Volume 5, Issue 1 - Special issue: Microwave energy treatment / Issue editor: Shaohua Ju

The present work attempts to convert walnut shell into a high surface area activated carbon by microwave heating and chemical activation. Different activation agents such as KOH, NaOH, K 2 CO 3 and Na 2 CO 3 were utilized to identify a suitable activation agent. The result indicated that KOH was the most suitable activation agent among those agents, with the highest porosity and surface area of activated carbon. The effect of KOH/C mass ratio on the pore structure characteristics of the activated carbon was investigated. An optimal KOH/C mass ratio of 4 was identified, beyond which the surface area as well as the pore volume were found to decrease. The surface area and the pore volume were estimated to be 3276 m 2 /g and 1.952 ml/g, respectively, meanwhile the microporous proportion was 77.51% under the optimized KOH/C mass ratio. The activated carbon was further characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The findings strongly support that the activation agent has a great effect on the preparation of activated carbon from walnut shell.

The process of microwave drying ammonium tetramolybdate is studied, and the process variables of drying time, drying temperature and material thickness are considered. Experiences of microwave drying ammonium tetramolybdate have been optimized using response surface methodology (RSM) technique and a CCD design. Effects of each factor and their interactions are researched, and a quadratic polynomial model for dehydration ratio is established. As can be seen from the ANOVA, the effects of the three process variables are found to be significant in the model, and the empirical model is fit and reliable to check the dehydration ratio of ammonium tetramolybdate. The optimum conditions for drying using microwave heating are found as follows: drying temperature 67°C, drying time 9.5 min and material thickness 15 mm. The optimum dehydration ratio is 79.82% and the last molybdenum content is not <56.3%, with the relatively error of 0.64%, which indicates the success of the process optimization experiments. This research has important significance to offer optimum conditions for industrial production.

In this research, the extraction of zinc from the blast furnace dust in the ammonia leaching system containing different leaching agents (NH 3 , (NH 4 ) 3 AC, (NH 4 ) 2 CO 3 , (NH 4 ) 2 SO 4 , NH 4 Cl) was investigated. Meanwhile, the effects of different total ammonia concentrations, ammonia/ammonium ratios, solid-liquid ratios, stirring speeds, and leaching temperatures on the extraction of zinc were studied. The results showed that ammonium sulfate was particularly effective and the extraction efficiency of zinc is up to 86.48% under the following conditions: total ammonia concentration of 5.0 mol/l, ammonia/ammonium ratio of 1:1, solid-liquid ratio of 1:5, temperature of 45°C, leaching time of 60 min, and stirring speed of 350 rpm.

In the process of steel manufacture, up to tens of millions of tons of sintering dusts are produced annually in China, which contain noble metals such as Ag. Therefore, the recovery of Ag from sintering dust could be a potential economic and environmental activity. The present work attempts to use ultrasound for leaching silver from the water-leaching residue of sintering dust (WLR-SD) by acidic thiourea at atmospheric pressure. The effects of particle size, leaching temperature, and thiourea concentration were assessed on the leaching efficiency. Mineralogical changes of the WLR-SD were estimated using X-ray fluorescence, X-ray diffraction, and scanning electron microscope. The results have shown that under the conditions used, up to 94% silver could be leached. The leaching kinetics was estimated to follow the first-order kinetic model, and the activation energy was estimated to be 20.7 kJ/mol, confirming an internal diffusion-controlled leaching process. The order of the reaction with respect to the thiourea concentration was estimated to be 0.68.

Roasting pretreatment and ammonia leaching were performed to extract zinc from complicated zinc ores. The residue of the unroasted ore showed that the zinc containing phase ZnCO 3 cannot be effectively leached in the ammonia leaching system. Mineral phase transformation of ZnCO 3 takes place at a roasting temperature of 673 K, and this is the reason for the improvement of zinc leaching recovery. Additionally, the parameters that can influence the leaching rate of zinc such as the calcined temperature, the total ammonia concentration, the ratio of liquid to solid, the stirring speed and the leaching time were also investigated. Zinc leaching recovery from the complicated zinc ores could reach 84.7% under the following optimized experiment conditions: roasting temperature of 673 K, leaching temperature of 298 K, stirring speed of 500 rpm, total ammonia concentration of 6 mol/l, liquid to solid ratio of 11:1 and leaching time of 60 min. Compared to the zinc leaching recovery from unroasted ore (49.7%, ammonia concentration 6 mol/l), roasting pretreatment and optimization of process parameters can increase the zinc leaching recovery by 70.4%.

Cavity perturbation method was used to determine the dielectric properties ( ε′ , ε ″, and tan δ ) of zinc oxide dust. The process of dechlorination from zinc oxide dust by microwave roasting was evaluated considering the effect of different roasting temperatures and holding times. The research results showed that the ZnCl 2 and PbCl 2 with high-loss factor were heated preferentially by microwave, and the dechlorination rate can reach 97.22% after microwave roasting at 650°C for 40 min. The phases of zinc oxide dust before and after microwave roasting were observed and characterized by X-ray diffraction (XRD) analysis. The kinetics of dechlorination from zinc oxide dust was investigated. The three kinetic factors were obtained by the dynamic isothermal method, which provided a theoretical basis for dechlorination from zinc oxide dust. Thermodynamic analysis showed that the volatilization of chlorides was mainly ionic crystal phase transition process. The volatile kinetics of zinc oxide dust were controlled by the solid state diffusion and interface chemical reaction, during the microwave heating, with an activation energy E =46.6 KJ/mol and the reaction order n is level 1.

A microwave (MW) roasting experiment of agglomerated flux for submerged-arc welding was carried out. The MW heating characteristics of agglomerated flux and influence of roasting temperature on weld surface were investigated. It was found that the heating rate of agglomerated flux becomes faster with the increase of MW powder. It only takes 17 min to heat the sample of 600 g from room temperature to 720°C. A neat and smooth weld surface can be obtained for agglomerated flux roasted by MW heating at 680°C for 30 min. Compared with conventional roasting methods, MW roasting has the advantage of lower temperature and shorter time.

Zr-based bulk metallic glass possesses the highest potential as a structural material among metallic glasses. However, the production conditions have a great effect on its glass-forming ability (GFA) and mechanical characteristics. In this paper, an attempt was made to find the effect of a hereditary structure on the GFA and mechanical properties of a solid Zr 52.8 Cu 29.1 Ni 7.3 Al 9.8 Y 1 bulk metallic glass in order to evaluate a novel process of using binary alloys as precursors, which have a hereditary relation to the aim metallic glass (MGs). When the quenching temperature is below the threshold overheating temperature, the hereditary process can improve the GFA and compressive strength obviously. At a quenching temperature of 1523 K, the hereditary process can improve the supercooled liquid region Δ T x from 33 K to 55 K and the compressive strength from 1555 MPa to 1652 MPa.

A simple and environmentally benign procedure for the bromination of substituted α,β-unsaturated ketones in good yield has been described using ammonium bromide as a brominating agent and ceric ammonium nitrate (CAN) as a single-electron oxidant to afford α,β-dibromoketones. The reaction involves C-Br bond formation by radical method generated by CAN. The reaction can be carried out by either at room temperature, stirring in solvent CH 3 CN or under aqueous moist condition with few drops of water by manual grinding in a mortar and pestle.

Waste dried Mangifera indica (mango) leaves were utilized as a promising source of mangiferin, a valuable biomolecule. Different extraction procedures like three-phase partitioning and batch extraction were evaluated to get an optimum yield of mangiferin. Various parameters affecting the extraction process like salts, time, slurry to t-butanol ratio, ammonium sulfate, pH 6 and solute to solvent ratio were optimized. In three-phase partitioning, the yield of mangiferin obtained was 28 mg/g at a concentration of 40% w/v ammonium sulfate, pH 6, slurry to t-butanol ratio 1:1, solute to solvent ratio 1:40 and time 2 h. Conventional batch extraction using water as solvent resulted in a yield of 23 mg/g in 2 h 40 min, while Soxhlet extraction, as a reference method, yielded 57 mg/g in 5 h. Thus, conventional batch extraction with water can be used for large-scale operations of mangiferin extraction.

Oolitic hematite abounds in the Guizhou Province of China but is hard to use with the traditional process. The reduction of Guizhou oolitic hematite by H 2 was studied. Ore microscopy, phase change, and the metallization rate of oolitic hematite under different reduction conditions were characterized by optical microscopy, X-ray diffraction, and chemical analysis, respectively. The metallization ratio of the reduced sample increased with the increase of reduction time. The metallization ratio reached 80.75% when the temperature was 1000°C and the reduction time was 120 min. The new phases of FeAl 2 O 4 and Fe 2 SiO 4 can be generated during the reduction process, which hindered the reduction of the oolitic hematite.

Considering the need of applicability of green chemistry in research, a series of heterogeneous catalysts, viz., sulfated iron oxide, zirconia supported tungstophosphoric acid and sulfated zirconia have been synthesized by a solvent-free method. The prepared catalysts were used in the esterification of nonanoic acid with methanol and were compared with ion exchange resins for the assessment of their catalytic performance. Sulfated iron oxide was found to be best with an acid conversion of 83%, which is quite comparable with Amberlyst 15 and Dowex50Wx2. The high catalyst loading, cost, low thermal stability, and long reaction time make ion exchange resins uneconomical to use over other alternatives that result in same efficiency with low cost. Sulfated iron oxide was further optimized for its preparation conditions for high catalytic performance in the esterification reaction. The catalysts were characterized for their crystallinity, surface morphology, composition, weight loss, and structure by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, and Fourier transform infrared spectroscopy. The evaluated catalysts were compared on the basis of their preparation time, catalytic performance, catalyst loading, reaction time, and overall cost.

A low-cost, efficient, and ecofriendly method for the synthesis of silver nanoparticles (AgNPs) using gums as reducing agent was performed. The obtained nanoparticles were characterized by UV-visible spectroscopy. The antibacterial activity of the prepared nanoparticles was tested against Gram-negative and Gram-positive bacteria. The in vitro toxicity was evaluated by performing hemolytic analysis. The mutagenic activity was evaluated using Ames test. The prepared nanoparticles possessed high antibacterial potential and also inhibited the biofilm formation. Under the conditions of this study, it is concluded that the prepared AgNPs were nontoxic and nonmutagenic and possessed pharmaceutical applications.