Alagoas state on alert as rock salt mine risks collapse
Residents of Maceió are going through days of tension. Last Wednesday (Nov. 29), the city council of the capital of Alagoas state, in Northeastern Brazil, declared a state of emergency over the imminent collapse of one of the rock salt mines operated in the Mustange district by the petrochemical company Braskem. The predicament is yet another chapter in a story started in 2018, when sinkholes were recorded in five neighborhoods. Approximately 60 thousand residents are estimated to have been forced to leave their homes behind and relocate.
The risk of collapse in one of the 35 mines Braskem is in charge of is being monitored by the Civil Defense of Maceió and was detected due to the advance in subsidence. The petrochemical company has confirmed there could be a major collapse in the area, but also said the ground could also settle. A collapse could trigger an earthquake and potentially open a crater larger than the Maracanã stadium. The consequences, however, are still uncertain. The federal government is also monitoring the situation.
Unlike the salt typically used in the kitchen, which is obtained from the sea, rock salt is found in underground deposits formed thousands of years ago from the evaporation of portions of the ocean. As a result, sodium chloride is accompanied by a variety of minerals.
Also known as halite, rock salt is marketed for use in the kitchen. Easy to find in supermarkets, the salt extracted in the Himalayas, which has a pink hue due to local characteristics, is a type of rock salt.
However, rock salt is also a versatile raw material for the chemical industry. It is used, for instance, in the production of caustic soda, hydrochloric acid, sodium bicarbonate, soap, detergent, and toothpaste, as well as in the manufacture of cleaning and hygiene products and pharmaceuticals.
Industry
Initially, operations in Maceió focused on the production of dichloroethane, a substance used in the manufacture of PVC (polyvinyl chloride). It is no coincidence that, since it opened an industrial unit in the town of Marechal Deodoro, next to Maceió, back in 2012, Braskem has become the top PVC producer on the American continent. Other industries, such as cellulose and glass, also use rock salt in their processes.
The exploitation of rock salt, like other minerals, hinges on environmental licensing. Exploration is supervised by Brazil’s mining authority ANM. The country is a major player on the international market. According to ANM data, production amounted to 7 million tons in 2022. Last year’s ranking, however, shows that the three world leaders have much more robust production than everyone else: China (64 million tons), India (45 million) and the US (42 million).
In Maceió, mining began in 1976 with the company Salgema Indústrias Químicas, which was soon nationalized and later privatized again. In 1996, it changed its name to Trikem and, in 2002, merged with other smaller businesses to finally become Braskem, with majority control held by the Novonor Group, formerly Odebrecht Group. Petrobras also has a stake in the company, with 47 percent of the shares, sharing control with Novonor. Braskem is currently active not only in Brazil, but also in other nations, such as the US, Mexico, and Germany.
Excavation
Exploration in Maceió involved digging wells down to the salt layer, which could be over a thousand meters deep. Water was then injected to dissolve the rock salt and form a brine. Next, using a pressure system, the solution was brought to the surface. At the end of the extraction, these wells need to be filled with a liquid solution to keep the soil stable.
The problem in Maceió occurred due to the leakage of this liquid solution, which left holes in the salt layer. One hypothesis raised by experts is that the incident is linked to geological faults in the region. Consequently, instability in the soil led to an earthquake felt in March 2018. The event caused sinkholes in five neighborhoods: Pinheiro, Mustange, Bebedouro, Bom Parto, and Farol.
With new tremors and the appearance of cracks in houses and streets, Braskem announced the end of mining operations in May 2019, stating it has already paid out BRL 3.7 billion in compensation and financial aid to residents and traders in these districts. Some of those affected are seeking redress through legal proceedings. The case is also being considered in lawsuits filed by federal prosecutors.
