Magnetic Beneficiation of Goryachegorsk Nepheline-Bearing Rocks

A. V. Petrov, S. S. Nesterenko

(Presented by the scientific seminar of the Department of Silicate Technology)

Along with the enormous deposits of nepheline rocks in Krasnoyarsk Krai, suitable for use as ore at the Achinsk Aluminum Combine, there is a large quantity of substandard nepheline-bearing rocks which, after appropriate processing, can be used as raw material for the glass and ceramic industries [1, 2].

In the laboratory of the Department of Silicate Technology, nepheline-bearing rocks from ten representative samples of theralite syenites and bereshites, selected over a large area of two deposits—the “Goryachegorsk Massif” and “Andryushkina Rechka”—are being studied. The rocks under study are similar in chemical and mineralogical composition, but differ in structure [3]. The former have a medium-grained holocrystalline structure. The principal minerals are represented by nepheline (30–70%), plagioclase (10–25%), and pyroxene in the form of titanaugite and augite (10–25%). The nepheline segregations are usually disrupted to one degree or another. Among the secondary minerals after it, cancrinite, sericite, and hydronepheline predominate; sodalite, libenerite, and carbonates are encountered. Fresh crystals are characteristic of plagioclase. Its composition varies from labradorite to albite; among secondary minerals, sericite predominates. Pyroxenes occur as irregular grains of titanaugite, more rarely augite; sometimes they are completely replaced by uralitic hornblende. Titanaugite grains are also replaced by magnetite and biotite. Among accessory minerals, apatite and titanomagnetite have been found.

Bereshites have a porphyritic texture and consist of phenocrysts represented by nepheline (≈70%), partly by plagioclase and augite, and of a fine-grained groundmass consisting of plagioclase, augite, and hornblende.

According to the data of chemical analysis (Table 1), the raw material studied belongs to the group of moderately alkaline, but strongly ferruginous nepheline-bearing rocks.

The considerable content of iron compounds limits their use in glass and ceramic production; however, the mineralogical composition shows that the iron oxides are not distributed throughout the entire rock, but belong to minerals of the titanaugite and ilmenite group, which makes it possible, by means of electromagnetic separation, to separate them from the light-colored minerals nepheline and feldspar.

For beneficiation by the method of electromagnetic separation, the initial samples were crushed in a laboratory-type jaw crusher to a grain size of 2–5 mm; then part of them was subjected to final grinding in a vibratory mill. The rock thus prepared was screened into fractions on sieves with openings of: 3, 2, 1, 0.6, 0.25, 0.086, and 0.075 mm.

Table 1

Percentage variation in the chemical compositions of nepheline-bearing rocks of the Goryachegorsk deposit

Each fraction was freed of fine particles by washing on a sieve, after which it was dried to constant weight at a temperature of 110°. Charges corresponding to a given fraction were beneficiated on an electromagnetic separator under the conditions \(I=10_a\), \(U=70_v\), according to the following scheme [4, 5].

The beneficiation results are presented in Table 2. The data in the table show that, as the grain size decreases, the yield of the beneficiated product increases. At the same time, the quality of its purification from iron oxides also improves, as reflected in Tables 3 and 4.

Table 2

Dependence of concentrate yield on grain size

During separation of the fraction smaller than 0.075 mm, the yield of the beneficiated product decreases sharply and does not exceed 19%. Large losses of nepheline

are explained by its being carried into the magnetic fraction. In this connection, the rock under study should be crushed before beneficiation to a size of 0.075 mm. To determine the optimal separation regime,

Table 3

Chemical composition of the beneficiated fractions of nepheline rock

Table 4

Chemical composition of the magnetic fractions

Table 5

Dependence of the yield of the beneficiated fraction on the separation regime

the fraction 0.25—0.086 mm was beneficiated at various magnetic-field intensities. An increase in field intensity entails a decrease in the yield of the beneficiated product (Table 5) as a result of a decrease in the content of dark-colored minerals.

As the study shows, to obtain the maximum purity of the concentrate, cleaning must be carried out at a magnetic-field intensity of 12,000 oersted.

The dependence of the yield of the beneficiated product on the number of separation stages was also studied. During recleaning of the concentrate, the Fe₂O₃ content decreases to 0.91% (Table 6).

Table 6

Chemical composition of the beneficiated fraction of nepheline rock after two-stage separation

A further increase in the number of separation stages does not lead to any appreciable improvement in the results; therefore, double separation is recommended for beneficiation.

Analyzing the beneficiation product, one may conclude that, in terms of the content of iron oxides, the concentrate is a material suitable for the ceramic and glass industries. The nepheline content in it is 71%, and the amount of alkalis reaches 10%; thus, after electromagnetic separation, the substandard nepheline-bearing rock becomes a good complex raw material from which high-alumina alkali glasses and facing ceramics can be produced, as confirmed by preliminary studies.

In addition, the alumina content in the concentrate increases to 31%. This makes it possible to classify it as standard raw material for processing into alumina.

REFERENCES

1. I. K. Bazhenov. Nepheline rocks of Mount Goryachaya. Materials on the Geology of Western Siberia, Issue 64, Gosgeoltekhizdat, 1963.

2. I. K. Bazhenov. Effusive and vein complex of alkaline and nepheline-alkaline rocks of the eastern slope of the Kuznetsk Alatau. Materials on the Geology of Western Siberia, Issue 64, Gosgeoltekhizdat, 1963.

3. I. V. Luchitskii. Nepheline ores and alkaline nepheline-bearing rocks of the south of Krasnoyarsk Krai. In: Mineral Resources of Krasnoyarsk Krai. Publishing House of the USSR Academy of Sciences, 1959.

4. R. B. Shapiro. Beneficiation of nepheline-syenite rock of the Uzhur deposit. In: Raw-Material Resources of Light Metals of Eastern Siberia, vol. II, Publishing House of the USSR Academy of Sciences, 1958.

5. I. N. Kitler, Yu. A. Lainer. Nephelines: a complex raw material for the aluminum industry. Metallurgizdat, 1962.