Effects of ionic strength and temperature on adsorption of atrazine by a heat treated kerolite
Introduction
Pollution of water environment by pesticides, particularly herbicides, has been recognised in agricultural areas of the world for many years, and considerable evidence has been accumulated to suggest that many water resources are contaminated with organic pesticides (Cohen, 1986, Chiron et al., 1993).
Triazines are used widely as herbicides and atrazine, despite being banned in most European countries, atrazine is the most widely used herbicide in the United States and is registered in more than 70 countries worldwide (Rippen, 1992, Kauffmann et al., 2000). Furthermore, atrazine has been identified as a potential leacher by using the ground water ubiquity score modelling technique (Gustafson, 1989), and it has been widely detected in ground water (Parrilla et al., 1994, Chiron et al., 1995), so it is potentially toxic to both humans and ecosystems.
A new class of kerolite/stevensite interstratified material has become of increasing interest because of its applications as a bleaching material and adsorbent of contaminant organic molecules (Pozo et al., 1999, González-Pradas et al., 2000, González-Pradas et al., 2003, Socías-Viciana et al., 2003). The kerolite/stevensite here cited belongs to the Madrid Basin and is a kerolite-rich material (80% of kerolite), (denoted kerolite in the text), with a structure similar to talc, although more disordered and with a higher degree of hydration (Brindley et al., 1977, Zelazny and White, 1989).
Given that adsorption on activated carbon or clay is a method used for decontaminating organic polluted waters, (Hutson and Roberts, 1990, Svoboda et al., 1991), we have studied the adsorption process of atrazine from aqueous solution on the above indicated kerolitic material.
In addition, several studies have shown that factors such as the temperature or the presence of ionic strength affects considerably the adsorption of certain pesticides such as atrazine (Hurle and Freed, 1972, Fruhstorfer et al., 1993).
Taking into account the above, and according to our previous research on the use of heat treated kerolites for removing atrazine from water, we have considered it useful to study the adsorption process of atrazine from both, pure water and 0.1 M KCl solutions at work temperatures of 10 °C, 25 °C and 40 °C, using a heat treated kerolite sample at 600 °C (González-Pradas et al., 2003).
The main objective of the present research was to evaluate the effects of temperature and the presence of one electrolyte in the medium (0.1 M KCl) for removing atrazine from aqueous solution by using kerolite activated at 600 °C.
Section snippets
Materials and methods
The clay used as adsorbent for this series of experiments was a 600 °C heat-treated kerolite from the Madrid Basin (Spain) (crushed to a particle size less than 150 μm), previously studied by other authors (Pozo et al., 1999).
Heat activation of the natural kerolite was carried out by heating it at 600 °C for 24 h. The material obtained was analysed chemically by X-ray fluorescence spectroscopy with a Philips PW 1404 instrument. Specific surface area and micropore volume were determined from N2
Results and discussion
Table 2 shows the solubility of atrazine, at 10 °C, 25 °C and 40 °C, in both, pure water and 0.1 M KCl solutions. As can be seen from Table 2, the solubility of atrazine increases from 30.2 mg l−1 at 10 °C up to 41.0 mg l−1 at 40 °C (pure water solution); the presence of ionic strength decreasing the solubility (from 30.2 mg l−1 to 27.1 mg l−1 at 10 °C and from 41.0 mg l−1 to 35.1 mg l−1 at 40 °C).
The pH values of the blanks containing no atrazine were 7.5 and 7.3 in pure water solution and in 0.1 M KCl solution,
Conclusions
These experiments indicate that the lower temperature, the more effective the adsorption of atrazine from both, pure water and 0.1 M KCl solutions. The presence of 0.1 M KCl in the medium tends also to increase the adsorption of atrazine in the range of temperature studied. The results obtained from this work could be of interest by showing the better experimental conditions for the potential use of the 600 °C heat-activated kerolite for adsorption of atrazine. It seems, in general, that by
Acknowledgment
We thank SÜDCHEMIE for the kerolite samples.
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