Research, development and application of compound-vertical-retort technology for magnesium production

This paper comprehensively introduces a new magnesium production technology the compound-vertical-retort technology, involving in the related fundamental researches, core equipment development, working flow, and technical characteristics. Scale-up test and an annual1200-ton-magnesium demonstration-level test was conducted to confirm the rationality, reliability, and advancement of the equipment, system and process design. It is indicated that the new technology solved a series of problems of traditional silicothermic process including adhesion and glaze, short life of retort, low efficiency, high impurity of crystallized magnesium, large heat losses, and poor working environment,making a great technological breakthrough in this field. Representatively, the new well-designed ceramic-lined steel retort serves 2~3 times in life than the normal retorts. The magnesium yield per retort is improved 4~5 times, with purity of >99.8%. The energy consumption in reduction stage is reduced by more than 20%. The mechanical production is fully realized and operating environment is significantly improved.

Mechanism of slag pellets sticking on the wall of reduction pot in magnesium production by Pidgeon process

In the preparation of magnesium by Pidgeon process,the phenomenon slag pellets sticking on the wall of reduction pot always appear,and the glaze sticking on the inner wall of the reduction pot is difficult to remove.The mechanism of this phenomenon is studied in this work by X-ray fluorescence spectrometer(XRF)measurement,electron probe microanalyzer scanning(EPMA)analysis,differential scanning calorimetry(DSC)analysis,and thermodynamic calculations.The main components of the glaze are MgO,Ca_(12)Al_(14)F_(2)O_(32),CaF_(2),CaO,and a small amount of Ca_(4)Si_(2)O_(7)F_(2).The solid-liquid transition temperature of Ca_(12)Al_(14)F_(2)O_(32)and CaF_(2)is close to the production temperature of Pidgeon process,which leads to the bonding between the slag pellets and the pot wall.The loss of CaF_(2)in glaze layer will reduce the total amount of liquid phase and increase the temperature at which Ca_(12)Al_(14)F_(2)O_(32)is completely transformed into liquid phase,which causes glaze layer sticking on the inner wall of the reduction pot.

Numerical simulation on gas-solid flow during circulating fluidized roasting of bauxite by a computational particle fluid dynamics method

A full-cycle numerical simulation of a circulating fluidized bed(CFB)by the use of the computational particle fluid dynamics(CPFD)method has been developed.The effects of the presence or absence of the secondary air,different secondary air positions,and different secondary air ratios on the gas–solid flow characteristics were explored.The results show that the presence of the secondary air makes a core-annular structure of the velocity distribution of particles in the fluidized bed,which enhances the uniformity of particles’distribution and the stability of fluidization.The position and the ratio of the secondary air have a significant impact on the particle distribution,particle flow rate,and gas flow rate in the fluidized bed.When the secondary air position and ratio are optimal,the particles,particle flow rate,and air flow rate in the CFB are evenly distributed,the gas–solid flow state is good,and the CFB can operate stably.

Albedo of Coastal Landfast Sea Ice in Prydz Bay,Antarctica:Observations and Parameterization

The snow/sea-ice albedo was measured over coastal landfast sea ice in Prydz Bay, East Antarctica（off Zhongshan Station）during the austral spring and summer of 2010 and 2011. The variation of the observed albedo was a combination of a gradual seasonal transition from spring to summer and abrupt changes resulting from synoptic events, including snowfall, blowing snow, and overcast skies. The measured albedo ranged from 0.94 over thick fresh snow to 0.36 over melting sea ice. It was found that snow thickness was the most important factor influencing the albedo variation, while synoptic events and overcast skies could increase the albedo by about 0.18 and 0.06, respectively. The in-situ measured albedo and related physical parameters（e.g., snow thickness, ice thickness, surface temperature, and air temperature） were then used to evaluate four different snow/ice albedo parameterizations used in a variety of climate models. The parameterized albedos showed substantial discrepancies compared to the observed albedo, particularly during the summer melt period, even though more complex parameterizations yielded more realistic variations than simple ones. A modified parameterization was developed,which further considered synoptic events, cloud cover, and the local landfast sea-ice surface characteristics. The resulting parameterized albedo showed very good agreement with the observed albedo.

The Spatial and Temporal Variation Characteristics of CH₄and CO₂Emission Flux under Different Land Use Types in the Yellow River Delta Wetland

The Yellow River Delta Wetland is one of the youngest wetlands, and also the most complete, extensive wetlands in China. The wetland in this delta is ecologically important due to their hydrologic attributes and their roles as ecotones between terrestrial and aquatic ecosystems. In the study, the spatial and temporal variation characteristics of CH4 and CO2 emission flux under five kinds of land use types in the wetland were investigated. The results indicated that the greenhouse gas emission flux, especially the CO2 and CH4, showed distinctly spatial and temporal variation under different land use types in the wetland. In the spring, the emission flux of CO2 was higher than that of CO2 in the autumn, and appeared negative in HW3 and HW4 in the autumn. CH4 emission flux of HW4 and HW5 was negative in the spring and autumn, which indicated that the CH4 emission process was net absorption. Among the five kinds of land use types, the CO2 emission flux of HW4 discharged the largest emission flux reaching 29.3 mg.m-2.h-1, but the CH4 emission flux of HW2 discharged the largest emission flux reaching 0.15 mg.m-2.h-1. From the estuary to the inland, the emission flux of CO2 was decreased at first and then appeared increasing trend, but the emission flux of CH4 was contrary to CO2.

Revealing the promising near-room-temperature thermoelectric performance in Ag_(2)Se single crystals

With high carrier mobility and intrinsic low lattice thermal conductivity,Ag_(2)Se compounds have attracted increasing attention for thermoelectric application near room temperature.Due to its phase transition at~406 K and resulting thermal volume expansion,the growth and thermoelectric properties of large-sized Ag_(2)Se single crystals have seldom been reported so far.In this work,the vertical Bridgeman method was used for growing bulk Ag_(2)Se single crystal,with an orientation preference along lowsymmetric(201)plane.The Hall mobility as high as 2000 cm^(2)/(V·s)and weak electron-phonon coupling contributes to a high electronic quality BE of~7.0 in near-room-temperature b-Ag_(2)Se single crystals,which is superior to the high-temperature phase a-Ag_(2)Se.The observed low lattice thermal conductivity of 0.8 W/(m·K)at 300 K is due to the low group speeds and strong anharmonicity.A promising peak zT of 0.66 at 375 K and an average zT of 0.65 at 300-375 K were realized in b-Ag_(2)Se crystals.The low Vickers hardness and good ductile properties were confirmed by experiment and theoretical analysis.This work not only synthesized large-sized and highly-orientated Ag_(2)Se crystals,but also revealed its great potential of thermoelectric performance and mechanical properties for various applications near room temperature.