Editor's note: As protection of the planet's flora, fauna and resources becomes increasingly important, China Daily is publishing a series of stories to illustrate the country's commitment to safeguarding the natural world.

After retiring, Hong Zengyi often returns to the alum mine in Hefei, the capital of East China's Anhui province, where he once worked.

A road divides the former mine area into two parts. On one side is the old mine's preserved residential area, and on the other is a tourist attraction being renovated from the old factory buildings, mostly built in the 1960s.

These structures are located at the foot of the hills. Nowadays, these hills are covered with green vegetation, with only a small, exposed hilltop left in its original, almost barren state.

This deliberately preserved area serves as a reminder of what this mountainous region once looked like.

Bustling epoch

This is Fanshan township in Lujiang county, governed by Hefei.

Fanshan, literally meaning "alum hill", has been one of China's most important alum-producing areas since the early eighth century in the Tang Dynasty (618-907).

Alum is a chemical compound, typically potassium aluminum sulfate, used in water purification and textile dyeing. Historically, alum was an important industrial material due to its versatile applications.

After the founding of New China, the Lujiang alum mine became one of the country's 18 key chemical mines. Its products were sold in dozens of countries and regions, including Singapore, Japan, Malaysia, and New Zealand.

Hong, born in 1961, joined his parents at the mine in 1981.

"At that time, the mine was like a small city," said Hong.

There were schools for children, a workers' hospital, a lighted sports field, and a thousand-seat auditorium. The weekly "Workers' Movie Day" was a festival for the mining area and surrounding villages.

"As the screen was drawn, the laughter of thousands resonated in unison. We were proud to say we were from the Lujiang alum mine," said Hong.

But in Hong's memory, there were no forests here.

"When I worked at the mine, I came home every day with black nostrils, and the collar of my white shirt would be covered with a layer of dust in half a day," he said.

With social progress and technological development, alum was gradually replaced by a range of new chemical products, leading to the decline of the alum mining industry.

In May 2001, the Lujiang alum mine ceased production, marking the end of a 1,300-year mining history.

"This was a market decision, not a human one," said Hong. Although he misses the years he worked there, he does not regret the closure of the alum mine. In 2002, although Hong was already one of the mine's managers, he, like all employees, was laid off in search of a new livelihood.

In 2014, the alum mine officially declared bankruptcy. In December 2020, the Lujiang alum mine was selected as one of the "Fourth Batch of National Industrial Heritage" sites.