Adsorption of Nitrate and Ammonium from Water Simultaneously Using Composite Adsorbents Constructed with Functionalized Biochar and Modified Zeolite

Abstract

The functionalized biochar was assembled on modified zeolite to synthesize a novel modified composite adsorbent. The latter was applied to simultaneous adsorption of ammonium and nitrate. The Box–Behnken design (BBD) in response surface methodology (RSM) was applied to optimize the parameters, which included ratio of raw materials, adsorbent dose, pH, and temperature. The chemical functional groups were determined by Fourier transform infrared adsorption (FT-IR). Stronger absorption peaks of amine groups indicated that the functionalized adsorbent could enhance the adsorption of contaminants. The composite adsorbent effectively increased NH4+ and NO3− adsorption capacity by porous structure recombination, change of surface morphology and further exposure of surface functional groups. The kinetic results indicate that the adsorption of both NH4+ and NO3− follows a pseudo-second-order nonlinear model. The Langmuir isotherm model fitted well the experimental data with a maximum adsorption capacity of 24.45 mg/g for nitrate and 24.63 mg/g for ammonium at 25°C. Nitrate was absorbed by electrostatic interactions with grafted amine groups and, in contrast, the ammonium adsorption was mainly related to ion exchange with Na+. The adsorption process of both nitrate and ammonium were spontaneous and exothermic. The adsorbents can be regenerated effectively in NaCl and NaOH mixed solutions, and the desorbed adsorbents are of high reusability and can be applied effectively at least for five cycles. Therefore, it has a great potential for nitrate and ammonium simultaneous removal from water environment.