Red Mud Pollution Challenges

Aluminum is the most common metal on the planet, as well as, one of the most recycled ones, accounting for more than 8 % of the total mass of the earth’s crust. It is light, strong, corrosion-resistant, and functional – this has made it the most used metal, however, in its pure form, aluminum is not found.

Today, the raw material for the production of aluminum is one of the most common in nature aluminum ore – bauxite. Bauxite is a clay rock that contains various modifications of aluminum hydroxide with an admixture of iron, silicon, titanium, sulfur, gallium, chromium, vanadium, calcium, iron, and magnesium carbonate salts. Bauxite is considered high-quality if it contains more than 50 % aluminum oxide, with a silicon ratio of at least 10. Typically, 4-5 tons of bauxite produces about 2 tons of alumina, from which 1 ton of aluminum is produced. The process of aluminum production is very complex and is associated with a big amount of waste.

Red mud is obtained by processing bauxite by the Bayer method – the process of obtaining pure aluminum oxide, which is later used in electrolysis. It is called red because of its characteristic color, caused by the fact that iron oxide is present in the composition of the sludge and makes up to 60% of the total mass. It also contains silicon oxide, aluminum oxide remaining after leaching, and titanium oxide. Usually, the production process produces twice as much red sludge as aluminum, which is due to the quality of the incoming bauxite. For each ton of aluminum oxide produced, there is from 360 to 800 kg of red mud.

There are 16 smelters in the EU, located in ten countries: France, Denmark, Germany, Netherlands, Spain, UK, Romania, Slovakia, Slovenia. There are ten smelters in EFTA countries (Norway and Iceland). China is responsible for around 57 percent of production globally. Europe represents about 7 percent, around half of which comes from within the EU28. Russian company RUSAL has more than 30 factories around the world.

Red Mud Landfills

Red Mud became widely known worldwide in 2010 when a major accident occurred at an aluminum plant near the town of Aika in Hungary. As a result of the explosion at the enterprise, the dam on the sludge field was partially destroyed. There was a leak of more than 1 million cubic meters of the toxic substance, which led to an environmental disaster and the introduction of a state of emergency in the disaster area. In total, more than 140 people were injured, 10 of them died, not only people were affected, but also the nearest regions, rivers, and representatives of the animal world.

Currently, it is difficult to calculate the approximate number of sludge fields in Russia. So, for almost 80 years, the Ural aluminum plant in the city of Kamensk-Uralsky, Sverdlovsk region was built three landfills which have accumulated more than 70 million tons of red mud with a total area of more than 500 hectares. 

Environmental damage is caused by rain or meltwater washed out of the sludge field dam. Water washed out of the sludge pool increases the pH of nearby rivers and lakes, making them sharply alkaline, if such water is irrigated, it will turn into a salt marsh. The water level in the field with sludge is replenished due to natural phenomena, such as rains, floods, downpours, etc. The risks of a repeat of a disaster similar to the Hungarian one are very high and are rapidly increasing. In addition, the red mud comes from the plant to the dam in liquid form, that is, more than 80% diluted with water.

Negative Impact of Red Mud

Red mud has a negative impact both on the environment and on the human body. In the event of a disaster, annuals and perennials are destroyed for almost 10 years in an area flooded with red sludge. The alkali in the ground damages the outer layers of fish, shellfish, and crustaceans, causing their immediate death or disease, depending on the chemicals that get into the water. For humans, red sludge is dangerous because, at the slightest contact, the alkali causes burns to the skin and mucous membranes. The pulp contains heavy metals, which, when interacting with or being close to them, reduces intellectual development, attention, and the ability to concentrate. In children, aggression develops, and in adults, blood pressure increases, numbness or tingling in the extremities. There are also muscle and headache, abdominal pain, constipation, memory loss, decreased potency, decreased immunity, anemia, and liver and kidney damage.

Red Mud Recycling and Reuse

Many experts do not consider red sludge to be waste, as it can serve as a raw material for processing. Scandium is also extracted from the red sludge for the further production of aluminum-scandium alloys. Scandium gives such alloys a special strength. Areas of use: automotive and rocket engineering, sports equipment, and the production of electrical wires. Also, red sludge can be used for the production of cast iron, concrete, and the production of rare earth and precious metals. The content of bicalcium silicate and other silicon-containing compounds in the red sludge can be used for the production of building materials, but the final product must contain a minimum amount of moisture, and the issue of dehydration of red sludge is not yet fully understood. In France, a patent was developed providing for the use of red sludge for the production of ceramic products, and in Germany red sludge is used as a filler for bituminous masses. According to recent studies, bauxite sludge can be used as a complex corrective additive in the production of Portland cement clinker of rational chemical and mineralogical composition.

The effects of sodium ferrate on red mud pollution remediation

One of the current research topics is related to red mud. Red mud – is an industrial waste forming in the aluminum production cycle. A large amount of this waste is stored in the Leningrad district (in the Boksitogorsk region). This waste poses a great danger, first of all, for the water bodies of the region. Therefore, we are now conducting experiments on ferrate purification of water contaminated with red mud.

Since soil and groundwater resources are other endangered resources by red mud, another survey is being conducted in which we are studying the contaminants transition, their behaviours and interactions in the soil environment.

The results of soil columns experiment will show how would be the transition of the red mud contaminants through the soil. Majed is also investigating the mitigation impacts of sodium ferrate on soil contaminated by red mud. Simulating by HYDRUS-1D software will provide the chance to understand the groundwater pollution hazard by red mud transmitted through the agricultural soil.