Method for removing trace iron in sodium aluminate solution dissolved out of diaspore type high-sulfur bauxite

Abstract

The invention discloses a method for removing trace iron in a sodium aluminate solution dissolved out of diaspore type high-sulfur bauxite, and belongs to the technical field of hydrometallurgy. The method comprises the following steps that a solution of a mixture of ferric salt and PAC is put into an industrial sodium aluminate solution of the diaspore type high-sulfur bauxite dissolved out through a high-temperature Bayer method, and the mass ratio of the ferric salt to the PAC is 1: 6-4: 1; the preparation method comprises the following steps: reacting at the temperature of 20-100 DEG C and at the rotating speed of 100-500rpm for 10-300min, and carrying out solid-liquid separation on the slurry after the reaction to obtain a mixture which meets the industrial production standard (Fe2O3lt; 5 mg / L), and the loss amount of alumina is less than 2%. The iron removal method is easy and convenient to operate and low in cost and energy consumption, and has a good iron removal effect on the crude liquid or the fine liquid dissolved out through the high-temperature Bayer process.

Description

Technical Field

[0001] The invention relates to a method for removing trace iron in a sodium aluminate solution dissolved from diaspore type high-sulfur bauxite, belonging to the technical field of hydrometallurgy. Background Art

[0002] Bauxite is the main mineral for producing alumina. The main mineral types of bauxite are gibbsite, diaspore and diaspore, and the difficulty of dissolution increases in turn. China's bauxite resources are mainly diaspore-type bauxite with many associated elements, and the bauxite reserves account for only 3% of the world, while China's alumina production ranks first in the world all year round, which has brought great challenges to China's aluminum industry production. In recent years, due to the depletion of high-quality bauxite resources, high-sulfur bauxite has to be developed as a long-term reserve resource. There are about 80,000 tons of high-sulfur bauxite (sulfur content higher than 0.7%) in China, which is widely distributed in southwest China. When treating diaspore-type bauxite with the traditional Bayer process, it is difficult to achieve effective leaching, so higher temperatures (530K~560K) and greater alkalinity (Na2O k Concentration>240g / L) for more effective leaching of bauxite. Higher temperature and greater alkalinity will lead to more impurities dissolving when dissolving high-sulfur bauxite, among which its associated elements sulfur and iron and other harmful substances are the most difficult impurities to separate. The accumulation of sulfur will cause the iron content in the sodium aluminate solution to seriously exceed the standard (Fe2O3 concentration>5mg / L). The process of dissolving high-sulfur bauxite with high-grade bauxite at a certain quota ratio can greatly reduce the iron content in the sodium aluminate solution, but its iron content (in terms of Fe2O3) is still about 30mg / L. If you want to achieve the conditions for producing high-purity alumina (Fe2O3 concentration <5mg / L), you need to increase the proportion of high-grade bauxite, which means that high-sulfur bauxite cannot be effectively developed and utilized. Therefore, it is urgent to explore an effective method for removing trace iron in sodium aluminate solution.

[0003] Extensive research has been conducted at home and abroad on how to effectively remove trace iron from sodium aluminate solution. Some studies have used pyrite as raw material, dissolved it under high-temperature Bayer process reaction conditions, and used the dissolution as raw material to prepare seeds in a water bath. The crystal seeds are put into the sodium aluminate solution to achieve the simultaneous removal of sulfur and iron. However, the preparation process of the seed is very slow. Only a small amount of seed crystals are precipitated from the dissolution after 72 hours, and the seed crystals can be completely precipitated after 120 hours. Moreover, the seed crystals are very easy to oxidize and deteriorate and cannot be stored. The Chinese patent with publication number CN101391790A discloses a method for removing iron from sodium aluminate solution. Granular or columnar activated carbon is added to the sodium aluminate solution and stirred at 55-65°C for iron removal, and then filtered with an activated carbon bed for deep iron removal. The operation of this method is relatively complicated, and the iron removal rate is only 60% to 80%. Chinese patent publication number CN104843752A discloses a method for removing iron from a sodium aluminate solution. Active calcium silicate is added to the sodium aluminate solution and stirred at 60-90°C to remove iron. The iron oxide content in the sodium aluminate solution can be reduced to <2 mg / L. However, due to the dissolution of silicon, it is not conducive to the recycling of the alkali solution. Summary of the invention

[0004] The object of the present invention is to provide a method for removing trace iron in a sodium aluminate solution dissolved from diaspore-type high-sulfur bauxite, which specifically comprises the following steps: adding iron salt and PAC (polyaluminium chloride) to the sodium aluminate solution dissolved from diaspore-type high-sulfur bauxite, stirring for a period of time at a certain temperature and speed, and then separating the solid and liquid to obtain a sodium aluminate solution after iron removal.

[0005] Preferably, the sodium aluminate solution dissolved from the diaspore-type high-sulfur bauxite is composed of: Na2O k The concentration is 100-250 g / L, and the caustic ratio of the solution is a k That is, Na2O in solution k The molecular ratio of Fe2O3 to Al2O3 is 1.2 to 3.0, and the concentration of Fe2O3 in the solution is 25 to 50 mg / L.

[0006] Preferably, the iron salt is one or more of ammonium ferrous sulfate, ammonium ferric sulfate, ferric sulfate, ferrous sulfate, ferric chloride, and ferrous chloride mixed in any proportion; and the PAC is one of a spray-type PAC and a drum-type PAC.

[0007] Preferably, the total amount of iron salt and PAC added to the sodium aluminate solution dissolved from diaspore-type high-sulfur bauxite is 100-350 mg / L, wherein the mass ratio of iron salt to PAC is 1:6-4:1.

[0008] Preferably, the iron salt and PAC are first dissolved in water and then added to the sodium aluminate solution dissolved from the diaspore-type high-sulfur bauxite.

[0009] Preferably, the stirring temperature is 20-100°C.

[0010] Preferably, the stirring speed is 100 to 500 rpm, and the stirring time is 10 to 300 min.

[0011] The principle of the present invention is to use a mixture of iron and PAC to react with sulfur ions in a sodium aluminate solution to generate ferrous sulfide compounds, and use these ferrous sulfide compounds as crystal seeds to achieve rapid removal of iron in the sodium aluminate solution. In addition, PAC can greatly accelerate the process of the reaction. The reason for achieving rapidity is that the ferrous sulfide compound seeds provide a large number of nucleation sites, increasing the contact opportunities with reactant molecules; these nucleation sites can effectively undergo heterogeneous nucleation reactions with iron in the sodium aluminate solution, greatly reducing the energy barrier of the reaction, and achieving rapid enrichment of iron.

[0012] The beneficial effects of the present invention are:

[0013] (1) The method of the present invention is green and efficient. It can effectively remove trace iron in industrial sodium aluminate solution by adding PAC, and the sodium aluminate solution after iron removal and the iron removal slag can be separated by simple filtration. The process is simple and the cost is low. The iron removal rate is as high as 85% or more, and the iron content (in terms of Fe2O3) in the sodium aluminate solution after iron removal is less than 5 mg / L.

[0014] (2) The present invention is effective for both crude liquid and fine liquid, and has almost no negative impact in the industrial production process. The loss of alumina content is less than 2%, and the amount of alumina loss with or without additives is basically the same. DETAILED DESCRIPTION

[0015] The present invention is further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the described contents.

[0016] Example 1

[0017] The sodium aluminate solution used in this example is a crude solution (Na2O k The concentration is 168.42 g / L, and the caustic ratio of the solution is a k is 2.4, the concentration of iron in the solution is 49.7 mg / L in terms of Fe2O3, the additives are ammonium ferric sulfate and spray-type PAC, and the steps are as follows:

[0018] 200 mg of a mixture containing ammonium ferric sulfate and spray-type PAC (the mass ratio of ammonium ferrous sulfate to spray-type PAC is 1:4) was dissolved in 50 ml of water and immediately added to 1 L of industrial sodium aluminate solution. The reaction was carried out at a speed of 200 rpm and a temperature of 25°C for 10 minutes. After the reaction was completed, a qualitative filter paper was used for solid-liquid separation to obtain a sodium aluminate solution after iron removal.

[0019] By titration and o-phenanthroline-ultraviolet spectrophotometry, the Al2O3 concentration in the de-ironified sodium aluminate was 113.64 g / L, the alumina loss rate was 1.85%, the Fe2O3 concentration was 4.31 mg / L, and the iron removal rate was 91.3%.

[0020] Example 2

[0021] The sodium aluminate solution used in this example is the concentrate (Na2O k The concentration is 159.31 g / L, and the caustic ratio of the solution is a k is 2.5, the concentration of iron in the solution is 35.4 mg / L in terms of Fe2O3, the additives are ferric chloride and drum-type PAC, and the steps are as follows:

[0022] 250 mg of a mixture containing ferric chloride and drum-type PAC (the mass ratio of ferric chloride to drum-type PAC is 2:3) was dissolved in 50 ml of water and immediately added to 1 L of industrial sodium aluminate solution. The reaction was carried out for 300 min at a speed of 100 rpm and a temperature of 35°C. After the reaction was completed, a qualitative filter paper was used for solid-liquid separation to obtain a sodium aluminate solution after iron removal.

[0023] By titration and o-phenanthroline-ultraviolet spectrophotometry, the Al2O3 concentration in the de-ironified sodium aluminate was 103.32 g / L, the alumina loss rate was 1.74%, the Fe2O3 concentration was 4.52 mg / L, and the iron removal rate was 87.3%.

[0024] Example 3

[0025] The sodium aluminate solution used in this example is the concentrate (Na2O k The concentration is 153.54 g / L, and the caustic ratio of the solution is a k is 2.4, the concentration of iron in the solution is 39.4 mg / L in terms of Fe2O3, the additives are spray-type PAC and ferrous sulfate, and the steps are as follows:

[0026] 150 mg of a mixture containing spray-type PAC and ferrous sulfate (the mass ratio of spray-type PAC to ferrous sulfate is 3:7) was dissolved in 50 ml of water and immediately added to 1 L of industrial sodium aluminate solution. The reaction was carried out at a speed of 500 rpm and a temperature of 45°C for 90 minutes. After the reaction was completed, a qualitative filter paper was used for solid-liquid separation to obtain a sodium aluminate solution after iron removal.

[0027] By titration and o-phenanthroline-ultraviolet spectrophotometry, the Al2O3 concentration in the de-ironified sodium aluminate was 103.78 g / L, the alumina loss rate was 1.69%, the Fe2O3 concentration was 4.49 mg / L, and the iron removal rate was 88.6%.

[0028] Example 4

[0029] The sodium aluminate solution used in this example is the concentrate (Na2O k The concentration is 148.75 g / L, and the caustic ratio of the solution is a k is 2.7, the concentration of iron in the solution is 34.5 mg / L in terms of Fe2O3, the additive is a mixture of ferrous sulfate and drum-type PAC, comprising the following steps:

[0030] 350 mg of a mixture of ferrous sulfate and drum-type PAC (the mass ratio of ferrous sulfate to drum-type PAC is 1:6) was dissolved in 50 ml of water and immediately added to 1 L of industrial sodium aluminate solution. The reaction was carried out at a speed of 200 rpm and a temperature of 55° C. for 150 min. After the reaction was completed, a qualitative filter paper was used for solid-liquid separation to obtain a sodium aluminate solution after iron removal.

[0031] By titration and o-phenanthroline-ultraviolet spectrophotometry, the Al2O3 concentration in the de-ironified sodium aluminate was 89.52 g / L, the alumina loss rate was 1.52%, the Fe2O3 concentration was 3.81 mg / L, and the iron removal rate was 89.1%.

[0032] Example 5

[0033] The sodium aluminate solution used in this example is the concentrate (Na2O k The concentration is 158.47 g / L, and the caustic ratio of the solution is a k is 2.8, the concentration of iron in the solution is 38.8 mg / L in terms of Fe2O3, the additives are ferric sulfate and spray-type PAC, and the method comprises the following steps:

[0034] A mixture of 250 mg of ferrous sulfate and spray-type PAC (the mass ratio of ferrous sulfate to spray-type PAC is 1:4) was dissolved in 50 ml of water and immediately added to 1 L of industrial sodium aluminate solution. The reaction was carried out at a speed of 300 rpm and a temperature of 75°C for 30 minutes. After the reaction was completed, a qualitative filter paper was used for solid-liquid separation to obtain a sodium aluminate solution after iron removal.

[0035] By titration and o-phenanthroline-ultraviolet spectrophotometry, the Al2O3 concentration in the de-ironified sodium aluminate was 92.11 g / L, the alumina loss rate was 1.38%, the Fe2O3 concentration was 3.90 mg / L, and the iron removal rate was 89.9%.

[0036] Example 6

[0037] The sodium aluminate solution used in this example is a crude solution (Na2O k The concentration is 154.87 g / L, and the caustic ratio of the solution is a k is 2.2, the concentration of iron in the solution is 42.8 mg / L in terms of Fe2O3, the additive is a mixture of ferrous chloride and drum-type PAC, comprising the following steps:

[0038] 100 mg of a mixture containing ferrous chloride and drum-type PAC (the mass ratio of ferrous chloride to drum-type PAC is 4:1) was dissolved in 50 ml of water and immediately added to 1 L of industrial sodium aluminate solution. The mixture was reacted for 210 min at a speed of 250 rpm and a temperature of 30°C. After the reaction was completed, a qualitative filter paper was used for solid-liquid separation to obtain a sodium aluminate solution after iron removal.

[0039] By titration and o-phenanthroline-ultraviolet spectrophotometry, the Al2O3 concentration in the de-ironified sodium aluminate was 114.24 g / L, the alumina loss rate was 1.65%, the Fe2O3 concentration was 2.94 mg / L, and the iron removal rate was 92.1%.

[0040] Example 7

[0041] The sodium aluminate solution used in this example is a crude solution (Na2O k The concentration is 167.82 g / L, and the caustic ratio of the solution is a k is 2.2, the concentration of iron in the solution is 31.6 mg / L in terms of Fe2O3, the additives are ammonium ferric sulfate and drum-type PAC, and the steps are as follows:

[0042] 150 mg of a mixture containing ammonium ferric sulfate and drum-type PAC (the mass ratio of ammonium ferric sulfate to drum-type PAC is 1:2) was dissolved in 50 ml of water and immediately added to 1 L of industrial sodium aluminate solution. The reaction was carried out at a speed of 200 rpm and a temperature of 95°C for 75 minutes. After the reaction was completed, a qualitative filter paper was used for solid-liquid separation to obtain a sodium aluminate solution after iron removal.

[0043] By titration and o-phenanthroline-ultraviolet spectrophotometry, the Al2O3 concentration in the de-ironified sodium aluminate was 123.51 g / L, the alumina loss rate was 1.87%, the Fe2O3 concentration was 4.71 mg / L, and the iron removal rate was 85.1%.

[0044] Comparative Example 1

[0045] As a comparison, the difference between this comparative example and Example 1 is that only ammonium ferric sulfate is used as the additive, and no spray-type PAC is used.

[0046] The sodium aluminate solution used in this comparative example is a crude solution (Na2O k The concentration is 167.34 g / L, and the caustic ratio of the solution is a k is 2.4, the concentration of iron in the solution is 47.8 mg / L in terms of Fe2O3, the additive is ammonium ferric sulfate, and the method comprises the following steps:

[0047] Dissolve 200 mg of ammonium ferric sulfate in 50 ml of water and immediately add it to 1 L of industrial sodium aluminate solution. React for 10 minutes at a speed of 200 rpm and a temperature of 25°C. After the reaction is completed, use qualitative filter paper to separate the solid and liquid to obtain the sodium aluminate solution after iron removal.

[0048] By titration and o-phenanthroline-ultraviolet spectrophotometry, the Al2O3 concentration in the de-ironified sodium aluminate was 112.75 g / L, the alumina loss rate was 1.99%, the Fe2O3 concentration was 21.2 mg / L, and the iron removal rate was 55.7%.

[0049] Comparative Example 2

[0050] As a comparison, the difference between this comparative example and Example 2 is that only ferric chloride is used as an additive, and drum-type PAC is not used.

[0051] The sodium aluminate solution used in this comparative example is a crude solution (Na2O k The concentration is 161.74 g / L, and the caustic ratio of the solution is a k is 2.4, the concentration of iron in the solution is 34.8 mg / L in terms of Fe2O3, the additive is ferric chloride, and the steps are as follows:

[0052] Dissolve 250 mg of ferric chloride in 50 ml of water and immediately add it to 1 L of industrial sodium aluminate solution. React for 300 min at a speed of 100 rpm and a temperature of 35°C. After the reaction is completed, use qualitative filter paper to separate the solid and liquid to obtain the sodium aluminate solution after iron removal.

[0053] By titration and o-phenanthroline-ultraviolet spectrophotometry, the Al2O3 concentration in the de-ironified sodium aluminate was 108.74 g / L, the alumina loss rate was 2.21%, the Fe2O3 concentration was 8.45 mg / L, and the iron removal rate was 75.7%.

[0054] Comparative Example 3

[0055] As a comparison, the difference between this comparative example and Example 7 is that only ammonium ferric sulfate is used as an additive, and drum-type PAC is not used.

[0056] The sodium aluminate solution used in this comparative example is a crude solution (Na2O k The concentration is 168.45 g / L, and the caustic ratio of the solution is a k is 2.2, the concentration of iron in the solution is 33.86 mg / L in terms of Fe2O3, the additive is ammonium ferric sulfate, and the method comprises the following steps:

[0057] Dissolve 150 mg of ammonium ferric sulfate in 50 ml of water and immediately add it to 1 L of industrial sodium aluminate solution. React for 75 minutes at a speed of 200 rpm and a temperature of 95°C. After the reaction is completed, use qualitative filter paper to separate the solid and liquid to obtain the sodium aluminate solution after iron removal.

[0058] By titration and o-phenanthroline-ultraviolet spectrophotometry, the Al2O3 concentration in the de-ironified sodium aluminate was 123.84 g / L, the alumina loss rate was 1.97%, the Fe2O3 concentration was 9.21 mg / L, and the iron removal rate was 72.8%.

[0059] It can be seen from the various embodiments and comparative examples that the iron removal rate can be effectively improved after adding PAC.

Claims

1. A method for removing trace iron in a sodium aluminate solution dissolved from diaspore-type high-sulfur bauxite, characterized in that: The specific steps include: Iron salt and PAC are added to the sodium aluminate solution dissolved from diaspore-type high-sulfur bauxite, and the mixture is stirred at a certain temperature and speed for a period of time to separate the solid and liquid, thereby obtaining the sodium aluminate solution after iron removal.

2. The method for removing trace iron in the sodium aluminate solution dissolved from diaspore-type high-sulfur bauxite according to claim 1, characterized in that: The sodium aluminate solution dissolved from the diaspore-type high-sulfur bauxite is composed of: Na2O k The concentration is 100-250 g / L, and the caustic ratio of the solution is a k That is, Na2O in solution k The molecular ratio of Fe2O3 to Al2O3 is 1.2 to 3.0, and the concentration of Fe2O3 in the solution is 25 to 50 mg / L.

3. The method for removing trace iron in the sodium aluminate solution dissolved from diaspore-type high-sulfur bauxite according to claim 1, characterized in that: The iron salt is one or more of ammonium ferrous sulfate, ammonium ferric sulfate, ferric sulfate, ferrous sulfate, ferric chloride, and ferrous chloride mixed in any proportion; and the PAC is a spray type PAC or a drum type PAC.

4. The method for removing trace iron in the sodium aluminate solution dissolved from diaspore-type high-sulfur bauxite according to claim 1, characterized in that: The total amount of iron salt and PAC added to the sodium aluminate solution dissolved from diaspore-type high-sulfur bauxite is 100-350 mg / L, wherein the mass ratio of iron salt to PAC is 1:6-4:

1.

5. The method for removing trace iron in the sodium aluminate solution dissolved from diaspore-type high-sulfur bauxite according to claim 1, characterized in that: The stirring temperature is 20-100°C.

6. The method for removing trace iron in sodium aluminate solution dissolved from diaspore-type high-sulfur bauxite according to claim 1, characterized in that: The stirring speed is 100-500 rpm, and the stirring time is 10-300 min.