Electrochemical Extraction of Pb and Zn from Raw Mineral …
431
and in during hydrometallurgical processing. A collective concentrate of the following chemical composition was used as an object of research: % (mass fraction.):
Si-14.94; Pb-5.68; Zn-14.57; Fe-6.26; S-14.96; C-6.94; and Ca-2.11.
The experiments were carried out in a reaction cell. The cell had a three-electrode
system consisting of a working electrode, a reference electrode, and an auxiliary
electrode. A sulfur-graphite electrode was used as a working electrode, in which
the ratio of sulfur to graphite was 65:35%. The silver chloride electrode served as
the reference electrode, and the graphite electrode served as the auxiliary electrode
(anode). The volume of alkaline solution in the reaction vessel contained a volume
of 150 ml. A sample was placed in a vessel with a ratio of T:W = 1:10, (sample 15 g:
sodium hydroxide 150 ml). The current density is from i-100 A/m
2 , the mixing speed
is 480 rpm, and the leaching time is 5–6 h. The alkali concentration in the solution
is 0.1, 0.2, 0.3, and 0.5 M.
In parallel with the experiment, the physicochemical characteristics of the solutions were determined, which changed as the leaching reagent formed and metal
compounds formed in the aqueous solution. Samples were taken every hour for analysis, the pH of the medium was determined, the potential of the cathode (sulfur
graphite electrode) was E
0 k, the electrical conductivity was Eh of the solution, and
the concentration of dissolved oxygen (DO) using the 856 Conductivity Module,
867 pH Module “Metrohm” (Switzerland), SensIon 156 handheld analyzer manufactured by HACH (USA). The amount of metals transferred to the solution was
determined on a contrAA 300 atomic absorption spectrometer. The concentrate was
leached for 300 min at concentrations of sodium hydroxide in the initial solution of
0.1 and 0.5 M NaOH.
Results and Discussion
The corresponding data are shown in Figs. 1, 2, 3, 4, and 5. As can be seen from
Figs. 1 and 2, a distinctive feature of the extraction of zinc and lead into solution
is a gradual increase in recovery followed by reverse deposition of metals. In this
case, lead begins to pass into solution only after 60 min of leaching, while zinc goes
into solution almost at the beginning of the experiment. It should be noted that, as
in the case of lead, zinc is extracted into the solution at a low rate during the first
60 min of leaching. After 60 min of leaching, the rate of transition of lead and zinc
into solution increases significantly. Moreover, the transition of lead into solution is
characterized by an increased rate. The most characteristic indicator is the effect of
the concentration of sodium hydroxide in the initial solution on the transition of lead
and zinc into the solution.
As can be seen from Figs. 1 and 2, an increase in the concentration from 0.1 to
0.5 M NaOH leads to the fact that both zinc and lead go into solution.
Figures 3 and 4 show the data on the change in pH and electrical conductivity of
solutions during leaching of sodium hydroxide 0.1 and 0.5 M in the course of leaching
decrease from 11.99 to 6.99 and from 13.047 to 10.39, respectively. The electrical
431
and in during hydrometallurgical processing. A collective concentrate of the following chemical composition was used as an object of research: % (mass fraction.):
Si-14.94; Pb-5.68; Zn-14.57; Fe-6.26; S-14.96; C-6.94; and Ca-2.11.
The experiments were carried out in a reaction cell. The cell had a three-electrode
system consisting of a working electrode, a reference electrode, and an auxiliary
electrode. A sulfur-graphite electrode was used as a working electrode, in which
the ratio of sulfur to graphite was 65:35%. The silver chloride electrode served as
the reference electrode, and the graphite electrode served as the auxiliary electrode
(anode). The volume of alkaline solution in the reaction vessel contained a volume
of 150 ml. A sample was placed in a vessel with a ratio of T:W = 1:10, (sample 15 g:
sodium hydroxide 150 ml). The current density is from i-100 A/m
2 , the mixing speed
is 480 rpm, and the leaching time is 5–6 h. The alkali concentration in the solution
is 0.1, 0.2, 0.3, and 0.5 M.
In parallel with the experiment, the physicochemical characteristics of the solutions were determined, which changed as the leaching reagent formed and metal
compounds formed in the aqueous solution. Samples were taken every hour for analysis, the pH of the medium was determined, the potential of the cathode (sulfur
graphite electrode) was E
0 k, the electrical conductivity was Eh of the solution, and
the concentration of dissolved oxygen (DO) using the 856 Conductivity Module,
867 pH Module “Metrohm” (Switzerland), SensIon 156 handheld analyzer manufactured by HACH (USA). The amount of metals transferred to the solution was
determined on a contrAA 300 atomic absorption spectrometer. The concentrate was
leached for 300 min at concentrations of sodium hydroxide in the initial solution of
0.1 and 0.5 M NaOH.
Results and Discussion
The corresponding data are shown in Figs. 1, 2, 3, 4, and 5. As can be seen from
Figs. 1 and 2, a distinctive feature of the extraction of zinc and lead into solution
is a gradual increase in recovery followed by reverse deposition of metals. In this
case, lead begins to pass into solution only after 60 min of leaching, while zinc goes
into solution almost at the beginning of the experiment. It should be noted that, as
in the case of lead, zinc is extracted into the solution at a low rate during the first
60 min of leaching. After 60 min of leaching, the rate of transition of lead and zinc
into solution increases significantly. Moreover, the transition of lead into solution is
characterized by an increased rate. The most characteristic indicator is the effect of
the concentration of sodium hydroxide in the initial solution on the transition of lead
and zinc into the solution.
As can be seen from Figs. 1 and 2, an increase in the concentration from 0.1 to
0.5 M NaOH leads to the fact that both zinc and lead go into solution.
Figures 3 and 4 show the data on the change in pH and electrical conductivity of
solutions during leaching of sodium hydroxide 0.1 and 0.5 M in the course of leaching
decrease from 11.99 to 6.99 and from 13.047 to 10.39, respectively. The electrical