The Effect of Red Mud on Sintering Processes and Minerals of Portland Cement for Roads

Xiao Wang,Ke Sun,Xin Li,Juntao Ma,Zhongtao Luo

doi:10.3390/cryst11101267

Xiao Wang, Ke Sun + Show 3 more

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https://doi.org/10.3390/cryst11101267

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Abstract

As a solid waste generated in the alumina industry, red mud poses a significant environmental hazard and a storage problem. In this study, red mud was added to road cement clinker in order to utilize it. The sintering red mud was first de-alkalized, and then mixed with fly ash, clay, limestone, and sandstone, among other materials, to make Portland cement for road clinker. The effect of the addition of red mud on the thermal decomposition characteristics of Portland cement for roads was studied. The existent states of alkali and radioactive elements in Portland cement for road clinker were investigated by XRD and SEM analysis. The research results showed that the addition of red mud in Portland cement for road raw material significantly promoted the decomposition of carbonates in raw material. The major mineral phases of Portland cement for road clinker were C3S with a polyhedral morphology, quasi-spherical C2S, and tubular C4AF. A small part of the alkali combined with the silicate phase to form a solid solution, and most of the alkali combined with S to form vermiform sulfate in the intermediate phase. The radionuclide 226Ra was mainly distributed in the silicate phase. 232Th was mainly distributed in interstitial phases and then silicate phases, while 40K was mainly distributed in the interstitial phases.

Highlights

Red mud is a strong alkaline solid waste that is discharged in the process of alumina production
The average discharge of red mud is 0.7–1.8 tons per ton of alumina production [1]
As a large alumina production country, China produces more than 30 million tons of red mud annually, and the cumulative stock of red mud is projected to reach 600 million tons by the end of 2021

Summary

Introduction

Red mud is a strong alkaline solid waste that is discharged in the process of alumina production. The average discharge of red mud is 0.7–1.8 tons per ton of alumina production [1]. Red mud is considered a hazardous industrial waste due to its high alkali content, as well as its small amount of heavy metals and radioactive materials. Global red mud reserves are close to 3 billion tons, and the annual growth rate is 120 million tons [2]. As a large alumina production country, China produces more than 30 million tons of red mud annually, and the cumulative stock of red mud is projected to reach 600 million tons by the end of 2021. On 16 September 2014, due to continuous heavy rains in Zhengzhou, a local collapse occurred in the No 2 dam of the No 5 Red Mud

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