JPS6058173B2 - 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, zinc, copper, and cadmium in addition to arsenic.
The present invention relates to a method for selectively recovering .

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. 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 the sulfurization method, separating each product into a dehydrated cake containing about 70% water, and then subjecting it to further dehydration and agglomeration treatment. 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, zinc, copper, and cadmium in addition to arsenic, this method is not suitable as a method for separating and recovering only arsenic. stomach. Unlike the conventional methods described above, if arsenic (2) can be directly recovered from an arsenic (1)-containing solution, there is no superior method.

There is a method called solvent extraction method that makes this possible. Solvent extraction method is specific! An organic solvent containing an extractant capable of selectively extracting the substance is used 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. 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 diluents. 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, the arsenic-containing solution produced in the nonferrous smelting process contains iron, zinc, copper, and cadmium, and trace amounts of these metals are inevitably mixed into the organic solvent during extraction. Therefore, measures must also be taken to remove these metals from the solvent after extraction. Under these various considerations, the present inventor has devised a method for extracting arsenic from an arsenic-containing aqueous solution by solvent extraction.
As a result of many trials with extractants for extraction,
Dialkyl dithiophosphate ester (alkyl group carbon number 8~
It has been found that 10) can be suitably used as the above-mentioned extractant. This extractant has excellent selectivity for arsenic (2), and is particularly excellent for the above-mentioned purpose in that it can extract 99% or more of arsenic (2) from an acidic sulfuric acid solution. Thus, the present invention provides an acidic sulfuric acid solution containing arsenic (1), iron (2), zinc and cadmium, an organic solvent containing as an extractant a dialkyldithiophosphate having an alkyl group of 8 to 10 carbon atoms, and a pH of 4 or lower. A method for separating and recovering arsenic is provided. The dialkyldithiophosphate ester having an alkyl group having 8 to 10 carbon atoms and used as an extractant in the present invention has the following structural formula: (R is an alkyl group having 8 to 10 carbon atoms, and the same It may be or be different.

) During the solvent extraction of arsenic using this extractant,
Trace amounts of iron, zinc, copper, and cadmium contained in the raw material solution inevitably become mixed into the organic solvent after arsenic extraction.

In order to recycle and use the organic solvent and separate and recover the arsenic, these small amounts of iron are removed.
, it is necessary to remove zinc, copper and cadmium from organic solvents. In this way, in order to remove heavy metals other than copper among the iron (2), zinc, copper and cadmium that are co-extracted with arsenic (1), it is extremely convenient to contact the solvent after extraction with 600y/' or less of sulfuric acid. It was discovered that this is a method. 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 00 f/e or less to wash and remove iron, zinc and cadmium contained in the solvent after the extraction. In this way, the organic solvent from which iron, zinc, and cadmium have been removed essentially contains only arsenic and copper. However, in order to recover arsenic from this and make it possible to recycle the organic solvent, it is necessary to convert arsenic into an organic solvent. It must be back extracted from the solvent. 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 the organic solvent containing arsenic and copper with an alkali after removing iron, zinc, and cadmium as described above. do. In this case, the alkaline concentration of the alkaline solution is preferably in the range of 0.01 to 5 mol. In this operation, copper in the organic solvent is not transferred to the back extraction step. 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 y/e or less to convert the organic solvent from an alkaline type to a hydrogen type. Provided is a method for separating and recovering arsenic containing arsenic. Furthermore, in order to prevent the copper extracted into the organic solvent from accumulating during the cyclic use of the organic solvent and the ability to extract arsenic from decreasing, part or all of the organic solvent converted to the hydrogen form is removed. Provided is a method for separating and recovering arsenic, which includes removing trace amounts of iron, zinc, and cadmium in addition to copper and arsenic by contacting with a nitric acid solution having a concentration of 600 y/e or less.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below, based on the recovery of arsenic (2) from dilute sulfuric acid generated from a 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 has a voltage of 5 to 300 V/', 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. containing sulfuric acid at a concentration of 0.5
It contains arsenic (2) at a concentration of ~30 y/e, other heavy metals such as iron, zinc, copper, and cadmium, 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 dilute sulfuric acid solution containing arsenic and others is brought into contact with an organic solvent, and as a result, the total amount of arsenic and copper in the solution and a portion of iron, zinc and cadmium are removed from the organic solvent. The post-extraction liquid 1 is produced. In this case, iron (2) in particular is hardly extracted when the sulfuric acid concentration of the solution becomes high. 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. The temperature is selected to be 80°C to 80°C, preferably 40°C to 60°C. The volume ratio of the organic phase (organic solvent) to the aqueous phase (liquid to be treated) at the time of contact (hereinafter referred to as 0/A ratio) is about 1115 to 5 ha, preferably 112 to 2 ha, and depends on the equipment and operation used. It can be selected as appropriate depending on the conditions. The contact time is
Although it depends on the contact efficiency, 2 to 3 gin, usually 5 to 1 gin, is sufficient. In the flow sheet of the drawing, an extraction step 2 is provided in addition to the extraction step 1.

This extraction step 2 is for completely extracting and removing a trace amount of arsenic contained in the liquid after arsenic (1) is crystallized as arsenous acid from the liquid after back extraction, which will be described later. 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 all arsenic and a slight amount of heavy metals, and depending on the concentration of hydrochloric acid and hydrofluoric acid contained therein, it may be subjected to a pickling step, for example, if necessary. It can be effectively recycled as sulfuric acid in other process departments.

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 has extracted the total amount of arsenic and copper from extraction step 1 and optionally after extraction step 2 as well as a portion of iron, zinc and cadmium contains the iron thus co-extracted with arsenic. (2) Sent to a cleaning process to remove zinc and cadmium.

The washing step is carried out by contacting the organic solvent after extraction with a sulfuric acid solution having a concentration of 600 y/e or less, preferably 100 to 400 y/e. The contact between the organic phase and the sulfuric acid solution in the washing step is from 111 to 1511, preferably 51
It is carried out at an O/A ratio of 1 to 10 Ha, 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 washing step may be processed alone, but is preferably repeated in extraction step 1 as described above. In the cleaning process, iron■,
The arsenic-containing organic solvent after zinc and cadmium has been removed is then subjected to a back extraction operation in a back extraction step.

In the back-extraction step, arsenic is back-extracted from the arsenic-containing organic solvent using a single alkali solution or a mixed solution of sodium carbonate, ammonium carbonate, sodium bicarbonate, sodium hydroxide, and the like. The alkaline concentration for optimal back extraction is 0.01~. It is said to be 5 moles. As for the back extraction conditions, the O/A ratio is 113 to 101 L, preferably 111 to 5 H, 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, the arsenic is removed. Organic solvent and arsenic ■
A back-extraction solution containing .

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 the separation process. 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 (3) in this liquid is extracted in extraction step 2. The organic solvent that has undergone the back extraction step is then subjected to an organic solvent regeneration step 1 in which the alkaline form of the organic solvent is reduced to 600 g/' or less, preferably 50 to 300 g/'.
It is treated with a sulfuric acid solution at a concentration of g/e to convert it into the hydrogen form.

A part of the organic solvent that has been regenerated in the organic solvent regeneration step 1 is recycled to the extraction step 1 and reused. Since the liquid after organic solvent regeneration step 1 contains a very small amount of arsenic, it is sent to extraction step 1 or 2 to recover arsenic. Since the copper extracted into the organic solvent in extraction step 1 is not removed from the organic solvent until organic solvent regeneration step 1, part or all of the organic solvent is removed in the next organic solvent regeneration step 2.
It is contacted with a nitric acid solution having a concentration of 0 y/l or less to wash away the copper and regenerate the organic solvent.

The organic solvent thus regenerated is recycled to extraction step 1 and reused. Since the treated solution treated in this process contains trace amounts of iron, zinc, cadmium, and arsenic in addition to copper, at least the copper of these components is converted into sulfide by the well-known method of adding a sulfiding agent. After removing the precipitate, the precipitate is repeated to the copper smelting process. The liquid containing components other than copper that have not been precipitated and removed as sulfides can be treated in extraction step 1 or extraction step 2, if necessary. As explained above, the organic solvent is used in the washing step after the total amount of arsenic and copper and part of the heavy metals of iron, zinc, and cadmium are extracted in the extraction step 1 and, if necessary, in the extraction step 2. Iron (2), zinc and cadmium are removed, and then the remaining arsenic (2) is back extracted in the back extraction step and converted from the alkaline form to the hydrogen form in the organic solvent regeneration step (1).

Finally, in the organic solvent regeneration step 2, the copper accumulated in the organic solvent is removed, and the organic solvent is recycled to the extraction step 1 in a completely regenerated state. Since the heavy metals have already been removed from the arsenic (2) that is back-extracted in the back-extraction process, it can be recovered with high purity. Examples are shown below.

Example 1 Di-2-ethylhexyl dithio diluted to 20% with dispersol (trade name of Shell Chemical Co., Ltd.) from a dilute sulfuric acid solution having the composition shown in Table 1 produced in the process of cleaning sulfur dioxide gas generated from the copper smelting process. A test was conducted to recover arsenic (2) using an organic solvent consisting of phosphoric acid ester.

The solvent extraction operation was performed using the following conditions.

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

The composition of the obtained post-extraction solution is: Arsenic: 0.001y/e1 Iron: 0.023y/', Zinc: 0.136d/', Copper: 0.0
01y/e or less and cadmium 0.115y/e, showing an arsenic extraction rate of 99.9% or more.

In this example, iron and cadmium were hardly extracted due to the relatively high sulfuric acid concentration. On the other hand, copper is 99
．． More than 9% was extracted. Example 2 An extraction test was conducted under the same conditions as in Example 1 using di3,5,5-trimethylhexyldithiophosphate and diisodecyldithiophosphate 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 300y/' sulfuric acid and an O/A ratio of 5ha. The cleaning effects were as follows. Next, arsenic was back-extracted from the washed organic solvent using a sodium carbonate solution with a concentration of 53 y/e.

The back extraction conditions were O/A ratio = 1'2, temperature 50°C, and contact time 1 powder. As a result, a back extraction rate of 98.7% was obtained. In the back extraction operation, the copper in the organic solvent still remains in the organic solvent, so after the above back extraction, the organic solvent converted from alkaline type to hydrogen type with a sulfuric acid solution with a concentration of 100 da/e was converted to 126 f/'. Nitric acid solution with concentration and O/A ratio,
112, copper was removed from the organic solvent by contacting at a temperature of 50° C. and a contact time of 30 minutes.

As a result, a copper removal rate of 90% was obtained.

Thus, according to the present invention, as shown in the specific example, arsenic in dilute sulfuric acid produced from the 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 has been established for recovering high-purity arsenic acid that does not contain heavy metals from the back-extraction solution, and as it is extremely effective and easy to recover arsenic compared to conventional methods, it has great industrial significance. It's so big.

[Brief explanation of drawings]

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, zinc, copper and cadmium 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, zinc, copper and cadmium 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. 60% solvent
A method for separating and recovering arsenic, which comprises contacting with a sulfuric acid solution having a concentration of 0 g/l or less to wash and remove iron II, zinc and cadmium contained in the solvent after the extraction. 3. A sulfuric acid acidic solution containing arsenic III, iron II, zinc, copper and cadmium 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. 60% solvent
Contact with a sulfuric acid solution having a concentration of 0 g/l or less to wash and remove iron II, zinc and cadmium contained in the extracted solvent,
Next, the organic solvent containing arsenic III is back-extracted with an alkaline solution to separate and recover arsenic. 4 Contact with an organic solvent containing as an extractant a dialkyldithiophosphate ester having arsenic III, iron II, zinc, copper and cadmium groups at a pH below 4, and after extraction contact the solvent with a sulfuric acid solution having a concentration below 600 g/l. After the extraction, iron II, zinc, and cadmium contained in the solvent are washed away, and then the organic solvent containing arsenic III after washing is back-extracted with an alkaline solution, and then the organic solvent after the back-extraction is A method for separating and recovering arsenic, which comprises contacting arsenic with a sulfuric acid solution having a concentration of 600 g/l or less to convert an organic solvent from an alkaline type to a hydrogen type. 5. A sulfuric acid acidic solution containing arsenic III, iron II, zinc, copper and cadmium 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. 60% solvent
Contact with a sulfuric acid solution having a concentration of 0 g/l or less to wash and remove iron II, zinc and cadmium contained in the extracted solvent,
Next, the washed organic solvent containing arsenic III is back-extracted with an alkaline solution, and then the extracted organic solvent is extracted with 6
Part or all of the organic solvent converted from alkaline form to hydrogen form by contacting with a sulfuric acid solution having a concentration of 00 g/l or less is accumulated in the organic solvent by contacting with a nitric acid solution having a concentration of 600 g/l or less. A method for separating and recovering arsenic, which consists of washing and removing copper and trace amounts of iron, zinc and cadmium.