Physicochemical and Microstructural Properties of Red Muds under Acidic and Alkaline Conditions

Qingke Nie,Youdong Li,Guohui Wang,Bing Bai

doi:10.3390/app10092993

Qingke Nie, Youdong Li + Show 2 more

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https://doi.org/10.3390/app10092993

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Abstract

The main purpose of this study was to characterize the mineral and chemical composition of typical red muds in China. Changes in the physicochemical and microstructural properties of red muds collected from the Shanxi and Shandong provinces were investigated after they were immersed in an alkaline NaOH or an acidic HCl solution for 7, 28, and 120 days. The results showed that red mud has a high cation exchange capacity and active physicochemical properties, which can be closely related to its extremely high alkalinity and complex microstructure. The neutralization of red mud with the HCl solution results in the release of Na+ from the red mud particles into the leachate and can effectively decrease the pH value of the filtrate. The neutralization process can result in a significant decrease in the liquid limit, plastic limit and plasticity index, whereas the opposite was observed for the different parameters after the addition of the NaOH solution. In this sense, acid neutralization can significantly improve the cementation property of the red mud. This result will increase the water permeability of the acid-treated soil layer and improve the growth ability of plants. The specific surface area of red mud immersed in the NaOH solution decreased, whereas the specific surface area of red mud immersed in the HCl solution increased. This study contributes to our understanding of red mud properties after the red mud has been subjected to acidic and alkaline treatments, and the results can provide insights into the safe disposal of red mud.

Highlights

Red mud is a highly alkaline ultrafine-grained waste material generated during the industrial production of aluminum oxide from bauxite [1,2,3]
In China, the red mud produced by the Bayer method is rich in ferric and aluminum oxides (Table 2), which are lower in ferric and aluminum oxides than those produced in other countries by the same method
The acid neutralization of red mud can result in a significant decrease in the liquid limit, plastic limit and plasticity index, whereas the opposite is observed for the addition of the NaOH solution

Summary

Introduction

Red mud (bauxite residue) is a highly alkaline ultrafine-grained waste material generated during the industrial production of aluminum oxide from bauxite [1,2,3]. In 2019, aluminum oxide production exceeded 70 million tons in China. This production will give rise to the formation of a large quantity of hazardous substances (e.g., heavy metal ions and radioactive elements) in the byproducts (e.g., solid waste materials and leachate), causing serious damage to the environment and human health [4,5]. The disposal of red mud requires a large storage space, and the infiltration of various chemical elements into soils may cause soil salinization and groundwater pollution [6]. There is an urgent need for the safe disposal of red mud in

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