RU2445265C1 - Method of removing impurities from aluminate solutions - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to nonferrous metallurgy and specifically to the technology of removing impurities from aluminate solutions when producing alumina from aluminium-containing material, including bauxites. Impurities are removed from aluminate solutions by adding said solutions to sodium sulphide pulp which is diluted after bauxide leaching to concentration 0.20-0.34 g/dm³. The obtained pulp is treated with air in amount of 0.2-0.3 nm³/m³ diluted pulp in steady conditions. The pulp is held in a purifier in continuous flow while stirring. The pulp is then taken for thickening and subsequent separation of sludge. The obtained thickener discharge is taken for post-filtration. The ratio of the volume of diluted pulp in the purifier to that of the pulp flowing through the purifier is equal to 2.7:1.

EFFECT: achieving purification not only from zinc oxide, but also from organic substances - humic acids and silicon oxide.

2 tbl, 2 ex

Description

The invention relates to non-ferrous metallurgy, and in particular to a technology for the purification of aluminate solutions from impurities in the production of alumina from aluminum-containing raw materials, including bauxite.

The composition of bauxite used to obtain alumina contains a number of inorganic and organic compounds, which, when processed by the Bayer method, are converted into aluminate solutions and impair the quality of alumina. Many problems arise due to contamination of aluminate solutions with organic matter. Moreover, humic acids, which affect the decomposition of aluminate solutions, the dispersed composition of aluminum hydroxide, the precipitation of sludge and overgrowing equipment, and the strong foaming of solutions, have the greatest impact on the technology. As for inorganic compounds, there are a number of bauxite deposits containing up to 0.02-0.04% ZnO, most of which goes into aluminate solutions. As a result, it is not possible to obtain alumina containing not more than 125 g / t ZnO, which is its ultimate norm. Exceeding the zinc content in aluminate solutions requires its mandatory removal. Existing problems are resolved in a number of well-known technical solutions.

There is a method of purification of aluminate solutions from impurities by adding a sorbent based on magnesium compounds interacting with the solution to the aluminate solution, separating the sorbent from the purified solution, regenerating it by heat treatment, and reusing it (patent RU 2302995, IPC C01F 7/47, 2007). The sorbent is added to the aluminate solution in the form of an aqueous pulp with a concentration of 100-150 g / dm ³ in terms of magnesium oxide. The method allows to achieve a high degree of purification from organic substances (59-72%).

However, the method involves the purification of aluminate solutions from impurities of organic substances and iron oxide. In the case of using bauxite enriched with zinc compounds as a feedstock, when their content exceeds the norm prescribed by the standards, the known method cannot be used.

A known method of purification of aluminate solutions of the Bayer process from impurities, which involves the purification of solutions from zinc, by adding a special seed — ZnS zinc sulfide to the solution (US patent 4282191, IPC C01F 7/47, 1981). Seed is obtained by dissolving zinc oxide in an alkaline solution and adding sodium sulfide or sodium hydrosulfide to the sodium zincate solution. The amount of seed introduced is 5-40 g / m ³ . The content of zinc oxide in the aluminate solution after control filtration is less than 0.015 g / m ³ .

The disadvantages of the known method include, firstly, the need to create an additional processing line for seed, and secondly, the instability of the cleaning results, since during the cleaning process it is possible to dissolve a certain amount of the seed in the aluminate solution, thereby increasing the zinc content in it.

Closest to the proposed technical solution is a method of purifying aluminate solutions of the Bayer process from impurities by introducing Na ₂ S sodium sulfide into a diluted pulp, treating it with air in a quiet mode, then holding it in a cleaner for 3.5 hours with continuous flow and stirring of the pulp and directions for sludge separation and control filtration of the thickener discharge (Gan Guoyao, Yang Shijie, Lin Mingxing J. Light Metals, “Research of zinc-removal in the Bayer process”, 1999, p. 45-48) (prototype). As the source of bauxite in the known method using bauxite with a high content of zinc. During the cleaning process, the content of zinc oxide in the aluminate solution (depending on the initial content of zinc oxide) decreases either from 0.0485 g / l to 0.020 g / l, or from 0.0153 g / l to 0.0107 g / l, which accounts for 59% or 30%, respectively. Along with this, there is a slight decrease in the content of carbon organic compounds.

However, the degree of purification of aluminate solutions with a high zinc content is insufficient. To obtain alumina that meets the standards for the content of zinc oxide, a deeper degree of purification of aluminate solutions is required.

Thus, the authors were faced with the task of developing a method for purification of ZnO-enriched aluminate solutions of the Bayer process, ensuring their deep purification from zinc impurities. Along with this, it is desirable to ensure the purification of aluminate solutions from organic impurities, especially derivatives of humic acids.

The problem is solved in the proposed method for the purification of aluminate solutions from impurities, including adding sodium sulfide pulp to the pulp diluted after bauxite leaching, treating the pulp with air in a quiet mode, subsequent exposure to the purifier with continuous flow and mixing of the pulp, directing the pulp to thicken and then separate the slurry and control filtration of the thickener discharge, in which sodium sulfide is added to the diluted pulp to a concentration of 0.20-0.34 g / dm ³ , air is supplied in an amount of 0.2-0.3 nm ³ / m ³ diluted pulp, while the ratio of the volumes of diluted pulp located in the purifier and flowing through it is 2.7: 1.

Currently, from the patent and scientific literature there is no known method for purifying aluminate solutions of the Bayer process from impurities, in which technological parameters would be used within the limits proposed by the authors.

In the known prototype method, zinc is removed from aluminate solutions with a high zinc content (0.0485 g / l ZnO in diluted pulp), reducing its content to 0.0201 g / l ZnO, i.e., ~ 60%, which is insufficient subject to generally accepted standards. Obviously, this is due to insufficient sulfide background, which does not exceed 0.06-0.07 g / dm ³ . To provide a deeper degree of purification from zinc, the authors of the proposed technical solution conducted a series of experimental studies both in laboratory and in production conditions, which made it possible to establish technological process parameters that ensure a decrease in the zinc content in the aluminate solution to 0.013 g / l and lower. The results of laboratory studies of the concentration of ZnO in the liquid phases of bauxite leaching products obtained with various sulfide backgrounds are shown in table 1.

Table 1 The concentration of ZnO, g / DM ³ Boiled pulp Diluted pulp Aluminate solution The concentration of S ² -ion in a dilute pulp 0,060-0,099 g / DM ³ 0,062 0,029 0,027 The concentration of S ² -ion in a diluted pulp 0,100-0,150 g / DM ³ 0.059 0,020 0.017 The concentration of S ² -ion in a diluted pulp 0.16-0.22 g / DM ³ 0,043 0.016 0.013 The concentration of S ² -ion in a diluted pulp 0.23-0.30 g / DM ³ 0,030 0.010 0.007

As a result of experimental studies, as can be seen from the table, the concentration range of the S ² ion was determined, which provides a sufficiently deep purification from zinc — the concentration of the S ² ion in the diluted pulp is 0.16-0.22 g / dm ³ . With a higher sulfide background, the degree of purification of aluminate solutions from zinc increases, but an increased sulfide background significantly increases the aggressiveness of the solution, reducing the corrosion resistance of the equipment. Thus, taking into account the range of zinc and elemental sulfur in the initial bauxite, it is necessary to adjust the sulfide background by adding sodium sulfide in an amount of 0.20-0.34 g / dm ³ to the diluted pulp, which ensures the concentration of S ² ion in the diluted pulp in the range of 0.16-0.22 g / DM ³ . In this case, it is necessary to ensure the conditions for treating the diluted pulp with air in a quiet mode when it is transported to a cleaner, in which the oxidation of the S ² ion does not exceed 0.02-0.03 g / dm ³ (to maintain the desired level of sulfide background). An experimentally established interval of air flow rate, which amounted to 0.2-0.3 m ³ / m ³ diluted pulp. Table 2 presents the results of laboratory tests for the purification of diluted pulp from impurities of zinc (ZnO) and organic compounds (derivatives of humic acids). In this case, a decrease or increase in the air supply rate leads to a significant deterioration in the degree of purification of the pulp from impurities. A decrease in the ratio of volumes of pulp located in the purifier and flowing through the purifier also degrades the degree of purification, and an increase in the ratio is impractical, since in this case the apparatus volumes increase without a visible improvement in the degree of purification.

table 2 The processing conditions of the diluted pulp at a concentration of S ^{2 -} 0.16-0.22 g / DM ³ Zno OM (humic acids) The degree of purification from impurities Zno OM (humic acids) Ref. The end. Ref. The end. g / dm ³ % g / dm ³ % Air supply at a speed of 0.1 nm ³ / m ³ pulp and a volume ratio of 2.0: 1 0.019 0.008 1,64 1.42 0.011 37.0 0.22 13,4 Air supply at a speed of 0.4 nm ³ / m ³ pulp and a volume ratio of 2.6: 1 0,022 0.013 1.9 1,6 0.009 41.0 0.3 15.6 Air supply at a speed of 0.2 nm ³ / m ³ pulp and a volume ratio of 2.7: 1 0,025 0.011 1.9 1.4 0.014 70.0 0.50 26.3 Air supply at a speed of 0.3 nm ³ / m ³ pulp and a volume ratio of 2.7: 1 0,025 0.007 1.92 1.46 0.018 72.0 0.46 24.0

The proposed method provides, along with the purification of aluminate solutions from zinc impurities, partial purification from humic acids, which is (as mentioned above) an important condition for obtaining high-quality alumina.

It should be noted that the cleaning process, subject to the technological parameters proposed by the authors, the exposure time of the diluted pulp in the intermediate tank (cleaner) is reduced to 2.7 hours (in the known method - 3.5 hours), which provides a significant reduction in the duration of the process.

The proposed method can be implemented as follows.

The method is intended for the purification of aluminate solutions of the Bayer process containing a significant amount of zinc (more than 125 g / t) in the presence of a free sulfide ion. Boiled alkaline-bauxite pulp obtained after leaching of the initial bauxite raw material enters the agitator, in which it is mixed with a dressing obtained after washing the red mud to obtain diluted pulp. At the same time, sodium sulfide is dosed into the promo based on the calculation of the concentration of sulfide ion 0.16-0.22 g / dm ³ pulp. The required amount of sodium sulfide in this case is 0.20-0.34 g / dm ³ pulp. Obtained after mixing, the diluted pulp from the agitator is pumped or by gravity to a cleaner. In this case, air is supplied to the diluted pulp in an amount of 0.2-0.3 nm ³ / m ^{3 of} diluted pulp, the oxidation of sulfide sulfur in this case does not exceed 0.01-0.02 sulfide ion. Thus, before entering the cleaner, the diluted pulp is treated with air in a quiet mode, either in the drain manifold, in the case of pulp by gravity, or in a receiving cup, if the pump pulp is used for transportation. In the purifier, the diluted pulp is kept under slow stirring for 2.7 hours. The ratio of the volumes of diluted pulp located in the purifier and flowing through it is maintained at 2.7: 1. After holding the diluted pulp in the cleaner for approximately 2.7 hours, the zinc concentration decreases to 0.011-0.013 g / dm ³ ZnO. Next, the diluted pulp through the bottom of the cleaner is sent to thicken the red mud. The drain of the thickener during the thickening of the red mud and subsequent control filtration (2.5-3.5 hours) is additionally purified from ZnO for another 0.003 g / dm ³ . Thus, the concentration of ZnO in the aluminate solution entering the decomposition is ≤0.01 g / dm ³ . Along with zinc, the aluminate solution is purified from part of the organic substances, and from the most harmful derivatives of humic acids.

The proposed method is illustrated by the following examples.

Example 1. The boiled alkaline-bauxite pulp obtained after leaching the feed of bauxite feed is sent to an agitator, in which it is mixed with the slurry obtained after washing the red mud to obtain diluted pulp. Get diluted pulp composition, g / DM ³ : Na ₂ O _ky - 135; Al ₂ O ₃ - 127; SiO ₂ - 0.51; S ^2- - 0.08; ZnO - 0.022; organic matter - 1.8 (O ₂ , oxidation with dichromate in the presence of Ag ₂ SO ₄ taking into account the content of sulfur and chlorine). Sodium sulfide is added to the promo based on the calculation of the concentration of sulfide ion in the liquid phase of a diluted pulp of 0.16 g / dm ³ pulp in an amount of 0.20 g / dm ³ pulp (in terms of 100% product). The resulting diluted pulp in an amount of 250 m ³ / h by the pump is sent to the receiving cup of the purifier with a working volume of 675 m ³ . At the same time, air is supplied to the glass at the rate of 0.2 nm ³ / m ^{3 of} diluted pulp - 50 nm ³ / h (8-9 m ^{3 of} compressed air with a pressure of ~ 6 atm). In the purifier, the diluted pulp is kept for 2.7 hours with slow stirring. The ratio of the volumes of diluted pulp located in the purifier and flowing through it is maintained at 2.7: 1. Next, the diluted pulp through the bottom of the cleaner is pumped into the thickener of the red mud. The concentration of ZnO in the discharge of the thickener is 0.013 g / DM ³ . The drain of the thickener during the thickening of the red mud and subsequent control filtration through a layer of tricalcium aluminate (2.5 hours) is further purified from ZnO by another 0.003 g / dm ³ . Thus, the concentration of ZnO in the aluminate solution entering the decomposition is 0.010 g / dm ³ . Along with zinc, the aluminate solution is purified from organic substances (derivatives of humic acids) by 0.46 g / dm ³ (by 25%) and from silicon oxide by 31%, the content of which decreases to 0.35 g / dm ³ .

Example 2. The boiled alkaline-bauxite pulp obtained after leaching the feed of bauxite feed is sent to an agitator, in which it is mixed with the slurry obtained after washing the red mud to obtain diluted pulp. Get diluted pulp composition, g / DM ³ : Na ₂ O _ky - 135; Al ₂ O ₃ - 127; SiO ₂ - 0.51; S ^2- - 0.08; ZnO - 0.022; organic matter - 1.8 (O ₂ , oxidation with dichromate in the presence of Ag ₂ SO ₄ taking into account the content of sulfur and chlorine). Sodium sulfide is added to the promo based on the calculation of the concentration of sulfide ion 0.22 g / dm ^{3 of} pulp in the amount of 0.34 g / dm ^{3 of} pulp in the liquid phase of the diluted pulp (in terms of 100% product). The resulting diluted pulp in an amount of 250 m ³ / h by the pump is sent to the receiving cup of the purifier with a working volume of 675 m ³ . At the same time, air is supplied to the glass at the rate of 0.3 nm ³ / m ^{3 of} diluted pulp - 100 nm ³ / h (16-18 m ^{3 of} compressed air with a pressure of ~ 6 atm). In the purifier, the diluted pulp is kept for 2.7 hours with slow stirring. The ratio of the volumes of diluted pulp located in the purifier and flowing through it is maintained at 2.7: 1. Next, the diluted pulp through the bottom of the cleaner is pumped to a thickener of red mud. The concentration of ZnO in the drain of the thickener is 0.016 g / DM ³ . The drain of the thickener during the thickening of the red mud and subsequent control filtration through a layer of tricalcium aluminate (2.5 hours) is further purified from ZnO by another 0.003 g / dm ³ . Thus, the concentration of ZnO in the aluminate solution entering the decomposition is 0.013 g / dm ³ . Along with zinc, the aluminate solution is purified from organic substances (derivatives of humic acids) by 0.50 g / dm ³ (by 27.8%) and from silicon oxide by 31%, the content of which decreases to 0.35 g / dm ³ .

Thus, the authors propose a method for purifying aluminate solutions of the Bayer process using bauxite with a high content of zinc oxide as a feedstock, which provides not only deep purification from zinc, but also purification from organic substances - the most harmful part of humic acids and silicon oxide.

Claims (1)

The method of purification of aluminate solutions from impurities, including adding sodium sulfide pulp to the pulp diluted after bauxite leaching, treating the pulp with air in a quiet mode, subsequent exposure to a purifier with continuous flow and stirring of the pulp, directing the pulp to thicken and then sending it to the separation of sludge and control filtration of the obtained thickener discharge, characterized in that sodium sulfide is added to the diluted pulp to a concentration of 0.20-0.34 g / dm ³ , air is supplied in an amount of 0.2-0.3 nm ³ / m ³ times pulp, and the ratio of the volumes of diluted pulp located in the purifier and flowing through it is 2.7: 1.