Jinhui Peng

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.

Highly selective removal of Zn(II) ion from hot-dip galvanizing pickling waste with amino-functionalized Fe3O4@SiO2 magnetic nano-adsorbent.

Amino-functionalized Fe3O4@SiO2 magnetic nano-adsorbent was used as a novel sorbent to highly selective removal of Zn(II) ion from hot-dip galvanizing pickling waste in the presence of Fe(II). These hot-dip galvanizing pickling waste mainly contain ZnCl2 and FeCl2 in aqueous HCl media. The properties of this magnetic adsorbent were examined by transmission electron microscopy (TEM), powder X-ray diffraction (XRD), infrared spectrometer (FT-IR) and BET surface area measurements. Various factors influencing the adsorption of Zn(II) ion such as initial concentration of metal ions, the amount of adsorbent, pH value of the solutions, the concentration of coexisting iron ion were investigated by batch experiments. The results indicated that the adsorption equilibrium data obeyed the Freundlich model with maximum adsorption capacities for Zn(II) to 169.5mg/g. The maximum adsorption occurred at pH 5±0.1 and Fe(II) interferences had no obvious influence. This work provides a potential and unique technique for zinc ion removal from hot-dip galvanizing pickling waste.

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.

Green evaluation of microwave-assisted leaching process of high titanium slag on life cycle assessment

A greenness evaluation index and system of microwave-assisted leaching method were established. The effects of the life cycle assessment variables, such as the resource consumption, environment impact, cost, time and quality, were investigated, and the concept of green degree was applied in the production of synthetic rutile. An analytic hierarchy process was utilized to assess matrix of greenness evaluation. The Gauss-Seidel iterative matrix method was employed to solve the assessment matrix and obtain the weights and membership functions of all evaluation indexes. A fuzzy decision-making method was applied to build the greenness evaluation model, and then the scores of green degree in microwave-assisted leaching process was obtained. The greenness evaluation model was applied to the life cycle assessment of the microwave-assisted leaching process. The results show that the microwave-assisted leaching process has advantages over the conventional ones, with respect to energy-consumption, processing time and environmental protection.

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).

Comparison of ultrasonic-assisted and regular leaching of germanium from by-product of zinc metallurgy.

A major source of germanium recovery and also the source of this research is the by-product of lead and zinc metallurgical process. The primary purpose of the research is to investigate the effects of ultrasonic assisted and regular methods on the leaching yield of germanium from roasted slag containing germanium. In the study, the HCl-CaCl2 mixed solution is adopted as the reacting system and the Ca(ClO)2 used as the oxidant. Through six single factor (leaching time, temperature, amount of Ca(ClO)2, acid concentration, concentration of CaCl2 solution, ultrasonic power) experiments and the comparison of the two methods, it is found the optimum collective of germanium for ultrasonic-assisted method is obtained at temperature 80 °C for a leaching duration of 40 min. The optimum concentration for hydrochloric acid, CaCl2 and oxidizing agent are identified to be 3.5 mol/L, 150 g/L and 58.33 g/L, respectively. In addition, 700 W is the best ultrasonic power and an over-high power is adverse in the leaching process. Under the optimum condition, the recovery of germanium could reach up to 92.7%. While, the optimum leaching condition for regular leaching method is same to ultrasonic-assisted method, except regular method consume 100 min and the leaching rate of Ge 88.35% is lower about 4.35%. All in all, the experiment manifests that the leaching time can be reduced by as much as 60% and the leaching rate of Ge can be increased by 3-5% with the application of ultrasonic tool, which is mainly thanks to the mechanical action of ultrasonic.

Extraction and separation of Ce(III) and Pr(III) in the system containing two complexing agents with di-(2-ethylhexyl) phosphoric acid

In order to develop a novel separation technology superior to the current extraction systems, the extraction behaviors of Ce(III) and Pr(III) from chloride medium with P204 in the presence of two complexing agents lactic acid (LA) and citric acid (H3cit) have been reported. The distribution ratios increase with the increase of the equilibrium pH and the ratio of [H3cit] : [LA] under certain conditions. The separation factors of Ce(III) and Pr(III) increase with the ratio of [H3cit] : [LA] at fixed pH, and the maximum value is as high as 5.78 in this complexing system. The maximum saturated extraction capacity is 27.08 g L−1 which is close to that in the current saponified P507 extraction system. The equilibrium constants and thermodynamic functions, ΔG, ΔH and ΔS have been calculated. Lactic acid and citric acid can be effectively recycled and enriched, providing possibilities for dissolving minerals in the circular process. By comparison with the experimental results, this complexing extraction method could be regarded as an effective strategy for separating REs.

Microwave assisted grinding of ilmenite ore

The influence of microwave heating on the grinding of Panzhihua ilmenite ore was investigated. Factors that influence the processing are: the microwave exposure time, power density and sample mass. 40 g sample was microwave heated for 30 s with 1 kW of microwave power and followed by water quenching. SEM analysis indicated that intergranular fractures occurred between ores and gangues other than transgranular fractures after microwave treatment, which would liberate minerals from each other effectively. The subsequently magnetic separation trials provided evidence that the recovery rate increased from 44% for raw ore to 72% by microwave treatment.

Selective removal of cationic dyes from aqueous solutions by an activated carbon-based multicarboxyl adsorbent

An activated carbon-based multicarboxyl adsorbent has been synthesized for selective removal of cationic dyes from aqueous solutions. The adsorbent was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), N2 adsorption measurement and zeta potential. The adsorption behavior of cationic rhodamine 6G on the activated carbon-based multicarboxyl adsorbent from an aqueous medium was studied by varying the parameters such as pH, contact time and initial dye concentration. Dye adsorption was dramatically dependent on solution pH and the optimum pH is 4.45. After being modified by multicarboxyls, the adsorption capacity of rhodamine 6G on the activated carbon dramatically increased from 33.18 mg L−1 to 122.55 mg L−1 at pH 4.45. The multicarboxyl adsorbent has obvious selectivity to cationic dyes. Adsorption isotherms could be well described by the Langmuir model, adsorption kinetics fitted well with a pseudo-second-order kinetic equation and exhibited a 3-stage intraparticle diffusion mode. The electrostatic interaction was the main mechanism for the cationic dye adsorption.