Cu2+-Ion-Substitution-Driven Microstructure and Microwave Dielectric Properties of Mg1-xCuxAl2O4 Ceramics.

In this work, Cu-substituted MgAl2O4 ceramics were prepared via solid-state reaction. The crystal structure, cation distribution, and microwave dielectric properties of Mg1-xCuxAl2O4 ceramics were investigated. Cu2+ entered the MgAl2O4 lattice and formed a spinel structure. The substitution of Cu2+ ions for Mg2+ ions contributed to Al3+ ions preferential occupation of the octahedron and changed the degree of inversion. The quality factor (Qf) value, which is correlated with the degree of inversion, increased to a maximum value at x = 0.04 and then decreased. Ionic polarizability and relative density affected the dielectric constant (εr) value. The temperature coefficient of the resonant frequency (τf) value, which was dominated by the total bond energy, generally shifted to the positive direction. Satisfactory microwave dielectric properties were achieved in x = 0.04 and sintered at 1550 °C: εr = 8.28, Qf = 72,800 GHz, and τf = -59 ppm/°C. The Mg1-xCuxAl2O4 solid solution, possessing good performance, has potential for application in the field of modern telecommunication technology.

Preparation and Characterization of Sludge-Based Magnetic Biochar by Pyrolysis for Methylene Blue Removal.

The development of low-cost adsorbent is an urgent need in the field of wastewater treatment. In this study, sludge-based magnetic biochar (SMB) was prepared by pyrolysis of sewage sludge and backwashing iron mud without any chemical agents. The samples were characterized by TGA, XRD, ICP, Organic element analysis, SEM, TEM, VSM and BET. Characterization analysis indicated that the magnetic substance in SMB was Fe3O4, and the saturation magnetization was 25.60 emu·g-1, after the adsorption experiment, SMB could be separated from the solution by a magnet. The batch adsorption experiment of methylene blue (MB) adsorption showed that the adsorption capacities of SMB at 298 K, 308 K and 318 K were 47.44 mg·L-1, 39.35 mg·L-1, and 25.85 mg·L-1, respectively. After one regeneration with hydrochloric acid, the maximum adsorption capacity of the product reached 296.52 mg·g-1. Besides, the adsorption kinetic described well by the pseudo-second order model revealed that the intraparticle diffusion was not just the only rate controlling step in adsorption process. This study gives a reasonable reference for the treatment of sewage sludge and backwashing iron mud. The product could be used as a low-cost adsorbent for MB removal.

Preparation of adsorbent based on water treatment residuals and chitosan by homogeneous method with freeze-drying and its As(V) removal performance.

Although the chitosan-WTRs particulate adsorbent prepared by embedding method has been proved to have arsenic adsorption capacity, the capacity of it is greatly weakened compared with the original water treatment residuals (WTRs). In this study, WTRs and chitosan were used as raw materials to prepare a new kind of adsorbent beads by a homogeneous method. At the same time, in order to enhance the adsorption capacity and reduce the limitation of kinetics, freeze-drying method was chosen to dry the adsorbent. The WTRs-chitosan beads by homogeneous method (WCB) were characterized by SEM, XRD, XPS and other methods. According to the characterization results, there are regularly arranged pores inside the particles, and the iron in the particles mainly exists in the form of amorphous iron oxyhydroxide. According to the results of batch experiment, the pseudo-second-order kinetic model has a higher degree of fit, indicating that the WCB adsorbs As(V) mainly by chemical adsorption. The maximum adsorption capacity estimated from the Langmuir isotherm model is 42.083 mg/g, which is almost same as the WTRs. Weak acid and neutral conditions are conducive to adsorption, while alkaline conditions have a significant inhibitory effect on arsenic adsorption.

Preparation of manganese sludge strengthened chitosan-alginate hybrid adsorbent and its potential for As(III) removal.

The manganese sludge from laboratory biological manganese removal filter column backwashing residue was used to modify the Chitosan Alginate Fe-sludge Beads. The Chitosan Alginate Fe-sludge Beads strengthened with manganese sludge (CAFBs) get the oxidation ability and can removal As(III) effectively without a pre-oxidation process. It was characterized by SEM (scanning electron microscopy), XRD (X-ray diffraction), and BET (Brunauer-Emmett-Teller analysis). Batch adsorption experiments were carried out to study the mechanism of As(III) removal. SEM-EDS shows that the surface is rough and rich in iron and manganese element (32.8%). The BET data shows that it is porous and has large surface area (99.20 m2·g-1). XRD proves that the main components of CAFBs are amorphous iron oxide and MnO2.Neutral and weak alkaline conditions (pH = 7-9) were favorable for the adsorption and H2PO4- had obvious inhibitory effect on As(III) removal. The experimental data shows that the Pseudo-second kinetic model, intra-granular diffusion model and Freundlich isotherm can better describe the adsorption process of As(III) by CAFBs. At 298 K, the maximum adsorption capacity of As(III) is 20.16 mg/g. Regeneration studies find that CAFBs can be effectively regenerated by aeration into the NaOH solution.