Chemical analysis, classical or instrumental using ICP and the XRF spectrometry, offers complete information on elemental composition and major chemical constituents of bauxite and bauxite residues resulted from the Bayer process. The XRD diffractometric analysis provides information on quantitative mineralogical composition of these materials and it enables the real identification of main chemical combinations, whose reactivity is essential in driving the process of obtaining alumina through the Bayer process. Mineralogical components identified in the bauxite samples were ,
The purity, structural surface, particle dimensions, particle size distribution, and the associated reactivity of chemical and surface properties are the most important and most required properties of alumina hydrate special brands. The purpose of this paper concerns the common metallic impurities accumulation on the surface of alumina hydrate particles, during the sodium aluminates decomposition in liquid phase, during the entire aluminum hydroxide crystallization stage in the Bayer technology.
This paper is presenting the investigations concerning a new approach in acid soil remediation by deep reshaping the land surface layer, in order to change its agrochemical composition and properties. IntroductionAfter 2009 retrofit of the landfill site at Vimetco Alum SA Tulcea refinery and significant improvements brought by switching from bauxite residue sludge lagoon impoundment to deep thickening and disposal in dry state, the dried bauxite residue disposal site met the terms of main EU directives recommendation regarding environmental protection. During the retrofit of landfill site and afterward, many noteworthy works were carried out for the sake of investment consolidation [1]. Thus, the environmental risks have been considerably reduced compared to previous applied technology for dumping the bauxite residue, and the disposal site environmental impact on the surrounding agricultural area is not significant anymore.Since 2011 Vimetco Alum SA Tulcea was using predominantly the bauxite originating from Sierra Leone. From thenceforth, the factory accumulated a good experience in processing this type of bauxite and started some projects carried out in its laboratory or in cooperation with other Romanian research -8 -Gheorghe Dobra, Laurentiu Filipescu… Bauxite Residue Safety Disposal and Possibilities to Further Utilization… institutes, trying to find new applications for the well characterized bauxite residue (bauxite residue chemical/mineralogical analysis and physical properties, new measurements of radioactivity, heavy metal content, composition and properties of the minimal processed bauxite residue at the disposal site location, and toxicity/irritation and dermal corrosivity thresholds) [1]. Many studies underlined that the bauxite residue application to any soil is very effective for reducing the phosphorous leaching, improving the pasture growth, ameliorating the soil acidity, increasing the plant metal sorption and decreasing the soluble metals concentration, and above all, the bauxite residue reduces the heavy metals availability [2][3][4][5][6][7]. But, the acid soil rehabilitation with bauxite residue is not just a simple problem of mixing and dispersing. The simple addition of bauxite residue to soils involves increases in pH, in total dissolved solids (TDS), in dissolved organic compounds (DOC), as well as some raises in the concentrations of oxy-anion-forming heavy metals in the soil solutions. The extent of these changes depends highly on the final mixture pH and also, on the soil natural or induced buffering capacity. It should be avoided the pH values above 8.5-9.0 (promoting some larger increases in the concentrations of aluminium, vanadium and arsenic), as well as the low organic carbon and high clay content (promoting the heavy metal mobilization). This is the reason for the bauxite residue association with other materials rich in organic carbon [1][2][3][4][5][6][7].Researches concerning the uses of bauxite residue in agriculture could be classified according to their disclosed specific...
In this paper will be presented some of the environmental programs developed by Vimetco Alum SA Tulcea, Romania during last 10 years, in order to identify and apply the appropriate ecological technologies for storage and valorization of the bauxite residue. These programs can be grouped in 3 main categories: A) Multi-annual programs for the construction, maintenance and alignment of the bauxite residue storage site in respect with the ecological and international safety standards; B) Multiannual programs for the complete analysis and characterization of Sierra Leone bauxite and its Bayer processing by-product, the bauxite residue; C) Multi-annual programs to investigate the possibilities of simple and complex use and valorization of bauxite residue. The last category encompasses the following investigations: a) Effects of bauxite residue bulk drying and carbonation at the surface of disposal site on its chemical properties and corrosivity, and b) Preliminary processing of the bauxite residue for use as raw materials in road infrastructure construction, which are the subject of this paper. The objectives of these researches were: a) deep understanding of all the bauxite residue physico-chemical and mechanical properties and the variation of these properties in the course of production and storage, and b) preparation of the bauxite residue as raw material for use in various applications.
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