Farmers living near the 10-square-kilometre expanse in northern China say they have lost teeth and their hair has turned white while tests show the soil and water contain high levels of cancer-causing radioactive materials.
"We are victims. The tailings dam has contaminated us," Wang, 60, told AFP at his home near Baotou city in Inner Mongolia, home to the world's largest deposits of rare earths, which are vital in making many high-tech products.
"In this place, if you eat the contaminated food or drink the contaminated water it will harm your body," Wang said, pointing towards lifeless fields now strewn with rubbish around Dalahai village, a few hundred metres from the dump.
China produces more than 95 percent of the world's rare earths -- 17 elements used in the manufacture of products ranging from iPods to flat-screen televisions and electric cars.
Two-thirds of that is processed in mineral-rich Baotou on the edge of the Gobi desert.
Environmental groups have long criticised rare earths mining for spewing toxic chemicals and radioactive thorium and uranium into the air, water and soil, which can cause cancer and birth defects among residents and animals.
Beijing, keen to burnish its green credentials and tighten its grip over the highly sought-after metals, has started cleaning up the industry by closing illegal mines, setting tougher environmental standards and restricting exports. (read more)