CN109821274B - Method for removing heavy metals in water-soluble tea extract by using amino modified silica gel material - Google Patents
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Abstract
The invention discloses a method for removing heavy metals in a water-soluble tea extract by using an amino modified silica gel material. The method for removing heavy metals in the water-soluble tea extract by using the amino modified silica gel material can quickly and continuously remove heavy metals such as lead, copper, cadmium, chromium and the like in the water-soluble tea extract, and the adsorption column has small adsorbability on the water-soluble tea extract, so that the loss of the water-soluble tea extract is small, the removal rate of the heavy metals such as lead, copper, cadmium, chromium and the like is more than 95%, and the loss rate of the water-soluble tea extract is less than 5%; in addition, the adsorption column prepared by the invention can be repeatedly used after the adsorbed heavy metals are eluted and removed by EDTA salt solution, so that the adsorption column can be well applied to the tea deep processing technology and has wide application prospect.
Description
Technical Field
The invention belongs to the technical field of food green processing, and relates to a method for removing heavy metals in a tea extract, in particular to a method for removing heavy metals in a water-soluble tea extract by using an amino modified silica gel material.
Background
Heavy metals are a class of pollutants that are not biodegradable, are easily absorbed and enriched by organisms, and have high toxicity to organisms. Industrial wastewater generated in industrial activities such as chemical manufacturing, mining, metallurgy and the like contains a large amount of heavy metals, and causes serious pollution to soil and crops, such as the excessive cadmium content in rice, the enrichment of lead, cadmium and zinc in corn, the excessive nickel, chromium, copper and lead in soybean, and the residual of heavy metals such as lead, arsenic, cadmium, copper, chromium, nickel and the like in tea. Heavy metal pollution not only causes a great deal of economic loss, but also poses great threat to human health.
The water-soluble tea extract such as tea polyphenol, theanine, tea polysaccharide and the like is a main deep-processing product of tea, and has physiological effects of resisting oxidation, reducing blood sugar, reducing blood fat and the like, so the water-soluble tea extract has higher nutritional value and wide market prospect. But heavy metal pollution can be generated in the tea planting, processing and storing processes. At present, the technology for removing heavy metals from wastewater is mature, and mainly comprises precipitation, filtration, ion exchange, reverse osmosis, adsorption, etc. (Fu F., Wang Q. removal of latent metals from water: a review [ J ]. J Environ manager, 2011,92(3):407 cake 418.); among them, adsorption technology is receiving much attention because of its advantages of flexible operation, low energy consumption, high selectivity, low cost, reversible regeneration of adsorbent (Hua M., Zhang S., Pan B., et al, heavy metal removal from water/water by nano oxides: a review [ J ] Hazard Mater,2012, 211. acetone 212:317-331.Paulino A.T., Belfiore L.A., Kubota L.T., et al. Effect of magnetic on the adsorption catalyst of Pb (II), Cd (II), and Cu (II) in a chemical-based hydrates [ J ] depletion, 2011,275(1-3): 187).
Along with the increasing serious pollution of soil, water source and ecological environment, the pollution of heavy metals in food is also impossible to prevent, so that the removal of the heavy metals in the food on the premise of not damaging the original components of the food becomes a hot topic. Zou[4]The studies by et al show that citric acid does not significantly affect the gamma-oryzanol content, tocopherol content and fatty acid composition in rice while significantly reducing the cadmium content in rice bran (zuo y., Zhang c., Ju x., et alal and microstructure properties of rice bran[J].Food Control, 2019,98:290-296.)。Shen[5]The research of the people shows that the P123-DA hydrogel can effectively remove Pb in milk2+And Hg2+While not destroying the nutrients of milk (Shen C., Peng B., Wang Y., et al. Pb (2+) and Hg) ((2+) removal from polluted milk by di-acrylated Pluronic P123hydrogels[J]Food Chem 2018,258: 331-. At present, methods for removing heavy metals in tea soup and instant tea exist, and patent CN106900923A discloses a method for reducing heavy metals in instant tea, which is to put all adsorption materials in a solution, stir for 1-7 days to adsorb heavy metals, and then filter the adsorption materials by using filter cloth to remove the rest. Therefore, the prior art has the defects of long treatment time and incapability of continuously recycling the treated solution. In addition, patent CN104642614A discloses a method for reducing the content of heavy metal ions such as arsenic, lead and the like in instant tea, the patent adopts a macroporous adsorption resin column to remove heavy metals in the instant tea, and the method in the prior art can realize that the content of the heavy metals in the instant tea is reduced by 50 percent, and the content of tea polyphenol is reduced by less than 5 percent.
Disclosure of Invention
The technical problem to be solved is as follows: in order to overcome the defects of the prior art and obtain a method which can efficiently remove heavy metals in a tea extract aqueous solution, has small tea polyphenol loss and can repeatedly use an adsorption column, the invention provides a method for removing heavy metals in a water-soluble tea extract by using an amino modified silica gel material.
The technical scheme is as follows: a method for removing heavy metals in a water-soluble tea extract by using an amino modified silica gel material, which comprises the following steps:
step 1, preparing an aqueous solution of tea extract
Preparing tea extractive solution or water soluble tea extract into 1-60wt% water solution, adjusting pH to 3-7, filtering with 0.45 μm filter membrane to remove insoluble solid, and collecting filtrate;
step 2, preparing amino modified silica gel adsorption column
Putting 1-10g of 50-600 mesh silica gel and 10-100mL of anhydrous toluene in a three-necked flask, magnetically stirring at 50-500rpm under the protection of nitrogen, dropwise adding 1-20mL of 3-Aminopropyltriethoxysilane (APTS), heating and refluxing the mixture at 50-150 ℃ for 4-36h, filtering to obtain a final solid product, washing with toluene, acetone, diethyl ether and methanol in sequence, and drying at 50-120 ℃ for 2-24h to obtain amino modified silica gel;
adding 100-1000mg of the modified silica gel into 1-5mL of ultrapure water, uniformly mixing, filling into an SPE small column containing a lower sieve plate, pressing into an upper sieve plate after all the silica gel is filled, and preparing to obtain an amino modified silica gel adsorption column;
step 3, passing through the column
Passing the filtrate prepared in the step 1 through an amino modified silica gel adsorption column with an upper sieve plate and a lower sieve plate prepared in the step 2, adjusting the flow rate to keep the flow rate at the column volume for 1-90min, controlling the temperature of the adsorption column at 25-50 ℃, eluting the tea extract remained in the adsorption column by adopting ethanol solution with the volume fraction of 50-100% and the volume of 1-10 times of the column volume, collecting the column liquid and the eluent, concentrating and drying, wherein the loss rate of the water-soluble tea extract is less than 5%, and the removal rate of heavy metals is more than 95%;
step 4, recycling
Passing the adsorption column with heavy metal in step 3 through 0.01-1M EDTA salt solution 1-20 times the column volume, controlling the flow rate to pass through the column liquid for 5-50min, eluting more than 95% of the heavy metal in the adsorption column, and recycling the adsorption column.
Preferably, the tea extract comprises an extract of leaves of a plant of Camellia genus, or tea polyphenols, theanine, tea polysaccharides, theaflavins.
Preferably, the weight percentage of the tea extract or the water-soluble tea extract aqueous solution in the step 1 is 40 wt%.
Preferably, the pH of the tea extract or the aqueous solution of water-soluble tea extract in the step 1 is 4.
Preferably, the column is packed by a wet method in the step 2.
Preferably, the column flow rate in step 3 is 10 mL/min.
Preferably, the volume fraction of the ethanol solution in step 3 is 80%.
Preferably, the EDTA salt in step 4 is disodium EDTA, dipotassium EDTA, tetrasodium EDTA, tetrapotassium EDTA, or other water-soluble compounds containing the EDTA structure.
Preferably, the concentration of EDTA salt in step 4 is 0.02M.
Preferably, the adsorption column can be recycled for 6 times, and the adsorption rate of the heavy metal reaches more than 96%.
The working principle of the method for removing heavy metals in the water-soluble tea extract by using the amino modified silica gel material is as follows: APTS compound with amino group is grafted on the surface of silica gel through chemical modification, so that ionic bond or coordination bond combination is formed between the APTS compound and heavy metal, and no adsorption effect is generated on tea polyphenol, therefore, the APTS compound has good capability of removing heavy metal. In addition, the amino modified silica gel column adsorbed with the heavy metal is eluted by an eluant EDTA salt solution, and the EDTA salt solution enables the heavy metal in the adsorption column to be eluted through the characteristic of heavy metal chelation, so that the adsorption column can be reused and has good repeatability.
Has the advantages that: the method for removing heavy metals in the water-soluble tea extract by using the amino modified silica gel material can quickly and continuously remove heavy metals such as lead, copper, cadmium, chromium and the like in the water-soluble tea extract, and the adsorption column has small adsorbability on the water-soluble tea extract, so that the loss of the water-soluble tea extract is small, the removal rate of the heavy metals such as lead, copper, cadmium, chromium and the like is more than 95%, and the loss rate of the water-soluble tea extract is less than 5%; in addition, the adsorption column prepared by the invention can be repeatedly used after the adsorbed heavy metals are eluted and removed by EDTA salt solution, so that the adsorption column can be well applied to the tea deep processing technology and has wide application prospect.
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FIG. 1 is a technical simulation of the method of the present invention.
Detailed Description
The following examples further illustrate the present invention but are not to be construed as limiting the invention. Modifications and substitutions to methods, procedures, or conditions of the invention may be made without departing from the spirit and substance of the invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art.
Example 1 removal of heavy metals from aqueous tea Polyphenol solution
The embodiment provides a method for removing heavy metals from a tea polyphenol aqueous solution, which is divided into 4 steps in total and comprises preparation and pretreatment of the tea polyphenol aqueous solution, preparation of a silica gel column, column chromatography adsorption and reuse of an adsorption column. The specific operation method comprises the following steps:
1) the preparation and pretreatment of the tea polyphenol aqueous solution are that 200g of tea polyphenol solid and 500mL of ultrapure water solution are weighed to prepare into 40% tea polyphenol solution, the pH value of the solution is adjusted to 4, and then the solution is filtered by 0.45 mu m for standby.
2) The preparation of the silica gel column is specifically that 10g of amino functional silica gel and 20mL of ultrapure water are uniformly stirred and then are filled into the column (rule 2X 20cm) by a wet method, and the volume of the column is about 90 mL.
3) Pumping the tea polyphenol water solution obtained in the step 1) into the amino-functional silica gel adsorption column prepared in the step 2) through a peristaltic pump, adjusting the flow rate to be 10mL/min, eluting the tea polyphenol remained in the adsorption column by 90mL 80% ethanol after 500mL of tea polyphenol solution is adsorbed, combining adsorption solutions, concentrating and drying. The content of heavy metals in the adsorbed tea polyphenol is detected, and the results are shown in the following table:
| heavy metals | Detection result/ppb |
| Pb | <1 |
| Cu | <5 |
| Cd | <1 |
| Cr | Not detected |
The removal rate of lead, copper, cadmium and chromium is more than 98 percent, and the loss of tea polyphenol is less than 2 percent.
4) Eluting the adsorption column in the step 3) by using 100mL of 0.02M EDTA disodium solution, combining the eluates, detecting heavy metals, and detecting the detection result to show that 98% of the heavy metals adsorbed in the adsorption column are eluted by the eluates.
5) The tea polyphenol water solution in the step 1) is circularly adsorbed for 6 times, and the adsorption rate of the tea polyphenol water solution on heavy metals such as lead, copper, cadmium, chromium and the like is still over 96 percent.
Example 2 removal of heavy metals from aqueous theanine solution
The embodiment provides a method for removing heavy metals in a theanine aqueous solution, which comprises the following specific operations:
1) the preparation and pretreatment of the theanine aqueous solution are that 50g of theanine solid and 500mL of ultrapure water solution are weighed to prepare 10% theanine solution, the pH of the solution is adjusted to 5.5, and then the solution is filtered by 0.45 mu m for standby.
2) The preparation of the silica gel column is specifically that 5g of amino functional silica gel and 10mL of ultrapure water are uniformly stirred and then are filled into the column (rule 2X 20cm) by a wet method, and the volume of the column is about 45 mL.
3) Pumping the theanine aqueous solution obtained in the step 1) into the amino-functional silica gel adsorption column prepared in the step 2) through a peristaltic pump, adjusting the flow rate to be 10mL/min, eluting the theanine remained in the adsorption column by using 150mL of 50% ethanol after 500mL of theanine solution is adsorbed, combining the adsorption solutions, concentrating, and detecting the content of theanine and heavy metal, wherein the removal rate of lead, copper, cadmium and chromium is more than 97%, and the loss of theanine is less than 3%.
4) Eluting the adsorption column in the step 3) by adopting 50mL of 0.1M EDTA disodium solution, combining the eluates, detecting heavy metals, and detecting the detection result to show that 95% of the heavy metals adsorbed in the adsorption column are eluted by the eluates.
5) After the theanine aqueous solution in the step 1) is circularly adsorbed for 6 times, the adsorption rate of the theanine aqueous solution on heavy metals of lead, copper, cadmium and chromium still reaches more than 97.5 percent.
EXAMPLE 3 removal of heavy metals from instant tea
The invention also provides a method for removing heavy metals in the tea water extract, which comprises the following specific operations:
1) the preparation and pretreatment of the instant tea water solution are that 300g of instant tea powder and 500mL of ultrapure water solution are weighed to prepare 60 percent instant tea solution, the pH value of the solution is adjusted to 5, and then the solution is filtered by 0.45 mu m for standby.
2) The preparation of the silica gel column is specifically that 5g of amino functional silica gel and 10mL of ultrapure water are uniformly stirred and then are filled into the column (rule 2X 20cm) by a wet method, and the volume of the column is about 45 mL.
3) And then pumping the instant tea water solution obtained in the step 1) into the amino functional silica gel adsorption column prepared in the step 2) through a peristaltic pump, adjusting the flow rate to be 10mL/min, eluting tea polyphenol remained in the adsorption column by using 150mL of 50% ethanol after 500mL of instant tea solution is adsorbed, combining adsorption solutions, concentrating and drying. The content of the instant tea and the heavy metal is detected, and the result shows that the removal rate of lead, copper, cadmium and chromium is more than 97 percent, and the loss of the instant tea is less than 5 percent.
4) Eluting the adsorption column in the step 3) by using 10mL of 0.05M EDTA disodium solution, combining the eluates, detecting heavy metals, and detecting the detection result to show that 95% of the heavy metals adsorbed in the adsorption column are eluted by the eluates.
5) After the instant tea aqueous solution in the step 1) is circularly adsorbed for 6 times, the adsorption rate of the instant tea aqueous solution on heavy metals of lead, copper, cadmium and chromium still reaches more than 95 percent.
Claims (8)
1. The method for removing heavy metals in the water-soluble tea extract by using the amino modified silica gel material is characterized by comprising the following steps of:
step 1, preparing an aqueous solution of tea extract
Preparing tea extractive solution or water soluble tea extract into 1-60wt% water solution, adjusting pH to 3-7, filtering with 0.45 μm filter membrane to remove insoluble solid, and collecting filtrate;
step 2, preparing amino modified silica gel adsorption column
Putting 1-10g of 50-600 mesh silica gel and 10-100mL of anhydrous toluene in a three-necked flask, magnetically stirring at 50-500rpm under the protection of nitrogen, dropwise adding 1-20mL of 3-aminopropyltriethoxysilane, heating and refluxing the mixture at 50-150 ℃ for 4-36h, filtering to obtain a final solid product, washing with toluene, acetone, diethyl ether and methanol in sequence, and drying at 50-120 ℃ for 2-24h to obtain amino modified silica gel;
adding 100-1000mg of the modified silica gel into 1-5mL of ultrapure water, uniformly mixing, filling into an SPE small column containing a lower sieve plate, pressing into an upper sieve plate after all the silica gel is filled, and preparing to obtain an amino modified silica gel adsorption column;
step 3, passing through the column
Passing the filtrate prepared in the step 1 through an amino modified silica gel adsorption column with an upper sieve plate and a lower sieve plate prepared in the step 2, adjusting the flow rate to keep the flow rate at the column volume for 1-90min, controlling the temperature of the adsorption column at 25-50 ℃, eluting the tea extract remained in the adsorption column by adopting ethanol solution with the volume fraction of 50-100% and the volume of 1-10 times of the column volume, collecting the column liquid and the eluent, concentrating and drying, wherein the loss rate of the water-soluble tea extract is less than 5%, and the removal rate of heavy metals is more than 95%;
step 4, recycling
Passing the adsorption column with heavy metal adsorbed in step 3 through 0.01-1M EDTA salt solution with 1-20 times column volume, controlling flow rate to pass through column liquid for 5-50min, eluting more than 95% of heavy metal in the adsorption column, and recycling the adsorption column;
the tea extract comprises extractive solution of leaves of Camellia sinensis of Camellia, or tea polyphenols, theanine, tea polysaccharide, and theaflavin;
after the adsorption column is recycled for 6 times, the adsorption rate of heavy metals reaches more than 96%.
2. The method for removing heavy metals in water-soluble tea extracts by using amino modified silica gel materials as claimed in claim 1, wherein the weight percentage of the tea extract or the water-soluble tea extract solution in the step 1 is 40 wt%.
3. The method for removing heavy metals from water-soluble tea extract by using amino modified silica gel material as claimed in claim 1, wherein the pH of the tea extract or the water solution of the water-soluble tea extract in the step 1 is 4.
4. The method for removing heavy metals from water-soluble tea extracts by using amino modified silica gel material as claimed in claim 1, wherein the step 2 is carried out by wet column packing.
5. The method for removing heavy metals from water-soluble tea extract by using amino modified silica gel material as claimed in claim 1, wherein the flow rate of column passing in step 3 is 10 mL/min.
6. The method for removing heavy metals from water-soluble tea extract by using amino modified silica gel material as claimed in claim 1, wherein the volume fraction of ethanol solution in the step 3 is 80%.
7. The method for removing heavy metals from water-soluble tea extracts by using amino modified silica gel material as claimed in claim 1, wherein the EDTA salt in the step 4 is disodium EDTA, dipotassium EDTA, tetrasodium EDTA, tetrapotassium EDTA or other water-soluble compounds containing EDTA structure.
8. The method for removing heavy metals from water-soluble tea extract with amino modified silica gel material according to claim 1, wherein the concentration of EDTA salt in the step 4 is 0.02M.
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