Method for recovering valuable metals by roasting waste coffee grounds and metallurgical waste residues

Abstract

The invention discloses a method for recovering valuable metals by roasting waste coffee grounds and metallurgical waste residues, and relates to the crossing field of biofuel and environmental engineering, the metallurgical waste residues and the waste coffee grounds are respectively pretreated and then mixed according to a certain mass ratio to obtain a mixture, and then the mixture is roasted and cooled to obtain molten residues; and finally, the molten slag is subjected to magnetic separation, and valuable metal is obtained through recovery. According to the method, the valuable metal is recycled through collaborative roasting of the waste smelting slag and the waste coffee grounds in the metallurgical production industry, secondary recycling of the copper slag is achieved, and meanwhile the problems of open circuit at the tail end of the copper slag and organic pollution of the waste coffee grounds are solved. Rich organic matters in the waste coffee grounds are used as a utilization target, so that waste is turned into wealth, and a green low-carbon economic sustainable development road is opened up for treatment of the waste grounds and the waste coffee grounds in the metallurgical industry.

Description

Technical Field

[0001] The invention relates to the intersection of biofuel and environmental engineering, and in particular to a method for recovering valuable metals by roasting waste coffee grounds in coordination with metallurgical waste residues. Background Art

[0002] With the rapid development of the smelting industry, a large amount of metallurgical waste slag has been piled up, causing pollution and harm to the ecological environment such as soil and groundwater. Taking the metallurgical slag of the copper smelting production industry as an example, my country's copper production through pyrometallurgy accounts for more than 95%, and about 2-3 tons of copper slag are produced for every 1 ton of refined copper. For a long time, the disposal method of copper slag has mostly adopted open-air stacking, and the valuable metals in it are difficult to recover. The main elements in copper slag are iron, silicon, and oxygen. The content of Fe is much higher than the exploitable grade of iron ore in my country (TFe>27%). Most of the iron exists in the form of olivine, and a small amount of iron exists in the form of magnetic iron oxide. At present, the research on the recovery of valuable metal iron in smelting slag by reduction method mostly uses carbon-containing solid reducing agents such as anthracite, petroleum coke, and lignite. Reduction roasting technology using liquid reducing agents (rubber seed oil, gutter oil, diesel) and gas reducing agents (natural gas) has also been developed. The metallurgical industry's dependence on fossil fuels is the main cause of high carbon emissions. It is urgent to explore a new alternative biomass energy source in order to use alternative energy to fossil fuels to reduce pollution and limit the greenhouse effect, promote the sustainable development of the metallurgical industry, and achieve low-carbon or even carbon-neutral industrial goals.

[0003] With the rapid increase in the demand for coffee consumption, more and more coffee grounds are being discarded, causing environmental pollution and waste of resources. Waste coffee grounds, as a potential new type of biomass fuel, contain a large number of specific compounds (fatty acids, amino acids, polysaccharides, etc.), which can not only provide a higher calorific value than fossil reducing agent materials, but also produce a large amount of reducing gas produced by the cracking of organic matter at high temperature, which can further promote the reduction of high-valent metals in metallurgical slag and realize the high-value conversion of valuable metals in metallurgical slag.

[0004] Waste coffee grounds can effectively replace some carbon-containing materials as a roasting aid for metallurgical waste residues. While reducing carbon emissions and saving energy, it can effectively realize the transformation of the metallurgical industry from energy consumption control to carbon emission control, thereby generating substantial economic value and social benefits. So far, there has been no research report on the use of waste coffee grounds and metallurgical waste residues to roast and recover valuable metals. Summary of the invention

[0005] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art and to provide a method for recovering valuable metals by roasting waste coffee grounds in conjunction with metallurgical waste residues.

[0006] The technical solution of the present invention is as follows:

[0007] A method for recovering valuable metals by roasting waste coffee grounds in combination with metallurgical waste grounds. The metallurgical waste grounds and waste coffee grounds are pretreated separately, then mixed in a certain mass ratio to obtain a mixture. The mixture is then roasted and cooled to obtain molten slag. Finally, the molten slag is magnetically separated to recover the valuable metals.

[0008] As a preferred embodiment of the present invention, the mass ratio of the waste coffee grounds to the metallurgical waste residues is (1:2)-(3:1).

[0009] As a preferred embodiment of the present invention, the metallurgical waste slag contains the following components in percentage by mass: 25%-45% SiO2, 30%-60% Fe, Cu<2%, 3%-10% CaO, and the rest are aluminum, zinc, magnesium and other metal oxides.

[0010] As a preferred embodiment of the present invention, the waste coffee grounds include fatty acids, amino acids, polyphenols, minerals and polysaccharides.

[0011] As a preferred embodiment of the present invention, the pretreatment of the metallurgical waste slag is as follows: the metallurgical waste slag is crushed, ground, dried and sieved in sequence to obtain metallurgical waste slag powder with a mesh size of 100-300.

[0012] As a preferred embodiment of the present invention, the drying temperature is 80-120° C. and the drying time is 8-12 hours.

[0013] As a preferred embodiment of the present invention, the pretreatment of the waste coffee grounds is as follows: the coffee grounds are dried, ground, and sieved in sequence to obtain waste coffee grounds powder with a mesh size of 100-300.

[0014] As a preferred embodiment of the present invention, the drying method is treatment at 80-120° C. for 8-36 hours, or microwave heating.

[0015] As a preferred embodiment of the present invention, the calcination is carried out in an inert atmosphere, the calcination temperature is 500-1500° C., the heating rate is 5-20° C. / min, and the holding time is 0.5-4h.

[0016] As a preferred embodiment of the present invention, the cooling rate is 5-20°C / min.

[0017] The beneficial effects of the present invention are:

[0018] (1) The smelting slag obtained by the present invention can directly recover metallic iron and has high industrial utilization value.

[0019] (2) Compared with the prior art, the present invention does not need to use fossil energy as a reducing agent, but directly utilizes waste coffee grounds as a heat source and a carbon source, thereby reducing air pollution and achieving green and efficient recovery of iron in the slag.

[0020] (3) The main raw materials used in the present invention are industrial waste slag and waste coffee slag, which turn waste into treasure, and open up a sustainable development path of green and low-carbon concept for the utilization of secondary resources of metallurgical slag and the high-value conversion of waste coffee slag. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a process flow chart of the method of the present invention;

[0022] Figure 2 This is a comparison diagram of XRD before and after roasting of copper slag in Example 1 of the present invention;

[0023] Figure 3 The XRD comparison diagram of the copper slag before and after roasting of Example 1 of the present invention and Comparative Example 1;

[0024] Figure 4 This is a sample diagram after calcination treatment of the present invention. DETAILED DESCRIPTION

[0025] The present invention provides a method for utilizing biomass solid waste of waste coffee grounds and coordinating roasting of metallurgical waste slag to realize secondary resources of valuable metals, thereby turning waste into treasure and expanding the resource utilization of waste coffee grounds and metallurgical slag.

[0026] To achieve the above object, the present invention provides a method for recovering valuable metals by roasting waste coffee grounds in combination with metallurgical waste residues. Figure 1 : After pretreatment, waste coffee grounds and metallurgical waste slag are mixed according to a certain mass percentage, placed in a heating device with programmable temperature control, and roasted under certain temperature conditions. After the reaction is completed, the mixture is taken out and cooled to finally obtain smelting slag. The obtained molten slag can be used to recover valuable metal iron by magnetic separation and other methods.

[0027] Specifically, the metallurgical waste slag takes the copper smelting production industry as an example. The raw materials come from the copper smelting smelting slow cooling process. The main components are SiO2 accounting for 25%-45%, Fe accounting for 30%-60%, Cu<2%, CaO accounting for 3%-10%, and the rest are small amounts of aluminum, zinc, magnesium and other oxides.

[0028] Specifically, the waste coffee grounds are solid wastes generated in the process of producing coffee products, and the main components are organic compounds such as fatty acids, amino acids, polyphenols, minerals and polysaccharides.

[0029] In some other embodiments, the metallurgical waste slag pretreatment method is crushing, grinding, drying (80-120°C drying pretreatment for 8-12h), and sieving (the sieving mesh is 100-300 mesh); further, the drying conditions are preferably dried at 105°C for 8h; the sieving mesh is preferably 200 mesh.

[0030] In some other embodiments, the waste coffee grounds are pretreated by drying (pre-treatment at 80-120°C for 8-36 hours or microwave heating), grinding, and sieving (screening mesh is 100-300 mesh). The drying condition is preferably 105°C for 15 hours; the sieving mesh is preferably 100 mesh.

[0031] The method described is as follows: the mass ratio of the waste coffee grounds and the metallurgical waste grounds is (1:2)-(3:1).

[0032] The method described is as follows: the reaction is carried out in air and / or an inert atmosphere, preferably an inert gas atmosphere. The calcination temperature is 500-1500°C, preferably 1050°C. The heating rate is 5-20°C / min, preferably 10°C / min. The heat preservation time is 0.5h-4h, preferably 1.5h.

[0033] In a preferred embodiment, the heating device capable of programmable temperature control is a heating temperature controllable device of the type of a tubular furnace, a muffle furnace, etc.

[0034] In a preferred embodiment, the cooling method is a programmed cooling method with a cooling rate of 5-20°C / min.

[0035] Waste coffee grounds are selected in the present invention mainly because waste coffee grounds are a fuel with more combustible components (lignin, cellulose, mannan, chlorogenic acid, etc.) and high calorific value (18.0-27MJ / kg) compared to other organic carbon sources. During the combustion and pyrolysis process, heat energy cuts the chemical bonds of biomass macromolecules, and the organic compounds therein are converted into low-molecular liquid bio-oil, combustible gas (hydrogen, methane, carbon monoxide mixed gas) and fixed carbon. The synergistic composite action of multiple components breaks the matrix structure of metallurgical waste slag and reduces high-valent metals to low-valent metals for recovery.

[0036] The components in waste coffee grounds mainly play the following roles:

[0037] (1) The fatty acid composition is C 16 -C 22 The main component is hexadecanoic acid (C 16 ), followed by 9,12-octadienoic acid (C 18：2 ), n-octadecanoic acid (C 18 ) and oleic acid (C 18：1 The most common fatty acid in biodiesel is C 16 and C 18 ; It may be the main source of high calorific value contribution.

[0038] (2) Amino acids are pyrolyzed under high temperature conditions, and the carboxyl and amino molecules inside react to form a series of gaseous products including ammonia, formaldehyde, etc., which contribute part of the reducing atmosphere.

[0039] (3) Polyphenols are natural green organic compounds with reducing properties that can promote catalytic reactions.

[0040] (4) The mineral components contain potassium, calcium, magnesium, iron, aluminum and other substances, and the valuable metal components can be recovered during the roasting and reduction process.

[0041] (5) Cellulose is a typical representative of the polysaccharide components in waste coffee grounds. The high-temperature pyrolysis of cellulose produces volatile gas hydrogen that participates in the reduction reaction.

[0042] Therefore, compared with chemical fuels such as anthracite, petroleum coke, lignite and other carbon-containing solid reducing agents, waste coffee grounds are a potential biomass resource. The carbon dioxide released by its combustion is absorbed during the growth process. Therefore, after combustion, it will not increase the carbon dioxide content in the atmosphere, has lower carbon emissions, and is more environmentally friendly. The carbon dioxide released by the combustion of traditional fossil fuels is organic matter buried underground for a long time. Its combustion will lead to a large amount of carbon emissions and is one of the main sources of greenhouse gases.

[0043] Secondly, the content of other pollutants released during the combustion of waste coffee grounds is relatively low, and has little impact on air quality. The combustion of traditional fossil fuels will release a large amount of harmful gases such as sulfur oxides and nitrogen oxides, which have a greater impact on the environment and human health.

[0044] Finally, the utilization of waste coffee grounds can reduce the processing pressure and soil absorption pressure of coffee grounds, help resource circulation and environmental protection, is more in line with the concept of sustainable development and environmental protection, and has more advantages than traditional fossil fuels.

[0045] The present invention is further described in detail below in conjunction with specific embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. The following examples and comparisons use smelting copper slag from a copper smelter in Hubei and waste coffee grounds from a chain coffee shop as raw materials, and their chemical compositions are shown in Tables 1 and 2:

[0046] Table 1 Chemical composition of copper smelting slag

[0047]

[0048] Table 2 Composition of waste coffee grounds

[0049]

[0050] Example 1

[0051] The spent coffee grounds were dried (baked at 105°C for 15h), ground until there were no more agglomerated particles, and passed through a 100-mesh sieve. The copper smelting slag was crushed, dried (baked at 105°C for 8h), and ground through a 200-mesh sieve. The two materials (waste coffee grounds: copper smelting slag) were mixed in a mass ratio of 2:1, placed in a ceramic crucible, and the ceramic crucible was placed in a tubular furnace and fired in an argon atmosphere. The heating rate was maintained at 10°C / min to 1050°C, and a high-temperature solid-phase reaction was carried out at this temperature for 60 minutes. After the reaction was completed, it was cooled and ground, and the resulting product was iron powder, reference Figure 4 , the recovery rate of iron in copper slag is 93%.

[0052] Example 2

[0053] The waste coffee grounds were dried (baked at 105°C for 15h), ground until there were no more agglomerated particles, and passed through a 100-mesh sieve. The copper smelting slag was crushed, dried (baked at 105°C for 8h), and ground through a 200-mesh sieve. The two materials (waste coffee grounds: copper smelting slag) were mixed in a mass ratio of 2:1, placed in a ceramic crucible, and the ceramic crucible was placed in a tubular furnace for firing in an argon atmosphere, maintaining a heating rate of 10°C / min to 1050°C, and a high-temperature solid-phase reaction was carried out at this temperature for 90 minutes. After the reaction was completed, it was cooled and ground, and the resulting product was iron powder, and the recovery rate of iron in the copper slag was 97%.

[0054] Example 3

[0055] The waste coffee grounds were dried (baked at 105°C for 15h), ground until there were no more agglomerated particles, and passed through a 100-mesh sieve. The copper smelting slag was crushed, dried (baked at 105°C for 8h), and ground through a 200-mesh sieve. The two materials (waste coffee grounds: copper smelting slag) were mixed in a mass ratio of 3:1, placed in a ceramic crucible, and the ceramic crucible was placed in a tubular furnace and fired in an argon atmosphere, maintaining a heating rate of 5°C / min to 900°C, and a high-temperature solid-phase reaction was carried out at this temperature for 90 minutes. After the reaction was completed, it was cooled and ground, and the resulting product was iron powder, and the recovery rate of iron in the copper slag was 93%.

[0056] Example 4

[0057] The waste coffee grounds were dried (baked at 105°C for 15 hours), ground until there were no more agglomerated particles, and passed through a 100-mesh sieve. The copper smelting slag was crushed, dried (baked at 105°C for 8 hours), and ground through a 200-mesh sieve. The two materials (waste coffee grounds: copper smelting slag) were mixed at a mass ratio of 2.5:1, placed in a ceramic crucible, and the ceramic crucible was placed in a tubular furnace for firing in an argon atmosphere, maintaining a heating rate of 10°C / min to 1000°C, and a high-temperature solid-phase reaction was carried out at this temperature for 120 minutes. After the reaction was completed, it was cooled and ground, and the resulting product was iron powder, and the recovery rate of iron in the copper slag was 92%.

[0058] Example 5

[0059] The waste coffee grounds were dried (baked at 105°C for 15h), ground until there were no more agglomerated particles, and passed through a 100-mesh sieve. The copper smelting slag was crushed, dried (baked at 105°C for 8h), and ground through a 200-mesh sieve. The two materials (waste coffee grounds: copper smelting slag) were mixed at a mass ratio of 1.5:2, placed in a ceramic crucible, and the ceramic crucible was placed in a tubular furnace for firing in an argon atmosphere, maintaining a heating rate of 5°C / min to 1050°C, and a high-temperature solid-phase reaction was carried out at this temperature for 120min. After the reaction was completed, it was cooled and ground, and the resulting product was iron powder, and the recovery rate of iron in the copper slag was 90%.

[0060] Comparative Example 1

[0061] Carbon powder and copper smelting slag (crushed, baked at 105°C for 8h, ground through a 200-mesh sieve) were mixed in a mass ratio of 2:1, placed in a ceramic crucible, and the ceramic crucible was placed in a tube furnace in an argon atmosphere for firing, maintaining a heating rate of 10°C / min to 1050°C, and a high-temperature solid-phase reaction was carried out at this temperature for 60min. After the reaction was completed, the mixture was cooled and ground, and the obtained product was iron powder. Graphite powder was used as a roasting aid, and the recovery rate of iron in the slag was 57%, which was greatly reduced compared with Example 1.

[0062] Comparative Example 2

[0063] The starch was mixed with copper smelting slag (crushed, baked at 105°C for 8h, and ground through a 200-mesh sieve) in a mass ratio of 2.5:1, placed in a ceramic crucible, and the ceramic crucible was placed in a tubular furnace for firing in an argon atmosphere, maintaining a heating rate of 10°C / min to 1000°C, and a high-temperature solid-phase reaction was carried out at this temperature for 120min. After the reaction was completed, the mixture was cooled and ground, and the resulting product was iron powder. Starch was used as a roasting aid, and the recovery rate of iron in the slag was 45%, which was greatly reduced compared with Example 4.

[0064] X-ray diffraction analysis was performed on Example 1 and Example 1 and Comparative Example 1, and the results are shown in Figure 2 and Figure 3 It can be seen that the embodiment adds waste coffee grounds as a reducing agent for roasting, which can achieve a higher efficiency of reducing metals. The purity of the reduced metal is related to the matrix structure composition of the metallurgical slag and the subsequent magnetic separation treatment or other treatment processes. Therefore, the main advantages of roasting coffee grounds are considered here as follows: on the one hand, under the same conditions of adding reducing agents, its high reduction efficiency (the degree of metal reduction before and after roasting); on the other hand, coffee grounds, as waste, solve the problem of handling waste coffee grounds. At the same time, waste coffee grounds are not purchased as materials, which effectively replaces carbon-containing materials as reducing agents, reducing carbon emissions and saving enterprise process operation costs.

[0065] The above-mentioned embodiments only express the preferred implementation modes of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, various other corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all these changes and deformations should fall within the scope of protection of the claims of the present invention.

Claims

1. A method for recovering valuable metals by roasting waste coffee grounds in combination with metallurgical waste residues, characterized in that: The metallurgical waste residue and the waste coffee residue are pretreated separately, and then mixed in a certain mass ratio to obtain a mixture. The mixture is then roasted and cooled to obtain molten slag. Finally, the molten slag is magnetically separated to recover valuable metals.

2. The method for recovering valuable metals by roasting waste coffee grounds in combination with metallurgical waste residues according to claim 1, characterized in that: The mass ratio of the waste coffee grounds to the metallurgical waste grounds is (1:2)-(3:1).

3. The method for recovering valuable metals by roasting waste coffee grounds in combination with metallurgical waste residues according to claim 1, characterized in that: The metallurgical waste slag contains the following components in percentage by mass: 25%-45% SiO2, 30%-60% Fe, Cu<2%, 3%-10% CaO, and the rest are aluminum, zinc, magnesium and other metal oxides.

4. The method for recovering valuable metals by roasting waste coffee grounds in combination with metallurgical waste residues according to claim 1, characterized in that: The spent coffee grounds include fatty acids, amino acids, polyphenols, minerals and polysaccharides.

5. The method for recovering valuable metals by roasting waste coffee grounds in combination with metallurgical waste residues according to claim 1, characterized in that: The pretreatment of the metallurgical waste slag is as follows: the metallurgical waste slag is crushed, ground, dried and sieved in sequence to obtain metallurgical waste slag powder with a mesh size of 100-300.

6. The method for recovering valuable metals by roasting waste coffee grounds in combination with metallurgical waste residues according to claim 5, characterized in that: The drying temperature is 80-120° C., and the drying time is 8-12 hours.

7. The method for recovering valuable metals by roasting waste coffee grounds in combination with metallurgical waste residues according to claim 1, characterized in that: The pretreatment of the waste coffee grounds is as follows: the coffee grounds are dried, ground, and sieved in sequence to obtain 100-300 mesh waste coffee grounds powder.

8. The method for recovering valuable metals by roasting waste coffee grounds in combination with metallurgical waste residues according to claim 7, characterized in that: The drying method is to treat at 80-120° C. for 8-36 hours, or to heat with microwave.

9. The method for recovering valuable metals by roasting waste coffee grounds in combination with metallurgical waste residues according to claim 1, characterized in that: The calcination is carried out in an inert atmosphere, the calcination temperature is 500-1500° C., the heating rate is 5-20° C. / min, and the holding time is 0.5-4h.

10. The method for recovering valuable metals by roasting waste coffee grounds in combination with metallurgical waste residues according to claim 1, characterized in that: The cooling rate is 5-20°C / min.

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