SU1717537A1 - Process for pelletizing phosphate stock - Google Patents

Abstract

The invention relates to the technology of agglomeration of phosphate raw materials for the preparation of it for processing into phosphorus by electrothermal method. The aim of the invention is to increase the strength and yield of pellets during the processing of phosphate-niobium raw materials. The method consists in wrapping the raw material with a fraction content of minus 0.074 mm 81-95%, drying the pellets, heat treatment at 420-500 ° C. C for 4-16 minutes, followed by firing. 1 tab.

Description

The invention relates to the preparation of phosphate raw materials for smelting reduction, in particular to the production of pellets from niobium phosphate raw materials.

A feature of phosphate-niobium raw materials, such as ores, sludge enrichment, is the presence of clay minerals and a high content of oxidized iron, represented in the form of goethite and hydrohetite, which contain a significant amount of chemically bound water. Therefore, obtaining pellets from phosphate-niobium raw materials according to the technology adopted for phosphate raw materials gives low results both in strength of the burned pellets and in yield of the suitable product.

The closest in technical essence to the present invention is a method of agglomeration of phosphate raw materials, including its rounding up with a fraction of minus 0; 074 mm in the feedstock 60-70 wt.%, Drying the pellets in three stages when feeding coolant in the first and third stages

from top to bottom, and the second from bottom to top with a filtration rate according to the stage of 0.3-0.5; 1.45-1.55; 1.3-1.4 Nm3 / m2-sec for 1-2, 13-14 and 3-4 min, respectively, and temperatures in stages 180-200; 200-220; 200-220 ° C

The disadvantage of this method in obtaining pellets from phosphate-niobium raw material is the impossibility of removing chemically bound water at a given drying temperature, as a result of which it will be intensively released during the burning step. Aetol leads to the formation of microcracks in the pellets, the destruction of part of them. Considering that when using this method, niobium phosphate raw materials will be fed to the rounding with a low content of minus 0.074 mm, the pellets obtained will have low strength. The yield of the product will also decrease.

The aim of the invention is to increase the strength of pellets and their output during the processing of phosphate-niobium raw materials.

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The feed of niobium phosphate raw materials for rounding with a fraction of minus 0.074 mm of 81-95 wt.% Is due to the need to obtain a pellet structure that allows free removal of chemically bound water from them without reducing the strength of the pellets. When the content of this fraction is more than 95% by weight, due to the presence of clay minerals in the raw material, represented by actinolite and montmorillonite, continuous zones are formed in the structure of the pellets that are difficult to permeable to water and water vapor. As a result, during thermal treatment, microcracks are formed in the pellets, which reduces the strength of the pellets and the yield of a suitable product. When the content of the fraction minus 0.074 mm is less than 81 wt.%, The pellets from the phosphate-niobium raw material are loose, the structure of the pellet is not sufficiently compacted when pelleted, which reduces their strength in the raw and then in the baked state.

To obtain pellets, raw materials are used that are presented in the form of a mixture of sludge enrichment of phosphate-niobium ore and directly ore.

The fraction fraction minus 0.074 mm in niobium phosphate sludge is 99 wt.% And cannot be reduced during the enrichment process, since this will be associated with a decrease in the yield of the main target product — niobium concentrate. However, this fractional composition is not optimal. to obtain pellets.

In order to increase the α-content of the minus 0.074 mm fraction in the phosphate-niobium raw material to 81–95 wt.%, The granular fraction of the phosphate-niobium ore is added to the sludge. The drying of pellets from phosphate-niobium raw material to remove the water of the physicomechanical form of the bond is carried out at 300 ° C (taking into account that the shock temperature for them is 320-340 ° C). Heat treatment at 420–500 ° C for 4–16 min before firing is necessary to remove chemically bound water from the sludge.

When heat treatment is performed at a temperature of less than 420 ° C, the chemically bound water is not completely removed from goethite and hydrohetite, and at a temperature of more than 500 ° C, it is released with a high intensity, which leads to the appearance of microcracks in the pellets, and hence their reduction strength in the calcined state and the yield of a suitable product.

The duration of heat treatment for 4–16 min is due to the fact that with a shorter time the process of removing chemically bound water does not have time to go to the end even at the maximum allowable temperature of 500 ° C, and the increase in time is not advisable due to the fact that by 17

In a minute, the chemically bound water is removed almost completely and at a minimum temperature of 420 ° C.

Thus, it is the combined combination of the proposed fractional composition of phosphate-niobium raw material before pelleting and the mode of heat treatment of the pellets before roasting can remove chemically bound water without disturbing the structure of the pellets, increase

pellet strength and yield. In addition, the proposed method allows to engage in the processing of a new type of phosphate raw material. The processing of this raw material gives a lower yield of yellow phosphorus compared to the traditional one due to the high content of iron oxides in it. However, this decrease overlaps with the production of a new target product — a niobium-containing ferrophosphorus.

In all experiments, phosphate-niobium sludge was used to obtain pellets with a fraction of minus

0.074 mm 99.2%, containing, in wt.%: P20s 20.5; Nb20s 0.98; SiOa 14.8; CaO 25.4; MgO 3.8; , 4; tReob 11.9 (16.9% Fe20s); MPO 1.1; ppt 8.3; impurities 2.72.

To adjust the fractional composition of the phosphate-niobium raw material, before applying it to the rounding, the granular fractions of the phosphate-niobium ore with a particle size of 0.14-0.074 mm were used for the experiment (by a known method) and grain size

0.315-0.074 mm for experiments of the same chemical composition according to the proposed method. Mixing sludge and ore granular fraction produced in a drum mixer, pelleting on a plate

a granulator with a diameter of 1.0 m. Drying, heat treatment, and calcination of pellets were carried out on a pan firing installation, which allows to control the temperature and filtration rate of the coolant. Strength

The calcined pellets and the yield of the product were determined by standard procedures.

PRI me R 1 (prototype). 10.5 kg 5 Sludge is mixed with 4.5 kg of the ore granular fraction. The resulting 15.0 kg of phosphate-niobium sludge with a friction content of minus 0.074 mm 69.5 wt.% Pelle, the obtained pellets are treated in the following mode:

drying at 190 ° C for 1.5 minutes with the flow of coolant from top to bottom;

drying at 210 ° C for 14 minutes when the coolant is supplied from the bottom up;

drying at 210 ° C for 4 minutes with the flow of coolant from top to bottom;

roasting at 1100 ° C for 20 min.

The pellets were calcined at a temperature lower than that proposed in the prototype, since sintering and melting of phosphate-niobium pellets occurs at the calcining temperature above 1100 ° C.

After sbling, 13.7 kg of pellets are obtained. The strength of the pellets was 110 kg / C, the yield of the product was 85%.

PRI mme R 2. 14.36 kg of sludge is mixed with 0.64 kg of the granular fraction of ore. The resulting 15.0 kg of phosphate-niobium sludge with the content of the fraction minus 0.074 mm 95 wt.% Pelle, the obtained pellets are treated in the following mode:

drying at 300 ° C for 20 minutes;

heat treatment at 420 ° C for 16 min;

roasting at 1100 ° C for 20 min.

After firing, 13.7 kg of pellets are obtained. The strength of the pellets was 140 kg / ok, the yield of the product was 89.5%.

PRI me R 3. 13.3 kg of sludge is mixed with 1.7 kg of the granular fraction of ore. The resulting 15.0 kg of phosphate-niobium sludge with the content of the fraction minus 0.074 mm 88 wt.% Pelle, the obtained pellets are treated in the following mode:

drying at 300 ° C for 20 minutes;

heat treatment at 460 ° C for 10 minutes;

roasting at 1100 ° C for 20 min.

After firing, 13.7 kg of pellets are obtained. The strength of the pellets was 140 kg / ok, the yield of the product was 90% (according to the prototype 110 kg / ok and 85%, respectively).

PRI me R 4. 12.25 kg of sludge is mixed with 2.75 kg of the granular fraction of ore. The resulting 15.0 kg of phosphate-niobium sludge with the content of the fraction minus 0.074 mm 81 wt.% Pelle, the obtained pellets are treated in the following mode:

drying at 300 ° C for 20 minutes;

heat treatment at 500 ° C for 4 min;

roasting at 1100 ° C for 20 min.

After firing, 13.7 kg are obtained. The strength of the pellets was 135 kg / ok, the yield of the product was 89% (according to the prototype 110 kg / ok and 85%, respectively).

EXAMPLE 5 (extreme values). 14.51 kg of sludge is mixed with 0.49 kg of the ore granular fraction. Received 15.0 kg of phosphate-niobium sludge with a content of 5 fractions minus 0.074 mm 96 wt.% Pelle, the obtained pellets are treated in the following mode:

drying at 300 ° C for 20 minutes; heat treatment at 400 ° C for 10 18 min;

roasting at 1100 ° C for 20 min. After the habitat, 13.7 kg of coils are obtained. The strength of the pellets was 110 kg / C, the yield of the product was 85.5%. 15 PRI me R 6. 11.95 kg of sludge is mixed with 3.05 kg of the ore granular fraction. The resulting 15.0 kg of phosphate-niobium sludge with a fraction content of minus 0.074 mm 79 wt.% Is coated, the pellets obtained are processed in the following mode:

drying at 300 ° C for 20 minutes; heat treatment at 510 ° C for 3 min;

roasting at 1100 ° C for 20 min. 5 After firing, 13.7 kg of pellets are obtained.

The strength of the pellets was 115 kg / ok, the yield of the product was 85.5%.

Example. 14.67 kg of sludge is mixed with 0.33 kg of the ore granular fraction. The resulting 15.0 kg of phosphate-niobium sludge with the content of the fraction minus 0.074 mm is 95 wt.% Pelleted, the obtained pellets are processed in the following;

drying at 300 ° C for 20 minutes; 5 heat treatment at 420 ° С for 16 min;

roasting at 1100 ° C for 20 min. After firing, 13.7 kg of coils are obtained. The strength of the pellets was 115 0 kg / ok, the yield of the product was 86.0%.

PRI me R 8. 12.25 kg of sludge is mixed with 2.75 kg of a granular fraction of ore. The resulting 15.0 kg of phosphate-niobium sludge with a fraction 5 content of minus 0.074 mm are coated with 81% by weight, the pellets obtained are processed in the following mode:

drying at 300 ° C for 20 minutes;

heat treatment at 520 ° C for 4 0 min;

roasting at 1100 ° C for 20 min.

After firing, 13.7 kg of pellets are obtained. The strength of the pellets was 110 kg / C, the yield of the product was 85%. 5 For convenience of comparison, the main results obtained in the experiments of examples 1-8 are tabulated.

The results of the experiments show that it is the combination of the proposed parameters for the fractional composition of the phosphate-niobium raw material before pelleting and the mode of heat treatment of the pellets before roasting allows to obtain a positive effect (experiments 2-4). When all parameters exceed the limiting values (experiments 5-6) or at least one of them (experiments 7-8), the obtained results are at the level of the prototype (experiment 1).

Thus, the proposed method allows the processing of phosphate-niobium raw materials to increase the strength

pellets up to 135-140 kg / ok and the yield of a suitable product is up to 89-90%.

Claims (1)

The invention of the process of agglomeration of phosphate raw materials, including its pelleting, drying and roasting of pellets, characterized in that, in order to increase the strength of pellets and their output during the processing of phosphate-niobium raw material, the feedstock is fed to the pellet containing fraction minus 0.074 mm 81 -95 wt.% And before calcining the pellets are subjected to heat treatment at 420-500 ° C for 4-16 minutes.