JPS6042170B2 - Arsenic separation and recovery method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering arsenic (■) from an acidic sulfuric acid solution containing arsenic (■). Arsenic (■) is extracted by solvent extraction from a sulfuric acid acidic solution containing iron (■) and zinc in addition to arsenic (■), such as dilute sulfuric acid.
(2) It relates to a method for selectively recovering .

Dilute sulfuric acid produced in the smelting exhaust gas cleaning process in nonferrous metal smelting, copper electrolysis solution produced in the copper electrolysis process, and other waste liquids contain a considerable amount of arsenic (■). Recently, arsenic (
(2) For recovery purposes, attempts have been made to recover arsenic (■) from these arsenic (■)-containing solutions.

The conventional arsenic recovery method involves converting arsenic into arsenic sulfide using the sulfurization method, separating it from house to house, collecting it, turning it into a dehydrated cake containing about 70% water, and then further dehydrating and agglomerating it. The resulting mass was stored in a bit.

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. This method involves oxidizing and leaching arsenic sulfide produced by the sulfurization method.
After reducing the leachate, it is concentrated and crystallized.
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, if arsenic (■) can be directly recovered from an arsenic (■)-containing solution, there is no superior method.

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 use an extraction method that has the ability to selectively and efficiently extract arsenic (■) ions from aqueous solutions. It is necessary to develop a drug. 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 included in the arsenic (■)-containing solution, and trace amounts of these metals inevitably get mixed into the organic solvent during extraction. Measures must also be taken to remove these metals from. With these various considerations in mind, the present inventor conducted many trials on extractants for arsenic (■) extraction from arsenic (■)-containing aqueous solutions by solvent extraction, and as a result, the inventors discovered dialkyldithiophosphate esters (alkyl group It has been found that a compound having 8 to 10 carbon atoms can be suitably used as the above-mentioned extractant.

This extractant has excellent selectivity for arsenic (■), and is particularly excellent for the purpose mentioned above in that it can extract more than 99% of arsenic (■) from an acidic sulfuric acid solution. be. Thus, the present invention provides an organic solvent containing as an extractant a dialkyldithiophosphate having an alkyl group having 8 to 10 carbon atoms, a sulfuric acid acidic solution containing arsenic (■), iron (■) and zinc, and a PH4 A method for separating and recovering arsenic is provided, which comprises contacting with the following:

Carbon number 8 to 10 used as an extractant in the present invention
The dialkyl dithiophosphate ester having an alkyl group has the following structural formula: (wherein R is an alkyl group having 8 to 10 carbon atoms, and may be the same or different.

) During the solvent extraction of arsenic (■) using this extractant, iron (■) and zinc contained in the raw material solution inevitably mix in small amounts into the organic solvent after the arsenic extraction.

In order to recycle and use the organic solvent and to separate and recover arsenic (■) separately, it is necessary to remove these contaminant iron (■) and zinc from the organic solvent. In this way, it has been found that in order to remove iron (■) and zinc that are co-extracted with arsenic (■), contacting the solvent after extraction with sulfuric acid of 600y1' or less is an extremely simple method. Served. Thus, the present invention also provides that after extraction the solvent is
A method for separating and recovering arsenic is also provided, which comprises contacting with a sulfuric acid solution having a concentration of 0yI1 or less to wash and remove iron (■) and zinc contained in the solvent after the extraction. In this way, iron (
■) and the organic solvent from which zinc has been removed contain 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. Must be.

For such a back extraction operation, an alkaline solution typified by sodium carbonate, ammonium carbonate, sodium bicarbonate, sodium hydroxide, etc. can be suitably used. Therefore,
The present invention also provides a method for separating and recovering arsenic, which includes back-extracting an organic solvent containing arsenic (■) with an alkali after removing iron (■) and zinc as described above. In this case, the alkaline concentration of the alkaline solution is 0.01~
A range of 5 moles is preferable. In the above-mentioned back-extraction operation using alkali, the organic solvent after back-extraction is in an alkaline form, so it must be converted into a hydrogen form in order to reuse the organic solvent.

This is easily effected by contacting with sulfuric acid. Thus, in another aspect of the present invention, the organic solvent after back-extraction with alkali is contacted with a sulfuric acid solution having a concentration of 600 Dal' or less to convert the organic solvent from an alkaline type to a hydrogen type. A method for separating and recovering arsenic is provided. Hereinafter, the present invention will be specifically explained based on the recovery of arsenic (■) from dilute sulfuric acid generated from the smelting exhaust gas cleaning process in non-ferrous smelting, with reference to the flow sheet of the attached drawings.

The dilute sulfuric acid solution generated from the gas cleaning process in nonferrous smelting generally contains 5 to 300 fIe of sulfuric acid, although the source of the gas varies depending on the process, such as whether the gas is smelted exhaust gas from sulfide ore or roasted gas from sulfide ore. Contains and 0.5-30
It contains H' 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 process in accordance with the present invention in a step shown as extraction step 1 at the far left in the flow sheet.

If desired, the after-liquid resulting from the subsequent washing step may be mixed (described below). In extraction step 1, the arsenic (■)
A dilute sulfuric acid solution containing other components 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, and a post-extraction liquid 1 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 organic solvent is a solution of the aforementioned dialkyldithiophosphate extractant having an alkyl group having 8 to 10 carbon atoms in a diluent. As the diluent, paraffinic, naphthenic and aromatic hydrocarbon mineral oils may be used alone or in combination. The contact 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 30°C. -80°C, preferably 400-60'C. The volume ratio of the organic phase (organic solvent) to the aqueous phase (liquid to be treated) during contact (hereinafter referred to as 0/A
ratio) is about 1/15 to 5/1, preferably 1/2
~2/1, and can be selected as appropriate depending on the equipment used and operating conditions. The contact time depends on the contact effect, but 2 to 3 powders, usually about 5 to 1 powder, is sufficient. In the flow sheet of the drawing, in addition to extraction process 1, extraction process 2
is provided.

In this extraction step 2, arsenic (■) is extracted from the back-extraction liquid as described below.
This is to completely extract and remove a trace amount of arsenic contained in the liquid after crystallizing it as arsenous acid. Although extraction step 2 is usually carried out using the organic solvent from extraction step 1, there is no problem in using an organic solvent that has not been passed through extraction step 1. The post-extraction solution 1 from extraction step 1 contains almost no arsenic and heavy metals, and may be subjected to other steps, such as pickling, as necessary, depending on the concentration of hydrochloric acid and hydrofluoric acid contained. It is effectively recycled as sulfuric acid in the department.

If it cannot be used effectively, it is discharged together with the post-extraction liquid 2 resulting from the extraction step 2 through a normal neutralization process by adding alkali. The post-extraction organic solvent that extracted arsenic (■) and iron (■) and zinc from extraction step 1 and optionally after extraction step 2 contains iron (■) co-extracted with arsenic (■). and sent to a cleaning process to remove zinc.

The washing step is carried out by contacting the organic solvent after extraction with a sulfuric acid solution of 600 flIe or less, preferably 100 to 400 yIe. The contact between the organic phase and the sulfuric acid solution in the washing step is 111-15, preferably 511-1.
The mixing temperature, contact time, equipment used, and other conditions 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 separately, it is preferably repeated in extraction step 1 as described above. After iron (■) and zinc have been removed in the washing step, the arsenic (■)-containing organic solvent is then subjected to a back extraction operation in a back extraction step.

In the back-extraction process, arsenic is back-extracted from the arsenic-containing organic solvent using 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 optimum back extraction is 0.01 to 5 mol. As for the back extraction conditions, the 01A ratio is 113 to 10 Ha, preferably 111 to 5 Ha, 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 step, a clean organic solvent from which arsenic (■) has been removed and a back extraction solution containing arsenic (■) are produced.

The solution 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 the solid phase arsenous acid is further converted into a liquid by filter press or centrifugation. 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 extraction step 2 above. Depending on the situation of the equipment, extraction step 2 can be omitted and only extraction step 1 is performed, and the liquid after arsenous acid separation can be repeated in extraction step 1. A trace amount of arsenic (■) in this liquid is extracted in extraction step 2. The organic solvent that has undergone the back extraction step is finally subjected to an organic solvent regeneration step in which the alkaline form of the organic solvent is reduced to 600 v'e or less, preferably 50 to 300 v'e.
It is treated with a sulfuric acid solution having a concentration of y1e to convert it into the hydrogen form.

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 extraction step 1 or 2 to recover arsenic. As explained above, the organic solvent extracts arsenic (■) and heavy metals such as iron (■) and zinc in extraction step 1 and, if necessary, in extraction step 2, and then removes iron (■) and zinc in the washing step. The remaining arsenic (■) is then removed in the back extraction step, and finally the alkaline form is converted into the hydrogen form in the organic solvent regeneration step, and the completely regenerated state is recycled to the extraction step 1.

The arsenic (■) that is back-extracted in the back-extraction process can be recovered in high purity because the heavy metals have already been removed. Examples are shown below. Example 1 Di-2 ethylbutylene diluted to 20% with Dispasol (trade name of Shell Chemical Co., Ltd.) from a dilute sulfuric acid solution having the composition shown in Table 1 produced from the process of cleaning sulfur dioxide gas generated from non-ferrous smelting. A test was conducted to recover arsenic (■) using an organic solvent consisting of hexyldithiophosphoric acid ester.

The solvent extraction operation was performed using the following conditions.

01A: 1c, temperature: 50°C, contact method: stirring method (75
0 rpm x 1 powder).

The composition of the obtained post-extraction liquid is arsenic (■) 0.001 fI'
, iron (■) 0.023y1e and zinc 0.136yI
e, and indeed showed an arsenic (■) extraction rate of 99.9% or more.

This example was hardly extracted. Example 2 An extraction test was conducted under the same conditions as in Example 1 using di3,5,5-trimethylhexylthiophosphate and diisodecyl dithiophosphate as extractants.

All showed a high arsenic extraction rate of 99% or more. Example 3 The post-extraction organic solvent obtained in Example 1 was washed.

The cleaning process was carried out using 300y1f sulfuric acid using a 0IA ratio of 5ha. The cleaning effects were as follows. Next, arsenic was back-extracted from the washed organic solvent using 0.5 mol of sodium carbonate 53yI'.

The back extraction conditions were: 0IA ratio = 112, temperature 50°C, and contact time 1C@. A back extraction rate of 7% was obtained.
Example 4 A test was conducted to recover arsenic using the same solution as in Example 1 from a dilute sulfuric acid solution having the composition shown in Table 2 produced from the cleaning process of roasted iron sulfide gas.

The extraction step, washing step and back extraction step were carried out sequentially.

The operating conditions and results of each step are summarized in Table 3.
Thus, according to the present invention, as specifically shown, arsenic in dilute sulfuric acid produced from a smelting exhaust gas cleaning process in nonferrous metal smelting is extracted and separated by solvent extraction, and a cleaning process with sulfuric acid is added. As a result, a method for recovering high-purity arsenic acid containing no heavy metals from the back-extraction solution has been established, and it has great industrial significance because arsenic can be recovered more effectively and easily than conventional methods. big.

[Brief explanation of the drawing]

The drawing is a flow sheet of an arsenic recovery process according to one embodiment of the present invention.

Claims (1)

[Scope of Claims] 1. A sulfuric acid acidic solution containing arsenic (III), iron (II) and zinc is mixed with an organic solvent containing a dialkyldithiophosphate having an alkyl group having 8 to 10 carbon atoms as an extractant, and a pH of 4 or less. A method for separating and recovering arsenic, which involves contacting with arsenic. 2. A sulfuric acid acidic solution containing arsenic (III), iron (II) and zinc is brought into contact with an organic solvent containing a dialkyldithiophosphate having an alkyl group having 8 to 10 carbon atoms as an extractant at a pH of 4 or less, and after extraction. 600g/l solvent
A method for separating and recovering arsenic, which comprises contacting with a sulfuric acid solution having the following concentration and washing and removing iron (II) and zinc contained in the solvent after the extraction. 3. A sulfuric acid acidic solution containing arsenic (III), iron (II) and zinc is brought into contact with an organic solvent containing a dialkyldithiophosphate having an alkyl group having 8 to 10 carbon atoms as an extractant at a pH of 4 or below, and after extraction. 600g/solvent medium
After the extraction, iron (II) and zinc contained in the solvent are washed away by contacting with a sulfuric acid solution having a concentration of 1 or less, and then arsenic (I) is removed.
II) A method for separating and recovering arsenic, which comprises back-extracting an organic solvent containing alkali solution. 4. A sulfuric acid acidic solution containing arsenic (III), iron (II) and zinc is brought into contact with an organic solvent containing a dialkyldithiophosphate having an alkyl group having 8 to 10 carbon atoms as an extractant at a pH of 4 or less, and after extraction. 600g/l solvent
After the extraction, iron (II) and zinc contained in the solvent are removed by contacting with a sulfuric acid solution having the following concentration, and then arsenic (III) is removed.
) is back-extracted with an alkaline solution, and then the back-extracted organic solvent is added to
A method for separating and recovering arsenic, which comprises converting an organic solvent from an alkaline type to a hydrogen type by contacting with a sulfuric acid solution having the following concentration.