1. Lounamaa N. and Mattila T. and Judin V. P. and Sund H. E. , 1980 ,Proc. 2nd Int. Cong. Phosph. CompParis , Institut Mondial du Phosphate , pp. 759 – 768
2. Judin V. P. and Sund H. E. , 1981 ,in Hydrometallurgy '81London Society of Chemical Industry , p. F4/1 – F4/14
3. Ionescu E. and Tomescu E. and Rachita R. , 1980 ,in Proc. 2nd Inr. Cong. Phosph. Comp.Paris Institut Mondial du Phosphate , pp. 745 – 758
4. Rusin N. F. and Deyneka G. F. and Andrianov A. M. , 1980 ,Proc. Int. Symp. on Phos-phogypsumFlorida Institute of Phosphate Research. Florida , Borris, D. P. and Boody , P. W. , 02 , pp. 407 – 423