JPS59227720A - Oxidative destruction of organic substance in sodium aluminate solution - Google Patents

Abstract

PURPOSE:To subject an organic substance in a sodium aluminate solution to oxidative destruction efficiently, and to remove it easily, by treating the solution prepared by Bayer's process with an oxidizing gas having a dew point higher than the temperature of the solution. CONSTITUTION:In preparation of alumina by Bayer's process, a sodium aluminate solution circulating in the process is sealed in a pressure container, steam is added to an oxidizing gas such as oxygen or an oxygen-containing gas, e.g., air, etc., the dew point of the gas is made higher than the circulating mother liquor, and the gas is introduced to the pressure container by pressure. By this treatment, an organic substance contained in the solution is efficiently decomposed, finally processed into oxalate, carbonate, etc., and exhausted easily form Bayer's process to the outside of the system, and total amounts of organic substances can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of alumina using the Bayer process.

This invention relates to a method for oxidatively decomposing organic substances, particularly polymeric substances, in a sodium aluminate solution (hereinafter referred to as circulating mother liquor) that is circulated in a process.

In the Bayer method, trace amounts of high-molecular organic matter contained in bauxite are eluted into the circulating mother liquor, and as the mother liquor is used nine times, it gradually accumulates in the mother liquor. It is known to have an adverse effect on the precipitation of aluminum hydroxide.

When the high-molecular-weight organic substances eluted into the circulating mother liquor undergo oxidative decomposition, they change into organic substances with small molecular weights, and eventually become low-molecular weight compounds such as oxalates and carbonates. The oxalate and carbonate produced in the manner described in (B) can be removed from the mother liquor by known methods, but generally the solubility of oxalate in the mother liquor is low, so the oxalate produced above the solubility is removed from the mother liquor. It naturally precipitates in the mother liquor and is discharged from the Bayer 1 process system together with red mud and precipitated aluminum hydroxide. Utilizing these various properties, various methods have been proposed in the past for oxidatively decomposing high-molecular organic substances in circulating IR mother liquor and precipitating and removing them as oxalate. Namely, 2. A method of bringing pressurized oxygen into contact with circulating mother liquor by the present inventors (Japanese Patent Publication No. 45-30458).

Method of contacting with pressurized air at 240°C or higher (Unexamined Japanese Patent Publication No. 55
-62809), pressurized oxygen'-! at 120-350°C! or a method of contacting with a gas containing oxygen (Japanese Patent Application Laid-open No. 1986-
71626).

However, in order to promote the oxidative decomposition reaction of organic matter using these methods, it is necessary to use a high-pressure vessel (usually in a high-pressure vessel).

The temperature of the circulating mother liquor must be raised to a high temperature by installing a high-pressure steam pipe inside and increasing the temperature by exchanging heat with the pipe or by directly blowing live steam into the pipe. As a result, a device for blowing oxygen or oxygen-containing gas (hereinafter referred to as oxidizing gas) into the high-pressure container and the high-pressure container were required to have a high pressure resistance, which had the disadvantage of requiring a large amount of extra cost for the equipment. .

In the course of various studies, the present inventors discovered that an oxidizing gas with water vapor added to the circulating mother liquor sealed in a pressurized container was injected and dispersed under pressure.

゛ 2 ° It was discovered that the oxidative decomposition of the polymeric organic matter in the mother liquor proceeded much faster than when only the oxidizing gas was simply introduced under pressure and dispersed, and the present invention was completed.

An object of the present invention is to oxidize and decompose polymeric organic substances more efficiently than conventional methods, and is characterized in that the mother liquor is treated with an oxidizing gas having a dew point higher than the temperature of the circulating mother liquor. be.

In the present invention, it goes without saying that the temperature of the oxidizing gas containing water vapor must be higher than the temperature of the mother liquor.
The dew point of the oxidizing gas containing water vapor must be higher than the temperature of the mother liquor. If the dew point of the oxidizing gas containing water vapor is lower than the temperature of the circulating mother liquor, no improvement in the efficiency of oxidative decomposition of the polymeric organic matter will be observed. Preferably, the oxidizing gas is saturated with water vapor.

It is desirable that the oxidizing gas and the steam be mixed as uniformly as possible when the oxidizing gas to which water vapor has been added is pressurized into the circulating mother liquor. The effects of the present invention cannot be achieved if oxidizing gas (with a dew point lower than the temperature of the circulating mother liquor) and water vapor are injected and dispersed into the circulating mother liquor sealed in a high-pressure container from different locations.

By processing according to the method of the invention.

High-molecular organic matter is oxidized and decomposed and ultimately becomes oxalate, carbonate, etc. As mentioned above, it is easily discharged from the system from the first step, so the amount of organic matter in the system is also reduced. Rikiki decides to do that.

If we try to achieve the same organic matter decomposition rate with this method and the conventional method, the treatment temperature of the circulating mother liquor will be lower in the single method, and therefore the usage value of steam will be lower and the pressure resistance required for the equipment will be lower. The strength also decreases. Furthermore, when the circulating mother liquor is treated at the same temperature in both methods, the oxidative decomposition rate of organic matter is higher in this method, and therefore the equipment scale can be reduced accordingly.

By the way, the reason why the oxidative decomposition rate of high-molecular organic substances in the circulating mother liquor is greatly improved by one method is not necessarily clear, but it is presumed to be as follows.

That is, when the oxidizing gas containing water vapor is pressurized and dispersed into the circulating mother liquor, it comes into contact with the mother liquor and is cooled. At that time,
At the gas-liquid interface between the oxidizing gas and the circulating mother liquor, water vapor contained in the gas condenses to generate a large amount of heat of condensation, and the temperature of the mother liquor locally increases near the gas-liquid interface. As a result, the oxidative decomposition reaction of organic matter present in the mother liquor increases. In this way, when the oxidative decomposition reaction of organic matter occurs extremely locally and rapidly, the reaction heat generated at that time is difficult to dissipate in a short period of time, so the temperature of the reaction area further increases, and therefore the oxidative decomposition reaction will be further accelerated.

Note that if the dew point of the oxidizing gas containing water vapor is lower than the temperature of the circulating mother liquor being treated, the heat of condensation of the water vapor, which has a large amount of heat, cannot be used, so no improvement in the efficiency of oxidative decomposition of organic matter is observed. it is conceivable that.

In carrying out the method of the present invention, not only is the circulating mother liquor taken out of the system in the first step of the buyer and treated, but also an oxidizing gas containing water vapor is injected into an autoclave in the step of extracting alumina from bauxite. It is also possible to decompose organic matter at the same time as alumina extraction.

Examples of the present invention are shown below along with comparative examples.

Here, 00 is the concentration (f/l) of organic carbon due to organic substances with a molecular weight of 500 or more contained in the liquid to be treated, and its measurement method is a known method (LEvBR).

G,,LIG)IT MBTAL8 107,7
1 (197B)), ultrafiltration is performed to fractionate and collect organic substances with a molecular weight of 500 or more in the liquid to be treated, and the organic carbon of this organic substance is extracted using a 00 analysis needle (for example, Shimadzu Too-1
0B) and combust it to quantify the amount of carbon.

Example 1 Pressurized stainless steel vessel (inner diameter 1
60M, internal height 600M), the precipitation finished liquid (Nan.

130 f/l * At, OB 71? /l*
OO9-2f/1)7t was sealed, and the temperature of the liquid to be treated was maintained at 200°C by heating or cooling the pressurized container from the outside.

The rotating cage contained in the contact device is fied by a magnetic diversion drive device.
While rotating at loooRPM, water vapor is saturated through the gas inlet pipe installed at the bottom of the pressurized container, and air at 7'C250℃ is released! The mixture was pressurized into the container for 120 minutes at a flow rate of 7 ft - (in terms of dry air at normal pressure and room temperature, hereinafter the same). The remaining air that was not absorbed into the liquid to be treated was released to the outside through a pressure-holding valve provided at the top of the pressurized container. The release pressure of the pressure holding valve is the saturated water vapor pressure of the precipitate and the air pressure (8ky/a at room temperature).
The pressure was set to be a composite pressure of rt (air pressure at a predetermined processing liquid temperature corresponding to absolute pressure).

During the oxidative decomposition treatment, the temperature of the liquid to be treated was controlled to be kept constant. After the treatment was completed, the liquid to be treated was cooled and taken out, and supersaturated oxalate and the like were naturally precipitated and removed at room temperature, and then 0OCf/l) in the liquid to be treated was measured.

Example 2 Exactly the same as Example 1 except that air with a temperature of 250°C and a dew point of 230°C was used as the oxidizing gas Example 3 Exactly the same as Example 1 except that the temperature of the liquid to be treated was maintained at 170°C It was conducted under the same conditions.

Example 4 The experiment was carried out under exactly the same conditions as in Example 1, except that oxygen saturated with water vapor (absolute partial pressure of oxygen in terms of room temperature was 6 ktlal) was used as the oxidizing gas.

Comparative example 1 Dry air at a temperature of 250°C at a flow rate of 17% S.

In addition, this was carried out under exactly the same conditions as in Example 1, except that saturated steam at a temperature of 250°C was passed through 14 points at a flow rate of &3r/min (same as the steam flow rate in Example 1) and was used as an oxidizing gas. .

Comparative Example 2 Exactly the same as Example 1 except that air with a temperature of 250°C and a moving point of 170°C was used as the oxidizing gas.
Shown in the table.

From the above results, it is clear that the method for oxidative decomposition of organic matter according to the present invention greatly exceeds the drawbacks of the conventional method for oxidative decomposition of organic matter.

Claims (1)

[Claims] A method in which a sodium aluminate solution is treated with oxygen or a gas containing oxygen to oxidize and decompose the platelets contained in the solution in the Bayer method, which is treated with the gas having a crocodile point higher than the temperature of the solution. A method for oxidative decomposition of organic matter in a sodium aluminate solution.