ON THE STABILITY OF XANTHATES UNDER THE ACTION OF ELECTRIC DISCHARGES

S. A. BABENKO, G. L. LOBANOVA

(Presented by the scientific seminar of the Department of Processes, Apparatuses, and Cybernetics of Chemical Production)

In the technological process of flotation concentration with selection of a collective concentrate, the stability of the layers of flotation reagents on the surface of minerals is of great importance. By smoothing out differences in the physicochemical properties of mineral surfaces, adsorption layers of flotation reagents hinder selection. The development of methods for destroying layers of flotation reagents on mineral surfaces has been the subject of studies by many authors. In the practice of flotation concentration of sulfide minerals, along with the classical method of destroying adsorption layers by the action of sodium sulfide, physical methods are beginning to be introduced, for example, the ultrasonic method [1].

We have studied the stability of xanthates under the action of electric pulsed discharges.

In the flotation of sulfide ores, potassium xanthates are used as a collector reagent:

\[ \mathrm{R{-}O{-}C} \begin{matrix} \mathrm{S}\\[-0.4em] \|\\[-0.4em] \mathrm{S{-}K} \end{matrix} \]

where \(R\) is the radical of the corresponding alcohol—ethyl, butyl, etc.

According to the chemical theory adopted as the working theory in selecting flotation reagents, potassium xanthate, chemisorbing on the surface of a sulfide mineral, enters into an ion-exchange reaction with the formation on the surface of the corresponding heavy-metal xanthate.

Heavy-metal xanthates are crystalline, poorly soluble, hydrophobic compounds. Under the action of oxygen they are oxidized with formation of dixanthogen. Modern studies prove that dixanthogen \((\mathrm{ROCSS})_2\) can also act as a collector. Consequently, in order to destroy the layers of flotation reagent on the surface of sulfide minerals, it is necessary either to create conditions for the decomposition of xanthates into the simplest compounds

\[ \mathrm{ROCSS}^{-} + \mathrm{HOH} \to \mathrm{ROH} + \mathrm{CS}_2 + \mathrm{OH}^{-}, \]

or to replace the xanthates of heavy metals on the surface of sulfide minerals with an even less soluble compound that does not possess hydrophobic properties.

For the experiments, xanthates of copper, zinc, and lead were synthesized by interaction of equivalent amounts of potassium xanthate and the corresponding acetic-acid salt of the heavy metal. The resulting precipitate was washed by decantation with water until negative …

Table 1

reaction for the heavy-metal ion, then with ethyl alcohol, and dried in a vacuum desiccator. The lead and copper xanthogenates were yellow; the zinc xanthogenate was white. Part of the synthesized preparation was used as a reference, and the other part was placed in a chamber with water and treated with high-voltage electric discharges. As the source of high-voltage electric pulsed discharges, [[unclear: text continues on next page]]

used an Arkad'ev–Marx generator. The electrodes built into the chamber were made of steel.

The state of copper, lead, and zinc xanthates before and after treatment was monitored by X-ray diffraction. In the pulp, decomposition products were determined: alkali by measuring the pH of the solution, and carbon disulfide by reaction with diethylamine and copper acetate [2].

The investigations carried out showed that copper, lead, and zinc xanthates, which were hydrophobic before treatment with high-voltage discharges, lose this property after treatment. After filtration of the xanthates treated by EIR and drying (under synthesis conditions), it was observed that the color of the salts had changed. Copper and lead xanthates acquired a reddish-brown shade, while zinc xanthate became gray. The pH of the pulp increases from 6.4 to 7–7.25. The test for carbon disulfide gives a positive reaction. These indicators confirm the possibility of decomposition of heavy-metal xanthates under conditions of treatment by electrical impulse discharges.

X-ray diffraction patterns obtained from copper xanthates (Table 1), lead (Table 2), and zinc (Table 3) without treatment and after treatment by electri-

Table 2

Table 3

… by electric pulse discharges show that qualitative changes have occurred in the structure of the samples.

The greatest structural changes are observed for copper xanthate. The principal intense line \(d/n\) 3,56 disappeared. In its place, two new principal lines appeared on the X-ray diffraction pattern at \(d/n\) 14,26 and 3,21. Some of the weak lines present before treatment of the copper xanthate disappeared on the X-ray diffraction pattern after treatment of the copper xanthate by electric pulse discharges. At the same time, a number of new lines appeared. Comparison of the obtained X-ray diffraction patterns with standards for CuO, Cu\(_2\)O, CuS, CuSO\(_4\), CuSO\(_4 \cdot\) H\(_2\)O, CuSO\(_4 \cdot\) 5H\(_2\)O, Cu\(_2\)SO\(_3 \cdot\) H\(_2\)O, and Cu makes it possible to suppose that, as a result of changes in the temperature of the suspension, light radiation, and ionization of gases accompanying the high-voltage electric discharge, decomposition of copper xanthate proceeds with the formation of copper sulfate.

The action of electrical pulsed discharges on zinc xanthate is accompanied by a decrease in the intensity of most lines on the X-ray diffraction pattern after treatment. The main intense line at \(d/n\ 12.627\) retains its position. A number of new, relatively weak lines appear. Comparison of the X-ray diffraction patterns with standards makes it possible to assume the formation of zinc sulfate.

Lead xanthate proved to be the most resistant to the action of electrical pulsed discharges. In the X-ray diffraction patterns before and after treatment of the xanthates, the intensity of the lines is weakened only slightly. Four relatively weak lines disappeared and several new ones appeared, of approximately the same intensity but with different \(d/n\). The new lines may be compared with a standard compound of the type \(\mathrm{PbO}\cdot\mathrm{PbSO}_4\).

On the basis of X-ray diffraction analysis, it may be concluded that xanthates of heavy metals decompose under the action of electrical pulsed discharges according to the same mechanism, with the liberation of carbon disulfide, alkali, and the sulfate of the corresponding metal.

The change in the structure of xanthate samples after treatment with electrical pulsed discharges and the decrease in their hydrophobic properties suggest the possibility of using high-voltage electrical pulsed discharges to destroy layers of flotation reagents on the surface of minerals.

REFERENCES

1. V. A. Glembotskii, A. E. Kolchemanova. Stability and Methods of Destruction of Adsorption Layers in Flotation. Moscow, Nauka Publishing House, 1967.

2. Yu. Yu. Lur’e, A. I. Rybnikova. Chemical Analysis of Industrial Waste Waters. Moscow, Khimiya Publishing House, 1966.