Aiyuan Ma

Study on non-isothermal kinetics of the thermal desorption of mercury from spent mercuric chloride catalyst

Kinetics of the thermal desorption of mercury from spent mercury chloride catalysts were investigated using non-isothermal thermal analysis technique. Complex mercury species absorbed on waste catalysts were revealed by sequential extraction procedure. A scheme of six reactions was applied to elucidate mercury desorption kinetics. Activation energy estimated by model-free isoconversional methods is a slightly increasing function of conversion, implying a variation in the mechanism controlling mercury desorption. Average value of apparent activation energy (116.32kJ/mol) calculated by isoconversional Starink method was used to determine reaction mechanism using model-fitting and z(α) master method. One dimensional diffusion appears to govern mercury desorption process in the conversion range of 10%-40%, and then the reaction kinetic is controlled by two and three dimensional diffusion at greater conversion.

Comparison of activated carbon and iron/cerium modified activated carbon to remove methylene blue from wastewater

The methylene blue (MB) removal abilities of raw activated carbon and iron/cerium modified raw activated carbon (Fe-Ce-AC) by adsorption were researched and compared. The characteristics of Fe-Ce-AC were examined by N2 adsorption, zeta potential measurement, FTIR, Raman, XRD, XPS, SEM and EDS. After modification, the following phenomena occurred: The BET surface area, average pore diameter and total pore volume decreased; the degree of graphitization also decreased. Moreover, the presence of Fe3O4 led to Fe-Ce-AC having magnetic properties, which makes it easy to separate from dye wastewater in an external magnetic field and subsequently recycle. In addition, the equilibrium isotherms and kinetics of MB adsorption on raw activated carbon and Fe-Ce-AC were systematically examined. The equilibrium adsorption data indicated that the adsorption behavior followed the Langmuir isotherm, and the pseudo-second-order model matched the kinetic data well. Compared with raw activated carbon, the maximum monolayer adsorption capacity of Fe-Ce-AC increased by 27.31%. According to the experimental results, Fe-Ce-AC can be used as an effective adsorbent for the removal of MB from dye wastewater.

Extraction of zinc from blast furnace dust in ammonia leaching system

Abstract In this research, the extraction of zinc from the blast furnace dust in the ammonia leaching system containing different leaching agents (NH3, (NH4)3AC, (NH4)2CO3, (NH4)2SO4, NH4Cl) 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.

Dechlorination of Zinc Oxide Dust from Waelz Kiln by Microwave Roasting

Abstract The new technology of dechlorination from zinc oxide dust by microwave roasting was investigated, combined with the advantages of microwave selective heating and based on a thermodynamic analysis of zinc and lead halides. The associated dechlorination reactions were discussed in details and the effect of all the influencing parameters such as roasting temperature, holding time, stirring speed and air flow were systematically investigated. Experimental results showed that zinc oxide dust dechlorination rate could reach over 95% and meet the requirements of wet smelting electrolysis, given an air flow of 300 L/h, a stirring speed of 60 r/min, a roasting temperature of 650 °C and a holding time of 30 min. Microwave roasting provided a new solution to the dechlorination from zinc oxide dust.

RSM Optimization of Process Parameters for Dechlorination by Microwave Roasting from Zinc Oxide Dust from Waelz Kiln

Abstract The response surface model for dechlorination process of zinc oxide dusts by microwave was built with an analysis of variance (ANOVA). It was introduced to analyze the dechlorination experimental results, and the model fit well. The central composite design (CCD) was applied to optimize and investigate the influence of roasting temperature, holding time, stirring speed and those interactions to dechlorination efficiency. According to the prediction and optimization function of Design Expert software, the optimum conditions of dechlorination by microwave roasting were found. When controlling roasting temperature to 626 °C, holding time 25 min and stirring speed 54 rpm, the experimental result of dechlorination efficiency could reach 90.13% which is very close to the predicted dechlorination efficiency of 90.48%, indicating that the response surface methodology optimization of process parameters for dechlorination of zinc oxide dusts by microwave roasting are reliable.

Effects of Sodium Citrate on the Ammonium Sulfate Recycled Leaching of Low-Grade Zinc Oxide Ores

Abstract The effects of sodium citrate on ammonium sulfate recycled leaching of low-grade zinc oxide ores were studied. By applying various kinds of detection and analysis techniques such as chemical composition analysis, chemical phase method, scanning electron microscopy and energy dispersive spectrum (SEM/EDS), X-ray diffraction (XRD) and Fourier-transforming infrared spectrum (FT-IR), zinc raw ore, its leaching slag and the functional mechanism of sodium citrate were investigated. Based on a comprehensive analysis, it can be concluded that in contrast to hemimorphite (Zn4Si2O7(OH)2 · H2O), amorphous smithsonite (ZnCO3) and zinc silicate (Zn2SiO4) prove to be refractory phases under ammonium sulfate leaching, while sodium citrate has a better chelating action with the refractory phases, resulting in a higher zinc leaching rate. Under conditions of [NH3]/[NH3]T molar ratio being 0.5, [NH3]T being 7.5 mol/L, [Na3C6H5O7] being 0.2 mol/L, S/L ratio being 1:5, temperature being 303 K, holding time being 1 h in each of the two stages, and stirring rate being 300 rpm, the leaching rate of zinc reached 93.4%. In this article, sulfate ammonium recycled technology also reveals its unique advantage in processing low-grade zinc oxide ores accompanied by high silicon and high alkaline gangue.

Effects of roasting pretreatment on zinc leaching from complicated zinc ores

Abstract 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 ZnCO3 cannot be effectively leached in the ammonia leaching system. Mineral phase transformation of ZnCO3 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%.

Extraction of gold and silver in the selective chlorination roasting process of cyanidation tailing

ABSTRACT The selective chlorination of cyanidation tailing (CT) for the extraction of gold and silver has been investigated. The reaction operated at different conditions and their effect on the extraction of Au and Ag was studied. The mineral samples were characterized by fire assay, X-ray diffraction (XRD), X-ray fluorescence (XRF) and scanning electronic microscopy (SEM). The best recovery values were 95.32% of Au and 85.32% of Ag at 1373 K and 1.5 h with 5% KCl. The results show that gold chlorination reaction was controlled by the interfacial chemical reaction, and the apparent activation energy was 40.05 kJ/mol. Silver has an activation energy of about 8.97 kJ/mol, and silver removal is performed by diffusion control.

Role of manganese dioxide in the recovery of oxide–sulphide zinc ore

In this article, the role of MnO2 in the recovery of oxide-sulphide zinc ore discussed. Through adopting various modern analysis techniques (such as X-ray diffraction pattern, X-ray photoelectron spectroscopy, scanning electron microscope, energy dispersive X-ray analysis, and fourier transform infrared spectroscopy), the function and mechanism of MnO2 during the phase transformation process is found out. Thermodynamic mechanisms involved in the phase transformation process with or without addition of manganese dioxide investigated by exploiting the Equilib module of FactSage. Whats more, XRD patterns, XPS spectra and SEM-EDAX analyses of zinc calcines verify well the calculations of FactSage. Results reveal that the addition of MnO2 will produce an aggregation of ZnMn2O4, a valuable energy material, while roasting on its own, results in generating undesirable Zn2SiO4, the oxidation degree being relatively low. Moreover, XRD pattern of zinc calcine and FT-IR spectrum of yellow product collected in the calcination process prove that the sulphur-fixing value of the additive MnO2, which can promote transforming to the elemental sulphur. The volatile S can be collected through a simple guiding device. In this process, the emission of SO2 effectively avoids, thus MnO2 deems as a potential additive in the recovery of oxide-sulphide zinc ore.

Study on regeneration of spent activated carbon by using a clean technology

Abstract In this paper, microwave regeneration of spent activated carbon saturated with organic compounds was investigated. It has been observed from the present experiments that the microwave regeneration temperature and time have significant influences on iodine adsorption value and yield of the regenerated activated carbon (RAC). The characteristics of the RAC were examined by Brunauer–Emmett–Teller (BET). The RAC has a greatly higher surface area (743.6~264.1 m2/g), total pore volume (0.54~0.22 cm3/g), and a relatively smaller average pore width (28.83~33.58 nm) compared to the spent catalyst. The separation mechanism for activated carbon and organic impurities was determined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) equipped with an energy-dispersive spectrometer (EDS). It was a process in which the organic impurities were aggregated from the pore internal migration to the surface at low temperatures, and the organic impurities were completely decomposed as the temperature increased to 900°C for 40 min. Simultaneously, a hexagonal crystal structure material of ZnO was obtained.