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Ozone to be used to treat mining waste

A São Paulo company plans to clean the water and soil contaminated by heavy metals at a uranium mine

Soil from the uranium mine in Caldas (Minas Gerais) where ozone will be injected

DELCY AZEVEDO / INBSoil from the uranium mine in Caldas (Minas Gerais) where ozone will be injectedDELCY AZEVEDO / INB

Oxygen taken from ambient circulating air is the raw material Brasil Ozônio will use. The company is located at the Center for Innovation, Entrepreneurship and Technology (Cietec) in Cidade Universitária, São Paulo. After the oxygen receives an electric discharge to break-up its molecules, it is transformed into ozone, a gas with a high bactericidal and oxidant power that is used for water treatment, in food hygiene, or to neutralize toxic gases. The useful life of ambient ozone is around seven minutes, after which it returns to its original state –– oxygen –– without leaving any residue.

Brasil Ozônio was founded in 2005 by Samy Menasce, an electronics engineer with extensive experience at multinational companies; its purpose was to manufacture and sell ozone generators for water treatment of swimming pools and wells. The first model was sold in 2006, and it went through five subsequent versions before the current equipment was developed, which is fully automated and uses components from more than 90 suppliers.

Now the company is preparing to take into the field an ambitious project in which ozone gas will be used to treat water, wastewater and soil contaminated by heavy metals at a uranium mine in Caldas, Minas Gerais, deactivated since 1995. The first test to evaluate the system was conducted in the São Paulo company’s laboratory. Twenty minutes after an application of ozone, heavy metals present in the sample were transformed into suspended solids. “The preliminary results were very encouraging,” says Maurício de Almeida Ribeiro, a chemical engineer and manager of the ore treatment unit of the state-owned Indústrias Nucleares do Brasil (INB) in Caldas, where uranium was mined in the 1980s and 1990s. Since that first test, several more have been carried out in the INB laboratory during the past 6 months. INB is responsible for uranium mining throughout Brazil and subordinate to the Ministry of Science, Technology and Innovation. The National Bank for Economic and Social Development (BNDES) has granted non-reimbursable aid in the amount of R$9.6 million for the project, and the company will provide R$1.2 million as a counterpart.

Brasil Ozônio has a record of experience, having already installed 2,000 pieces of equipment to deodorize the environments of large hotel chains, eliminate gases generated at fertilizer and cigarette factories, treat water in gymnasiums, and make food preparation hygienic, in addition to other applications. The ozone water treatment for the São Paulo Aquarium, located in the Ipiranga neighborhood of the city of São Paulo, with creatures as diverse as manatees, sharks, stingrays and penguins, was developed by the company and tailored to the needs of each species.

Polluted waters will be treated to separate out heavy metals

DELCY AZEVEDO / INBPolluted waters will be treated to separate out heavy metalsDELCY AZEVEDO / INB

“At first we captured the air and dumped it directly into the ozone generation system, a widespread practice but one that was off on the wrong track, because along with oxygen come other gases, such as nitrogen, which in the process turns into acid,” says Menasce. In partnership with the São Paulo Institute for Technological Research (IPT), the company developed an ozone production system that captures, filters, and dries the air and then separates out the oxygen, which represents about 21% of the total present in the environment. All equipment has three main components: an oxygen concentrator, an ozone generator, and an automated command center.

Expanded partnership
The project to treat the deactivated uranium mine has several partners: the University of South Santa Catarina (Unesc) in the city of Criciúma, and the Region of Iperó and Environs High Technology Park Foundation (Patria) in São Paulo’s interior. The foundation operates under the umbrella of the Navy, which shares responsibility for the nuclear sector in Brazil with the National Nuclear Energy Commission (CNEN). Researchers from the University of São Paulo (USP) and the Nuclear and Energy Research Institute (IPEN) are also working on the project.

The problem of water pollution from mining is due to the presence of minerals such as pyrite, which contain sulfur. “When it rains, the minerals found in mining waste are oxidized in the presence of water, producing a solution called acid mine drainage,” says Professor Elídio Angioletto, of the department of chemical, environmental and materials engineering at Unesc and the project coordinator at the university. Acid mine drainage, consisting of dissolved metals and sulfuric acid, is one of the most serious environmental impacts associated with mining activity. If it reaches nearby rivers, such drainage can pollute them and make the rivers unsuitable for use.

Environmental liabilities
Uranium mining generates huge quantities of waste, because the mineral itself is only present in small amounts ranging from 0.5% to 1% of the total. “To remove the uranium from the water, we use ion exchange columns,” says Ribeiro, of INB. The environmental liability at the INB’s installations in Caldas is around 45 million metric tons of waste — composed of mounds of earth, stone and clay containing heavy metals such as manganese. The conventional treatment for this type of waste consists of adding lime to the water, which raises its pH and precipitates the metals. Each day INB uses a 25-metric-ton truckload of lime. The total annual cost of this product is R$2 million. “We used to have no other technology to remove the manganese from the water,” says Ribeiro. “Each liter of water from the mine contains about 180 milligrams of manganese,” says Menasce. According to Ribeiro, the application of ozone demonstrated that not only the manganese but all the other metals precipitate in an insoluble form. Once the metals are separated from the water, they can be put to other uses. “The use of ozone will generate a savings of 60% over the cost of lime,” says Ribeiro.

078-081_ResiduosNucleares_205“The conventional method treats 300,000 liters of effluent per hour,” he says. In the tests done so far with ozone around 2,000 liters of effluent have been treated. It seems like a small amount, but if the system is as efficient in the field as in the laboratory, it will represent an innovative solution not only for the waste from uranium extraction but residues from other minerals. It is expected that within the first six months of this year, the pilot plant will be operating in Caldas. Brasil Ozônio has developed the prototype for the ozone generation systems that will go to the site. The company will also remotely monitor the equipment and every two weeks a team will be present onsite to make the necessary adjustments. INB will be in charge of the effluent treatment. “We hope that by the end of the project, two years from now, from 5% to 10% of all effluents will have been fully treated,” says Menasce. After project completion, with all parameters scaled to the application of ozone, INB will be responsible for continuing the treatment.

Unesc was chosen for the partnership, because Criciúma and the surrounding municipalities are facing severe environmental problems caused by centuries of coal mining activity in the region. “The region is quite polluted with coal waste containing sulfur compounds. These compounds, when they come in contact with air and water, end up making the medium acidic, and in the process releasing heavy metals,” says Angioletto. The contaminated area is about 5,000 hectares, spread out over almost all of the 12 municipalities that make up the Santa Catarina coal mining region. “In Criciúma and the coalfield region, major sections of rivers are dead. When mining waste comes into contact with water, the pH is around 3, too acidic for the survival of fish and most aquatic plants,” he says. The use of water for agriculture or supply to the public is also unfeasible. But it is not just the waste from coal mining and uranium extraction that is problematic. “Any mineral associated with sulfur, such as coal from Santa Catarina, will generate acid drainage when removed from the subsoil and exposed to the air and rain.”

São Paulo Aquarium, in Ipiranga, where water is treated with ozone

EDUARDO CESARSão Paulo Aquarium, in Ipiranga, where water is treated with ozoneEDUARDO CESAR

Angioletto coordinated several tests using the ozone system to treat the effluents. “We tested drainage from the mouths of three different mines, each with different physicochemical conditions and the results were excellent.” The next step will be to construct specific equipment to treat the Santa Catarina waste.

Although ozone has been applied for decades to water – cleaning the water consumed in Paris, for example, is largely done with this gas – treating uranium waste with this system is something new, says Angioletto. “The great innovation, however, will be the application of ozone to contaminated soil, which is one aspect of the project.” Maria Eugenia Gimenez Boscov, a professor of Civil and Environmental Engineering at the USP Polytechnical School, is in charge. The soil treatment project for the uranium mine will open the doors to treatment  of other types of contaminants in Brazilian soils,” says Professor Boscov, who began working with soil contamination while studying for her doctorate in 1994. “For now the project is still in the research phase, since there are few references, even in scientific literature.”

The studies she will coordinate will begin with controlled experiments in the laboratory. One idea is to inject ozone directly into the mountains of waste in order to eliminate the bacterium Thiobacillus ferrooxidans, which is responsible for the production of ferrous sulfate in large quantities when it comes in contact with metals such as pyrite, which leads to the production of acid drainage. “As ozone is germicidal and an oxidant, it will kill that bacterium,” says Menasce.

Currently, the company is finalizing tests on a sterilizer that is ozone-based and fully automated for use in hospitals, surgical centers and drug manufacturing. Developed with the support of FAPESP under the Innovative Research in Small Businesses (Pipe) grant mechanism, the equipment consumes a minimal amount of electricity and works simply at the push of a button. “The typical sterilization processes, based on formaldehyde, ethylene oxide and hydrogen peroxide plasma require trained personnel, and there is a risk of failures occurring during the procedure,” says Menasce.

Project
Ozone Autoclave – constructive and process optimization of sterilizing equipment based on ozone with microbiological validation by means of challenge tests with bacterial spores (nº 10/50281-8); Grant Mechanism Innovative Research in Small Businesses Program (Pipe); Coordinator Frederico de Almeida Lage Filho – Brasil Ozônio; Investment R$186,888.67 (FAPESP).

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