Cleaner metallurgical industry in Serbia: a road to the sustainable development

Since the sustainable development has been a global and fundamental objecttive, a metallurgical industrial sector faces some of the most difficult sustainability challenges of any industrial sector. On the other hand, the metallurgical production in Serbia is a very important part of the economy. Due to present facilities and technologies, metallurgical companies face a great challenge to fulfill the requirements introduced by legislature referring to the cleaner production and sustainable development. The state of art in the production, facilities, pollution with some answers to imposed challenges is presented

Distribution of uranium, thorium and potassium in the Bayer process

Uranium, thorium, potassium and their decay product mass flows were analysed in the Bayer process. Gamma-ray spectroscopy was used to measure the radionuclide content in samples provided by Aluminium of Greece and to model their mass flows. We observed that at any analysed stage, the radionuclide content does not exceed the allowed safety limits set in the European Basic Safety Standard. Another important observation is that a minor portion of uranium from bauxites (3%) ends up in alumina, while the rest is accumulated in the bauxite residue (BR). All of the 226Ra (long-lived decay product of uranium), as well as all decay products of thorium accumulated in the BR. We observed accumulation of 40K in the process liquors, while this radionuclide was not found in the alumina

Radiological assessment of the Bayer process

Naturally occurring radionuclides were studied through the Bayer process by calculating their mass flows. Aluminium of Greece (AoG) provided sample materials and plant data from several process stages. Measurements of radionuclide concentrations were carried out by gamma-ray spectroscopy. The performed measurements show that in the specific case of the AoG plant, the majority of the natural radionuclides were introduced with karst bauxites, which showed higher activity concentrations for nuclides compared to lateritic bauxites. Most of these nuclides accumulated in the bauxite residue, while only a minor portion of uranium isotope 238U was found in alumina, corresponding to 3% of its input value. Uranium was observed to partially dissolve in the process liquors similarly to 40K, whereas the latter was not associated with aluminium hydroxide. All the materials studied in the current research work had radionuclide concentrations well below the exemption limits set by EURATOM Basic Safety Standard, indicating that these naturally occurring radionuclides do not pose a radiological hazard for workers of the AoG plant or the public.https://doi.org/10.1016/j.mineng.2019.04.01

Carbothermic Reduction of Bauxite Residue for Iron Recovery and Subsequent Aluminium Recovery from Slag Leaching.

Industrially and historically, alternative processes were developed to recover alumina from low-grade ores of non-bauxitic origin as well as for economic reasons. The Pedersen process from Norway was adapted towards high ferruginous and high silica containing bauxitic ores. This paper considers the adaptation of the Pedersen pyro-hydrometallurgical route of reductive smelting with lime and coke to recover iron and aluminium from bauxite residue (BR), which is the by-product of the Bayer process where aluminium is typically lost in complex desilication product matrices. Greek BR was firstly smelted in an Electric Arc Furnace (EAF) to recover pig iron (>95 %). The fluxing strategy entailed feeding lime to favour lower operating temperatures (1500–1550 °C) and slag viscosities, and to produce a slag containing calcium aluminate phases (12CaO·7Al2O3, 3CaO·Al2O3 and CaO.Al2O3). The calcium aluminates were identified as thermodynamically favourable in descending order to form NaAlO₂ when leached in Na₂CO₃ solution (ΔGrxn298K= -782, -188 and -68 kJ/mol, respectively). Leaching temperature, Na2CO3 concentrations, residence time and different particle sizes were varied to investigate the leachability of slags for aluminium recovery; up to 43 % aluminium was recovered with 95 % of silicon content remaining in leached residue. SEM studies also aided understanding of interstitial leaching mechanism

Review of Technologies in the Recovery of Iron, Aluminium, Titanium and Rare Earth Elements from Bauxite Residue (Red Mud)

Bauxite residue (BR), also known as red mud (RM), is the main waste product of the Bayer process in producing alumina from bauxite ores and is currently being managed via stockpiling, storage within settling pond and landfilling. However, these approaches are disadvantageous in terms of potential risk for the environment and the processing of RM as raw material brings about its own challenges. In recent years, research has been focused on the reuse of RM and the recovery of metals to transform the waste into a more viable secondary source of raw materials. This paper will further explore and thoroughly review technologies and processing techniques that have been previously available as well as ones that are currently being developed. The scope of this paper will be focused on iron, aluminium, titanium and rare earths

Extraction of Aluminium from Kaolin: a Comparative Study of Hydrometallurgical Processes

Abstract -The increase of aluminium demand globally, raises the interest of developing alternative technologies to produce alumina from non-bauxitic sources, especially clays. This paper studies the extraction of aluminium from kaolin through leaching process, using aqueous solutions of acids and bases, as leaching agents. For this study, crude kaolin excavated in Milos Island, Greece, was used. Before leaching, crude kaolin was calcined; calcination achieves the dehydroxylation of kaolinite, which is the main mineralogical phase of kaolin and its transformation to metakaolin, an amorphous Al-Si phase from which aluminium is easily leached. Calcination of the crude kaolin used in this work was taken place at 850 o C for 2 h, given that these conditions revealed as optimum in the relevant experimental investigation. Leaching of aluminium from the calcined kaolin was performed with aqueous solutions of mineral acids (HCl, HNO 3 and H 2 SO 4 ), organic acids (C 2 H 2 O 4 , C 2 H 4 O 2 and C 6 H 8 O 7 ) and bases (NaOH, KOH and NH 4 OH). All leaching experiments were performed under constant conditions, regardless the leaching agent used. According to the experimental results, acids were proved more effective in aluminium extraction, than bases. However, aluminum extraction was accompanied by simultaneous extraction of Si which comprises an important impurity for the production of alumina from the pregnant liquor. Based on this consideration, oxalic acid was revealed as the most effective leaching agent, yielding more than 75% extraction of Al and less than 5% Si extraction

Bauxite residue sinter phase transformations

In the Bayer Process, between 2-35% aluminium (as wt. Al2O3%) is lost with bauxite residue (BR). This is primarily due to the inefficient dissolution of aluminium-bearing minerals during caustic leaching or from the formation of desilication product (DSP) that also constrains the recycling of caustic soda from the circuit. If these lost alumina and caustic can be recovered from BR, numerous potential processing options become available which could lead to zero-waste BR valorisation. Whilst the pyrometallurgical routes (lime soda and lime-soda sintering) have been extensively discussed in the literature for recovering alumina and sodium from BR, understanding of the mineralogical phase formation during sintering and the relationship to the thermodynamic driving forces are poorly reported .This paper presents the investigation of sintering tests conducted on two separate residues with different characteristics; Greek BR and Australian Br, and mineral phases present both before and after sintering for two distinctly different BRs. These mineral phases were characterised and quantified using XRD and XDB software. The Factsage thermodynamic software package was used to analyse reaction equilibria with potential sintering chemical reaction pathways being described

Investigations of geopolymeric mixtures based on phosphate washing waste

The extraction of the phosphate ore produces a high amount of waste causing serious environmental problems. This waste, termed as phosphate washing waste, was filtered and dried at 105 °C for 24 h to remove the water. The dried waste was milled and then sieved in a 100 ?m sieve. The resulting phosphates washing waste (PWW) particles size are below 70 ?m. The phosphate washing waste was calcined at 700 °C and 900 °C. Both calcined and uncalcined waste were investigated with X-ray fluorescence (XRF), X-ray powder diffraction (DRX), Fourier transform infrared (FTIR), simultaneous differential thermal and thermogravimetric analyses (DTA-TG) and particle size analysis. This waste was activated with sodium hydroxide (NaOH) and sodium silicate in order to produce geopolymeric materials. The influence of replacing PWW by 15% of metakaolin was also study. The results show that the highest compressive strength is obtained with metakaolin. The results also showed that compressive strength decreased with the increase of NaOH concentration.Gafsa Phosphate Company “CPG Tunisia” for providing us the phosphate washing waste sample and the Portuguese Foundation for Science and Technology (FCT) for the finance of the project UID/ECI/04047/2013info:eu-repo/semantics/publishedVersio