Survey of efficiency evaluation of modified and unmodified Clinoptilolite for nitrate removal from aqueous solutions

The aim of this study was to evaluate the nitrate removal using modified and unmodified natural zeolite, Clinoptilolite, from aqueous solutions.
In this study, due to low removal efficiency of unmodified zeolite, the zinc chloride and ferrous sulfate were used for adsorbent modification. The studied parameters were pH (1-12), contact times (2-186 min), nitrate concentration of the solutions (50-100 mg/l) and the adsorbent dose (5-20 g/l).
Findings: The nitrate removal efficiency by unmodified zeolite was about 40%, so, in the next series of experiments, the modified zeolites were used as adsorbent. The optimum conditions of nitrate removal for modified zeolite with zinc chloride and ferrous sulfate samples were pH=5 and 3, the contact times 66 and 66 min, the adsorbent doses 15 and 20 g/l and the initial nitrate concentrations 100 and 50 mg/l, respectively. The maximum obtained nitrate removals were 78.8% and 90.8%, respectively. The adsorption process by modified zeolite with zinc chloride and ferrous sulfate follows the Freundlich and Langmuir isotherm equations, respectively.
The results showed that the modified zeolite due to several adsorbent sites, simplicity, and high efficiency removal was more efficient than unmodified zeolite for nitrate removal. Therefore, at high nitrate concentrations the appropriate adsorbent was the zeolites that modified with zinc chloride, however, at low nitrate concentrations, the modified zeolites by ferrous sulfate showed high nitrate removal efficiency.