Synthesis and characterization of a magnetic adsorbent from negatively-valued iron mud for methylene blue adsorption
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With increasing awareness of reduction of energy and CO2 footprint, more waste is considered recyclable for generating value-added products. Here we reported the negatively-valued iron mud, a waste from groundwater treatment plant, was successfully converted into magnetic adsorbent. Comparing with the conventional calcination method under the high temperature and pressure, the synthesis of the magnetic particles (MPs) by Fe2+/Fe3+ coprecipitation was conducted at environment-friendly condition using ascorbic acid (H2A) as reduction reagent and nitric acid (or acid wastewater) as leaching solution. The MPs with major component of Fe3O4 were synthesized at the molar ratio (called ratio subsequently) of H2A to Fe3+ of iron mud ≥ 0.1; while amorphous ferrihydrite phase was formed at the ratio ≤ 0.05, which were confirmed by vibrating sample magnetometer (VSM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). With the ratio increased, the crystalline size and the crystallization degree of MPs increased, and thus the Brunauer-Emmett-Teller (BET) surface and the cation-exchange capacity (CEC) decreased. MPs-3 prepared with H2A to Fe3+ ratio of 0.1 demonstrated the highest methylene blue (MB) adsorption of 87.3 mg/g and good magnetic response. The adsorption of MB onto MPs agreed well with the non-linear Langmuir isotherm model and the pseudo-second-order model. Pilot-scale experiment showed that 99% of MB was removed by adding 10 g/L of MPs-3. After five adsorption-desorption cycles, MPs-3 still showed 62% removal efficiency for MB adsorption. When nitric acid was replaced by acid wastewater from a propylene plant, the synthesized MPs-3w showed 3.7 emu/g of saturation magnetization (Ms) and 56.7 mg/g of MB adsorption capacity, 2.8 times of the widely used commercial adsorbent of granular active carbon (GAC). The major mechanism of MPs adsorption for MB was electrostatic attraction and cation exchange. This study synthesized a magnetic adsorbent from the negatively-valued iron mud waste by using an environment-friendly coprecipitation method, which had a potential for treatment of dye wastewater.Keywords:
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To get CaTiO3catalyst with high photocatalytic properties,the effect of calcination conditions,on the photocatalytic activity of CaTiO3 was investigated.The calcination conditions included heating rate of calcination precursors,calcination temperature,calcination time and cooling rate of calcination products,The catalyst was synthesized by solid-state reaction method with Ca(NO3)2and TiO(OH)2as raw materials and NaOH as mineralizer.The physical properties of the catalyst were characterized using XRD and SEM.The experimental results showed that the activity increased until reached a maximum,and then decreased with the increasing heating rate of calcination precursors;the photocatalytic activity decreased drastically with the fast cooling rate of calcination products.Moreover,the optimal values of calcination temperature and calcination time were obtained.As a result,the CaTiO3catalysts with high photocatalytic activity can be obtained under an optimized calcination conditions after loading CoO(0.2 wt%)co-catalyst.
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In the process of biological desulfurization of gases from landfills, huge amounts of biologically produced Sulfur (BPS) were produced as by-products. A study was conducted to find out the possibility of using it as an adsorbent for Pb2+. BPS was subjected to an adsorption test in an aqueous solution in the presence of Pb2+ and compared with the removal efficiency of granular activated carbon (GAC), which is mainly used as an adsorbent for heavy metal. As a result of the Pb2+ removal experiment using BPS, it was a two-step process in which 54.5% of the initial Pb2+ was removed within 5 minutes by fast initial adsorption followed by slow adsorption. As a result of the isotherm adsorption experiment, the Pb2+ adsorption to BPS was fitted the Langmuir isotherm model, and the maximum adsorption capacity of BPS (175.4 mg g-1) was about 3 times higher than that of GAC (67.11 mg g-1). The data from XPS demonstrated that the main adsorption mechanism was the complexation of Pb2+ with the sulfide in the BPS. Therefore, it was confirmed that BPS has sufficient value to be recycled as a new adsorbent for Pb2+ removal in wastewater. Result of adsorption isotherm test and High-resolution XPS spectra of Pb of biologically produced Sulfur after Pb adsorption.
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In order to improve the activation effect of deactivation catalysts, calcination of V2O5-WO3-MoO3/TiO2 catalysts were investigated. The experimental results demonstrate that calcination time have an effect for recovering the activity of V2O5-WO3-MoO3/TiO2 catalyst. Calcination not only ensures the better mechanical strength and integrity of the catalyst, but also plays an important role in the denigration activity of the catalyst. However, the particles of the catalyst surface enlarged with the increase of the calcination temperature. The suitable calcination time can improve the denigration efficiency and increase the mechanical strength of the catalyst. In addition, the calcination time mainly affects the formation of MoO3. These findings can provide reference for the activation of SCR-Den Ox catalyst.
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The adsorption of thiophene on HZSM-5 was studied by using frequency response(FR) and intelligent gravimetric analyzer(IGA).An adsorption isotherm was recorded by IGA at 373 K and the FR spectrum of thiophene on HZSM-5 was recorded at the pressure range of(0.2-6.0)×133.3 Pa and the temperature range of 302-623 K.The results were interpreted according to the Yasuda model and Langmuir model,suggesting that the adsorption process was the rate controlling step for the mass transfer process of thiophene on HZSM-5,and two different adsorption processes,high frequency adsorption and low frequency adsorption,occured in the system.At 373 K,for the high frequency adsorption process,the Langmuir model can be applied,implying that a single layer adsorption takes place with an adsorption site number,N(2)s,of 0.922 mmol/g,while for the low frequency adsorption the Langmuir model cannot be applied and the adsorption site number,N(1)s,is 0.588 mmol/g.The high frequency adsorption is the main process for the adsorption of thiophene on HZSM-5.
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We calcined six kinds of limestone from various localities up to 900, 1000, 1100, 1200, 1300 and 1400°C with or without NaCl, and observed the growth of CaO crystals in their thin sections. The CaO crystals occurring in the specimens calcined with NaCl are, as usual, better grown than those without NaCl, and it is more evident at lower temperature calcination. In the case of higher temperature calcination, the formers are hardly over-burnt.With regard to the limestones, those of cryptcrystalline make finer CaO crystals. Especially it is evident at higher temperature calcination. This may show to have larger range for optimum calcination, that is easy to work with.
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Mg was extracted from boron mud through calcining method. The technological process is that the boron mud was calcined at 700 °C for 3 h then uniformly mixed with (NH 4 ) 2 SO 4 in proportion and calcined. The reaction process was studied by TG-DTA and XRD, which is that MgO in calcined boron mud reacts with (NH 4 ) 2 SO 4 to produce (NH 4 ) 2 Mg 2 (SO 4 ) 3 at low temperature, then with increasing the temperature, (NH 4 ) 2 Mg 2 (SO 4 ) 3 decomposes into MgSO 4 . The effects of calcination temperature, mol ratio of reaction substrates and calcination time on conversion rate of Mg were studied. The results indicate that the conversion rate of Mg increases with the increasing of calcination temperature first then decreases, increases with the increasing of calcination time and mol ratio of (NH 4 ) 2 SO 4 and MgO. When the calcination temperature is 500 °C, the calcination time is 3 h, the mol ratio of (NH 4 ) 2 SO 4 and MgO is 0.9:1, the conversion rate of Mg is 81.9 %.
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