Bauxite residue issues: I. Current management, disposal and storage practices

Bauxite residue has been continuously produced since the inception of the alumina/aluminium industry in the late nineteenth century. The global inventory of bauxite residue reached an estimated 2.7 billion tonnes in 2007 increasing at 120 million tonnes per annum. This growth highlights the urgency to develop and implement improved means of storage and remediation, and to pursue large-volume utilization options of residue as an industrial by-product. This review looks at current management practices for disposal and amendment, and how each unit process influences residue properties. Since 1980 the trend has been away from lagoon-type impoundments towards “dry” stacking; this reduces the potential for leakage, reduces the physical footprint and improves recoveries of soda and alumina. Associated technical developments in residue neutralization are considered with possible future practices in residue disposal and how that might best integrate with future utilization. For example, hyperbaric steam filtration is an emerging technology that could discharge residue as a dry, granular material of low soda content. Such properties are beneficial to long term storage and remediation, but importantly also to future utilization. Although residue has a number of characteristics of environmental concern, the most immediate and apparent barrier to remediation and utilization (improved sustainability) is its high alkalinity and sodicity. The sustained alkalinity is the result of complex solid-state and solution phase interactions while its sodicity arises from the use of caustic soda (NaOH) for digestion. This is the first in a series of four related reviews examining bauxite residue issues in detail.