Thermal transformation in phosphorites and their use for the beneficiation of phosphate rockVeiderma, Mihkel; Knubovets, RenaActes du Congres International sur les Composés Phosphores, 2nd: April, 21-25, 1980, Boston, Mass., USA = International Congress on Phosphorus Compounds, 2nd: April, 21-25, 1980, Boston, Mass., USA1980 / p. 345-362