By Amy Lv, Dylan Duan and Ryan Woo BEIJING (Reuters) -China, the world's biggest copper smelter, is studying ways to strengthen regulation on the expansion of smelting capacity, a state news outlet said on Thursday, as record low processing fees have curbed profits. Chen Xuesen, vice chairman at the China Nonferrous Metals Industry Association, was quoted as telling a meeting on Wednesday that low concentrate processing fees were the "most prominent" problem the industry faces. The fees that miners pay ...