RU2241672C2 - METHOD OF PRODUCING LOW-ALKALINITY FINE α-ALUMINA - Google Patents

Abstract

FIELD: inorganic compounds technology.

SUBSTANCE: low-alkalinity fine α-alumina is obtained from recycled calcination furnace electrofilter dust by way of leaching, filtration, and calcination, in particular in presence of mineralizers. Recycled dust is leached at 80^оС and heating is accomplished in two steps: from 20 to 800^оС at the rate 150^оС/h and from 800 to 1200^оС at the rate 250^оС/h.

EFFECT: simplified process, reduced power consumption, and enabled production of alumina with uniform granulometric composition.

2 cl, 2 tbl

Description

The invention relates to the aluminum industry, and in particular to methods for the production of alumina.

A known method of producing low-alkaline α-alumina, consisting in the fact that alumina is repeatedly calcined and leached [1]. Further, to obtain finely dispersed alumina, grinding in ball or vibratory mills is necessary.

The disadvantage of this method is the complexity of the hardware-technological scheme, the impossibility of obtaining alumina of the desired degree of alkalinity and the need to introduce a stage of fine grinding, which is associated with significant energy costs.

The closest technical solution, selected as a prototype, is a method for producing low-alkaline α-alumina from recycled technological dust from calcination furnaces. The trapped alumina dust is separated from the main stream and leached with water at W: T = 3: 1 by repulping and stirring for 0.5-1 hours at a temperature of 85-90 ° C and atmospheric pressure. Then the suspension is separated on the filter, the precipitate is calcined at a temperature of 1200-1250 ° C. Get a product with an alkali content of 0.1% [2].

The disadvantage of this method is the use of recycled dust of various stages of dust collection. When processing such alumina raw materials, α-alumina of uneven particle size distribution is obtained. Therefore, to transfer such alumina to a finely divided state, it is necessary to introduce a grinding stage.

The technical result of the invention is to simplify the process, reduce energy costs and obtain alumina uniform particle size distribution.

The specified technical result is achieved by the fact that in the method of producing finely divided finely dispersed α-alumina from recycled dust of electrostatic precipitators of calcination furnaces by leaching, filtering and calcining at a temperature of 1200 ° C, it is new that recycled dust is leached at a temperature of 80 ° C and heating is carried out in two stages: from 20 ° C to 800 ° C at a speed of 150 ° C / h, from 800 ° C to 1200 ° C at a speed of 250 ° C / h, and recycle dust is calcined in the presence of mineralizers.

The dust of electrostatic precipitators of calcination furnaces is characterized by a high content of alkaline compounds (Na ₂ O + K ₂ O = 0.6-0.8%) and a finely dispersed structure (particle size less than 20 microns, average particle size 5-7 microns).

As a result of the use of recycled dust from electrostatic precipitators of calcination furnaces as alumina raw materials to obtain a finely alkaline fine-dispersed α-alumina, the grinding stage is eliminated, which leads to lower energy costs.

Table 1 shows the chemical composition of the initial dust of the electrostatic precipitators of calcination furnaces in comparison with the composition of the dust of electrostatic precipitators washed from alkali at a temperature of 80 ° C, the ratio W: T = 3: 1 and the duration of 15 minutes

Washing was carried out in a laboratory stirrer with automatic temperature stabilization with constant stirring. After washing, the dust was filtered off and dried in an oven at a temperature of 100 ° C.

The washed dust was calcined in a laboratory silica shaft furnace at a temperature of 1200 ° C in the following mode: from 20 ° C to 800 ° C, heating rate of 150 ° C / h, from 800 ° C to 1200 ° C, heating rate of 250 ° C / h, holding time at a given temperature of 30 minutes The samples were cooled together with the furnace and then analyzed for the content of α-phase and alkaline compounds. Before calcination, mineralizers were added to one of the samples, for example, A1F ₃ in the amount of 0.75% by weight of the sample.

The results of the experiment on the calcination of dust washed from alkali from electrostatic precipitators of calcination furnaces are given in table 2.

The powder after calcination consists of particles from 0.4 to 1 μm in size, the amount of submicron fraction increases significantly.

Implementation of the proposed method in an industrial environment is as follows: the captured alumina dust of electrostatic precipitators is separated from the main stream and leached in a mixer. Then the pulp is filtered and the precipitate is dried. Further, the precipitate is subjected to additional grinding and calcined.

An analysis of the experimental results showed that washing water with dust of electrostatic precipitators from alkali reduces the R ₂ O content from 0.58% to 0.23% (Table 1). Further calcination of electrostatic dust washed from alkali reduces the R ₂ O content from 0.23% to 0.16% (Table 2). The addition of AlF ₃ before calcination as a mineralizer reduces the alkali content from 0.23% to 0.074% (Table 2). The obtained alkalescent α-alumina has a particle size of from 0.4 to 1 μm with a significant amount of submicron fraction. Thus, the results confirm that the use of recycled dust from electrostatic precipitators of calcination furnaces as a raw material for the production of low-alkaline fine-dispersed α-alumina allows us to simplify the technological scheme and reduce energy costs. In addition, the removal of dust from electrostatic precipitators from the calcination process improves the physicochemical properties of metallurgical alumina.

Sources of information

1. Hanamirova A.A. Alumina and ways to reduce the content of impurities in it. Repl. ed. I.Z. Pevzner. - Yerevan publishing house of the Academy of Sciences of the ArmSSR, 1983, p.186.

2. A.S. 196752, MKI C 01 F 7/30, publ. 05/31/67, bull. No. 12 (prototype).

Claims (2)

1. A method of producing a fine alkaline fine α-alumina from recycled dust of electrostatic precipitators of calcination furnaces by leaching, filtering and calcining at a temperature of 1200 ° C, characterized in that the recycle dust is leached at a temperature of 80 ° C, and heating is carried out in two stages: from 20 ° C to 800 ° C at a rate of 150 ° C / h, from 800 ° C to 1200 ° C at a speed of 250 ° C / h. 2. A method of producing a small alkaline α-alumina according to claim 1, characterized in that the recycle dust is calcined in the presence of mineralizers.