KR102761014B1 - Composition comprising non-aqueous anhydride solvent for selective and rapid recovery and gold recovery method using the same - Google Patents

Abstract

The present invention relates to a composition capable of rapidly and selectively leaching Au from WRAM (Waste Random Access Memory), including a non-aqueous anhydrous solvent, a leaching agent, an oxidizing agent, and a moisture removing agent, and a method for recovering gold using the same.

Description

Composition comprising non-aqueous anhydride solvent for selective and rapid recovery and gold recovery method using the same

The present invention relates to a composition for gold leaching including a non-aqueous solvent and a method for recovering gold using the same, and more specifically, to a composition including a non-aqueous solvent, a leaching agent, an oxidizing agent and a moisture removing agent capable of rapidly and selectively leaching Au from WRAM (Waste Random Access Memory), and a method for recovering gold using the same.

As industrial development progresses, the amount of electronic waste such as WRAM (Waste Random Access Memory) and waste printed circuit boards is rapidly increasing, and the environmental pollution caused by this is becoming a social problem. However, the metals contained in electronic waste are not only very important as raw materials for advanced industries, but also expensive and have high added value, so it is a very precious resource to be treated as waste, and therefore, it is economically necessary for the country to recover them in terms of resource recycling. In addition, it can be said that recovering and recycling them is very useful in terms of effective use of resources.

As is well known, e-waste from electrical or electronic devices such as mobile phones and computers contains a large amount of metals such as gold, silver, and palladium, as well as valuable metals such as copper, tin, and iron. In particular, the gold (Au) content of RAM or printed circuit boards (WPCBs) is known to be much higher than that of Au ore (Lin et al., 2022), and therefore RAM or WPCB are recognized as valuable secondary resources for Au recovery.

The most common method for extracting Au from electronic waste is the hydrometallurgical process. Although the hydrometallurgical process is highly efficient, it causes serious environmental problems due to the use of excessive water and toxic chemicals such as cyanide and aqua regia. In addition, gold extraction methods using thiosulfate, thiourea, and amino acids have been proposed, but these methods still have the problem of using considerable chemicals.

The present invention provides a method for separating and purifying gold (Au) which can reduce the use of toxic chemicals and water.

The present invention provides a composition capable of rapid and selective leaching of gold.

One aspect of the present invention is

The present invention relates to a gold leaching composition comprising a mixture of a non-aqueous solvent, a leaching agent, an oxidizing agent and a moisture removing agent.

The composition of the present invention can rapidly and selectively leach gold from WRAM (Waste Random Access Memory) using acetic anhydride as a non-aqueous solvent.

The present invention comprises a step of adding electronic waste to the composition to leach gold;

A dilution step of adding water to the above composition;

The present invention relates to a method for selectively recovering gold, comprising the step of reducing gold by adding a reducing agent to the diluted composition.

The gold leaching composition of the present invention can rapidly and selectively leach Au by including acetic anhydride as a non-aqueous solvent, HCl as a chlorinating reagent, H ₂ O ₂ as an oxidizing agent, and CaCl ₂ as a moisture removing agent.

More specifically, the present invention can significantly reduce the amount of chemicals and process volumes and usage for Au separation and purification by replacing water used as a solvent with non-aqueous acetic anhydride. In addition, the acetic anhydride used in the present invention can effectively remove water (water contained in hydrochloric acid) present in a reaction vessel to provide more free Cl ^- ions capable of reacting with gold, thereby increasing the leaching efficiency. In addition, it is environmentally friendly because it has no possibility of bioaccumulation due to its short half-life (4.4 minutes) in the hydrosphere (rapidly converted to acetic acid).

In addition, HCl used in the present invention provides Cl ^- ions for Au dissolution as a leaching agent, and hydrogen peroxide acts as an oxidizing agent of hydrochloric acid.

Meanwhile, when water exists in the leaching reactor, since the hydrogen ions of the water strongly bind with Cl ^- , the presence of water in the reactor acts as a factor that inhibits the binding of Cl ^- with gold. The CaCl ₂ used in the present invention acts as a moisture removing agent that absorbs and removes such water molecules, and at the same time can provide additional Cl ^- .

Figure 1a is a photograph of WRAM before and after leaching, Figure 1b is a graph showing the leaching efficiency for each metal, and Figure 1c is the WRAM leaching efficiency according to the presence or absence of CaCl ₂ addition.
Figure 2 is a graph showing the leaching efficiency according to the input concentration of each component.
Figure 3 shows FTIR spectra for acetic anhydride (AA), leachate solution before leaching (AA, HCl, H ₂ O ₂ , and CaCl ₂ ), and leachate solution after gold leaching.
Figure 4a shows the leaching mechanism in acetic anhydride, and Figure 4b shows the leaching mechanism in water.
Figure 5 shows the leaching efficiency and metal concentration in unpulverized WRAM and crushed WRAM.
Figure 6a is a SEM-EDX image of the surface of WRAM, and Figures 6b and 6c illustrate the leaching mechanism in acetic anhydride for unpulverized WRAM and pulverized WRAM, respectively.
Figure 7a shows the leaching efficiency according to the number of recycling cycles of the leachate, and Figure 7b shows the leaching efficiency according to the number of recycling cycles when using a hydrochloric acid solution with silica gel added and some of the water removed.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the scope of the present invention is not limited to the description of the embodiments below or the drawings. That is, the terms used in this specification are only used to describe specific embodiments and are not intended to limit the present invention. The singular expression includes plural expressions unless the context clearly indicates otherwise. In addition, it should be understood that the terms "comprises" or "has" described in this specification are intended to specify that a feature, number, step, operation, component, part or combination thereof described in the specification exists, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

The gold leaching composition of the present invention comprises a non-aqueous solvent, a leaching agent, an oxidizing agent and a moisture removing agent.

The above non-aqueous solvent may be acetic anhydride, Propionic anhydride, Butyric anhydride, Isobutyric anhydride, Valeric anhydride, Citraconic anhydride, Trifluoromethanesulfonic anhydride, Methacrylic anhydride, Dodecenylsuccinic anhydride, 4-pentenoic anhydride, and preferably acetic anhydride.

The gold leaching composition of the present invention uses an anhydrous non-aqueous solvent as a base solvent. Since the anhydrous solvent easily hydrolyzes water to produce acetic acid, propionic acid, butanoic acid, etc., using the anhydrous solvent as a base solvent can effectively remove water present in a leaching reactor (e.g., water contained in hydrochloric acid) to provide more free Cl ^- ions that can react with Au. As a result, the non-aqueous anhydrous solvent can increase the gold leaching efficiency.

In addition, the non-aqueous anhydride can significantly reduce the amount of chemicals (chemicals, etc.) and water used for Au separation and purification by replacing aqueous solvents (water). In addition, the anhydride is environmentally friendly because it has no possibility of bioaccumulation due to its short half-life in the hydrosphere.

The above leaching agent may be hydrochloric acid, Thionyl chloride, CuCl ₂ -CaCl ₂ , (COCl) 2 , and preferably hydrochloric acid.

The above hydrochloric acid provides Cl ^- ions for Au dissolution as a leaching agent. Cl ^- ions can act as stable ligands in the bonding with Au(III).

The leaching reaction of gold in the above composition is as shown in the following reaction scheme 1.

[Reaction Formula 1]

Au + 4Cl ^- → AuCl ₄ ^-

The above oxidizing agent may be hydrogen peroxide, nitric acid, ozone, potassium permanganate, and preferably hydrogen peroxide. Hydrogen peroxide acts as an oxidizing agent for hydrochloric acid. The higher the concentration of H2O2, the more the dissolution of Au is accelerated, but if added in excess, a highly exothermic reaction may occur due to the hydrolysis of acetic anhydride.

The above-mentioned moisture remover may include at least one of calcium chloride, magnesium chloride, potassium chloride, calcium sulfate, and calcium phosphate. When the leaching composition includes acetic anhydride, hydrochloric acid, and an oxidizing agent, due to the water contained in the hydrochloric acid, water (molecule) and Cl ^- strongly hydrogen bond, and therefore, the reaction of the reaction formula 1 between chloride ions and gold is inhibited, thereby reducing the gold leaching efficiency. The leaching composition of the present invention can increase the leaching efficiency by using a moisture remover to absorb water molecules (for example, Ca(OH)2, Mg(OH)2), etc.) and additionally providing chloride ions in order to prevent the bonding of water molecules and chloride ions.

The above composition can be used in a non-aqueous solvent containing 180 to 550 mM leaching agent, 50 to 150 mM oxidizing agent and 10 to 45 mM moisture removing agent.

For example, the composition may comprise 180 to 550 mM HCl, 50 to 150 mM H2O2 and 10 to 45 mM CaCl2 in the non-aqueous solvent.

When the above hydrochloric acid and hydrogen peroxide exceed the range of 550 mM and 150 mM, respectively, the solution boils due to hydrolysis of acetic anhydride.

The above calcium chloride is not sufficient for moisture removal when it is less than 10 mM, and does not dissolve completely when it exceeds 45 mM.

Meanwhile, the present invention provides a method for selectively recovering gold, including a step of introducing electronic waste into the composition to leach gold, a dilution step of adding water to the composition, and a step of introducing a reducing agent into the diluted composition to reduce gold.

The above electronic waste may be a circuit board, waste random access memory (WRAM), CPU, MLCC, IC chips, etc., and preferably may be waste RAM (WRAM).

The above electronic waste can be immersed in the composition without being crushed, or can be cut into pieces of several centimeters or more and then immersed in the composition. When electronic waste such as WRAM is crushed, the exposed area of copper or nickel layered under the gold becomes similar to that of gold. In this case, as copper, which is contained hundreds of times more than gold, reacts with chloride ions (Cl ^- reacts with Cu to form CuCl ₂ ), the reaction between gold and chlorine is relatively reduced, which may lower the gold leaching efficiency.

When using a crushed sample, the gold leaching step may be performed when the pulp density in the composition of electronic waste is 300 g/l or less, preferably 1 to 250 g/l, and more preferably 50 to 200 g/l. The pulp density may be the mass of electronic waste added to the leaching solution (L). When the pulp density is higher than 300 g/l, the leaching efficiency decreases.

The above dilution step may be performed by adding water as a diluent in an amount of 100 to 600 parts by weight, preferably 200 to 500 parts by weight, and more preferably 300 to 400 parts by weight, relative to 100 parts by weight of the acetic anhydride.

The above dilution step can be incubated at room temperature for a predetermined period of time after adding water. The above dilution step can be stored at room temperature for about 12 to 48 hours so that acetic anhydride in the solution is converted to acetic acid.

The reducing agent may be at least one of Na ₂ S ₂ O ₄ , Dithiothreitol (DTT), Dithioerythritol (DTE), Tris(2-carboxyethyl)phosphine hydrochloride (TCEP), Na ₂ S ₂ O _{4 ,} Na ₂ SO3, NaBH4, and Hydrazine, and preferably sodium dithionite (Na ₂ S ₂ O ₄ ) having low toxicity.

The redox reaction between gold ions and sodium dithionite (Na ₂ S ₂ O ₄ ) can be represented by the following reaction scheme 5.

[Reaction Formula 2]

S ₂ O ₅ ^2- + 4OH ^- + Au ⁺ → Au + 2SO ₄ + 2H ₂ O

As an example, the reducing agent may be added to the diluted composition at 1 to 10 g/l, preferably 1 to 5 g/l.

In addition, the composition of the present invention can be recycled and reused. A method of leaching gold by recycling the composition is as follows.

(1) A first leaching step for leaching gold by introducing electronic waste into a composition containing a non-aqueous anhydrous solvent, a first leaching agent, an oxidizing agent, and a moisture removing agent;

(2) A dilution step of adding water to the composition from which the gold has been leached;

(3) A step of reducing gold by adding a reducing agent to the diluted composition;

(4) A step of separating gold from the above composition;

(5) A step of adding silica gel to the second leaching agent to remove some of the water from the second leaching agent;

(6) a step of adding the second leaching agent to the composition from which gold was separated in step (4);

(7) A second leaching step of adding another electronic waste to the composition and leaching it;

(8) A gold recovery method that performs the dilution step of (2), the reduction step of (3), and the separation step of (4),

The above method relates to a method for recovering gold by repeating steps (5) to (8) to recycle the composition several times.

Preferably, the method of leaching gold is

(1) A first leaching step for leaching gold by introducing electronic waste into a composition containing a non-aqueous anhydrous solvent, a first hydrochloric acid solution, an oxidizing agent, and calcium chloride;

(2) A dilution step of adding water to the composition from which the gold has been leached;

(3) A step of reducing gold by adding a reducing agent to the diluted composition;

(4) A step of separating gold from the above composition;

(5) A step of removing some of the water from the second hydrochloric acid solution by adding silica gel to the second hydrochloric acid solution;

(6) A step of adding the second hydrochloric acid solution to the composition from which gold was separated in step (4);

(7) A second leaching step of adding another electronic waste to the composition and leaching it;

(8) A gold recovery method that performs the dilution step of (2), the reduction step of (3), and the separation step of (4),

The above method can recycle the composition several times by repeating steps (5) to (8).

(5) Step: Silica gel can be added to the (second) hydrochloric acid solution in the range of 20 to 500 g/l.

Hereinafter, the present invention will be described in detail with reference to the attached examples and drawings. However, the attached examples are only intended to illustrate specific embodiments of the present invention and are not intended to limit the scope of the present invention.

Example 1

WRAM samples (SK Hynix, stick type, 16 g) and crushed WRAM samples (pulverized to less than 3 mm) were used. Reagents such as acetic anhydride (95%), hydrogen peroxide (H ₂ O ₂ - 30%), hydrochloric acid (HCl, 36%), and nitric acid (HNO ₃ 60%) were purchased from Samsung Chemical Co., Ltd. (Seoul, Korea).

Leaching

In the leaching experiment, acetic anhydride was used as a solvent in the reaction of HCl and H ₂ O ₂ , chlorine was used as a leaching agent, and CaCl ₂ was used as a moisture removing agent. One WRAM stick (~16 g) or one WRAM module (~110 g) was used as a sample. The Au extraction reaction for leaching is as follows.

0.5 g (45 mM) CaCl ₂ was directly added to 94 ml acetic anhydride containing WRAM, followed by 3 ml (360 mM) HCl using a micropipette and finally 1 ml (100 mM) H ₂ O ₂ was added in the same manner. The reaction proceeded rapidly and the solution changed from colorless to yellow. To this point, a WRAM stick (~16 g) was added to the solution and the solution was mixed for 10 min. Unless specified, other leaching experiments using acetic anhydride as a solvent were performed in the same manner but with different concentrations of CaCl ₂ , HCl or H ₂ O ₂ . Pulp density: 160 g/L, leaching temperature: 25oC, and working volume: 100 ml. The leaching efficiency was calculated as shown in the following reaction scheme 3.

Reduction reaction

The WRAM stick was removed from the solution after leaching. The solution from which the stick was removed was diluted with three times the amount of water compared to the amount of acetic anhydride solution (added during the preparation of the leachate). After dilution, Na ₂ S ₂ O ₅ was added to the solution while stirring constantly using a magnetic stirrer. Then, the solution was filtered, and the remaining amount of Au was confirmed, and the reduction efficiency was calculated as in Scheme 4.

[Reaction Formula 3]

Leaching efficiency = Ci/Cw×100%

Here, Ci is the metal concentration in the leachate and Cw is the metal content in the WRAM.

[Reaction Formula 4]

Reduction (recovery) efficiency = ((Cw-Ci)/Cw) × 100% (2)

Here, Cw and Ci are the metal concentrations in the leachate before and after reduction, respectively.

Figure 1a shows photographs of WRAM before and after leaching. It can be seen that the Au coated on the upper side is almost removed from the RAM after leaching.

Figure 1b is a graph showing the leaching efficiency for each metal calculated using Reaction Scheme 3. Referring to Figure 1b, the leaching efficiency of gold is 97 ± 0.4%, and that of Cu and Ni is 0.3 ± 0.02% and 0.7 ± 0.1%, respectively, showing excellent selectivity for Au compared to Cu and Ni.

Figure 1c shows the WRAM leaching efficiency (under the same conditions) depending on the presence or absence of CaCl ₂ addition. Referring to Figure 1c, it can be seen that the gold leaching efficiency is very low when CaCl ₂ is not added.

Fig. 2a is a graph showing the leaching efficiency according to the input concentrations of HCl (A) and H2O2 (B), Fig. 2b shows the leaching efficiency according to the input concentrations of CaCl2 (C) and HCl (A), and Fig. 2c shows the leaching efficiency according to the input concentrations of CaCl2 (A) and H2O2. Fig. 2d is a graph showing the experimental values and the predicted Au leaching efficiency.

In addition, the optimal leaching efficiency according to the input concentrations of HCl, H2O2, and CaCl2 was modeled using the following equation.

Au leaching efficiency = -140.037 - 159.19[H2O2] + 1077.29[HCl] - 166.344[CaCl2] + 1306.67[H2O2] ² - 100.0[H2O2][HCl] - 1514.29[H2O2][CaCl2] - 1154.37[HCl] ² + 370.656[HCl][CaCl2] + 136.054[CaCl2] ²

The optimal concentration conditions showing the highest gold leaching efficiency were determined to be 550 mM HCl, 150 mM H2O2, and 27.5 mM _CaCl2 , and the Au leaching efficiency at this time was approximately 98.3%.

Figure 3 shows the FTIR spectra for acetic anhydride (AA), the leachate solution before leaching (AA, HCl, H ₂ O ₂ , and CaCl ₂ ), and the leachate solution after gold leaching, and Figure 4a shows the leaching mechanism in acetic anhydride, and Figure 4b shows the leaching mechanism in water.

Referring to Fig. 3, after adding all components (HCl, H2O2, and CaCl2), the OH spectrum appeared at 3425 cm ^-1 , whereas the C=O spectrum showed a much stronger peak at 1721 cm ^-1 and a weaker peak at 1823 cm ^-1 in comparison. This shows that a hydrolysis reaction occurred in which acetic anhydride was converted to acetic acid.

Referring to Fig. 4b, when water is present in the system, water molecules (H2O) form hydrogen bonds with Cl ^- to prevent the leaching reaction between chloride ions and Au. On the other hand, referring to Fig. 4a, since acetic anhydride does not interfere with the bonding with Cl ^- , bonding between gold and Cl - can be possible. However, since a large amount of water is present in the acetic anhydride system of Fig. 4a (water contained in hydrochloric acid), it can be seen that it is very difficult to dissolve Au unless CaCl2, which can remove water as in the present invention, is added.

Figures 5a and 5b show the leaching efficiency and metal concentration when using unpulverized WRAM, and Figures 5c and 5d show the leaching efficiency and metal concentration when using pulverized WRAM. Figures 5e and 5f show the effect of pulp density on metal leaching from pulverized WRAM.

Figure 6a is a SEM-EDX image of the surface of WRAM, and Figures 6b and 6c illustrate the leaching mechanism in acetic anhydride for unpulverized WRAM and pulverized WRAM, respectively.

Referring to Figures 5a to 5d, for the unmilled WRAM, the reaction occurred rapidly and selectively for Au, achieving a remarkable leaching efficiency of 99.7 ± 0.9% for Au, whereas the leaching efficiencies of Cu and Ni were negligible after 5 min (Figure 5a). In terms of metal concentration, Au also showed a much better leaching rate at 534.2 ± 4.6 ppm even after 5 min. In contrast, Cu leaching showed higher concentrations of 267.0 ± 3.0 ppm and 63.9 ± 8.3 ppm than Ni during the same period, reflecting the Cu and Ni contents in the RAM (Figure 5b). For the milled WRAM, the leaching data showed that Au was not extracted. Only Cu and Ni were leached over 30 min, and the metal concentrations in the aqueous solution were similar to the unmilled sample (Figures 5c, 5d).

Referring to Figures 5e and 5f, it can be confirmed that the Au leaching efficiency increases when the pulp density is reduced.

Referring to FIGS. 5a to 5d and FIGS. 6a and 6b, in the case of the unpulverized WRAM, the Au plated on the outer layer is eluted first, but in the pulverized WRAM, a much larger amount of positive Cu (Au: Cu = 0.04 wt.%: 22.8 wt.%) than Au is exposed to the outside and exists, so it appears that most of the Cl ^- reacts with the copper.

Figure 7a shows the leaching efficiency according to the number of recycling cycles of the leachate, and Figure 7b shows the leaching efficiency according to the number of recycling cycles when using a hydrochloric acid solution with silica gel added and some of the water removed.

As shown in Fig. 7a, when the leachate was recycled, the Au leaching efficiency decreased over time. In contrast, when a hydrochloric acid solution with silica gel added and some of the water removed was used, as shown in Fig. 7b, a high Au leaching efficiency was maintained for seven leaching cycles.

Although preferred embodiments of the present invention have been described in detail above, these are for the purpose of explanation only and the protection scope of the present invention is not limited to these.

Claims (10)

A gold leaching composition comprising a non-aqueous solvent, a leaching agent, an oxidizing agent and a moisture removing agent, wherein the non-aqueous solvent is selected from at least one of acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, valeric anhydride, citraconic anhydride, trifluoromethanesulfonic anhydride, methacrylic anhydride, dodecenoyl succinic anhydride and 4-pentenoic anhydride. A gold leaching composition according to claim 1, characterized in that the leaching agent comprises at least one of hydrochloric acid, thionyl chloride, copper chloride-calcium chloride (CuCl2-CaCl2), and oxalyl chloride ((COCl)2). A gold leaching composition according to claim 1, characterized in that the oxidizing agent comprises at least one of hydrogen peroxide, nitric acid, ozone, and potassium permanganate. A gold leaching composition according to claim 1, characterized in that the moisture removing agent comprises at least one of calcium chloride, magnesium chloride, potassium chloride, calcium sulfate, and calcium phosphate. A gold leaching composition according to claim 1, characterized in that the composition comprises 180 to 550 mM of a leaching agent, 50 to 150 mM of an oxidizing agent, and 10 to 45 mM of a moisture removing agent in the non-aqueous solvent. A step of leaching gold by adding electronic waste to the composition of any one of claims 1 to 5;
A dilution step of adding water to the above composition;
A method for selectively recovering gold, comprising the step of reducing gold by adding a reducing agent to the diluted composition. A method for selectively recovering gold, characterized in that in claim 6, the electronic waste is immersed in the composition without crushing waste random access memory (WRAM). In claim 6, the gold leaching step is a method for selectively recovering gold, characterized in that when a crushed sample is used, the pulp density in the composition of electronic waste is 300 g/l or less. A method for selective recovery of gold, characterized in that in the 6th paragraph, the dilution step comprises adding 100 to 600 parts by weight of water per 100 parts by weight of the non-aqueous solvent of the composition. (1) A first leaching step for leaching gold by introducing electronic waste into a composition containing a non-aqueous anhydrous solvent, a first leaching agent, an oxidizing agent, and a moisture removing agent;
(2) A dilution step of adding water to the composition from which the gold has been leached;
(3) A step of reducing gold by adding a reducing agent to the diluted composition;
(4) A step of separating gold from the above composition;
(5) A step of adding silica gel to the second leaching agent to remove some of the water from the second leaching agent;
(6) a step of adding the second leaching agent to the composition from which gold was separated in step (4);
(7) A second leaching step of adding another electronic waste to the composition and leaching it;
(8) A gold recovery method that performs the dilution step of (2), the reduction step of (3), and the separation step of (4),
The method is a gold recovery method characterized in that the composition is recycled several times by repeating steps (5) to (8).