Marina Trgo

Interaction of the zeolitic tuff with Zn-containing simulated pollutant solutions

The possibility of removing Zn2+ cations from wastewater by ion exchange using natural zeolites as exchangers has been investigated. The process of binding of zinc ions into zeolite structure has been established by several reaction mechanisms as a fast chemical reaction of ion exchange, accompanied by slower adsorption of different ionic species and possible precipitation or coprecipitation with the zeolite structure. The physicochemical phenomena such as hydrolysis and dissolution of surface layers are the result of interaction of zeolite with hydrogen or hydroxyl ions from the solution. Complexation of OH- with Zn2+ to form the zinc-hydroxy species strongly depends on pH value and affect the uptake mechanism as to lower dissolution of surface aluminosilicate layers. Structure imperfections as a surface property of mineralogical nonhomogeneous zeolitic grains can lead to formation of sorption surface sites with different energy, which affects the nonuniform distribution of different zinc species adsorbed. It is particularly possible in zeolitic tuff samples with relatively high content of aluminosilicates as minor mineralogical components, which is characteristic of Croatian deposits.

Testing of Breakthrough Curves for Removal of Lead Ions from Aqueous Solutions by Natural Zeolite‐Clinoptilolite According to the Clark Kinetic Equation

Abstract The kinetics of removal of lead ions from aqueous solutions using the column method with a fixed bed of natural zeolite clinoptilolite has been examined. Experimental results are presented as breakthrough curves, and tested according to the kinetic equation developed by Clark by means of the linear and non‐linear regression analysis. Both mathematical methods attain the same values for parameters A and r of the Clark equation. These parameters are used for the calculation of the sorption rate coefficient k and the removal capacity q. The removal capacity obtained from the experimental results and the capacity calculated using the Clark kinetic equation have shown excellent agreement. The Clark kinetic equation has been found suitable for description of removal of lead on zeolite for different experimental conditions. Based on the calculated parameters, the theoretical breakthrough curves have been plotted and compared with the experimental ones. Applicability of the kinetic equation used has been additionally confirmed by the good fit of experimental and modelled breakthrough curves. Based on the parameters calculated, the behavior of modelled breakthrough curves was predicted for different depths of fixed bed of zeolite.

The Effect of Zeolite Fixed Bed Depth on Lead Removal from Aqueous Solutions

Abstract The effect of zeolite bed depth on lead removal from aqueous solutions by the column method has been examined. The results indicate that the increase of bed depth delays the breakthrough point and exhaustion point, and increases the contact time of the zeolite – lead solution, and the height of the mass transfer zone, hz. The increase of the bed depth lowers the effect of axial dispersion on the mass transfer process. In order to predict the time necessary for exceeding the defined effluent concentration for a constant bed depth, the bed depth service time (BDST) approach has been used. Experimentally obtained breakthrough curves for the flow rate of 1 ml/min were used to derive the BDST approach equations. These equations were successfully used for modelling of the system for flow rates of 2 and 3 ml/min. The BDST equations have yielded modelled linear equations used for calculation of hz. The increase of the flow rate increases hz, which indicates that the zeolite–solution contact time is not sufficient. This may be attributed to the affect of axial dispersion on mass transfer on the solid-liquid interface.

Monitoring of hydrolysis in natural zeolite-H2O systems by means of pH and electrical conductivity measurements

Hydrolysis of a natural zeolite and of the same zeolite converted into its Na^+ form by conditioning with 2M NaCl, has been carried out with high purity ion-free water by means of the batch method. The process of hydrolysis was monitored by continuous measurements of changes in pH values and in electrical conductivity in the zeolite-water suspension. The results obtained for the hydronium ion exchange have been analysed kinetically according to the heterogeneous diffusion model and the first-order rate model.

Competitive removal of lead(II) and zinc(II) from a binary aqueous solution on a fixed bed of natural zeolite

Abstract The column method using a fixed bed of zeolite clinoptilolite was applied to remove lead and zinc ions from binary metal ions solutions. The raw zeolite sample used in this study was obtained from the Vranjska Banja deposit (Serbia) and contained more than 80% of clinoptilolite. The breakthrough curves have an S-shape for the total as well as for the single metal ions in binary solution. Lead and zinc ions bind simultaneously on the zeolite bed, and as the service cycle progresses lead ions displace a great portion of bound zinc. During the regeneration cycle, the quantity of lead desorbed is =15 times higher than the quantity of zinc, which means that mostly lead ions were bound on the zeolite. Breakthrough curves have been interpreted quantitatively by means of the Michaels method, and the results calculated have been compared with the results for single metal ions solutions.

The effect of concentration and pH on selectivity of ion exchange in system natural zeolite—Na+/Zn2+ aqueous solutions

The removal of zinc ions from synthetic binary solutions on natural zeolite clinoptilolite has been studied. The investigations were conducted to study the effect of concentration and pH value on the selectivity of natural zeolitic tuff (>80% clinoptilolite) for zinc ions. The results for different concentrations of binary solutions have yielded ion exchange isotherms that show sigmoid shape for all examined concentrations. This indicates a substantial unselectivity for zinc ions that decreases by the decrease of total concentration. The selectivity is significantly improved if solutions originate from acetate than from sulphate salts, and by increasing of pH in the solution from 4 to 5 or 6. This could be explained by changes of hydration energy of divalent zinc ion.

Uptake of Pb and Zn from a binary solution onto different fixed bed depths of natural zeolite – the BDST model approach

Abstract The removal of lead and zinc from a binary solution by fixed bed depths (40, 80 and 120 mm) of a natural zeolite was examined at a flow rate of 1 mL/min. The results obtained were fitted to the Bed Depth Service Time (BDST) model and the parameters of the model (q and k) were used to design a column system for flow rates of 2 and 3 mL/min at a bed depth of 80 mm. The experimental results were in excellent agreement with those predicted and experimental breakthrough curves for the binary systems were obtained. This approach facilitates the design of effective binary column processes without additional experimentation. Two major design parameters, the Empty Bed Contact Time (EBCT) and the zeolite usage rate, were calculated. The highest EBCT value of 13.56 min represents the optimal conditions for the binary (Pb+Zn) solution.

A study of kinetics and successive sorption/desorption of Zn and Cd uptake onto iron-modified zeolite

Abstract The sorption properties of iron-modified zeolite (IMZ) and the kinetics of zinc and cadmium uptake by the IMZ were investigated by the batch method. Two kinetic stages were observed, fast uptake up to 240 min, followed by slow uptake up to equilibrium. Kinetic results were fitted to the reaction and diffusion kinetic models, which indicated that intra-particle diffusion was the rate-limiting step. The Vermeulen’s approximation model was used to predict the quantity of Zn and Cd ions removed per gram of IMZ. The results of the successive sorption and desorption of Zn and Cd ions, with different electrolyte solutions, showed the best desorption efficiency with sodium salt solutions. Four successive repetitions of the sorption/desorption cycles showed a small difference between the amount of sorbed and desorbed Zn and Cd ions from the second to the fourth cycle. This indicates excellent sorption/regeneration properties of the IMZ.

01-P-17 - The sorption equilibria in natural zeolite-aqueous solutions systems

Publisher Summary This chapter discusses the equilibrium properties of the hydrolysis and ion-exchange process for natural and pretreated zeolite-clinoptilolite by measuring the concentration of exchangeable sodium (Na + ), potassium (K + ), calcium (Ca 2+ ), and magnesium (Mg 2+ ) ions with time in the liquid phase. The analysis of the relation of the concentrations of ionic species leaving the zeolite and those entering the zeolite structure has found to be a nonstoichiometric process. The established nonstoichiometry of the overall mass transfer process through the outer and inner surface of zeolite particles is due to the strength of the bond of exchangeable ions in the structure, as a phenomenon of sorption. The sorption takes place on characteristic locations on the zeolite particle surface, which has been confirmed by scanning electron microscope (SEM) images and energy-dispersive X-ray spectroscopy (EDX) analysis.

Optimization of Removal Efficiency and Minimum Contact Time for Cadmium and Zinc Removal onto Iron-modified Zeolite in a Two-stage Batch Sorption Reactor

In highly congested industrial sites where significant volumes of effluents have to be treated in the minimum contact time, the application of a multi-stage batch reactor is suggested. To achieve better balance between capacity utilization and cost efficiency in design optimization, a two-stage batch reactor is usually the optimal solution. Thus, in this paper, a two-stage batch sorption design approach was applied to the experimental data of cadmium and zinc uptake onto iron-modified zeolite. The optimization approach involves the application of the Vermeulen’s approximation model and mass balance equation to kinetic data. A design analysis method was developed to optimize the removal efficiency and minimum total contact time by combining the time required in the two-stages, in order to achieve the maximum percentage of cadmium and zinc removal using a fixed mass of zeolite. The benefits and limitations of the two-stage design approach have been investigated and discussed.