Fly ash as a permeable cap for tailings management: pedogenesis in bauxite residue tailings

Abstract

PurposeClosure of tailings facilities typically involves either a 'cap and store' or 'direct revegetation' approach. Both have been used in the management of bauxite residue (alumina refining tailings), with mixed results. This study evaluated the merit of an intermediate approach, using a permeable cap, and examined the pedogenic trajectory of the Technosol. Materials and methodsChemical, mineralogical and physical properties of samples from a Brazilian bauxite residue deposit, which had been capped with fly ash 14 years prior and supported a vegetation cover, were compared to evaluate soil formation and pedogenic trajectory of the developing Technosol according to the World Reference Base for Soil Resources. Samples were collected at three points along an elevation gradient, and from 0 to 150 cm below the surface. Results and discussionRainfall leaching was identified as the most important pedogenic process occurring in the tailings, lowering salinity and pH. The Technosol classification was poorly suited to describe the soil materials within the study site because two wastes (fly ash and bauxite residue) were co-disposed in discrete layers. ConclusionsThe permeability of the fly ash cap is key to soil development in these tailings: it provides a suitable medium for plant growth whilst still allowing contact between the tailings and the surrounding environment. The introduction of a novel prefix qualifier, 2 ordic, would enable more accurate description of layered Technosols. The Technosol at this site is likely to develop towards an Andosol or Ferralsol.

Development of alkaline electrochemical characteristics demonstrates soil formation in bauxite residue undergoing natural rehabilitation

“…Understanding the influences of bauxite residue mineralogy on the proton adsorption behavior is important in relation to environmental issues of BRDAs. Complex mineralogy often dominates residue disposal areas, leading to long term leakage of alkaline compounds, and diffusion and/or overflow of alkaline dust and efflorescence substances formed at the surface of BRDAs during storm events (Courtney & Harrington, ; Higgins et al, ; Higgins et al, ; Santini & Fey, ; Zhu et al, ). Therefore, understanding the effects of different disposal years on bauxite residue mineralogy and the influences of mineralogy on proton adsorption behavior of bauxite residue highlight the requirement for effective environmental management and rehabilitation of BRDAs.…”

Experimental Simulation of Long Term Weathering in Alkaline Bauxite Residue Tailings

“…This reflects the fact that weathering of primary minerals, an essential part of soil formation, can be a slow process in the field which is partially constrained by reaction kinetics. Limited evidence of mineral weathering has also been reported in other studies of soil development in bauxite residue [8,9]. Laboratory simulation of weathering is therefore essential in order to understand how this material behaves over longer weathering timescales and ensure that management strategies are effectively designed to minimize adverse environmental impacts over the long term.…”

Pedogenetic Trends in Soils Formed in Technogenic Parent Materials

“…The first group of processes reported refers to the biogeochemical weathering of technogenic materials under the influence of climatic conditions and then of organisms. Leaching of soluble compounds (e.g., chlorides, sulfates, carbonates) driven by rainfall has often been documented in the first stages of weathering (e.g., Zikeli et al, 2002;Séré et al, 2010;Abel et al, 2014;Scholtus et al, 2009Scholtus et al, , 2014Huot et al, 2015;Santini and Fey, 2015). Mineral transformations are important indicators of the evolution of technogenic materials under environmental factors.…”

“…The structure in technogenic materials generally shows weak development. But blocky peds due to desiccation cracks and granular structure in topsoil due to root activity have been observed in industrial by-products (e.g., Grünewald et al, 2007;Santini and Fey, 2015).…”