Nuclear Minerals Plants in Brazil—Case Studies

TSINGHUA SCIENCE AND TECHNOLOGY I S S N 1 0 0 7 - 0 2 1 4 1 2 / 1 8 p p 2 1 7 -221 Volume 11, Number 2, April 2006

Nuclear Minerals Plants in Brazil—Case Studies Jeaneth dos S. Benedetto ** Centro de Desenvolvimento da Tecnologia Nuclear—CDTN/CNEN, Belo Horizonte, Brazil Abstract: This paper presents the process flow sheet of the main nuclear industrial units in Brazil and discusses some solvent extraction technical support required for these plants. The Center for the Development of Nuclear Technology—CDTN has been investigating alternative ways to supply the nuclear industry in order to improve the industrial processes. Some case study examples are presented, Emulsion from Uranium Solvent Extraction Plant and Itataia Uranium Developments. In Caitité industrial plant the water recirculation has caused continuous changes in the composition of pregnant liquor mainly in the sulfate and chloride concentrations. After some water recirculation cycles, a decrease in the uranium extraction efficiency was noted which was followed by the formation of stable emulsion at the uranium extraction stage. Itataia Uranium Developments were performed in a pilot plant for Itataia ore. This ore has the uranium mineral associated to the phosphate. The process consists of four main steps: 1) phosphate concentration, 2) chemical digestion of the concentrate to produce phosphoric acid with dissolved uranium, 3) uranium recovery, and 4) phosphoric acid purification by solvent extraction. Key words: uranium recovery process; solvent extraction; nuclear plants

Introduction The nuclear industry of Brazil—INB (Indústrias Nucleares do Brasil), a mixed economy Brazilian company connected with the Comissão Nacional de Energia Nuclear (CNEN) under the authority of the Ministry of Science and Technology is actively participating in the development of nuclear projects to generate nuclear-electric power. The projects encompass uranium exploration, mining and primary processing as well as the production and assembly of fuel elements that power in the nuclear power plant reactors. The company also provides technologies for heavy minerals including prospecting and research, mining, industrialization and marketing of monazite sand[1]. Three INB units are in operation and the industrial Received: 2005-10-09

﹡﹡ E-mail: [email protected]; Tel: 55-31-34993316; Fax: 55-31-34993399

project of Itataia mines implantation is in its final phase. The Mineral Department of the Center for the Development of Nuclear Technology—“Centro de Desenvolvimento da Tecnologia Nuclear”—CDTN/ CNEN has worked with nuclear industries on research projects aiming at finding solutions for operating problems that occur during uranium ore processing. This paper presents the process flow sheet of the main industrial units and discusses solvent extraction technical support projects for the plants.

1

Nuclear Minerals Plants

1.1

INB Caldas

INB Caldas, the first mineral-industrial complex of this nature in the country, was set up in the Municipality of Caldas, State of Minas Gerais, in 1982. Basically, INB Caldas meets the reload demands for the Angra I reac-

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tor and technology development programs. The complex mineralogical formation and unique characteristics of the ore found in Caldas led to the development of an original process by INB technicians developed to extract uranium and associated elements. The open sky mining enabled better use of the uranium ore. The company started with development of nuclear fuel cycle technology to generate electric power with chemical processing of uranium to transform it into yellow cake. Once the economically feasible uranium is exhausted, the work will shift to the extraction and processing of minerals at Caitité. From start-up, control operations have sought to minimize, reintegrate, and stabilize the potential pollution in the area through the development of environmental protection and control programs. The mine is under decommissioning and its facilities, equipment, and especially the knowledge of its technical staff, are being used to develop new projects. The plant is now using sophisticated Monazite chemical treatment technology. The ore is obtained from the physical treatment in Buena-Rio de Janeiro[1]. 1.2

INB Caetité—Mining and processing Fig. 1

One of the major uranium producing sites in Brazil is located in the Southeast Bahia State. The site has reserves estimated to be 100 000 t of pure uranium oxide without any other minerals of interest so INB’s is very interested in exploring the site. This quantity is enough to supply the Nuclear Power Station “Almirante Álvaro Alberto” (Angra I, II, and III Plants) for 100 years. The research and prospecting activities may increase substantially. INB currently has a production capacity of 350 t/a of uranium concentrate, with the goal in the next few years to reach 800 t/a. The uranium ore process uses leaching in piles (static). After being crushed, the ore is placed in piles and irrigated with a sulfuric acid solution to remove the uranium. Figure 1 shows a schematic diagram of the process. This technique leads to lower costs, due to the reduced amount of equipment and operational units involved. The uranium concentration is made using the extraction by organic solvents followed by precipitation separation, drying, and packing in drums. This uranium ore processing unit is a modular

INB Caetité—process flow sheet.

mineral-industrial enterprise designed with the purpose of developing the uranium use in approximately 33 occurrences forming the currently known reserve. The environmental impact is reduced by the absence of fine solid waste so dams are not needed to contain the waste. The use of fewer chemicals further reduces the impact. However, the most important aspect is the possibility of recycling for the total return of liquid effluents to the process, ensuring no release of effluents to the environment[1]. 1.3

INB Buena—Monazite sand treatment

The Buena Unit, located in the Rio de Janeiro state, is responsible for prospecting, research, mining, industrialization, and marketing of heavy minerals popularly known as “monazite sands”. The physical processes for the ores treatment include mining and hydrogravimetric concentration followed by dry separation (physical separation through electrostatic, magnetic, and gravimetric processes). The ore is processed by hydrogravimetric concentration to obtain the heavy

Jeaneth dos S. Benedetto：Nuclear Minerals Plants in Brazil—Case Studies

concentrate. The sterile material goes back to be recomposed with the mined soil. The final phase of the process at the Dry Separation Unit produces the ilmenite, zirconite, and rutile that are marketed as well as monazite that is sent for processing to obtain rare-earth elements at INB-Caldas[1]. 1.4

INB Itataia

The Itataia deposit includes phosphorous uraniferous ore located in the central part of Ceará State, in northeast Brazil. The Itataia deposit has geological reserves of 142 t of phosphate associated with uranium. The mining reserve has 79.5 Mt of ore with 11% P2O5 and about 1000 ppm U3O8. It can generate 8.9 Mt of P2O5 and 79.3 t of U3O8. Also, the mine has about 3×108 m3 of totally uranium free marble. The region is 212 km from Fortaleza, where the major economic activity is farming and cattle-raising. Although it is the largest uranium reserve in the country, its economic feasibility depends on exploration of the associated phosphate. This means that the uranium extraction is conditioned to the production of phosphoric acid, which is used in fertilizer production[1]. The proposed industrial plant is in the final engineering design phase and is set for completion in the next two years. The process was refined in the CDTN pilot plant where the engineering parameters for the industrial implantation were defined.

2

Case Studies

The Center for the Development of Nuclear Technology has been investigating alternative ways to supply the nuclear industry in order to improve industrial processes. For example, case studies that have been developed in pilot plants before industrial implementation will be presented here. 2.1 Emulsion in uranium solvent extraction plant Because of water shortages in the Caetité region, all water used for uranium processing is recycled back to the process. However, the water recirculation causes continuous changes in the composition of the rich liquor mainly in the sulfate and chloride concentrations. The uranium extraction efficiency decreased for several water recirculation cycles followed by formation of a stable emulsion at the uranium

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extraction stage, as shown in Fig. 2. This study provides a detailed characterization of the process flows and some types of treatment to reduce the raffinate sulfate content and alkaline treatment of the stripped solvent. This study helped to not only identify the causes of emulsion formation at the solvent extraction stage but also to find ways to prevent emulsion formation.

Fig. 2 Stable emulsion from the uranium extraction stage.

2.2

Itataia uranium developments

Figure 3 shows the flow sheet established in a pilot plant for Itataia ore which has the uranium mineral associated with phosphate. The process consists of four main steps: 1) phosphate concentration, 2) chemical digestion of the concentrate to produce phosphoric acid with dissolved uranium, 3) uranium recovery, and 4) phosphoric acid purification by solvent extraction. In the first step, the phosphate rock is pulverized to below 48 meshes with the fines below 5 µm removed by cyclones. The phosphate is concentrated by twostep column flotation in order to separate the silicates and carbonates from the original ore. The phosphate concentrate with most of the uranium minerals is fed to the chemical reactor with the diluted phosphoric acid and the concentrated sulfuric acid. This step produces the phosphoric acid containing 30% uranium. This liquor is fed to the uranium solvent extraction step after pretreatment where the fines containing gypsum and organic matter are removed[2]. The high concentration of uranium, compared with other phosphate ores, makes possible a simpler solvent extraction circuit where the uranium recovery uses only one cycle of extraction/stripping. The mixture of D2EHPA/TOPO is used to extract the uranium and to strip the mixture of ammonium carbonate and

Tsinghua Science and Technology, April 2006, 11(2): 217-221

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Fig. 3

Itataia process flow sheet.

ammonium bicarbonate used in the first stage. An iron removing step before stripping is necessary to avoid contamination of the final product. This solvent extraction step is carried out in a mixer settler cascade with eight stages of extraction, two stages of impurity removal, two stages of washing, four stages of uranium stripping, and two stages of solvent regeneration with sulfuric acid[3]. Further phosphoric acid purification is carried out in pulsed perforated columns using tributylphosphate (TBP) as the acid extractant and water for stripping. Experiments in a pilot plant investigated the main operational and process conditions. The test showed that the process can significantly reduce the level of impurities in the phosphoric acid produced in the process. The P2O5 recovery was higher than 62% using only one column[4]. The uranium recovery also gives high yields, higher than 97%. Higher losses, around 20%, are associated with the physical treatment of the ore . This process has been studied for the liquor generated by the Itataia ore digestion and gives good uranium recovery yields. The main problem is the impurity removal step using high-purity phosphoric acid in order to remove the iron in the solution. This step was included in the process to avoid iron precipitation during the stripping step which forms a crud that is not desirable in the solvent extraction process. This step also represents an increase in the operation cost. Another recent investigation sought to identify another stripping reagent that avoids the iron precipitation while maintaining the high levels of uranium recovery to eliminate the impurity removal step. Some potential stripping reagents have been identified and tested in pilot experiments. The main

parameters of the process have already been studied with the uranium recovery >99% with one of the reagents. This work is being complemented by uranium selective precipitation in order to remove the small quantity of iron that remains in the uranium stripped liquor. 2.3

Rare earth processing from monazite

Studies of rare earth separation and purification from monazite were carried out to support the INB industrial implementation. First, a process was developed to separate rare earth elements in groups. Then, individual rare earth oxides separation and purification processes were studied in order to obtain more valuable products. High-purity gadolinium was obtained by solvent extraction using D2EHPA. A twostage Jones column was used for the purification of Eu from a commercial rare earth chloride solution. The process consists of the reduction of Eu(III) to Eu(II) by a zinc amalgam, followed by the precipitation of Eu(II) sulfate (EuSO4) in an inert atmosphere (CO2). Maximum recovery was achieved with an aging time of 2 h or more. The experiments yielded a final product assay of 99.99% Eu2O3 from a feed containing 5.0 g/L Eu2O3 and 138.2 g/L Gd2O3 in two stages of reductionprecipitation. The overall recovery rate was 94%. Samarium was also separated by solvent extraction with a high yield of high purity product[5]. The factors influencing europium photo reduction/ EuSO4 precipitation were investigated using a lowpressure mercury lamp (germicidal lamp) with photon emissions at 253.7 nm as a light source. The goal of this study was to provide better results than the conventional reduction-extraction process[6]. A solvent extraction process was also developed for the recovery of high-grade lanthanum oxide from a

Jeaneth dos S. Benedetto：Nuclear Minerals Plants in Brazil—Case Studies

light rare earth (La, Pr, Nd) chloride solution. Process parameters and experimental conditions were explored in bench-scale experiments. The effect of variables such as nature and extractant concentration (D2EHPA and HEH(EHP)), contact time, acidity, and rare earth concentration in the extraction stage, as well as the effect of the hydrochloric acid concentration in the stripping stage were investigated. Continuous countercurrent experiments were carried out in a mini-battery of mixer-settlers. The final set-up included 22 stages: 8 for extraction, 8 for scrubbing, and 6 for stripping. A high-grade oxide (>99.9% La2O3) was obtained with a yield >99.9%[7].

[3]

Indústrias Nucleares do Brasil INB. http://www.inb.com.br.

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Coelho S V. Projeto Itataia—Desenvolvimento de Proc-

Benedetto J S. Processos Alternativos de Recuperação de Urânio de Ácido Fosfórico. In: Proc. XII Encontro Nacional de Tratamento de Minérios e Metalurgia Extrativa, 1987.

[4]

Benedetto J S, Morais C A. Phosphoric acid extraction from an uranium phosphorous liquor. In: Proc. 5th International Symposium Honoring Professor Ian M. Ritchie, Vancouver. Hydrometallurgy, 2003, 1: 861-867.

[5]

Morais C A, Ciminelli V S T. Recovery of europium by chemical reduction of a commercial solution of europium and gadolinium chlorides. Hydrometallurgy, 2001, 60: 247-253.

[6]

Morais C A, Ciminelli V S T. Europium recovery by photochemical reduction from Eu and Eu-Gd chloride solu-

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