A Study on the Effect of Different Ball Milling Methods on the NH3-SCR Activity of Aluminum-Laden Bayan Obo Tailings

Jiawei Lin,Limin Hou,Wenfei Wu,Xinrui Bai,Zedong Chen

doi:10.3390/catal11050568

Abstract

Rich in Fe, Ce, Mn, Si and other elements which have good catalytic activity, Bayan Obo rare-earth tailings are naturally advantaged as the carrier of denitrification catalysts. In this paper, pseudo boehmite (γ-Al2O3) was mixed with Bayan Obo tailings using different ball milling methods for modification to prepare NH3-SCR catalysts. The effect of different mixing methods on the SCR denitrification activity at a low temperature was investigated and the prepared catalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), temperature programed desorption (NH3-TPD), temperature programed reduction (H2-TPR) and other means. The conversion rate of NOx at 250–350 °C was above 80% and the highest conversion rate of NOx of 90% was achieved at 300 °C. SEM and XRD revealed that the tailings modified by pseudo boehmite (γ-Al2O3) using the ordinary ball milling method have loose structure and good dispersion of active substances, and specific surface area (BET) analysis shows that the tailings have the maximum specific surface area and pore volume. However, over grinding and secondary spheronization were observed in the tailings modified by pseudo boehmite (γ-Al2O3) using high energy ball milling method, leading to the decrease of specific surface area and pore volume, poor dispersion of active substances, and ultimately low denitrification rate.

Highlights

The Bayan Obo mine, the largest polymetallic iron–niobium–REE deposit in the world, is characterized by a wide variety of elements, fine-grained dissemination and complex mineral compositions
Fe2O3, MnO, TiO2, ZnO are transition metal oxides, which are the main elements that determine the performance of the catalyst, and them content in the rare earth tailings accounts for a large proportion, indicating that the rare earth tailings are suitable for the preparation of denitration catalyst
Bayan Obo rare-earth tailings are rich in Fe, Ti, Ce, Mn and other minerals that can be used as active carriers, and Al, Si and other minerals that can be used as rigid carriers, making Bayan Obo a natural advantage as a denitration catalyst carrier

Summary

Introduction

The Bayan Obo mine, the largest polymetallic iron–niobium–REE (rare earth elements) deposit in the world, is characterized by a wide variety of elements, fine-grained dissemination and complex mineral compositions. The average grade of rare earth oxides, which are minerals with good catalytic activity in Bayan Obo rare-earth tailings is still as high as 6%~8%. There are a large number of minerals containing Al and Si in the tailings that can be doped into the catalyst to provide specific surface area and act as the rigid carrier Transition metal elements such as Fe, Nd, Mn, Cu are the main active compositions of the catalyst and can act as the active carrier. Preparing denitrification catalysts from tailings can achieve good catalytic effect at low temperature, and can play a major role in improving the utilization rate of mineral resources in China [6,7,8,9,10]. The addition of Ce increases the Mn valence, and improves its oxidizing ability [16,17,18]

Methods

Results

Conclusion