CN108689522B - Method for treating and recycling mixed acid wastewater in photovoltaic industry - Google Patents

Method for treating and recycling mixed acid wastewater in photovoltaic industry Download PDF

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CN108689522B
CN108689522B CN201810507326.1A CN201810507326A CN108689522B CN 108689522 B CN108689522 B CN 108689522B CN 201810507326 A CN201810507326 A CN 201810507326A CN 108689522 B CN108689522 B CN 108689522B
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defluorination
calcium
fluorine
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CN108689522A (en
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汪林
李丽芳
唐凯
马信
张建春
张炜铭
何锐
吕振华
王利慧
邵燕
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Jiangsu Nju Environmental Technology Co ltd
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    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F9/00Multistage treatment of water, waste water, or sewage
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    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/02Treatment of water, waste water, or sewage by heating
    • C02F1/04Treatment of water, waste water, or sewage by heating by distillation or evaporation
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/46Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/469Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis
    • C02F1/4693Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis electrodialysis
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/52Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F1/5236Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
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    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/66Treatment of water, waste water, or sewage by neutralisation; pH adjustment
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    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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    • C02F2001/007Processes including a sedimentation step
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    • C02F2101/00Nature of the contaminant
    • C02F2101/10Inorganic compounds
    • C02F2101/12Halogens or halogen-containing compounds
    • C02F2101/14Fluorine or fluorine-containing compounds
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    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2301/00General aspects of water treatment
    • C02F2301/08Multistage treatments, e.g. repetition of the same process step under different conditions
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    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F3/00Biological treatment of water, waste water, or sewage
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    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F5/00Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
    • C02F5/02Softening water by precipitation of the hardness

Abstract

The invention relates to a method for treating mixed acid wastewater in the photovoltaic industry and recycling the mixed acid wastewater, and belongs to the technical field of wastewater treatment. The method comprises the following steps: a) respectively introducing the wastewater into a first fluorine removal tank and a second fluorine removal tank; b) adding calcium hydroxide emulsion into the first defluorination tank, and introducing the mud-water mixture into the second defluorination tank; c) adding calcium carbonate into the second defluorination tank, introducing the mud-water mixture into a first sedimentation tank for treatment, and introducing the supernatant into a softening tank; d) adding carbonate into the softening tank, precipitating and recycling the formed calcium carbonate into a second fluorine removal tank, and introducing the mud-water mixture into a second precipitation tank for treatment; e) and treating the supernatant of the second sedimentation tank by an electrodialyzer to obtain a byproduct. The method realizes resource recovery of nitrogen element while removing fluorine, has high fluorine removal efficiency by a two-step method, can effectively reduce the operation cost of wastewater treatment, and can realize zero emission of mixed acid wastewater in the photovoltaic industry.

Description

Method for treating and recycling mixed acid wastewater in photovoltaic industry
Technical Field
The invention belongs to the technical field of wastewater treatment, and particularly relates to a method for treating mixed acid wastewater in the photovoltaic industry and recycling the mixed acid wastewater.
Background
The photovoltaic industry is one of important development industries of new energy, is rapidly developed in China in the last decade, and the rapid development of the photovoltaic industry brings great economic benefits to the modern society and also brings new environmental problems. In the production process of the polycrystalline silicon wafer, nitric acid and hydrofluoric acid are mixed for etching, and etching waste liquid contains a large amount of fluorine ions and nitrate nitrogen. Generally, the concentration of fluorine ions in the mixed acid wastewater in the photovoltaic industry exceeds 3000mg/L, the concentration of nitrate nitrogen is more than 1000mg/L, and the pH value is less than 4. If the treatment is improper, the environment can be seriously polluted, and the serious threat to the human health is formed. For this reason, the fluorine content in the wastewater discharged by national regulations must not exceed 10mg/L (GB 8978-.
At present, in order to avoid the influence of fluorine ions on the denitrification process when treating the mixed acid wastewater, calcium salt is mostly adopted for removing fluorine by a chemical precipitation method, and then biological denitrification is carried out. Generally, before defluorination, the pH value of the wastewater needs to be adjusted to be alkaline, and then calcium oxide or calcium hydroxide is added to precipitate and defluorinate. The method can achieve the aim of removing fluorine, but precipitates are difficult to separate, and a large amount of acid is required to be added to lower the pH value before the subsequent biological denitrification so as to ensure that microorganisms have activity in the denitrification process, so that the treatment cost is higher. In addition, because a large amount of nitrate needs huge tank capacity for treatment, the civil engineering cost is undoubtedly increased by adopting the biological denitrification method, and the nitrogen element is not recycled, so that the great waste of the nitrogen resource is caused.
Research shows that the calcium carbonate is adopted to remove fluorine, and precipitates are fast to settle and easy to separate. In order to facilitate solid-liquid separation of precipitates and simultaneously realize resource recovery of ammonia nitrogen, the application of Chinese patent application No. 201110047708.9, published as 2011.8.10, discloses a method for treating alkaline high-concentration fluorine-containing wastewater, which adopts a mixture of calcium carbonate and calcium hydroxide as a precipitator for defluorination, then utilizes phosphoric acid to recover ammonia gas generated in the defluorination process, and realizes resource recovery of ammonia nitrogen while defluorination. The separation difficulty of the precipitated product is reduced by using the mixed precipitator of calcium carbonate and calcium hydroxide, but the method is not suitable for treating mixed acid wastewater containing a large amount of fluoride ions and nitrate nitrogen because the calcium carbonate and H are mixed under an acidic condition+Reaction to produce a large amount of CO2Gas generates a large amount of foam, which affects the fluorine removal process and causes the fluorine removal efficiency to drop sharply, and in addition, a large amount of mixed acid wastewater containing a large amount of fluoride ions and nitrate nitrogen needs to be addedCalcium carbonate and calcium hydroxide, which are expensive.
Chinese patent application No. CN201410159394.5, published as 2014.07.23, discloses a zero emission approach method for wastewater produced by a high fluorine-containing nitrogen-containing battery in the photovoltaic industry, and the wastewater produced by the high fluorine-containing nitrogen-containing battery is firstly sent into a regulating tank for homogenization; then enters a defluorination reaction tank, and the effluent of the reaction tank enters a sedimentation tank; supernatant in the sedimentation tank enters an intermediate water tank; then the fresh water enters a first-stage reverse osmosis membrane for treatment through a quartz sand filter and an active carbon filter; the concentrated water of the reverse osmosis membrane passes through a concentrated water induction accelerated crystallization tank, so that calcium ions and fluoride ions in the concentrated water are accelerated to form precipitates on the seed crystals, the concentrations of the calcium ions and the fluoride ions are effectively reduced, the concentration multiple of the reverse osmosis concentration membrane is improved, and the supernatant passes through a cartridge filter and then enters the reverse osmosis concentration membrane for circular concentration; a small amount of concentrated water of the reverse osmosis concentration membrane enters the evaporator, the cost required by evaporation is greatly reduced, steam condensate water enters a reuse water pool and is completely reused for industrial water, and residues generated by evaporation are treated as solid wastes. However, the method of this application has the following drawbacks: 1) although the method is provided with the defluorination reaction tank and the defluorination reaction tank respectively, the concentration of fluorine ions after passing through the defluorination reaction tank still can not reach the standard, the subsequent induced accelerated crystallization tank needs to be removed again, a large amount of reagents need to be added in the defluorination process, and the cost is high; 2) the wastewater in the photovoltaic industry contains a large amount of silicon, a small amount of fluoride ions and calcium ions, and is easy to cause membrane blockage under high pressure, the membrane flux and the separation efficiency are easily reduced rapidly by adopting a reverse osmosis membrane for treatment, the membrane cleaning frequency is accelerated, the equipment maintenance and replacement period is greatly shortened, the operation cost of wastewater treatment is greatly increased, and the industrial application of the technology in the field is severely restricted; 3) the whole operation process is complex and not beneficial to popularization.
The electrodialysis technology is a membrane separation technology which realizes concentration, refining or purification by utilizing the selective permeability of an ion exchange membrane and moving anions and cations to an anode and a cathode respectively under the driving of an external direct current electric field at normal temperature and normal pressure. The electrodialysis membrane can effectively solve the problem of membrane blockage which is very easy to occur in the treatment process of the pressure driving membrane, but the application of the electrodialysis membrane in the field of wastewater treatment in the photovoltaic industry is rarely reported.
In conclusion, for those skilled in the art, how to treat the mixed acid wastewater in the photovoltaic industry with high efficiency and low cost and realize resource recycling is an unsolved technical problem.
Disclosure of Invention
1. Problems to be solved
Aiming at the defects that a large amount of chemical reagents are required to be added when the mixed acid wastewater in the photovoltaic industry is subjected to fluorine removal and the removal efficiency is low in the prior art, the invention aims to provide a method for treating and recycling the mixed acid wastewater in the photovoltaic industry, so that the resource recycling of nitrate nitrogen is realized while the mixed acid wastewater in the photovoltaic industry is treated efficiently and at low cost.
2. Technical scheme
In order to solve the problems, the technical scheme adopted by the invention is as follows:
the invention provides a method for treating mixed acid wastewater in the photovoltaic industry, which comprises a fluorine removal step, wherein the fluorine removal step comprises two fluorine removal steps, calcium hydroxide emulsion is added in the first fluorine removal step, and calcium carbonate is added in the second fluorine removal step.
As a further improvement of the invention, in the first step of defluorination, the molar concentration of the fluorine ions is measured, and the molar concentration of the calcium ions in the calcium hydroxide emulsion is 30-40% of the molar concentration of the fluorine ions in the first defluorination pool. The non-sufficient amount is added to ensure that calcium ions are completely converted into calcium fluoride precipitate.
As a further improvement of the invention, the molar concentration of the fluorine ions is measured in the second fluorine removal step, and the molar concentration of the calcium ions added with the calcium carbonate is 54-60% of the molar concentration of the fluorine ions in the second fluorine removal tank. The excess of calcium ions is to ensure that the fluoride ion concentration in the supernatant of the first sedimentation tank is less than 10 mg/L.
As a further improvement of the invention, the fluorine removal step comprises the following steps:
a) respectively guiding the wastewater into a first defluorination pool and a second defluorination pool, wherein the volume ratio of the wastewater guided into the first defluorination pool to the wastewater guided into the second defluorination pool is (1-3): (3-1), controlling the pH value of the first defluorination pool to be 4-6;
b) adding calcium hydroxide emulsion into the first defluorination tank, and introducing the first defluorination tank mud-water mixture into a second defluorination tank;
c) and adding calcium carbonate into the second fluorine removal tank for treatment.
The invention also provides a resource recovery method of the mixed acid wastewater in the photovoltaic industry, which comprises the following steps on the basis of the treatment method of the mixed acid wastewater in the photovoltaic industry:
1) introducing a mud-water mixture obtained after adding calcium carbonate into the second defluorination tank into a first sedimentation tank for treatment, measuring the concentration of calcium ions in the supernatant, and introducing the supernatant into a softening tank;
2) adding carbonate into the softening tank, precipitating and recycling the formed calcium carbonate into a second defluorination tank, introducing the mud-water mixture into a second precipitation tank for treatment, and treating the supernatant through an electrodialyzer to obtain a byproduct.
As a further improvement of the invention, the carbonate is any one of sodium carbonate and potassium carbonate.
As a further improvement of the invention, the molar concentration of carbonate ions in the carbonate in the step 2) is 150-200% of the molar concentration of calcium ions in the supernatant. The carbonate excess is to ensure that all of the calcium ions in the softening tank are converted to calcium carbonate precipitate.
As a further improvement of the invention, a nanofiltration unit is added after the second sedimentation tank, the supernatant of the second sedimentation tank is led into the nanofiltration unit for quality separation and desalination, and the divalent ions in the wastewater are removed and then led into the electrodialyzer.
As a further improvement of the invention, hydrochloric acid is used for adjusting the pH value to 4-5.
As a further improvement of the invention, the salt content of the concentrated water of the electrodialyzer is 15.0-20.0%, the salt content of the fresh water of the electrodialyzer is 0.1-0.5%, and the salt content of the electrodialyzer is 1-3 poles.
3. Advantageous effects
Compared with the prior art, the invention has the beneficial effects that:
(1) the resource treatment method of the mixed acid wastewater in the photovoltaic industry has the effect of efficiently removing fluorine, adopts a two-step method to remove fluorine according to the characteristics of the mixed acid wastewater in the photovoltaic industry, adopts calcium hydroxide emulsion to remove fluorine in the first step, and consumes H in the mixed acid wastewater while removing fluorine+Avoiding directly adopting calcium carbonate powder and H+The reaction produces a large amount of CO2Gas, reduce the formation of foam, raise the treatment efficiency; and in the second step, calcium carbonate is adopted for defluorination, precipitates are easy to separate, and the precipitates are easy to absorb fluoride ions in the wastewater due to the large specific surface area, so that calcium fluoride precipitates can be quickly formed, and the defluorination efficiency is effectively improved.
(2) According to the resource treatment method of the mixed acid wastewater in the photovoltaic industry, the two-step method is adopted for defluorination, so that calcium fluoride precipitate can be quickly formed, the defluorination efficiency is effectively improved, calcium carbonate precipitate generated in the subsequent calcium removal reaction process can be added as a raw material for second-step defluorination, the calcium carbonate precipitate is recycled in a system, the defluorination process only needs to be started to supplement a small amount of calcium carbonate, the consumption of reagents is greatly reduced, the treatment cost is effectively reduced, compared with the prior art, a large amount of reagents are not needed to be added for an acid-base repeated adjustment process, and the treatment cost is further reduced.
(3) According to the characteristic that the mixed acid wastewater in the photovoltaic industry contains high-concentration fluoride ions and nitrate nitrogen, the two-step method is effectively combined with the resource recovery of the nitrate nitrogen, carbonate is added after the second step of fluoride removal, calcium ions can be effectively removed, a recyclable calcium carbonate raw material is generated, nitrate can be formed, the recovery of the nitrate is carried out by combining an electrodialysis technology, the great waste of nitrogen resources caused by a biological denitrification method for treating a large amount of nitrate in the prior art is avoided, on the other hand, the requirement of the biological denitrification method on the wastewater is harsh, and the concentration of the fluoride ions in the wastewater in the preorder process is required to reach a higher standard.
(4) According to the resource treatment method of the mixed acid wastewater in the photovoltaic industry, the electrodialysis technology is adopted to recycle the nitrogen element in the follow-up process, the problem that the membrane is easy to block under the pressure driving condition in the prior art is solved, the problem of membrane blocking can be avoided even if a small amount of fluoride ions and calcium ions exist in the wastewater by adopting the electrodialysis technology, the treatment efficiency is obviously improved, and the operation cost is further reduced.
(5) According to the resource treatment method of the mixed acid wastewater in the photovoltaic industry, a nanofiltration unit is adopted for pretreatment, the supernatant of the second sedimentation tank is subjected to quality-based desalting, divalent ions in the wastewater are removed, the purity of the by-product is improved, and the purity of the finally obtained by-product is 90.0% -98.0%; the recovery rate is 95.0-99.0%, and the recovery rate and purity of the by-product are high, thus being beneficial to popularization.
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FIG. 1 is a simplified process flow diagram of the present invention.
Detailed Description
The invention is further described with reference to specific examples.
Example 1
Fig. 1 is a simple process flow diagram of the invention, and with reference to fig. 1, the method for treating and recycling mixed acid wastewater in photovoltaic industry of this embodiment includes the following steps:
a) in the embodiment, the molar concentration of fluorine ions in the mixed acid wastewater in the photovoltaic industry is 0.637mol/L, the molar concentration of nitrate nitrogen is 0.04mol/L, the wastewater is led into a regulating tank for water quality homogenization, and is led into a first fluorine removal tank and a second fluorine removal tank according to the volume ratio of 1: 3;
b) adding a calcium hydroxide emulsion into the first defluorination pool, wherein the molar concentration of calcium ions in the calcium hydroxide emulsion is 30% of the molar concentration of fluoride ions in the first defluorination pool, namely the molar concentration of the calcium ions is 0.191mol/L, the pH value of the first defluorination pool is 4.0, so that calcium fluoride precipitates are formed by the fluoride ions and the calcium ions, and introducing the first defluorination pool mud-water mixture into the second defluorination pool;
c) determining the molar concentration of fluoride ions in the second defluorination tank to be 0.541mol/L, supplementing calcium carbonate powder into the second defluorination tank to enable the fluoride ions and calcium ions to form calcium fluoride precipitate, wherein the molar concentration of the calcium ions in the calcium carbonate powder is 54% of the molar concentration of the fluoride ions in the second defluorination tank, namely the adding concentration of the calcium ions is 0.29mol/L, introducing the sludge-water mixture of the second defluorination tank into the first sedimentation tank for precipitation, discharging precipitates in the first sedimentation tank, wherein the concentration of the fluoride ions in the supernatant of the first sedimentation tank is 9.2mg/L, and introducing the supernatant of the first sedimentation tank into the softening tank;
d) determining the molar concentration of calcium ions in the softening tank to be 0.022mol/L, adding sodium carbonate into the softening tank to enable the calcium ions and carbonate ions to form calcium carbonate precipitates, wherein the molar concentration of the carbonate ions in the sodium carbonate is 150% of the molar concentration of the calcium ions in the softening tank, namely the molar concentration of the carbonate ions is 0.033mol/L, introducing the softening tank sludge-water mixture into a second precipitation tank for precipitation, and recycling the calcium carbonate precipitates in the second precipitation tank into a second fluorine removal tank;
e) introducing the supernatant of the second sedimentation tank into an electrodialyzer for separation, wherein the electrodialyzer is 1 pole, the salt content of fresh water of the electrodialyzer is 0.1 percent, introducing the electrodialyzer into a biochemical tank for biochemical treatment, and the salt content of concentrated water of the electrodialyzer is 15.0 percent, introducing the electrodialyzer into an evaporator for evaporation;
f) the evaporator condensed water is used for dissolving the medicine, the solid obtained by evaporation is a byproduct sodium nitrate, the recovery rate of the sodium nitrate is 99.0 percent, and the purity is 98.0 percent.
Example 2
The method for treating and recycling mixed acid wastewater in the photovoltaic industry comprises the following steps:
a) in the embodiment, the molar concentration of fluorine ions in the mixed acid wastewater in the photovoltaic industry is 0.342mol/L, the molar concentration of nitrate nitrogen is 0.064mol/L, the wastewater is led into a regulating reservoir for water quality homogenization, and the volume ratio is 3: 1, leading the fluorine into a first fluorine removal tank and a second fluorine removal tank;
b) adding a calcium hydroxide emulsion into the first defluorination tank, wherein the molar concentration of calcium ions in the calcium hydroxide emulsion is 40% of that of fluorine ions in the first defluorination tank, namely the molar concentration of the calcium ions is 0.137mol/L, the pH value of the first defluorination tank is 6.0, so that calcium fluoride precipitates are formed by the fluorine ions and the calcium ions, and introducing the first defluorination tank sludge-water mixture into the second defluorination tank;
c) measuring the molar concentration of fluoride ions in the second defluorination tank to be 0.137mol/L, supplementing calcium carbonate powder into the second defluorination tank to enable the fluoride ions and calcium ions to form calcium fluoride precipitate, wherein the molar concentration of the calcium ions in the calcium carbonate powder is 60% of that of the fluoride ions in the second defluorination tank, namely the adding concentration of the calcium ions is 0.082mol/L, introducing the sludge-water mixture of the second defluorination tank into the first sedimentation tank for precipitation, discharging precipitates in the first sedimentation tank, wherein the concentration of the fluoride ions in the supernatant of the first sedimentation tank is 5.7mg/L, and introducing the supernatant of the first sedimentation tank into the softening tank;
d) determining the molar concentration of calcium ions in the softening tank to be 0.014mol/L, adding sodium carbonate into the softening tank to enable the calcium ions and carbonate ions to form calcium carbonate precipitates, wherein the molar concentration of the carbonate ions in the sodium carbonate is 200% of the molar concentration of the calcium ions in the softening tank, namely the molar concentration of the carbonate ions is 0.028mol/L, introducing the softening tank mud-water mixture into a second precipitation tank for precipitation, and recycling the calcium carbonate precipitates in the second precipitation tank into a second fluorine removal tank;
e) introducing the supernatant of the second sedimentation tank into an electrodialyzer for separation, wherein the electrodialyzer is 3 poles, the salt content of fresh water of the electrodialyzer is 0.5%, introducing the electrodialyzer into a biochemical tank for biochemical treatment, and the salt content of concentrated water of the electrodialyzer is 20.0%, introducing the electrodialyzer into an evaporator for evaporation;
f) the evaporator condensed water is used for dissolving the medicine, the solid obtained by evaporation is sodium nitrate as a byproduct, the recovery rate of the sodium nitrate is 95.0 percent, and the purity is 90.0 percent.
Example 3
The method for treating and recycling the mixed acid wastewater in the photovoltaic industry comprises the following operation steps:
a) in the embodiment, the molar concentration of fluorine ions in the mixed acid wastewater in the photovoltaic industry is 1.158mol/L, the molar concentration of nitrate nitrogen is 0.086mol/L, the wastewater is led into a regulating reservoir for water quality homogenization, and the volume ratio is 1: 1, leading the fluorine into a first fluorine removal tank and a second fluorine removal tank;
b) adding a calcium hydroxide emulsion into the first defluorination tank, wherein the molar concentration of calcium ions in the calcium hydroxide emulsion is 35% of that of fluorine ions in the first defluorination tank, namely the molar concentration of the calcium ions is 0.405mol/L, the pH value of the first defluorination tank is 5.2, so that calcium fluoride precipitates are formed by the fluorine ions and the calcium ions, and introducing the slurry-water mixture of the first defluorination tank into the second defluorination tank;
c) determining the molar concentration of fluorine ions in the second fluorine removal tank to be 0.753mol/L, supplementing calcium carbonate powder into the second fluorine removal tank to enable the fluorine ions and the calcium ions to form calcium fluoride precipitates, wherein the molar concentration of the calcium ions in the calcium carbonate powder is 56% of that of the fluorine ions in the second fluorine removal tank, namely the adding concentration of the calcium ions is 0.421mol/L, introducing the sludge-water mixture of the second fluorine removal tank into the first sedimentation tank for precipitation, discharging precipitates in the first sedimentation tank, enabling the concentration of the fluorine ions in the supernatant of the first sedimentation tank to be 7.3mg/L, and introducing the supernatant of the first sedimentation tank into the softening tank;
d) determining the molar concentration of calcium ions in the softening tank to be 0.045mol/L, adding potassium carbonate into the softening tank to enable the calcium ions and carbonate ions to form calcium carbonate precipitates, wherein the molar concentration of the carbonate ions in the sodium carbonate is 170% of the molar concentration of the calcium ions in the softening tank, namely the molar concentration of the carbonate ions is 0.077mol/L, introducing the softening tank sludge-water mixture into a second precipitation tank for precipitation, and recycling the calcium carbonate precipitates in the second precipitation tank into a second fluorine removal tank;
e) a nanofiltration unit is added behind the second sedimentation tank, the supernatant of the second sedimentation tank is led into the nanofiltration unit to remove residual divalent ions, hydrochloric acid is used for adjusting the pH value of the effluent of the nanofiltration unit to be 4.1, and then the effluent is led into an electrodialyzer for separation, the electrodialyzer is 2 poles, the salt content of the fresh water of the electrodialyzer is 0.25%, the fresh water of the electrodialyzer is led into a biochemical tank for biochemical treatment, the salt content of the concentrated water of the electrodialyzer is 16.1%, and the brine is led into an evaporator for evaporation;
f) the evaporator condensed water is used for dissolving the potassium nitrate, the solid obtained by evaporation is a byproduct potassium nitrate, the recovery rate of the potassium nitrate is 93.6%, and the purity of the potassium nitrate is 97.8%.
Example 4
The method for treating and recycling mixed acid wastewater in the photovoltaic industry comprises the following steps:
a) in the embodiment, the molar concentration of fluorine ions in the mixed acid wastewater in the photovoltaic industry is 1.158mol/L, the molar concentration of nitrate nitrogen is 0.086mol/L, and after the wastewater is introduced into a regulating reservoir for water quality homogenization, the mixed acid wastewater is prepared by the following steps: 1, leading the fluorine into a first fluorine removal tank and a second fluorine removal tank;
b) adding calcium hydroxide emulsion into the first defluorination pool, wherein the molar concentration of calcium ions in the calcium hydroxide emulsion is 37.5 percent of that of fluorine ions in the first defluorination pool, namely the molar concentration of the calcium ions is 0.434mol/L, the pH value of the first defluorination pool is 4.6, so that calcium fluoride precipitate is formed by the fluorine ions and the calcium ions, and introducing the first defluorination pool mud-water mixture into the second defluorination pool;
c) determining the molar concentration of fluoride ions in the second defluorination tank to be 0.724mol/L, supplementing calcium carbonate powder into the second defluorination tank to enable the fluoride ions and calcium ions to form calcium fluoride precipitate, wherein the molar concentration of the calcium ions in the calcium carbonate powder is 57.5% of the molar concentration of the fluoride ions in the second defluorination tank, namely the adding concentration of the calcium ions is 0.416mol/L, introducing the sludge-water mixture of the second defluorination tank into the first sedimentation tank for precipitation, discharging precipitates in the first sedimentation tank, wherein the concentration of the fluoride ions in the supernatant of the first sedimentation tank is 6.1mg/L, and introducing the supernatant of the first sedimentation tank into a softening tank;
d) determining the molar concentration of calcium ions in the softening tank to be 0.054mol/L, adding potassium carbonate into the softening tank to enable the calcium ions and carbonate ions to form calcium carbonate precipitates, wherein the molar concentration of the carbonate ions in the sodium carbonate is 165% of the molar concentration of the calcium ions in the softening tank, namely the molar concentration of the carbonate ions is 0.089mol/L, introducing the softening tank sludge-water mixture into a second precipitation tank for precipitation, and recycling the calcium carbonate precipitates in the second precipitation tank into a second fluorine removal tank;
e) adjusting the pH value of the supernatant of the second sedimentation tank to be acidic, then introducing the supernatant into an electrodialyzer for separation, wherein the electrodialyzer is 1 pole, the salt content of fresh water of the electrodialyzer is 0.3%, introducing the fresh water of the electrodialyzer into a biochemical tank for biochemical treatment, and the salt content of concentrated water of the electrodialyzer is 17.6%, introducing the concentrated water of the electrodialyzer into an evaporator for evaporation;
f) the condensed water of the evaporator is used for dissolving the potassium nitrate for recycling, the solid obtained by evaporation is a byproduct potassium nitrate, the recovery rate of the potassium nitrate is 97.8 percent, and the purity of the potassium nitrate is 90.3 percent.
Example 5
The method for treating and recycling mixed acid wastewater in the photovoltaic industry comprises the following steps:
a) in the embodiment, the molar concentration of fluorine ions and the molar concentration of nitrate nitrogen in the mixed acid wastewater in the photovoltaic industry are respectively 1.368mol/L and 0.069mol/L, and after the mixed acid wastewater is introduced into a regulating tank for water quality homogenization, the mixed acid wastewater is prepared by the following steps of: 1.2 leading into a first fluorine removal tank and a second fluorine removal tank;
b) adding a calcium hydroxide emulsion into the first defluorination pool, wherein the molar concentration of calcium ions in the calcium hydroxide emulsion is 32.5 percent of that of fluorine ions in the first defluorination pool, namely the molar concentration of the calcium ions is 0.445mol/L, the pH value of the first defluorination pool is 5.3, so that calcium fluoride precipitate is formed by the fluorine ions and the calcium ions, and introducing the first defluorination pool mud-water mixture into the second defluorination pool;
c) determining the molar concentration of fluoride ions in the second defluorination tank to be 0.767mol/L, supplementing calcium carbonate powder into the second defluorination tank to enable the fluoride ions and calcium ions to form calcium fluoride precipitate, wherein the molar concentration of the calcium ions in the calcium carbonate powder is 55% of that of the fluoride ions in the second defluorination tank, namely the adding concentration of the calcium ions is 0.422mol/L, introducing the sludge-water mixture of the second defluorination tank into the first sedimentation tank for precipitation, discharging precipitates in the first sedimentation tank, wherein the molar concentration of the fluoride ions in the supernatant of the first sedimentation tank is 5.8mg/L, and introducing the supernatant of the first sedimentation tank into the softening tank;
d) determining the molar concentration of calcium ions in the softening tank to be 0.038mol/L, adding potassium carbonate into the softening tank to enable the calcium ions and carbonate ions to form calcium carbonate precipitates, wherein the molar concentration of the carbonate ions in the sodium carbonate is 186% of the molar concentration of the calcium ions in the softening tank, namely the molar concentration of the carbonate ions is 0.071mol/L, introducing the softening tank mud-water mixture into a second precipitation tank for precipitation, and recycling the calcium carbonate precipitates in the second precipitation tank into a second fluorine removal tank;
e) a nanofiltration unit is added behind the second sedimentation tank, the supernatant of the second sedimentation tank is led into the nanofiltration unit to remove residual divalent ions, hydrochloric acid is used for adjusting the pH value of the effluent of the nanofiltration unit to be 4.45, and then the effluent is led into an electrodialyzer for separation, the electrodialyzer is a 2-pole electrodialyzer, the salt content of fresh water of the electrodialyzer is 0.40%, the fresh water of the electrodialyzer is led into a biochemical tank for biochemical treatment, the salt content of concentrated water of the electrodialyzer is 18.1%, and the electrodialyzer is led into an evaporator for evaporation;
f) the condensed water of the evaporator is used for dissolving the potassium nitrate for recycling, the solid obtained by evaporation is a byproduct potassium nitrate, the recovery rate of the potassium nitrate is 96.2 percent, and the purity is 97.9 percent.
Comparative example
Referring to the photovoltaic mixed acid wastewater of example 1, the initial molar concentration of fluoride ions is 0.637mol/L, and the amount of raw materials to be added when calcium carbonate or calcium hydroxide or calcium carbonate or calcium hydroxide is added together with calcium carbonate or calcium hydroxide in the prior art is shown in Table 1.
The fluorine removal feed ratio for the process of the present invention and the prior art process is shown in Table 1 assuming a wastewater volume of 1L.
TABLE 1 comparison of defluorination feedstocks for the process of the present invention and the prior art process
As can be seen from Table 1, in the treatment of 1L wastewater by the method of the present invention, compared with the prior art, the method of the present invention significantly reduces the amount of calcium hydroxide and calcium carbonate added, when calcium hydroxide + calcium carbonate is mixed, but calcium carbonate is mixed with H under acidic conditions+Reaction to produce a large amount of CO2The gas generates a large amount of foam, which affects the fluorine removal process and causes the rapid decrease of the fluorine removal efficiency, so although the adding amount is reduced to a certain extent, the rapid decrease of the fluorine removal efficiency causes the poor treatment effect, and compared with the mixed adding of calcium hydroxide and calcium carbonate, the method of the invention also has obvious decrease of the adding amount of the calcium hydroxide and the calcium carbonate, and the added calcium hydroxide and the calcium carbonate are mixed and addedCalcium carbonate is added only when the system is started, and is not needed to be added in the later period. Therefore, when a large amount of mixed acid wastewater in the photovoltaic industry is treated, the method provided by the invention can greatly reduce the addition of raw materials, has high defluorination efficiency and is beneficial to popularization.
The treatment results of the mixed acid wastewater in the photovoltaic industry of examples 1 to 5 are shown in Table 2.
Table 2 examples 1-5 results of mixed acid wastewater treatment in photovoltaic industry
As can be seen from Table 2, the fluoride ion concentration of the method is lower than 10mg/L before the calcium ion removal reaction, the emission standard is met, the calcium ion removal reaction does not need to be carried out again in the subsequent process, and the recovery rate of the obtained by-product is 95.0-99.0%; the purity of the by-product is 90.0-98.0%.
The present invention and its embodiments have been described in detail in the foregoing for illustrative purposes, and the description is not intended to be limiting, and the embodiments shown in the drawings are only one embodiment of the present invention, and the actual flow is not limited thereto. Therefore, if the person skilled in the art receives the teaching, without departing from the spirit of the invention, the person skilled in the art shall not inventively design the similar structural modes and embodiments to the technical solution, but shall fall within the scope of the invention.

Claims (8)

1. A resource recovery method of mixed acid wastewater in photovoltaic industry is characterized by comprising the following steps: the method comprises a fluorine removal step, wherein the fluorine removal step comprises two fluorine removal steps, calcium hydroxide emulsion is added in the first fluorine removal step, calcium carbonate is added in the second fluorine removal step, and the fluorine removal step comprises the following steps:
a) respectively guiding the wastewater into a first defluorination pool and a second defluorination pool, wherein the volume ratio of the wastewater guided into the first defluorination pool to the wastewater guided into the second defluorination pool is (1-3): (3-1), controlling the pH value of the first defluorination pool to be 4-6;
b) adding calcium hydroxide emulsion into the first defluorination tank, and introducing the first defluorination tank mud-water mixture into a second defluorination tank;
c) adding calcium carbonate into the second fluorine removal tank for treatment;
the method further comprises the steps of:
1) introducing a mud-water mixture obtained after adding calcium carbonate into the second defluorination tank into a first sedimentation tank for treatment, measuring the concentration of calcium ions in the supernatant, and introducing the supernatant into a softening tank;
2) adding carbonate into the softening tank, precipitating and recycling the formed calcium carbonate into a second defluorination tank, introducing the mud-water mixture into a second precipitation tank for treatment, and treating the supernatant through an electrodialyzer to obtain a byproduct.
2. The resource recovery method of the mixed acid wastewater in the photovoltaic industry according to claim 1, characterized in that: and in the first step of defluorination, the molar concentration of the fluorine ions is measured, and the molar concentration of the calcium ions in the added calcium hydroxide emulsion is 30-40% of that of the fluorine ions in the first defluorination pool.
3. The resource recovery method of the mixed acid wastewater in the photovoltaic industry according to claim 1 or 2, characterized in that: and in the second fluorine removal step, the molar concentration of fluorine ions is measured, and the molar concentration of calcium ions added into the calcium carbonate is 54-60% of that of the fluorine ions in the second fluorine removal tank.
4. The resource recovery method of the mixed acid wastewater in the photovoltaic industry according to claim 3, characterized in that: the carbonate is any one of sodium carbonate and potassium carbonate.
5. The resource recovery method of the mixed acid wastewater in the photovoltaic industry according to claim 4, characterized in that: the molar concentration of carbonate ions in the carbonate in the step 2) is 150-200% of the molar concentration of calcium ions in the supernatant.
6. The resource recovery method of the mixed acid wastewater in the photovoltaic industry according to claim 5, characterized in that: and a nanofiltration unit is added behind the second sedimentation tank, the supernatant of the second sedimentation tank is led into the nanofiltration unit for quality separation and desalination, and the divalent ions in the wastewater are removed and then led into an electrodialyzer.
7. The resource recovery method of the mixed acid wastewater in the photovoltaic industry according to claim 6, characterized in that: the pH value of the inlet water of the electrodialyzer is acidic.
8. The resource recovery method of the mixed acid wastewater in the photovoltaic industry according to claim 7, characterized in that: the salt content of the concentrated water of the electrodialyzer is 15.0-20.0%, the salt content of the fresh water of the electrodialyzer is 0.1-0.5%, and the salt content of the electrodialyzer is 1-3 grades.
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CN101823799A (en) * 2009-03-06 2010-09-08 昆山工研院华科生物高分子材料研究所有限公司 Method for treating acidic fluorine-containing waste water
CN105502782A (en) * 2015-12-07 2016-04-20 湖南湘牛环保实业有限公司 Technology for recovering water resources and salt from coking wastewater in coal chemical industry

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