EDITORIAL
J. Cent. South Univ. (2019) 26: 265-267
DOI: https://doi.org/10.1007/s11771-019-3999-5
Soil formation in bauxite residue: The most promising way to large-scale and ecological disposal
XUE Sheng-guo(薛生国)
School of Metallurgy and Environment, Central South University, Changsha 410083, China
Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2019
Aluminum is an important basic raw material for national economic development. The alumina industry has been expanding rapidly due to the increasing demand for aluminum. Bauxite residue is a highly alkaline solid by-product generated when alumina is extracted from bauxite ore in alumina refineries [1,2]. The global bauxite residues inventory reached approximately 4.6 billion tons in 2018, with a production rate of approximately 200 million tons per annum, which is the largest emission of smelting waste in the non-ferrous metal industry [3,4]. Disposal and storage of the vast amounts of bauxite residue remains an environmental and logistic problem to the industry. It has been reported that in some areas of China, Hungary and India there were serious soil and water pollution due to dam-failures [5]. Ideally, bauxite residue would be utilized as an industrial by-product for other applications, leading to a zero waste situation. However, little evidence exists of any significant utilization of bauxite residue. Establishment of a vegetation cover is a simple way forward for the management of bauxite residue disposal areas [6]. Spontaneous vegetation colonization on disposal areas in Central China has revealed that bauxite residue can be converted to a soil-like medium. Soil formation is the most promising way to deal with bauxite residue, which can get huge economic, environmental and social benefits with low-cost [7].
This Special Issue of Journal of Central South University is a collection of Reviews and Research Articles on the subject of disposal technology for bauxite residue with particular emphasis on soil formation. Recent research involving the intersection of soil science, metallurgy, materials science, chemistry and physics is highlighted to showcase the latest advances in bauxite residue disposal. This Special Issue features 2 Reviews and 20 Research articles, with a focus on bauxite residue in the fields of 1) reduction of bauxite residue during the alumina production process, 2) soil formation and ecological remediation, 3) recycling of bauxite residue and 4) environmental protection. The authors are mainly the faculty members of school and alumni around the world. This Special Issue, based on the example of bauxite residue, demonstrates the need for further research and its application in order to develop practical and sustainable disposal strategies for mineral processing tailings.
In the field of reduction of bauxite residue during alumina production, HUANG et al has developed an intensified gibbsite precipitation process for commercial alumina manufacture by adding mixed industrial and self-prepared active seeds. LI et al provided a valuable perspective on removal/extraction of lithium from sodium aluminate solutions in alumina refineries by elevating temperature, increasing caustic soda concentration, reducing alumina concentration or raising the molar ratio to increase the lithium ion concentration in solution.
In this Special Issue, the field of soil formation and ecological remediation in bauxite residue is divided into four sub-topics. These are (i) alkalinity regulation, (ii) aggregation and structural formation, (iii) screening tolerant microorganisms and plants and (iv) rehabilitation/revegetation technologies. From the aspect of alkalinity regulation, KONG et al suggested that citric acid and gypsum amendments may be used to initially amend bauxite residues to neutralize caustic conditions prior to soil formation. In an attempt to understand alkalinity stabilization, LI et al investigated stabilization of alkalinity and the effects of gypsum addition on variation in composition of alkaline anions, the alkaline phase transformation pathway, and micro- morphological transition characteristics. XUE et al investigated the effects of addition of typical industrial waste materials on transformations of alkalinity in bauxite residues thus providing a scientific reference point for their potential use as amendments to enhance soil formation and vegetation establishment on bauxite residue disposal areas.
From the aspect of aggregation, LI et al suggested that phosphogypsum addition increased Ca, decreased Na and Al on the surfaces of residue particles thus promoting formation of macroaggregate structure and ultimately promoting soil formation in bauxite residue. TIAN et al gave a brief account of the effects of additions of phosphogypsum and vermicompost in decreasing pH, EC, ESP, exchangeable Na+ concentration and the percentage of alkaline minerals and increasing exchangeable Ca2+ and aggregate stability in bauxite residue.
In relation to screening tolerant microorganisms and plants for bauxite residue, LIAO et al indicated that waste biomaterial associated with Penicillium oxalicum could achieve an excellent effect on remediation. Organic matter content and enzyme activities were strikingly increased at 0-25 cm depth of residue. The alkalinity of the residue was reduced significantly, and micro-aggregates became more uniform. Moreover, alkalinity was reduced due to the effect of acidity produced by P. oxalicum. P. oxalicum also had an effect on the distribution of Na in the mesoporous range. WU et al screened an efficient acid producing bacterium from bauxite residues which exhibited adaption to extremely alkaline conditions. HUANG et al also suggested that four pioneer plant species including K. scoparia, M. bracteate, C. dactylon and D. sanguinalis could be suitable for revegetation at residue disposal areas.
In the context of rehabilitation and revegetation of bauxite residue disposal areas, WANG et al demonstrated that Na+, HCO3- and CO32- were the major salt ions with a high coefficient of variation in bauxite residue. Na+, HCO3- and CO32- were positively correlated to pH and ESP. In relation to standards for soils, bauxite residue would be considered to be an alkaline soil. GUO et al constructed a diagnostic model for bauxite residue to provide data support for the regeneration of vegetation on disposal areas. A minimum data set which deserved comprehensive consideration included available phosphorus, moisture content, C/N, sand content, total nitrogen, microbial biomass carbon, and pH. LV et al demonstrated the possibility for revegetation of bauxite residue using ryegrass mainly through the growth indications and transfer of heavy metal ions in BR and plants. COURTNEY et al revealed that application of gypsum with organic wastes is an effective method for overcoming the physical and chemical restraints and nutrient deficiencies exhibited by residue. He provided evidence from field experiments for soil development and support of soil functions on revegetated bauxite residue. HAYNES et al summarized the major steps and the processes involved in successful revegetation of bauxite residues. These included natural physical, chemical and microbial ripening of the profile, tillage of the surface layer and incorporation of gypsum and organic matter, choice of suitable plant species tolerant to salinity/sodicity and local environmental conditions and the addition of balanced fertilizer applications.
In the field of recycling of bauxite residue, GAO et al demonstrated the use of an effective poly-aluminum ferric chloride coagulant derived from bauxite residue for treating effluents high in printing and dyeing chemicals. ZHANG et al proposed a feasible approach to selectively recover iron and rare earth elements from bauxite residue through acid leaching-coordination-solvent extraction. TAO et al prepared an absorbent composed of bauxite residue and water, which was applied to remove SO2 from flue gas with high-efficiency.
In relation to environmental protection on the bauxite residue drying areas, REN et al provided a detailed understanding of the composition, buffering capacity, surface charge properties, and metal leaching behavior of bauxite residue. DING et al demonstrated that even a single application of polymer can improve the unconfined compressive strength of treated sand and that the combination of non-ionic and cationic polymers can result in an increased effectiveness. With identification of the optimal mix ratio of polymers, a more economical dust control strategy can be achieved.
Although this Special Issue cannot cover all the research on disposal technology for bauxite residue, it reflects the aspiration to address the environmental problem of bauxite residue storage through collaboration of multiple disciplines including edaphology, materialogy, chemistry, physics and mathematics. We hope that its content will inspire workers towards more research breakthroughs in the area and also foster increased interdisciplinary collaboration. We are grateful to Prof. Haynes, and the editorial team of Journal of Center South University for their great efforts to make this Special Issue possible. The full Projects (41842020, 41877511) supported by the National Natural Science Foundation of China have been vital for the research discussed in this publication. Finally, we would like to take this opportunity to thank all the co-authors who have made important contributions to this Special Issue.
XUE Sheng-guo
Prof. XUE Sheng-guo is a professor at Central South University. He serves as the director of Department of Environmental Science and Engineering, School of Metallurgy and Environment, CSU. His research is supported by the Environmental Protection’s Special Scientific Research for Chinese Public Welfare Industry and National Natural Science Foundation of China.
During the last five years, he has achieved a series of innovative outcomes in the field of soil formation and ecological rehabilitation in bauxite residue. He sets up the first domestic research group on soil formation of bauxite residue, and leads the research direction of large-scale and ecological disposal with bauxite residue in China. His group has demonstrated that natural weathering processes could improve physical and chemical properties of bauxite residue and convert it to a soil-like medium. Furthermore, several novel analytical and regulation techniques on alkaline removal, aggregation, and ecological risk control have been developed.
Prof. XUE has published more than 130 papers in Chinese or international journals, 60 of which are indexed by SCI.
XUE Sheng-guo
(PhD, Professor; Tel: +86- 13787148441; Email: gxue@ csu.edu.cn; ORCID: 0000- 0002-4163-9383; School of Metallurgy and Environment, Central South University, Changsha 410083, China)
References
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