— 0.14; \(Al_2O_3\) — 0.11; \(TiO_2\) — 0.07; \(MnO\) — 0.10; \(CaO\) and \(MgO\) — 0.12; the total impurity content is 0.54%.

The concentrate obtained is suitable for producing the highest grades of powdered iron and for the manufacture of storage batteries. At the Sulin Metallurgical Plant the concentrate was reduced to powdered iron, which in purity surpasses the analogous product of foreign firms. A batch of powdered iron was sent to the Volga Automobile Plant for the manufacture of experimental automobile parts.

The results obtained by no means exhaust the possibilities of the autoclave–alkaline method. Using equation (3), cited above, it is not difficult to show that increasing the leaching temperature to \(220^\circ C\) will make it possible to bring the residual \(SiO_2\) content in the ore to 0.012% and, correspondingly, to reduce the content of other impurities. Consequently, in the industrial use of the autoclave–alkaline method for purifying magnetite ores, it should be recommended that the leaching process be carried out at a higher temperature.

Literature

1. N. A. Vozova, L. L. Kuz’min, Izvestiya VUZov. “Khimiya i khim. tekhnologiya”, 8, 5, 623, 1965.

2. N. P. Kurin, N. F. Stas’. ZhPKh, 44, 10, 2251, 1971; 44, 8, 1710, 1970.

INDUSTRIAL TESTING OF THE AUTOCLAVE–ALKALINE METHOD FOR PURIFYING IRON ORES FROM IMPURITIES

N. P. Kurin, N. F. Stas’

In previous works /1, 2/ we showed that, when iron ores are treated with caustic soda solutions, silicon and aluminum impurities are leached into solution in the form of sodium silicate and aluminate. A sharp increase in the reaction rate is observed when the process is carried out at elevated temperatures in an autoclave: for example, at \(200^\circ C\) the leaching of silicon and aluminum oxides is completed in 15 minutes, at \(140^\circ C\) in 2.5 hours, whereas at \(100^\circ C\) the process continues for several days. The rate of the process at constant temperature is expressed by the equation of first-

in order, and with a smooth increase in temperature—by the equation

\[ 10^6 \cdot \lg \frac{2.3}{T^2} \lg \frac{1}{1-\alpha} = 11.37 - 4283/T . \tag{1} \]

When the autoclave-alkaline method was used under laboratory conditions, an iron-ore concentrate of such purity was obtained that it is unattainable by physico-mechanical beneficiation methods /2/.

Taking into account that a number of branches of industry—powder metallurgy, battery technology, certain chemical industries, and electronics—have an acute need for a high-grade concentrate, we continued research in this direction. Industrial tests were carried out with the aim of checking the autoclave-alkaline method under plant conditions, the reproducibility of the results when the size of the apparatus was increased, and also obtaining a large batch of concentrate.

The tests were conducted in an autoclave with a capacity of 1000 l, designed for a pressure of 2.5 atm. The autoclave was heated with “dead” steam, and mixing was by an anchor agitator at a speed of 50 rpm. Leaching was carried out according to the following procedure. First, a measured amount of sodium hydroxide solution was fed into the autoclave; then, with the agitator switched on, a specified amount of ore was charged through the hatch. After this, the hatch was hermetically closed and hot steam was fed into the autoclave jacket. After heating and holding at the specified temperature, the steam supply was shut off, mixing was turned off, the excess pressure was released, and the pulp was allowed to settle for 20 minutes. The decantate (alkali solution containing impurities extracted from the ore) was transferred by compressed air to a separate vessel, and hot condensate was poured into the autoclave for washing. Washing continued for approximately 15–20 minutes, after which the pulp was directed to a Nutsch filter. The filtered purified ore (concentrate) was additionally washed with hot condensate and dried.

In the tests, ore from the Krivoy Rog deposit was used, with an iron oxide content of 91.5%, silicon impurities calculated as \(SiO_2\)—5.3%, and aluminum impurities calculated as \(Al_2O_3\)—about 1.0%; the particle-size composition of the ore was maintained within 2 mm. Sodium hydroxide solutions were prepared from solid caustic soda of the “Diaphragm” grade (GOST 2263-59). In view of the low operating pressure of the autoclave, the process temperature could not be maintained above

142°C did not appear possible; in this connection, the duration of holding the ore in the autoclave was increased.

The parameters of the technological regime and the results for purification of the ore from silicon impurities are given in Table I.

Table I

Leaching regimes and indicators for the purification from silicon of Krivoy Rog iron ore in an industrial autoclave

As follows from Table I, despite the comparatively low process temperature (according to the results of laboratory studies, it is desirable to maintain the temperature at the level of 160–200°C / 2 /), the degree of extraction of silicon impurities in both operations was more than 98%.

Analyses of the ore and concentrate for the content of the main components and macroimpurities were carried out by spectral methods. The results of the analyses, given in Table 2, indicate that, despite the reduced temperatures, along with silicon the impurities of aluminum, magnesium, titanium, and manganese are leached.

It follows from Table 2 that the content of iron oxides in the resulting concentrate is 98.0%, silicon oxide is 0.08%, aluminum is 0.06%, calcium and magnesium are 0.37. The remaining 1.36% consists of oxides of alloying metals—titanium and manganese. An iron-ore concentrate of such high purity on an industrial

equipment was obtained for the first time.

Table 2

Chemical composition of Krivoy Rog ore before and after
treatment in an industrial autoclave

Sieve analysis and measurements of bulk density and specific surface showed that the structural characteristics of the ore after purification from impurities improve: the ore is noticeably comminuted, and the specific surface increases by 25–30%, which should facilitate the process of reducing the concentrate at plants producing iron powders and storage batteries.

The concentrate yield was 91.7% of the processed ore; leached impurities amounted to 6.6%, and mechanical losses to 1.7%. For comparison, it may be noted that the concentrate yield when flotation and magnetic separation methods are used is 70%.

The tests confirmed the possibility of industrial use of the autoclave–alkaline method for beneficiating iron ores. The observed degree of purification of the ore from silicon oxide in industrial and laboratory autoclaves at a temperature of 141.5°C was, respectively, 98.5 and 98.8% (calculated according to equation (1)). The agreement of the results of industrial and laboratory experiments indicates that a significant increase in the size of the appa-

is not accompanied by fundamental changes in the kinetic regularities governing the course of the processes of mass and heat transfer and chemical reaction. In this connection, the design of industrial equipment can be carried out on the basis of laboratory studies by the method of scale modeling.

References

1. N. P. Kurin, N. F. Stas’. ZhPKh, 44, 1710, 1971.
2. N. P. Kurin, N. F. Stas’. ZhPKh, 44, 2251, 1971.

RESEARCH IN THE FIELD OF THE CHEMISTRY OF CARBAZOLE DERIVATIVES. STUDY OF THE MECHANISM OF THE INTERACTION OF OLEFIN OXIDES WITH CARBAZOLES IN AN ALKALINE MEDIUM. II. KINETICS OF THE INTERACTION OF PROPYLENE OXIDE WITH NITROCARBAZOLES.

I. P. Zherebtsov, V. P. Lopatinskii, S. P. Yudina, V. V. Gal’tsova, T. N. Zorina

Earlier /1/ the kinetics of the reaction of 3-nitrocarbazole (3-NC) with propylene oxide under conditions of base catalysis was studied. It was shown that the reaction consists of several stages, the first of which is the ionization of 3-NC under the action of caustic potassium and the medium. In the second, rate-limiting stage, a trimolecular complex is formed, consisting of 3-NC, propylene oxide, and a proton-donor solvent (alcohol).

It was of interest to trace the behavior of nitrocarbazoles having both electron-acceptor and electron-donor substituents in the nucleus in this reaction at both stages. We studied the kinetics of the reaction in ethyl alcohol for the following nitrocarbazoles: 3-methyl-6-nitrocarbazole (3-M-6-NC), 3-chloro-6-nitrocarbazole (3-Cl-6-NC), 3-iodo-6-nitrocarbazole (3-I-6-NC), and 3,6-dinitrocarbazole (3,6-DNC).

All these compounds are weak acids which, upon ionization, can give, like 3-NC, colored anions, whose optical properties make it possible to use a photometric method to monitor the unreacted nitrocarbazole /2/.

The $pK_a$ values of the nitrocarbazoles as acids are given in the table.