Reactivity of oil shale ashes towards sulfur dioxide. 3, Recurrent use of ash for flue gas purificationKuusik, Rein, keemik; Kaljuvee, Tiit; Veskimäe, Helgi; Roundygin, Yu.; Keltman, A.Oil shale1999 / 4, p. 303-313: ill https://artiklid.elnet.ee/record=b1000612*est