EQUILIBRIUM AND KINETIC MODELLING FOR THE ADSORPTIVE REMOVAL OF '2.-AMINOPYRIDINE FROM AQUEOUS SOLUTION

Abstract

2-aminopyridine (2-AP) is toxic by ingestion, interaperitoneal, subcutaneous, and intravenous routes. It is hygroscopic, highly toxic material with Characteristic unpleasant odor. This is used in the production of sulfasalazine, an antibacterial used for veterinary purposes. This is also used in the synthesis of a number of a number of antihistamines including metha pyriline hydrochloride and pyrilamine maleate. In industrial experience, intoxication has occurred from inhalation of the dust or vapour or by skin absorption after direct contact. When heated, vapour form explosive mixture with air such as indoor, outdoor and sewer explosive hazards. An estimated bioconcentration factor (log BCF) of 0.14 indicates 2-aminopyridine should not bioconcentrate among aquatic organisms. The substance decomposes on burning produces toxic gases and vapour such as nitrogen oxide, carbon monoxide, carbon dioxide. It reacts with strong oxidants causing fire and explosion hazard. The 2003 ACGIH threshold limit value-time-weighted average (TLV-TWA) for 2-aminopyridine is 0.5 ppm (1.9 mg/m3). A harmful contamination of air can be reached very quickly on evaporation of this substance at 20°C. 2-aminopyridine wastewater emanates from pyridine manufacturing units, pharmaceutical units, etc. During spill episodes. the concentration can increase considerably. These plants are plagued with the problem of intense odour emanating rather from the wastewater or from handling and storage facilities. The adsorption process can be attractive in wastewater treatment, if it is cost-effective. Agro-based waste materials are generally inexpensive and have high adsorption capacity for many solute components. The BFA, after separation and dewatering, can be dried and used as a fuel in furnaces/incinerators, etc., to recover its energy value. Among various low-cost adsorbents, bagasse fly ash (BFA) has been reported to be very effective and promising in regard to the removal of organics, dyes, phenols, etc. The aim of the present research is to explore the possibility of utilizing bagsse fly ash for the removal of 2-aminopyridine. Proximate analysis, particle size analysis, ifi surface area determination, XRD, SEM and TGA studies were conducted for the characterization of adsorbents. The adsorption capacity of bagasse fly ash has been compared with activated carbon commercial. Batch studies were conducted to see the effect of adsorbent dosage, pH, contact time, initial concentration on the removal of 2-aminopyridine. The effect of initial pH of the solution (2 < pHo < 12), adsorbent dose (1 < m < 7 g 1-1), contact time (0 < t < 6 hrs), initial 2-AP concentration (50 < Co < 500 mg 1-1), and temperature (293 K < T < 323 K) on the adsorption of 2-AP onto BFA and ACC have been investigated. Optimum initial pH (pHo) of aqueous solution for 2-aminopyridine solution was found to be 6 for 2-aminopyridine-BFA system, whereas in 2-aminopyridine-ACC system, change in removal was insignificant with variation in pHo. Adsorbent dose (m) of 5g/1 and 10 g/1 were found for BFA and ACC, respectively. Equilibrium time was 5 h for both BFA and ACC. Adsorption kinetics and equilibrium characteristics have also been studied. The adsorption of 2-Ap onto both the adsorbents, BFA and ACC followed pseudo-second order kinetics. Various equilibrium isotherm equations viz., the Freundlich, Langmuir, Redlich-Peterson (R-P) and Tempkin equations have been used to test their validity for the experimental equilibrium sorption data. Error analysis has also been performed to test the adequacy and the accuracy of the isotherm equations. Redlich-Peterson isotherm was found to best represent the data for 2-aminopyridine adsorption onto BFA and ACC, respectively. Adsorption of 2-AP was to be endothermic in nature. The high negative value of change in Gibbs free energy (AG) indicated the feasible and spontaneous adsorption of 2-AP onto BFA and ACC. iv