Wen Ni

Recovery of iron from copper slag by deep reduction and magnetic beneficiation

Aiming at recovering iron from high-iron-content copper slag, this article introduced a combination technology of deep reduction and magnetic beneficiation, investigated the iron recovery efficiency and optimized the technical conditions. When coke powder with 86wt% fixed carbon was used as a reductant, iron was successfully extracted from the copper slag. Under the optimized condition of the coke powder content of 14wt%, the calcium-to-silicon mass ratio (Ca/Si) of 0.2, the roasting temperature of 1300°C, the roasting time of 3 h, the grinding time of 20 min, and the magnetic field intensity of 61 kA·m−1, the iron recovery rate of the copper slag can reach 91.82%, and the extracted iron powder has an iron grade of 96.21%. With the characteristics of high iron grade and low impurity content, the extracted iron powder can be used as high-quality raw materials of weathering steel.

Effect of Hydraulic Classification on Iron Ore Tailings Preparing High Strength Construction Materials

The aim of this study is to understand the effect of hydraulic classification on the iron ore tailings, and develop the cementitious activity of tailings to prepare construction materials. It was indicated that hydraulic classification can effectively divide the particulates of tailings into coarse and fine powders. The compression strength of the prepared construction materials are 87.83 MPa at 28 days, which have higher strength than the construction materials using original tailing, The variation in the tailings samples after hydraulic classification and the cementitious material after step-milling was characterized by sieve analysis, complete chemical analysis, scanning electron microscopy (SEM), and the particles size distribution. By mechanical properties testing and microstructure analysis shows that after hydraulic classification of tailings under the same conditions, the strength of the 3 days, 7 days, 28 days are higher than that of the original tailings. The main phases in the system are the rod of ettringite and low crystallinity or the amorphous C-S-H gel, and residual Ca(OH)2.

Study on Thermal Stability of Nano-Silica Thermal Insulating Composites

This work investigated the thermal stability of nano-silica thermal insulating composites, which consisted of fumed silica, fibers and opacifiers. The volume shrinkage was introduced as an evaluation index to characterize thermal stability of the composites at different temperatures. The effects of serving temperature, serving time, particle size of fumed silica and mass ratio of SiC were discussed. The results indicated nano-silica thermal insulating composites have excellent thermal stability under the temperature of 800°C. The volume shrinkage was correlated positively with serving time. High specific surface area of fumed silica could bring good thermal insulating performance, but at the same time caused high volume shrinkage when applied at high temperatures. SiC as an opacifier has little influence on volume shrinkage, but too much amount may yet increase solid heat transfer and lead to the drop of thermal insulating properties.

Hydrates and Paste Structure of Slag-Fly Ash Based Cementitious Materials

Cascade grinding mode is often applied to prepare Slag-Fly Ash Based cementitious materials with high volume of fly ash and slag and less cement clinker. This process has low water requirement and well fluidity, which is suitable to prepare HPC．When the W/C is 0.36, the 28d compressive strength is 58.93 Mpa, 28d flexural strength is 14.26 Mpa. By X-Ray diffraction analysis (XRD) and Scanning Electron Microscope (SEM) analysis the results show that main materials in grinded sample are well activated by mechanical force and chemical action; more Aft are produced and observed in 3 days hydration products and the great amount of C-S-H gel has continuously generated with the growth of hydration time. By Infrared(IR) analysis, the results show that in the hydration products, the network of Silicon Oxygen Tetrahedron and Aluminum Oxygen Tetrahedra have depolymerized significantly; in the hydration process and various raw materials mutually promoted each other to accelerate the hydration reaction. The hydrates and paste structure of slag-fly ash based cementitious materials were explained．

Effect of Fumed Titanium Oxide on Thermal Stability of Nano-Silica Thermal Insulating Composites

This work investigated the effects of fumed titanium oxide on thermal stability of nano-silica thermal insulating composites prepared by dry process. The results showed that the composites could keep excellent thermal stability at the temperatures below 800°C. However, when the samples were used at higher temperatures (>800°C), the volume shrinkage increased sharply, which directly led to a serious deformation and then affected thermal insulating properties in applications. The utilization of fumed titanium oxide could significantly improve thermal stability of the composites. When 10wt% fumed titanium oxide was added, the service temperature can increase from 800°C to 900°C. The desirable results would be achieved by adjusting the amount of additives according to practical using temperature. In addition, field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD) were employed to characterize the microstructure and phase transformations of the composites treated at different temperatures.

Effect of Nucleating Agents on Crystallization Glass Ceramics Produced from Nickel Slag

A laboratory preparation process of glass ceramics from nickel slag was introduced. The controlled heat treatment processes were carried out on the basis of differential scanning calorimetric (DSC) measurements. Mineral phase and microstructure of crystallized glass were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The modified Kissinger equation was employed to investigate the crystallization kinetic parameters, activation energy E and the k(Tp). The Avrami exponent, n, was calculated by Augis-Bennett equation. Analysis indicated that the glass with 10%TiO2 added was peril to crystallize, of a large value of k(Tp), its k(Tp) is 0.244, E is 522.76kJ/mol and n is 3.42. The crystal phase is diopside.