JPH08157219A - Separating and recovering method of chromium - Google Patents

Abstract

PURPOSE: To obtain a method for efficiently and advantageously in cost separating and recovering high purity chromium with excellent operability from a raw material containing chromium and iron. CONSTITUTION: Chromium is separated and recovered by dissolving the raw material containing chromium and iron in a sulfuric acid aq. solution, oxidizing to convert the iron and chromium in the solution respectively to trivalent iron sulfate and trivalent chromium sulfate, converting the trivalent chromium sulfate to hexa-aquachromium (11) sulfate by aging the solution and after that, adding a water soluble organic solvent as a crystallizing agent at 10-40 deg.C to selectively crystallize chromium sulfate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating and recovering chromium from a raw material containing chromium and iron, such as scrap of ferrochromium, chrome iron ore, and chromium-iron alloy material.

[0002]

2. Description of the Related Art Chromium is an extremely important metal element industrially used as a raw material for stainless steel, super alloys, heat-resistant materials and the like. However, there is currently no chromium ore production in Japan, and all chromium resources depend on imports from abroad. For this reason, the supply system of raw materials is fragile and the market price is extremely unstable, and securing raw materials is an important issue.

The main ore of chromium is chromite (main component F
eCr ₂ O ₄ ), which is supplied in the form of metallic chromium and ferrochrome through processing steps of beneficiation and smelting. Since the main coexisting element in chromium minerals is iron,
Separation and removal of iron is an important process in the manufacturing process of chromium metal. Furthermore, in recent years, countries that hold chromium resources have a strong tendency to process chromium ore into intermediate products such as ferrochrome by direct carbon reduction and then export it in order to increase added value. It is becoming an increasingly important task to remove the contaminants, separate and recover the chromium, and refine it into high-purity chromium for a special alloy having corrosion resistance, heat resistance or wear resistance.

Conventionally, as a method for separating and recovering chromium from the above-mentioned raw material containing chromium and iron, an aluminothermite method and an alum salt crystallization separation-electrolysis method have been industrially carried out. In the aluminothermite method, chromium concentrate is used as a raw material to selectively reduce chromium oxide at a high temperature of 1000 ° C. or higher and separate and recover it. With this method, it is difficult to obtain high-purity chromium due to residual iron, aluminum, silicon, and the like. In addition, it cannot be applied to the separation and recovery of chromium from ferrochrome. The crystallization separation method of alum salt is performed by dissolving raw materials containing chromium and iron with sulfuric acid,
Iron and other metal impurities are separated and removed as a precipitate of ammonium alum salt by adding ammonia and repeatedly adjusting the temperature, and chromium in the solution is recovered by electrowinning. In this method, ammonium alum salts such as iron are present in the form of fine colloid in the precipitation step, so that there are many losses due to the inclusion of chromium ions, and the filterability of the precipitate is poor, so separation from the solution is not easy. . Further, if the rate of changing the temperature in the process of adjusting the temperature of the solution is not appropriate, some chromium may be precipitated as chromium ammonium alum with low solubility.

Thus, an economical and rational method for industrially separating and recovering chromium from a raw material containing chromium and iron has not been established.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above problems of the prior art and to develop a method for efficiently and economically recovering chromium from a raw material containing chromium and iron, that is, Another object of the present invention is to provide a method for separating and recovering chromium, which uses an inexpensive reagent and has good operability, and separates and recovers chromium in a high yield and at a usable purity.

[0007]

The above objects are achieved by the present invention described in (1) to (3) below. (1) A method of separating and recovering chromium from a raw material containing chromium and iron, wherein the raw material containing chromium and iron is dissolved in a sulfuric acid aqueous solution and oxidized, and iron in the solution is trivalent iron. 10% to 40% after converting the solution of the trivalent chromium sulfate to hexavalent chromium (III) sulfate in the form of hexavalent chromium sulfate.
A method for separating and recovering chromium in which a crystallization agent is added to this solution at a temperature of ℃ to selectively crystallize chromium sulfate. (2) The aging is carried out at a temperature of 10 to 30 ° C. and at this temperature 1
The method for separating and recovering chromium as described in the above item (1), which is performed by holding for 0 hour or more. (3) The method for separating and recovering chromium according to (1) or (2) above, wherein the crystallization agent is a water-soluble organic solvent of at least one of alcohols, ketones, aldehydes and carboxylic acids.

[0008]

In the present invention, when chromium is separated and recovered from the raw material containing chromium and iron, the raw material containing chromium and iron is dissolved in an aqueous sulfuric acid solution to convert iron to iron (III) and chromium to chromium ( III) and oxidize under conditions that do not give chromium in the oxidation state with a valence of more than 3 to form a sulfate of iron (III) and a sulfate of chromium (III). After this, the oxidizing solution is aged to form the chromium (III) sulfate in the form of purple hexaaquachromium (III) sulfate in which six water molecules are coordinated to chromium (III). Since a crystallization agent is added at a temperature of 40 ° C. to selectively crystallize chromium as a sulfate, a high-purity chromium sulfate crystallized product can be recovered at a high recovery rate.

As described above, according to the present invention, by increasing the difference in solubility between the iron salt and the chromium salt in the mixed solvent of the water-soluble organic solvent which is the crystallization agent and water, the chromium crystallization product is increased. It achieves high purity and high recovery rate. That is, chromium (III) sulfate, which exists in the form of hexaaquachromium (III) sulfate in the solution during crystallization, has high solubility in water and low solubility in the water-soluble organic solvent that is the crystallization agent. The iron (III) sulfate has a large solubility in the mixed solvent, and the crystallization and separation of the chromium (III) sulfate in the mixed solvent as a solvent becomes easy. In addition, by controlling the temperature during crystallization within the above range, hexaaquachrome
In (III) sulfate, the water molecules coordinated to chromium (III) are partially substituted with sulfato (SO ₄ ²⁻ ) ligands, and the solubility in water is lower than that of hexaaquachromium (III) sulfate, It has a high solubility in solvents and prevents conversion to aquasulfatochromium (III) sulphate.
I) It facilitates the crystallization separation of sulfate.

Further, the present invention is more advantageous in cost than the alumino-thermite method and ammonium alum precipitation method which have hitherto been industrially carried out. That is, the present invention is advantageous in terms of energy cost because the reagents used are inexpensive, no special device is required.

In Japanese Patent Laid-Open No. 3-207825, a raw material containing a rare earth element such as Nd and iron is dissolved in sulfuric acid and an aqueous sulfuric acid solution, and then alcohol is added to the obtained solution to add the rare earth element. The method of selectively crystallizing the sulfate of the above is shown. However, unlike the present invention, the above publication does not describe that the solution is aged prior to crystallization to form a hexaaqua complex of a rare earth element for crystallization.

Further, Japanese Patent Laid-Open No. 6-65656 discloses that
A raw material containing nickel and iron is dissolved in an aqueous solution containing sulfuric acid and oxidized, and iron in this solution is converted to iron (III), and then an organic solvent is added to this solution to form a nickel sulfate salt. A method for selective crystallization is shown. However, in the above publication, unlike the present invention, there is no description that the solution is aged prior to crystallization to form a hexaaqua complex of nickel for crystallization.

[0013]

Specific Structure The specific structure of the present invention will be described in detail below.

The present invention is a method for selectively separating and recovering chromium from a raw material containing chromium and iron (hereinafter, also referred to as "raw material"). Mainly, (1) the raw material is dissolved in an aqueous sulfuric acid solution. And (2) dissolution and oxidation of chromium (III) sulfate in the solution.
A ripening step to form a sulfate, (3) a crystallization step in which a water-soluble organic solvent is used as a crystallization agent and crystallization of chromium as a sulfate at a temperature of 10 to 40 ° C., and (4) a crystallized product as a solution From the separation step.

The raw material to which the present invention is applied is not particularly limited as long as it contains chromium and iron. Specifically, any of ferrochrome, chromium iron ore, scrap of chromium-iron alloy, etc. May be In particular, a chromium-containing raw material containing iron in an amount of about 5 to 80% by weight in terms of metal element is preferable. Main elements such as metals contained in addition to chromium and iron are usually manganese, calcium, nickel, cobalt, copper, aluminum, oxygen, silicon, carbon, sulfur, phosphorus and the like.

The contents of the main elements such as metals in the raw materials are determined from the results of measurement by high frequency inductively coupled plasma (ICP) emission analysis for metals and silicon, and the combustion infrared absorption method for carbon and the like. It can be obtained from the measurement result according to. Further, the contents of main elements such as metals in the recovered material can be similarly obtained.

Next, the separation and recovery method of the present invention will be described in detail by dividing it into (1) dissolution and oxidation step, (2) aging step, (3) crystallization step and (4) separation step.

(1) Dissolution Oxidation Step In the present invention, a raw material containing chromium and iron is first dissolved in an aqueous sulfuric acid solution. The amount of sulfuric acid used is 1 to 3 of the stoichiometric amount required for chromium and iron in the raw material to form a sulfate.
Double, preferably 1-2 times. With such an amount ratio, all the chromium and iron present can be converted to sulfate. On the other hand, if the amount of sulfuric acid is too small, the conversion to the sulfate becomes incomplete, and if the amount of sulfuric acid is too large, it is not only wasteful but also an undesired undesired reaction occurs.

The concentration of sulfuric acid in the sulfuric acid aqueous solution is 12
It is suitable to be less than or equal to the stipulated level, preferably 1 to 8 stipulated. With such a sulfuric acid concentration, all the chromium and iron present can be converted to sulfate. On the other hand, if the concentration is too high, sulfuric acid may act with a crystallization agent to be added later to form a sulfuric acid ester or the like. Sulfuric acid ester is a non-volatile oily liquid and is not preferable because it adheres to the crystallized product and makes it difficult to filter and dry it.

The temperature at the time of melting is preferably raised to about 50 to 120 ° C., whereby the melting can be promoted.

Next, such a solution is oxidized to oxidize ferrous sulfate in the solution to ferric sulfate. The oxidation in this case may be carried out after the dissolution, or may be carried out simultaneously with the dissolution, and is not particularly limited.

In this way, ferrous sulfate is oxidized to ferric sulfate because the solubility of ferric sulfate is higher than that of ferrous sulfate in an aqueous solution of a water-soluble organic solvent to be added later. This is to facilitate the crystallization separation with chromium sulfate in the crystallization step of.

The oxidation may be carried out by any method,
Fe²⁺Electrochemically Fe³⁺Has the ability to oxidize to
r³⁺It is necessary not to have the ability to oxidize. material
Chromium is usually a trivalent chromium ion, sulfuric acid, when dissolved in sulfuric acid.
It becomes a salt, but if it is oxidized to a higher valence, chromate
ON (CrO_Four ^2- ) And dichromate ion (Cr₂ O
₇ ^{2 -} ) And other anions, and these anions
Is bound to iron ions during crystallization, and iron chromate etc.
May be deposited in the form of.

Among them, the oxidation is preferably performed by air oxidation. Specifically, it is preferable that the air oxidation be simultaneously advanced while the raw materials are dissolved in the sulfuric acid aqueous solution. Such air oxidation is preferably carried out at the same temperature as that during the melting for about 1 to 10 hours including the melting step. Such air oxidation is preferable from the viewpoint of operability and the like, but not limited to the air, an oxidizing atmosphere may be used, and the oxygen concentration in the oxidizing atmosphere may be 20% by volume or more. In addition, the oxidation can be promoted by blowing oxygen into the solution. Further, the oxidation may be performed using an oxidizing agent such as nitric acid (HNO ₃ ). When nitric acid is used, a nitric acid aqueous solution of about 6 to 14 N may be added. In such a case, the amount of the oxidizing agent to be used is appropriately about 1 to 2 times the stoichiometric amount required for the oxidation of ferrous iron, depending on the iron content in the raw material.

Due to such oxidation, almost all of the iron sulfate present in the solution [95% or more of the iron (elemental weight) present, preferably approximately 100%] is oxidized to sulphate iron (III). It becomes salt.

By the method described above, chromium and iron in the raw material are easily dissolved as a sulfate solution, and iron (II
It exists in the form of sulfate salts of I) and chromium (III). In addition,
Chromium (III) sulfate is mainly composed of tetraaquachromium (III) sulfato complex salt and triaquachromium (III) sulfato complex salt [60 to 90% of existing chromium (elemental equivalent weight)].
%], And in addition to these, hexaaquachromium (III) sulfate, pentaaquachromium (III) sulfato complex salt and diaquachromium (III) sulfato complex salt, and in some cases monoaquachromium (III) sulfato complex salt and anhydrous chromium sulfate, etc. It coexists in a small amount. However, the sulfate of chromium (III) such as monoaquachromium (III) sulfato complex salt and anhydrous chromium (III) sulfate is substantially absent, and the amount thereof is usually about 0 to 5%. The presence and proportion of these salts can be confirmed by a spectrophotometric method or the like.

The above solution is preferably filtered. As a result, hardly soluble impurities (for example, carbon, calcium, etc.) are separated and removed by filtration.

Further, in order to prevent the hydrolysis of iron and chromium ions in the above solution, it is preferable to adjust the pH value of the solution to about 0.5 to 2. Iron (III) and chromium (III) exist most stably in this pH range. In addition, it is preferable to use dilute sulfuric acid or pure water to adjust the pH.

(2) Aging Step Next, this solution is aged at a temperature of 10 to 30 ° C. while stirring or shaking, and the sulfate of chromium (III) in the solution is converted into hexaaquachromium (III) sulfate (purple). Salt). By using such a purple salt form, the subsequent crystallization separation can be easily performed. By this aging, 95% or more, preferably almost 100%, of chromium (elemental weight) present in the solution is present as a purple salt. Further, the aging time is not particularly limited, but in order to increase the above conversion rate, it is preferable to hold at the above temperature for 10 hours or more, further preferably about 10 to 48 hours. The temperature of the solution is set within the above range so that the conversion of chromium (III) sulfate to purple salt is ensured and the purple salt is coordinated as shown in formula (1) of the following chemical formula 1. This is to prevent the reaction that changes to the isomer green salt. This green salt has a lower solubility in water and a higher solubility in a water-soluble organic solvent which is a crystallization agent, as compared with a purple salt, and thus is disadvantageous in the subsequent crystallization separation. On the other hand, if the temperature is too low, the conversion of chromium (III) sulfate to purple salt will be difficult to proceed, or iron sulfate will be precipitated. If the temperature becomes too high, the water molecule, which is the ligand of the purple salt, will be replaced by the sulfato (SO ₄ ²⁻ ) ligand, and a green salt will be produced.

[0030]

Embedded image

The conversion of chromium (III) sulfate from purple salt to purple salt and purple salt to green salt can be confirmed by a visible ultraviolet absorption spectrum or the like. Further, the quantification of these salts can be carried out by a spectrophotometric method or ICP emission spectrometry.

(3) Crystallization Step A crystallization agent is added to the obtained solution to precipitate a sulfate of chromium as a crystalline substance. The crystallization agent used is at least one water-soluble organic solvent selected from alcohols, ketones, aldehydes and carboxylic acids. These crystallization agents have a total number of carbon atoms in the molecule of 8 or less, preferably 4
Hereafter, it is more preferably 2 to 4.
These organic solvents have a relatively small number of carbon atoms and have a high polarity due to the structure of the molecule, and thus are well soluble in water. In a solution containing a solvent mixture of these crystallization agents and water, the solubility of ferric sulfate is much higher than the solubility of hexaaquachromium (III) sulfate or chromium sulfate. By adding chromium, it is possible to selectively crystallize chromium as a sulfate and separate it from iron.

Specific examples of such a crystallization agent include methyl alcohol (CH ₃ OH), ethyl alcohol (C ₂
H ₅ OH), alcohols such as propyl alcohol (C ₃ H ₇ OH), ketones such as acetone (CH ₃ COCH ₃ ), methyl ethyl ketone (C ₂ H ₅ COCH ₃ ), propionaldehyde (C ₂ H ₅ CHO) Aldehydes such as, formic acid (HCOOH), acetic acid (CH ₃ COO
And carboxylic acids such as H). The solubility of such a water-soluble organic solvent in water is 15 g to ∞ with respect to 100 g of water at 25 ° C., and the boiling point is about 45 to 100 ° C.

The amount of the crystallization agent to be added must naturally depend on the contents of chromium and iron in the solution in which the raw materials are dissolved, and is not particularly limited. Usually, good results are obtained in a wide range of the crystallization agent addition amount of 10 to 90% by weight based on the weight of the solution, depending on the contents of chromium and iron in the solution in which the raw materials are dissolved.

The crystallization operation is carried out at a temperature of 10 to 40 ° C., preferably 10 to 30 ° C. At a temperature higher than 40 ° C., as shown in the above formula (1), the reaction of changing the chromium sulfate from a purple salt to a green salt occurs. Crystallization decomposition becomes difficult because the green salt has a higher solubility in an aqueous solution of an organic solvent than the purple salt. Also, at temperatures below 10 ° C,
The solubility of iron (III) and sulfates of other metal impurities is also lowered, and the amount thereof is mixed into the chromium sulfate crystallized product, and the purity of the crystallized product is decreased. It should be noted that this temperature range can be realized extremely easily industrially.

Crystallization of chromium sulfate by the addition of the organic solvent proceeds extremely rapidly. For example, when the container is placed in a constant temperature water tank and shaken for several minutes, crystals of chromium sulfate start to precipitate. However, in the present invention, it is usually preferable to shake for about 1 to 5 hours. The crystals of chromium sulfate thus precipitated are sufficiently aged, and the sedimentation filterability is good.

The container used in the present invention is not particularly limited, and a known crystallizer or the like can be used.

(4) Separation Step After the chromium sulfate is completely crystallized, when a container is installed, a precipitate having a good settling property begins to settle. Separation of the crystallized product and the solution is easily performed by, for example, a decantation method in which the supernatant is flown or a filtration method using a suction filter. Then, the crystallized product is dried thereafter.

Through each of the above steps, iron and other small amount of metal impurities are removed by remaining in the solution as a sulfate.
In addition, most of non-metal impurities such as carbon and hardly soluble metal impurities in the raw materials are removed as insoluble residues in the dissolution step or remain in the solution using the above mixed solvent as a solvent in the crystallization step and removed. To be done. Therefore, a high-purity chromium sulfate crystallization product (usually represented by Cr ₂ (SO ₄ ) ₃ ) can be obtained. The purity of the crystallized product can be further increased by repeating the above crystallization process and separation process.

Thus, in the present invention, 97% by weight
The above-mentioned purity is obtained. Chromium sulfate as a recovered product was analyzed by X-ray diffraction analysis, thermogravimetric analysis-differential thermal analysis (TG-D).
TA). The recovery rate of chromium is 90% or more, and particularly 95 to 100%.

The obtained chromium sulfate crystallization product can be easily dissolved in water and dissolved in water to produce high-purity chromium by a known electrolytic reduction method. Alternatively, the crystallized product can be converted to a chromate or oxide form for use in the chemical industry, chromium plating, refractory materials, and the like.

Since the crystallization agents used for crystallization separation are organic solvents having a sufficient vapor pressure difference with water, they can be easily recovered by a known distillation separation method. By recycling the recovered organic solvent, it is possible to sufficiently reduce the processing cost.

[0043]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention. Example 1 30.00 g of high carbon ferrochrome raw material powder was placed in a glass Erlenmeyer flask, and 5N sulfuric acid aqueous solution 400 was added therein.
ml was added and stirred, and then the sample was almost completely dissolved in 5 hours while heating at 80 to 100 ° C. At the same time, the solution is air-oxidized during this dissolution process, and iron (III) sulfate and chromium
(III) Sulfate was formed. The chromium (III) sulfate in this case is mainly composed of tetraaquachromium (III) sulfato complex salt and triaquachromium (III) sulfato complex salt (about 47% and 35%, respectively, of the total amount of chromium present).
In addition to these, pentaaquachromium (III) sulfato complex salt, diaquachromium (III) sulfato complex salt and the like were present. The presence and proportion of these salts were confirmed by measurement with a visible ultraviolet spectrophotometer. Then, this solution was filtered, and a small amount of insoluble matter was removed by filtration. The pH of the solution at this time was about 1.

The solution thus obtained was adjusted to a constant volume of 500 ml, placed in a constant temperature water bath at 15 ° C. and aged for 24 hours with shaking. Due to this aging, the chromium (III) sulfate in the solution becomes [Cr (H ₂ O) ₆ ] (SO ₄ ) _3/2 (purple salt).
Approximately 100% of the chromium present in the solution was converted to a purple salt. This conversion was confirmed by measurement with a visible ultraviolet spectrophotometer. The conversion rate was determined by quantifying the total chromium content in the solution by ICP emission analysis.

The solution after this aging was made of chromium 40.6.
It was g / l, iron 15.0 g / l and pH about 1.

To this solution was added 750 ml of ethyl alcohol having a purity of 99.5% (the amount of ethyl alcohol added to the solution weight: about 50% by weight), and the mixture was shaken at 20 ° C. for 4 hours for crystallization. The precipitated crystallization product was collected by filtration from the mother liquor by suction filtration, and then dried at 150 ° C. for 24 hours (about 24 hours) to remove the water content by evaporation.
The recovered dried product weighed 72.72 g.

The composition of the high carbon ferrochrome raw material powder and the above-mentioned recovered material was determined by chemical analysis. Table 1 shows the results. The chemical analysis was carried out by ICP emission spectrometry for metallic elements and silicon, and by combustion infrared absorption method for carbon. Incidentally, the drying after harvest X-ray diffraction analysis and thermogravimetry - differential thermal analysis (TG-DTA) results identified by, most of anhydrous chromium sulfate crystals (Cr ₂
(SO ₄ ) ₃ ) and its purity was 97.13% by weight. Table 1 shows the recovery rate of chromium.

[0048]

[Table 1]

As is clear from Table 1, the method of the present invention can efficiently recover chromium with high purity.

Although high carbon ferrochromium was used as a raw material in the above-mentioned examples, the present invention is not limited to this, and any raw material containing chromite or chromium and iron can be applied.
Good results equivalent to the above were obtained with other materials.

The ethyl alcohol used as the crystallization agent could be separated from the aqueous solution by distilling the filtrate and could be reused.

Further, in the above, when acetone, propionaldehyde, or acetic acid was used as the crystallization agent instead of ethyl alcohol, good results equivalent to those of ethyl alcohol were obtained.

On the other hand, when crystallization was carried out without aging in the above, precipitation of chromium sulfate was slow, and fine colloidal green salt was deposited, resulting in a precipitate having poor sedimentation filterability. When the crystallized product after 10 hours had passed was dried and analyzed, the recovery rate of chromium was 53.8%. Further, when the same operation was performed except that the crystallization was performed at 5 ° C., the purity of the recovered product decreased to 74.2% by weight. on the other hand,
When crystallization was carried out at 50 ° C, the purple salt changed to a green salt, the crystallization of chromium sulfate was very slow, and it precipitated as a fine colloidal green salt with poor sedimentation filterability, resulting in crystallization separation. Was difficult.

[0054]

EFFECTS OF THE INVENTION According to the present invention, chromium can be separated and recovered from a raw material containing chromium and iron in good yield and high purity. The method of the present invention is a novel method that is completely unknown, uses a reagent that is epoch-making less expensive than the conventional method, and surely recovers chromium with a simple device and easy operation. be able to. Therefore, industrial implementation is economical and rational.

Claims (3)

[Claims] 1. A method for separating and recovering chromium from a raw material containing chromium and iron, which comprises dissolving the raw material containing chromium and iron in a sulfuric acid aqueous solution and oxidizing the raw material to trivalent iron in the solution. Iron sulphate, chromium is trivalent chromium sulphate, and this solution is aged to convert hexavalent chromium sulphate to hexaaquachromium (III)
A method for separating and recovering chromium in which a crystallization agent is added to this solution at a temperature of 10 to 40 ° C. to selectively crystallize a sulfate of chromium after the form of sulfate. 2. The method for separating and recovering chromium according to claim 1, wherein the aging is carried out at a temperature of 10 to 30 ° C. for 10 hours or more. 3. The method for separating and recovering chromium according to claim 1, wherein the crystallization agent is a water-soluble organic solvent of at least one of alcohols, ketones, aldehydes and carboxylic acids.