Abstract
An increasing amount of red mud (RM) is being generated globally due to the growth in aluminum production. To avoid RM pollution, low-cost methods for effectively recycling RM are being investigated. We propose a method for recycling RM as a construction material. Liquefied RM (LRM) was neutralized by nitric acid and added to cement paste, and the hydration heat, compressive strength, and hydration products were investigated. The cement paste with neutralized LRM had a higher compressive strength than that of plain cement paste and cement paste with LRM without neutralization at 1 day of aging; this indicates that nitric acid neutralization increases the early-age strength. Furthermore, the cement paste with 10% neutralized LRM showed 28 days-compressive strength and hydration heating curves similar to the plain mixture, indicating the positive impact of LRM neutralization on the strength. It was noted that a greater quantity of portlandite was produced earlier in cement paste with neutralized LRM than in that without. Therefore, the proposed method of using RM as a concrete additive has the potential to reduce the cost and environmental impact of both construction materials and RM waste management.
Highlights
Red mud (RM) is the waste generated when bauxite is processed into alumina, a raw material for aluminum production [1,2]
Liquefied RM (LRM) is considered to have reduced compressive strength when added to cement paste because it is strong alkaline
The compressive strengths of the samples with neutralized LRM were higher than those of the LRM samples strength of Plain aged for 28 days was 61.0 MPa
Summary
Red mud (RM) is the waste generated when bauxite is processed into alumina, a raw material for aluminum production [1,2]. With the rapid development of the aluminum industry, approximately 1.7 billion tons of RM is generated per year globally [5,6,7]. The pH of RM is typically 10.5–12.5 owing to the hydroxide (NaOH) added during aluminum production [7,8,9]. Red mud (RM) leads to serious environmental problems due to its mass disposal and strong alkalinity [3]. Improper treatment of RM can contaminate the soil and seriously impair the soil fertility. Due to its detrimental effects on the environment, it is necessary to recycle it after proper treatment when discharging [3,12]
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