CN107540041B - Application of waste concrete in water body defluorination - Google Patents
Application of waste concrete in water body defluorination Download PDFInfo
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Abstract
The invention discloses an application of waste concrete in water body defluorination, which comprises the following steps: (1) waste concrete is used as a raw material, after primary crushing and calcination, set cement is screened out, powder selection and separation are carried out on the set cement after ball milling, and particles with the particle size of below 80 mu m are collected to obtain the water body defluorinating agent; (2) and (2) putting the water defluorinating agent obtained in the step (1) into the fluorine-containing wastewater to remove fluorine from the wastewater. The application of the waste concrete building waste is expanded to the field of fluorine-containing wastewater treatment, the water body fluorine removal material is prepared, the reaction speed is high in the water body fluorine removal process, the limit doping amount does not exist, the utilization efficiency is high, the fluorine removal effect is stable, the water body fluorine removal material can be operated at room temperature, the resource utilization efficiency of waste set cement is improved, and a technical path is provided for high value-added utilization of hardened set cement in waste concrete.
Description
Technical Field
The invention belongs to the field of waste resource utilization, and particularly relates to application of waste concrete in water body defluorination.
Background
A large amount of construction waste can be generated in construction industry activities such as construction, decoration, removal and the like of buildings or structures, and the generation amount of the construction waste is continuously increased along with the rapid promotion of infrastructure and the acceleration of urbanization rate in China. According to statistics, 1/3 in the urban garbage is about building garbage; the stock of the building garbage is over 20 hundred million tons by the end of 2011, and over 3 hundred million tons of building garbage are newly added every year. Because the site selection of the building garbage landfill plants in most cities is improper or the plants are stacked temporarily, not only is a great deal of waste of land resources caused, but also great potential safety hazards exist. Meanwhile, the construction waste interacts with water in the surrounding environment during the stacking and landfill processes, and leachate of the construction waste can pollute surface water or underground water.
The waste concrete is an important part of the construction waste and accounts for about 34 percent of the total amount of the construction waste. But the resource utilization rate of the waste concrete in China is less than 5 percent. At present, the main resource utilization approach is to prepare recycled concrete aggregate, but a large amount of hardened set cement is adhered to the surface of the recycled aggregate, and due to the high porosity, the water absorption and the low strength of the hardened set cement, the mechanical property of the recycled aggregate is reduced, the workability of the recycled concrete is poor, and the volume stability of the hardened set cement is deteriorated. Therefore, a large amount of hardened set cement in the waste concrete becomes a main factor for restricting the preparation of the recycled aggregate from the waste concrete.
At present, resource utilization research on hardened set cement in waste concrete is relatively lacked, and most of the research is focused on the field of preparing building materials, such as building blocks or cement preparation through calcination again. However, the waste set cement has high porosity, high water requirement for thickening, low activity index and limited mixing amount in the use process, and the building material product prepared by the waste set cement has poor construction performance and mechanical property. Meanwhile, because the gelling matrix separated from the waste concrete contains a certain amount of inert silicon dioxide, the difficulty is brought to the grinding of cement raw materials and the calcination of clinker, the content of f-CaO in the clinker is increased, the quality of the clinker is reduced, and the production cost is increased.
Fluorine is one of trace elements necessary for maintaining normal life activities of human bodies, is also an important industrial raw material, and has wide application in the fields of chemical fertilizers, metallurgy, aerospace, refrigeration, organic synthesis, integrated circuits, glass and the like. In the application, a large amount of fluorine-containing wastewater is inevitably generated, and if the fluorine-containing wastewater is not treated well, not only is environmental pollution generated, but also the health of human beings is threatened finally. For example, a small amount of fluorine (up to 150 mg) can cause a series of ailments, and ingestion of more fluorine-containing compounds in humans can cause acute toxicity. Depending on the intake, various conditions may arise, such as anorexia, nausea, abdominal pain, gastric ulcers, cramped bleeding and even death.
The current common methods for treating fluorine-containing wastewater include chemical precipitation, adsorption, coagulation and sedimentation, reverse osmosis, ion exchange, electrochemical treatment, and the like. Among the numerous treatment methods, the chemical precipitation method, the adsorption method and the coagulation sedimentation method are the most important technical method for treating the fluorine-containing wastewater at present due to the advantages of stable treatment effect, simple process, low operation cost, large treatment capacity, suitability for treating high-concentration fluorine-containing wastewater and the like.
The precipitation method and the adsorption method mainly depend on adding a large amount of chemical agents to form fluoride precipitates or fluoride is adsorbed on the surfaces of precipitates to form coprecipitation in the treatment process, or remove fluorine ions in water in a physical and chemical adsorption mode, and finally remove the fluorine ions in the water in a solid-liquid separation mode. In the process, technological parameters and processes such as stirring intensity, reaction time, initial concentration of fluorine-containing wastewater, pH and the like are important factors influencing the fluorine removal effect. Since the entire process requires the use of large amounts of chemicals, the cost of chemicals becomes a significant source of the overall process cost. Therefore, the development of new, less costly, more environmentally friendly treatment agents is an important research direction in this area.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide the application of the waste concrete in water body defluorination, so as to solve the problem of secondary pollution caused by a large amount of waste concrete and solve the problem of high cost of defluorination of the existing chemical agents.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention discloses an application of waste concrete in water body defluorination, which comprises the following steps:
(1) waste concrete is used as a raw material, after primary crushing and calcination, set cement is screened out, powder selection and separation are carried out on the set cement after ball milling, and particles with the particle size of below 80 mu m are collected to obtain the water body defluorinating agent;
(2) and (2) putting the water defluorinating agent obtained in the step (1) into the fluorine-containing wastewater to remove fluorine from the wastewater.
Preferably, the particle size of the waste concrete after the preliminary crushing in step (1) is 10mm or less. The smaller the particle size of the concrete after the initial crushing is, the more favorable the calcination is, and the cement stone can be conveniently screened from the concrete.
Preferably, the calcination conditions in step (1) are: raising the temperature to 200-400 ℃ at the speed of 5-8 ℃/min, keeping the temperature for 10-30 min, and then naturally cooling. The bonding strength of aggregate and set cement in the waste concrete can be weakened through calcination, so that the set cement can be screened out from the concrete, the muffle furnace can be adopted for calcination, and the electromagnetic oscillation crusher can be adopted for oscillation separation after calcination.
Preferably, a surfactant is added in the ball milling process of the set cement in the step (1), wherein the surfactant is at least one of lignosulfonate, ethylene glycol and triisopropanolamine, and the addition amounts of the lignosulfonate, the ethylene glycol and the triisopropanolamine are respectively 0.06-0.1%, 0.02-0.1% and 0.03-0.1% of the mass of the set cement. . The ball milling can further increase the microstructure defects of the set cement, increase the surface area of the set cement, and improve the ball milling effect by adding the surfactant.
Preferably, the ball milling time is 20-50 min.
Preferably, the mass ratio of the water body fluorine removal agent input in the step (2) to the mass of the fluorine ions in the wastewater is 30-550: 1.
Preferably, the time for removing fluorine in the step (2) is 5-30 min.
Preferably, the stirring speed during the defluorination in the step (2) is 40-200 r/min.
Preferably, the pH value of the wastewater is adjusted to 5-6 during the defluorination in the step (2).
Compared with the prior art, the invention has the following beneficial effects:
1. the invention widens the application of the waste concrete as the building waste to the field of fluorine-containing wastewater treatment, prepares the water body fluorine removal material, has high reaction speed in the water body fluorine removal process, does not have limit mixing amount, has high utilization efficiency and stable fluorine removal effect, can be operated at room temperature, improves the resource utilization efficiency of the waste set cement, provides a technical path for the high added value utilization of the hardened set cement in the waste concrete, and avoids the problems of high porosity, high water absorption, low strength, limited mixing amount and the like in the process of preparing recycled concrete materials, building blocks or calcining cement clinker again by the waste concrete in the prior art.
2. The method for preparing the water body defluorinating agent by using the waste concrete has the advantages of wide raw material source and low cost, and provides a new way for resource utilization of a large amount of waste concrete; also provides a process method which is simple and convenient to operate, wide in application range, low in cost, green and environment-friendly and can treat toxicity by waste for the treatment of fluoride-containing wastewater of rivers, lakes, industry, life and the like in China; the method meets the strategic requirements of national development cycle economy, enjoys the support of national and local related industrial policies, and has wide development and application prospects.
3. The invention separates cement from waste concrete and grinds the cement to prepare the water body defluorinating agent, wherein, the main composition of the cement screened from the waste concrete is hydrated calcium silicate gel (C-S-H), ettringite (AFt) and unhydrated dicalcium silicate (C-S-H)2S) and the like. Under the condition of water saturation, the C-S-H gel has a very large specific surface area, and after ball milling dispersion, microscopic defects are increased, the specific surface area is increased, and active point positions are further increased. On one hand, the structure ensures that the hydration product of the calcium-containing cement is easy to interact with water molecules, so that calcium ions are dissolved out to enter into the fluorine-containing water solution and to be mixed with F in the fluorine-containing wastewater-Combined to form CaF precipitate which is separated out from the fluorine-containing wastewater; on the other hand, F in the fluorine-containing wastewater-The fluorine ions are easy to adsorb on the surface of the C-S-H gel and then removed by subsequent filtration, and under the action of the two aspects, the fluorine ions in the water can be effectively removed.
4. The water body defluorinating agent prepared by utilizing the waste concrete has wide adaptability to the initial concentration of the fluorine-containing wastewater, the fluorine ions in the fluorine-containing wastewater can be effectively removed no matter the fluorine-containing wastewater is low-concentration or high-concentration, and the removal rate of the fluorine-containing wastewater can reach 95 percent under the treatment condition of the water body defluorinating agent.
Drawings
FIG. 1 is a graph showing the fluorine removal effect of water body fluorine removal agents prepared in example 2 at different dosage amounts;
FIG. 2 is a graph showing the fluorine removal effect of the fluorine removal agent for water prepared in example 2 at different treatment times;
FIG. 3 is a diagram showing the defluorinating effect of the water defluorinating agent prepared in example 2 at different stirring speeds;
FIG. 4 is a graph showing the fluorine removal effect of the fluorine-containing wastewater with different initial concentrations by using the water body fluorine removal agent prepared in example 2;
FIG. 5 is a graph showing the fluorine removal effect of the water body fluorine removal agent prepared in example 2 at different pH values;
FIG. 6 is a scanning electron microscope image of the water defluorinating agent particles prepared in example 2;
FIG. 7 is an energy spectrum analysis (EDS) spectrum of the particles of the water body fluorine removal agent prepared in example 2 before fluorine removal;
FIG. 8 is an energy spectrum analysis (EDS) spectrum of a precipitation product after the fluorine removal by the water body fluorine removal agent prepared in example 2.
Detailed Description
The present invention will be described in further detail with reference to specific examples.
Example 1
The method comprises the following steps of treating fluorine-containing wastewater by using waste concrete, and firstly preparing a water body fluorine removal agent by using the waste concrete:
(1) selecting waste concrete from construction waste, carrying out primary crushing by using a small hammer crusher, controlling the particle size d of the waste concrete after the primary crushing by using a square hole sieve to be less than or equal to 10mm, and loading the waste concrete after the primary crushing into a muffle furnace for low-temperature pre-calcination to weaken the bonding strength of aggregate and cement stone in the waste concrete, wherein the concrete calcination conditions are as follows: heating to 200 deg.C at a speed of 6 deg.C/min, holding the temperature for 20min, and naturally cooling to 25 deg.C.
(2) Carrying out vibration treatment on calcined waste concrete in an electromagnetic vibration crusher to separate coarse aggregate from waste set cement, adding the set cement obtained by separation into a ball mill for grinding to further increase the microstructure defects and increase the specific surface area, and adding ethylene glycol with the mass of 0.06% of the set cement into the grinding process to carry out surface dispersion treatment in order to improve the grinding effect; meanwhile, the ball milling time is controlled to be 40 min.
(3) The ground materials will generate 'split phase' due to different physical properties, the air classifier is used for powder selection and separation, and particles with the particle size less than or equal to 80 mu m are collected to obtain the water body defluorinating agent.
Putting the obtained water body fluorine removal agent into fluorine-containing wastewater for fluorine removal, wherein the initial concentration of fluorine ions in the wastewater is 200mg/l, and the treatment conditions are as follows: the mass ratio of the water body fluorine removal agent to the fluorine ions is 442:1, the treatment time is 5min, the stirring speed is 200r/min, the pH value of the wastewater is 5-6, and the concentration of the fluorine ions in the wastewater is 12.5mg/l after treatment.
Example 2
Firstly, preparing a water body defluorinating agent by using waste concrete, and the steps are as follows:
(1) selecting waste concrete from construction waste, carrying out primary crushing by using a small hammer crusher, controlling the particle size d of the waste concrete after the primary crushing by using a square hole sieve to be less than or equal to 10mm, and loading the waste concrete after the primary crushing into a muffle furnace for low-temperature pre-calcination to weaken the bonding strength of aggregate and cement stone in the waste concrete, wherein the concrete calcination conditions are as follows: heating to 400 ℃ at the speed of 8 ℃/min, keeping the temperature for 20min, and naturally cooling to 20 ℃.
(2) Carrying out vibration treatment on calcined waste concrete in an electromagnetic vibration crusher to separate coarse aggregate from waste set cement, adding the set cement obtained by separation into a ball mill for grinding to further increase the microstructure defects and increase the specific surface area, and adding lignosulfonate accounting for 0.08 percent of the mass of the set cement, ethylene glycol accounting for 0.06 percent of the mass of the set cement and triisopropanolamine accounting for 0.06 percent of the mass of the set cement in the grinding process for carrying out surface dispersion treatment in order to improve the grinding effect; meanwhile, the ball milling time is controlled to be 30 min.
(3) The ground materials can generate 'split phase' due to different physical properties, the air classifier is used for powder selection and separation, and particles with the particle size less than or equal to 80um are collected to obtain the water body fluorine removal agent.
Putting the obtained water body fluorine removal agent into fluorine-containing wastewater for fluorine removal, wherein the initial concentration of fluorine ions in the wastewater is 200mg/l, and the treatment conditions are as follows: the mass ratio of the water body fluorine removal agent to the fluorine ions is 221:1, the treatment time is 30min, the stirring speed is 200r/min, the pH value of the wastewater is 5-6, the wastewater is treated for 30min, then the wastewater is kept stand for 12h and filtered, and the concentration of the fluorine ions in the filtrate is 10 mg/l.
Fig. 6 is a microscopic scanning electron microscope image of the water body fluorine removal agent particles prepared in example 2, and it can be seen from the image that the particle size of the water body fluorine removal agent particles prepared in the present invention is about 10 μm, and the surface is formed by a large number of tiny scale-like and short column-like cement hydration products which are mutually interpenetrated and lapped into an irregular network, which is loose and porous, the specific surface area is increased, and the active point sites are further increased, which is also the reason why the water body fluorine removal agent prepared in the present invention can effectively remove fluorine ions in water. Table 1 shows the chemical composition of the water defluorinating agent prepared in example 2.
TABLE 1 chemical composition (w) of water defluorinating agent preparedt%）
| SiO2 | CaO | Al2O3 | Fe2O3 | MgO | K2O | NaO | SO3 | TiO2 |
| 48.8295 | 30.7955 | 8.9764 | 3.8741 | 1.5689 | 1.6376 | 1.0428 | 2.0102 | 0.7680 |
The filter residue after filtration in example 2 was vacuum dried at 105 ℃, and the dried sample was subjected to EDS energy spectrum test to analyze the defluorination mechanism of the water defluorinating agent of the present invention, and fig. 7 and 8 are respectively energy spectrum (EDS) analysis diagrams of the water defluorinating agent before and after the reaction. As can be seen from the figure, compared with the water body before the reaction, obvious fluorine element diffraction peaks appear in the X-ray energy spectrum (EDS) on the surfaces of the fluorine removing agent particles in the water body after the reaction, which indicates F in the solution after the reaction-Adsorbed or deposited on the surface of the fluorine-removing material in the form of calcium fluoride, thereby being removed from the solution.
Determination of optimal process parameters:
(1) in order to determine the optimal adding amount, a certain amount of analytically pure NaF is accurately weighed, 200mg/l of fluorine-containing simulated wastewater is configured by a volumetric flask, 100ml of the fluorine-containing simulated wastewater is sequentially weighed by a measuring cylinder into 6 clean beakers, and 0.5g, 1.0g, 2.0g, 3.0g, 4.0g and 5.0g of the water body defluorinating agent prepared in the embodiment 2 are simultaneously and sequentially added, and a magnetic stirrer is utilized for defluorination reaction. And controlling the stirring strength to be 200r/min in the defluorination process, taking down the reaction product from the magnetic stirrer after reacting for 30min at room temperature, standing for 12h and filtering. According to the method specified in national standard of the people's republic of China, "determination of Water quality fluoride ion Selective electrode method (GB 7484-1987)", the concentration of the fluorine ions in the filtrate is determined by adopting a fluorine ion selective electrode so as to represent the actual use effect of the prepared active fluorine removal particles, and the experimental result is shown in figure 1.
As can be seen from FIG. 1, when the addition amount of the water body fluorine removal agent is 0.5g, the fluorine-containing concentration of the treated wastewater is 21mg/l, when the addition amount is 1g, the fluorine-containing concentration of the treated wastewater is 20mg/l, when the addition amount is increased to 2g, the fluorine-containing concentration of the treated wastewater is 10mg/l, when the addition amount is continuously increased to 5g, the fluorine-containing concentration of the treated wastewater is only 5mg/l, and therefore, when the addition amount is more than 2g, the influence of the continuous increase of the addition amount on the treatment effect is small, the addition amount of 2g is considered comprehensively as the optimal addition amount, namely, the mass ratio of the added water body fluorine removal agent to the fluorine ions in the wastewater is 221: 1.
(2) Determining the optimal reaction time, sequentially measuring 100ml of fluorine-containing simulated wastewater with the concentration of 200mg/l by using a measuring cylinder, sequentially adding 4.0g of the water body defluorinating agent prepared in the embodiment 2, placing the water body defluorinating agent on a magnetic stirrer to perform defluorination reaction at room temperature, controlling the stirring strength to be 200r/min, sequentially reacting for 5min, 10min, 15min, 20min, 25min and 30min, then taking down the beaker, standing for 12h, filtering, and testing the fluorine ion concentration of the filtered supernatant to determine the optimal reaction time, wherein the result is shown in fig. 2.
As can be seen from the figure, F in the waste liquid increased with the reaction time within the first 5min-The concentration is rapidly reduced, and F in the waste liquid along with the increase of the reaction time after 5min-The concentration decrease is gradual and basically kept unchanged, and 5min can be selected as the optimal reaction time in consideration of the actual production efficiency.
(3) And determining the optimal stirring strength, namely measuring 100ml of fluorine-containing simulated wastewater with the concentration of 200mg/l in 9 clean beakers by using a measuring cylinder, sequentially adding 4.0g of the water body defluorinating agent prepared in the example 2, placing the water body defluorinating agent on a magnetic stirrer to perform defluorination reaction at room temperature, changing the stirring strength to 200r/min, 190r/min, 170r/min, 150r/min, 100r/min, 80r/min and 40r/min respectively, reacting for 30min, standing for 12h, filtering, and testing the fluorine ion concentration of the filtered supernatant to determine the optimal stirring strength, wherein the result is shown in fig. 3. As can be seen from the figure, the stirring intensity does not greatly affect the defluorination effect, and the stirring intensity is selected to be 40r/min in consideration of the power energy consumption.
(4) Initial concentration (C) of fluorine-containing waste liquid0) Influence on defluorination effect, 100ml of fluorine-containing simulated wastewater with the concentration of 200mg/l and 20mg/l is respectively measured by a measuring cylinder and put into 2 clean beakers, 4.0g of the water defluorination agent prepared in the example 2 is sequentially added, the water defluorination reaction is carried out on a magnetic stirrer at room temperature, the stirring speed is 200r/min, the reaction time is 30min, the filtering is carried out after standing for 12h, the fluorine ion concentration of the filtered supernatant is tested, and the experimental result is shown in figure 4. As can be seen from the figure, the prepared water body fluorine removal agent has wide adaptability to the initial concentration of fluorine-containing wastewater, and can effectively remove fluorine ions in the fluorine-containing wastewater regardless of low concentration or high concentration, so that the fluorine concentration of the effluent is reduced to a lower level, and the lower the concentration is, the lower the fluorine ion concentration of the effluent is.
(5) Determining the optimal reaction pH, sequentially measuring 100ml of fluorine-containing simulated wastewater with the concentration of 200mg/l in 2 clean beakers by using a measuring cylinder, researching the actual use effect of the system in removing fluorine under different reaction pH (pH = 5-6 and pH = 11-12), respectively adding 4.0g of the water body fluorine removing agent prepared in the example 2 into the two systems, placing the two systems on a magnetic stirrer for carrying out fluorine removal reaction at room temperature, stirring at the rotating speed of 200r/min, reacting for 30min, standing for 12h, filtering, and testing the fluorine ion concentration of the filtered supernatant, wherein the result is shown in figure 5. As can be seen from the figure, the prepared fluorine removal agent has better fluorine removal effect under different reaction pH conditions. When the pH = 11-12, the removal rate reaches nearly 80% when the concentration of the fluorine-containing wastewater is reduced to about 40mg/L with the progress of the reaction, and reaches 95% when the pH of the reaction system is reduced to 5-6, the concentration of the fluorine-containing wastewater is reduced to less than 10mg/L with the progress of the reaction. The optimum reaction condition is preferably an acid system, and the pH is preferably controlled to 5 to 6.
As can be seen from the above experiments, the preferred conditions for treating the fluorine-containing wastewater by using the waste concrete of the invention are as follows: stirring at the rotating speed of 40r/min, controlling the pH value of the wastewater to be 5-6, treating for 5min, and controlling the mass ratio of the added water defluorinating agent to the fluorine ions to be 221: 1.
The above examples of the present invention are merely illustrative of the present invention and are not intended to limit the embodiments of the present invention. Variations and modifications in other variations will occur to those skilled in the art upon reading the foregoing description. Not all embodiments are exhaustive. All obvious changes and modifications of the present invention are within the scope of the present invention.
Claims (2)
1. The application of the waste concrete in water defluorination is characterized in that a water defluorination agent is put into fluorine-containing wastewater to adjust the pH of the wastewater to be 5-6; stirring at 40-200 r/min for 5-30 min to remove fluorine from the wastewater;
the preparation method of the water body defluorinating agent comprises the following steps: (1) selecting waste concrete from construction waste, carrying out primary crushing by using a small hammer crusher, controlling the particle size d of the waste concrete after the primary crushing by using a square hole sieve to be less than or equal to 10mm, and loading the waste concrete after the primary crushing into a muffle furnace for low-temperature pre-calcination to weaken the bonding strength of aggregate and cement stone in the waste concrete, wherein the concrete calcination conditions are as follows: heating to 400 ℃ at the speed of 8 ℃/min, keeping the temperature for 20min, and naturally cooling to 20 ℃;
(2) carrying out vibration treatment on calcined waste concrete in an electromagnetic vibration crusher to separate coarse aggregate from waste set cement, adding the set cement obtained by separation into a ball mill for grinding to further increase the microstructure defects and increase the specific surface area, and adding lignosulfonate accounting for 0.08 percent of the mass of the set cement, ethylene glycol accounting for 0.06 percent of the mass of the set cement and triisopropanolamine accounting for 0.06 percent of the mass of the set cement in the grinding process for carrying out surface dispersion treatment in order to improve the grinding effect; meanwhile, the ball milling time is controlled to be 30 min;
(3) the ground materials can generate 'split phase' due to different physical properties, the air classifier is used for powder selection and separation, and particles with the particle size less than or equal to 80um are collected to obtain the water body fluorine removal agent.
2. The application of the method according to claim 1, wherein the mass ratio of the input water body fluorine removal agent to the mass of the fluorine ions in the wastewater is 30-550: 1.
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