Preliminary investigation points to unsuitable dam foundations as a potential cause of Hungary’s Oct. 4 tailings dam collapse. Seven people died, 150 were injured, and approximately 1,000 hectares of land were polluted heavily by caustic “red mud” surging from an alumina plant at Ajka, say Interior Ministry officials.
Hungarian emergency teams appear to have saved the Raba, Moson-Danube and Danube rivers from the caustic pollution. But heightened pH levels caused by the sludge devastated fish populations in the Marcal River, according to government officials. Hungary’s other tailings dams are under investigation.
Interior Ministry officials estimate that more than 600,000 cubic meters of red sludge burst out of the plant’s reservoir No. 10 when part of its roughly 30-m-tall western retaining embankment collapsed. Some 40 m of the 20-m-wide embankment, built in the 1990s, failed for unknown reasons, says an Interior Ministry spokesman.
The reservoir and nine others previously used at Ajka are owned by Hungary’s only alumina production company, Magyar Aluminium Zrt. (MAL). Hungarian police on Oct. 11 arrested Zoltán Bakonyi, MAL’s chief executive. If convicted of criminal negligence, he could face 10 years in prison.
MAL officials deny having prior knowledge of engineering investigations made before the company’s 1995 privatization. Gusztav Winkler, an associate professor of civil engineering at Budapest University, investigated the Ajka plant; his study suggested sand and clay were unsuitable materials for the dam foundations as they would separate in wet conditions. Winkler was unavailable for comment.
Interior Ministry officials say they will investigate Winkler’s report and others alleging reservoir leaks that occurred five years ago.
Dams at Ajka were “built in a proper way and [with] appropriate materials,” claim MAL officials. They say a survey in 1995 by Budapest-based consultant Melyepterv Kultúrmérnöki Kft. declared the dams to be sound. Recent monitoring revealed no danger signs, they add.
Most of the immediate environmental damage occurred in the villages of Devecser, Kolompár and Somlyószentpéter. Signs of continuing embankment movement after the failure led to the evacuation of Kolompár. However, the red mud remaining in the reservoir is dense and flows slowly, says a MAL official.
Government teams took the precaution of constructing hundreds of meters of emergency embankments around the stricken reservoir to capture rain runoff and other flows. To limit the spread of caustic flows into downstream rivers, emergency crews dumped large quantities of gypsum and acetic acid into waterways and built impromptu weirs to capture the resulting salt deposits.
Contaminated soil in affected communities will be scraped up and dumped in some of Ajka’s remaining reservoirs.
Red mud, seen above flowing through a breach in the Ajka tailings-pond wall, is a by-product of the Bayer chemical process for refining ores containing aluminium into alumina oxide. The mud is alkaline, typically with 10-12 pH.
Bauxite mainly contains hydrated aluminium oxide, iron oxide, silicates and titanium dioxide. Producing one tonne of aluminium metal from alumina generates 1.5 to four tonnes of waste product on a dry basis, according to data from the Aluminum Association, Washington, D.C.
The alumina industry globally produces around 120 million tonnes of red mud annually, according to industry sources.