TY JOUR TI Testing the fractional dissolution method for ashless concentrates obtained from solid fossil fuels KW oil shales KW coal sludge KW hypercoaler KW fractional dissolution JO Proceedings of the Komi Science Centre of the Ural Division of the Russian Academy of Sciences AU Kuzmin, D.V. AU Burcev, I.N. PY 2026 IS 0 PB FSBI FIC "Komi Scientific Center of the Ural Branch of the Russian Academy of Sciences"