Disclosure of Invention
In order to solve the technical problems, the invention provides a method for removing micro-plastics in a water body by electrolytic air flotation, which comprises the following steps:
(1) adding a complex of long-chain alkylamine and copper ions into the water body dispersed with the micro-plastics, fully mixing,
wherein the long-chain alkylamine is dodecylamine, the complex of the long-chain alkylamine and copper ions is obtained by mixing and heating copper salt and the long-chain alkylamine for reaction,
when the complex is added, the complex is firstly dispersed in ethanol, and then the obtained ethanol dispersion liquid of the complex is added into a water body, wherein the mass ratio of the complex to the ethanol is 1: 15-1: 30, of a nitrogen-containing gas;
(2) carrying out electrolytic treatment on the mixed water body obtained in the step (1),
during electrolytic treatment, correspondingly arranged anodes and cathodes are inserted into the mixed water body, graphite electrodes are adopted as the anodes and the cathodes, and the current density of direct current applied during electrolytic treatment is 80-200A/m2。
In the scheme, the electrolysis measures are utilized to generate bubbles in the mixed water body, specifically, hydrogen is generated on the cathode, oxygen is generated on the anode, the gas bubbles rise and simultaneously drive micro plastic in the water body to float, finally, the micro plastic concentrated on the upper layer of the water body is collected and removed together, the separation of the micro plastic and the water body is realized, meanwhile, the electrolysis gas floating method also generates electrode reaction, and the electrolysis gas floating method has the effects of electrochemical oxidation, electrochemical reduction and the like, and can simultaneously degrade organic pollutants in the water body. According to the principle that the water body is electrolyzed, the generated hydrogen has larger molar weight, and meanwhile, because the density of the hydrogen is obviously lower than that of the oxygen, the tendency that hydrogen bubbles generated by electrolysis float upwards to flush out of the water body is stronger, and the contribution to air floatation is obviously larger than that of oxygen bubbles generated on an anode;
before the electrolytic treatment, the complex of the long-chain alkylamine and the copper ion is fully dispersed in the water body containing the micro-plastic, the complex structurally has both a long-chain alkyl group and the copper ion complexed with the long-chain alkyl group, so that the complex has the property of a surfactant, the complex can be combined with the micro-plastic through the long-chain alkyl group, but the complex is different from a common ionic surfactant, the common ionic surfactant can be electrically ionized and decomposed in water, and the complex used in the scheme has stronger binding force between the copper ion and the long-chain alkyl group, and can possibly promote the copper ion to be also combined with the micro-plastic. On the basis, because copper ions in the water body can migrate to the cathode during electrolysis, in the scheme, the copper ions in the complex compound drive the micro-plastic to migrate to the cathode, and hydrogen bubbles are generated from the cathode and concentrated near the cathode, so that more micro-plastic floats upwards under the action of the hydrogen bubbles, and the removal effect on the micro-plastic in the water body is improved;
although the copper ions are inIn rank compared to H2The hydrogen ions in O preferentially obtain electrons, but in the scheme, microscopic copper ions drag a micro plastic to the cathode, so that the copper ions move forward under load and cannot easily reach the cathode, and a part of water still can be ionized to generate bubbles. In this embodiment, therefore, the sequence of electrons of the hydrogen ions and the copper ions on the cathode should not be obvious, in other words, the generation of bubbles and the migration of the micro-plastic to the cathode should be performed simultaneously.
Detailed Description
Preparation of the complex: dodecylamine and copper nitrate were mixed in a ratio of 9.5: 1, stirring and reacting fully at 110 ℃, discharging,
mixing the obtained materials according to the proportion of 1: the mass ratio of 20 was sufficiently dispersed in ethanol to obtain an ethanol dispersion of the complex.
Example 1
Weighing a plurality of circular micro plastic sheets with the diameter of 2mm, fully dispersing the circular micro plastic sheets into pure water to obtain a simulated dispersion liquid in which micro plastic pollution is stably suspended, wherein the concentration of the micro plastic sheets in the simulated dispersion liquid is 1g/L (176 pieces/L), adding the obtained ethanol dispersion liquid of the complex into the simulated dispersion liquid, and fully stirring the mixture until the mixture is in a suspended state, wherein the mass-volume ratio of the ethanol dispersion liquid of the complex to the simulated dispersion liquid is 100 g: 1L of the total weight of the mixture is obtained,
vertically inserting correspondingly arranged anodes and cathodes into the suspended mixed water body to a position close to the water bottom for electrolysis treatment, wherein the anodes and the cathodes are graphite electrode plates with the thickness of 4mm, the distance between the electrode plates is 30mm, 380V direct current voltage is applied in electrolysis, and the current density is 100A/m2The electrolysis time was 20 min. And after the electrolysis is finished, quickly pumping away and removing the liquid layer enriched with the micro-plastics on the upper layer of the water body, sampling at the middle position of the water body (on the height position) after the remaining water body is basically stable, and after the filtration is dried, finding that the average concentration of the micro-plastics in the water body at the moment is 9.3/L (sampling at three different positions on the same height respectively, calculating the average value, and the same below).
Comparative example 1
The procedure is as in example 1 except that no complex of a long chain alkylamine with copper ions is added:
ethanol was added to the simulated dispersion of example 1 and stirred well, the mass to volume ratio of ethanol to simulated dispersion was 95 g: 1L, adding sodium nitrate crystal powder, stirring fully to enable the density of a water body mixture in subsequent electrolysis to be the same as that in example 1 (avoiding the influence on the rise rate of the micro-plastic caused by different system densities), and then inserting an electrode for electrolysis treatment.
And after the electrolysis is finished, quickly pumping away and removing the liquid layer enriched with the micro-plastics on the upper layer of the water body, sampling at the middle position of the water body (in the height position) after the remaining water body is basically stable, and after the filtration is dried, finding that the average concentration of the micro-plastics in the water body at the moment is 73.3/L.
Comparative example 2
The procedure of example 1 was repeated except that the "complex of a long-chain alkylamine with copper ions" in example 1 was replaced with "copper dodecylbenzenesulfonate" containing copper ions in an equal molar amount with respect to the simulated dispersion liquid in example 1.
And sampling the purified water body, and after the purified water body is drained, finding that the average concentration of the micro-plastics in the water body is 94.7/L.
From the purification effect of the comparative example 2, the applicant believes that the copper dodecylbenzene sulfonate is basically ionized and decomposed into independent dodecylbenzene sulfonate ions and copper ions after entering the water body, so that the long-chain dodecylbenzene sulfonate ions and the micro plastic combined with the long-chain dodecylbenzene sulfonate ions cannot be simultaneously drawn close to the cathode region where the hydrogen bubbles float intensively when the copper ions migrate to the cathode, and the floating efficiency of the micro plastic along with the hydrogen bubbles cannot be improved; in contrast, the long-chain dodecylbenzene sulfonate ions have the function of emulsion stabilization, so that the micro-plastic can be more stably kept in the water body, and the purification effect is not as good as that of the blank control of the comparative example 1.
Example 2
Taking a ground surface water body which is concentrated by 100 times (sampling, filtering and weighing the ground surface water body which is concentrated by 100 times and is in a suspended state to obtain the mass concentration of the micro-plastic in the concentrated ground surface water body of 0.56g/L), adding the obtained ethanol dispersion liquid of the complex into the concentrated ground surface water body, and fully stirring the mixture until the mixture is in the suspended state, wherein the mass-volume ratio of the ethanol dispersion liquid of the complex to the concentrated ground surface water body is 56 g: 1L of the total weight of the mixture is obtained,
vertically inserting correspondingly arranged anodes and cathodes into the suspended mixed water body to a position close to the water bottom for electrolysis treatment, wherein the anodes and the cathodes are graphite electrode plates with the thickness of 4mm, the distance between the electrode plates is 30mm, 380V direct current voltage is applied in electrolysis, and the current density is 100A/m2The electrolysis time was 20 min. And after the electrolysis is finished, quickly pumping away and removing the liquid layer enriched with the micro-plastics on the upper layer of the water body, sampling at the central position of the water body (on the height position) after the remaining water body is basically stable, and after the filtration is dried, finding that the average mass concentration of the micro-plastics in the water body at the moment is 0.027g/L (sampling at three different positions on the same height respectively, calculating the average value, and the same below).
For comparison:
on the basis of example 2, the same procedure as in example 2 was followed except that no complex prepared as described above was added (likewise, the concentrated surface water was sufficiently dispersed by adding an amount of sodium nitrate crystal powder to the concentrated surface water so that the density of the water mixture at the time of subsequent electrolysis was the same as in example 2).
After the electrolyzed water body (the liquid layer with the upper layer enriched with the micro-plastics is extracted) is sampled and drained, the average mass concentration of the micro-plastics in the water body is found to be 0.263 g/L.
Example 3
Taking a soil sample polluted by micro-plastics, and mixing the soil and pure water according to a mass ratio of 1: 10 to be mixed and fully stirred to be suspended (the average concentration of the micro-plastics in the water body of the stirred mixture is 17.5/L), and the rest of the purification operation is the same as that of the example 2.
And (4) sampling, observing and detecting the electrolyzed water body (after the liquid layer with the upper layer enriched with the micro-plastics is extracted), and finding that the average concentration of the micro-plastics in the water body at the moment is 4/L.
For comparison:
on the basis of example 3, the same procedure as in example 3 was repeated except that no complex prepared as described above was added (similarly, the same amount of sodium nitrate crystal powder as that added to the water body of the mixture after stirring was sufficiently dispersed so that the density of the water body mixture at the time of subsequent electrolysis was the same as that of example 3).
Sampling, observing and detecting the electrolyzed water body (after the liquid layer with the upper layer enriched with the micro-plastics is extracted), and finding that the average concentration of the micro-plastics in the water body at the moment is 10.7/L.
Example 4
Taking sludge sediment at the bottom of the Yangtze river polluted by micro plastics, and mixing the sediment and pure water according to a mass ratio of 1: 10 mixing and fully stirring to a suspension state (the average concentration of the micro-plastics in the stirred mixture water body is 22.4/L), and the other purification operations are the same
Example 2.
Sampling, observing and detecting the electrolyzed water body (after the liquid layer with the upper layer enriched with the micro-plastics is extracted), and finding that the average concentration of the micro-plastics in the water body at the moment is 5.7/L.
For comparison:
on the basis of example 4, the same procedure as in example 4 was repeated except that no complex prepared as described above was added (similarly, the same amount of sodium nitrate crystal powder as that added to the water body of the mixture after stirring was sufficiently dispersed so that the density of the water body mixture at the time of subsequent electrolysis was the same as that of example 4).
Sampling, observing and detecting the electrolyzed water body (after the liquid layer with the upper layer enriched with the micro-plastics is extracted), and finding that the average concentration of the micro-plastics in the water body at the moment is 13/L.