JP2002226211A - Recovery method for gypsum and magnesium hydroxide and recovery system therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means which recovers high purity magnesium hydroxide from a precipitations of gypsum and magnesium hydroxide. SOLUTION: The gypsum and magnesium hydroxide are formed by adding a quick lime, a slaked lime or slaked lime slurry into a solution introduced into a crystallization vessel by preferably warming up at 30-80 deg.C, the precipitated gypsum is extracted from the bottom of the vessel, on the other, the suspension containing unprecipitated gypsum particles and magnesium hydroxide particles is introduced into a liquid cyclone, then the magnesium hydroxide particles in the upper parts of the cyclone are recovered, moreover the recovery method of the gypsum and magnesium hydroxide is characterized by returning a mixture of the gypsum particles and the magnesium hydroxide in the lower parts of the cyclone to the crystallization vessel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for effectively separating and recovering gypsum and magnesium hydroxide from a solution to be treated. The recovery method of the present invention is suitable as a method for separating and recovering gypsum and magnesium hydroxide in a step of regenerating magnesium hydroxide used as a desulfurizing agent or a step of treating petroleum-based combustion ash.

[0002]

2. Description of the Related Art Various types of exhaust gas often contain sulfur oxides, and M is used as a desulfurizing agent to remove sulfur oxides.
A method using a mixed slurry of g (OH) ₂ and Ca (OH) ₂ is conventionally known. In this desulfurization method, the mixed slurry that has absorbed sulfur oxides is air-oxidized under acidic conditions to form MgSO 4.
₄ and CaSO ₄ (gypsum), and the gypsum is separated and recovered, while quick lime or slaked lime is added to the liquid containing MgSO ₄ to obtain M
g (OH) ₂ and CaSO ₄ , the gypsum is separated,
Mg (OH) ₂ is reused as a desulfurizing agent.

[0003] Further, a method of treating the combustion ash of petroleum fuel discharged from boilers and the like of thermal power plants and various industrial plants with water or sulfuric acid and recovering valuable metals such as nickels and vanadium from the leached slurry. Although it is known, as a treatment method after recovering valuable metals, quick lime is added to wastewater, sulfate ions in the liquid are turned into gypsum and precipitated, and while this is recovered, slaked lime or slaked lime slurry is added. Separation of magnesium ions in the solution by precipitation as magnesium hydroxide has been performed.

[0004]

When gypsum and magnesium hydroxide precipitates are formed and separated and recovered in this way, gypsum particles that have aggregated or crystallized precipitate at the bottom of the tank, but fine gypsum particles do not. Dispersed in liquid, and also easy to disperse in liquid because magnesium hydroxide particles are also fine,
Therefore, even if the gypsum precipitate is extracted from the tank bottom, there is a problem that it is difficult to separate and recover magnesium hydroxide from gypsum because fine gypsum particles and magnesium hydroxide particles are mixed in the liquid. .

[0005] The present invention has solved such a problem in the conventional treatment method, and the gypsum precipitate and the magnesium hydroxide precipitate can be easily separated from each other by a simple means combining a crystallization tank with a hydrocyclone. A recovery method and apparatus are provided. This method can be widely applied to a treatment system in which gypsum and magnesium hydroxide are precipitated, and is particularly suitable in a treatment process of a desulfurizing agent and a treatment process of petroleum combustion ash.

[0006]

According to the present invention, (1) a calcium compound is added to a solution containing sulfate ions and magnesium ions, and this solution is heated to 5 to 80 ° C. to form gypsum and magnesium hydroxide; The present invention relates to a method for recovering gypsum and magnesium hydroxide, which comprises separating the solid and liquid to recover gypsum and magnesium hydroxide. This method is (2)
After addition of the calcium compound, the solution is
Includes a recovery method that produces gypsum and magnesium hydroxide by heating to ° C.

[0007] According to the above method, the solution in the crystallization tank is 5-8.
By increasing the crystallization temperature by heating to 0 ° C, preferably 30 to 80 ° C, the solubility of slaked lime and the like increases, so that it is not necessary to add slaked lime and the like in excess. Therefore, the amount of undissolved slaked lime mixed in the product is small, and the purity of magnesium hydroxide can be increased. Further, since the crystallization temperature is increased, the formation of gypsum is promoted, and the effect of separating gypsum and magnesium hydroxide is improved.

The present invention also provides (3) a solution containing sulfate ions and magnesium ions, which is introduced into a crystallization tank, a calcium compound is added to form gypsum and magnesium hydroxide, and the precipitated gypsum is extracted from the bottom of the tank. On the other hand, a suspension containing gypsum particles and magnesium hydroxide particles that do not precipitate is led to a liquid cyclone, the magnesium hydroxide fine particles at the upper part of the cyclone are collected, and a mixture of the gypsum particles and magnesium hydroxide at the lower part of the cyclone is crystallized. And a method for recovering gypsum and magnesium hydroxide.

According to the above-mentioned recovery method, gypsum having a relatively large particle size is deposited on the bottom of the crystallization tank, so that it is extracted and recovered, and fine particles such as magnesium hydroxide are introduced into a liquid cyclone and classified. Therefore, gypsum having many coarse particles and magnesium hydroxide having many fine particles can be efficiently separated and collected.

In the recovery method of the present invention, (4) a liquid cyclone is provided in two stages, and a suspension containing gypsum particles and magnesium hydroxide particles which do not precipitate in a crystallization tank is led to a first liquid cyclone. The mixture having an average particle size of about 20 to 80 μm collected in the lower part of the first hydrocyclone is returned to the crystallization tank, while
The suspension containing the fine particles at the upper part of the first hydrocyclone is led to the second hydrocyclone, and the magnesium hydroxide fine particles that aggregate at the upper part of the second hydrocyclone are collected, while the average particle size of the particles collected at the lower part of the second hydrocyclone is about 2 μm. A recovery method characterized by returning the mixture of 〜20 μm to the crystallization tank or the crystallization tank and the first hydrocyclone.

According to the above-mentioned recovery method, the liquid cyclone is provided in two stages, and the coarse particles collected from the first stage cyclone are returned to the crystallization tank for circulation and used, and the fine particles are guided to the second stage cyclone. Therefore, it is possible to recover magnesium hydroxide having a large amount of fine particles at a high concentration, and it is possible to recover magnesium hydroxide which has a high effect of separating from gypsum and hardly contains gypsum.

Further, as an application example of the recovery method of the present invention, (5) a treatment solution of petroleum-based combustion ash is led to a crystallization tank,
Gypsum and magnesium hydroxide are formed by adding any of quick lime, slaked lime or slaked lime slurry to the solution, the precipitated gypsum is withdrawn from the bottom of the tank, and a suspension containing unprecipitated gypsum particles and magnesium hydroxide particles is subjected to liquid cyclone. (6) The treatment solution of petroleum-based combustion ash is a raffinate solution obtained by extracting nickel or vanadium with a solvent, and slaked lime slurry is added to the solution to produce gypsum and magnesium hydroxide, which are separated and collected. About the method.

According to the above recovery method, gypsum and magnesium hydroxide can be efficiently separated and recovered from a processing solution of petroleum-based combustion ash, for example, a processing solution obtained by extracting vanadium or nickel.

Further, the recovery method of the present invention is suitable as a method for treating a magnesium hydroxide slurry used as a desulfurizing agent. Examples of its application include (7) a treatment solution of a magnesium hydroxide slurry absorbing sulfur oxides. The method includes a recovery method in which the gypsum is led to a crystallization tank, the precipitated gypsum is extracted from the bottom of the tank, and a suspension containing unprecipitated gypsum particles and magnesium hydroxide particles is led to a liquid cyclone. Furthermore, (8) the recovery method according to any of the above, wherein the solution in the crystallization tank is heated to 30 to 80 ° C. to form gypsum and magnesium hydroxide.

According to the above-mentioned recovery method, gypsum and magnesium hydroxide produced by the desulfurization treatment can be separated and recovered from the magnesium hydroxide slurry used as the desulfurizing agent. , And can be reused as a desulfurizing agent.

The present invention further provides (9) a crystallization tank for adding gypsum and magnesium hydroxide by adding a calcium compound to the solution to be treated, a liquid cyclone communicating with the crystallization tank, and gypsum particles which do not settle in the crystallization tank. It has a liquid feed line for guiding a suspension containing magnesium hydroxide particles to a hydrocyclone, a feed line for returning a sediment at the bottom of the hydrocyclone to the crystallization tank, and means for collecting fine particles at the top of the hydrocyclone. Gypsum and magnesium hydroxide recovery equipment. In this recovery device, (10) storage tanks are provided in each of a liquid sending pipe, a feeding pipe, a discharge pipe of the crystallization tank, and a discharge pipe leading from the upper part of the liquid cyclone to the fine particle collecting means. Includes embodiments that include

According to the above recovery apparatus, the recovery method of the present invention can be carried out efficiently, and gypsum and magnesium hydroxide can be separated and recovered efficiently. Further, the purity of the recovered gypsum and magnesium hydroxide is high.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. Unless otherwise indicated,% is% by weight.
And the gypsum is dihydrate gypsum. FIG. 1 shows an example of an apparatus configuration for implementing the recovery method of the present invention. In the illustrated recovery apparatus, a crystallization tank 10 for adding a calcium compound to the solution to be treated to generate gypsum and magnesium hydroxide, a crystallization tank 10
Cyclones 11 and 12 communicating with the crystallization tank 10
A liquid feed line 13 for guiding gypsum particles and magnesium hydroxide particles that do not settle in the liquid cyclone together with the solution, a feed line 14 for returning the sediment below the liquid cyclone to the crystallization tank, and a means for collecting fine particles above the liquid cyclone. A hydrocyclone is provided in two stages. A means for extracting and recovering gypsum is provided at the bottom of the crystallization tank 10. Further, a storage tank 15 for adjusting the supply amount of the solution is interposed in each pipe. The crystallization tank preferably has a draft tube.

The solution to be treated can be widely applied as long as gypsum and magnesium hydroxide precipitate in the solution. As a specific example, a treatment solution such as a magnesium hydroxide slurry that has absorbed a sulfur oxide, or an aqueous solution that has been treated with petroleum-based combustion ash is used.
Note that this petroleum-based combustion ash is dust ash generated when burning petroleum-based fuels such as tar fuel, heavy oil, petroleum coke, petroleum pitch, and asphalt. Minutes are eluted.

A calcium compound, for example, quicklime powder or slaked lime slurry, is added to the solution to be treated (a solution containing sulfate ions and magnesium ions) introduced into the crystallization tank 10 and uniformly stirred. PH of 10
As described above, the pH is preferably adjusted to the range of 10 to 12.
Further, the crystallization tank is heated to raise the liquid temperature to 5 to 80C, preferably 30 to 80C. Usually, slaked lime or the like is added in a slightly excessive amount to sufficiently precipitate magnesium and sulfate groups in the liquid. However, in this case, undissolved slaked lime and the like remain and become mixed with magnesium hydroxide to become impurities. In the present invention, since the solubility of slaked lime and the like is increased by heating the solution to increase the crystallization temperature, it is not necessary to add these in excess. Therefore, the amount of undissolved slaked lime mixed in the product is small, and the purity of magnesium hydroxide can be increased. Further, since the crystallization temperature is increased, the formation of gypsum is promoted, and the effect of separating gypsum and magnesium hydroxide is improved.

In the crystallization tank, sulfate ions in the liquid react with lime to form calcium sulfate (gypsum), and magnesium ions in the liquid form fine particles of magnesium hydroxide. Since the agglomerated gypsum particles settle at the bottom of the tank, they are extracted from the bottom of the tank, and the gypsum cake obtained by solid-liquid separation is washed with sulfuric acid and further washed with water to collect gypsum. On the other hand, fine gypsum particles and magnesium hydroxide particles do not settle and float in the liquid, and thus this suspension is led to the first liquid cyclone 11 through the liquid feed pipe 13.

In the liquid cyclone 11, fine particles in the liquid collect at the upper part of the cyclone, and relatively coarse particles collect at the lower part of the cyclone. Since magnesium hydroxide particles are generally finer than gypsum particles, magnesium hydroxide particles mainly aggregate at the upper part of the cyclone, and a mixture mainly composed of gypsum particles and partially containing magnesium hydroxide particles at the lower part of the cyclone. The mixture at the lower part of the cyclone is withdrawn and returned to the crystallization tank 10 through the feed line 14. On the other hand, the suspension above the cyclone was transferred to the second liquid cyclone 12.
Send to

In the second hydrocyclone 12, finer particles collect at the upper part of the cyclone, and coarser particles collect at the lower part of the cyclone. Since most of the fine particles in the upper part of the cyclone are magnesium hydroxide, this suspension is extracted from the second liquid cyclone 12, and the solid-liquid separation is performed to recover the magnesium hydroxide. Second hydrocyclone 12
Is a mixture of magnesium hydroxide and gypsum, which are finer than those agglomerated in the lower part of the first hydrocyclone 11, so that a part of this mixture is passed through the circulating duct 14 11 and the rest is returned to the crystallization tank 10.

Since the mixture particles agglomerated in the lower part of the cyclone are mostly gypsum, the gypsum particles are returned to the crystallization tank 10 to promote the aggregation of the gypsum particles and precipitate, thereby increasing the recovery rate of the gypsum. Further, since magnesium hydroxide is separated from gypsum by the liquid cyclone, high-purity magnesium hydroxide with a significantly reduced amount of gypsum can be finally recovered. In the case of performing the continuous treatment, in each of the liquid feed pipe, the feed pipe, the discharge pipe of the crystallization tank, and the discharge pipe leading from the upper part of the liquid cyclone to the fine particle collecting means, when performing the continuous treatment. It is preferable to interpose a storage tank 15. Storage tank 15
Is provided, the supply amount of the liquid to the next step can be adjusted, and the classification effect at the time of continuous operation can be improved. In the case of a small batch processing, a storage tank may not be provided.

Vanadium and nickel can be separated from the processing solution of petroleum-based combustion ash by solvent extraction.
Since this raffinate solution contains magnesium ions and sulfate ions, it can be treated by the method of the present invention. As an example, the raffinate solution and slaked lime slurry are introduced into the crystallization tank 10 and uniformly stirred. After overflow, the precipitate at the bottom of the tank is extracted, and solid-liquid separation is performed to collect gypsum. On the other hand, the suspension in the upper part of the crystallization tank is guided to the first liquid cyclone 11, and after classification, the aggregates in the lower part of the cyclone are returned to the crystallization tank 10. The agglomerates are generally particles having an average particle size of about 20 to 80 μm, most of which have an average particle size of about 50 μm, and mainly contain gypsum and partially contain magnesium hydroxide. Further, the suspension is extracted from the upper part of the first hydrocyclone 11 and sent to the second hydrocyclone 12. After the differentiation class, a part of the aggregates in the lower part of the cyclone was returned to the first liquid cyclone 11, and the remainder was left in the crystallization tank 1.
Return to 0. The agglomerates are particles having an average particle size of about 2 to 20 μm, mostly having an average particle size of about 15 μm, and mainly contain gypsum and partially contain magnesium hydroxide. On the other hand, magnesium hydroxide having a concentration of about 90% or more and an average particle size of about 2 μm can be recovered by extracting the suspension above the second hydrocyclone and performing solid-liquid separation.

Since the raffinate solution contains ammonium ions in which ammonium sulfate in the ash is dissolved, and the pH is adjusted to neutral or weakly alkaline by adding ammonia during solvent extraction, gypsum is used. When magnesium hydroxide and magnesium hydroxide are recovered by solid-liquid separation, ammonia can be recovered from the filtrate. This ammonia can be recovered by a distillation operation such as steam distillation or simple distillation.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the recovery method of the present invention will be specifically described with reference to examples.

[Embodiment] Using the recovery apparatus shown in FIG. 1, a petroleum-based combustion ash treatment liquid was introduced into a crystallization tank, the liquid temperature was raised to 50 ° C., and slaked lime slurry was added thereto and uniformly stirred. did.
Next, after the suspension in the upper part of the crystallization tank is led to the first liquid cyclone and operated for about 2 minutes, the aggregate in the lower part of the cyclone is returned to the crystallization tank, and the suspension in the upper part of the cyclone is introduced into the second liquid cyclone. did. After operating for about 11 hours, the fine particles on the upper part of the cyclone were collected, and the aggregates on the lower part of the cyclone were returned to the crystallization tank. The precipitate was recovered from the bottom of the crystallization tank. Table 1 summarizes the amount of the processing solution, the components of the recovered material, and the recovered amount. Gypsum and magnesium hydroxide were recovered from the petroleum-based combustion ash treatment liquid in the same manner as in Example 1 except that the liquid cyclone was not used (Comparative Example 1). Further, precipitation was performed without heating the crystallization tank (Comparative Example 2). The result is shown in comparison with Table 1. As shown in the processing results in Table 1, in the method of the present invention, the purity of the recovered gypsum is 99% or more, and the purity of magnesium hydroxide is 91%, all of which are high purity. On the other hand, in Comparative Example 1, the recovered amount of gypsum was about half that of the example, and the purity of the recovered magnesium hydroxide was 10%.
And extremely low. In Comparative Example 2, the purity of magnesium hydroxide was even lower.

[0029]

[Table 1]

[0030]

According to the recovery method and the recovery apparatus of the present invention, gypsum and magnesium hydroxide can be effectively separated from the solution to be treated. Therefore, while recovering gypsum, high-purity magnesium hydroxide containing almost no gypsum can be recovered.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a recovery device according to the present invention.

[Explanation of symbols]

10-crystallization tank, 11-first hydrocyclone, 12-second hydrocyclone, 13-liquid feed line, 14-feed line, 1
5-Storage tank.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01D 9/02 615 B01D 9/02 615Z 616 616 625 625A 53/34 ZAB C01F 11/46 Z 53/50 102B 53/77 B01D 53/34 125R C01F 11/46 ZAB102 (72) Inventor Keiichi Miura 2-4-2, Daisaku, Sakura-shi, Chiba F-term in the Central Research Institute of Taiheiyo Cement Co., Ltd. 4D002 AA02 AC01 BA02 DA05 DA06 DA11 DA12 EA07 FA03 GA01 GA03 GB03 GB09 GB12 HA04 4G076 AA10 AA14 AB18 BA13 GA00

Claims (10)

[Claims] 1. A calcium compound is added to a solution containing sulfate ions and magnesium ions, and the solution is added to a solution containing 5 to 8
Heated to 0 ° C. to form gypsum and magnesium hydroxide,
A method for recovering gypsum and magnesium hydroxide, comprising separating the solid and liquid into gypsum and magnesium hydroxide. 2. The method according to claim 1, wherein after adding the calcium compound, the solution is heated to 30 to 80 ° C. to form gypsum and magnesium hydroxide. 3. A solution containing a sulfate ion and a magnesium ion is led to a crystallization tank, and a calcium compound is added to generate gypsum and magnesium hydroxide. And a suspension containing magnesium hydroxide particles into a hydrocyclone,
Collect the magnesium hydroxide fine particles at the top of the cyclone,
A method for recovering gypsum and magnesium hydroxide, further comprising returning a mixture of gypsum particles and magnesium hydroxide below the cyclone to a crystallization tank. 4. A hydrocyclone is provided in two stages, and a suspension containing gypsum particles and magnesium hydroxide particles which do not precipitate in a crystallization tank is led to a first hydrocyclone, and an average particle size collected under the first hydrocyclone The mixture of about 20-80 μm is returned to the crystallization tank, while the suspension containing the fine particles at the top of the first hydrocyclone is led to the second hydrocyclone, and the magnesium hydroxide fine particles that aggregate at the top of the second hydrocyclone are collected. 4. The method according to claim 3, wherein the mixture having an average particle size of about 2 to 20 [mu] m collected under the second hydrocyclone is returned to the crystallization tank or the crystallization tank and the first hydrocyclone. 5. A treatment solution for petroleum-based combustion ash is guided to a crystallization tank, and any of quick lime, slaked lime or slaked lime slurry is added to the solution to form gypsum and magnesium hydroxide, and the precipitated gypsum is removed from the bottom of the tank. The method according to claim 3 or 4, wherein the suspension containing the gypsum particles and magnesium hydroxide particles that are extracted and settled is guided to a liquid cyclone. 6. The processing solution for petroleum-based combustion ash is a raffinate solution obtained by solvent extraction of nickel or vanadium,
6. The recovery method according to claim 5, wherein a slaked lime slurry is added to the solution to produce gypsum and magnesium hydroxide, which are separated and recovered. 7. A treatment solution of a magnesium hydroxide slurry having absorbed sulfur oxides is introduced into a crystallization tank, and the precipitated gypsum is extracted from the bottom of the tank, and a suspension containing non-precipitated gypsum particles and magnesium hydroxide particles is converted into a liquid. The method according to claim 3 or 4, which leads to a cyclone. 8. The solution in the crystallization tank is heated to 30 to 80 ° C. to form gypsum and magnesium hydroxide.
8. The collection method according to any one of items 7 to 7. 9. A crystallization tank for adding gypsum and magnesium hydroxide by adding a calcium compound to the solution to be treated, a liquid cyclone connected to the crystallization tank, gypsum particles and magnesium hydroxide particles which do not settle in the crystallization tank. Gypsum and magnesium hydroxide, having a liquid feed line for guiding the suspension to the hydrocyclone, a feed line for returning the sediment below the liquid cyclone to the crystallization tank, and a means for collecting fine particles above the liquid cyclone Recovery equipment. 10. A storage tank is provided in each of a liquid feed line, a feed line, a discharge line of the crystallization tank, and a discharge line leading from the upper part of the liquid cyclone to the fine particle recovery means. 9. The recovery device according to 9.