Abstract
In this study, 4A zeolite was prepared from opal waste rock by hydrothermal method and applied in ammonium ion adsorption. To optimize synthesis conditions, the effect of crystallization time (1–8 h), crystallization temperature (65–115°C), Na2O/SiO2 (0.6–2.0), H2O/Na2O (20–70), and SiO2/Al2O3 (1.0–3.5) was investigated. X-ray diffraction, scanning electron microscope imaging, cation exchange capacity, static water adsorption, Fourier transform infrared spectroscopy, and N2 adsorption–desorption isotherm were used for assessing properties of 4A zeolite. Adsorption experiments were performed by 1.0 g l−1 4A zeolite with NH4+ solution (5–300 mg l−1) for 4 h at room temperature. The experiment results revealed with a crystallization time of 3 h, a crystallization temperature of 85°C, Na2O/SiO2=1.0, H2O/Na2O = 40, and SiO2/Al2O3=2.0, the 4A zeolite synthesized had excellent performance with cation exchange capacity of 2.93 mmol (g dry zeolite)−1 and static water adsorption of 22.3%. The adsorption process was described by Freundlich model (R2>0.99) and the maximum adsorption capacity could reach to 53.11 mg g−1. The experimental results provided a novel approach for the utilization of opal waste rock, which is produced during the mining of opal-rich palygorskite, and for the synthesis of 4A zeolite and the removal of ammonium ion.
Highlights
The increase of ammonium ion pollution in waters has drawn extensive concern owing to its harmful effects, such as the eutrophication of lakes and rivers, low dissolved oxygen, harm for aquatic life, and the corrosion acceleration of soil materials (Cheng et al, 2017; Huang et al, 2015)
These reflections at 2h 1⁄4 20.9 and 35.7 are found and identified as tridymite, the reflection of 2h 1⁄4 21.6 is identified as cristobalite, the reflection at 2h 1⁄4 8.3 is identified as palygorskite, and the reflection at 2h 1⁄4 30.9 is identified as dolomite according to the comparison with standard pattern
From X-ray diffraction (XRD) pattern of purified opal waste rock (OWR), the reflection of palygorskite becomes weaker, and the reflection of dolomite vanishes when compared with raw OWR, i.e. the structure of palygorskite is destroyed and the dolomite is removed
Summary
The increase of ammonium ion pollution in waters has drawn extensive concern owing to its harmful effects, such as the eutrophication of lakes and rivers, low dissolved oxygen, harm for aquatic life, and the corrosion acceleration of soil materials (Cheng et al, 2017; Huang et al, 2015). The dispose of ammonium ion pollution in water counts a great deal. Conventional removal methods for ammonium ion from wastewater comprise steam stripping, adsorption, ion exchange, and biological nitrification–denitrification (Sun et al, 2017a; Zadinelo et al, 2015). Adsorption has achieved wide-ranging attention for its simplicity and high efficiency for elimination of ammonium ion (He et al, 2016). Amongst adsorption materials for NH4þ ions of aqueous solutions and wastewater, zeolite is especially promising because of the considerable ions exchange capacity and intense affinity for NH4þ compared with other adsorbents (Mazloomi and Jalali, 2016)
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