Anion Effect and Mechanism of Sodium Modified Clinoptilolite for Ammonia Nitrogen Removal from Aqueous Solution

摘要

In this article, effects of different sodium salts on the adsorption capacity of modified clinoptilolite for ammonia nitrogen were systematically compared. Natural clinoptilolite (C-Natural) was modified with sodium chloride (NaCl), sodium hydroxide (NaOH), sodium citrate (Citra), and sodium dodecyl sulfate (SDS). Effect of anions on modification mechanisms of sodium compounds was studied. The mesopore proportion increased from 63.82% to 73.78%, 74.52%, 74.48%, and 74.85% in NaCl-modified clinoptilolite (C-NaCl), low concentration of NaOH-modified clinoptilolite (C-NaOH), Citra-modified clinoptilolite (C-Citra), and SDS-modified clinoptilolite (C-SDS), respectively. Results of X-ray powder diffraction, Fourier transform infrared spectrometry, and X-ray photoelectron spectrometry showed that the crystal and the skeleton structure of clinoptilolite did not change. Anion exerted a certain influence on modification with sodium compounds; that is, OH~(−) increased the number of the hydroxyl groups of the framework and slightly reduced the adsorption capacity. The function of citric acid root improved the adsorption capacity of C-Citra. C-NaCl demonstrated improved adsorption ability than C-SDS because the radius of Cl~(−) is smaller compared to that of anions in SDS. The efficiency of C-NaCl, C-NaOH (L), C-Citra, and C-SDS to remove ammonia nitrogen in water was significantly increased from 53.15% to 82.17%, 79.66%, 85.57%, and 80.06%, respectively. The modification mechanism of sodium compound modified clinoptilolite mainly involved the exchange of Na~(+) with the metal cation, resulting in widened pore channels and increased proportion of mesopores; consequently, ammonia nitrogen removal was improved.