Red mud as an amendment for pollutants in solid and liquid phases

Red mud is a solid waste derived from bauxite refining processes, chiefly the Bayer process. Its disposal poses a significant environmental problem due to its high alkalinity and fine particle size. This paper presents a critical review of techniques currently being used or proposed for the utilization of red mud to minimize its harmful impact on the environment if disposed on land or in water bodies. Bulk uses, including its use as building materials, soil amendments and landscaping and conventional landfill, are continually being investigated for environmental friendly and economical efficient applications. Other applications, such as metal recovery (Fe, Al, and Ti), synthesis of radio-opaque materials, functional composites and catalysts are being investigated. Recently, red mud as an agent for removing and immobilizing pollutants in liquid and solid phases has become the focus of much new research. Although many different applications of red mud have been demonstrated at bench scale, few have been successfully implemented in the field thus resulting in the disposal of large volumes of red mud in prescribed land fill sites. One of the major limitations of the available technologies is the lack of cost benefit analyses given the large transport costs associated with the transfer of red mud from its disposal sites to the point of application. Research with novel applications of red mud for removing and immobilizing pollutants in liquid and solid phases presents new opportunities for the efficient removal of phosphates, nitrates, fluoride, dye, phenol, bacteria, and heavy metals. Different strategies for managing red mud, its efficiency for removing pollutants in liquid and solid phases as well as comparison with other low-cost adsorbents, and activation methods currently in use are summarized in this review.