JPS6220134B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for recovering arsenic ( ) from a sulfuric acid acidic solution containing arsenic ( )
The present invention relates to a method for selectively recovering arsenic () from a sulfuric acid acidic solution containing iron () and zinc in addition to arsenic () by a solvent extraction method. Dilute sulfuric acid produced in the smelting exhaust gas cleaning process in non-ferrous metal smelting, the post-copper electrolysis solution produced in the copper electrolysis process, and other waste liquids contain a considerable amount of arsenic. At the time, attempts have been made to recover arsenic () from these arsenic ()-containing solutions for the purpose of preventing pollution and recovering arsenic () as a by-product. The conventional arsenic recovery method involves converting arsenic into arsenic sulfide using a sulfurization method, then separating and recovering it into a dehydrated cake containing about 70% water, which is then further dehydrated and agglomerated. The resulting mass was stored in a pit. Although this method is simple, it requires a large amount of storage space. Recently, a method has been proposed for recovering arsenic sulfide obtained by the above-mentioned sulfurization method as arsenous acid. In this method, arsenic sulfide produced by the sulfurization method is oxidized and leached, and after reducing the leachate,
Although it performs concentration and crystallization, the process is long and complicated, and requires troublesome operations. Furthermore,
If the arsenic ()-containing liquid contains iron () or zinc in addition to arsenic, this method is not suitable as a method for separating and recovering only arsenic (). Unlike the conventional methods described above, there is no substitute for directly recovering arsenic () from an arsenic ()-containing solution. There is a method called solvent extraction method that makes this possible. Solvent extraction uses an organic solvent containing an extractant capable of selectively extracting a particular substance to separate it from an aqueous solution containing the substance. Therefore, in order to use the solvent extraction method to recover arsenic () from aqueous solutions containing arsenic (), it is necessary to develop an extractant that has the ability to selectively and efficiently extract arsenic () ions from aqueous solutions. It is necessary to. In this case, the extractant needs to be immiscible with the arsenic-containing aqueous solution, and the extractant is diluted with a diluent to reduce its viscosity, improve dispersibility, and increase contact efficiency. Since it is common, it is also necessary that it dissolves well in the diluent.
In addition, since back-extraction is performed after the extraction operation, it is also necessary to easily perform the back-extraction operation. Furthermore, in addition to arsenic, iron () and zinc are contained in the arsenic ()-containing solution, and trace amounts of these metals inevitably get mixed into the organic solvent during extraction, so these metals are removed from the solvent after extraction. Measures must also be taken to remove metal. Under these various considerations, the inventors:
As a result of many trials regarding extractants for arsenic () extraction from arsenic ()-containing aqueous solutions by solvent extraction, dialkyldithiophosphate esters (alkyl group having 8 to 10 carbon atoms) can be suitably used as the above extractant. I discovered that. This extractant has excellent selectivity for arsenic (2), and is particularly excellent for the purpose mentioned above in that it can extract 99% or more of arsenic (2) from an acidic sulfuric acid solution. The present applicant provided a method for separating and recovering arsenic using the above extractant in a previously filed Japanese Patent Application No. 54-151575. However, in the above invention, there was a problem in that an emulsion was formed in the step of back-extracting arsenic () and separation of the organic phase and the aqueous phase was insufficient. In view of the above-mentioned drawbacks, the present inventor has conducted intensive research and found that alcohol and/or
Alternatively, it has been found that phosphoric acid esters act suitably. Thus, the present invention uses a sulfuric acid acidic solution containing arsenic (2), iron (2), and zinc as an extractant, and a dialkyldithiophosphate having an alkyl group having 8 to 10 carbon atoms, and a higher carbon ester having 6 to 20 carbon atoms. Contact with an organic solvent containing alcohol and/or phosphoric acid ester as a phase separation improver at a pH of 4 or below, and after extraction, contact the solvent with a sulfuric acid solution having a concentration of 600 g/min or less to remove the iron () and zinc contained in the solvent after extraction. Provided is a method for separating and recovering arsenic, which comprises washing and removing arsenic () and then back-extracting an organic solvent containing arsenic () with an alkaline solution. The dialkyldithiophosphate ester having an alkyl group having 8 to 10 carbon atoms used as an extractant in the present invention has the following structural formula: (However, R is an alkyl group having 8 to 10 carbon atoms, and may be the same or different.) Also, higher alcohol and/or phosphoric acid ester that acts as a phase separation improver in the back extraction step described below. is not limited as long as it is insoluble in the treated aqueous solution at 80°C or lower and nonvolatile at 80°C or lower, but is preferably a higher alcohol having 6 to 20 carbon atoms and/or a phosphoric ester. You should choose from. The organic solvent of the present invention is prepared by dissolving the aforementioned dialkyldithiophosphate extractant having an alkyl group having 8 to 10 carbon atoms and a higher alcohol and/or phosphate ester phase separation improver having 6 to 20 carbon atoms in a diluent. It is something. As the diluent, parfine-based, naphthenic-based and aromatic hydrocarbon mineral oils are appropriately selected and used alone or in combination. During solvent extraction of arsenic (2) using this organic solvent, iron (2) and zinc contained in the raw material solution inevitably mix in small amounts into the organic solvent after arsenic extraction. In order to recycle and use the organic solvent and to separate and recover arsenic (2), it is necessary to remove these contaminant iron (2) and zinc from the organic solvent. In this way, in order to remove iron () and zinc co-extracted with arsenic (), the solvent after extraction may be brought into contact with 600 g/or less of sulfuric acid. In this way, the organic solvent from which iron () and zinc have been removed contains only arsenic (), but in order to recover arsenic () from this and make it possible to recycle the organic solvent, arsenic must be back-extracted from the organic solvent. I have to. For such a back extraction operation, an alkaline solution typified by sodium carbonate, ammonium carbonate, sodium bicarbonate, sodium hydroxide, etc. can be suitably used. In this case, the alkaline concentration of the alkaline solution is 0.01
It is preferable to set it as the range of -5 mol. In the alkali back extraction operation described above,
Since the organic solvent after back extraction is in an alkaline form, it must be converted into a hydrogen form in order to recycle the organic solvent. This is easily effected by contacting with sulfuric acid. Hereinafter, the present invention will be specifically explained based on the recovery of arsenic () from dilute sulfuric acid generated from a smelting exhaust gas cleaning process in non-ferrous smelting. The dilute sulfuric acid solution generated from the gas cleaning process in nonferrous smelting generally contains 5 to 300 g of sulfuric acid, although the source of the gas varies depending on the process, such as whether the gas is smelting exhaust gas from sulfide ore or roasting gas from sulfide ore. It also contains 0.5 to 30 g of arsenic (), other heavy metals such as iron and zinc, and hydrochloric acid and hydrofluoric acid. In any case, such a dilute sulfuric acid solution is subjected to a solvent extraction treatment in the extraction step (1). If desired, the after-liquid resulting from the subsequent washing step may be mixed (described below). In the extraction step (1), the dilute sulfuric acid solution containing arsenic () and others is brought into contact with an organic solvent, and as a result, arsenic (), iron (), and zinc in the solution are transferred into the organic solvent. , a post-extraction liquid is produced. A new organic solvent is used for the first time, but after that, the used organic solvent is recycled and reused as described below. The contacting operation can be carried out either batchwise or continuously using well-known mixers/settlers, extraction towers, centrifugal extractors, and the like. The mixing temperature depends on the diluent used, but is selected to be 30-80°C, preferably 40°-60°C. The volume ratio of the organic phase (organic solvent) to the aqueous phase (liquid to be treated) during contact (hereinafter referred to as O/A ratio) is 1/
The ratio is about 15 to 5/1, preferably 1/2 to 2/1, and can be appropriately selected depending on the equipment used and operating conditions. The contact time depends on the contact efficiency, but 2 to 30 minutes, usually about 5 to 10 minutes, is sufficient. In this example, in addition to extraction step (1),
(2) is provided. This extraction step (2) is for completely extracting and removing a trace amount of arsenic contained in the liquid after crystallizing arsenic () as arsenous acid from the liquid after back extraction, which will be described later. Although the extraction step (2) is usually carried out using the organic solvent from the extraction step (1), there is no problem in using an organic solvent that has not been passed through the extraction step (1). The post-extraction liquid from extraction step (1) contains almost no arsenic and heavy metals, and depending on the concentration of hydrochloric acid and hydrofluoric acid it contains, it can be used in other process sections, such as the pickling step, if necessary. It can be effectively recycled as sulfuric acid. Arsenic () from extraction step (1) and optionally after extraction step (2)
The post-extraction organic solvent that has extracted the iron() and zinc is sent to a washing step to remove the iron() and zinc thus co-extracted with the arsenic(). The washing process involves washing the organic solvent at 600 ml after extraction.
It is carried out by contacting with a sulfuric acid solution of up to 100 g/g/g, preferably from 100 to 400 g/g/g/g. The contact between the organic phase and the sulfuric acid solution in the washing step is 1/1 to 15/
1, preferably at an O/A ratio of 5/1 to 10/1, and other conditions such as mixing temperature, contact time and equipment used are appropriately selected in the same manner as in the extraction step. The processed liquid from the cleaning process is
Although it may be treated alone, it is preferably repeated in the extraction step (1) as described above. The arsenic ()-containing organic solvent after iron () and zinc have been removed in the washing step is then subjected to a back extraction operation in a back extraction step. In the back-extraction step, arsenic is back-extracted using an arsenic-containing organic solvent, such as a single alkali solution or a mixed solution, typified by sodium carbonate, ammonium carbonate, sodium bicarbonate, sodium hydroxide, and the like. The alkaline concentration for optimal back extraction is 0.01 to 5.
It is considered a mole. As for the back extraction conditions, the O/A ratio is 1/3 to 10/1, preferably 1/1 to 5/1, and the mixing temperature, contact time and equipment used can be selected in the same manner as in the extraction process. In the back extraction process, a clean organic solvent from which arsenic ( ) has been removed and a back extraction liquid containing arsenic ( ) are produced. The liquid after back extraction is usually made acidic by adding sulfuric acid, and then arsenic is precipitated as arsenous acid in a crystallization step provided as necessary, and then the solid phase arsenous acid is converted into a liquid by filter press, centrifugation, etc. Arsenous acid is recovered in a separation process in which it is separated from the arsenic acid. The liquid after arsenous acid separation in the separation step can be reprocessed as a stock solution to be processed in the previous extraction step (2). Depending on the situation of the equipment, it is also possible to omit the extraction step (2) and perform only the extraction step (1), and repeat the arsenous acid separation solution to the extraction step (1). A trace amount of arsenic () in this liquid is extracted in the extraction step (2). The organic solvent that has gone through the back extraction process is finally converted into an alkaline form of the organic solvent by 600% in the organic solvent regeneration process.
It is treated to convert it into the hydrogen form with a sulfuric acid solution having a concentration of less than 50 g/g/g/g/g/g/g/g/g/g/g/g/g/g/g/g/g/g/g/g/g/g/g/g/g/g/g/g/, preferably 50-300 g/m. The organic solvent that has been regenerated in the organic solvent regeneration step is recycled to the extraction step (1) and reused. Since the liquid after the organic solvent regeneration step contains a very small amount of arsenic, it is sent to the extraction step (1) or (2) to recover arsenic. Above, we have described an acidic sulfuric acid solution containing arsenic (), iron (), and zinc as the aqueous solution to be treated, but this also applies when the aqueous solution to be treated is an acidic sulfuric acid solution that further contains cadmium and copper in addition to the above components. By applying the invented method, it is possible to separate and recover arsenic (). In other words, if the aqueous solution to be treated is an acidic sulfuric acid solution containing arsenic (), iron (), zinc, cadmium and copper, cadmium behaves in the same way as iron () and zinc, so after extraction the solvent should be added at 600g/
Cadmium can be washed away along with iron and zinc in the following washing step in which it is brought into contact with a sulfuric acid solution. On the other hand, copper is accumulated in the organic solvent during its cyclic use, so by contacting part or all of the organic solvent after the organic solvent regeneration process with a nitric acid solution with a concentration of 600 g/or less, copper can be removed from the organic solvent. Copper can be removed. Examples are shown below. Example: The extractant di-2-ethylhexyl dithiophosphate is added to the diluent Dispersol (trade name of Ciel Chemical Co., Ltd.) from a sulfuric acid solution having the composition shown in Table 1 produced from the cleaning process of sulfur dioxide gas generated in non-ferrous smelting. 20
% and phase separation improver tridecyl alcohol 10%
A test was conducted to recover arsenic () using an organic solvent containing arsenic.

[Table] The solvent extraction operation was performed using the following conditions. O/A: 1/1, temperature: 50°C, contact method: stirring method (750 rpm x 10 minutes). The composition of the obtained post-extraction liquid is arsenic () 0.001
g/, iron () 0.023 g/ and zinc 0.136
g/, showing an arsenic extraction rate of over 99.9%. In this example, almost no iron was extracted because the sulfuric acid concentration was relatively high. After the above extraction, the organic solvent was then washed away. The cleaning process was carried out using 30g/sulfuric acid and an O/A ratio of 5/1. The cleaning effects were as follows.

[Table] Furthermore, arsenic was back-extracted from the organic solvent after washing using a sodium carbonate solution with a concentration of 53 g/ml. The back extraction conditions were O/A ratio = 1/2, temperature 50C, and contact time 10 minutes. The results are shown in Table 2 in comparison with a comparative example which is the same as this example except that no phase separation improver was used.

[Table] As is clear from the table, the organic solvent of the present invention does not form an emulsion phase in the process of back-extracting arsenic, and the back-extraction rate is high. Moreover, it has the effect of increasing the back extraction rate of arsenic and shortening the phase separation time. Thus, according to the present invention, as shown in the specific examples, arsenic in sulfuric acid produced in various steps in nonferrous metal smelting can be efficiently recovered with high purity, which has extremely great industrial significance.

Claims (1)

[Claims] 1 A sulfuric acid acidic solution containing arsenic (), iron () and zinc is extracted with a dialkyldithiophosphate having an alkyl group having 8 to 10 carbon atoms, and a higher alcohol having 6 to 20 carbon atoms and/or
Or, contact with an organic solvent containing phosphate ester as a phase separation improver at pH4 or lower, and remove the solvent after extraction.
Arsenic removal consists of contacting with a sulfuric acid solution with a concentration of 600 g/min or less to wash and remove iron () and zinc contained in the solvent after the extraction, and then back-extracting the organic solvent containing arsenic () with an alkaline solution. Separation and recovery method.