Application of the combined depressant Na2SO3 and FeSO4 in chalcopyrite-pyrite low-alkaline flotation separation: Experimental mechanisms and DFT study - Xianhui Qiu; Jieming Hu; Xianren Dai; Wenhui Yang; Qizheng Xia; Quanfan Ling; Pan Yang; Tingsheng Qiu (Minerals Engineering, 2026)