Adsorption studies of azotetrazolate and 3,6-dihydrazinotetrazine on peat

Abstract

The objective of our studies was the evaluation of the adsorption process of two high-nitrogen compounds–dihydrazinotetrazine (DHTz) and azotetrazolate ion (AZ)−on a chosen peat. The experiments were performed using a static method at three different temperatures (283, 298, and 333 K). The adsorption process of DHTz and AZ on peat was characterized by isotherms according to the Freundlich and Langmuir models. The obtained correlations between adsorption and equilibrium concentration were in good accordance with the Freundlich and Langmuir models, as confirmed by high values of the correlation coefficients (0.97−0.99). Adsorption of AZ on peat was less efficient than that of DHTz, and this inference was experimentally proven. The maximum surface coverages of peat particles with adsorbate according to the Langmuir model were calculated as 0.02 and 0.17 mol kg⁻¹ (at 298 K) for AZ and DHTz, respectively. The determined adsorption equilibrium constants confirmed greater adsorption of DHTz on the investigated peat. It can be concluded that adsorption of AZ occurred to a much lesser extent compared to that of DHTz, pointing to a potentially greater threat of migration of soluble azotetrazolates in soil. Standard enthalpies of adsorption estimated for AZ and DHTz were −11.1 and −23.7 kJ mol⁻¹, respectively. Based on these adsorption enthalpy values, it can be stated that both investigated compounds are adsorbed on peat by a physisorption process.

Keywords:

• Adsorption isotherms
• high-nitrogen compounds
• azotetrazole salt
• 3,6-dihydrazinotetrazine
• peat
• thermodynamic parameters.

Acknowledgments

The study was supported by the Ministry of Science and Higher Education through the Institute of Chemistry, Military University of Technology, Grant No. 08-984 and University of Warsaw DSM 100600/14.