Method for synthesis of copper sulfides covellite and digenite

Abstract

The method for the mechanochemical synthesis of copper sulfides of covellite and digenite is carried out by mechanically induced self-propagating reaction (MSR) without the use of grinding balls. The steel grinding chamber is filled with copper and sulfur particles to at least 40% of the chamber volume, the stoichiometric ratio of the dosed copper and sulfur is in the range from 0.6:1 to 1:1 and the reaction mixture is ground at the milling speed at least 800 revolutions per minute. During the grinding process, the temperature of the reaction mixture is monitored using a temperature sensor, the MSR mechanism of the process is automatically started after 70 to 95 seconds from the start of grinding, when the temperature in the chamber increases by at least 150°C for 1 to 2 seconds. Subsequently, the grinding process is terminated.

Description

[0001] Method for the Synthesis of Copper Sulfides Covellite and Digenite

[0002] Field of Technology

[0003] The subject of the patent application is a method for preparing copper sulfides, specifically covellite CuS and digenite 19S5 using intensive mixing in the grinding chamber of a planetary mill without the use of grinding balls.

[0004] State of the Art

[0005] By using planetary milling with grinding balls, it is possible to prepare compounds of several metals and sulfur by simply grinding powders of metal elements and elemental sulfur using mechanical energy (so-called mechanochemical synthesis). This process has been investigated many times in the past. In general, metal reactions with sulfur can occur gradually, or through the so-called mechanically induced self-propagating reaction (MSR), when after a certain time of grinding powders of elements with the help of grinding balls, during which there is no significant conversion to the product, a phase of instant product formation follows, which is accompanied by a sudden increase in temperature and pressure. The MSR process is well known for various metal-sulfur systems (e.g. Zn-S, Cd-S, or Pb-S), but for the Cu-S system the MSR reaction was observed for the first time in the work: Balaz, M.; Zorkovska, A.; Urakaev, F.; Balaz, P.; Briancin, J.; Bujnakova, Z.; Achimovicova, M.; Gock, E., Ultrafast mechanochemical synthesis of copper sulfides. RSC Adv. 2016, 6 (91), 87836-87842. In the above work, copper from four different manufacturers and sulfur from two different manufacturers were investigated and the MSR method was used to prepare covellite CuS and chalcocite CU2S. It was found that if the particles of the reacting copper are small enough and have a specific morphology (needle-shaped), this reaction takes place within a few seconds. In the following work Balaz, M.; Augustyniak, A.; Tatykayev, B.; Shalabayev, Z.; Burashev, G.; Dutkova, E.; Daneu, N.; Briancin, J.; Balazova, E.; Stahorsky, M.; Achimovicova, M.; Balaz, P., Mechanochemical synthesis of non-stoichiometric copper sulfide Cui.sS applicable as photocatalyst and antibacterial agent and synthesis scalability verification. Faraday Discuss. 2023, 241, 367-386 another copper sulfide, namely digenite Cu9S5, was also synthesized using the above method. Various ratios of copper and sulfur were investigated, resulting in either pure digenite or its composite with covellite CuS or chalcocite Cu2S.

[0006] Summary of the Invention

[0007] The summary of the invention consists in a method for producing copper sulfides by mechanically induced self-propagating reaction (hereinafter referred to as MSR), namely covellite CuS and digenite Cu9S5, by means of intensive mixing of powders of copper and sulfur elements in the grinding chamber of a planetary mill. The novelty of this method compared to the methods according to the prior art lies primarily in the fact that the method according to the invention proceeds without the use of grinding balls. Only copper and sulfur powders are put into the grinding chamber and, by intensive mixing, which ensures good contact between the reagents, an effective reaction occurs under certain conditions. Copper sulfides can also be produced by a stepwise, i.e. gradual reaction, but in this case, after grinding for 10 minutes, the product contains a significant amount of starting materials. The transformation of the resulting product occurs only after its storage for several months, which is disadvantageous from a technological point of view. Therefore, it is more advantageous to prepare the product using MSR. The present research has found that the MSR mechanism of the process only occurs when:

[0008] - mixing in the grinding chamber must be sufficiently intensive, i.e. the planetary mill speed must be at least 800 rpm (revolutions per minute), when using balls even 300 rpm is sufficient;

[0009] - the grinding chamber must be filled sufficiently - at least 40 vol. %; in the case of a lower filling of the grinding chamber, the MSR process does not occur and a gradual reaction takes place, which results in the fact that mostly unreacted copper remains on the walls of the grinding chamber and sulfur powder condenses in the center of the container (in the MSR reaction, any unreacted sulfur partially passes into a gaseous state); the process also successfully takes place at a filling level of 48 vol. %; when using balls, the chamber is usually filled with copper and sulfur at around 3 vol. % and the ground material together with the grinding balls represents a filling of the grinding chamber at around 30 vol. %;

[0010] - the stoichiometric ratio between the dosed copper and sulfur must be between 0.6: 1 and 1 : 1, when using balls the reaction can be observed between the Cu:S ratios 2: 1 and 1 : 1;

[0011] - the reacting copper particles must have a mean particle size below 30 pm and must have a specific morphology (needle-like).

[0012] Mixing of reagents in the grinding chamber is carried out at the specified milling speed for 60 to 120 seconds. Increasing the milling speed results in an acceleration of the process (see examples below). During the grinding process, the temperature in the grinding chamber is continuously monitored and the grinding process is terminated either after 10 minutes (gradual reaction) or with a sudden increase in the temperature in the grinding chamber (MSR). If a sudden increase in temperature of at least 150 °C occurs within one or two seconds, then MSR has occurred and the process must be terminated immediately. Therefore, the issue of correct control of the termination of the process is very important for a positive result of the process.

[0013] The fact that with a higher filling of the grinding chamber with copper and sulfur reagents and the fulfillment of the above conditions, MSR can be achieved even without the use of grinding balls significantly simplifies the potential preparation technology and prevents unwanted abrasion. This results in a significant increase in the efficiency of this process compared to the process using grinding balls, which are costly. In addition, after the reaction in the presence of balls, the balls need to be separated from the product and cleaned before further use, which requires additional operations and costs.

[0014] Overview of figures in the drawings

[0015] The following figures illustrate the process of mechanochemical synthesis of copper sulfides

[0016] - covellite and digenite under various process conditions described in the following examples.

[0017] The figures show:

[0018] Fig. la: Temperature dependence on grinding time of a mixture of Cu:S in a stoichiometric ratio of 1 : 1 at a milling speed of 800 rpm and a chamber filling of 40% vol., the grinding time was 95 seconds. Fig. lb: X-ray diffraction pattern of the reaction product, with all unlabeled diffraction peaks corresponding to covellite, CuS (C) and those marked as (D) belong to digenite, Cu9S5.

[0019] Fig. 2: Temperature dependence of grinding time of a mixture of Cu:S in a stoichiometric ratio of 1 : 1 at a milling speed of 800 rpm and a chamber filling of 20% vol.; the grinding time was 10 minutes.

[0020] Fig. 3: Temperature dependence on grinding time of a Cu:S mixture in a stoichiometric ratio of 1 : 1 at a milling speed of 800 rpm and a chamber filling of 28% vol.; grinding time was 10 minutes.

[0021] Fig. 4: Temperature dependence on grinding time of a Cu:S mixture in a stoichiometric ratio of 1 : 1 at a milling speed of 800 rpm and a chamber filling of 32% vol.; grinding time was 10 minutes.

[0022] Fig. 5: Temperature dependence on grinding time of a Cu:S mixture in a stoichiometric ratio of 1 : 1 at a milling speed of 800 rpm and a chamber filling of 36% vol.; grinding time was 10 minutes.

[0023] Fig. 6a: Temperature dependence on grinding time of a Cu:S mixture in a stoichiometric ratio of 1 : 1 at a milling speed of 800 rpm and a chamber filling of 48% vol.; grinding time was 95 seconds.

[0024] Fig. 6b: X-ray diffraction pattern of the product (all unmarked diffraction peaks correspond to covellite, CuS (C), those marked as (D) belong to digenite Cu9S5.

[0025] Fig. 7: Temperature dependence on grinding time of a Cu:S mixture in a stoichiometric ratio of 1 : 1 at a milling speed of 700 rpm and a chamber filling of 40% vol.; grinding time was 10 minutes (temperature changes were only detected within 3 minutes due to a sensor failure).

[0026] Fig. 8: Temperature dependence on grinding time of a Cu:S mixture in a stoichiometric ratio of 1 : 1 at a milling speed of 750 rpm and a chamber filling of 40% vol.; the grinding time was 15 minutes (temperature changes were only detected within 3 minutes due to a sensor failure).

[0027] Fig. 9a: Temperature dependence on grinding time of a Cu:S mixture in a stoichiometric ratio of 1 : 1 at a milling speed of 850 rpm and a chamber filling of 40% vol.; the grinding time was 70 seconds.

[0028] Fig. 9b: X-ray diffraction pattern of the product (all unlabeled diffraction peaks correspond to covellite, CuS (C), those marked as (D) correspond to digenite Cu9Ss).

[0029] Fig. 10: Temperature dependence on grinding time of a Cu:S mixture in a stoichiometric ratio of 1.125: 1 at a milling speed of 800 rpm and a chamber filling of 39.69% vol.; grinding time was 10 minutes.

[0030] Fig. I la: Temperature dependence on grinding time of a Cu:S mixture in a stoichiometric ratio of 0.75: 1 at a milling speed of 800 rpm and a chamber filling of 40.31% vol.; grinding time was 90 seconds.

[0031] Fig. 11b: X-ray diffraction pattern of the product (all unlabeled diffraction peaks correspond to covellite, CuS (C), those marked as (D) correspond to digenite Cu9Ss and those marked as (S) belong to elemental sulfur). Fig. 12a: Temperature dependence on grinding time of a Cu:S mixture in a stoichiometric ratio of 0.625: 1 at a speed of 800 rpm and a chamber filling of 40.63% vol.; grinding time was 90 seconds.

[0032] Fig. 12b X-ray diffraction pattern of the product (all unlabeled diffraction peaks correspond to covellite, CuS (C), those marked as (D) correspond to digenite Cu9S5).

[0033] Fig. 13: Temperature dependence on grinding time of a Cu:S mixture in a stoichiometric ratio of 0.5: 1 at a speed of 800 rpm and a chamber filling of 41.25% vol.; the grinding time was 10 minutes.

[0034] Examples of the Invention Embodiments

[0035] In order to identify the parameters necessary for the successful implementation of the process, several experiments were carried out, which are summarized in Table 1 and the details are given in the description of the individual examples below. Both examples with the successful achievement of the MSR mechanism of the process (examples 1, 6, 9, 11, 12), and also examples with the achievement of only the gradual mechanism of the process, which were part of the research to determine the conditions for the desired MSR mechanism of the process, are given. The process was carried out in a steel grinding chamber with a volume of 20 mL.

[0036] Table 1: Table of examples

[0037] Example 1

[0038] The example was carried out at a milling speed of 800 rpm with a total weight of 10 g and a stoichiometric ratio of Cu:S of 1 :1 in a steel grinding chamber with a volume of 20 mL. 6.6463 g of electrolytically prepared copper and 3.3537 g of sulfur were put into the grinding chamber, which corresponds to the weight of CuS, i.e. a stoichiometric ratio of Cu:S of 1 : 1. Before starting the grinding process, the copper and sulfur powders were mixed in a plastic cup until large clusters of sulfur particles were not visible to the naked eye. After filling, the grinding chamber was closed with a lid and placed in a Pulverisette 7 premium line planetary ball mill. The mixture was then ground for 95 seconds at a milling speed of 800 rpm, while the temperature inside the grinding chamber was monitored using a temperature sensor. After recording an immediate significant increase in temperature by 226 °C (i.e. more than the threshold of 150 °C after 91 seconds) proving the course of MSR (see the course of temperature over time in Fig. la), the grinding was stopped as quickly as possible manually and the chamber was opened (according to the values in the table, the time shift from the end of the MSR process to the stop of grinding was 3-5 seconds). The resulting blue powdery product was agglomerated into several larger pebble-like particles that could be easily crushed again into a fine powder. There was a slight smoke coming from the grinding chamber. The composition of the resulting product after the MSR reaction was determined by X-ray diffraction analysis, the X-ray pattern of the product is shown in Fig. lb, with all unmarked diffraction peaks corresponding to covellite CuS (C) and those marked as (D) belonging to digenite 19S5. Given that at a stoichiometric ratio of input Cu:S 1 : 1, the output product contains 19S5 in addition to CuS, a small amount of unreacted sulfur vapors escaped - after the reaction, there was a slight smoke coming out from the grinding chamber.

[0039] Example 2

[0040] In this example, the total weight was reduced to 5 g, i.e. the chamber filling was also reduced by half (20% vol.) and the stoichiometric ratio Cu:S and the milling speed was identical to those in example 1. During grinding for 10 min, no MSR occurred (see the temperature-time dependence in Fig. 2).

[0041] Example 3

[0042] In this example, the total weight was increased to 7 g, i.e. the chamber filling was increased to 28% and the stoichiometric ratio Cu:S and the milling speed was identical to those in example 1. No MSR occurred, the powder in the chamber was heated to approximately 40 °C and no further heating occurred (Fig. 3).

[0043] Example 4

[0044] In this example, we increased the total weight to 8 g, and thus the chamber filling increased to 32% vol. and the stoichiometric ratio of Cu:S and the milling speed was identical to those in example 1. MSR did not occur, but significant heating during grinding did (Fig. 4). During the 4 to 8 minutes of grinding, the temperature was kept at approximately 40°C as observed in the previous example, then there was a significant increase, which continued until the end of grinding and in the last two minutes the temperature increased by 40°C. However, MSR did not occur, since an immediate increase in temperature was not observed as in example 1.

[0045] Example 5

[0046] In this example, we increased the total weight to 9 g, and thus the chamber filling increased to 36% vol. and the stoichiometric ratio Cu:S and the milling speed was identical to those in example 1. MSR did not occur, but significant heating did occur (Fig. 5). After about 2.5 minutes of grinding, particles with a temperature of about 70°C were present. During subsequent grinding, the reaction mixture gradually cooled.

[0047] Example 6 In this example, the weight was increased to 12 g and the total filling of the chamber volume to 48% vol. The milling speed was 800 rpm. From the temperature monitoring graph (Fig. 6a) it can be seen that after 90 seconds a very intense MSR occurred and after recording two points at very high temperatures the sensor was destroyed (it subsequently shows the value of absolute zero). X-ray diffraction analysis (Fig. 6b) showed the absence of reactants Cu and S and the main product is digenite CU9S5, with an admixture of covellite CuS. Given the composition of the product, residual sulfur should also be present, but this evaporated during MSR due to the sudden increase in pressure and temperature.

[0048] Example 7

[0049] In this example, identical experimental conditions were used as in Example 1, except that the milling speed was reduced to 700 rpm. As can be seen from Fig. 7, no MSR was observed within 3 minutes and the temperature continued to increase more or less linearly. Milling was then continued for 10 minutes.

[0050] Example 8

[0051] In this example, the milling speed was increased to 750 rpm, the other conditions remained the same as in example 1. This increase led to a faster increase in temperature resembling an exponential function (Fig. 8). MSR was not observed within 3 minutes and the temperature continued to increase more or less linearly. Grinding was then continued for 15 minutes.

[0052] Example 9

[0053] In example 9, the milling speed was increased compared to example 1 to 850 rpm. The result was MSR after 70 seconds (Fig. 9a), i.e. about 15 seconds earlier than in example 1 at the milling speed of 800 rpm. Grinding was stopped as soon as possible. Subsequent X-ray diffraction analysis showed the main product to be digenite CU9S5 with an admixture of covellite CuS (Fig. 9b). Given the composition of the product, residual sulfur should also be present, but this has evaporated during MSR due to the sudden increase in pressure and temperature. Thus, increasing the number of revolutions results in an acceleration of the MSR process.

[0054] Example 10

[0055] In Example 10, identical conditions were used as in Example 1, but the stoichiometry was changed, i.e. the molar ratio between the reacting copper and sulfur was 1.125: 1. The minimum difference was also in the volume % filling of the chamber (Table 1). Grinding this mixture did not lead to MSR, as after 5 minutes a maximum temperature of 47°C was reached, which then slowly decreased (Fig. 10).

[0056] Example 11

[0057] In Example 11, a stoichiometric ratio of Cu:S of 0.75: 1 was used, the other conditions were identical to Example 1. The minimum difference was also in the volume % filling of the chamber (Table 1). MSR was observed after 86 seconds (Fig. I la). The temperature increase was so sharp that the temperature sensor was subsequently disabled. X-ray diffraction analysis confirmed the main product to be covellite, with a small amount of unreacted sulfur and a small amount of digenite (Fig. 1 lb).

[0058] Example 12 In this example, a stoichiometric ratio of Cu:S of 0.625: 1 was used, otherwise everything was identical to example 1. The minimum difference was also in the volume % of chamber filling (Table 1). MSR occurred after 90 seconds, but due to the high intensity of MSR, the sensor was destroyed, which could not capture the sharp increase in temperature, but immediately began to show absolute zero (Fig. 12a). X-ray diffraction analysis confirmed pure CuS copper with a small amount of digenite Cu9S5(D) in the product (Fig. 12b).

[0059] Example 13

[0060] In this example, unlike example 1, a stoichiometric ratio of Cu:S of 0.5: 1 was used and the volume of chamber filling was 41.25 vol.%. MSR did not occur during 10 min of grinding, after reaching a temperature of 40 °C, no further increase was observed (Fig. 13).

[0061] Conclusions from the above examples of implementation

[0062] The evaluation of the examples of implementation shows that if the process is carried out by the MSR mechanism, this phase of the process is always started automatically within two minutes from the start of grinding and this time interval is approximately between 70 and 95 seconds, while it is shortened when the milling speed is increased. In the examples where a sudden increase in temperature to a higher value is achieved at the onset of MSR (examples 6 and 9), digenite is formed as the main product due to the volatilization of part of the elemental sulfur as a result of the sudden increase in temperature and pressure. The composition of the product after MSR is influenced by the initial stoichiometric ratio between Cu and S, namely with an excess of sulfur, covellite, CuS, is formed as the main product, because there is enough sulfur despite its partial volatilization during the MSR phase of the process.

[0063] The examples also show cases where the MSR mechanism of the process is not started, when the grinding process is usually stopped after 10 minutes. In these examples, during the gradual change in temperature, i.e. during the gradual process, it was also shown that although copper sulfides are also formed, the majority of Cu and S do not react and remain unreacted in the chamber after completion, so the process is incomparably more disadvantageous than in the case of the MSR mechanism and obviously unsuitable when considering its use in practice. The implementation of these examples was necessary to determine the conditions necessary for achieving the MSR mechanism of the process. As we can see from the examples, it is necessary to comply with all conditions simultaneously, because even if one of the conditions for the MSR mechanism (milling speed, vol.% chamber filling, stoichiometric ratio of copper and sulfur) is not met, the process will proceed gradually.

[0064] Industrial applicability

[0065] By mechanochemical processing of metallic copper with sulfur according to the invention, it is possible to prepare copper sulfides, namely CuS (covellite) and CU9S5 (digenite) in various ratios, depending on the experimental conditions used. The compounds have a wide range of applications, e.g. in photocatalysis, thermoelectric materials, solar cells, in water splitting reactions to obtain hydrogen, as diagnostic agents in the fight against cancer, as antibacterial agents, etc.

Claims

ClaimsA method for synthesizing copper sulfides covellite and digenite by mechanically induced self-propagating reaction, characterized in that the steel grinding chamber is filled with copper and sulfur particles to at least 40% of the chamber volume, the stoichiometric ratio of the dosed copper and sulfur is in the range of 0.6: 1 to 1 : 1, the reaction mixture is ground at the milling speed at least 800 revolutions per minute, the temperature of the reaction mixture is monitored during the grinding process using a temperature sensor and the grinding process is terminated after a spontaneous sharp increase in temperature by at least 150°C for 1 to 2 seconds, the grinding process being terminated after 70 to 95 seconds from the start of grinding.

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