Dalibor Kuchar

Uptake of Fluoride by Al3+ Pretreated Low‐Silica Synthetic Zeolites: Adsorption Equilibrium and Rate Studies

Abstract The removal of fluoride from single component aqueous solution using Al3+‐ pretreated low‐silica synthetic zeolites (Al‐Na‐HUD, Al‐HUD, Al‐F9, and Al‐A4) was studied. The effects of adsorbent mass, initial solution pH, and initial concentration on fluoride removal in a batch system were evaluated. Equilibrium data were simulated using simple isotherms such as the Freundlich (F), Langmuir‐Freundlich (LF), Redlich‐Peterson (RP) and Dubinin‐Radushkevitch (DR) isotherms. From the DR model, initial pH effects and desorption studies, it was considered that the fluoride adsorption onto the zeolites proceeded by ion‐exchange or chemisorption mechanism. In interpreting the kinetic results, reaction kinetics (using Elovich equation) and mass transfer processes (both external mass transfer and intraparticle diffusion) were considered. Equilibrium and kinetic results of fluoride adsorption onto the adsorbents demonstrated the following order of performance: Al‐Na‐HUD>Al‐F9> Al‐HUD>Al‐A4.

Study on reaction kinetics and selective precipitation of Cu, Zn, Ni and Sn with H2S in single-metal and multi-metal systems

Determination of reaction kinetics and selective precipitation of Cu, Zn, Ni and Sn with H(2)S in single-metal and multi-metal systems were studied to develop a process of metal recovery from plating wastewater. As samples, single-metal model wastewaters containing Cu, Sn, Zn or Ni, and multi-metal model wastewater containing Cu-Zn-Ni or Sn-Zn mixtures were used. In both single-metal and multi-metal systems, the pH value was precisely controlled at a value of 1.5 for CuS and SnS precipitation, 4.5 for ZnS precipitation and 6.5-7.0 for NiS precipitation. Subsequently, the sulfidation of Cu, Sn, Zn and Ni was evaluated. It was found that an amount of H(2)S equimolar to a given metal was sufficient to achieve almost complete precipitation of the particular metal. Further, the selectivity of metal precipitation was found to be higher than 95% in the Cu-Zn-Ni multi-metal system and higher than 91% in the Sn-Zn system. It was also found that the sulfidation reaction proceeded in accordance with Higbies penetration theory and reaction rate constants and mass-transfer coefficients under various experimental conditions were determined. Finally, the reaction rate constants obtained in single-metal and multi-metal systems were found to be almost the same indicating that the precipitation of a particular metal was not significantly affected by the presence of other components.

Ultrasound assisted extraction and decomposition of Cl-containing herbicide involved in model soil

This work focused on ultrasound assisted extraction and decomposition of MCPA [(4-chloro-2-methylphenoxy) acetic acid] from model soil under argon atmosphere. In the experiments, 10 g model soil containing 1.75 x 10(-5) mol MCPA mixed with 90 g of de-aired water was used. For a comparison, the experiments were also carried out using MCPA aqueous solution of which the concentration was adjusted to 1.75 x 10(-4) mol/l. The results showed that complete MCPA decomposition was achieved after 120 min in the case of MCPA aqueous solution. Meanwhile, in the case of model soil, the MCPA decomposition ratio of 0.9 was obtained after 600 min. This result was attributed to combined effect of MCPA adsorption on kaolin and to attenuation of ultrasound by solid particles of kaolin. To evaluate ultrasound attenuation in the presence of solid particles, experiments with slurry consisting of alumina particles and MCPA solution were carried out at alumina particles concentration range of 0.1-100g/l. The results showed that the MCPA initial decomposition rate significantly decreased with an increase in alumina particles concentration. Thus, it was concluded that the solid particles reduced the MCPA decomposition ratio by reducing the formation of reactive species such as hydroxyl radicals which are know to be necessary for MCPA decomposition.

Enhanced dechlorination of chlorobenzene and in situ dry sorption of resultant Cl-compounds by CaO and Na2CO3 sorbent beds incorporated with Fe2O3.

The dechlorination of C(6)H(5)Cl and the in situ dry sorption of Cl-compounds produced by C(6)H(5)Cl decomposition in an alkaline sorbent of CaO or Na(2)CO(3) incorporated with Fe(2)O(3) were studied. A sample gas containing C(6)H(5)Cl at an initial concentration of 500 ppm balanced by either N(2), O(2) (5%)-N(2) or H(2)O (10%)-N(2) carrier gas was introduced into a lab-scale quartz tube reactor where CaO or Na(2)CO(3) sorbent was packed with Fe(2)O(3). Subsequently, the effect of Fe(2)O(3) addition to CaO or Na(2)CO(3) on the removal of C(6)H(5)Cl, achieved by the decomposition of C(6)H(5)Cl as well as the dry sorption of Cl-compounds produced by C(6)H(5)Cl decomposition, was investigated. It was found that the decomposition of C(6)H(5)Cl in CaO or Na(2)CO(3) sorbent bed incorporated with Fe(2)O(3) occurred in the lower temperatures, compared to the case when only CaO or Na(2)CO(3) sorbent bed was used. Thus, Fe(2)O(3) was found to play a catalytic role in the oxidative decomposition of C(6)H(5)Cl. Further, the decomposition of C(6)H(5)Cl in a bed containing only Fe(2)O(3) was promoted by the presence of O(2) and H(2)O in the reaction atmosphere. Moreover, a higher amount of Cl was absorbed in the combined CaO/Fe(2)O(3) and Na(2)CO(3)/Fe(2)O(3) beds, compared to the absorption of Cl-compounds in only CaO or Na(2)CO(3) sorbent bed. Finally, the comparison of CaO and Na(2)CO(3) sorbents showed that the decomposition of C(6)H(5)Cl and the in situ dry sorption of the resultant Cl-compounds in the combined Na(2)CO(3) and Fe(2)O(3) beds were higher than those in the combined CaO and Fe(2)O(3) beds.