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2. 2) J. Newton and C. L. Wilson: Metallurgy of Copper, (J. Wiely & Sons, London, 1942) pp. 244–246.
3. 3) K. Jia Jun and C. Chia Yung: Hydrometallurgy 12 (1984) 217–224.
4. 4) J. D. Prater and J. S. Wells: US Patent, 4149880, July 19 (1978).
5. 5) W. H. Kruesi and P. R. Kruesi: US Patent, 5332560, March 5 (1993).