Reduction of Cr(Ⅵ) with a relative high concentration using different kinds of zero-valent iron powders: Focusing on effect of carbon content and structure on reducibility

Reduction of Cr(VI)using zero-valent iron(ZVI)could not only decrease the amounts of chemicals used for reduction,but also decrease the discharge of sludge.In order to find a desirable ZVI material,reduction of Cr(VI)with a relative high concentration using different kinds of ZVI powders(mainly carbon differences)including reduced Fe,grey cast iron,pig iron,nodular pig iron was carried out.Parameters such as ZVI dosage,type and size affecting on Cr(VI)reduction were firstly examined and grey cast iron was selected as a preferable reducing material,followed by pig iron.Additionally,it was found that the parameters had significant influences on experimental kinetics.Then,morphology and composition of the sample before and after reaction were characterized by SEM,EPMA and XPS analyses to disclose carbon effect on the reducibility.In order to further interpret reaction mechanism,different reaction models were constructed.It was revealed that not only the carbon content could affect the Cr(VI)reduction,but also the carbon structure had an important effect on its reduction.

Analysis of Correlation between Concentration of Atmospheric Particulates and Humidity Based on the Aerodynamic Particle Sizer

The TSI-3321 APS was used to measure concentration of atmospheric particulates in Ranjiaba region of Yubei District in Chongqing City during March 21- 29,2014,and the temporal variations in the hourly average mass and number concentration and median particle diameter of PM10 and PM2.5 as well as their correlation with relative humidity were analyzed. The results showed that the three indicators of PM10 and PM2.5 except for the mass concentration correlated with relative humidity,of which the correlation between the mass median particle diameter and relative humidity was the best. The correlation coefficient R^2 between the mass median particle diameter of PM10（ PM2.5） and relative humidity was up to 0. 943（ 0. 832）. Therefore,relative humidity and pressure are key impact factors of indicators of particles.

The Spectral Emission Characteristics of Laser Induced Plasma on Tea Samples

Laser induced breakdown spectroscopy （LIBS） provides a useful technique for food security as well as determining nutrition contents. In this paper, optical emission studies of laser induced plasma on commercial tea samples were carried out. The spectral intensities of Mg, Mn, Ca, A1, C and CN vibration bands varying with laser energy and the detection delay time of an intensified charge coupled device were studied. In addition, the relative concentrations of six microelements, i.e., Mg, Mn, Ca, Al, Na and K, were analyzed semi-quantitatively as well as H, for four kinds of tea samples. Moreover, the plasma parameters were explored, including electron temperature and electron number density. The electron temperature and electron number density were around 11000 K and 1017 cm-3, respectively. The results show that it is reasonable to consider the LIBS technique as a new method for analyzing the compositions of tea leaf samples.

Optimization of environmental maintenance system used in a refuge chamber

Mine refuge chambers are used to shield miners who fail to escape from the mine when incidents occur. Environment maintaining system plays a key role in stabilizing thermal environment of a mine refuge chamber against heat emitted from metabolism and transferred from outside. The safety and comfort of refugees are closely related to the environment maintaining system design. In order to improve the comfort of refugees, optimization on the environment maintaining system has been done based on the previous work. To evaluate the environment of the chamber, eight volunteers were involved into the experiment. Under close observation and safety protection, they lived in a heat-isolated test chamber for 106 hours. The volunteers were asked to maintain low level of activities to simulate refugees＇ situation. It shows that the environment maintaining system worked well and the temperature, relative humidity and emitted harmful air content such as CO2 and CO were all kept in the safety level, and no discomfort was felt by volunteers at all.

Stepwise superposition approximation approach for analytical solutions with non-zero initial concentration using existing solutions of zero initial concentration in contaminate transport

Analytical solutions for contaminant transport are widely used for both theoretical and practical purposes.However,many existing solutions are obtained subject to an initial condition of zero concentration,which is often unrealistic in many practical cases.This article proposed a stepwise superposition approximation approach to solve the non-zero initial concentration problem for first-type and third-type boundary conditions by using the existing zero initial concentration solution.Theoretical examples showed that the approach was highly efficient if a proper superposition scheme with relative concentration increments was constructed.The key parameter that controlled the convergence speed was the time increment（△t） multiplied by the rate constant（λ）.The approach served also as an alternative way to make a convenient concentration calculation even if the non-zero initial concentration solution of a problem was known.

MODELING AND ANALYSIS OF SALT TRANSPORT IN THE SINGLE CYLINDRICAL ROOT WITH FINITE LENGTH

A mathematical model for salt transport by a cylindrical root in an infinite extent of soil is derived and solved analytically by asymptotic matching of the inner and outer solutions. By asymptotic analysis it is shown that the salt solution uptake by a single cylindrical root in the absence of competition does not influence the overall salt concentration in the soil even when the soil moisture concentration is less than full saturation.