C-A-S-H Gel and Pore Structure Characteristics of Alkali-Activated Red Mud-Iron Tailings Cementitious Mortar.

Chao Li,Na Zhang,Yihe Zhang,Shuai Song,Jiancong Zhang

doi:10.3390/ma15010112

Abstract

Red mud and iron tailings are representative solid wastes in China, which have caused serious environmental pollution and potential harmful risk to people. Based on the alkali characteristic of Bayer red mud and natural fine-grained feature of iron tailings, these two solid wastes were used as raw materials to prepare alkali-activated cementitious mortar (AACM). The microstructure of C-A-S-H gel, pore structure characteristics, environmental impact and economic potential of this AACM were investigated. The results show that C-A-S-H gel was mainly composed of SiQ3 structure in the 28-day cured AACM. The relative content of SiQ4 structure increased while that of SiQ2 structure decreased as the hydration time advanced from 7 to 28 days, resulting in the increase of relative bridge oxygen value by 11.02%. The pores in the AACM sample accounted for 6.73% of the total volume, and these pores were not connected. The pore distribution was relatively uniform, which supported the good development of mechanical strength for AACM. This research elucidates the formation mechanism of C-A-S-H gels in the Bayer red mud–iron tailings-based AACM. In addition, the lower embodied carbon and material cost demonstrate that the prepared AACM has great environmental benefit and certain economic potential.

Highlights

Red mud is a kind of industrial solid waste produced in the process of extracting alumina from bauxite
As the origins of red mud, iron tailings, and blast furnace slag have changed in this work, the different chemical and mineralogical compositions of red mud and iron tailings result in the strength difference
The cost of alkali activator accounts for 41.6% of the total material cost, this activated cementitious mortar (AACM) attains lower materials cost than the reference C30 concrete

Summary

Introduction

Red mud is a kind of industrial solid waste produced in the process of extracting alumina from bauxite. Every one ton of alumina is produced with the discharge of 1.0–1.8 tons of red mud. As a major producer of alumina, China emits millions of tons of red mud each year [3]. China’s alumina production in 2018 is about 69 million tons [4]. Just as other solid wastes need to be disposed with detoxification and solidification, such as municipal solid waste incineration fly ash [5], the hazardous components of red mud need to be disposed of, and the heavy metals need to be solidified and stabilized before it can be used

Methods

Results

Conclusion