A method for enriching and extracting gallium from alumina seed liquor by utilizing discarded persimmons without waste

Abstract

The present invention discloses a method for enriching and extracting gallium from alumina mother liquor by utilizing discarded persimmons without waste, comprising the following steps: cutting the discarded persimmons into small pieces and mixing them with a urea solution, adding them to a high-pressure hydrothermal reactor for hydrothermal carbonization reaction, and separating the solid and liquid to obtain solid hydrothermal charcoal and a hydrothermal solution; freeze-drying the obtained hydrothermal charcoal and mixing it with zinc chloride in proportion, and pyrolyzing to obtain porous carbon aerogel and pyrolysis gas; passing the obtained pyrolysis gas into the alumina mother liquor, and adding the porous carbon aerogel to the neutralized alumina mother liquor for gallium enrichment and extraction. The present invention uses discarded persimmons as raw materials, obtains porous carbon aerogel adsorption materials through hydrothermal carbonization-pyrolysis two-stage surface modification treatment, realizes the enrichment and extraction of gallium in the alumina mother liquor through the high specific surface area and rich adsorption sites of the adsorbent, and all the wastewater and waste gas generated during the preparation of the adsorbent material are recycled, which has the characteristics of being green, efficient and pollution-free.

Description

Technical Field

[0001] The invention relates to a method for resource utilization of solid waste, and in particular to a method for enriching and extracting gallium from alumina seed denominator liquid by utilizing discarded persimmons without waste. Background Art

[0002] my country is the origin of persimmons, with an annual output of 1.8 million tons, accounting for about 70% of the world's total output. Most of the persimmons in my country are astringent. Because of their astringent taste, the content of persimmon tannins in them is very high, accounting for about 2% of the fresh weight of persimmons. Persimmon tannins, also known as plant polyphenols, are a natural high-molecular compound with abundant resources, low price and easy access. They are widely distributed in plants and are mainly complex polyphenols with catechol and pyrogallol groups. Their molecular structures have a large number of phenolic hydroxyl groups, large relative molecular mass and wide distribution, which give tannins unique physiological activity and chemical properties, and can react with a variety of metal ions by complexation and electrostatic action. Therefore, they are widely favored in the extraction of target metal ions from mixed metal solutions.

[0003] Persimmon tannin has a certain effect on the enrichment and extraction of strategic metal gallium, but its adsorption capacity for gallium is not high enough and cannot meet people's requirements. Therefore, many scientific researchers have improved its adsorption capacity by chemically modifying persimmon tannin. Studies have reported that adsorbents with both =NOH and another active group, such as =NH, -NH2, -SH or -OH, have a strong affinity for gallium; at the same time, a higher specific surface area can not only increase the mass transfer rate of the adsorption process, but also increase its surface active sites and improve the adsorption capacity. Therefore, enriching the nitrogen-containing groups on the adsorbent surface and increasing the specific surface area are effective means to enhance the enrichment and extraction of gallium by tannin-based adsorbents. Summary of the invention

[0004] The purpose of the present invention is to provide a method for enriching and extracting gallium from alumina seed liquor by utilizing discarded persimmons without waste, so as to realize the value-added utilization of discarded persimmons and improve the adsorption capacity of the gallium enrichment and extraction process.

[0005] To achieve the above object, the present invention adopts the following technical solution: a method for enriching and extracting gallium from alumina seed liquor by utilizing discarded persimmons without waste, comprising the following steps:

[0006] 1) Wash the discarded persimmons and cut them into small pieces;

[0007] 2) Mix the persimmon pieces with the urea solution at a ratio of 1 g persimmon pieces to 0.1 mol urea, then add the mixture into a high-pressure hydrothermal reactor, heat the mixture to 180-260° C., keep the temperature for 2-6 hours, and cool the mixture naturally to room temperature to obtain a hydrothermal reaction product;

[0008] 3) performing solid-liquid separation on the hydrothermal reaction product obtained in step 2) to obtain hydrothermal charcoal and a hydrothermal solution;

[0009] 4) freeze-drying the hydrothermal charcoal obtained in step 3) to obtain persimmon aerogel, and the hydrothermal solution containing urea is an organic fertilizer required by plants;

[0010] 5) mixing the persimmon aerogel obtained in step 4) with zinc chloride in a mass ratio of 1:1-1:4, and then placing it in a tubular furnace for pyrolysis to obtain pyrolysis gas and porous carbon aerogel respectively;

[0011] 6) introducing the pyrolysis gas obtained in step 5) into the alumina mother liquor for neutralization;

[0012] 7) The porous carbon aerogel obtained in step 5) is added to the neutralized alumina mother liquor in step 6) for adsorption to enrich and extract gallium.

[0013] Preferably, the urea solutions of different concentrations in step 2) are 1 mol / L, the purpose of which is to modify the persimmon tannin on the surface of persimmon to increase the nitrogen-containing groups on the surface of the aerogel.

[0014] Preferably, the freeze-drying temperature in step 4) is -30°C and the time is 24 hours.

[0015] Preferably, the pyrolysis conditions in step 5) are: temperature 700-950°C, insulation 30-90min, heating rate 5-15°C / min.

[0016] Preferably, the porous carbon aerogel in step 7) is added in an amount of 1-2 g / L of alumina mother liquor after neutralization, and the enrichment and extraction effect of gallium is best when the addition amount is 1.5 g / L.

[0017] Preferably, the step of enriching and extracting gallium in step 7) is oscillating adsorption, and the adsorption time is not less than 6 hours.

[0018] The present invention proposes to use discarded persimmon as a material, and to design a low-cost porous carbon aerogel adsorption material by surface modification through the secondary coupling of hydrothermal carbonization-pyrolysis; and the gas, liquid and solid products generated in the synthesis process of the porous carbon aerogel are all utilized as resources, and the obtained porous carbon aerogel can achieve efficient enrichment of gallium in the mixed solution. Within the research scope of the present invention, the adsorption capacity of the porous carbon aerogel obtained by this method for gallium in the alumina mother liquor can reach 190mg / g.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention uses discarded persimmon as raw material, and obtains an adsorbent through hydrothermal carbonization-pyrolysis coupling modification. The rich nitrogen-containing groups and large specific surface area on the surface of the adsorbent realize efficient extraction of gallium from alumina seed liquor.

[0021] 2. The waste water and waste gas generated during the synthesis of the porous carbon aerogel of the present invention can all be recycled. The hydrothermal solution contains abundant organic matter, especially CHON elements. The organic matter such as reducing sugars, acetic acid and furfural contained therein can provide nutrients for plant growth. The acidic gases such as CO2 in the pyrolysis gas can significantly reduce the strong alkalinity of the alumina mother liquor, which is not only beneficial to protect the structure of the porous carbon aerogel, but also beneficial to the enrichment and extraction of gallium in the mixed solution.

[0022] 3. The present invention is simple to operate, low in cost, and has significant extraction and enrichment effects. It not only realizes the value-added utilization of discarded persimmons, but is also easy to apply on a large scale in industry, and has good economic and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flow chart of the present invention.

[0024] Figure 2 This is a physical picture of the appearance of the porous carbon aerogel synthesized in Example 1 of the present invention.

[0025] Figure 3 This is a SEM image of the porous carbon aerogel synthesized in Example 1 of the present invention.

[0026] Figure 4 This is a N2 adsorption-desorption diagram of the porous carbon aerogel synthesized in Example 1 of the present invention.

[0027] Figure 5 The neutralization performance of persimmon aerogel and ZnCl2 pyrolysis gas on alumina mother liquor.

[0028] Figure 6 The adsorption effect of gallium in the neutralized alumina mother liquor at different porous carbon aerogel dosages.

[0029] Figure 7 This is the SEM image of the surface of porous carbon aerogel after adsorption when the dosage is 1.5 g / L.

[0030] Figure 8 This is the EDS graph of the surface of porous carbon aerogel after adsorption when the dosage is 1.5 g / L.

[0031] Fig. 9 The adsorption effect of porous carbon aerogel on gallium in neutralized alumina mother liquor at different adsorption times. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Example 1: Preparation of porous carbon aerogel

[0034] 1) Wash the discarded persimmons with deionized water and cut them into small pieces of about 3 cm in size;

[0035] 2) adding 10 g of the wet persimmon pieces obtained in step 1) into a high-pressure hydrothermal reactor containing 100 mL of 1 mol / L urea solution, then heating the high-pressure hydrothermal reactor to 220° C., keeping the temperature for 6 h, and naturally cooling to room temperature to obtain a hydrothermal reaction product;

[0036] 3) The hydrothermal reaction product obtained in step 2) is subjected to solid-liquid separation to obtain hydrothermal charcoal and a hydrothermal solution.

[0037] 4) placing the hydrothermal carbon obtained in step 3) into a low-temperature refrigerator and pre-freezing it at -20°C for 12 hours, and then placing the hydrothermal carbon frozen into a hard block into a freeze dryer and freeze-drying it at -30°C for 24 hours to obtain persimmon aerogel;

[0038] 5) The persimmon aerogel obtained in step 4) is mixed with ZnCl2 in a mass ratio of 1:3, and then placed in a tubular furnace for pyrolysis at a heating rate of 5°C / min and a temperature of 800°C for 60 minutes to obtain pyrolysis gas and porous carbon aerogel. ZnCl2 is a pore-forming agent, and the purpose of mixing the persimmon aerogel and ZnCl2 for pyrolysis is to increase the specific surface area of ​​the aerogel.

[0039] Figure 2 and Figure 3 The appearance and SEM images of the porous carbon aerogel are shown respectively. It can be seen from the figure that the synthesized porous carbon aerogel has the characteristics of low density and light weight; at the same time, it has a loose sponge-like structure and porous structure inside. Figure 4 The N2 adsorption-desorption results of porous carbon aerogels show that the specific surface area of ​​the synthesized porous carbon aerogels is 1648.91m 2 / g, and has a relatively high specific surface area.

[0040] Example 2: Neutralization performance of pyrolysis gas on strong alkalinity of alumina mother liquor

[0041] The pyrolysis gas generated during the pyrolysis of the persimmon aerogel and ZnCl2 mixture in Example 1 was introduced into 20 mL of strongly alkaline alumina mother liquor. Figure 4 The pH change of the strongly alkaline alumina mother liquor during pyrolysis. Figure 5It can be seen that the pyrolysis gas (acidic gases such as CO2) produced by the pyrolysis process of persimmon aerogel and ZnCl2 can significantly reduce the strong alkalinity of the alumina mother liquor, and the pH value of the solution after neutralization is significantly reduced to about 11.

[0042] Example 3: Composition analysis of hydrothermal solution after hydrothermal carbonization of discarded persimmons

[0043] The hydrothermal solution obtained in step 3) of Example 1 was analyzed for organic matter, and the results showed that the contents of reducing sugar, acetic acid, furfural and 5-hydroxymethylfurfural in the hydrothermal solution were 10.340 g / L, 2.271 g / L, 0.303 g / L and 0.156 g / L, respectively. This shows that the hydrothermal solution contains rich organic components such as reducing sugars, which can provide organic nutrients for plant growth.

[0044] Example 4: Adsorption performance of porous carbon aerogel at different dosages on the alumina mother solution in Example 2

[0045] 1) The porous carbon aerogel synthesized in Example 1 was added into 20 mL of the alumina mother solution of Example 2 with a pH of 11 and an initial gallium concentration of 160 mg / L at a solid-liquid ratio of 0.25 g / L, 0.5 g / L, 1 g / L, 1.5 g / L and 2 g / L respectively;

[0046] 2) placing the mixed solution obtained in step 1) in a constant temperature water bath oscillator, adsorbing and oscillating at a speed of 300 r / min for 24 hours, and then filtering;

[0047] 3) The filtrate obtained in step 2) is measured by ICP-MS.

[0048] Figure 6 The adsorption effect of different porous carbon aerogel dosages on gallium in the neutralized alumina mother liquor is shown in Figure 2. Figure 6 It can be seen that porous carbon aerogel can achieve high-capacity adsorption of alumina mother solution, and with the increase of the dosage of porous carbon aerogel, the adsorption capacity of gallium shows a trend of first increasing and then stabilizing. When the dosage to solution ratio is 1.5g / L, the maximum adsorption capacity of porous carbon aerogel for gallium is 190mg / g.

[0049] Figure 7 , Figure 8 Table 1 and Table 2 are respectively the SEM-EDS images of the surface of the porous carbon aerogel after adsorption and the proportion table of each element when the dosage is 1.5 g / L, which further illustrates that the porous carbon aerogel can achieve efficient adsorption of gallium in the alumina mother liquor.

[0050] Table 1 Composition of elements after adsorption on porous carbon aerogel

[0051]

[0052]

[0053] Example 5: Adsorption performance of porous carbon aerogel for alumina mother solution in Example 2 at different adsorption times

[0054] 1) The porous carbon aerogel synthesized in Example 1 was added to 20 mL of the alumina mother solution of Example 2 with a pH of 11 and an initial gallium concentration of 160 mg / L at a solid-liquid ratio of 1.5 g / L;

[0055] 2) placing the mixed solution obtained in step 1) in a constant temperature water bath oscillator, adsorbing and oscillating at a oscillation speed of 300 r / min for 5 min, 10 min, 20 min, 30 min, 40 min, 1 h, 2 h, 4 h, 6 h and 24 h, and filtering;

[0056] 3) The filtrate obtained in step 2) is measured by ICP-MS.

[0057] Fig. 9 The adsorption effect of porous carbon aerogel on gallium in neutralized alumina mother liquor at different adsorption times. Fig. 9 It can be seen that with the increase of adsorption time, the adsorption capacity of porous carbon aerogel for gallium in alumina mother liquor gradually increases. When the adsorption time is 6h, the adsorption capacity of porous carbon aerogel basically reaches equilibrium.

[0058] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for enriching and extracting gallium from alumina seed liquor by utilizing discarded persimmons without waste, characterized in that: The steps include: 1) Wash the discarded persimmons and cut them into small pieces; 2) Mix the persimmon pieces with the urea solution at a ratio of 1 g persimmon pieces to 0.1 mol urea, then add the mixture into a high-pressure hydrothermal reactor, heat the mixture to 180-260° C., keep the temperature for 2-6 hours, and cool the mixture naturally to room temperature to obtain a hydrothermal reaction product; 3) performing solid-liquid separation on the hydrothermal reaction product obtained in step 2) to obtain hydrothermal charcoal and a hydrothermal solution; 4) freeze-drying the hydrothermal charcoal obtained in step 3) to obtain persimmon aerogel, and the hydrothermal solution containing urea is an organic fertilizer required by plants; 5) mixing the persimmon aerogel obtained in step 4) with zinc chloride in a mass ratio of 1:1-1:4, and then placing it in a tubular furnace for pyrolysis to obtain pyrolysis gas and porous carbon aerogel respectively; 6) introducing the pyrolysis gas obtained in step 5) into the alumina mother liquor for neutralization; 7) The porous carbon aerogel obtained in step 5) is added to the neutralized alumina mother liquor in step 6) for adsorption to enrich and extract gallium.

2. The method for enriching and extracting gallium from alumina seed liquor by utilizing discarded persimmons without waste according to claim 1, characterized in that: The concentration of the urea solution in step 2) is 1 mol / L.

3. The method for enriching and extracting gallium from alumina seed liquor by utilizing discarded persimmons without waste according to claim 1, characterized in that: The freeze-drying temperature in step 4) is -30°C and the time is 24 hours.

4. The method for enriching and extracting gallium from alumina seed liquor by utilizing discarded persimmons without waste according to claim 1, characterized in that: The pyrolysis conditions described in step 5) are: temperature 700-950° C., insulation 30-90 min, and heating rate 5-15° C. / min.

5. The method for enriching and extracting gallium from alumina seed liquor by utilizing discarded persimmons without waste according to claim 1, characterized in that: The amount of the porous carbon aerogel added in step 7) after neutralization of the alumina mother liquor is 1-2 g / L.

6. The method for enriching and extracting gallium from alumina seed liquor by utilizing discarded persimmons without waste according to claim 5, characterized in that: The dosage of the alumina mother liquor after neutralization of the porous carbon aerogel is 1.5 g / L.

7. The method for enriching and extracting gallium from alumina seed liquor by utilizing discarded persimmons without waste according to claim 1, characterized in that: The step of enriching and extracting gallium in step 7) is oscillating adsorption, and the adsorption time is not less than 6 hours.

Images