JPH024355B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for separating and recovering cobalt components from acidic wastewater in which cobalt salts are dissolved. More specifically, after adjusting the acidic wastewater to a specified pH with an alkali, it is precipitated as a cobalt hydroxide salt, and a flocculant is added while maintaining a constant temperature to grow the cobalt hydroxide into a stable floc. The cobalt salts are efficiently collected and recovered by floating the wastewater by blowing air to separate solid and liquid, and the concentration of cobalt salts in the wastewater after recovery is reduced as much as possible. . It is a well-known fact that in recent years, cobalt has been used as a catalyst in olefin oxation reactions. However, since it is used as a catalyst,
It is inevitable that it will become deactivated during its use. Moreover, in industrial processes, most of these deactivated cobalt salts are mixed into waste water in some form and discharged out of the system. Therefore, in pursuit of economic efficiency in industrial processes, efficient recovery of cobalt salts contained in wastewater has been an urgent need. Furthermore, in order to prevent pollution, it was necessary to reduce the amount of heavy metal components such as cobalt in the waste water as much as possible. Therefore, the establishment of a technology for collecting and recovering cobalt salts in wastewater has been attracting attention from both the economic efficiency of the oxo reaction industrial process and the prevention of pollution. Conventionally, this type of acidic wastewater is first neutralized with alkali, then led to a settling tank and left to stand for a long time.
The method of collecting settled solid components was thought to be the cheapest. In a state where solid-liquid separation is possible, wastewater is prevented by an overflow, and the slurry containing cobalt salt collected at the bottom of the sedimentation tank is separately filtered and recovered. One drawback of this method is that although the wastewater is neutralized, it still contains a large amount of cobalt salt and the concentration of heavy metals in the wastewater does not meet the emission regulation value for wastewater. Another problem is that it takes a lot of effort to pump up the slurry from the sedimentation tank and filter it, making it difficult to manage the operation of the sedimentation tank. Other methods include peroxide decomposition,
There have been proposals for combustion recovery methods, but none of them satisfy the two requirements of economical recovery of cobalt salts and prevention of wastewater pollution. After various studies on the properties of acidic wastewater, the present inventors neutralized the acidic wastewater, recovered cobalt salt at a high rate using an extremely simple method, and minimized the cobalt concentration in the aqueous phase. The method was established and the present invention was completed. The focus of the present invention is as explained in detail below. The starting material of interest is strongly acidic wastewater containing hundreds of ppm of cobalt salts. Although it contains almost no suspended matter, it has a slightly brownish color. Add an alkaline aqueous solution to this wastewater to adjust the pH. Examples of the alkali used here include water-solubilized products of alkali metals and alkaline earth metals, but sodium hydroxide is considered to be preferable because it is inexpensive. It does not have to be a pure product, and alkaline process wastewater may be used. Since PH has a very subtle effect, its adjustment is first done with a highly concentrated alkali.
Next, minor adjustments should be made with low concentrations of alkali. It can be seen that as the pH increases, cobalt salts begin to precipitate in the form of fine particles. Here, for solid-liquid separation, there are two methods: allowing it to settle for a long time and forcing it through filtration. At the experimental stage, we searched for conditions using the latter method. After removing the precipitate by filtration, we tracked the concentration of cobalt salt in the filtrate. When the pH reached 9 or higher, the cobalt concentration decreased sharply, but especially when the pH reached 9.
In 12.0, the decrease is significant. Therefore, if the pH is set within this range, most of the dissolved cobalt salt will precipitate as fine particles, making solid-liquid separation possible.
A similar phenomenon can be seen even if the PH is higher than 12.0, but in terms of actual process operation management, it is meaningless to set the PH higher than this, so 10.0 to 12.0 should be selected as the preferred condition. It is. Looking at the behavior of the produced particles, at room temperature, the diameter of the produced particles is minute, so it takes time for precipitation. Moreover, even if it is filtered in this state, it is difficult to filter because the particles are so small. In order to perform solid-liquid separation efficiently, it is necessary to promote particle size growth in some way. To achieve this objective, we focused on adding a polymer flocculant. The flocculant has the effect of binding multiple microparticles together to form a stable floc, which apparently has the same effect as creating large particles. Therefore, it is observed that the precipitation rate increases, the efficiency of solid-liquid separation improves, and the aqueous phase is rapidly clarified. Next, when the types and effects of flocculants were compared, it was found that anionic flocculants were more effective than cationic and nonionic flocculants for the wastewater.
That is, when using the same wastewater and measuring the clearing rate of the aqueous phase by adding various flocculants in the range of 1 to 50 ppm, it was found that addition of 1 ppm or more of anionic agents had a significant effect. When looking at the actual effect, ~20ppm is sufficient to achieve the purpose. Adding more than this is considered to be economically ineffective. Next, we investigated the effect of temperature on the atmosphere when adding the flocculant, and found that the sedimentation rate was faster at 30°C or higher than at room temperature. In actual processes, it is conceivable to adjust the temperature to a predetermined level using high-temperature waste water, or it is also possible to use waste steam blowing. In any case, it seems better to actively process at an elevated temperature than to process at room temperature. Furthermore, the present inventors investigated solid-liquid separation techniques. It is not advisable to precipitate the solid content and then recover it in solid-liquid separation, as has been done in the past, as it requires a great deal of labor and is not suitable for practical application. If particles produced by flotation separation can be collected on the liquid surface, process management will be easier. In the above experiment, solid-liquid separation of stable particles was performed by sedimentation, but we continued to investigate the floating properties of these particles. After adjusting the pH of the waste water, air is introduced from the bottom of the container as bubbles with a diameter of 1 mm or less, and the temperature is maintained at 30 to 50°C while the waste water is gently stirred. When flocculant was added to a predetermined concentration in this state, a phenomenon was observed in which cobalt hydroxide particles were bound together by the flocculant and grew into larger flocs, and at the same time the flocs contained air bubbles, causing the flocs to float up. It was done. It has become clear that flocs containing air bubbles are extremely stable and will reliably float to the surface without settling to the bottom unless agitated by an external mechanical force. Moreover, the cobalt concentration in the aqueous phase at the base was not much different from that in the filtrate after filtration of the wastewater, confirming that solid-liquid separation was achieved by the flotation method. From what has been explained in detail above, according to the present invention, it has been possible to efficiently recover the cobalt content in acidic wastewater and to minimize the heavy metal concentration in the wastewater after solid-liquid separation. Next, examples of the present invention will be shown. In the following examples, the starting material is strongly acidic (PH
= 1 or less), and an aqueous solution (hereinafter abbreviated as raw wastewater) containing 240 ppm of cobalt and free of suspended solids was selected. The concentration of dissolved cobalt salts was measured by atomic absorption spectrometry using a cobalt lamp. The flocculants used were all easily available. Anionic type: AP-120 manufactured by Diafloc Co., Ltd. Cationic type: KP-201A manufactured by Diafloc Co., Ltd. Nonionic type: NP-800 manufactured by Diafloc Co., Ltd. Example 1 Effect of PH Place the raw wastewater in a 500 ml beaker (85 mm diameter, 120 mm height) and place it in a magnetic stirrer. After adjusting the pH to the desired value while stirring gently, continue stirring for 5 minutes, then stop stirring and let stand. Each time you adjust the pH,
The cobalt concentration remaining in the filtrate was measured after filtering through a 5-10 μm glass filter. As shown in Table 1, it was found that almost no cobalt remained in the filtrate in the pH range of 10.0 to 12.0.

[Table] Example 2 Effect of adding flocculant After adjusting the raw wastewater to pH = 10.0 according to Example 1, three types of flocculants, anionic, cationic, and nonionic, were gently stirred with a magnetic stirrer. 10 ppm of each was added dropwise. then 1
After separating, stop stirring and let stand. Immediately after standing, the slow settling of solids was observed as the aqueous phase became clearer. After allowing the solution to stand for 10 minutes, the aqueous phase at the liquid surface was sampled to measure the cobalt concentration. As shown in Table 2, the results clearly show that anion systems promote sedimentation.

[Table] Next, we compared the effect of the concentration to be added only for anionic compounds. The experiment was conducted at a concentration range of 1 to 50 ppm, and the results obtained are shown in Table 3.
It was found that there was no difference in sedimentation rate if it was 1 ppm or more. Furthermore, after 10 minutes of standing still, samples were taken from the liquid surface to measure the cobalt concentration in the aqueous phase, and it can be said that there is no problem if it is 1 to 20 ppm.

【table】

[Table] Example 3 Effect of temperature Following Example 1 above, the raw wastewater was set at a predetermined temperature in advance, and while stirring with a magnetic stirrer, alkali was added to adjust the pH to 10.0, and anionic coagulation was performed. The agent was added dropwise to a concentration of 10 ppm. . After 1 minute had passed after the completion of the dropwise addition, stirring was stopped, and the sedimentation rate was then observed. As shown in Table 4, when the temperature was 30°C or higher, the entire body became clear within just 30 seconds after being left to stand, whereas when it was at room temperature (15°C), it took more than 30 seconds. This made the influence of heating clear.

[Table] Example 4 Effect of flotation Raw wastewater is poured into a cylindrical glass tube with an inner diameter of 100 mm and a height of 800 mm, almost full. The entire tube is kept at 40°C, and air is forced into the cylindrical part as small bubbles with a diameter of 1 mm or less at a rate of 50 ml/min. Therefore, the inside of the cylinder is constantly gently stirred by air bubbles. Next, alkali was injected from the bottom of the cylinder to adjust the pH to 10.0, and 20 ppm of anionic flocculant was added. After adding the flocculant, air was continued to be injected for about 1 minute, and then the aqueous phase at the bottom of the cylinder was sampled to measure the cobalt concentration, and the cobalt concentration was approximately 1 to 3 ppm. This revealed that the analyzed solid content was reliably separated by the flotation method.

Claims (1)

[Claims] 1. After adding an alkali to acidic wastewater containing cobalt and adjusting the pH of the wastewater, a flocculant is added to the wastewater at a predetermined temperature to remove the solid components containing cobalt salts. A method for separating and recovering cobalt components from wastewater, which is characterized by flotation separation. 2. The method according to claim 1, which comprises adding an alkali to acidic wastewater containing cobalt to adjust the pH of the wastewater to 10.0 to 12.0. 3. The method according to claim 1, characterized in that after adjusting the pH of the acidic wastewater containing cobalt, a flocculant is added thereto at a temperature of 30°C or higher. 4. The method according to claim 1, wherein the flocculant to be added is anionic and the amount added is 1 to 20 ppm based on the wastewater. 5. The solid component containing cobalt salt produced by the addition of a coagulant is floated and separated by simultaneously blowing pressurized air into the waste water, as set forth in claim 1. Method.