AU2002322888A1 - Hydrogen evolution inhibiting additives for zinc electrowinning - Google Patents

Description

HYDROGEN EVOLUTION INHIBITING ADDITIVES FOR ZINC ELECTROWINNING

FIELD

• The invention is related to additives for zinc

electrowinning that inhibit hydrogen evolution and/or improve

current efficiency for zinc electrodeposition, specifically

cetylpyridinium-based additives .

BACKGROUND

Improving the energy efficiency of the zinc electrowinning

process by inhibition of the parasitic hydrogen evolution

reaction, which occurs in parallel with zinc deposition, is of

major technological and commercial interest. One way of

minimizing the cathodic hydrogen evolution is by the use of

additives, generally organic compounds, which selectively increase the hydrogen evolution overpotential . Mackinnon et al .

(Journal of Applied Electrochemistry, Volume 20, pages 728-736,

1990) and Scott et al. (Journal of Applied Electrochemistry,

Volume 18, pages 120-127, 1988) describe the use of animal glue

in combination with antimony to improve the current efficiency

for zinc electrowinning when compared to additive-free

electrolytes .

There is a need for improved additives that minimize hydrogen evolution during zinc electrowinning while providing

the same or improved performance over traditional additives .

Therefore, it is an object of this invention to provide

improved additives for zinc electrowinning that minimize

hydrogen evolution while providing similar or improved

performance over traditional additives .

SUMMARY

Cetylpyridinium chloride (CPC) , a cetylpyridinium salt, was

tested as an additive in a zinc electrowinning process in two

separate zinc electrowinning electrolyte compositions: 1) with

antimony and 2) with both antimony and glue.

The CPC additive had the most significant influence in the presence of antimony or antimony + glue combination, where it

increased the current efficiency by 23.2% and 7.6%,

respectively. Moreover, the presence of 0.05 mM CPC did not

increase the overall cell voltage.

DETAILED DESCRIPTION

Methods And Apparatus

Commercial beaker test cells containing a commercial

electrowinning electrolyte (liquor) were connected to a power

supply and placed in a 37 °C water bath. The anodes and cathodes were made of lead and aluminium, respectively. The laboratory

supplied MSDS sheet indicated for the electrolyte the following

composition: zinc sulfate 28 - 34% by weight, magnesium sulfate

9 - 15 g/1 (grams/litre) and manganese 1.5 - 2.5 g/1.

After allowing the temperature inside the test cells to

reach the desired value of 37 °C, a constant current of 0.045 A,

representing an electrowinning current density of 450

amperes/meter², was applied for either 4 or 20 hours to a non-

agitated electrolyte. After completion of the experiment the

electrode assembly was removed from the glass beaker, rinsed

with distilled water and the cathode deposit carefully scraped

off and weighed with four digits precision using a digital

Mettler AE 100 analytical balance. The test cells were rinsed

between experiments with distilled water and acetone in order to

remove traces of the organic additives . Replicates were also

performed and the standard deviation was estimated.

The zinc electrodeposition current efficiency was

calculated based on Faraday's law:

C£(%)=— MOO (1)

where

CE - current efficiency for Zn electrodeposition (%) z - no. of electrons exchanged [=2] F - Faraday's number [=96485.3 C mol^"1] m_d - amount of zinc deposit (g) /- applied current [=0.045 A] t - time (s)

Az_n - atomic weight of zinc [=65.39].

The cetylpyridinium chloride (CPC) (e.g. Sigma-Aldrich,

U.S.) had the following structure:

Example 1

Zinc Electrowinning Liquor with antimony present

Antimony (Sb) in 0.04 mg/1 (milligrams/litre) concentration

was added as antimony - potassium tartrate to the zinc

electrowinning electrolyte. Both four and twenty hour runs were

performed. The experimental results of the four-hour runs are

summarized in Table 1.

Without the CPC additive present in the electrolyte, Sb had

a detrimental effect on the current efficiency, i.e. between 65.1% (cell no. 15) and 74.7% (cell no. 14). On average, the

current efficiency without the CPC additive present was 69.9%.

Adding CPC improved the current efficiency on average by 23.2%,

i.e. from 69.9% to 93.1%.

Table 1: Effect of CPC on the current efficiency of zinc electrowinning in the electrolyte containing 0.04 mg/1 Sb (as Sb-tartrate) .

CA

The effect of CPC in^Λlonger-term (20 hours) experiment is

shown in Table 2. Without the CPC additive, the current

efficiency of cell no. 15 was only 36.6%, whilst with 0.05 mM

CPC present the zinc electrowinning current efficiency was

58.9%. Thus, with the CPC additive the current efficiency was

higher by 22.3%. Table 2: Effect of CPC on the zinc electrowinning current efficiency in 20 hour experiment with 0.04 mg/1 Sb in the electrolyte.

"5

Example 2

Zinc Electrowinning Liquor with both antimony and glue

Similar experiments to those in Example 1 were performed

with an electrolyte containing 0.04 mg/1 of Sb and 10 mg/1 of

10 glue (e.g. "pearl glue" supplied by Hudson Industries,

Johnstown, New York) . Both 4 and 20 hour runs were carried out,

The effect of the CPC additive on the zinc electrowinning .

current efficiency in the 4 hour runs is shown in Table 3.

15 The presence of glue minimizes to a certain extent the

negative effect of antimony, yielding current efficiencies

between 88.9% and 90%. However, adding 0.05 mM CPC brought

about additional increases of current efficiency, i.e. from

89.4% on average in the absence to 97% in the presence of CPC

20 (Table 3) . Table 3: Effect of CPC on the current efficiency of zinc electrowinning in the electrolyte containing 0.04 mg/1 Sb (as Sb-tartrate) + 10 mg/1 glue.

The 20 hour experiments (Table 4) showed that CPC in 0.05

mM concentration increased the current efficiency of cell no . 16

from 77.2% to 87.3%.

Table : Effect of CPC on the zinc electrowinning current efficiency in 20 hour experiment with 0.04 mg/1 Sb and 10 mg/1 glue in the electrolyte.

The cell voltage is another important figure of merit of

the electrowinning process. An increase in the cell voltage

represents an increase in the amount of energy required and, therefore, a less efficient electrowinning process. Table 5

shows that using 0.05 mM CPC in conjunction with Sb and glue did

not induce an increase of the cell voltage.

Table 5 : Effect of CPC on the average cell voltage in 4 hour experiments with 0.04 mg/1 Sb and 10 mg/1 glue in the electrolyte.

Accordingly, while this invention has been described with

reference to illustrative embodiments, this description is not

intended to be construed in a limiting sense. Various

modifications of the illustrative embodiments, as well as other

embodiments of the invention, will be apparent to persons

skilled in the art upon reference to this description. It is

therefore contemplated that the appended claims will cover any

such modifications or embodiments as fall within the scope of the invention.

Claims (9)

WE CLAIM :

1. A method of improved zinc electrowinning, comprising : adding a cetylpyridinium salt additive to a zinc electrowinning electrolyte .

2 . A method according to claim 1, wherein said cetylpyridinium salt is a cetylpyridinium halide .

3 . A method according to claim 2 , wherein said cetylpyridinium halide is cetylpyridinium chloride .

4 . A method according to claim 3 , wherein said cetylpyridinium chloride is at 0 . 05 millimolar (mM) concentration in said zinc electrowinning liquor.

5. A method according to claim 1, wherein said zinc

electrowinning electrolyte contains zinc sulfate.

6. A method according to claim 1, wherein said zinc

electrowinning electrolyte contains antimony.

7. A method according to claim 1, wherein said zinc

electrowinning electrolyte contains glue.

8. A method according to claim 7 , wherein said glue is animal

glue.

9. A method according, to claim 8 , wherein said animal glue is

gelatin.