tailieunhanh - Extractive Metallurgy of Copper 4th ed. - W. Davenport_ et. al. (2002) WW Part 11

Tham khảo tài liệu 'extractive metallurgy of copper 4th ed. - w. davenport_ et. al. (2002) ww part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Electrolytic Refining 111 Step a may also be done by evaporation crystallization of C11SO4 Bravo 1995 . The remaining concentrated acid -1000 kg H2SO4 1ĨI3 is returned to electrolyte storage to maintain the refinery s acid balance. A small portion is neutralized or sold to prevent a gradual buildup of Ca K Mg and Na ions in the refinery. As Bi Co and Sb may also be removed by solvent extraction Rondas et al. 1995 ion exchange Dreisinger and Scholey 1995 Roman et a . 1999 chelating resins Sasaki et al. 1991 and activated carbon Toyabe et al. 1987 . Addition agents Deposition of smooth dense pure copper is promoted by adding leveling and grain-refining agents to the electrolyte De Maere and Winand 1995 . Without these the cathode deposits would be dendritic and soft. They would entrap electrolyte and anode slimes. The principal leveling agents are protein colloid bone glues . All copper refineries use these glues to kg per tonne of cathode copper Davenport et al. 1999 . The glues consist of large protein molecules MW 10 000 to 30 000 which form large cations in the electrolyte. Their leveling efficacy varies so they must tested thoroughly before being adopted by a refinery. The principal grain-refining agents are thiourea to kg per tonne of cathode copper and chloride to kg m3 in electrolyte added as HC1 or NaCl . Avitone a sulphonated petroleum liquid is also used with thiourea as a grain refiner. Leveling and grain-reftning mechanisms The leveling action of glue is caused by electrodeposition of large protein molecules at the tips of protruding rapidly growing copper grains. This deposition creates an electrically resistant barrier at the tips of the protruding crystals encouraging sideways crystal growth Hu et al. 1973 Saban et al. 1992 . The net result is encouragement of dense and level growth. The grain-refining action of chlorine ions and thiourea has not been well explained. They may form Cu-Cl-thiourea cations .