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Copper Electrowinning and Cr+6 Reduction in Spent Etchants Using Porous Fixed Bed Coke Electrodes.
U S Pat 4 256 557 1981 Mar; :
Residual cr6+ is electrochemically reduced to cr3+ with the simultaneous electrowinning of copper from spent cr6+ oxidizing solutions containing cu2+. A spent cr6+ etching solution for brass was electrolyzed using electrodes of a metallurgical coke (-8+16 mesh particles) contained in plexiglass frames having on opposite surfaces polypropylene screens. Electrical contact was provided by small platinum strips. The solution was electrolyzed for 24-48 h at 4-6 V. A cell efficiency after 24 h of electrolysis was 89 pct with a cu removal efficiency of 96 pct.
U.S. Pat. 4,256,557, Mar. 17, 1981; Chem. Abstr. 93:122,646T
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