heated in the “mineralogist´s” blowpipe. Volcanic rocks containing natural zeolites, i.e., hydrated aluminosilicate minerals, have been mined worldwide perhaps for more than thousand years, mostly for use as cement and building stones. Since that time, the progress in marketing natural zeolites as building stones, as lightweight aggregate or pozzolans in cements and concretes, as filler in paper, in uptake of radiocesium and strontium from nuclear waste and fallout, as soil amendments in agronomy and horticulture, in the removal of ammonia from municipal, industrial or agricultural waste and drinking waters, as energy supplier in solar refrigerators, as dietary supplements in animal diets, as consumer deodorizers, in pet litters, in uptake of ammonia from animal manures, as ammonia filters in kidney-dialysis units and as zeoponic substrate for growing plants on space missions to their recent success in healing of cuts and wounds or even as anti-tumour adjuvants has been encouraging, manifesting that the natural zeolites have been considered for a commodity of a great potential, application of which promises to expand even in near future.

From about 80 known types of natural zeolites, at least 20 have been reported from repositories in zeolitically altered rocks. However, only the following nine (analcim, chabazite, clinoptilolite, erionite, ferrierite, heulandite, laumontite, mordenite and phillipsite) are known to occur in repositories large enough to mine. These zeolites, which were formed by the natural alteration of volcanic aluminosilicate ash, occur in either closed system or open system deposits. Clinoptilolite is by far the most common zeolite. These minerals occur in rocks and sediments, seemingly formed in widely disparate environments, which include deep sea sediments, continental accumulations in thick basin fills or in shallow lakes, and also in some lava flow sections. Currently, over thousand occurrences of zeolite minerals have been reported, predominantly from sedimentary rocks of volcanic origin in more than 50 countries of the world. The ready availability of zeolite-rich rocks at low cost and the shortage of competing minerals are probably the most important factors for its large-scale use. In this chapter crystal structure of sodalite, LTA, faujasite, erionite and clinoptilolite is described, in conclusion focussing on the Slovakian clinoptilolite-rich tuff, respectively.

The topic of ion exchange and adsorption has been passed through an interesting historical and scientific development as the first section of this chapter entitled as: “Introduction to historical background of ion exchange and adsorption phenomena” reports. The current adsorption theory and relevant applications initiated by Langmuir´s fundamental work have been developed extensively more or less during the last 80 years, as some general aspects of adsorption as the next section of this chapter discusses. History of radioactive waste treatment worldwide using natural zeolite is also shortly reported. An approach to physical characterization of fundamental ion exchange and adsorption behaviors (kinetic and thermodynamic parameters) of Slovakian and Chinese clinoptilolite- and mordenite-rich tuffs in aqueous solutions of NH4+, Cu2+, Pb2+, Zn2+ and Fe3+ ions as case studies are presented furthermore. Ion exchange isotherms for the exchange of NH4+, Co2+, Cs+, Ba2+, Ag+ and Zn2+ onto native and Na-pretreated Slovakian clinoptilolite- and mordenite-rich tuffs are described and graphically illustrated, finally.

Human industrial, agricultural and mining activities are the reason, why the most of our water bodies suffer on superfluos concentrations of phosphorus and thus eutrophication and water quality deterioration. In this chapter some attention is focused on the various traditional adsorbents (Fe-oxyhydroxide GEH104, montmorillonite, slovakite, calsit, various deposit clinoptilolite-rich tuffs, alginite, Chinese slag, chitosan composed zeolite), a few of the local repositories, which prove enhanced performance for phosphate removal. Slovakian clinoptilolite-rich tuff effectively removed phosphate ions from waters. Although, the montmorillonite, slovakite and GEH104 product proved slightly higher uptake capacities towards phosphate ions at the ambient temperature than the clinoptilolite-rich tuff did, the increased temperature of systems supported the uptake performance only by clinoptilolite-rich tuff, not by montmorillonite and GEH104 adsorbents. The film-diffusion was the rate-limiting step in all of the adsorbents examined, what simultaneously confirmed the results of the applied Weber-Morris mass transfer model. Energetically lower surface physisorption of phosphate onto clinoptilolite-rich tuff, GEH and montmorillonite, however the chemisorption by slovakite was confirmed. Under the standard conditions the adsorption of phosphate onto all adsorbents examined occurred spontaneously. The results of standard free energies indicated simultaneously that the spontaneity slightly decreased with temperature. The highest elution of phosphate was observed by montmorillonite (about 50%), while by clinoptilolite-rich tuff the elution with tap water was rather low. In dynamic regime the best performance in phosphate uptake proved GEH product. According to MAS NMR measurements the best symmetry in the spectrum of P-clinoptilolite indicated, that Ca2+ cations are most frequently occurring in clinoptilolite-rich tuff framework and dominant signal at chemical shift of 2.7-2.8 ppm may be assigned as surface precipitate Ca3(PO4)2.

In different period of time, various adsorption materials have been fabricated and industrially applied, based at that time accessible raw materials as well as that time state of the knowledge. Before World War I, the carbon adsorbents were mostly produced, during the period between World War I and World War II, the active carbons, silica gels and aluminium oxides, but after World War II revolutionary progress has been made in discovery and application of synthetic zeolites and zeolitelike adsorbents traditionally known as molecular sieves. The main class of microporous materials are zeolites, the only existing crystalline materials with a well defined pore structure in a microporous range. Consequently to above short historical excurse and based on encouraging results of Slovakian clinoptilolite-rich tuff producer (Zeocem Company) achieved since 1980, the topic of this chapter is to review the author´s most recognized efforts contributing to water cleanup innovation by using the Slovakian natural zeolite clinoptilolite. A laboratory model was installed at Water Research Institute in Bratislava in the spring of 1986, before the pilot examination started to be realized in the field. To save one of the Eastern Slovakian surface water reservoirs (upper part of the river Ondava) in 1984, in the region with a critical deficiency of high quality drinking water, the local Water Works applied for surface water purification a powderized natural zeolite (clinoptilolite-rich tuff) from the nearby repository Nižný Hrabovec, together with the primary coagulant Al2(SO4)3. 18H2O. Similar operation with the same hydraulic loading rates through the zeolite beds as by the drinking water purification units (900 L/h) was used for ammonia removal of mixed tannery and sewage sludge wastewater at Shoe Manufactury Wastewater Reclamation Plant in Otrokovice (former Czechoslovakia) in the 1987. The 3-fractional regeneration and adequate ammonia stripping process used for regenerant recovery and recycling in this zeolite ion exchange pilot installation was proposed.

The Slovakian clinoptilolite-rich tuff was chosen as the interface carrier (interface consisting mostly from polymeric substances) based on its huge abundance in the country, accessibility and feasibility, cost effectiveness and sufficiently large surface area, rigidity and surface functionality. Simple pretreatment of zeolite samples to homoionic forms with ion exchange was done at the laboratory to enhance the ion exchange capacity of the raw zeolite. The octadecylammonium (ODA) cationic surfactant loaded and surface carbonized clinoptilolite-rich tuff as well as powdered zeolite-gel beads (alginate pelletized clinoptilolite-rich tuff) were prepared furthermore, to prove the adsorption performance of such modifications towards various, mostly anionic and organic pollutants, i.e., chromate, arsenate, sulphate, nitrate, chloride, iodide, bromide, fluoride, azodyes-acid red and indigotine, cefazoline and phenol. To examine the zeolite adsorbents for their performance, batch and column (packed bed) laboratory setup was used. Complementary analytical methods, e.g., FTIR, Raman, TG, DTA, S(BET), SEM, HR TEM, UV-VIS diffuse reflectance, SIMS, NMR, XPS, SAXS, Mössbauer spectroscopy were applied for the characterization of the prepared ODA hydrophobized, alginate pelletized and carbonized clinoptilolite-rich tuffs. Removal performance of zeolite adsorbents was compared with other on the market accessible adsorption materials, like active coke of Slovakian trade mark HYS-N and of German provenience silcarbon, industrial ashes chezacarb (amorphous carbon) from Chemopetrol Litvínov (Czech Republic), commercial Happy End products from Great Britain (mostly natural resources derived and mixed products denoted as SK1, SK2, DN2 and CB18), Nanofer 25S from Czech Company Nanoiron, Ltd. and some others.