Studies on the Decomposition of Spent Drawing Emulsion Using Inorganic Salts
Abstract Generated abstract
This study examines alternatives to direct sulfuric acid treatment for decomposing spent emulsions from copper rod drawing, a process that consumes substantial acid and yields dilute copper sulfate solutions that are difficult to process. The authors investigate preliminary decomposition using a copper sulfate and sulfuric acid pickling solution, as well as sodium chloride, and compare their effects on phase separation, reagent consumption, and copper concentration. The pickling solution reduces sulfuric acid use by about threefold and produces copper sulfate solutions containing 7 to 9 g/L copper, while sodium chloride at 18 kg/m³ decomposes the emulsion within 20 minutes at 17°C and separates an oil and soap phase from a copper-free saline aqueous phase.
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Studies on the Decomposition of Spent Drawing Emulsion Using Inorganic Salts
S. A. Babenko, N. T. Bolotkina, N. M. Denisova
(Presented by the scientific seminar of the Departments of PMAChP and OChT)
The spent emulsion obtained as a result of drawing copper rod stock is readily decomposed by sulfuric acid. At a consumption of 15 kg/m³ of emulsion, copper soaps, interacting with sulfuric acid, form copper sulfate and fatty acids. Part of the sulfuric acid, by destroying the sodium soaps, promotes the coalescence of oil droplets. Mixing with the fatty acids, the oil rises to the surface. The copper remains in solution in the form of copper sulfate, the copper content in which does not exceed 1.5 g/L. The ratio of oil to copper sulfate solution is 1:20–1:25. Thus, sulfuric-acid decomposition of spent emulsion makes it possible to obtain oil that can be reused for preparing emulsion. However, this method is not without drawbacks.
First, there is a considerable consumption of sulfuric acid. Specially conducted studies showed that the liberation of free fatty acid occurs at pH below 3. Since the spent emulsion contains more than 90% water, the greater part of the sulfuric acid is consumed in creating the required pH.
Second, the copper present in the spent emulsion in small quantities in the form of copper soap and sludge, upon decomposition of the emulsion with 20% sulfuric acid, forms a dilute solution of copper sulfate.
The use of more concentrated sulfuric acid is undesirable, since the quality of the separated oil deteriorates.
The recovery of copper from the dilute solution presents considerable difficulty.
Third, the oils separated during sulfuric-acid decomposition are partly present in combination with copper and sodium soaps in the form of amorphous precipitates called foots.
In the present work, in order to eliminate the indicated shortcomings, the influence of copper sulfate and common salt on the preliminary decomposition of spent emulsion was investigated.
For the work, a mixture of copper sulfate with sulfuric acid was used, which is formed in the pickling bath where the rod stock is treated before drawing. As a result of the studies it was found that the optimum consumption of pickling solution ($\mathrm{Cu}^{2+}$—5.2 g/L) for decomposition of spent emulsion and separation of copper soap is 20 L/m³. The copper soaps formed in this process, containing about
10% of the emulsion being treated can be decomposed with sulfuric acid. Its consumption, in comparison with the usual method, is reduced threefold. In this case the copper sulfate solutions contain 7–9 g/l of copper.
Common salt (Table 1), in an amount of 18 kg/m³ of emulsion, leads to decomposition of the spent emulsion within 20 min. These experiments were carried out at a temperature of 17°C. With an increase in temperature to
Table 1
Effect of common-salt consumption
on the decomposition of spent emulsion
(temperature 17°C, pH = 8.0)
| Common-salt consumption, kg/m³ | 8 | 12 | 16 | 18 |
|---|---|---|---|---|
| Decomposition time, min | no decomposition | 73 | 48 | 20 |
50°C, the rate of emulsion decomposition increases somewhat and is 16 min. Decomposition of the emulsion under the action of common salt is expressed in the fact that oil and sodium and copper soaps rise to the top. The mixture of these substances constitutes about 15% of the total volume of the spent emulsion. The remainder is a solution of common salt in water, which can be discharged into the sewer system.
Thus, preliminary decomposition of the spent emulsion with etching solution makes it possible to reduce sulfuric acid consumption threefold and to obtain a copper sulfate solution with a copper concentration 4–6 times higher than with acid decomposition alone. Common salt makes it possible to obtain a final decomposition product that contains no copper, thereby ensuring substantial removal of the dispersed phase of the emulsion from further treatment.