July 7 (Reuters) - China's export restrictions on rare earths brought parts of the global auto supply chain to a halt and U.S. President Donald Trump to the negotiating table. But at home, they're a big headache for companies already struggling with a slow economy.

Low environmental standards helped China become the world’s low-cost producer of rare earths, but Beijing was also focused on helping the industry.

Mines in Kachin state, notably those north of the strategically important garrison town of Bhamo, provide about half of the world’s supply of heavy rare earths. After that, they are sent to China to b