英语翻译3.Results and discussionFig.2 shows the plot of metal re

英语翻译
3.Results and discussion
Fig.2 shows the plot of metal reduction and the solution
pH as a function of electrolysis time.As expected,th e
deposition of copper increased slowly during the first 6 h,
then it increased dramatically.More than 99% of copper
was reduced within 12 h whereas the percentage of
chromium and nickel reduction had changed only slightly.
After 12 h,the current density was changed to 90A/m2.
During this period,both chromium and nickel were
reacted with hydroxide ions and precipitated rapidly.The
precipitation of their ions started at 13.5 h corresponding
to the increasing solution pH.More than 99.9% of
chromium and nickel was reduced within 15 h.The
remaining concentrations of copper,chromium and nickel
in outlet solution were lower than 0.01?.13,0.19?.20 and
0.05?.13 ppm,res pectively.In all cases,metal concentration
was lower than the acceptable value limited by the
Thai Government (Cuo1ppm,Ni o0.2 ppm,
Cro0.5 ppm).The power consumption and total operating
cost were approximately 42.30kWh/kg metal and
5.43 US$/m3,respectively.Table 2 shows the comparison
of operating costs of this work with other three previous
works (Kongsricharoern and Polprasert,1995 ; Chawalkitcharoen
et al.,1993 ; Visvanathan et al.,1993 ).The results
demonstrate that all treatment processes have almost the
same operating cost.However,o ur operation should be
easier than the others.In addition,our work succeeds to
recover many metals (copper,chromium and nickel),
whereas only one metal was removed by three other works.
3.1.Effect of some parameters on copper reduction
Because copper is a valuable metal and it can be
removed as a metallic form as it is deposited on cathode,
the effective parameters for its reduction were also
investigated.
3.1.1.Effect of brightener
Effects of brighteners such as Elecopper 25A,
Elecopper 25MU and Elecopper 25B (Okuno Chemical
Industries Co.,Ltd.) (Table 3) on copper reduction were
investigated with synthetic copper solution.In each
experiment,0.15 vol% of each brightener was added at a
current density of 10 A/m2 and a copper concentration
of 15.74 mol Cu/m3 at pH 1.No significant difference
in terms of the percentage of copper reduction were
observed between the experiments with and without
brightener (Fig.3).More than 99% of copper was
reduced within 6 h with more than 60% total current
efficiency.
3.1.2.Effect of Cr and Ni ions in solution
The further experiment was conducted to observe the
effect of other metals (Cr6+,Ni 2+) on copper reduction
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