Browsing by Department "Alum Tulcea"
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Publication Application of sodium aluminate from alumina Bayer process to the treatment of surface water, wastewater and sludge from tannery industry
(National Research and Development Institute for Industrial Ecology, INCD-ECOIND , 2024-07); ; ; ; ; ; ; This paper presents the application of sodium aluminate, directly or after small adjustments in concentration and purity, in some other valuable intermediary products. Sodium aluminate is an intermediary product in Bayer technology applied by Alum SA Tulcea production of alumina and alumina products. Mainly, sodium aluminate is a carrier of aluminum hydroxide between important manufacturing stages in the Bayer process, bauxite processing, and aluminum hydroxide crystallization. After a short investigation of the uses of sodium aluminate, it was decided to choose and study the possibility of converting this secondary product into ecological material for the treatment of natural or industrial wastewater. Actually, on the market, products similar to sodium aluminate from Alum SA Tulcea provide treated waters with high purity and reasonable quality, excellent coagulation rates, rapid flotation, and sedimentation, and in addition, significant side effects, such as excellent removal of phosphorus and silica from treated water. Treatments do not require lime or hydroxide to control alkalinity, and chemical sludge remains at a minimum volume and mass. The test performed with sodium aluminate from Alum SA Tulcea was comparable with other tests with Al2(SO4)3 and FeCl3. The maximum removal yields of global organic load expressed by chemical oxygen demand (COD) and biochemical oxygen demand (BOD5), chromium (Cr VI), and total suspended solids (TSS) were: 83%COD, 71% BOD5, 99.7% Cr VI and 93% TSS.2 Publication Heavy metals as impurities in the Bayer production cycle of the aluminum hydroxide from Sierra Leone Bauxite. Preliminary study.
(Siberian Federal University , 2021-03); ; ; ; ; ; ; This paper is reporting the data of a preliminary study on heavy metals distribution in the fluid and solid phases involved in dry and classified aluminum hydroxide production through the Bayer process. For heavy metals released in the fluid phases, the main source of contamination is the bauxite through its mineralogical phases soluble or insoluble in alkaline solution. It was shown that the predominant way to transfer contaminating elements in aluminum hydroxide particles is the occlusion of very fine particles coming from mineralogical phases of bauxite residue. Newborn mineralogical phases from bauxite residue, like poor crystallized sodalite and cancrinite, are the most active occlusion contaminants.Publication Lanthanides as impurities in the Bayer production cycle of the aluminum hydroxide from Sierra Leone bauxite
(Romanian Journal of Ecology & Environmental Chemistry , 2022-06); ; ; ; ; ; ; This paper is describing a careful study on content and distribution of rare elements in the fluid and solid phases involved in dry and classified aluminum hydroxide production through Bayer process at Alum SA,Tulcea, Romania. The source of rare elements in Bayer process is the bauxite from Sierra Leone, a particular type of aluminous goethite-lateritic bauxite, not fully studied yet. Rare earth elements are fairly abundant in the nature, but their distribution is very large, encompassing hundreds of types of minerals where rare element appears as minor crystalline and amorphous compounds, solid solutions, or as ions adsorbed on the surface of common natural rocks. This study data show that Sierra Leone bauxite has only a small content in rare elements. Mainly, only the scandium and cerium concentrations (44.84 mg/kg and 11.49 mg/kg in bauxite residue) may reach the expected values required for eventually valorization. On the Bayer cycle, the rare metals enter with bauxite and concentrate in bauxite residues. Solubility of the rare element compounds in the Bayer process fluid phases is close to zero. In the final product, the aluminum hydroxide dried, milled and classified grades, the rare metals appear only as occlusion contaminants.Publication Short review on mechanical activation in non-metallurgical alumina production
(Romanian Journal of Ecology & Environmental Chemistry , 2022-12-28); ; ; ; ; ; The terms mechano-chemistry and mechanical activation of solid materials were introduced in chemical literature by Ostwald at the beginning of the XX century. Both terms cover a whole range of interconnected phenomena taking place during the mechanical action on solids or their separate parts participating in chemical reactions, phase transitions, mixing and creating composite materials, alloying and crystal growth in the solid state, deformation and changing physical and thermal properties, all of them at low temperature. The common effects of the mechanical activation on solid material are fracturing and reduction of particle sizes, generation of new reactive surfaces, diffusion of atoms of the reactant phase through the product phase, and quite significantly, accumulating energy in crystalline or amorphous structure (enough twists in atomic and molecular networks, tensions in atomic bond and active sites to trigger the nucleation of new phases). Mechanical activation is very used to produce all clean alumina mineralogical phases with uniform particle size dimensions from nano to macro size. Also, mechanical activation may extend the specific surface of some minerals, enhancing the yields in the solid-liquid extraction process. With adequate precursors, all phase transitions from amorphous to alfa α-Al2O3 can be carried out on the same route as in thermally activated alumina, but some other routes, impossible by thermal activation, might be followed. The difference between the two activation ways is that mechanical activation is made at room temperature.1