Mariza Ramalho Franklin

Management of uranium mill tailing: Geochemical processes and radiological risk assessment

This paper describes the geochemical processes regulating the mobilisation of heavy metals and radionuclides in the tailing dam of the uranium mining and milling facilities of Pocos de Caldas, Brazil. The operational effluent release pollution of surface and groundwater was evaluated by means of monitoring data. The potential environmental impact after the future closure of the installation was assessed by means of dose estimations assuming the absence of remedial measures. Residual tailing pyrite oxidation was found to be the critical factor in the transfer of metals and radionuclides to seepage water. No contamination of deep groundwater was observed. On the other hand, the surface water of a nearby river revealed greater uranium concentrations in the tailing dam effluent discharge area than in a background river location sampling station. Lead-210 and 210Po were the principal contributors to the total dose while vegetables were the chief pathways of exposure, both for adults and children, to the studied radionuclides after closure. The results of the dose assessment indicate that permanent remedial actions will have to be adopted in the decommissioning phase.

Acid rock drainage and radiological environmental impacts ; A study case of the uranium mining and milling facilities at Pocos de Caldas

Acid rock drainage generated as a result of sulphitic minerals oxidation is a source of pollution in many mining sites all around the world. This is the case at the Uranium Mining Site of Pocos de Caldas, Brazil. The present study was aimed at studying the geochemical mechanisms involved on the mobilization of radionuclides from the waste rocks that occurs along with the acid drainage. The environmental radiological impacts caused by these pollutants were also assessed. It has been shown that precipitation of Ra and Pb as sulfates was the most important mechanism in the reduction of both radionuclides activity concentration in the acid drainage. A result of this study was that uranium isotopes were the most important radionuclides in terms of the exposure of the critical group. It has been suggested that the recovery of uranium from the acid drainage would be a feasible practice, economical aspects taken into account. It has also been estimated that pyrite oxidation will occur for more than a thousand years. The long time scale involved on the oxidation of the pyritic material implies the need for the adoption of permanent remedial actions. To assess applicable remediation strategies it has been suggested that oxygen and temperature profile determinations should be carried out in the dump.

Assessment of acid rock drainage pollutants release in the uranium mining site of Poços de Caldas--Brazil.

We compared three different techniques to assess acid drainage occurrence connected to pyritic waste rock piles at a uranium mining and milling site in Poços de Caldas--Brazil: (1) mass balance calculations, (2) column leaching experiments and (3) geochemical modelling. The study site was chosen because all the drainage coming from the pile is collected in one holding pond and a huge database (monitoring program) was available. The three independent methods predicted similar values for the intrinsic oxidation rate (IOR) (about 10(-9) kg m-3 s-1). We estimate the total time for consumption of all oxidizable material in the dump to be greater than 500 years. Geochemical model results showed a good agreement between predicted sulphate concentrations in relation to those found in the waste pile drainage, although the Al values were overestimated and pH values were underestimated.

Identifying and overcoming the constraints that prevent the full implementation of decommissioning and remediation programs in uranium mining sites

Environmental remediation of radioactive contamination is about achieving appropriate reduction of exposures to ionizing radiation. This goal can be achieved by means of isolation or removal of the contamination source(s) or by breaking the exposure pathways. Ideally, environmental remediation is part of the planning phase of any industrial operation with the potential to cause environmental contamination. This concept is even more important in mining operations due to the significant impacts produced. This approach has not been considered in several operations developed in the past. Therefore many legacy sites face the challenge to implement appropriate remediation plans. One of the first barriers to remediation works is the lack of financial resources as environmental issues used to be taken in the past as marginal costs and were not included in the overall budget of the company. This paper analyses the situation of the former uranium production site of Poços de Caldas in Brazil. It is demonstrated that in addition to the lack of resources, other barriers such as the lack of information on site characteristics, appropriate regulatory framework, funding mechanisms, stakeholder involvement, policy and strategy, technical experience and mechanism for the appropriation of adequate technical expertise will play key roles in preventing the implementation of remediation programs. All these barriers are discussed and some solutions are suggested. It is expected that lessons learned from the Poços de Caldas legacy site may stimulate advancement of more sustainable options in the development of future uranium production centers.

Modeling the water flow in unsaturated waste rock pile: an important step in the overall closure planning of the first uranium mining site in Brazil

Release of acid drainage from mining-waste disposal areas is a problem found in many mine sites all around the world. An understanding of waster flow and the geochemical processes within mining-waste is important to the long-term prediction of contaminant loading to the environment. This is the first of two papers and describes the water flow in one of the waste rock piles of the first uranium-mining site in Brazil by the use of the numerical model HYDRUS-2D. The obtained results indicated that a steady state condition is achieved after 500 days of simulation. The average flow inside the pile was about 0.4 cm/d. The outflow estimated by the model was in good agreement with the measured values. However, it must be emphasized that result only improved when the flux through the macropores was taken into account.

The use of kinetic modeling as a tool in the understanding of the geochemical processes at a uranium mine site

Release of acid drainage from mining-waste disposal areas is a problem found in many mine sites all around the world. An understanding of waster flow and the geochemical processes within mining-waste is important to the long-term prediction of contaminant loading to the environment. This is the second of two papers and describes how useful it is the use of kinetic models in the evaluation of the geochemical processes in one of the waste rock piles of the first uraniummining site in Brazil. The model chosen (STEADYQL v.4) predicts the steadystate composition of the drainage resulting from the interactions between the aqueous and solid phases being this interaction subjected to a combination of kinetic and equilibrium reactions (homogeneous and heterogeneous). The obtained results show that the concentrations of SO4, K e F were underestimated by 2% 13% e 5% respectively if compared to the average concentrations of these elements in the drainage waters. On the other hand Al concentrations were overestimated by in 19% The model was not able to reproduce the concentrations of U and Fe satisfactorily. But, in a general way it can be affirmed that the simulations allow a coherent representation of the monitored conditions within the waste rock pile.

Use of Na-Ferrate (VI) to prevent acid drainage from uranium mill tailings

Ferrate (VI) is a powerful oxidizing agent in aqueous media. Despite numerous beneficial properties in environmental applications, ferrate (VI) has remained commercially unavailable. Producing the dry, stabilized ferrate (VI) product required numerous process steps which led to excessive synthesis costs (over

PROPOSAL FOR AN INNOVATIVE APPROACH TO PREVENT ACID DRAINAGE FROM URANIUM MILL TAILINGS BASED ON THE APPLICATION OF NA-FERRATE (IRON VI) 1

20/lb) thereby preventing bulk industrial use. Recently a novel synthesis method for the production of a liquid ferrate (VI) based on hypochlorite oxidation of ferric ion in strongly alkaline solutions has been discovered (USPTO 6,790,428; September 14, 2004). This breakthrough means that for the first time ferrate (VI) can be an economical alternative to treating acid mining drainage generating materials. The objective of the present study was to investigate a methodology of preventing the generation of acid drainage by applying ferrate (VI) to acid generating materials prior to the disposal in impoundments or piles. Oxidizing the pyritic material in mining waste could diminish the potential for acid generation and its related environmental risks and long-term costs at disposal sites. Preliminary results presented in this paper show that the oxidation of pyrite by ferrate has half-life of about six hours. The stability of Fe(VI) in water solutions will not influence the reaction rate in a significant manner. New low-cost production methods for making liquid ferrate on-site makes this technology a very attractive option to mitigate one of the most pressing environmental problems in the mining industry.

Application of a Dry Cover to Remediate the Acid Rock Drainage Generation in the Uranium Mining and Milling Site of Poços de Caldas - Brazil

The operation of uranium mining and milling plants gives rise to huge amounts of wastes from both mining and milling operations. Terrestrial deposition is the predominant method of disposal for waste-rock and tailings. When pyrite is present in these materials, the generation of acid drainage can take place and result in the contamination of underground and surface waters through the leaching of heavy metals and radionuclides. Ferrate (VI) is a powerful oxidizing agent in aqueous media. Under acidic conditions, the redox potential of the Ferrate (VI) ion is the highest of any other oxidant used in wastewater treatment processes. The standard half-cell reduction potential of ferrate (VI) has been determined as +2.20 V to + 0.72 V in acidic and basic solutions, respectively. Despite numerous beneficial properties in environmental applications, ferrate (VI) has remained commercially unavailable. Producing the dry, stabilized ferrate (VI) product required numerous process steps which led to excessive synthesis costs (over

Radioecological characterization of a uranium mining site located in a semi-arid region in Brazil

20/lb) thereby preventing bulk industrial use. Recently a novel synthesis method for the production of a liquid ferrate (VI) based on hypochlorite oxidation of ferric ion in strongly alkaline solutions has been discovered (USPTO 6,790,428; September 14, 2004). This on-site synthesis process dramatically reduces manufacturing cost for the production of ferrate (VI) by utilizing common commodity feedstocks. This breakthrough means that for the first time ferrate (VI) can be an economical alternative to treating acid mining drainage generating materials. The objective of the present study was to investigate a methodology of preventing the generation of acid drainage by applying ferrate (VI) to acid generating materials prior to the disposal in impoundments or piles. Oxidizing the pyritic material in mining waste could diminish the potential for acid generation and its related environmental risks and long-term costs at disposal sites. Preliminary results presented in this paper show that the oxidation of pyrite by ferrate has half-life of about six hours. The stability of Fe(VI) in water solutions will not influence the reaction rate in a significant manner. New low-cost production methods for making liquid ferrate on-site makes this technology a very attractive option to mitigate one of the most pressing environmental problems in the mining industry.