Compound collectors are employed to construct surface hydrophobic sites on long-flame coal, thus improving the flotation-based preparation of ultra-low ash coal - Guolong Zhong; Xiaowei Deng; Chaojun Fang; Ruixue Lou; Yao Zhang; Yunlai Chen; Yang Ju; Chuanxiang Zhang; Baolin Xing; Hongxiang Xu; Guixia Fan; Yijun Cao (Journal of Environmental Chemical Engineering, 2026)