Characteristics of Volcanic Tuff from Macicasu (Romania) and Its Capacity to Remove Ammonia from Contaminated Air.

In the present work, the capability of the volcanic tuff from Macicasu (Romania) to remove ammonia (NH 3 ) from air with different contamination levels during 24 h of adsorption experiments was investigated. The natural zeolitic volcanic tuff was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), the Brunauer-Emmett-Teller (BET) method, inductively coupled plasma optical emission spectrometry (ICP-OES), and thermogravimetric analysis (TGA). The adsorption capacities varied between 0.022 mg NH 3 g -1 zeolite and 0.282 mg NH 3 g -1 zeolite, depending on the NH 3 concentrations in the air and at the contact time. The nonlinear forms of the Langmuir and Freundlich isotherm models were used to fit the experimental data. Additionally, the adsorption of NH 3 was studied using nonlinear pseudo-first-order (PFO), pseudo-second-order (PSO), and Elovich kinetic model. Based on the total volume of pores of used volcanic tuff, the NH 3 was removed from the air both due to the physical adsorption of NH 3 gas and the ion exchange of NH 4 + (resulted from a reaction between NH 3 and H 2 O adsorbed by the zeolite). Depending on the initial NH 3 concentration and the amount of volcanic tuff, the NH 3 concentrations can be reduced below the threshold of this contaminant in the air. The adsorption capacity of NH 3 per unit of zeolite (1 g) varied in the range of 0.022-0.282 mg NH 3 g -1 depending on the NH 3 concentration in the air.