Ljiljana Rožić

THE INFLUENCE OF ACID TREATMENT ON THE COMPOSITION OF BENTONITE

Bentonite from the ‘Bogovina’ coal mine in Serbia, was characterized. The influence of acid treatment on its composition, as well as mathematical descriptions of this influence are reported. The purpose of this work was to correlate the concentration of the acid used for the treatment with the resulting bentonite composition. X-ray diffraction (XRD), infrared spectroscopy and quantitative chemical analysis were employed to define the changes caused by acid treatment.The contents of all the cations, except Si, decreased exponentially with increasing concentration of the HCl used for the treatment of the bentonite. This approach was tested on previously published data and was shown to be valid.The basal reflections of smectite decreased gradually and eventually disappeared after intense treatment, while the other reflections remained in the XRD patterns of all the samples, but decreased slightly with increasing acid strength. In addition, the amount of X-ray amorphous matter formed increased rapidly with increasing acid concentration up to 4.5 M. With further increase in the acid strength, the amount of X-ray amorphous matter remained virtually constant.

Photocatalytic degradation of azo pyridone dye: Optimization using response surface methodology

Abstract Response surface methodology (RSM) and central composite design have been applied to describe and optimize photocatalytic degradation of azo pyridone dye using TiO2, H2O2, and simulated sun light. The mutual interactions between three independent variables, viz. H2O2 concentration, irradiation time, and TiO2 content were obtained. The results revealed that the most influential variables under selected reaction conditions were irradiation time and TiO2 content. The optimized conditions for the photocatalytic degradation of azo pyridone dye were as follows: H2O2 concentration: 130.5 mg/L, irradiation time: 54.8 min, and TiO2 content: 2.48 g/L. Under these conditions, the maximum decolorization efficiency of 96.43% was achieved. This experimental value was in good agreement with the predicted one, which proved the validity of the model. Operation cost analysis indicated that irradiation time had the major influence on total process cost. The RSM based on the central composite design was shown to be ...

RESPONSE SURFACE OPTIMIZATION FOR ACTIVATION OF BENTONITE USING MICROWAVE IRRADIATION

Microwave irradiation as a means for heating bentonites during acid activation has been investigated in the past but it has never been optimized for industrial applications. The purpose of this study was to apply a factorial 23 experimental design to a Serbian bentonite in order to determine the influence of microwave heating on the acid-activation process. The effect of acid activation under microwave irradiation on the textural and structural properties of bentonite was studied as a model reaction. A mathematical, second-order response surface model (RSM) was developed with a central composite design that incorporated the relationships among various process parameters (time, acid concentration, and microwave heating power) and the selected process response of specific surface area of the bentonite. The ranges of values for the process parameters chosen were: time, 5–21 min; acid concentration, 2–7 M; and microwave heating power, 63–172 W. The effect of individual variables and their interaction effects on the textural and structural properties of the bentonite were determined. Statistical analysis showed that the duration of microwave irradiation was less significant than the other two factors. The model showed that increasing the time and acid concentration improved the textural properties of bentonites, resulting in increased specific surface area. This model is useful for setting an optimum value of the activation parameters for achieving the maximum specific surface area. An optimum specific surface area of 142 m2g−1 was achieved with an acid concentration of 5.2 M, activation time of 7.4 min, and microwave power of 117 W.

Study of the effect of Mg(II) addition and the annealing conditions on the structure of mesoporous aluminum oxide using Plackett–Burman design

A statistical design was used to investigate the effect of various pro- cessing conditions on the structure of sol-gel derived Mg(II) doped alumina. Six process variables were selected based on the Plackett-Burman design: concentration of magnesium nitrate, time and temperature of alcohol evapor- ation, temperature and time of annealing and heating rate were changed at two levels. For every set of conditions, samples with different specific surface area and degree of crystallinity were obtained. Analysis of the results showed that the annealing temperature, heating rate and concentration of magnesium nitrate were the main factors affecting the average crystallite size of the predominant alumina phase. In the case of the specific surface area, two of selected six variables had pronounced effects; however, the temperature of annealing was more effective than others. The present results showed that the proposed model that uses crystallite size as a response variable is preferable to other research.

β-Carotene removal from soybean oil with smectite clay using central composite design

In this study removal of β-carotene from soybean oil by adsorption on acid activated smectite clay from Serbia was investigated and a factorial 23 experimental design was applied. The effects of relevant factors, such as temperature, solid-to-liquid ratio and time, on removal of β-carotene were investigated. In order to check these factors and their effect on the removal of β-carotene, we have established a model of this technique following a methodological strategy using experiments design. The mathematical model is established using a central composite design. The model describes the changes of the measured responses of β-carotene removal efficiency according to the temperature, solid-to-liquid ratio and time. The graphical representation of this model in the space of the variables enabled us to define the optimum conditions of these parameters. The optimum conditions to obtain the maximum removal of β-carotene from soybean oil were a temperature of 80°C, a solid-to-liquid ratio of 1: 25 and a time of 1255 s. Under these optimal conditions, the experimental values agreed with the predicted values, using analysis of variance, indicating a high goodness of fit of the model used and the success of response surface methodology for optimizing adsorption β-carotene of acid activated smectite clay from soybean oil.