SovietRxiv

Roasting-magnetic refining of chromium-bearing electrocorundum

G. S. Frolova, L. V. Sokolov, V. V. Koydin, V. M. Vittogin
Submitted 1973 | SovietRxiv: ru-197301.12849 | Translated from Russian

Abstract Generated abstract

This study examines roasting and magnetic beneficiation as a means of purifying chromium electrocorundum grain products containing white electrocorundum, metallic chromium and iron, carbides, and other impurities. Samples of the impurity-rich +0.16 mm fraction were oxidatively roasted at varying temperatures and holding times, then separated at different magnetic-field intensities, with the magnetic fractions assessed by microanalytical methods. The results indicate that roasting before magnetic separation can convert some initially nonmagnetic contaminants into magnetically susceptible forms, improving their removal while limiting loss of useful electrocorundum. Optimum conditions were identified as roasting at 500°C for 30 minutes followed by magnetic separation at 3500 oersteds, and these conditions were supported by tests on several additional grinding-powder fractions.

Full Text

Roasting-Magnetic Refining of Chromium Electrocorundum

G. S. Frolova, L. V. Sokolov, V. V. Koydin, V. M. Vittogin

(Presented by the scientific seminar of the Department of General Chemical Technology)

Chromium electrocorundum (CE), produced at the Yurginsk Abrasive Plant, has a highly heterogeneous composition. Along with grains of CE itself, the fractions contain, in significant quantities, particles of white electrocorundum (WE), metallic chromium and iron, metal carbides, and other impurities.

Mineralogical analysis [1] of the finished product showed that the amount of impurities in the abrasive grain varies from 3.2 to 11%.

The purpose of the present work is to remove, as completely as possible, the indicated contaminants from grain products by means of roasting-magnetic beneficiation.

The process of heat treatment of electrocorundum has been studied in works [2–9], which note the considerable influence of oxidizing roasting on increasing the mechanical strength, microhardness, and brittleness of the grain. With such treatment of electrocorundum grains, the formation of cracks is observed, which destroy large grains, as well as the sintering of fine grain classes.

In all these studies, the concentrate after magnetic separation was subjected to heat treatment. If, however, oxidizing roasting is carried out before magnetic separation, then certain nonmagnetic impurities, in particular particles of metallic chromium, will pass into a magnetically susceptible form. Thus, during subsequent magnetic separation and at a sufficiently high magnetic-field intensity, the indicated impurities will pass into the magnetic fraction. Consequently, oxidative treatment will have a positive effect not only on the quality of the grain, but will also make it possible to convert nonmagnetic impurities into their magnetic form.

To determine the optimum conditions for roast–magnetic concentration, the \(+0.16\) mm fraction was used, as it contained the greatest amount of impurities (11%).

Heat treatment was carried out as follows: a 25 g weighed portion of EC was placed in a porcelain cup and held in a muffle furnace for 10, 30, 60, and 120 minutes at temperatures of 400, 500, 600, 700, 800, and 900°C. After this, the samples were concentrated on a laboratory single-roller separator of type 138°-C, at magnetic-field intensities of 700, 3500, 7500, and 11000 oersteds. The results of the magnetic separation performed showed that the yield of the magnetic fraction is greater the higher the heat-treatment temperature, the holding time of the sample in the furnace, and the field intensity. However, at the same time the entrainment of EC with the magnetic fraction also increases. Consequently, the objective of the study was to find such optimum conditions under which the maximum yield of the magnetic fraction would be obtained with minimum entrainment of EC.

A quantitative microanalytical analysis of the magnetic fractions obtained was then carried out; its results are presented in the table.

From the analysis data it may be concluded that the best results are obtained at a temperature of 500°C, a heat-treatment time of 30 min, and concentration of the calcined product at a magnetic-field intensity equal to 3500 oersteds.

Subsequently, the possibility was investigated of applying the optimum conditions obtained to the thermal treatment of other EC grinding-powder fractions, Nos. 12, 20, 25, and 32.

The results of microanalytical determinations of the magnetic fractions of these products confirm the heat-treatment conditions previously found to be optimum for grinding powder No. 16.

On the basis of the work performed, the following conclusions may be drawn:

  1. The expediency has been established of oxidizing heat treatment of granular products, which makes it possible to convert nonmagnetic impurities into a magnetically susceptible form, which in turn permits, during subsequent magnetic separation, the production of a purer product.

  2. It has been determined that the optimum conditions for oxidizing treatment are: a temperature of 500°C, a treatment duration of 30 min, and subsequent separation at a magnetic-field intensity equal to 3500 oersteds.

  3. In order to intensify production, the oxidizing treatment of EC grinding powder should be carried out in a fluidized bed.

Table

min Phase °C 750 Oe, 400 750 Oe, 500 750 Oe, 600 750 Oe, 700 3500 Oe, 400 3500 Oe, 500 3500 Oe, 600 3500 Oe, 700 7500 Oe, 400 7500 Oe, 500 7500 Oe, 600 7500 Oe, 700
10 Fe–C, carbides 46,48 59,47 44,86 52,28 55,34 54,09 42,23 48,66 38,46 39,05 41,24 41,08
10 $Fe_2O_3$ - 10,95 7,60 2,29 - 10,40 7,26 5,99 - 6,95 6,46 7,16
10 $Cr_2O_3$ - 1,18 4,98 0,51 - 1,57 1,44 1,49 - 0,52 1,31 0,73
10 CE 53,52 28,40 42,56 44,92 44,66 33,94 49,07 43,86 61,54 53,48 50,99 51,08
30 Fe–C, carbides 39,58 64,72 56,59 62,13 42,55 66,06 47,62 46,67 33,35 43,13 30,58 37,63
30 $Fe_2O_3$ - 5,96 9,36 2,10 - 7,61 4,69 5,46 - 10,09 7,94 5,45
30 $Cr_2O_3$ - 0,41 1,20 1,52 - 1,71 0,73 2,10 - 1,15 2,95 3,61
30 CE 60,42 28,91 32,91 34,25 57,45 24,62 46,96 45,59 66,95 45,63 58,53 53,31
60 Fe–C, carbides 46,64 63,13 66,70 43,91 43,96 59,93 50,60 39,35 31,11 35,89 29,21 26,76
60 $Fe_2O_3$ - 8,70 3,98 4,89 - 8,38 6,12 9,07 - 7,06 5,55 6,46
60 $Cr_2O_3$ - 2,06 2,25 0,86 - 0,53 0,61 0,72 - 0,65 0,57 1,69
60 CE 53,36 26,11 27,07 50,34 56,04 31,11 42,67 50,86 68,89 56,40 64,67 65,09
120 Fe–C, carbides 43,03 60,25 53,96 49,12 39,97 55,62 51,10 31,32 44,61 36,75 32,92 35,39
120 $Fe_2O_3$ - 5,75 3,84 2,08 - 8,15 7,31 8,82 - 10,00 3,01 11,05
120 $Cr_2O_3$ - 0,96 0,79 - - 1,46 1,14 1,17 - 0,50 0,69 0,71
120 CE 56,97 33,04 41,42 49,80 60,03 34,77 40,45 58,69 55,39 52,75 63,38 6,85

References

  1. Methods for Studying Sedimentary Rocks. Edited by N. M. Strakhov, Vol. I, Gospolittekhizdat, 1957.

  2. V. A. Rybakov. Introduction into industry of a new scheme for processing electrocorundum. In: Abrasives, Issue 3, Moscow, TsBTI, 1952.

  3. N. E. Filonenko. Anomalous expansion of electrocorundum. In: Abrasives, Issue 5, Moscow, TsBTI, 1952.

  4. M. V. Kamentsev. Questions of the quality of normal electrocorundum. In: Abrasives, Issue 6, Moscow, TsBTI, 1953.

  5. M. I. Fedotov. Production of powders from monocrystalline corundum. In: Abrasives, Issue 18, Moscow, TsBTI, 1957.

  6. S. I. Khitrik, M. I. Gasik, E. A. Vukolov. Investigation of chlorinating roasting of electrocorundum grain. In: Abrasives, Issue 3, Moscow, TsBTI, 1966.

  7. Turnovec Ivan. Telepna roctaznost brusnych zrn elektrit a 96. “Sklar a keramik”. 1969, 19, No. 1, 14–16.

  8. J. Patzak, K. Wahleben, H. R. Müller. Studien zu verunreinigungen in elektrokorunden. “Ber. Dtsch. keram. Ges.” 1969, 46, No. 3, 120–125.

  9. F. F. Lange, T. K. Supta. Crack healing by heat treatment. “J. Am. Ceram. Soc.” 1970, 53, No. 1, 54–55.

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[v1] 1973

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Roasting-magnetic refining of chromium-bearing electrocorundum