JPS636490B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for separating and concentrating sodium oxalate for removing sodium oxalate from a slurry liquid in a Bayer process. In the Bayer method, when producing alumina from alumina-containing ore, organic matter contained in the ore,
Sedimentation aids such as sodium polyacrylate, carbon dioxide gas in the air, etc. dissolve in the high temperature caustic aluminate solution,
It combines with Na, Ca, Al, etc. to form organic acid salts and accumulates in the process liquid. As organic matter accumulates in the solution, the equilibrium solubility in the aluminate solution increases,
The precipitation rate when precipitating aluminum hydroxide deteriorates, production efficiency decreases, and serious problems occur in production. To solve this problem, it is usually considered to remove sodium carbonate and sodium oxalate, which are the final forms of organic matter in the liquid, in order to reduce the concentration level of organic matter in the liquid. When aluminum hydroxide is precipitated from a supersaturated aluminate solution, sodium oxalate crystallizes as fine crystals at the same time as aluminum hydroxide in the initial stage of precipitation. This solid sodium oxalate deteriorates the sedimentation and separation properties of aluminum hydroxide particles in an aluminate liquid containing solid aluminum hydroxide (hereinafter referred to as white mud slurry liquid). For this reason, sodium oxalate must be removed. In order to remove solid sodium oxalate from the white mud slurry, the white mud slurry is usually classified or clarified, the classified upper or lower liquid is filtered and washed, and the washed filtrate is supplied to the oxalic acid removal process. . this is,
By washing the solid sodium oxalate contained in the filter cake with warm water, the sodium oxalate is dissolved and a washed filtrate containing a relatively large amount of sodium oxalate can be obtained, so this method can be used to remove sodium oxalate. be done. A part or the entire amount of this filtrate may be used as it is, or after being concentrated and directly reacted with slaked lime, or by using solid organic matter such as sodium oxalate as a seed to precipitate organic matter such as sodium oxalate, and then reacting the precipitate with lime or incinerating it. It is known to recover caustic sodium and remove organic matter. In the above-mentioned removal of sodium oxalate, it is clear that if the content of sodium oxalate contained in the washing filtrate is high, the sodium oxalate removal efficiency or removal efficiency will be improved. For this purpose, it is necessary to increase the content of sodium oxalate in the white mud slurry and to increase the content of sodium oxalate contained in the filtered washing liquid of the white mud slurry. It is known that a relatively large amount of solid sodium oxalate adheres to the fine particles of aluminum hydroxide in the white mud slurry, so it is possible to filter and wash the white mud slurry liquid containing relatively fine grains by classification, etc. . The present inventors, when classifying white mud slurry liquid,
It has been discovered that by mixing air bubbles into white mud and supplying the foam-containing white mud slurry to a classifier, sodium oxalate can be concentrated by 2 to 4 times compared to conventional classification due to the flotation separation effect. If a gas such as air is blown into the white mud slurry liquid and stirred, and the thus obtained foam-containing white mud slurry liquid is placed in a sedimentation tube and observed, it is found that there are countless bubbles with diameters of 2 mm or less in the white mud slurry liquid. are doing. If left as it is, the foam will float to the surface while enveloping the aluminum hydroxide particles, and eventually a layer of foam-containing particles, a clear aluminate liquid layer,
Phase separation occurs into a layer of deposited particles. The solid sodium oxalate in the foam particle portion is concentrated 2 to 4 times based on the weight of solid aluminum hydroxide in the raw white mud slurry. This is considered to be because the solid sodium oxalate particles were selectively separated and concentrated due to the mixing of air bubbles into the white mud slurry liquid. To mix foam into the white mud slurry, a foam generator known in the field of flotation may be used, or a gas such as air may be introduced into the suction side of the white mud slurry pump. You may. Furthermore,
When the white mud slurry liquid is introduced into the white mud slurry liquid storage tank, a device such as mixing a gas such as air may be implemented. In any case, it is desirable to mix in a large amount of fine foam with a diameter of about 2 mm or less, but the size and amount of foam will depend on the condition of the white mud slurry (composition concentration, solid particle size, etc.) and will be determined through experiments. determined. The gas to be introduced is preferably decarbonized air and/or a gas that is inert to the caustic aluminate liquid, such as nitrogen, and is a gas that does not cause carbonation of the caustic alkali in the white mud slurry liquid. Although this is necessary, since the foamability of the white mud slurry liquid is quite good, the amount of gas introduced is relatively small, and in fact, untreated air can be used. In the following, the present invention will be explained in more detail using examples. Example 1 White mud slurry liquid 3 with a solid concentration of 500 g/m and an average particle size of 45 μm was put into a sedimentation tube (15 cmφ x 40 cm height), and the stainless steel powder sintered body connected to the tip of the compressed air pipe was sunk to the bottom of the sedimentation tube. The white mud slurry was stirred by fine air bubbles generated from the sintered body. The air feed rate was 0.1 Nm ³ /min for 10 minutes.
After stopping the air supply and allowing the tube to stand still for 10 minutes, a layer of foam-containing particles containing floated and separated fine bubbles was clearly visible in the sedimentation tube, a clear aluminate liquid layer below that, and a layer of sedimented particles below. There was phase separation. The foam-containing particle layer was collected by suction and analyzed to determine the aluminum hydroxide solid concentration and the solid sodium oxalate content (based on solid aluminum hydroxide weight) (Method A). On the other hand, for comparison, air was not introduced into the white mud slurry, but after it was simply allowed to stand for 10 minutes, the slurry at the same depth as the foam-containing particle layer was collected by suction and analyzed for the same components as above. . (Method B) The results are shown in Table 1.

[Table] Therefore, it is recognized that solid sodium oxalate was concentrated by 3.2 times if the foam was allowed to stand after forming. Example 2 A white mud slurry liquid (solid concentration 400 g/average particle size 40 μm) is introduced from conduit 6 shown in FIG. 1 and supplied to storage tank 1 via pump 3 and conduit 7 or 8. Then, it is transferred from the pump 4 through the conduit 9 to the classifier 2, where it is classified. Through the conduit 7, the white mud slurry liquid is poured into the storage tank 1 from a high point above the liquid level and falls into the storage tank 1 while entraining air. (Method A) or conduit 8
It is connected below the liquid level of the storage tank 1 via the , to prevent foam from getting mixed into the white mud slurry liquid.
(Method B) For both methods A and B, white mud slurry liquid with an actual volume of 200 M ³ /H is introduced into the classification tube 2 through the conduit 9, and the underflow flow rate of the classification tube 2 is controlled so that the rising speed is 0.8 M/H. did. Under this condition, in the case of method A, the classifier 2
Inside, a clear aluminate liquid layer was formed above the settled particle layer, and a foam-containing particle layer floated above the liquid layer, and the foam-containing particle layer was overflowed and separated from the conduit 10. On the other hand, in the case of method B, the above foam-containing particle layer was not formed in the classifier 2, and the clarified aluminate liquid overflowed from the conduit 10 and was separated. The overflow from the conduit 10 in methods A and B was collected and analyzed for its composition, and the results shown in Table 2 were obtained.

[Table] From Table 2, when foam is mixed, sodium oxalate is concentrated by 2.55 times based on the weight of solid aluminum hydroxide. As is clear from the above explanation, according to the method of the present invention, sodium oxalate in the white mud slurry can be concentrated by the simple method described above, and the efficiency of sodium oxalate removal from the Bayer process can be dramatically improved. It can be increased. Due to the properties of the Bayer process liquid, the present invention can achieve sufficient industrial effects without adding any special blowing agent; however, even greater effects can be achieved by adding an appropriate blowing agent as necessary. Needless to say, I can give you a lot.

[Brief explanation of the drawing]

FIG. 1 is a system diagram for explaining an embodiment of the present invention. 1... Slurry storage tank, 2... Classifier, 3, 4,
5... pump, 6, 7, 8, 9, 10, 11...
conduit.

Claims (1)

[Claims] 1. In the Bayer process, air and/or inert gas is introduced and stirred into the slurry liquid containing the caustic aluminate liquid, aluminum hydroxide particles, and sodium oxalate particles to mix fine air bubbles into the slurry liquid. A method for separating and concentrating sodium oxalate in a Bayer process slurry liquid, which is characterized by forming a foam-containing particle layer enriched with sodium oxalate particles in the upper layer of the liquid by the floating of the microbubbles, and then separating this layer. .