1. A resource treatment device for washing water in sodium-method ferric phosphate production is characterized by comprising a pretreatment system, a membrane concentration and purification system and an evaporative crystallization system; wherein the washing water is connected to the water inlet of the pretreatment system, the sludge outlet of the pretreatment system sends out sludge cakes, and the water outlet of the pretreatment system sends out the effluent of the pretreatment system to the No. 1 water inlet of the membrane concentration and purification system; pure water is sent out from a water outlet of the membrane concentration and purification system, backflow concentrated water is sent out from a concentrated water outlet of the membrane concentration and purification system to a backflow water inlet of the pretreatment system, a liquid outlet of the membrane concentration and purification system is sent out of a liquid outlet of the membrane concentration and purification system to a liquid inlet of the evaporative crystallization system, condensed water is sent out from a water outlet of the evaporative crystallization system to a No. 2 water inlet of the membrane concentration and purification system, and anhydrous sodium sulphate is sent out from a salt outlet of the evaporative crystallization system; a resource treatment device for washing water produced by sodium-method ferric phosphate is characterized in that firstly a pretreatment system is utilized to remove phosphate ions, heavy metal ions and suspended matters in the washing water; then, concentrating the sodium sulfate in the pretreated effluent by using a membrane concentration and purification system, and purifying the purified water for recycling; finally, centrifugally separating anhydrous sodium sulphate by using an evaporative crystallization system; the aim of recycling treatment of the washing water in the sodium method ferric phosphate production is fulfilled.

2. The recycling treatment device for the washing water produced by the sodium-method iron phosphate according to claim 1, which is characterized in that the structure of the pretreatment system comprises a washing water tank, a primary reaction tank, a primary sedimentation tank, a secondary reaction tank, a secondary sedimentation tank, an immersed ultrafiltration device, an intermediate water tank, a weak acid resin exchange bed, a sodium hydroxide and phosphorus removal agent adding device, a sodium hydroxide adding device, a sulfuric acid adding device, a resin regeneration and medicine adding device, a sludge concentration tank, a filter press, a filter pressing liquid tank, a lifting pump, a suction pump, a booster pump, a backwashing pump, a sludge pump, a pressure filtrate reflux pump and a backwashing fan; wherein the washing water is connected to the water inlet of the washing water tank, the water outlet of the washing water tank is connected with the water inlet of the first-stage reaction tank through a lift pump, the medicine outlet of the sodium hydroxide and phosphorus removing agent adding device is connected to the medicine inlet of the first-stage reaction tank, the water outlet of the first-stage reaction tank is connected to the water inlet of the first-stage sedimentation tank, the water outlet of the first-stage sedimentation tank is connected to the water inlet of the second-stage reaction tank, the medicine outlet of the sodium hydroxide adding device is connected to the medicine inlet of the second-stage reaction tank, the water outlet of the second-stage reaction tank is connected to the water inlet of the second-stage sedimentation tank, the water outlet of the second-stage sedimentation tank is connected to the water inlet of the immersed ultrafiltration device, the water outlet of the sulfuric acid adding device is also connected to the water inlet of the immersed ultrafiltration device, the water outlet of the immersed ultrafiltration device is connected with the No. 1 water inlet of the intermediate water tank through a suction pump, the reflux concentrated water is connected to the No. 2 water inlet of the intermediate water tank, and the No. 1 water outlet of the intermediate water tank is connected with the backwash pump, the air outlet of the backwashing fan is connected to the backwashing air inlet of the immersed ultrafiltration device; a backwashing water outlet of the immersed ultrafiltration device, a sludge discharge port of the primary sedimentation tank and a sludge discharge port of the secondary sedimentation tank are all connected to a sludge inlet of a sludge concentration tank, a sludge outlet of the sludge concentration tank is connected with a sludge inlet of a filter press through a sludge pump, a sludge cake is sent out from a sludge discharge port of the filter press, a pressure filtrate outlet of the filter press is connected to a No. 1 water inlet of a pressure filtrate tank, and a water outlet of the pressure filtrate tank is connected with a reflux water inlet of a washing water tank through a pressure filtrate reflux pump; the No. 2 water outlet of the middle water tank is connected with the water inlet of the weak acid resin exchange bed through a booster pump, the medicine outlet of the resin regeneration medicine adding device is connected to the regeneration medicine inlet of the weak acid resin exchange bed, the regeneration water outlet of the weak acid resin exchange bed is connected to the No. 2 water inlet of the filter pressing liquid pool, and the water outlet of the weak acid resin exchange bed is sent out of the pretreatment system.

3. The recycling treatment device for the washing water produced by the sodium-method iron phosphate according to claim 1, which is characterized in that the membrane concentration and purification system structurally comprises a primary scale inhibitor adding device, a concentrated water scale inhibitor adding device, a primary security filter, a primary reverse osmosis device, a primary reverse osmosis concentrated water tank, a concentrated water security filter, an ultrahigh pressure reverse osmosis device, an ultrahigh pressure reverse osmosis concentrated water tank, a primary reverse osmosis produced water tank, a secondary security filter, a secondary reverse osmosis device, a secondary reverse osmosis produced water tank, a tertiary security filter, an electrodeionization device, a pure water tank, a primary high-pressure pump, a concentrated water booster pump, a high-pressure plunger pump, a liquid supply pump, a secondary booster pump, a secondary high-pressure pump, a tertiary booster pump and a pure water delivery pump; the water outlet of the pretreatment system is connected to the water inlet of a first-stage cartridge filter, the drug outlet of a first-stage scale inhibitor adding device is also connected to the water inlet of the first-stage cartridge filter, the water outlet of the first-stage cartridge filter is connected with the water inlet of a first-stage reverse osmosis device through a first-stage high-pressure pump, the concentrated water outlet of the first-stage reverse osmosis device is connected to the water inlet of a first-stage reverse osmosis concentrated water tank, the water outlet of the first-stage reverse osmosis concentrated water tank is connected with the water inlet of a concentrated water cartridge filter through a concentrated water booster pump, the drug outlet of the concentrated water scale inhibitor adding device is also connected to the water inlet of the concentrated water cartridge filter, the water outlet of the concentrated water cartridge filter is connected with the water inlet of an ultrahigh-pressure reverse osmosis device through a high-pressure plunger pump, the concentrated water outlet of the ultrahigh-pressure reverse osmosis device is connected to the water inlet of the ultrahigh-pressure reverse osmosis concentrated water tank, and the water outlet of the ultrahigh-pressure reverse osmosis concentrated water tank is pumped out of the membrane purification system; the water outlet of the first-stage reverse osmosis device and the water outlet of the ultrahigh-pressure reverse osmosis device are connected to the No. 1 water inlet of the first-stage reverse osmosis water production tank, condensed water is connected to the No. 2 water inlet of the first-stage reverse osmosis water production tank, the water outlet of the first-stage reverse osmosis water production tank is connected with the water inlet of the second-stage safety filter through a second-stage booster pump, the water outlet of the second-stage safety filter is connected with the water inlet of the second-stage reverse osmosis device, the water outlet of the second-stage reverse osmosis water production tank is connected with the water inlet of the third-stage safety filter through a third-stage booster pump, the water outlet of the third-stage safety filter is connected with the water inlet of the electrodeionization device, the pure water outlet of the electrodeionization device is connected to the water inlet of the pure water tank, and pure water is pumped out from the water outlet of the pure water tank through a pure water delivery pump; and a concentrated water outlet of the secondary reverse osmosis device and a concentrated water outlet of the electrodeionization device send out backflow concentrated water.

4. The recycling device for washing water in the production of iron phosphate by sodium method according to claim 1, characterized in that the evaporative crystallization system structurally comprises a preheater, a 1# heat exchanger, an evaporator, a 2# heat exchanger, a crystallization separator, a condensed water tank, a steam compressor, a thickener, a centrifugal separator, a centrifugal mother liquor tank, a delivery pump, a discharge pump, a 1# circulating pump, a 2# circulating pump, a condensed water pump and a mother liquor pump; wherein, the water outlet of the membrane concentration system is connected with the liquid inlet of the preheater, the liquid outlet of the preheater is connected with the liquid inlet of the 1# heat exchanger, the liquid outlet of the 1# heat exchanger is connected with the liquid inlet of the evaporator, the circulating liquid outlet of the evaporator is connected with the circulating liquid inlet of the 1# heat exchanger through the 1# circulating pump, the liquid outlet of the evaporator is connected with the liquid inlet of the 2# heat exchanger through the delivery pump, the liquid outlet of the 2# heat exchanger is connected with the liquid inlet of the crystallization separator, and the circulating liquid outlet of the crystallization separator is connected with the circulating liquid inlet of the 2# heat exchanger through the 2# circulating pump; a steam outlet of the evaporator and a steam outlet of the crystallization separator are connected to a steam inlet of a steam compressor, and a high-pressure steam outlet of the steam compressor is connected to a steam inlet of the No. 1 heat exchanger and a steam inlet of the No. 2 heat exchanger; a condensed water outlet of the No. 1 heat exchanger and a condensed water outlet of the No. 2 heat exchanger are connected to a water inlet of a condensed water tank, a water outlet of the condensed water tank is connected with a hot water inlet of the preheater through a condensed water pump, and condensed water is sent out from a hot water outlet of the preheater; the discharge port of the crystallization separator is connected with the feed port of the thickener through a discharge pump, the discharge port of the thickener is connected to the feed port of the centrifugal separator, and the salt outlet of the centrifugal separator sends anhydrous sodium sulphate out; the filtrate outlet of the centrifugal separator is connected to the liquid inlet of the centrifugal mother liquid tank, and the liquid outlet of the centrifugal mother liquid tank is also connected to the circulating liquid inlet of the 2# heat exchanger through the mother liquid pump.

5. The resource treatment method for the washing water produced by the sodium-method iron phosphate as claimed in claim 1, which is characterized by comprising the following steps:

1) through a pretreatment system, reacting, precipitating and filtering washing water generated in the production of sodium-method iron phosphate, and removing phosphate ions, heavy metal ions and suspended matters in an oxidation mother liquor;

2) through the membrane concentration and purification system, the TDS of the pretreated effluent is concentrated to 120-180 g/L concentrated water, and pure water with the TDS not more than 0.2mg/L is produced.

3) And evaporating and crystallizing 99% of anhydrous sodium sulphate in the membrane concentrated solution through an evaporation and crystallization system, and finally achieving the purpose of recycling treatment of the washing water in the sodium-method iron phosphate production.

6. The resource treatment method of the washing water produced by the sodium-method iron phosphate according to claim 5, characterized in that the step 1) is implemented by a pretreatment system, specifically, 30% of sodium hydroxide and 10% of phosphorus removal agent are added into a primary reaction tank, the pH value of the washing water is adjusted from 2.0-3.5 to 5.0-6.0, phosphate ions are removed by using a primary sedimentation tank, 30% of sodium hydroxide is added into a secondary reaction tank, the pH value is adjusted to 8.0-9.5, heavy metal ions are removed by using a secondary sedimentation tank, the pH value is adjusted back to 6.5-7.5 by adding 50% of sulfuric acid, and the concentration of the residual fine iron phosphate, metal hydroxide crystals and suspended matters in the waste liquid is effectively filtered through immersed ultrafiltration filtration with the membrane aperture being less than or equal to 50nm, and the concentration of the suspended matters in the pretreated liquid is controlled to be less than or equal to 0.1 mg/L; automatically carrying out air-water combined backwashing for 30-90 seconds every 30-90 minutes by the immersed ultrafiltration device so as to maintain long-term stable operation of the immersed ultrafiltration; and (5) carrying out outward transportation treatment on the precipitated sludge and the sludge cake obtained by backwashing, draining and press-filtering.

7. The recycling treatment method of the washing water produced by sodium ferric phosphate according to claim 5, characterized in that the step 2) is implemented by a membrane concentration and purification system, specifically, by two-stage concentration of 6-8 times of first-stage reverse osmosis and 2-4 times of ultrahigh pressure reverse osmosis on the pretreated effluent with TDS concentration of 4000-8000 mg/L, the TDS concentration of the concentrated water is concentrated to 120-180 g/L, and the sodium sulfate concentration is 12-18%; meanwhile, the three-stage purification is formed by the desalination rate of more than 98 percent of the first-stage reverse osmosis, the desalination rate of more than 90 percent of the second-stage reverse osmosis and the desalination rate of more than 90 percent of the electrodeionization device, and pure water with the TDS concentration of less than or equal to 0.2mg/L is produced.

8. The resource treatment method of the washing water liquid produced by the sodium-method iron phosphate according to claim 5, characterized in that in the step 3), secondary steam is compressed to 90-100 ℃ by an evaporative crystallization system, specifically, a steam compressor aiming at sodium sulfate with the concentration of 12-18% in a membrane concentrated solution, 99% of anhydrous sodium sulfate is separated by forced circulation heat exchange evaporative concentration and then forced circulation heat exchange crystallization, and the feed liquid is preheated by condensed water and then sent back to the membrane concentration purification system for deep purification, so that the purpose of resource treatment of the washing water produced by the sodium-method iron phosphate is finally realized.

Background

The ferric phosphate is an ideal precursor of lithium iron phosphate which is a positive electrode material of the lithium ion battery. At present, two main production process paths of the iron phosphate exist. One is the ammonium method iron phosphate production technology, utilize ferrous sulfate to add hydrogen peroxide solution earlier and turn the ferrous iron into ferric iron, react with phosphoric acid again, control the pH value of reaction through throwing diammonium hydrogen phosphate or aqueous ammonia simultaneously, synthesize the iron phosphate, except a small amount of heavy metal in the production waste water that produces, mainly be ammonium ion, phosphate radical ion, sulfate radical ion. The other is a sodium method iron phosphate production process, namely ferrous sulfate and hydrogen peroxide are firstly utilized to oxidize ferrous iron into ferric iron, and then the ferric iron is reacted with phosphoric acid, except that sodium hydroxide is added to control the pH value of the reaction, the iron phosphate is synthesized, and the produced production wastewater mainly contains sodium ions, phosphate ions and sulfate ions except a small amount of heavy metals.

The wastewater produced by the sodium-method ferric phosphate can be divided into three types according to the production process and the wastewater quality. The first is oxidation mother liquor which mainly contains high-concentration sodium sulfate, a small amount of heavy metal ions and sodium phosphate, is phosphorus-containing high-salt wastewater and is seriously polluted. The second is aging mother liquor which mainly contains dilute phosphoric acid, a small amount of heavy metal ions and sodium sulfate and is a precious phosphoric acid resource. The third is washing water which mainly contains a small amount of heavy metal ions, sodium phosphate and sodium sulfate and is the salt-containing wastewater containing phosphorus and heavy metals. The invention mainly aims at the washing water generated in the production of sodium-method iron phosphate and provides a device and a method for recycling the washing water generated in the production of the sodium-method iron phosphate.

Disclosure of Invention

The invention provides a resourceful treatment device and a resourceful treatment method for washing water produced by sodium-method iron phosphate, aiming at solving the problem that the washing water produced by the sodium-method iron phosphate contains a small amount of heavy metal ions, sodium phosphate and sodium sulfate, and the typical washing water comprises the following components: PO (PO)₄ ^3-(phosphate radical) 350-650 mg/L, Na⁺1290-2400 mg/L, SO of (sodium ion)₄ ^2-(sulfate radical) 2370-4400 mg/L, Fe³⁺(iron ion) 10-30 mg/L, Mg²⁺(magnesium ion) 30-70 mg/L, Mn²⁺(manganese ion) 5-15 mg/L, Ca²⁺3-7 mg/L, Si (calcium ion) (silicon) 3-7 mg/L, SS (suspended substance) 5-15 mg/L, TDS (dissolved total solid) 4060-7580 mg/L, pH 2.0-3.5. Washing water resource produced by sodium method ferric phosphateFirstly, removing phosphate ions, heavy metal ions and suspended matters in washing water by using a pretreatment system, and controlling the concentration of the suspended matters in pretreated outlet water to be less than or equal to 0.1 mg/L; then, concentrating the TDS concentration in the pretreated effluent from 4000-8000 mg/L to 120-180 g/L by using a membrane concentration and purification system, simultaneously obtaining pure water with the TDS concentration less than or equal to 0.2mg/L, and recycling the pure water to the sodium-method iron phosphate production process; finally, 99 percent of anhydrous sodium sulfate (anhydrous sodium sulfate) is centrifugally separated by an evaporative crystallization system.

The immersed ultrafiltration membrane in the pretreatment system is made of PVDF (polyvinylidene fluoride), is acid-resistant and alkali-resistant, has long service life, has the membrane pore diameter less than or equal to 50nm, and has high filtration precision and good effect; the ultrahigh pressure reverse osmosis device in the membrane concentration system adopts a 120 kg-grade ultrahigh pressure composite membrane, the TDS of the ultrahigh pressure reverse osmosis concentrated water can reach 12-18%, the evaporation capacity is reduced, and therefore the operating cost of the system is reduced.

The technical solution of the invention is as follows: the sodium-method iron phosphate production washing water recycling treatment device structurally comprises a pretreatment system, a membrane concentration and purification system and an evaporative crystallization system; wherein the washing water is connected to the water inlet of the pretreatment system, the sludge outlet of the pretreatment system sends out sludge cakes, and the water outlet of the pretreatment system sends out the effluent of the pretreatment system to the No. 1 water inlet of the membrane concentration and purification system; pure water is sent out from a water outlet of the membrane concentration and purification system, backflow concentrated water is sent out from a concentrated water outlet of the membrane concentration and purification system to a backflow water inlet of the pretreatment system, a liquid outlet of the membrane concentration and purification system is sent out of a liquid outlet of the membrane concentration and purification system to a liquid inlet of the evaporative crystallization system, condensed water is sent out from a water outlet of the evaporative crystallization system to a No. 2 water inlet of the membrane concentration and purification system, and anhydrous sodium sulphate is sent out from a salt outlet of the evaporative crystallization system; a resource treatment device for washing water produced by sodium-method ferric phosphate is characterized in that firstly a pretreatment system is utilized to remove phosphate ions, heavy metal ions and suspended matters in the washing water; then, concentrating the sodium sulfate in the pretreated effluent by using a membrane concentration and purification system, and purifying the purified water for recycling; finally, centrifugally separating anhydrous sodium sulphate by using an evaporative crystallization system; the aim of recycling treatment of the washing water in the sodium method ferric phosphate production is fulfilled.

The invention has the advantages that the device and the method for recycling the washing water produced by the sodium-method ferric phosphate are used for removing phosphate ions, heavy metal ions and suspended matters in the washing water by utilizing a pretreatment system and controlling the concentration of the suspended matters in the pretreated outlet water to be less than or equal to 0.1mg/L aiming at the characteristic that the washing water produced by the sodium-method ferric phosphate contains a small amount of heavy metal ions, sodium phosphate and sodium sulfate; then, concentrating the TDS concentration in the pretreated effluent from 4000-8000 mg/L to 120-180 g/L by using a membrane concentration and purification system, simultaneously obtaining pure water with the TDS concentration less than or equal to 0.2mg/L, and recycling the pure water to the sodium-method iron phosphate production process; finally, an evaporative crystallization system is used for centrifugally separating 99 percent of anhydrous sodium sulphate; thereby realizing the purpose of recycling the washing water in the sodium-method iron phosphate production.

Drawings

FIG. 1 is a schematic diagram of the general structure of a washing water resource treatment device for sodium-method iron phosphate production.

In the drawing, WW represents washing water, SC represents mud cake, PW represents pure water, SSDH represents anhydrous sodium sulphate, CLW represents condensed water, BCW represents backflow concentrated water, PTO represents effluent of a pretreatment system, MSO represents effluent of a membrane concentration and purification system, PTS represents a pretreatment system, MCPS represents a membrane concentration and purification system, and MVRS represents an evaporative crystallization system.

FIG. 2 is a schematic structural diagram of a pretreatment system of a washing water recycling treatment device for sodium-method iron phosphate production.

In the figure, PTS represents a pretreatment system, WW represents washing water, SC represents mud cake, BCW represents backflow concentrated water, PTO represents pretreatment system outlet water, WWT represents a washing water tank, and RT₁Denotes a first-order reaction tank, ST₁Denotes the primary sedimentation tank, RT₂Denotes a secondary reaction tank, ST₂Representing a secondary sedimentation tank, SUF an immersion ultrafiltration unit, MT an intermediate water tank, WACB a weak acid resin exchange bed, D₁₁Means for adding sodium hydroxide and phosphorus-removing agent D₁₂Means for sodium hydroxide addition apparatus D₁₃Indicating sulfuric acid addition apparatus, D₁₄Showing a resin regeneration dosing device, SCT showing a sludge concentration tank, PF showing a filter press, FLT showing a filter pressing liquid tank, P₁₁Denotes a lift pump, P₁₂Denotes a suction pump, P₁₃Showing a booster pump, P₁₄The back-wash pump is shown,P₁₅indicating a sludge pump, P₁₆The pressure filtrate reflux pump is shown, and the backwashing fan is shown.

FIG. 3 is a schematic structural diagram of a membrane concentration and purification system of a recycling treatment device for washing water in the production of iron phosphate by a sodium method.

In the figure, MCPS represents a membrane concentration purification system, PTO represents effluent of a pretreatment system, CLW represents condensate water, BCW represents backflow concentrated water, PW represents pure water, MSO represents effluent of the membrane concentration purification system, D₂₁Denotes a first-order scale inhibitor addition device, D₂₂Means for adding scale inhibitor to concentrate, SAF₁Indicating a first-level cartridge filter, RO₁Representing a first-stage reverse osmosis plant, CWT₁Showing a first-stage reverse osmosis concentrate tank, SAFC a concentrate cartridge filter, UHPRO an ultra-high pressure reverse osmosis unit, CWT₂Indicating an ultra-high pressure reverse osmosis concentrate tank, PWT₁Representing a first-stage reverse osmosis product water tank, SAF₂Indicating two-stage Security Filter, RO₂Showing a two-stage reverse osmosis unit, PWT₂Indicating a two-stage reverse osmosis product water tank, SAF₃Representing three-stage cartridge filters, EDI representing electrodeionization device, PWT₃Indicating pure water tank, P₂₁Indicating a first-stage high-pressure pump, P₂₂Indicates a concentrate booster pump, P₂₃Indicating a high-pressure plunger pump, P₂₄Denotes a liquid supply pump, P₂₅Indicating a two-stage booster pump, P₂₆Indicating a second-stage high-pressure pump, P₂₇Representing a three-stage booster pump, P₂₈A pure water supply pump is shown.

FIG. 4 is a schematic structural diagram of an evaporative crystallization system of a washing water recycling treatment device for sodium-method iron phosphate production.

In the drawing, MVRS represents an evaporative crystallization system, MSO represents effluent of a membrane concentration system, CLW represents condensed water, SSDH represents anhydrous sodium sulfate, PHE represents a preheater and CHE₁Showing a 1# heat exchanger, EVE showing an evaporator, CHE₂Denotes a 2# heat exchanger, CSE denotes a crystal separator, CLWT denotes a condensate tank, SPE denotes a vapor compressor, CE denotes a thickener, CFE denotes a centrifuge, CMLT denotes a centrifuge mother liquor tank, P₃₁Denotes a delivery pump, P₃₂Indicating discharge pump, P₃₃Denotes the 1# circulating pump, P₃₄Denotes 2# circulating pump, P₃₅Denotes a condensate pump, P₃₆The mother liquor pump is shown.

FIG. 5 is a process flow diagram of an embodiment of the recycling treatment of washing water in the production of iron phosphate by a sodium method.

FIG. 6 is a water quality and water quantity balance diagram of a washing water recycling treatment example in the sodium-method iron phosphate production.

Detailed Description

Referring to the attached figure 1, the washing water recycling treatment device for sodium-method iron phosphate production structurally comprises a pretreatment system PTS, a membrane concentration and purification system MCPS and an evaporative crystallization system MVRS; wherein the washing water WW is connected to a water inlet of the pretreatment system PTS, a mud outlet of the pretreatment system PTS sends out mud cakes SC, and a water outlet of the pretreatment system PTS sends out a pretreatment system water outlet PTO to a No. 1 water inlet of the membrane concentration purification system MCPS; pure water PW is sent out from a water outlet of the membrane concentration and purification system MCPS, backflow concentrated water BCW is sent out from a concentrated water outlet of the membrane concentration and purification system MCPS to a backflow water inlet of the pretreatment system PTS, a liquid outlet of the membrane concentration and purification system MCPS is sent out from a liquid outlet of the membrane concentration and purification system MSO to a liquid inlet of the evaporative crystallization system MVRS, condensed water CLW is sent out from a water outlet of the evaporative crystallization system MVRS to a No. 2 water inlet of the membrane concentration and purification system MCPS, and anhydrous sodium sulphate SSDH is sent out from a salt outlet of the evaporative crystallization system MVRS; a resource treatment device for washing water produced by sodium-method ferric phosphate is characterized in that firstly a pretreatment system is utilized to remove phosphate ions, heavy metal ions and suspended matters in the washing water; then, concentrating the sodium sulfate in the pretreated effluent by using a membrane concentration and purification system, and purifying the purified water for recycling; finally, centrifugally separating anhydrous sodium sulphate by using an evaporative crystallization system; the aim of recycling treatment of the washing water in the sodium method ferric phosphate production is fulfilled.

Referring to FIG. 2, the pretreatment system PTS comprises a wash water tank WWT and a primary reaction tank RT₁First-stage sedimentation tank ST₁Second stage reaction tank RT₂Second-stage sedimentation tank ST₂SUF, an intermediate water tank MT, a weak acid resin exchange bed WACB, and a sodium hydroxide and phosphorus removal agent feeding device D₁₁Sodium hydroxide adding device D₁₂Sulfuric acid adding device D₁₃Resin regeneration dosing device D₁₄Thickening the sludgeReducing pool SCT, filter press PF, filter pressing liquid pool FLT and lift pump P₁₁A suction pump P₁₂And a booster pump P₁₃And a backwash pump P₁₄And a sludge pump P₁₅Filtrate return pump P₁₆And a backwashing fan B; wherein the wash water WW is connected to the water inlet of the wash water tank WWT, and the water outlet of the wash water tank WWT is connected to the water inlet of the wash water tank WWT through the lift pump P₁₁With a first-stage reaction tank RT₁Is connected with a water inlet, and a sodium hydroxide and phosphorus removing agent adding device D₁₁The drug outlet is connected to a first-stage reaction tank RT₁The first-stage reaction tank RT₁The water outlet of the water tank is connected to a first-stage sedimentation tank ST₁Water inlet of the first-stage sedimentation tank ST₁The water outlet of the reaction tank is connected to a secondary reaction tank RT₂Water inlet, sodium hydroxide feeding device D₁₂The drug outlet is connected to a secondary reaction tank RT₂A medicine inlet of the second-stage reaction tank RT₂The water outlet of the water tank is connected to a secondary sedimentation tank ST₂Water inlet of the second-stage sedimentation tank ST₂The water outlet of the device is connected to the water inlet of an immersed ultrafiltration device SUF, and a sulfuric acid adding device D₁₃The drug outlet of the device is also connected to the water inlet of the SUF of the immersed ultrafiltration device, and the water outlet of the SUF of the immersed ultrafiltration device passes through the suction pump P₁₂The No. 1 water inlet of the intermediate water tank MT, the backflow concentrated water BCW is connected to the No. 2 water inlet of the intermediate water tank MT, and the No. 1 water outlet of the intermediate water tank MT is connected with the No. 2 water inlet of the intermediate water tank MT through the backwashing pump P₁₄The air outlet of the backwashing fan B is connected to the backwashing air inlet of the immersed ultrafiltration device SUF; backwash water outlet of SUF (submerged Ultrafiltration) device and primary sedimentation tank ST (sludge test)₁And a second-stage sedimentation tank ST₂All the sludge discharge ports are connected to a sludge inlet of a sludge concentration tank SCT, and a sludge outlet of the sludge concentration tank SCT passes through a sludge pump P₁₅The sludge inlet of the filter press PF is connected with the sludge outlet of the filter press PF, the sludge outlet of the filter press PF delivers sludge cakes SC, the filter liquor outlet of the filter press PF is connected to the No. 1 water inlet of the filter liquor pool FLT, and the water outlet of the filter liquor pool FLT passes through the filter liquor reflux pump P₁₆Is connected with a return water inlet of the wash water tank WWT; the 2# water outlet of the middle water tank MT passes through a booster pump P₁₃Connected with the water inlet of the WACB of the weak acid resin exchange bed, and a resin regeneration dosing device D₁₄The medicine outlet is connected to the regeneration inlet of the WACBA medicine port, wherein a regeneration water outlet of the weak acid resin exchange bed WACB is connected to a No. 2 water inlet of the filter pressing liquid pool FLT, and a water outlet of the weak acid resin exchange bed WACB is sent out of a pre-treatment system water outlet PTO; through a pretreatment system, specifically, adding 30% of sodium hydroxide and 10% of phosphorus removal agent into a primary reaction tank, adjusting the pH value of washing water from 2.0-3.5 to 5.0-6.0, removing phosphate ions by using a primary sedimentation tank, adding 30% of sodium hydroxide into a secondary reaction tank, adjusting the pH value to 8.0-9.5, removing heavy metal ions by using a secondary sedimentation tank, adjusting the pH value back to 6.5-7.5 by adding 50% of sulfuric acid, filtering by immersion ultrafiltration with the membrane aperture less than or equal to 50nm, effectively filtering out residual fine iron phosphate and metal hydroxide crystals and suspended matters in waste liquid, and controlling the concentration of the suspended matters in a pretreated liquid to be less than or equal to 0.1 mg/L; automatically carrying out air-water combined backwashing for 30-90 seconds every 30-90 minutes by the immersed ultrafiltration device so as to maintain long-term stable operation of the immersed ultrafiltration; and (5) carrying out outward transportation treatment on the precipitated sludge and the sludge cake obtained by backwashing, draining and press-filtering.

Referring to the attached figure 3, the membrane concentration and purification system MCPS structurally comprises a primary scale inhibitor feeding device D₂₁Concentrated water scale inhibitor feeding device D₂₂SAF filter₁First-stage reverse osmosis device RO₁First-stage reverse osmosis concentrated water tank CWT₁SAFETY FILTER SAF FOR CONCENTRATED WATER_CUHPRO (ultra high pressure) reverse osmosis device and CWT (ultra high pressure) reverse osmosis concentrated water tank₂First-level reverse osmosis water producing tank PWT₁SAF filter of two-stage safety filter₂Second stage reverse osmosis device RO₂Secondary reverse osmosis water producing tank PWT₂SAF filter with three stages₃EDI and pure water tank PWT of electric deionizing device₃First-stage high-pressure pump P₂₁And a concentrated water booster pump P₂₂High pressure plunger pump P₂₃And a liquid feed pump P₂₄Second stage booster pump P₂₅Second-stage high-pressure pump P₂₆Three-stage booster pump P₂₇Pure water delivery pump P₂₈(ii) a Wherein the output water PTO of the pretreatment system is connected to a first-stage security filter SAF₁Water inlet, first-level scale inhibitor feeding device D₂₁The medicine outlet is also connected with a first-stage security filter SAF₁Water inlet (2)First-level security filter SAF₁The water outlet of the pump passes through a first-stage high-pressure pump P₂₁RO with a first-stage reverse osmosis device₁Is connected with the water inlet of the first-stage reverse osmosis device RO₁The concentrated water outlet is connected to a first-stage reverse osmosis concentrated water tank CWT₁The first-level reverse osmosis concentrated water tank CWT₁The water outlet of the water pump passes through a concentrated water booster pump P₂₂SAFETY FILTER SAF WITH CONCENTRATED WATER_CThe water inlets of the two devices are connected, and a concentrated water scale inhibitor feeding device D₂₂The drug outlet is also connected to a SAF filter of concentrated water_CThe SAF filter is arranged at the water inlet of the concentrated water_CThe water outlet of the pump passes through a high-pressure plunger pump P₂₃Connected with the water inlet of the ultra-high pressure reverse osmosis device UHPRO, and the concentrated water outlet of the ultra-high pressure reverse osmosis device UHPRO is connected to the ultra-high pressure reverse osmosis concentrated water tank CWT₂The water inlet of the water tank is a super-high pressure reverse osmosis concentrated water tank CWT₂The water outlet of the water pump passes through a liquid supply pump P₂₄Sending the effluent MSO of the membrane concentration purification system; first-stage reverse osmosis device RO₁The water outlet of the water production device and the water production outlet of the ultra-high pressure reverse osmosis device UHPRO are connected to a first-stage reverse osmosis water production tank PWT₁1# water inlet, the condensed water CLW is connected to a first-level reverse osmosis water production tank PWT₁2# water inlet, first-level reverse osmosis water production tank PWT₁The water outlet of the water pump passes through a secondary booster pump P₂₅And a secondary security filter SAF₂Connected with the water inlet of the filter, a secondary security filter SAF₂The water outlet of the water pump passes through a second-stage high-pressure pump P₂₆With a second-stage reverse osmosis unit RO₂Is connected with the water inlet of the second-stage reverse osmosis device RO₂The water production outlet is connected to a secondary reverse osmosis water production tank PWT₂Water inlet of the water tank, a secondary reverse osmosis water production tank PWT₂The water outlet of the water pump passes through a three-stage booster pump P₂₇And three-stage security filter SAF₃Connected with the water inlet of the three-stage security filter SAF₃The water outlet of the water tank is connected to the water inlet of the electrodeionization device EDI, and the pure water outlet of the electrodeionization device EDI is connected to the pure water tank PWT₃Water inlet, pure water tank PWT₃The water outlet of the water pump passes through a pure water delivery pump P₂₈Pure water PW is sent out; two-stage reverse osmosis device RO₂The concentrated water outlet of the electric deionization device EDI and the concentrated water outlet of the electric deionization device EDI are sent out to return concentrated water BCW; purification by membrane concentrationThe system specifically comprises a step of concentrating the TDS concentration of concentrated water to 120-180 g/L and the sodium sulfate concentration to 12-18% by utilizing two-stage concentration of 6-8 times of first-stage reverse osmosis and 2-4 times of ultrahigh-pressure reverse osmosis aiming at pretreated effluent with the TDS concentration of 4000-8000 mg/L; meanwhile, the three-stage purification is formed by the desalination rate of more than 98 percent of the first-stage reverse osmosis, the desalination rate of more than 90 percent of the second-stage reverse osmosis and the desalination rate of more than 90 percent of the electrodeionization device, and pure water with the TDS concentration of less than or equal to 0.2mg/L is produced.

Referring to the attached figure 4, the evaporative crystallization system MVRS structurally comprises a preheater PHE and a No. 1 heat exchanger CHE₁EVE evaporator and 2# heat exchanger CHE₂A crystallization separator CSE, a condensate water tank CLWT, a vapor compressor SPE, a thickener CE, a centrifuge CFE, a centrifuge mother liquor tank CMLT and a delivery pump P₃₁A discharge pump P₃₂1# circulating pump P₃₃2# circulating pump P₃₄Condensate pump P₃₅Mother liquor pump P₃₆(ii) a Wherein the effluent MSO of the membrane concentration system is connected to the liquid inlet of a preheater PHE, and the liquid outlet of the preheater PHE is connected to a # 1 heat exchanger CHE₁Liquid inlet of (1) # Heat exchanger CHE₁The liquid outlet of the evaporator EVE is connected with the liquid inlet of the evaporator EVE, and the circulating liquid outlet of the evaporator EVE passes through a 1# circulating pump P₃₃And 1# Heat exchanger CHE₁The circulation liquid inlet of the evaporator EVE is connected with the circulation liquid inlet of the evaporator EVE, and the liquid outlet of the evaporator EVE is connected with the circulation liquid inlet of the evaporator EVE through a delivery pump P₃₁And 2# Heat exchanger CHE₂The liquid inlet of the heat exchanger is connected with the heat exchanger CHE No. 2₂The liquid outlet of the crystallization separator is connected to the liquid inlet of a crystallization separator CSE, and the circulating liquid outlet of the crystallization separator CSE passes through a No. 2 circulating pump P₃₄And 2# Heat exchanger CHE₂The circulating liquid inlets are connected; the steam outlet of the evaporator EVE and the steam outlet of the crystallization separator CSE are connected to the steam inlet of the vapor compressor SPE, and the high-pressure steam outlet of the vapor compressor SPE is connected to the 1# heat exchanger CHE₁Steam inlet and 2# heat exchanger CHE₂The steam inlet of (a); 1# Heat exchanger CHE₁The condensate water outlet and the 2# heat exchanger CHE₂The condensed water outlet of the condensed water tank is connected to the water inlet of the condensed water tank CLWT, and the water outlet of the condensed water tank CLWT passes through a condensed water pump P₃₅The hot water outlet of the preheater PHE is used for sending out condensed water CLW; discharge of the crystallization separator CSEThe material port passes through a discharging pump P₃₂The discharging port of the thickener CE is connected with the feeding port of the centrifuge CFE, and the salt outlet of the centrifuge CFE sends anhydrous sodium sulphate SSDH; the filtrate outlet of the CFE of the centrifugal separator is connected to the liquid inlet of a centrifugal mother liquor tank CMLT, and the liquid outlet of the CMLT of the centrifugal mother liquor tank passes through a mother liquor pump P₃₆Is also connected to the 2# heat exchanger CHE₂The circulating liquid inlet; through an evaporative crystallization system, specifically, aiming at sodium sulfate with the concentration of 12-18% in a membrane concentrated solution, secondary steam is compressed at 90-100 ℃ by a steam compressor, evaporative concentration is carried out through forced circulation heat exchange, 99% of anhydrous sodium sulphate is separated through forced circulation heat exchange crystallization, feed liquor is preheated by condensed water and then is sent back to a membrane concentration purification system for deep purification, and finally the purpose of recycling treatment of washing water in sodium-method iron phosphate production is achieved.

The method for recycling the washing water produced by the sodium-method ferric phosphate comprises the following steps:

1) through a pretreatment system, reacting, precipitating and filtering washing water generated in the production of sodium-method iron phosphate, and removing phosphate ions, heavy metal ions and suspended matters in an oxidation mother liquor;

2) through the membrane concentration and purification system, the TDS of the pretreated effluent is concentrated to 120-180 g/L concentrated water, and pure water with the TDS not more than 0.2mg/L is produced.

3) And evaporating and crystallizing 99% of anhydrous sodium sulphate in the membrane concentrated solution through an evaporation and crystallization system, and finally achieving the purpose of recycling treatment of the washing water in the sodium-method iron phosphate production.

The step 1) is implemented through a pretreatment system, specifically, 30% of sodium hydroxide and 10% of phosphorus removal agent are added into a primary reaction tank, the pH value of washing water is adjusted to 5.0-6.0 from 2.0-3.5, phosphate ions are removed by using a primary sedimentation tank, 30% of sodium hydroxide is added into a secondary reaction tank, the pH value is adjusted to 8.0-9.5, heavy metal ions are removed by using the secondary sedimentation tank, the pH value is adjusted to 6.5-7.5 by adding 50% of sulfuric acid, and the residual fine iron phosphate, metal hydroxide crystals and suspended matters in waste liquid are effectively filtered through immersed ultrafiltration with the membrane aperture of less than or equal to 50nm, so that the concentration of the suspended matters in the pretreated liquid is controlled to be less than or equal to 0.1 mg/L; automatically carrying out air-water combined backwashing for 30-90 seconds every 30-90 minutes by the immersed ultrafiltration device so as to maintain long-term stable operation of the immersed ultrafiltration; and (5) carrying out outward transportation treatment on the precipitated sludge and the sludge cake obtained by backwashing, draining and press-filtering.

The step 2) is implemented through a membrane concentration and purification system, specifically, aiming at pretreated effluent with TDS concentration of 4000-8000 mg/L, two-stage concentration of 6-8 times of first-stage reverse osmosis and 2-4 times of ultrahigh pressure reverse osmosis is utilized to concentrate the TDS concentration of concentrated water to 120-180 g/L, and the sodium sulfate concentration is 12-18%; meanwhile, the three-stage purification is formed by the desalination rate of more than 98 percent of the first-stage reverse osmosis, the desalination rate of more than 90 percent of the second-stage reverse osmosis and the desalination rate of more than 90 percent of the electrodeionization device, and pure water with the TDS concentration of less than or equal to 0.2mg/L is produced.

And 3) compressing secondary steam at 90-100 ℃ by using a steam compressor, specifically aiming at the sodium sulfate with the concentration of 12-18% in the membrane concentrated solution, performing evaporative concentration by forced circulation heat exchange, crystallizing and separating 99% of anhydrous sodium sulfate by the forced circulation heat exchange, preheating the inlet liquid by condensed water, then feeding the preheated inlet liquid back to the membrane concentration and purification system for deep purification, and finally achieving the purpose of recycling the washing water in the sodium-process iron phosphate production.

Examples

The iron phosphate is produced by 5 ten thousand tons in a certain group company annually, a sodium method process is adopted for producing the iron phosphate, ferrous sulfate and hydrogen peroxide are firstly utilized to oxidize ferrous iron into ferric iron, then the ferric iron is reacted with phosphoric acid, the pH value of the reaction is controlled by adding sodium hydroxide to synthesize the iron phosphate, and the iron phosphate is aged by the phosphoric acid. Three types of wastewater are generated in the production process of the iron phosphate, wherein one type of wastewater is an oxidation mother liquor containing a large amount of sodium sulfate, a small amount of heavy metal ions and phosphate radical ions, the other type of wastewater is an aging mother liquor containing a large amount of dilute phosphoric acid, a small amount of heavy metal ions, suspended matters and sodium sulfate, and the third type of wastewater is low-concentration washing water containing a large amount of heavy metal ions, phosphate radical ions and sodium sulfate. The embodiment designs a set of resource treatment system for washing water produced by producing iron phosphate by a sodium method aiming at the characteristic that the washing water contains heavy metal ions, phosphate ions and sodium sulfate, and effectively recovers anhydrous sodium sulphate and pure water in the washing water.

1. Designing the washing water component and the waste water quantity

The water quality of the washing water produced by the sodium-method ferric phosphate is as follows (wherein the pH value is not a unit):

composition (I)	pH	Na+	SO4 2-	PO4 3-	Fe3+	Mg2+
							Concentration (mg/L)	2.7	1850	3380	500	25	50
Composition (I)	Mn2+	Ca2+	Si	TDS	SS
							Concentration (mg/L)	10	5	5	5820	10

The waste water amount of the washing water produced by the sodium method ferric phosphate is 280T/H.

2. Process flow

2.1 Process flow

The process flow is shown in the attached figure 5, and the process flow chart of the washing water recycling treatment embodiment in the sodium method iron phosphate production is shown in the figure.

2.2 flow sheet description

Washing water produced in the production of sodium-method iron phosphate enters a washing water tank, the washing water is pumped into a first-stage reaction tank and a first-stage sedimentation tank through a lift pump, 30% of sodium hydroxide and 10% of phosphorus removal agent are added into the first-stage reaction tank, the pH value of the washing water is adjusted to 5.5 +/-0.2 from 2.7, phosphate ions are removed by using the first-stage sedimentation tank, liquid outlet enters a second-stage reaction tank and a second-stage sedimentation tank, 30% of sodium hydroxide is added into the second-stage reaction tank to adjust the pH value to 9.0 +/-0.2, heavy metal ions are removed by using the second-stage sedimentation tank, water outlet enters an immersed type super-filter tank, the pH value is adjusted to 7.0 +/-0.2 by adding 50% of sulfuric acid, PVDF immersed type suction filtration with the membrane pore diameter of less than or equal to 50nm is carried out, residual fine iron phosphate, metal hydroxide crystals and suspended matters in the wastewater are effectively filtered, and the concentration of the suspended matters in the pretreated water outlet is controlled to be less than or equal to 0.1 mg/L; the immersed ultrafiltration device automatically carries out air-water combined backwashing for 1 minute every 60 minutes and manually carries out chemical cleaning for 6 months so as to maintain long-term stable operation of the immersed ultrafiltration; the immersed ultrafiltration backwashing liquid discharge, the sludge discharge of the primary sedimentation tank and the secondary sedimentation tank enter a sludge concentration tank, the sludge is pressurized by a sludge pump and then is pumped into a plate-and-frame filter press for sludge dehydration, a sludge cake is transported and disposed, and a filter press liquid is sent back to a washing water tank by a filter press liquid tank and a filter press liquid reflux pump for retreatment; the immersed ultrafiltration effluent enters an intermediate water tank, is pumped into a first-stage cartridge filter through a booster pump, is added with a scale inhibitor to protect a reverse osmosis membrane, is pumped into a first-stage reverse osmosis membrane through a first-stage high-pressure pump to carry out first-stage concentration and purification, and the first-stage reverse osmosis concentrated water is pumped into a 120 kg-stage ultrahigh-pressure reverse osmosis membrane group through a first-stage reverse osmosis concentrated water tank, the booster pump concentrated water cartridge filter and a high-pressure plunger pump in sequence to concentrate TDS (total dissolved solids) in the concentrated water to 15.2 percent and then is subjected to evaporative crystallization to separate 99 percent anhydrous sodium sulphate; the primary reverse osmosis produced water, the ultrahigh-pressure reverse osmosis produced water and evaporative crystallization condensate water are pumped into secondary reverse osmosis by a primary reverse osmosis produced water tank, a secondary booster pump, a secondary cartridge filter and a secondary high-pressure pump in sequence for secondary purification, the secondary reverse osmosis produced water enters an electrodeionization device by a secondary reverse osmosis produced water tank, a tertiary booster pump and a tertiary cartridge filter in sequence for tertiary purification, and pure water with TDS (Total dissolved solids) less than or equal to 0.2mg/L is produced; the second-stage reverse osmosis concentrated water and the electrodeionization concentrated water are returned to the first-stage reverse osmosis inlet water for retreatment.

3. Water quality and quantity balance

The water quality and water quantity balance of the washing water treatment system for the sodium-method ferric phosphate production is shown in the attached figure 6, which is a water quality and water quantity balance diagram of a recycling treatment embodiment of the washing water for the sodium-method ferric phosphate production.

4. System main equipment