Abstract
Nitrogen and phosphorus are commonly recognized as causing eutrophication in aquatic systems, and their transport in subsurface environments has also aroused great public attention. This research presented four natural clay minerals (NCMs) evaluated for their effectiveness of NH4 + and PO4 3- adsorption from wastewater. All the NCMs were fully characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), BET analysis, and adsorption kinetics and isotherms to better understand the adsorption mechanism-property relationship. The results show that the adsorption efficiency of the four NCMs for phosphate was better than that for ammonia nitrogen. The removal rate of phosphate was higher than 65%, generally in the range of 80%-90%, while the removal rate of ammonia nitrogen was less than 50%. The adsorption kinetic behavior followed the pseudo-second-order kinetic model. The ammonia nitrogen adsorption isotherm was in good agreement with the Freundlich isotherm equilibrium model, and the phosphate adsorption isotherm matched the Langmuir model. Among all the NCMs studied, bentonite (7.13 mg/g) and kaolinite (5.37 mg/g) showed higher adsorption capacities for ammonia nitrogen, while zeolite (0.21 mg/g) and attapulgite (0.17 mg/g) showed higher adsorption capacities for phosphate. This study provides crucial baseline knowledge for the adsorption of nitrogen and phosphate by different kinds of NCMs.
Highlights
With the development of human society, the impacts on water quality from industrial and human activity continue to increase [1, 2]
This study evaluated four common natural clay minerals, namely, kaolinite, zeolite, attapulgite, and bentonite, as adsorbents under the same experimental conditions, and studied the adsorption behavior of ammonium ions and phosphate on the surface of NCMs
KF and n are the Freundlich constants, which are related to the adsorptive capacity and the intensity of adsorption, T is the absolute temperature (K), R is the universal gas constant (8.314 J−1), BT is the heat of adsorption, and AT is the equilibrium binding constant (L/min), corresponding to the maximum binding energy [39]
Summary
With the development of human society, the impacts on water quality from industrial and human activity continue to increase [1, 2]. The adsorption behavior of natural clay minerals would have more practical applications, especially for eutrophic water bodies with slightly higher nitrogen of 0.2–0.3 mg/L and phosphorus concentrations of 0.01–0.02 mg/L. We focused on the natural clay minerals and chose eutrophic waters with slightly higher nitrogen and phosphorus concentrations, which helped us to understand the structure and properties of NCMs and their adsorption effects on NH4+ and PO43-. This study evaluated four common natural clay minerals, namely, kaolinite, zeolite, attapulgite, and bentonite, as adsorbents under the same experimental conditions, and studied the adsorption behavior of ammonium ions and phosphate on the surface of NCMs. We made a comprehensive comparison of adsorption capacities, adsorption kinetics, adsorption isotherms, and different influencing factors such as pH, adsorbent dose, and temperature. This research could provide meaningful references for the exploration of the self-purification function of NCMs
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