Nitrite removal from water using water-soluble polymers in conjunction with liquid-phase polymer-based retention technique

Abstract

The retention properties of water-soluble metal polymers for nitrite anions from aqueous solution are investigated. The preparation of cationic water-soluble polymers containing –RN +X − groups, and their nitrite retention performance was investigated using the liquid-phase polymer-based retention (LPR) technique. Poly((3-methacryloylamine)propyl)trimethyl ammonium chloride, P(ClMPTA), poly((2-acryloyloxy)ethyl)trimethyl ammonium chloride, P(ClAETA), and poly(ar-vinylbenzyl)trimethyl ammonium chloride, P(ClVBTA) were prepared by water solution radical polymerization. Structural analyses were performed using infrared (FT-IR) and nuclear magnetic resonance (NMR H 1)spectroscopy as well as thermogravimetry (TG-DSC). The LPR technique was employed in the retention assays. The studies evaluated the effect of polymer concentration and pH on retention. The change in the pH value of the aqueous solution has a great influence on nitrite retention. Specifically, P(ClVBTA) and P(ClAETA) presented higher nitrite retention at pH 6 and 8 and a lower retention capacity at pH 4. However, P(ClMPTA) behavior was virtually constant, independently of the medium’s pH. The polymer: NO 2 - mole ratios of (20:1), (40:1), (60:1), (80:1), and (100:1) were essayed as washing methods at pH 8. The mole ratios (60:1) and (100:1) in basic media presented higher retention capacity for all polymers. In general, the polymer’s saturation capacity was around 32–37 mg/g with the enrichment factor 4.5–5.6. The addition of monovalent and divalent anions competing for reactive sites, decreased the selectivity for NO 2 - anion in P(ClVBTA) in around 90%. Assays with drinking water for P(ClVBTA) with mole ratio polymer: NO 2 - (120:1) presented retention near to 80%.