Sorption phenomena of modification of clinoptilolite tuffs by surfactant cations.

The sorption of cationic surfactant hexadecyltrimethylammonium (HDTMA) onto the solid/liquid interfaces of different clinoptilolite rich tuffs (CT) is examined. Examined were CT from Serbia with 75% clinoptilolite, CT from Turkey with 70% clinoptilolite, and CT from Croatia with 60% clinoptilolite. The sorption of HDTMA cations increased in the following order: CT from Serbia>CT from Turkey>CT from Croatia. The maximum amounts of sorbed HDTMA cations, normalized with regard to external cation exchange capacities of tuffs, were 1.79, 1.70, and 1.14 for Serbian, Turkish, and Croatian CT. FTIR analysis of samples with the maximum amount of sorbed HDTMA cations showed that HDTMA chains on Serbian CT adopt mainly a stretched all-trans conformation, while at the surfaces of CT from Turkey and Croatia the amount of gauche conformations increased. The zeta potentials of CT samples with the maximum amount of sorbed HDTMA cations and the sorption of benzoate anions on these samples increased in the following order: CT from Turkey>CT from Serbia>CT from Croatia. It can be assumed that on the surface of CT from Turkey iron (hydr)oxide clusters or nanoparticles with positive surface sites are present, due to which the isoelectric point is sifted toward lower and the zeta potential toward higher values. Therefore, the sorption of benzoate anions on modified CT from Turkey is also higher.

Interaction of surfactant-modified zeolites and phosphate accumulating bacteria.

The aim of this study was to determine the interaction of surfactant-modified zeolites (SMZ) and orthophosphate (P)-accumulating bacteria in the process of P removal from wastewater. The SMZ were prepared from the natural zeolite (NZ) of size fractions <0.122 mm and 0.25-0.5 mm. The hexadecyltrimethylammonium (HDTMA) bromide was used to modify the NZ surface from partial monolayer to the bilayer coverage. The surface modification of NZ resulted in the change of zeta potential of particles from negative to positive and great enhancement of the P-adsorption capacity. Only in reactors containing <0.122 mm fraction of partial monolayer coverage of the SMZ, the P was efficiently removed from wastewater by combined adsorption onto the SMZ and bacterial uptake in the biomass. The SMZ with bilayer or patchy bilayer coverage showed the bactericidal effect. To enhance the P removal from wastewater in the aerated biological system, the SMZ can be used, but the special attention should be given to the configuration of sorbed HDTMA molecules and its potential desorption.

Decationization and dealumination of clinoptilolite tuff and ammonium exchange on acid-modified tuff.

The paper presents results of investigation of exchange of the clinoptilolite tuff cations with hydrogen ions from HCl solution of concentration 0.1 mmol cm(-3) and ammonium ions solutions of concentrations 0.0071 to 2.6 mmol cm(-3). Molal concentrations, x (mmol g(-1)) of cations exchanged in acid solution and in ammonium ions solutions were compared with molal concentrations of cations obtained by determination of the cation-exchange capacity of clinoptilolite tuff. The obtained results show that at ammonium ion concentrations lower than 0.1 mmol cm(-3), with regard to exchange capacity for particular ions, best exchanged are Na+ ions, followed by Mg2+ and Ca2+ ions, while exchange of K+ ions is the poorest (Na+ > Mg2+ > Ca2+ > K+). At ammonium concentrations from 0.2 to 1 mmol cm(-3) the order is Na+ > Ca2+ > Mg2+ > K+. At concentrations higher than 1 mmol cm(-3) the order is Na+ > Ca2+ > K+ > Mg2+. The results are a consequence of the uptake of hydrogen ions by zeolite samples in ammonium ions solutions at concentrations lower than 1 mmol cm(-3) and indicate the importance of Mg2+ (besides Na+ ions) for the exchange between clinoptilolite cations and H+ ions, in contrast to K+ ions, whose participation in the reaction with H+ ions is the lowest. During decationization of the clinoptilolite in acid solution, best exchanged are Na+, Mg2+, and Ca2+ ions, while exchange of K+ ions is the poorest. Due to poor exchange of K+ and H+ ions and good exchange of Na+, Mg2+, and Ca2+ ions, it is to be assumed that preservation of stability of the clinoptilolite structure is caused by K+ ions present in the channel C. Clinoptilolite is dissolved in the clinoptilolite A and B channels where Na+, Mg2+, and Ca2+ ions are present. On the acid-modified clinoptilolite samples, exchange of ammonium ions is poorer than on natural zeolite. The longer the contact time of the zeolite and acid solution, the worse ammonium ions exchange. It can be assumed that H+ ions exchanged with zeolite cations are consumed for solution of aluminum in the clinoptilolite structure; therefore the concentration of H+ ions as exchangeable cations decreases. In the ammonium ion solution at a concentration of 0.0065 mmol cm(-3), from the acid-modified zeolite samples, Al3+ ions are exchanged best, followed by Na+, Mg2+, Ca2+, and K+ ions. Further to the results, it is to be assumed that exchangeable Al3+ ions available from clinoptilolite dissolution are best exchanged with H+ ions in acid solution.

Ammonium exchange in leakage waters of waste dumps using natural zeolite from the Krapina region, Croatia.

The paper presents the results of investigating the treatment of leakage waters from waste dumps using activated carbon and natural zeolite clinoptilolite, known as a very selective and efficient cation exchanger for ammonium ions. The results are presented of chemical and physical analyses of leakage waters characterized by a high content of ammonium (820 mg L(-1)) and organic pollutants (1033 mg L(-1) C). Physical and chemical characteristics of zeolite and the exchange of ammonium ions in model and real solutions were determined in laboratory trials. Treatment of leakage water with 0.04-2.5% (w/w) activated carbon (Norit 0.8 Supra) led to a reduction of total organic carbon in leakage water from 1033 to 510 mg L(-1). Pretreatment of leakage water with activated carbon did not improve the exchange of ammonium ions on zeolite. Without pretreatment of leakage water, the exchange of ammonium ions amounted to 4.2 mg NH4+/g zeolite. Addition of activated carbon, regardless of its mass, increased the exchange of ammonium ions to only 5.7 mg NH4+/g zeolite. In the model solution of an equal concentration of ammonium as the real solution, 17.70 mg NH4+/g zeolite was exchanged. Organic pollutants that were not eliminated by activated carbon (most probably components of natural origin) adsorbed to zeolite and prevented the exchange of NH4+ ions, which was also reduced due to the presence of K+ and Ca2+ ions.