An Eco-Friendly Acid Leaching Strategy for Dealkalization of Red Mud by Controlling Phase Transformation.

Jiaming Wu,Shuwei Ma,Beibei Wang,Tianyu Lei,Yulong Lin,Xiaolei Lu,Zhengmao Ye

doi:10.3390/ma15020580

Abstract

The alkaline components in red mud represent one of the crucial factors restricting its application, especially for the construction and building industry. The phase state of alkaline components has a significant influence on the dealkalization of red mud. In this work, an environmentally friendly acid leaching strategy is proposed by controlling the phase transformation of red mud during active roasting pretreatment. With a moderate roasting temperature, the alkaline component is prevented from converting into insoluble phases. After acid leaching with a low concentration of 0.1 M, a high dealkalization rate of 92.8% is obtained. Besides, the leachate is neutral (pH = 7) and the valuable metals in red mud are well preserved, manifesting a high selectivity and efficiency of diluted acid leaching. The calcination experiment further confirms the practicability of the strategy in the construction field, where the cementitious minerals can be formed in large quantities. Compared with the traditional acid leaching routes, the diluted acid leaching strategy in this work is acid saving with low valuable element consumption. Meanwhile, the secondary pollution issue can be alleviated. Hence, the findings in this work provide a feasible approach for the separation and recovery of alkali and resource utilization of red mud.

Highlights

Red mud is the industrial waste discharged from the alumina preparation with bauxite [1,2]
High alkalinity is a critical factor limiting the use of red mud, such as in the iron industry, construction industry, catalysts, energy storage, and wastewater treatment [15,16,17]
The first stage of mass loss is presented at 200–400 ◦ C, and the second mass loss is mud usually undergoes phase transformation during the active roasting process

Summary

Introduction

Red mud is the industrial waste discharged from the alumina preparation with bauxite [1,2]. Extracting 1 t of alumina would produce about 0.5–2.0 t of red mud [3,4,5]. Red mud occupies vast areas of agricultural land and causes a certain degree of environmental pollution on soil and groundwater [9,10,11]. In the Bayer process (Figure 1), bauxite is treated with sodium hydroxide solution in a pressure vessel, leading to the high alkalinity of red mud [12,13,14]. High alkalinity is a critical factor limiting the use of red mud, such as in the iron industry, construction industry, catalysts, energy storage, and wastewater treatment [15,16,17]. The dealkalization of red mud is beneficial to promoting the recycling of red mud and reducing environmental problems

Methods

Results

Conclusion