A Study on Evaluating the Usefulness and Applicability of Additives for Neutralizing Extremely Alkaline Red Mud Waste
The chemico-mineralogical compositions of red mud lead to its abnormal pH (>11), rendering it unusable as a resource material for civil engineering applications. Such extreme alkalinity accentuates the dearth of contriving a solution to ensure the acce
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Abstract The chemico-mineralogical compositions of red mud lead to its abnormal pH (>11), rendering it unusable as a resource material for civil engineering applications. Such extreme alkalinity accentuates the dearth of contriving a solution to ensure the acceptability and reutilization of the waste. Curing period has considerable significance in the context that the previous studies reported reversal of pH of the red mud after neutralization. Thus, efforts are made in the present study to evaluate the usefulness and applicability of a variety of additives for neutralizing the red mud waste. Additives such as lime, ground granulated blast furnace slag, fly ash, gypsum in different proportions, and acids such as nitric acid and hydrochloric acid of varying strengths were employed, aiming at investigating the alkalinity mitigation capacity in the red mud. The results demonstrated a substantial reduction in the alkalinity levels of the red mud immediately after treatment, but the post-neutralization pH results exhibited noteworthy reversal with time. It has also been found that the type of neutralizing additives has considerable influence on the chemistry which in turn might have affected alkalinity levels in the red mud. Keywords Red mud · Additives · Alkalinity reduction · Neutralization · pH rebound
M. C. Mishra · N. Gangadhara Reddy · B. Hanumantha Rao (B) School of Infrastructure, IIT Bhubaneswar, Khordha 752050, Odisha, India e-mail: [email protected] M. C. Mishra e-mail: [email protected] N. Gangadhara Reddy e-mail: [email protected] S. Kumar Das Department of Civil Engineering, IIT (ISM) Dhanbad, Dhanbad 826004, Jharkhand, India e-mail: [email protected] © Springer Nature Switzerland AG 2020 K. R. Reddy et al. (eds.), Sustainable Environmental Geotechnics, Lecture Notes in Civil Engineering 89, https://doi.org/10.1007/978-3-030-51350-4_16
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1 Introduction A slurry-based residue is generated along with alumina from bauxite ore by Bayer process. This bauxite residue, also known as red mud (RM), is classified as extreme alkaline waste material primarily due to its pH in excess of 11.5 and high sodic content. A few other associated problems of RM include dispersivity, low compressive strength, a variable degree of compactibility, dusting behavior, and leaching, which undergo changes with variations in pH conditions [1–5]. Of the total RM produced worldwide in a year, the utilization is limited to a bare 2–3% [6]. The utilization of RM has been limited to a few applications in the construction industry [7, 8]. However, it should be noted that resource materials with pH more than 8.5 have been recommended not to be used for civil engineering applications as per Indian Standards [9, 10]. Therefore, it is essential not only to stabilize the RM but also to maintain a lower pH of the waste to render it environmentally benign enough to be utilized as a resource material. Of late, endeavors [11–15] are made at the reutilization of RM as an adsorbent to retrieve phosphates, fluoride
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