Bauxite Residue Safety Disposal and Possibilities to Further Utilization. Part 1. Acid Soils Remediation

Abstract

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...

Heavy Metals as Impurities in the Bayer Production Cycle of the Aluminum Hydroxide from Sierra Leone Bauxite. Preliminary Study

“…In the case of bauxite residue stored in monitored dumps, the chance of trivalent chromium to oxidize is minimal, and as a result, only small amounts of hexavalent chromium were found in the bauxite residue. Also, the results of our previous research corroborated with other data from the literature [3][4][5][6] show that changing the pH of Bayer liquors does not affect the status of chromium in these liquors.…”