## Results: 6

2.

(a) Cu

(b) Net Cu

^{2+}, Ni^{2+}, and Cd^{2+}electrowinning in the CEP SPE at 50°C, pH 4, with 3.5 SLM nitrogen sparging. The initial ion concentrations prior to electrowinning in each case were 100 ppm from a prepared solution. The symbols are the experimental data, and the curves are the polynomial fits.(b) Net Cu

^{2+}, Ni^{2+}, and Cd^{2+}removal rates,*R,*calculated with the polynomial fits from (a). The values in parentheses are the electrowinning times,*t*and the corresponding metal ion removal rates at the maxima_{e},3.

Cu

^{2+}, Ni^{2+}, and Cd^{2+}concentrations in a ternary mixture over multiple CEP cycles. Three P/R steps were employed to accumulate the initial ion concentrations for electrowinning. After that, each CEP cycle consisted of one 300 min SPE step and one P/R step. The P/R pH values were 11.0 and 4.0, respectively, and electrowinning was conducted at 20A, 50°C, pH 4, with 3.5 SLM nitrogen sparging. The solid curves are the electrowinning steps; the fine dashed vertical lines are precipitation; and the coarse dashed vertical lines are redissolution.4.

(a) Cu

(b) Ni

^{2+}concentration in the process water over multiple CEP cycles at 15A. Four P/R steps were used to accumulate the initial Cu^{2+}concentration for electrowinning. After that, each CEP cycle consisted of one SPE and three P/R steps.(b) Ni

^{2+}concentration in the process water over multiple CEP cycles at 20A. Four P/R cycles were employed to accumulate the initial Ni^{2+}concentration for electrowinning. After that, each CEP cycle consisted of one 180 min. SPE and two P/R steps. In both cases: the P/R steps were conducted at pH 11.0 and 4.0, respectively; electrowinning was conducted at 50°C, pH 4, with 3.5 SLM nitrogen sparging. The solid curves are the electrowinning steps; the fine dashed vertical lines are precipitation; and the coarse dashed vertical lines are redissolution.5.

Binary metal ion concentrations in the process water over multiple CEP cycles. In each case, three P/R steps were employed to accumulate the initial ion concentrations for electrowinning. After that, each CEP cycle consisted of one SPE step for the

*t*values specified below, and two P/R steps (16 min.). The pH values for the P/ER steps were 11.0 and 4.0, respectively, and electrowinning was conducted at 20A, 50°C, pH 4, with 3.5 SLM nitrogen sparging. The solid curves are the electrowinning steps, the fine dashed vertical lines are precipitation, and the coarse dashed vertical lines are redissolution. (a) Cu_{e}^{2+}and Ni^{2+}for*t*= 180 min.; (b) Cu_{e}^{2+}and Cd^{2+}for*t*= 240 min.; (c) Ni_{e}^{2+}and Cd^{2+}for*t*= 300 min._{e}6.

(a) Copper electrowinning in the SPE as a function of applied current. The initial Cu

^{2+}concentration in each case was 99.5 ppm, which was prepared from the 20 ppm stock solution with five P/R cycles. The symbols are the experimental data, and the curves are the polynomial fits for copper electrowinning at 50°C, pH 4, with 3.5 SLM nitrogen sparging. (b) Net CEP copper removal rates, R, as a function of electrowinning time, te, constructed from the electrowinning data in (a) for a fixed value of tp = 40 min., as a function of applied current. The initial Cu^{2+}concentration in each case was 99.5 ppm. The values in the parentheses are the resultant optimal electrodeposition times, te, and the corresponding copper removal rates at the maxima for the same electrowinning conditions as in (a).