Silent pollution

After the mine was shut down, people left, the bustling days ended, leaving only barren mountains and memories slowly eroding over time.

"In the following 20 years, this abandoned mine posed significant ecological challenges," said Hu Zhiwei, chief planner of Lujiang's natural resources and planning bureau.

The official showed the monitoring data before treatment: the pH value of the acidic wastewater from the mining area was as low as 2.0, comparable to vinegar.

It was rich in heavy metals such as iron, aluminum, and manganese, continuously seeping from mine pits and waste residue, flowing into rivers, and eventually reaching Chaohu Lake and the Yangtze River, according to Hu.

Chaohu is China's fifth-largest freshwater lake and an important ecological barrier for Hefei. The alum mine is located in a sensitive area upstream of this lifeline.

"At that time, the county had obvious deficiencies in funding and technology," said Hu.

In 2021, an adaptive experiment quietly started at the edge of a mine pit considered an "ecological dead zone".

"When we first arrived, this area was basically barren," said Jia Zenghua, an engineer responsible for the following restoration project.

Start of restoration

In February 2021, the Ministry of Finance, the Ministry of Natural Resources, and the Ministry of Ecology and Environment jointly issued a notice, organizing local governments to apply for central financial support for the "Mountain-River Projects".

Such projects aimed at integrated protection and restoration of mountains, rivers, forests, fields, lakes, grasslands and sand.

The Anhui Chaohu Lake Watershed Integrated Protection and Restoration Project thus became one of the first batch of such projects for the 14th Five-Year Plan period (2021-25).

"Lujiang keenly saw this significant opportunity to restore the abandoned alum mine," said Hu.

In May 2021, Hefei began investing 15.1 billion yuan ($216 million) to package relevant projects, including alum mine treatment, into an overall plan to protect the Chaohu Lake watershed.

It was successfully listed as a national project, receiving 2 billion yuan in central financial support. The Lujiang county government actively secured 20 sub-projects, obtaining 7.4 billion yuan in investment, including 980 million yuan in central funds.

As one of the sub-projects, the alum mine treatment project alone received 160 million yuan in central financial support.