A process for causticizing in the guinean bauxite to alumina process

Abstract

The present invention discloses a causticizing method in the process of producing alumina from Guinea bauxite, which comprises the following steps: S1: crushing and wet-grinding the Guinea bauxite to obtain a pulp; S2: diluting the pulp and performing sedimentation separation to obtain a crude liquid and an underflow red mud pulp; filtering the crude liquid to obtain a fine liquid; the underflow red mud pulp enters a washing tank for washing, and the overflow of the washing tank flows back into the pulp diluted in S2, and the underflow red mud enters a red mud dump; S3: adding lime milk to the washing tank; C in the lime milk is a O f The concentration of lime is 100-150 g / L, and the amount of lime milk added is 1-5% of the overflow volume of the washing tank. The present invention directly adds lime milk to the washing tank for causticization, eliminating the need for an additional causticization system, energy consumption, or personnel. While achieving a causticization rate of 70-80%, the alumina loss is only 5-8%, demonstrating significant results.

Description

TECHNICAL FIELD

[0001] The present application relates to the chemical technology field, and in particular to a method for causticization in the process of producing alumina from Guinea bauxite. BACKGROUND

[0002] In the process of producing alumina, sodium carbonate in the process is mainly brought in by the following reasons: 1. The bauxite contains carbonate minerals, and the lime as an additive also often contains limestone due to insufficient calcination, and these carbonates react with caustic soda to eventually form sodium carbonate. 2. The bauxite contains organic matter, and some additives such as flocculants and scale inhibitors also contain organic matter, and part of the organic matter reacts with caustic soda to eventually form sodium carbonate. 3. Carbon dioxide in the air in the seeding and grading systems also reacts with caustic soda to form sodium carbonate.

[0003] The formation of these sodium carbonates not only consumes caustic soda, causing increased alkali consumption, but also easily precipitates in the leaching flash, causing blockage, and precipitates on the evaporation heat exchange surface, reducing heat exchange efficiency, and also causing difficulties in classification and sedimentation.

[0004] In the prior art, in order to reduce sodium carbonate in the process of producing alumina and eliminate the adverse effects of sodium carbonate, alumina enterprises usually have two methods: one is to concentrate the sodium aluminate solution in the evaporation process, and then add lime milk for causticization to causticize sodium carbonate into sodium hydroxide. The causticization rate of this method is 85-90%, and the loss of alumina is 10-20%; the second is to introduce part of the overflow of the first few washing tanks with high concentration in the washing system, and then add lime milk for causticization. The causticization rate of this method is less than 50%, and the loss of alumina is more than 30%. Both methods require an additional causticization system, a separate causticization tank, a supporting stirring system, and a solid-liquid separation settling tank and pumping system to send the overflow and underflow to different places. In addition, steam is used to heat the causticized slurry to a certain temperature. Therefore, the entire causticization system is complex, with many devices, and additional power consumption and steam consumption, and personnel are needed to operate. Therefore, it is necessary to improve the existing causticization process, save a large amount of investment, reduce energy consumption, and be easy to operate under the premise of a certain causticization rate and small loss of alumina. SUMMARY

[0005] The present application overcomes the technical problems of large investment and high energy consumption in the additional causticization process in the prior art process of producing alumina, and provides a method for causticization in the process of producing alumina from Guinea bauxite.

[0006] A method for causticization in the process of producing alumina from Guinea bauxite, comprising the following steps:

[0007] S1: Guinea bauxite is crushed and wet ground to obtain a slurry after leaching;

[0008] S2: diluting the slurry and then performing sedimentation separation to obtain a thick liquid and a bottom flow red mud slurry respectively; the thick liquid is filtered to obtain a refined liquid; the bottom flow red mud slurry is introduced into a washing tank for washing, and overflow of the washing tank is returned to the slurry after dilution in S2, and the bottom flow red mud is discharged into a red mud yard;

[0009] S3: adding lime milk into the washing tank; the concentration of CaO in the lime milk is 100-150 g / L, and the addition amount of the lime milk is 1-5% of the overflow amount of the washing tank. a O f The concentration of CaO in the lime milk is 100-150 g / L, and the addition amount of the lime milk is 1-5% of the overflow amount of the washing tank.

[0010] Further, when the lime milk is added into the washing tank, the temperature of the washing tank is 75-95°C, and the concentration of NT in the overflow of the washing tank is 5-50 g / L.

[0011] Compared with the prior art, the present application has the following beneficial effects:

[0012] In the present application, the lime milk is directly added into the washing tank for causticization reaction, the causticization solution is the overflow of the washing tank, and the causticization residue is settled to the bottom of the tank together with the red mud, without additional causticization system, energy consumption, and personnel operation; at the same time, the causticization rate reaches 70-80%, which is sufficient to prevent the accumulation of sodium carbonate in the process, and the loss of alumina is only 5-8%, which is significantly lower than the loss rate of alumina in the two traditional causticization systems, and the effect is remarkable. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is the process flow chart of the present application;

[0014] Figure 2 is the process flow chart of the control group 6 of the present application;

[0015] Figure 3 is the process flow chart of the control group 7 of the present application. DETAILED DESCRIPTION

[0016] The present application will be further described below in combination with examples and tests.

[0017] Example 1

[0018] This example is an improvement on the causticization process in the Bayer process for producing alumina in the prior art. The specific alumina production process flow is shown in Figure 1 The causticization method in the alumina production process of bauxite in Guinea according to the present application comprises the following steps:

[0019] S1: dissolving bauxite in Guinea after crushing and wet grinding to obtain a slurry;

[0020] S2: the ore slurry is diluted in a dilution tank and then enters a separation tank for sedimentation separation to obtain a thick liquid and a bottom flow of red mud slurry; the thick liquid is filtered to obtain a refined liquid; the bottom flow of red mud slurry enters a washing tank for washing, and overflow of the washing tank is returned to the ore slurry (i.e. the dilution tank) after dilution in S2, and the bottom flow of red mud enters a red mud yard;

[0021] S3: the NT concentration of the overflow of the washing tank is 50 g / L, lime milk is added to the washing tank; the concentration of CaOf in the lime milk is 150 g / L, and the addition amount of the lime milk is 5% of the overflow amount of the washing tank, and the temperature of the washing tank is 95℃.

[0022] Example 2

[0023] This embodiment is an improvement on the causticizing process in the Bayer process for producing alumina in the prior art. For details of the alumina production process, please refer to the following figure: Figure 1 The method for causticizing in the process for producing alumina from bauxite in Guinea in this embodiment comprises the following steps:

[0024] S1: the bauxite in Guinea is crushed and wet ground, and then dissolved to obtain an ore slurry;

[0025] S2: the ore slurry is diluted in a dilution tank and then enters a separation tank for sedimentation separation to obtain a thick liquid and a bottom flow of red mud slurry; the thick liquid is filtered to obtain a refined liquid; the bottom flow of red mud slurry enters a washing tank for washing, and overflow of the washing tank is returned to the ore slurry (i.e. the dilution tank) after dilution in S2, and the bottom flow of red mud enters a red mud yard;

[0026] S3: the NT concentration of the overflow of the washing tank is 5 g / L, lime milk is added to the washing tank; the concentration of CaOf in the lime milk is 100 g / L, and the addition amount of the lime milk is 1% of the overflow amount of the washing tank, and the temperature of the washing tank is 75℃.

[0027] Example 3

[0028] This embodiment is an improvement on the causticizing process in the Bayer process for producing alumina in the prior art. For details of the alumina production process, please refer to the following figure: Figure 1 The method for causticizing in the process for producing alumina from bauxite in Guinea in this embodiment comprises the following steps:

[0029] S1: the bauxite in Guinea is crushed and wet ground, and then dissolved to obtain an ore slurry;

[0030] S2: the ore slurry is diluted in a dilution tank and then enters a separation tank for sedimentation separation to obtain a thick liquid and a bottom flow of red mud slurry; the thick liquid is filtered to obtain a refined liquid; the bottom flow of red mud slurry enters a washing tank for washing, and overflow of the washing tank is returned to the ore slurry (i.e. the dilution tank) after dilution in S2, and the bottom flow of red mud enters a red mud yard;

[0031] S3: the NT concentration of overflow of the washing tank is 20 g / L, lime milk is added into the washing tank; the concentration of CaOf in the lime milk is 120 g / L, the adding amount of the lime milk is 3% of the overflow amount of the washing tank, and the temperature of the washing tank is 90℃.

[0032] Control Group 1

[0033] The method of causticizing in the process of producing alumina from bauxite in Guinea in Control Group 1 is the same as that in Example 1, except that when the lime milk is added into the washing tank in Control Group 1, the temperature of the washing tank is 100℃.

[0034] Control Group 2

[0035] The method of causticizing in the process of producing alumina from bauxite in Guinea in Control Group 2 is the same as that in Example 1, except that when the lime milk is added into the washing tank in Control Group 2, the temperature of the washing tank is 65℃.

[0036] Control Group 3

[0037] The method of causticizing in the process of producing alumina from bauxite in Guinea in Control Group 3 is the same as that in Example 1, except that the lime milk is added into the washing tank in Control Group 3 under the condition that the NT concentration of overflow of the washing tank is 60 g / L.

[0038] Control Group 4

[0039] The method of causticizing in the process of producing alumina from bauxite in Guinea in Control Group 4 is the same as that in Example 1, except that the lime milk is added into the washing tank in Control Group 4 under the condition that the NT concentration of overflow of the washing tank is 2 g / L.

[0040] Control Group 5

[0041] The method of causticizing in the process of producing alumina from bauxite in Guinea in Control Group 5 is the same as that in Example 1, except that in Control Group 5, the adding amount of the lime milk is 8% of the overflow amount of the washing tank.

[0042] Control Group 6

[0043] The process of Control Group 6 is that part of overflow of the first several washing tanks with higher concentration in the washing system is led out and heated, and then causticized by adding lime milk. Specifically, refer to Figure 2 As shown in FIG. 4, four causticizing tanks with stirring are arranged, and a continuous causticizing process is adopted. The first washing liquid or the second washing liquid of the washing tank and the lime milk are simultaneously fed into the first causticizing tank, the NT concentration of the overflow of the washing tank is controlled at 30 g / L, the solid content of the lime milk is controlled at 160 g / L, and the adding amount is controlled at [CaO] / [Na2O c] = 1.2. The causticizing slurry flows from the first causticizing tank to each causticizing tank in turn, each causticizing tank is equipped with a steam pipeline to heat to 85°C, and the total residence time is 2h. After causticizing, the slurry returns to the red mud settling and washing process.

[0044] Control group 7

[0045] Combined Figure 3 As shown in the figure, the causticizing process of control group 7 is to continue evaporation of part of the evaporation mother liquor to NT > 300g / l with a forced circulation evaporator, precipitate carbonates, separate with a settling tank, filter through a salt filter, dissolve in a salt dissolving tank, mix the dissolved salt with lime milk in a mixing tank, and then enter the causticizing tank of the continuous causticizing process for causticizing. The causticizing temperature is controlled at 95°C, the lime milk concentration is controlled at 160g / l, the lime milk addition amount is controlled at [CaO] / [Na2O c ] = 1.2, and the causticizing time is 2h. After causticizing, separation is performed with a filter, and the causticizing residue returns to the red mud settling and washing process.

[0046] The causticizing rate and alumina loss in the above-mentioned examples 1-3 and control groups 1-7 are shown in Table 1 below.

[0047] Table 1

[0048]

[0049] As can be seen from Table 1, the causticizing rate of examples 1-3 is slightly lower than that of control group 7, and significantly higher than that of control group 6, and the alumina loss of examples 1-3 is significantly lower than that of control groups 6 and 7, indicating that the present application has a significant causticizing technical effect compared to the prior art by adding lime milk to the washing tank for causticizing. Moreover, the present application directly adds lime milk to the washing tank for causticizing reaction, the causticizing solution is the overflow of the washing tank, the causticizing residue settles to the bottom of the tank with the red mud, without additional causticizing system, without additional energy consumption, and without additional personnel operation. Compared to control groups 6 and 7 which need to additionally increase the causticizing system, the present application not only has low energy consumption but also reduces labor, so the present application also has the technical advantages of low energy consumption, reduced labor, and low cost compared to control groups 6 and 7. By comparing example 1 with control groups 1-5, it is found that under different lime milk addition conditions, the causticizing rate and alumina loss are different. Only under the conditions of adding lime milk to the washing tank when the NT concentration of the overflow of the washing tank is 5-50g / L, the addition amount of lime milk is 1-5% of the overflow amount of the washing tank, and the temperature of the washing tank is 75-95°C, can the technical effects of high causticizing rate and low alumina loss be achieved. The present application adds lime milk to the washing tank for causticizing, and strictly limits the causticizing conditions, and the causticizing effect is significant.

[0050] The above description is for the preferred embodiment of the present application, but the embodiment is not intended to limit the scope of the patent application of the present application. Any equivalent changes or modifications made under the technical spirit of the present application should be covered by the patent scope of the present application.

Claims

1. A method for causticizing in the production of alumina from bauxite in Guinea, characterized in that: The steps include: S1: Guinea bauxite is crushed, wet-milled and then dissolved to obtain slurry; S2: The diluted slurry obtained after dilution is subjected to sedimentation separation to obtain a crude liquid and an underflow red mud slurry; the crude liquid is filtered to obtain a fine liquid; the underflow red mud slurry enters a washing tank for washing, and the overflow of the washing tank is returned to the diluted slurry in S2, and the underflow red mud enters the red mud dump; S3: adding lime milk to the washing tank; the concentration of CaOf in the lime milk is 100-150 g / L, and the amount of lime milk added is 1-5% of the overflow of the washing tank; When the lime milk is added to the washing tank, the temperature of the washing tank is 75-95° C., and the NT concentration of the washing tank overflow is 5-50 g / L.

Images