Decomposition of Spent Emulsions Used for Drawing Copper Wire
Abstract Generated abstract
This paper investigates methods for decomposing spent oil in water emulsions used in copper wire drawing, with the aim of recovering oil and copper from waste streams. The authors compare demulsifier ANP, copper sulfate, alkali treatment, and sulfuric acid, examining their effects on separation of copper soaps, oil release, decomposition time, and copper concentration in solution. ANP, copper sulfate, and alkali were found suitable for separating copper soaps but not for oil recovery, while sulfuric acid enabled oil separation from both emulsions and copper soaps. The study identifies 20 percent sulfuric acid, corresponding to 20 kg of 96 percent acid per cubic meter of emulsion, as providing good oil quality and rapid decomposition, with subsequent copper recovery possible by cementation on iron turnings.
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DECOMPOSITION OF SPENT EMULSIONS USED FOR DRAWING COPPER WIRE
S. A. Babenko, N. T. Bolotkina
(Presented by the scientific seminar of the Department of Processes, Machines, and Apparatuses of Chemical Production)
In the drawing of copper wire, an oil–water type emulsion is used to lubricate the surface of the metal being drawn and the drawing channel. The emulsion is prepared by heating a mixture consisting of linseed oil, water, and caustic soda in a weight ratio of 125:5:1, followed by dilution with water in mechanical mixers and ultrasonic treatment.
During the drawing process, aqueous emulsions gradually become spent. Owing to the hydrolysis of sodium soap, fatty acids are released which, interacting with copper, form copper soaps. The alkalinity of the emulsion increases significantly. In addition, metallic copper particles accumulate in the emulsion. Such an emulsion becomes unsuitable for the drawing process; it is removed from the production cycle and, after the metallic copper has been separated, is pumped into pits.
The purpose of the present work was to find the optimal conditions for decomposing spent drawing emulsions with subsequent recovery of the oil and copper.
The following substances were tested for decomposing the emulsion: demulsifiers, copper sulfate, caustic sodium, and sulfuric acid.
Of the demulsifiers used in domestic practice, only aminonitroparaffin (ANP) decomposes the emulsion. At an ANP consumption of 3 kg/m³ of spent emulsion, its complete decomposition occurs into copper soaps in the form of a green pasty mass, amounting by volume to about 20% of the entire initial emulsion, and a solution of sodium soap. The copper soaps readily float to the top and can be separated from the remaining solution.
Copper sulfate, at a consumption of 0.5 kg/m³ of spent emulsion, begins to decompose it into copper soaps and a solution containing copper. We carried out studies on decomposing emulsions with an etching solution containing 5.3 g/l Cu²⁺. At a consumption of 25 l/m³ of spent emulsion, about 20% copper soap is obtained, along with a solution in which the copper content was 2.5 g/l.
Both of these methods of decomposing the emulsion were carried out at a temperature of 18–20°C. Freshly spent emulsion has pH = 9. When the pH is raised to 10 (by adding caustic sodium) and the emulsion is heated to 70°C, it decomposes into copper and sodium soaps. In this method, unlike the first two, the separation of copper soaps proceeds slowly.
It should be noted that, as the spent emulsion is stored at room temperature, copper soaps float to the top. This process
is very prolonged; moreover, complete decomposition of the emulsion and separation of copper soaps does not occur even after 6 months of storage.
As is evident from the above, the use of ANP, copper sulfate, and alkali does not ensure the recovery of oil when decomposing the emulsion.
To separate oil from the spent emulsion, sulfuric acid was used. The effect on the rate of emulsion decomposition with oil separation was studied for the emulsion temperature, the sulfuric acid concentration, and the type of emulsion.
The decomposition time was counted from the moment the acid was added until the first droplets of oil appeared on the surface of the solution.
The copper content in the solutions after decomposition of the emulsion with sulfuric acid was determined by the iodometric method. It was found that the acid concentration has practically no effect on the rate of emulsion decomposition. It is advantageous, of course, to use a more concentrated acid, since in this case the solution will contain more copper. However, an excessively high concentration of sulfuric acid worsens the quality of the oil (it becomes dark). It was found experimentally that the best results in terms of oil quality are obtained with 20% sulfuric acid.
The decomposition time of the emulsion as a function of its type is shown in Table 1. It can be seen that copper soaps decompose very slowly, but at the same time they ensure a considerable concentration of copper in the solution (a 20-fold increase).
Table 1
Dependence of the decomposition time of the spent emulsion on its type
(temperature 20°C, sulfuric acid concentration 20%)
| Type of emulsion | Decomposition time, h | Copper content in solution, g/l |
|---|---|---|
| Freshly spent | 0.2 | 1.20 |
| Emulsion with traces of copper soap | 3.0 | 1.48 |
| Copper soap | 48.0 | 12.0 |
With an increase in temperature, the decomposition rate of the freshly spent emulsion increases (Table 2), from 12 min at a temperature of 20°C to 3 min at 40°C and 2 min at 80°C.
Table 2
Dependence of the decomposition time of a freshly spent emulsion on temperature
(sulfuric acid concentration 20%)
| Emulsion temperature, °C | Decomposition time, min | Copper content in solution, g/l |
|---|---|---|
| 20 | 12 | 1.2 |
| 40 | 3 | 1.15 |
| 80 | 2 | 1.35 |
Thus, as a result of the work carried out, it was found that the demulsifier ANP, copper sulfate, or alkali can be used to separate copper soap from the emulsion. This ensures a considerable concentration of copper in the solution after decomposition of the soap. Oil can be separated from the emulsion and from copper soap by sulfuric acid.
The optimum conditions for the interaction of the acid with the emulsion have been found, under which good oil quality and a high rate of decomposition are ensured. The consumption of 96% \( \mathrm{H_2SO_4} \) is 20 kg per 1 m³ of emulsion. Copper can be recovered from the solution on iron turnings by the cementation method.