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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. [ABSTRACT FROM AUTHOR]

Abstract To availably utilize opal-palygorskite clay, dry beneficiation technique was applied to separate opal and palygorskite clay. Based on separated opal from opal-palygorskite clay, 4A zeolite was successfully synthesized by using a hydrothermal method. Box-Behnken was used to optimize Na 2 O/SiO 2 , H 2 O/Na 2 O and SiO 2 /Al 2 O 3 with cation exchange capacity (CEC) as the response value. The optimum parameters was determined to be Na 2 O/SiO 2 = 1.0, H 2 O/Na 2 O = 40, and SiO 2 /Al 2 O 3 = 2.0, and CEC got the maximum of 2.99 mmol/(g·dry zeolite) under the conditions. The as-obtained 4A zeolite was characterized by using X-ray diffraction (XRD), thermo gravimetric analysis (TG), acid-base titration, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and then was applied to remove Hg2+ from aqueous solution. The maximum removal capacity of Hg2+ was 41.99 mg/g and adsorption equilibrium was obtained with contact time of 2 h. Effects of pH, ionic strength, temperatures, metal cations, strippant kinds and cycle times on removal behaviors of Hg2+ onto 4A zeolite were investigated by batch experiments. The kinetics and isotherms of Hg2+ adsorption fitted well by pseudo-second kinetic and Langmuir models. When Hg2+-adsorbed 4A zeolite was desorbed using 1 mol/L NaNO 3 solution, the adsorption efficiency was maintained about 70% after four cycles. Highlights • Opal-palygorskite clay was separated by dry beneficiation technique. • 4A zeolite was synthesized successfully based on the separated opal. • The synthetic conditions of the 4A zeolite were optimized. • The performance of the 4A zeolite on removal of Hg2+ was evaluated. • The isotherms, kinetics, selectivity and effect of water chemistry were investigated. [ABSTRACT FROM AUTHOR]

Traditional local active contour models mainly depend on the data fitting term to obtain image edge information, which are sensitive to the position of initial contour. In fact, setting an unreasonable initial contour will result in a time-consuming image segmentation process and difficult evolution at weak boundary. To solve this problem, we come up with a second-order edge detection operator which is based on the global gradient image information to replace the traditional data fitting term, and to obtain edge information with higher speed and accuracy. In addition, the anisotropic edge enhancement method has been introduced to improve the robustness to the weak boundary. In this way, an active contour model which is insensitive to initial contour position is proposed to achieve a faster and more accurate image segmentation result. [ABSTRACT FROM AUTHOR]