TWI704109B - Method of recovering gold using thiourea graphene - Google Patents

Abstract

A method of recovering gold using thiourea graphene includes the following steps. Providing a thiourea graphene. The thiourea graphene is added to the wastewater to carry out an adsorption reaction. The wastewater includes at least gold ions, and the thiourea graphene selectively adsorbs the gold ions. The thiourea graphene adsorbing the gold ions is separated from the wastewater. The thiourea graphene adsorbing the gold ions is subjected to a desorption reaction to obtain an aqueous solution containing the gold ions.

Description

Method for recovering gold using thiourea graphene

The present invention relates to a method for recovering gold, and particularly to a method for recovering gold using thiourea graphene.

At present, the method of recovering gold from waste water is mainly based on ion exchange resin as the adsorption material. Compared with the traditional electrolysis method, it is more in line with the trend of environmental protection and energy saving, and has good adsorption efficiency and recovery rate. . However, ion-exchange resin has no effect in the nitric acid system, and its minimum adsorption limit for gold ions is only 1 mg/liter. Therefore, when the concentration of gold ions in the wastewater is less than 1 mg/liter, the absorption efficiency of the ion exchange resin for gold ions will be significantly worse.

The present invention provides a gold recovery method using thiourea graphene, which utilizes the high selectivity of thiourea graphene for gold ions, so that the gold recovery method using thiourea graphene can have a lower adsorption limit and better Adsorption efficiency and higher saturated adsorption capacity.

The method for recovering gold using thiourea graphene of the present invention includes the following steps. First, provide thiourea graphene. Next, graphene thiourea is added to the wastewater to perform an adsorption reaction. Among them, the wastewater includes at least gold ions, and thiourea graphene can selectively adsorb gold ions. Then, the thiourea graphene that adsorbs gold ions is separated from the wastewater. Finally, the thiourea graphene adsorbing gold ions is subjected to a desorption reaction to obtain a solution containing gold ions.

In an embodiment of the present invention, the nitrogen content of the above-mentioned thiourea graphene is 2 to 4% by weight and the sulfur content is 20 to 23% by weight.

In an embodiment of the present invention, the above-mentioned thiourea graphene is 0.5 mg to 2.0 mg.

In an embodiment of the present invention, the reaction conditions of the aforementioned adsorption reaction include: a pH value of 2 to 6 and a reaction time of more than 96 hours.

In an embodiment of the present invention, the concentration of gold ions in the wastewater is 0.01 mg/liter to 10 mg/liter.

In an embodiment of the present invention, the above-mentioned thiourea graphene has an adsorption efficiency of 95% to 100% for gold ions.

In an embodiment of the present invention, when the wastewater further includes copper ions, lead ions, zinc ions, or a combination thereof, the adsorption efficiency of thiourea graphene for lead ions is 1% to 2%, and the adsorption efficiency for copper ions and zinc The adsorption efficiency of ions is 0%.

In an embodiment of the present invention, the above-mentioned saturated adsorption capacity of gold ions per gram of thiourea graphene is 833.33 mg.

In an embodiment of the present invention, the step of performing the desorption reaction on the thiourea graphene adsorbing gold ions includes: adding a desorbent to the thiourea graphene adsorbing gold ions, so that the gold ions are removed from the thiourea graphene Desorption on graphene.

In an embodiment of the present invention, the aforementioned gold ion desorption efficiency is 93% to 96%.

Based on the above, in the method for recovering gold using thiourea graphene provided by the present invention, the high selectivity of thiourea graphene for gold ions enables the use of thiourea graphene to adsorb gold ions in wastewater. It can have a lower adsorption limit, better adsorption efficiency and higher saturated adsorption capacity.

In order to make the above-mentioned features and advantages of the present invention more comprehensible, the following specific embodiments are described in detail in conjunction with the accompanying drawings.

FIG. 1 shows a flowchart of a method for recovering gold from thiourea graphene according to an embodiment of the present invention.

Please refer to FIG. 1 to perform step S110 to provide thiourea graphene. In this embodiment, for example, the following steps are used to prepare thiourea graphene, but it is not limited thereto. First, graphene oxide (GO) is mixed with ultrapure water to form a colloidal suspension of graphene oxide. Dissolve thiourea in ultrapure water to form a thiourea solution. Then, the thiourea solution was added to the colloidal suspension of graphene oxide, and stirred with a magnetic stir bar at 95° C. for 8 hours to form thiourea graphene (TU-rGO). Subsequently, the TU-rGO solution was washed with ultrapure water and filtered to obtain thiourea graphene solids. Finally, after drying the solid at 50° C. for 24 hours, the thiourea graphene solid was ground with an agate mortar. Then, pass through a 30-mesh sieve and a 60-mesh sieve in sequence to obtain thiourea graphene with a particle size between 0.25 mm and 0.59 mm.

Next, the elemental components and contents in graphene oxide and graphene thiourea were analyzed, and the results are shown in Table 1.

Table 1 C (%) O (%) H (%) N (%) S (%) GO 47.21±0.01 39.99±1.70 2.75±0.08 0.13±0.02 3.72±0.00 TU-rGO 60.38±1.22 10.00±0.08 1.05±0.10 2.01±0.22 22.87±0.34

From the results in Table 1, it can be seen that compared with graphene oxide, the nitrogen content and sulfur content of thiourea graphene increased to 2.01% and 22.87%, respectively, and the oxygen content decreased to 10.00%. It means that graphene thiourea increases the content of nitrogen and sulfur by replacing oxygen.

Next, from the X-ray diffraction analysis result of Fig. 2A, it can be seen that, compared to the diffraction peak position of graphene (2θ=26.5°) and the diffraction peak position of graphene oxide (2θ=26.5° or 10.5°), The diffraction peak position of thiourea graphene is 2θ = 23.05°.

From the analysis result of the scanning electron microscope in FIG. 2B, it can be seen that the surface of the graphene thiourea has a highly folded structure in a magnified view of 3000 times. From the analysis result of the transmission electron microscope in FIG. 2C, it can be seen that in the 60,000 times magnification, the thiourea graphene has a multilayer structure, and the measured specific surface area is 4.5 m ² /g.

Then, step S120 is performed to add thiourea graphene to the wastewater to perform an adsorption reaction. In this embodiment, the wastewater includes at least gold ions.

In the following, different examples will be used to discuss the reaction conditions for the adsorption reaction of thiourea graphene to gold ions in wastewater.

Example 1 ：The influence of reaction time on adsorption efficiency

In this embodiment, the reaction conditions are: graphene thiourea is 0.5 mg, the concentration of gold ions is 10 mg/liter, the reaction temperature is 30°C, the oscillation speed is 150 rpm, the pH value is 2, and the reaction volume is 50 ml. , And the reaction time is 12, 24, 48, 72, 96, 120 hours.

It can be seen from the result of Figure 3A that when the reaction time is 96 hours, the adsorption efficiency of thiourea graphene for gold ions is about 82.7±6.1%. When the reaction time is 120 hours, the adsorption efficiency of thiourea graphene for gold ions does not increase significantly. That is to say, when the reaction time is 96 hours, the adsorption kinetics of thiourea graphene to gold ions can reach an equilibrium, and can exhibit good adsorption efficiency.

It should be noted that in this embodiment, the adsorption efficiency is calculated according to Formula 1. Formula 1: Adsorption efficiency (%)=(C ₀ -C _t )/C ₀ ×100%, where C ₀ is the gold ion concentration before the adsorption reaction (mg/liter), and C _t is the gold ion concentration after the adsorption reaction (Mg/liter).

Example 2 :react pH Value pair adsorption The impact of efficiency

In this example, the reaction conditions are: graphene thiourea is 0.5 mg, the concentration of gold ions is 10 mg/liter, the reaction temperature is 30°C, the oscillation speed is 150 rpm, the reaction time is 96 hours, and the reaction volume is 50. Milliliters, and the pH values of the reaction were 2, 3, 4, 5, 6, 7, 8, 9, 10, respectively.

It can be seen from the results of Figure 3B that when the pH of the reaction is 2~5, the adsorption efficiency of thiourea graphene for gold ions is about 80~85%. When the pH of the reaction is 6, the adsorption efficiency of thiourea graphene for gold ions is about 40-50%. However, when the pH of the reaction exceeds 6, the adsorption efficiency of thiourea graphene for gold ions quickly drops below 20%. In other words, when the pH of the reaction is 2~5, thiourea graphene can exhibit good adsorption efficiency for gold ions.

Example 3 ：The influence of the dosage of thiourea graphene on the adsorption efficiency

In this embodiment, the reaction conditions are: the concentration of gold ions is 10 mg/liter, the reaction temperature is 30° C., the shaking speed is 150 rpm, the reaction time is 96 hours, the reaction volume is 50 ml, the pH is 5, and The dosage of thiourea graphene is 0.5, 1.0, 1.5, 2.0 mg, respectively.

It can be seen from the results of Figure 3C that when the dose of thiourea graphene is 0.5 mg, the adsorption efficiency of thiourea graphene for gold ions is about 82.7±6.1%. However, when the dose of thiourea graphene is 1.0, 1.5, or 2.0 mg, the adsorption efficiency of thiourea graphene for gold ions only slightly increases. In other words, when the dosage of thiourea graphene is 0.5 to 2.0 mg, it can show good adsorption efficiency for gold ions.

Then, step S130 is performed to separate the thiourea graphene adsorbing gold ions from the wastewater. In this embodiment, after the thiourea graphene adsorbs the gold ions in the wastewater, for example, it is filtered with a Syringe filter with a pore size of 0.45 microns, so that the reacted thiourea graphene cannot pass through. The pores further separate the thiourea graphene adsorbing gold ions from the wastewater after the reaction. Next, an inductively coupled plasma emission spectrometer (ICP-OES) is used to measure the gold ion concentration in the separated wastewater, which is used as the gold ion concentration after the reaction in Formula 1.

Finally, step S140 is performed to perform a desorption reaction on the thiourea graphene adsorbing gold ions to obtain gold ions. In this embodiment, for example, a desorbent is added to the thiourea graphene separated from the wastewater after the reaction and adsorbed with gold ions, so that the gold ions can be desorbed from the thiourea graphene. In this embodiment, the desorption agent is, for example, ammonium thiosulfate, but it is not limited to this.

In the following, different examples will be used to discuss the reaction conditions for the desorption reaction of thiourea graphene with gold ions adsorbed by ammonium thiosulfate.

Example 4 ：The influence of the concentration of ammonium thiosulfate solution on the desorption efficiency

In this embodiment, the concentration of the ammonium thiosulfate solution used is divided into three groups, A, B, and C, and each group performs two desorption reactions. First, each group adds 0.2M ammonium thiosulfate solution to 2.0 mg of thiourea graphene with gold ions adsorbed (the content of gold ions adsorbed per gram of thiourea graphene is 2500 mg) to perform the first Second desorption reaction. Then, after the first desorption reaction is completed, the three groups A, B, and C are respectively used for the second desorption reaction with 0.05, 0.1 or 0.2M ammonium thiosulfate solution. In addition, the first desorption reaction and the second desorption reaction are carried out according to the following reaction conditions: reaction temperature is 30°C, shaking speed is 150 rpm, reaction time is 24 hours, reaction volume is 50 ml, reaction pH The values are 7.4 respectively.

From the results in Figure 3D, it can be seen that the first desorption reaction can desorb most of the gold ions from the thiourea graphene, and the desorption efficiency is over 93%. In the second desorption reaction, 0.2M ammonium thiosulfate solution (group C) can increase the desorption efficiency by about 1.4%. In other words, the desorption reaction with ammonium thiosulfate solution can make the desorption efficiency of gold ions on the thiourea graphene be 93% to 96%.

It should be noted that in this embodiment, the desorption efficiency is calculated according to Formula 2. Formula 2: Desorption efficiency (%)=M _t /M ₀ ×100%, where M ₀ is the weight (mg) of gold ions on the thiourea graphene before the desorption reaction, and C _t is the weight after the desorption reaction The weight of gold ions in solution (mg).

It is worth noting that, in order to further understand the adsorption effect of thiourea graphene on gold ions, the experimental data of the above examples can be applied to the Langmuir adsorption equation to simulate the adsorption isotherm curve. The results are shown in Figure 4. Show. It can be seen from the simulation result of FIG. 4 that the correlation coefficient R ² of the adsorption isotherm curve is 0.91, and the saturated adsorption capacity of gold ions per gram of thiourea graphene is 833.33 mg.

Since the above adsorption experiments all take the gold ion concentration of 10 mg/liter as an example, the concentration of gold ions in the wastewater in the real environment may be lower than 10 mg/liter, and may also contain other metal ions, such as copper. Ion, lead ion, zinc ion, or a combination thereof. Therefore, in the following, different examples will be used to discuss the minimum adsorbable concentration of thiourea graphene for gold ions, and to discuss the selectivity of thiourea graphene for gold ions and other metal ions.

Example 5 ：Comparing graphene oxide and graphene thiourea, respectively, the adsorption efficiency of gold ion, copper ion, lead ion and zinc ion

In this embodiment, 2.0 mg of graphene oxide (or 2.0 mg of thiourea graphene) is used with gold ions (denoted as Au) at a concentration of 10 mg/liter and copper ions at a concentration of 20 mg/liter ( The adsorption reaction is carried out with lead ions with a concentration of 20 mg/liter (marked as Pb) and zinc ions with a concentration of 20 mg/liter (marked as Zn), and the reaction conditions are: reaction temperature of 30°C, The shaking speed is 150 rpm, the pH is 2, the reaction volume is 50 ml, and the reaction time is 96 hours.

From the result of Figure 5A, it can be seen that the adsorption efficiency of graphene oxide on gold ions is about 12%, the adsorption efficiency of thiourea graphene on gold ions is about 98%, and the adsorption efficiency of thiourea graphene on copper ions, lead ions and zinc ions None have adsorption efficiency. Therefore, compared with graphene oxide, graphene thiourea has a higher adsorption efficiency for gold ions. In addition, compared with copper ions, lead ions and zinc ions, thiourea graphene has high selectivity to gold ions.

Example 6 ：The selectivity of thiourea graphene to gold ion, copper ion, lead ion and zinc ion in wastewater

In this embodiment, the wastewater is divided into experimental example 1, experimental example 2, and experimental example 3 according to the composition and content of the wastewater. Among them, the wastewater of Experimental Example 1 includes gold ions with a concentration of 10 mg/liter, copper ions with a concentration of 20 mg/liter, lead ions with a concentration of 20 mg/liter, and zinc ions with a concentration of 20 mg/liter. The wastewater of Experimental Example 2 includes gold ions with a concentration of 1 mg/liter, copper ions with a concentration of 20 mg/liter, lead ions with a concentration of 20 mg/liter, and zinc ions with a concentration of 20 mg/liter. The wastewater of Experimental Example 3 includes gold ions with a concentration of 0.1 mg/liter, copper ions with a concentration of 20 mg/liter, lead ions with a concentration of 20 mg/liter, and zinc ions with a concentration of 20 mg/liter. The wastewater of Experimental Example 4 includes gold ions with a concentration of 0.01 mg/liter, copper ions with a concentration of 20 mg/liter, lead ions with a concentration of 20 mg/liter, and zinc ions with a concentration of 20 mg/liter. The reaction conditions of Experimental Example 1, Experimental Example 2, Experimental Example 3, and Experimental Example 4 are: thiourea graphene is 2.0 mg, the reaction temperature is 30°C, the oscillation speed is 150 rpm, the pH value is 2, and the reaction volume is 50 ml, the reaction time is 96 hours.

It can be seen from the result of FIG. 5B that in Experimental Example 1, the adsorption efficiency of thiourea graphene for gold ions is 98.3±0.8%, but it has no adsorption efficiency for copper ions, lead ions, and zinc ions. In Experimental Example 3, the adsorption efficiency of thiourea graphene for gold ions is 98.9±0.3%, and the adsorption efficiency for lead ions is about 1% to 2%, but it has no adsorption efficiency for copper ions and zinc ions. In Experimental Example 4, the adsorption efficiency of thiourea graphene for gold ions is 100%, but it has no adsorption efficiency for copper ions, lead ions, and zinc ions. Therefore, the lowest adsorbable concentration (lowest adsorption limit) of thiourea graphene for gold ions is 0.01 mg/L. In addition, when gold ions range from 0.01 mg/liter to 10 mg/liter, thiourea graphene has high selectivity for gold ions and an adsorption efficiency of over 98%.

Example 7 ：The influence of copper ion concentration in wastewater on the adsorption efficiency of thiourea graphene

In this embodiment, the wastewater is divided into experimental example 5, experimental example 6, experimental example 7, and experimental example 8 according to the composition and content of the wastewater. The wastewater of Experimental Example 5 includes gold ions with a concentration of 10 mg/liter, copper ions with a concentration of 100 mg/liter, lead ions with a concentration of 20 mg/liter, and zinc ions with a concentration of 20 mg/liter. The wastewater of Experimental Example 6 includes gold ions with a concentration of 1 mg/liter, copper ions with a concentration of 100 mg/liter, lead ions with a concentration of 20 mg/liter, and zinc ions with a concentration of 20 mg/liter. The wastewater of Experimental Example 7 includes gold ions with a concentration of 0.1 mg/liter, copper ions with a concentration of 100 mg/liter, lead ions with a concentration of 20 mg/liter, and zinc ions with a concentration of 20 mg/liter. The wastewater of Experimental Example 8 includes gold ions with a concentration of 0.01 mg/liter, copper ions with a concentration of 100 mg/liter, lead ions with a concentration of 20 mg/liter, and zinc ions with a concentration of 20 mg/liter. The reaction conditions of Experimental Example 5, Experimental Example 6, Experimental Example 7 and Experimental Example 8 are: thiourea graphene is 2.0 mg, the reaction temperature is 30°C, the oscillation speed is 150 rpm, the pH value is 2, and the reaction volume is 50 ml, the reaction time is 96 hours.

It can be seen from the results in Figure 5C that compared to Experimental Example 1 in Figure 5B, the adsorption efficiency of thiourea graphene for gold ions in Experimental Example 5 is slightly reduced to 95.4±0.5%, but for copper ions, lead ions, and zinc ions. It still does not have adsorption efficiency. In addition, compared with Experimental Example 3 in Figure 5B, the thiourea graphene in Experimental Example 7 has an adsorption efficiency of 98±1.5% for gold ions, and the adsorption efficiency for lead ions is still about 1% to 2%, but the Copper and zinc ions still have no adsorption efficiency. Compared with Experimental Example 4 in Figure 5B, the thiourea graphene in Experimental Example 8 has an adsorption efficiency of 100% for gold ions and an adsorption efficiency of about 5% for lead ions, but it still has no effect on copper and zinc ions. Adsorption efficiency. Therefore, even if the concentration of copper ions in wastewater is increased, graphene thiourea still has high selectivity for gold ions and an adsorption efficiency of 95% to 100%.

To sum up, in the method for recovering gold using thiourea graphene provided by the present invention, the high selectivity of thiourea graphene for gold ions makes it possible to use thiourea graphene for gold ions in wastewater. During the adsorption reaction, it can have a lower adsorption limit, better adsorption efficiency and higher saturated adsorption capacity.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field can make some changes and modifications without departing from the spirit and scope of the present invention. The scope of protection of the present invention shall be determined by the scope of the attached patent application.

S110, S120, S130, S140: steps

FIG. 1 shows a flowchart of a method for recovering gold from thiourea graphene according to an embodiment of the present invention. Figure 2A shows the analysis result of X-ray diffraction. Figure 2B shows the analysis result of the scanning electron microscope. Figure 2C shows the analysis result of a transmission electron microscope. Figure 3A shows the effect of different reaction times on the adsorption efficiency of thiourea graphene. Figure 3B shows the effect of different reaction pH values on the adsorption efficiency of thiourea graphene. Figure 3C shows the effect of different doses of thiourea graphene on its adsorption efficiency. Figure 3D shows the effect of different concentrations of ammonium thiosulfate solution on its desorption efficiency. Figure 4 shows the isothermal adsorption curve of thiourea graphene for gold ions. Figure 5A shows the adsorption efficiency of graphene oxide and graphene thiourea for gold ions, copper ions, lead ions, and zinc ions, respectively. Figure 5B shows the selectivity and lowest adsorption limit of thiourea graphene for gold ions, copper ions, lead ions and zinc ions in wastewater. Figure 5C shows the effect of copper ion concentration in wastewater on the adsorption efficiency of thiourea graphene.

S110, S120, S130, S140: steps

Claims (11)

A method of using thiourea graphene includes: providing a thiourea graphene, and the thiourea graphene has a particle size between 0.25 mm and 0.59 mm; adding the thiourea graphene to an aqueous solution to perform An adsorption reaction, wherein the aqueous solution includes at least one gold ion, and the thiourea graphene selectively adsorbs the gold ion, wherein the reaction conditions of the adsorption reaction include: a pH value of 2 to 6 and a minimum adsorption of the gold ion The limit is 0.01 mg/liter; the thiourea graphene adsorbing the gold ion is separated from the aqueous solution; and the thiourea graphene adsorbing the gold ion is subjected to a desorption reaction to obtain a solution containing the gold ion. According to the method for using graphene thiourea as described in item 1 of the scope of patent application, the nitrogen content of graphene thiourea is 2 to 4% by weight, and the sulfur content is 20 to 23% by weight. The method for using graphene thiourea as described in item 1 of the scope of the patent application, wherein the graphene thiourea is 0.5 mg to 2.0 mg. According to the method for using graphene thiourea as described in item 1 of the scope of patent application, the reaction conditions of the adsorption reaction further include: the reaction time is more than 96 hours. In the method for using graphene thiourea as described in item 1 of the patent application, the concentration of the gold ion in the aqueous solution is 0.01 mg/liter to 10 mg/liter. According to the method for using graphene thiourea as described in item 1 of the scope of patent application, the adsorption efficiency of graphene thiourea for gold ions is 95% to 100%. The method for using graphene thiourea as described in item 1 of the scope of patent application, wherein when the aqueous solution further includes copper ions, lead ions, zinc ions, or a combination thereof, the adsorption efficiency of the graphene thiourea for lead ions is 1% to 2%, and the adsorption efficiency of copper ions and zinc ions is 0%. The method for using graphene thiourea as described in item 1 of the scope of patent application, wherein the saturated adsorption capacity of the graphene thiourea for gold ions per gram is 833.33 mg. The method for using graphene thiourea as described in item 1 of the scope of the patent application, wherein the step of performing the desorption reaction on the graphene thiourea that adsorbs the gold ion includes: adding a desorbent to adsorb the gold ion In the thiourea graphene, the gold ions are desorbed from the thiourea graphene. According to the method for using graphene thiourea as described in item 9 of the scope of patent application, the desorption efficiency of the gold ion is 93% to 96%. A use of the method for using thiourea graphene as described in any one of the first to the tenth items of the scope of patent application, which is used to recover gold from wastewater.

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