Libo Zhang

Preparation of high surface area activated carbon from coconut shells using microwave heating

The present study attempts to utilize coconut shell to prepare activated carbon using agents such as steam, CO(2) and a mixture of steam-CO(2) with microwave heating. Experimental results show that the BET surface area of activated carbons irrespective of the activation agent resulted in surface area in excess of 2000 m(2)/g. The activation time using microwave heating is very much shorter, while the yield of the activated carbon compares well with the conventional heating methods. The activated carbon prepared using CO(2) activation has the largest BET surface area, however the activation time is approximately 2.5 times higher than the activation using steam or mixture of steam-CO(2). The chemical structure of activated carbons examined using Fourier transformed infra-red spectra (FTIR) did not show any variation in the surface functional groups of the activated carbon prepared using different activation agents.

Preparation of activated carbon from coconut shell chars in pilot-scale microwave heating equipment at 60 kW

Experiments to prepare activated carbon by microwave heating indicated that microwave energy can decrease reaction temperature, save the energy and shorten processing time remarkably compared to conventional heating, owing to its internal and volumetric heating effects. The above results were based on the laboratory-scale experiments. It is desirable to develop a pilot-scale microwave heating equipment and investigate the parameters with the aim of technological industrialization. In the present study, the components and features of the self-invented equipment were introduced. The temperature rise curves of the chars were obtained. Iodine numbers of the activated carbons all exceed the state standard of China under the following conditions: 25 kg/h charging rate, 0.42 rev/min turning rate of ceramic tube, flow rate of steam at pressure of 0.01 MPa and 40 kW microwave heating power after 60 kW pre-activation for 30 min. Pore structure of the sample obtained at a time point of 46 h, which contained BET surface area, and pore size distributions of micropores and total pores, was tested by nitrogen adsorption at 77K.

Microwave drying characteristics and kinetics of ilmenite

The microwave drying of ilmenite was investigated. The effects of power levels and sample mass on drying characteristics of moisture content, drying rate, moisture ratio were studied, with microwave power ranging from 119 W to 700 W and sample mass from 5 g to 25 g. The drying processes were completed within 2-8 min at different conditions. The moisture content and drying rates are found to be dramatically affected by microwave power density. For all drying processes the prior microwave absorption of moisture produces an accelerating peak on the drying rate curves in the initial stage. For the sample mass of 25 g and power of 385 W, the drying kinetics were studied. The experimental results fit better to the Henderson-Pabis index model rather than the Page’s semi-empirical model; the drying rate constant k is increased with the increase of microwave power and decrease of sample mass.

Leaching zinc from spent catalyst: Process optimization using response surface methodology

The spent catalyst from vinyl acetate synthesis contains large quantity of zinc. The present study attempts to leach zinc using a mixture of ammonia, ammonium carbonate and water solution, after microwave treatment. The effect of important parameters such as leaching time, liquid/solid ratio and the ammonia concentration was investigated and the process conditions were optimized using surface response methodology (RSM) based on central composite design (CCD). The optimum condition for leaching of zinc from spent catalyst was identified to be a leaching time of 2.50 h, a liquid/solid ratio of 6 and ammonia concentration 5.37 mol/L. A maximum of 97% of zinc was recovered under the optimum experimental conditions. The proposed model equation using RSM has shown good agreement with the experimental data, with a correlation coefficient (R(2)) of 0.95. The samples were characterized before and after leaching using X-ray diffraction (XRD), nitrogen adsorption and scanning electron microscope (SEM).

Rapidly sintering of interconnected porous Ti-HA biocomposite with high strength and enhanced bioactivity.

In this work, interconnected porous Ti-HA biocomposites with enhanced bioactivity, high porosity and compressive strength were prepared by spark plasma sintering (SPS) and space holder method. Pore characteristics, mechanical properties, corrosion behaviors and in vitro bioactivity of the porous Ti-HA were investigated. Results showed that porous Ti-HA with 5-30wt% HA contents possessed not only low elastic modulus of 8.2-15.8GPa (close to that of human bone) but also high compressive strength (86-388MPa). Although the HA partially decomposed and formed secondary phases, the sintered porous Ti-HA can still be good bioactivity. The homogeneity and the thickness of apatite layer increased significantly with the increase of HA. But with the thickness of apatite layer increased, micro-cracks appeared on the surface of porous Ti-30%HA. A model was built to discuss the current distribution and sintering mechanism of HA on Ti matrix during SPS process. It indicated that the excessive addition of HA would deteriorate the sintering quality, thus decreasing the mechanical properties and corrosion resistance. However, the combination of interconnected pore characteristics, low elastic modulus, high compressive strength and enhanced bioactivity might make porous Ti-HA biocomposites prepared by SPS a promising candidate for hard tissue implants.

Process Optimization for the Preparation of Activated Carbon from Jatropha Hull Using Response Surface Methodology

Abstract Preparation of activated carbon has been attempted using CO2 as the activating agent from Jatropha hull, one of the popular feed stocks for biodiesel manufacture. The response surface methodology technique is utilized to optimize the process conditions. The influences of the three major parameters, activation temperature, activation time, and CO2 flow rate on the properties of activated carbon, are investigated using analysis of variance to identify the significant parameters. The optimum conditions for preparation of activated carbon has been identified to be an activation temperature of 950°C, activation time of 40 min, and CO2 flow rate of 500 ml/min, an iodine number of 1,008 mg/g, and a yield of 18% were obtained, respectively. The BET surface area evaluated using nitrogen adsorption isotherm for the optimal sample corresponds to a 1,207 m2/g, with the pore volume of 0.86 cc/g. The activated carbon is heteroporous with the micropore volume contributing to 58%.

Removal of cadmium from aqueous solutions using red mud granulated with cement

Abstract A novel adsorbent was prepared from granular red mud mixed with cement and its potential to be a suitable adsorbent for the removal of cadmium ions from aqueous solutions was evaluated. The wet red mud was directly mixed up with cement at different mass fractions of 2%–8% and their properties were investigated. Based on the textural characteristics and strength, the granular red mud with 2% addition of cement maintaining for 6 d is identified to have better properties. The batch adsorption experiments for adsorption of Cd 2+ ions from solution were performed at 30, 40 and 50 °C at different initial concentrations under the condition of constant pH of 6.5. The equilibrium adsorption was found to increase with the increase of temperature during the adsorption process. Langmuir adsorption isotherm model was found to match the experimental adsorption isotherm better. The kinetics of adsorption was modeled using a pseudo second order kinetic model and the model parameters were estimated.

Effects of microwave pretreatment on zinc extraction from spent catalyst saturated with zinc acetate

Abstract A new technology for microwave pretreatment of spent catalyst on Zn extraction by HCl leaching was proposed and the temperature-change curve of spent catalyst under microwave irradiation was measured. The influence of microwave pretreatment temperature and microwave irradiation time on zinc extraction was investigated and the mechanism of microwave pretreatment for spent catalyst was analyzed. The results show that microwave pretreatment can greatly enhance the leaching rate of Zn. The Zn extraction reaches 96.58% under the conditions of microwave pretreatment temperature of 950 °C and the microwave irradiation time of 12 min. The blocked pores of spent catalyst can be opened through microwave pretreatment, increasing the contact area of leaching reagent and zinc.

Thermodynamics of leaching roasted jarosite residue from zinc hydrometallurgy in NH4Cl system

Abstract The thermal decomposition process of jarosite residue and the solubility of various oxides presented in the decomposed residue in NH 4 Cl-H 2 O system were studied. The results of heat decomposition of jarosite residue show that the insoluble ZnFe 2 O 4 phase in the residue can be decomposed at temperatures ranging from 500 °C to 650 °C for 1 h. The OLI Systems software was used to study the thermodynamics of the solubility of various metal oxides existing in the decomposed residue in NH 4 Cl-H 2 O system. The results show that the solubility of ZnO, PbO, CdO, CuO and Ag 2 O is high, while the solubility of Fe 2 O 3 is less than 10 −4 mol/L in the pH range from 4.0 to 9.0. The calculated data are in accordance with the experimental results.

Microwave-assisted regeneration of spent activated carbon containing zinc acetate and its application for removal of congo red

AbstractThe spent activated carbon (AC) loaded with zinc acetate from the vinyl acetate synthesis industry has been used as a raw material to prepare AC-ZnO porous adsorbents using microwave irradiation technique with three different activating agents. The morphology and surface chemical compositions of the prepared samples were characterized by X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, and N2 adsorption–desorption isotherm. The regenerated AC-ZnO composites exhibited a well-developed porous structure with Brunauer–Emmett–Teller surface area in excess of 1,100xa0m2/g, and the ZnO nanoparticles decomposed from zinc acetate loaded on the surface of the regenerated AC without aggregation. The adsorption performance of the AC-ZnO composites was further evaluated by adsorbing Congo Red (CR) from aqueous solutions. The experimental isotherms data were analyzed using Langmuir, Freundlich, and Temkin models. Langmuir and Temkin models were found to satisfactorily matc...