JPS60103138A - Method for recovering gold and silver from aqueous solution containing thiourea as well as gold and silver - Google Patents

Abstract

PURPOSE:To recover gold and silver at a good yield by adding an alkali to an aq. soln. contg. thiourea compd. of gold and silver to specific pH in the presence of iron ion and separating the formed precipitate. CONSTITUTION:An alkali hydroxide and potassium carbonate or calcium carbonate are added to an aq. soln. contg. thiourea compd. of gold and silver to adjust the pH thereof to >=6.5 without adding ferric sulfate or ferric chloride thereto if the substantial amt. (about 10-100 times the gold) of trivalent or vivalent iron ion exists or after adding preferably a suitable amt. of ferric fulfate or ferric chloride thereto if the soln. contains the iron ion in the smaller amt. The soln. is preferably aerated to adjust the pH to >=4.0. The precipitate formed by such addition is separated by a filtering and washing method or the like by which gold is recovered directly at an actual yield of about 90-92wt% and silver at about 90-95wt%.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering gold and silver from an aqueous solution containing a thiourea compound of gold and silver.

More specifically, a method in which iron ions are added to an aqueous solution containing a thiourea compound of gold and silver as necessary, the Phi of the aqueous solution is increased, and gold and silver are co-precipitated with iron to separate them. It is related to.

Conventionally, as a method for recovering gold and silver from ores containing gold and silver by hydrometallurgy, the ore is crushed and then the gold and silver are leached using a sodium cyanide aqueous solution. The so-called ossification smelting method, in which silver is reduced with zinc powder, is widely used industrially.

However, as is well known, the above sodium cyanide is a chemical that is harmful to humans and animals, and during operation, it must be contained in wastewater.
Strict management is required in terms of pollution and the environment, such as discharging the ore so that it is below pm and thoroughly washing the ore after leaching so that no cyanide remains.

On the other hand, in recent years, a method of leaching gold and silver contained in ores with thiourea has been investigated domestically and internationally as a pollution-free process that does not use sodium cyanide.

This method uses thiourea as a gold and silver leaching agent and, for example, a ferric salt as an oxidizing agent, and the reaction is considered as follows.

Au-1-Fe +, 2 Cps (Nl2) 2→A
u (as (Nl2) 2)2', -1-1t's The inventors of the present application conducted a second experiment on the method of leaching gold from ores containing gold and silver based on the above method, and found that thiourea leached gold into ores. The leaching of gold depends on the leaching conditions, but when the initial concentration of thiourea is 10 g/l, the leaching rate of Au is about 93% by weight in 3 hours, and the leaching time of the blue smelting method is xti-tttg. It was found that the leaching rate was extremely high compared to the leaching rate of 70 to 93% by weight of Au.

By the thiourea method, the leached gold and silver are dissolved in an aqueous solution as a thiourea complex;
As a method for recovering silver, /) zinc dust, hydrazine, '
A method of precipitating gold and silver by adding a reducing agent such as sodium ric acid, and a method of adsorbing gold and silver on activated carbon have been proposed.

However, in the case of the above method /), thiourea (10 g/7'), sulfuric acid (10 g/l), ferrous sulfate (Fe/gll) is added to the fine powder ore containing gold and silver.
) were added and stirred for 3 hours, followed by solid-liquid separation to obtain an aqueous solution of PH, 2,3 containing 2,3 mg/l of gold, /, 11 m9/l of silver/7! When adding zinc powder with different poisons to reduce gold and silver, as shown in Figure 1, it takes more than 711 to recover gold and silver of about 3 to 17 +++v'7. There were problems in that zinc was required and the direct yield was insufficient.

The main reason for the large amount of reducing agent used is ＼Gold from thiourea,
Extraction of silver is carried out in acidic conditions of about P, H”2 (PH
This is due to poor extraction of gold and silver when Pli is higher than 2, and similar results are obtained even if a reducing agent other than zinc is used.

In addition, in the case of method 2), as shown in Fig. 2, the isothermal adsorption lines for the cyanide aqueous solution containing a trace amount of gold and the thiourea aqueous solution containing a trace amount of gold, respectively, on activated carbon. The aqueous solution has a considerably lower adsorption amount of gold, and in this case activated carbon also has a cost disadvantage, as it adsorbs most of the thiourea.

The vertical axis in FIG. 2 shows the amount of gold adsorbed per gram of activated carbon (1119).

An object of the present invention is to provide a method for recovering gold and silver in an aqueous thiourea solution that eliminates the above-mentioned drawbacks.

In order to achieve this objective, the inventors of the present application have conducted intensive studies and discovered that when the pH of a thiourea aqueous solution containing gold and silver is increased in the presence of iron, hydroxyl oxide is generated. The present invention was achieved by experimentally discovering that most of gold and silver can be co-precipitated during iron precipitation.

That is, the method of the present invention involves adding an equivalent amount of trivalent iron ions or divalent iron ions (
(preferably about 10 to 700 times the amount of gold), it can be used as is, or when iron ions are low, it is preferable to add an appropriate amount of ferrous sulfate or ferric chloride, preferably after aeration. For example, a combination of alkali hydroxide and calcium carbonate is used to raise the pH to ≧≧0, and the resulting precipitate is separated by a filtration washing method to recover gold and silver.

In the method of the present invention, it is essential to have iron ions present in the thiourea-containing aqueous solution equivalent to IJ1 relative to the amount of gold and silver in the aqueous solution in order to almost completely coprecipitate the silver.

When leaching gold and silver in ores with an aqueous solution of thiourea at about /θg/l, ferric sulfate or ferric chloride is added as an oxidizing agent, usually about 0.7 to /g/l as Fe. Therefore, in such cases, there is no need to add additional iron ions.

However, in the above case, since the added Fe acts as an oxidizing agent during leaching of gold and silver, the iron ions in the leaching solution are reduced and exist as Fe, so it is preferable to carry out aeration before adding the alkali.

If the aeration operation is omitted and alkali is added, as shown in B in Figure 3 (Au 3 mg/l),
In order to recover 90% by weight or more of gold and silver, it is necessary to set the PHA preferably to pH 7 or higher, but in the case of alkali addition after aeration, A is PII 4 or higher, which gives almost the same yield. can get. High student, PH in case of A in Figure 2
is fine within the range of t to ot, and even if the pH is higher than that, gold,
No improvement in silver recovery rate is observed 0 Next, as the alkali to be added to the leachate, sodium hydroxide, potassium hydroxide, calcium carbonate, calcium hydroxide, etc. can be used, but it is possible to use only alkali hydroxide. It is preferable to use alkali hydroxide and, for example, calcium carbonate in combination, from the viewpoint of filterability of the iron hydroxide precipitate.

The above operations can usually be performed at room temperature.

If desired, the temperature can be maintained at 30 to SθC, but this only slightly improves the floc growth and bendability of the precipitate after neutralization, and does not particularly contribute to improving the actual yield of gold and silver.

According to the method of the present invention, an alkali is added to the aqueous solution to form an iron precipitate, and the iron precipitate is separated. ~WaS car 11:%
They can be collected by I&T.

If ores containing gold and silver are treated with an aqueous solution containing thiourea and iron ions, and the method of the present invention is applied to the resulting leachate, the iron used as an oxidizing agent during leaching will be further converted to gold and silver. Since it can be used as a coprecipitant, it has the advantage of not only cost but also simplified operation.

In addition, in actual operations, the ore is crushed using iron boat mills, etc., so it is possible that a small amount of iron powder may be mixed in, but even in such cases, the mixed iron powder can be effectively used as iron. .

Although ferrous salt has been described as the oxidizing agent in the method of the present invention, it goes without saying that ordinary oxidizing agents such as hydrogen peroxide, bromine, potassium permanganate, etc. can also be used in the same manner. However, if an oxidizing agent other than iron ions is used, it is necessary to add an appropriate amount of iron to the treated leachate.

The precipitate obtained by the method of the present invention can be roasted and then treated in a silver fractionating furnace or the like, and the filtrate can be discharged as it is.

Examples will be described below.

Example / 30 g of gold, 7't%, which was crushed to qg% by weight of 32 tons or less, 5゜g of ore containing 2.3.0 g/l of silver, 3g of thiourea, 71 g of ferrous sulfate, Fe
0.3 g/l of sulfuric acid and 3 g//l of sulfuric acid (both grade 7 reagents were used). ! ; Suction i1 using 218 paper of B
When passing M, gold 7.7 mf no silver/, , 2g m
A leachate g2θml of ti/l was obtained. Gold, silver 24jl
was performed using atomic absorption spectrometry.

Next, add 0.0% to the above exudate. g 3 air at a rate of 11 minutes
Blow in for 0 minutes, then add trial M IMr calcium hydroxide o, sg as an emulsion to -C, and gradually add / specified sthorium hydroxide aqueous solution to PH'f'! , 5, and then stirred for 20 minutes with the above stirrer.
When SO12 was suction filtered using paper, 0.0 gold was found.
/2'1 mg/l, silver o, / /3 mal filtrate 900me was obtained, the direct yield here was Auη,2
%, Ag90. /%, which is an almost satisfactory result.

Example - Gold and silver were leached from the ore used in Example 7 in the same manner as in Example 1, except that 0.2 g of potassium permanganate (grade 7) was used as the oxidizing agent and no iron ions were added. , ferrous chloride→2 was added to the obtained leachate to give 300 mg/l Ice, /, /) 3 m
While stirring 300 rne of an aqueous solution containing g/l of Au and 0.32 m4 (/l of Ag) with a magnetic cooler, add 0.2 m of calcium carbonate of reagent grade 7 at room temperature.
g and then gradually added a specified amount of sodium hydroxide starting from picolet to obtain P1i7. ．． It was set as 2.

The aqueous solution was subsequently stirred for 20 minutes, and then suction filtered and washed using ASC filter paper to recover gold and silver in a precipitate.
Au, A, and g remaining in the filtrate 330 me were measured by Fufu atomic absorption spectrometry and found to be AuO,/θnIt)/l %
AgO,02rr? l, and the respective recovery rates are Au73
．． 3%, Ag content was 3.7%, and almost satisfactory results were obtained.

The method of the present invention can be used to collect gold from scraps containing trace amounts of gold or silver.
It can also be applied to silver recovery.

It goes without saying that the scope of the present invention also includes a case where an aqueous solution containing a thiourea compound containing only gold or silver is treated according to the present invention.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the recovery rates of gold and silver with respect to the amount of zinc added to an aqueous solution containing gold, silver, thiourea, sulfuric acid, and ferrous sulfate.
Figure contains gold. Figure 3 is a diagram showing isothermal adsorption lines for activated carbon of chemical solution A1 and gold-containing thiourea solution B, and Figure 3 is a diagram showing the relationship between PH and recovery rates of gold and silver. A: Those that have been aerated. B: Those that were not aerated. Applicant Sumitomo Metal Mining Co., Ltd. Agent Katsunari Nakamura Figure 1 ■ Amount of zinc added (ga) Total residual concentration (m) H

Claims (4)

[Claims] (1) Add an alkali to an aqueous solution containing a thiourea compound of gold A and silver in the presence of iron ions to adjust the pH to 6.S or higher,
A method for recovering gold and silver from an aqueous solution containing thiourea and gold and silver, the method comprising separating a generated precipitate. (2) A method for recovering gold and silver from an aqueous solution containing thiourea and gold and silver according to claim (1), wherein the alkali consists of an alkali hydroxide and calcium hydroxide or calcium carbonate. . (3) Thiourea and gold, characterized in that an aqueous solution containing gold and silver as a thiourea compound is aerated in the presence of iron ions, and then an alkali is added to the aqueous solution to adjust the pH to 1.0 or higher. , a method for recovering gold and silver from an aqueous solution containing silver. (4) Recovering gold and silver from an aqueous solution containing thiourea and gold and silver according to claim (3), wherein the alkali consists of alkali hydroxide and calcium hydroxide or calcium carbonate. Method.