This following relates to the treatment of environment-polluting wastes, specifically to the mechanochemcial treatment of solid wastes containing perfluorinated or polyfluorinated compounds.
Perfluorinated or polyfluorinated compounds refer to a type of compounds wherein all or part of hydrogens (H) connecting to the carbons (C) are substituted by fluorine (F). The most representative perfluorinated compounds include perfluorooctane sulfonic acid and its salts (PFOS) and perfluorooctanoic acid and its salts (PFOA). They have been widely used in industrial products and consumer goods since 1950s: PFOS is an outstanding surfactant, during the past fifty years, it was extensively used as textile or leather finishing agent, foam extinguishing agent, oil drilling additive and fog inhibitor in electroplating; PFOA is an important raw material for the manufacture of high-effective fluoropolymers, which is used in the surface coating of aviation devices, electronic components and kitchen wares.
However, recent researches show that the perfluorinated or perfluorinated compounds, with PFOS and PFOA as their representatives, present such disadvantages as long-term persistence, high bioaccumulation, strong biotoxicity and capability for long-distance migration. They hardly degrade in the natural environment. Since 1990s, PFOS and PFOA have been frequently detected out in surface water, ground water, sediments, bodies of both animals and human beings. These facts have caused great concerns throughout the world and many actions have been taken to deal with the PFOS- and PFOA-related pollution. In 2006, the European Union issued Restrictions on the Marketing and Use of Perfluorooctane Sulfonate. In the same year, the United States Environmental Protection Agency (EPA) also launched a self-initiated plan requiring the related enterprises to reduce 95% of PFOA discharge by 2010 and to realize zero discharge of PFOA by 2015. In May of 2009, the Fourth Session of the Conference of Parties listed PFOS in Annex A of Stockholm Convention on Persistent Organic Pollutants (POPs Treaty).
With PFOS being listed in the POPs Treaty and banned internationally, some other perfluorinated or polyfluorinated compounds appeared on the market as substitutes to PFOS and PFOA. These compounds include perfluorinated ones such as perfluorobutane sulfonic acid and its salts (PFBS) (typical CAS numbers: 375-73-5, 29420-49-3), perfluorohexane sulfonic acid and its salts (PFHxS), (typical CAS numbers: 355-46-4, 3871-99-6) and perfluoroalkyl ether potassium sulfonate (trade name: F-53B) (typical CAS number: 73606-19-6), and polyfluorinated ones such as 6:2 fluorotelomer sulfonic acid and its salts (6:2 FTS) (typical CAS numbers: 27619-97-2, 425670-75-3). Except presenting lower bioaccumulation, these new compounds do not show significant improvements in respect of degradation or persistence in comparison with PFOA and PFOS.
In view of this situation, finding appropriate methods to treat solid wastes containing perfluorinated or polyfluorinated compounds are of great practical importance. Currently, the commonest way to degrade solid wastes containing perfluorinated compounds is high-temperature incineration, which not only requires strict reaction conditions and reaction equipments, but also is likely to produce hydrogen fluoride, an acidic corrosive gas, and even the byproduct dioxin. Therefore, it is very urgent to develop non-incineration technologies for treating solid wastes containing perfluorinated or polyfluorinated compounds.
The mechanochemical method is to degrade the pollutant by mixing the solid pollutant and the reaction reagent together into a high-energy ball milling reactor and starting chemical reaction between them by means of mechanic force. Most of existing documents, including patents and articles, on the mechanochemical method involves the treatment of chlorinated persistent organic pollutants, and currently there is only one document [Masayuki Shintani, Yuta Naito, Shingo Yamada, et, al. “Degradation of Perfluorooctansulfonate (PFOS) and Perfluorooctanoic Acid (PFOA) by Mechanochemical Treatment” Kagaku Kogaku Ronbunshu (Journal of Chemical Engineering of Japan) 34.5 (2008): 539-544.] disclosed a mechanochemical method for treating fluorinated persistent organic pollutants (such as PFOS or PFOA), the carbon-fluorine bond of which contains higher bond energy. In this essay, the common calcium oxide was mixed with PFOS and PFOA separately, then the mixture was put into a planetary ball mill and milled at the rotation rate of 700 rpm; after 3 hours (for PFOS) and 18 hours (for PFOA) of reaction, both PFOS and PFOA are almost completely decomposed. However, the detected amount of inorganic fluorine is negligible (lower than 1% of theoretical yield), and in the case of PFOS, the highest amount of detected sulfate ion is lower than 50% of theoretical yield. The result of this disclosed document suggests that on the one hand, the mechanochemical method is technically feasible for treatment of PFOS and PFOA, and on the other, the adoption of calcium oxide as the reaction reagent presents considerable limitations.
In practical process of wastes treatment, we not only expect transformation of the target material, but also hope that the fluorine therein can effectively turn inorganic, which is an extremely important sign of defluorination and detoxication of PFOS and PFOA. That is to say, the existing method should be further improved. In addition, in view of the fact that most of perfluorinated or polyfluorinated substitutes still present high indegradability and strong persistence, it is necessary to find out suitable treatment methods for high-effectively degrading these new compounds.
An aspect relates to a method for mechanochemical treatment of solid wastes containing perfluorinated or polyfluorinated compounds.
A method for mechanochemical treatment of solid wastes containing perfluorinated or polyfluorinated compounds, comprising the following steps: mixing the solid waste containing perfluorinated or polyfluorinated compounds with the defluorination reagent under normal temperature and pressure conditions; putting the mixture into the dry ball milling pot of a planetary high-energy ball milling reactor, adding the milling balls into the ball milling pot and sealing it tight; securing the loaded ball milling pot on the ball mill and starting the milling process at the revolution rate of 200-400 rpm; changing the direction of revolution every 30 minutes till the perfluorinated or polyfluorinated compounds are completely degraded and defluorinated through the mechanochemical reaction; the said defluorination reagent is solid potassium hydroxide (KOH) and the mass ratio between the defluorination reagent and the perfluorinated or polyfluorinated compounds is 5-95:1.
The perfluorinated compounds include perfluorooctane sulfonic acid and its salts, perfluorooctanoic acid and its salts, perfluorobutane sulfonic acid and its salts, perfluorohexane sulfonic acid and its salts, and perfluoroalkyl ether potassium sulfonate.
The polyfluorinated compounds include 6:2 fluorotelomer sulfonic acid and its salts.
In comparison with the prior art, the present invention has following beneficial effects: 1) KOH is adopted as the defluorination reagent during the ball milling process, which realizes not only complete degradation of perfluorinated or polyfluorinated compounds, but also 90% recovery rate of fluoride ions. The high defluorination efficiency means that a solid defluorination reaction in real sense has been realized. In contrast, in the above mentioned reference document, calcium oxide was adopted as the defluorination reagent in the ball milling process. Though such a choice assures smooth degradation of the perfluorinated compounds, the recovery rate of fluoride ions was almost zero, which means the defluorination reaction was not obtained in effect. 2) after being treated with the mechanochemical method disclosed in the present invention, the organic fluorine and sulfonic acid are transformed into inorganic fluoride ions and sulfate ions, which means that the perfluorinated or polyfluorinated compounds with POPs properties are effectively degraded into nontoxic, inorganic fluorides. 3) the mechanochemical reaction is a type of solid reactions. It does not require any organic solvents or hydrogen-donating reagents in liquid form; neither does it produce any harmful end products (including gas or liquid). 4) the technical procedure and reaction conditions of the method disclosed in the present invention is easy to be realized. The revolution rate of the ball mill is kept at medium speed (275 rpm), namely 60% lower than the speed disclosed in the said reference document (700 rpm), which consequently greatly reduces energy consumption and strength requirements on equipments. 5) the energy consumption and operating cost is much lower than that of the traditional high-temperature incineration.
The following provides a method for mechanochemical treatment of solid wastes containing perfluorinated or polyfluorinated compounds. This method can degrade the perfluorinated or polyfluorinated compounds into harmless inorganic fluoride salts. As the perfluorinated or polyfluorinated compounds are detoxicated and completely transformed into inorganic substances, their threat to the natural environment and the health of living organisms is prevented. In the following paragraphs, the present invention is more specifically described by way of example with reference to the attached drawings.
In order to compare the performance of solid KOH with other defluorination reagents, the same mass of CaO, mixture of iron and silica sand (Fe—SiO2, mass ratio of Fe and SiO2 is 10:1), sodium hydroxide (NaOH) and solid KOH are used as defluorination reagents and are put through the processing steps shown in
Separately mixing different defluorination reagents with the solid waste containing 85% potassium perfluorooctane sulfonate (PFOS) together at the mass ratio of 23:1 (namely 4.6 g defluorination reagent and 0.2 g PFOS waste) and putting 4.8 g of different mixtures so obtained into ball milling pots, adding 20 big milling balls (9.60 mm in diameter and weight 4.15 g in average) and 90 small milling balls (5.50 mm in diameter and weight 0.88 g in average) into each pot. All the ball milling pots are 45 mm in depth, 50 mm inner diameter and with 85 mL of effective volume; there is an elastic gasket between the pot opening and the lid for tight sealing. Securing the loaded ball milling pots on the planetary ball mill, setting the revolution rate of the mill at 275 rpm and changing the direction of revolution every 30 minutes. Milling the samples containing different defluorination reagents for 4 hours, collecting the powder from the ball milling pots into a sealed bag. During the laboratory analysis, dissolving 0.050 g powder containing different defluorination reagents in 50 mL high-purity water separately and using ultrasonic vibration 30 minutes to ensure complete dissolution. Analyzing the solutions so obtained with the liquid chromatography—mass spectrometry—mass spectrometry (LC-MS-MS) to determine the residual amount of PFOS and with ion chromatography (IC) to determine the concentration of fluoride ions. As is shown in
Adopting solid KOH as the defluorination reagent and keeping the reaction conditions the same as in example 1, this example is designed to determine the influence of different milling time upon the effect of ball milling process. Milling the different batches of the same sample for 0.5 h, 1h, 2 h, 3 h, 4 h, 6 h, 8 h respectively, collecting the powder from the ball milling pots into a sealed bag. During the laboratory analysis, dissolving 0.050 g powder obtained after different milling time in 50 mL high-purity water separately and using ultrasonic vibration 30 minutes to ensure complete dissolution. Analyzing the solutions so obtained with the liquid chromatography—mass spectrometry—mass spectrometry (LC-MS-MS) to determine the residual amount of PFOS and with ion chromatography (IC) to determine the concentration of fluoride ions and sulfate ions. As is shown in
Adopting different mass ratios of reactants (KOH: PFOS=5:1, 7:1, 11:1, 15:1, 23:1, 47:1 and 95:1 respectively) and keeping the total mass of reactants 4.8 g, adding the mixtures of different mass ratios into ball milling pots and conducting the milling experiment under the same conditions as in example 1. As is shown in
In order to show the mechanochemical reaction of perfluorinated or polyfluorinated compounds and its end products more clearly, the Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometry (XRD) are adopted in this example to characterize the samples obtained after the milling process. Raising the concentration of PFOS and keeping the mass ratio of the reactants at 5:1 (namely 4.0 g KOH and 0.8 g PFOS) so that the change of PFOS and the end products can be more clearly shown in the images. The FTIR image of PFOS after different milling time is shown in
Mixing the defluorination reagent solid KOH with the solid waste containing 95% of sodium perfluorooctanoate (PFOA) together at the mass ratio of 23:1 (namely 4.6 g solid KOH and 0.2 g PFOA waste) and putting 4.8 g mixture into ball milling pots, adding 20 big milling balls (9.60 mm in diameter and weight 4.15 g in average) and 90 small milling balls (5.50 mm in diameter and weight 0.88 g in average) into each pot. All the ball milling pots are 45 mm in depth, 50 mm inner diameter and with 85 mL of effective volume; there is an elastic gasket between the pot opening and the lid for tight sealing. Securing the loaded ball milling pots on the planetary ball mill, setting the revolution rate of the mill at 275 rpm and changing the direction of revolution every 30 minutes. Milling the different batches of the same sample for 20 min, 40 min, 1 h, 2 h, 3 h and 4 h respectively, collecting the powder from the ball milling pots into a sealed bag. During the laboratory analysis, dissolving 0.050 g powder obtained after different milling time in 50 mL high-purity water separately and using ultrasonic vibration 30 minutes to ensure complete dissolution. Analyzing the solutions so obtained with the liquid chromatography—mass spectrometry—mass spectrometry (LC-MS-MS) to determine the residual amount of PFOS and with ion chromatography (IC) to determine the concentration of fluoride ions. As is shown in
Mixing the defluorination reagent solid KOH with the solid waste containing 92% of PFBS and 96% of PFHxS respectively at the mass ratio of 23:1 (namely 4.6 g KOH and 0.2 g PFBS or PFHxS waste) and putting 4.8 g mixture so obtained into ball milling pots, adding 20 big milling balls (9.60 mm in diameter and weight 4.15 g in average) and 90 small milling balls (5.50 mm in diameter and weight 0.88 g in average) into each pot. All the ball milling pots are 45 mm in depth, 50 mm inner diameter and with 85 mL of effective volume; there is an elastic gasket between the pot opening and the lid for tight sealing. Securing the loaded ball milling pots on the planetary ball mill, setting the revolution rate of the mill at 275 rpm and changing the direction of revolution every 30 minutes. Milling the samples containing different solid wastes for 4 hours, collecting the powder from the ball milling pots into a sealed bag. During the laboratory analysis, dissolving 0.050 g powder obtained after the milling process in 50 mL high-purity water separately and using ultrasonic vibration 30 minutes to ensure complete dissolution. Analyzing the solutions so obtained with the liquid chromatography—mass spectrometry—mass spectrometry (LC-MS-MS) to determine the residual amounts of the target materials and with ion chromatography (IC) to determine the concentration of fluoride ions and sulfate ions. As is shown in
Mixing the defluorination reagent solid KOH with the solid waste containing 98% of F-53B and 95% of 6:2 FTS respectively at the mass ratio of 23:1 (namely 4.6 g KOH and 0.2 g F-53B or 6:2 FTS waste) and putting 4.8 g mixture so obtained into ball milling pots, adding 20 big milling balls (9.60 mm in diameter and weight 4.15 g in average) and 90 small milling balls (5.50 mm in diameter and weight 0.88 g in average) into each pot. All the ball milling pots are 45 mm in depth, 50 mm inner diameter and with 85 mL of effective volume; there is an elastic gasket between the pot opening and the lid for tight sealing. Securing the loaded ball milling pots on the planetary ball mill, setting the revolution rate of the mill at 275 rpm and changing the direction of revolution every 30 minutes. Milling the samples containing different solid wastes for 4 hours, and collecting the powder from the ball milling pots into a sealed bag. During the laboratory analysis, dissolving 0.050 g powder obtained after the milling process in 50 mL high-purity water separately and using ultrasonic vibration 30 minutes to ensure complete dissolution. Analyzing the solutions so obtained with the liquid chromatography—mass spectrometry—mass spectrometry (LC-MS-MS) to determine the residual amounts of the target materials and with ion chromatography (IC) to determine the concentration of fluoride ions. As is shown in
Number | Date | Country | Kind |
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201210321589.6 | Sep 2012 | CN | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/CN2012/001262 | 9/13/2012 | WO | 00 | 1/9/2014 |