Potential of Citric Acid for Treatment of Extremely Alkaline Bauxite Residue: Effect on Geotechnical and Geoenvironmental Properties

Abstract

In this paper, citric acid (CA) is chosen as an additive for the treatment of bauxite residue, a by-product generated by the aluminum industry. The potential of CA to improve geotechnical (e.g., compaction, strength, consolidation, and collapse potential) and geoenvironmental (e.g., pH and leaching) properties are explored by conducting elaborate laboratory experimental investigations on the treated bauxite residue samples. CA concentrations of 0.1, 0.5, 1, 2, 4, and 6 M are considered in this paper. The emphasis, in particular, is on the quantification of pH change in terms of rebound rate of pH (RRP) and rebound termination period (trt). It has been found from various results that 1 M CA successfully heightened the desirable properties and overcame the limitations of the treated bauxite residue simultaneously. The mineralogical analysis revealed minuscule changes in mineral phases, the formation of cementitious compounds (C-S-H), and fast crystallization of hydroxy sodalite, which is further confirmed by morphological studies. The leachability of potentially toxic elements (PTEs) is observed to be within the regulatory permissible limits of the USEPA and the Resource Conservation and Recovery Act (RCRA), demonstrating that the posttreated bauxite residue is environmentally benign and is safe to be used as a geomaterial. It is concluded based on the results that CA is a very good additive to convert the highly alkaline bauxite residue into a usable green geomaterial.