Kinetic and Thermodynamic Studies for Phosphate Removal Using Natural Adsorption Materials

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.

Keywords: Alginite, calsit, Chinese blust furnace slag, clinoptilolite-rich tuff from various deposits, composed chitosan-zeolite, dynamic experiments, granulated ferric hydroxide GEH, isotherm calculation, kinetics, MAS NMR, montmorillonite-rich bentonite, phosphate elution, phosphate removal, SEM, slovakite, soil farming, the point of zero charge (PZC), thermodynamics.