CN111747565A - Zero-discharge and chromium-recovery method for chromium-containing wastewater in steel industry - Google Patents

Zero-discharge and chromium-recovery method for chromium-containing wastewater in steel industry Download PDF

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CN111747565A
CN111747565A CN202010617403.6A CN202010617403A CN111747565A CN 111747565 A CN111747565 A CN 111747565A CN 202010617403 A CN202010617403 A CN 202010617403A CN 111747565 A CN111747565 A CN 111747565A
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chromium
wastewater
water
tank
reduction
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张垒
舒纯
俞琴
王丽娜
刘璞
刘尚超
付本全
卢丽君
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Wuhan Iron and Steel Co Ltd
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Wuhan Iron and Steel 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
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01GCOMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G37/00Compounds of chromium
    • C01G37/02Oxides or hydrates thereof
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01PINDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00Physical properties of inorganic compounds
    • C01P2006/80Compositional purity
    • 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
    • C02F1/001Processes for the treatment of water whereby the filtration technique is of importance
    • 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
    • C02F1/02Treatment 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
    • C02F1/44Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/441Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
    • 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
    • C02F1/44Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/444Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by ultrafiltration or microfiltration
    • 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
    • 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
    • C02F1/5281Installations for water purification using chemical agents
    • 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
    • C02F1/54Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using organic material
    • C02F1/56Macromolecular compounds
    • 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
    • C02F1/70Treatment of water, waste water, or sewage by reduction
    • 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
    • C02F2001/007Processes including a sedimentation step
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00Nature of the contaminant
    • C02F2101/10Inorganic compounds
    • C02F2101/20Heavy metals or heavy metal compounds
    • C02F2101/22Chromium or chromium compounds, e.g. chromates
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/16Nature of the water, waste water, sewage or sludge to be treated from metallurgical processes, i.e. from the production, refining or treatment of metals, e.g. galvanic wastes
    • CCHEMISTRY; METALLURGY
    • 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
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2303/00Specific treatment goals
    • C02F2303/04Disinfection
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02ATECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A20/00Water conservation; Efficient water supply; Efficient water use
    • Y02A20/124Water desalination
    • Y02A20/131Reverse-osmosis
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00Technologies relating to chemical industry
    • Y02P20/10Process efficiency
    • Y02P20/129Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines

Abstract

The invention relates to a zero discharge and chromium recovery method of chromium-containing wastewater in the steel industry, the chromium-containing wastewater generated in the steel rolling procedure is sent into a wastewater adjusting tank for pretreatment, a flocculating agent is added into the wastewater adjusting tank for precipitation, and sludge is discharged and sent to sintering treatment; supernatant wastewater in the wastewater regulating tank is sequentially sent into a multi-media filter and a security filter for filtration treatment, then sequentially sent into a microfiltration membrane component for filtration and a reverse osmosis membrane component for desalination, produced water desalted by the reverse osmosis membrane component is recycled into a circulating water system to replace fresh water or soft water, and reverse osmosis concentrated water is sent into a reduction tank for reduction and detoxification; after detoxificationContaining Cr (OH)3The suspension enters a spray evaporation system and is spray dried to generate Cr (OH)3A crude product; mixing Cr (OH)3And placing the crude product in a calcining furnace, and calcining at 1050-1150 ℃ to obtain the chromium green crude product. The beneficial effects are that: the occupied area is small, the operation is stable, and zero discharge of waste water and recycling of chromium resources are realized.

Description

Zero-discharge and chromium-recovery method for chromium-containing wastewater in steel industry
Technical Field
The invention relates to the technical field of chromium-containing wastewater treatment, in particular to a zero-discharge and chromium-recovery method for chromium-containing wastewater in the steel industry.
Background
The chromium-containing wastewater from steel rolling process (cold rolling, silicon steel) mainly comes from partial high-valence chromium solution sprayed when passivating the surface of steel plate with high-valence chromium-containing compound (such as chromic acid) passivating solution and wastewater generated by washing ground, and water-soluble Cr contained in the wastewater6+It is very toxic and is a carcinogen, often CrO4 2-And Cr2O7 2-The form of (a) is difficult to handle and dispose of.
The conventional treatment technologies at present comprise a physical method (adsorption, membrane method and ion exchange method), a chemical method (precipitation and reduction), a physical-chemical method (electrodialysis) and a biological method and related combined processes and the like, the methods can achieve chromium removal in different degrees, and the effects on the detoxification of hexavalent chromium are good, but the methods all have the problems in the aspect of recycling of subsequent chromium elements, and have high operation cost and no advantages in the aspect of engineering. The most common treatment process in the actual industry is to reduce Cr (VI) into Cr (III) in two stages by adopting a sodium sulfite (sodium bisulfite) reduction method, then add alkali (sodium hydroxide, lime, flocculating agent and the like) for precipitation to generate sludge containing Cr (III), discharge the wastewater after the discharged water Cr (VI) reaches the water pollution emission standard (GB13456-2012) of the steel industry, and the conventional treatment method has the problems of large occupied area, high treatment cost, more sludge, excessive hexavalent chromium, secondary pollution of chromium mud, incapability of recycling chromium resources, and environmental risk possibly caused by improper treatment of hazardous waste outsourcing.
Disclosure of Invention
The invention aims to provide a zero discharge and chromium recovery method for chromium-containing wastewater in the steel industry, which improves the clean production level of steel rolling procedures in the steel industry, realizes zero discharge of chromium wastewater on one hand, and recovers chromium resources for main pigments of ceramic coatings on the other hand, thereby thoroughly solving the problem of secondary pollution of chromium, avoiding environmental risks and increasing the environmental benefits and the economic benefits of enterprises.
The technical scheme for solving the technical problems is as follows: a zero discharge and chromium recovery method for chromium-containing wastewater in the steel industry comprises the following steps:
s100, sending chromium-containing wastewater generated in the steel rolling process into a wastewater adjusting tank for pretreatment, adding a flocculating agent into the wastewater adjusting tank for precipitation, and discharging sludge for sintering treatment;
s200, sequentially feeding supernatant wastewater in the wastewater adjusting tank into a multi-media filter and a security filter for filtration treatment, sequentially feeding the supernatant wastewater into a microfiltration membrane component for filtration and a reverse osmosis membrane component for desalination, recycling produced water desalted by the reverse osmosis membrane component into a circulating water system to replace fresh water or soft water, and feeding reverse osmosis concentrated water into a reduction tank for reduction and detoxification;
s300, detoxicated Cr (OH)3The suspension enters a spray evaporation system and is spray dried to generate Cr (OH)3A crude product;
s400, mixing Cr (OH)3And placing the crude product in a calcining furnace, and calcining at 1050-1150 ℃ to obtain the chromium green crude product.
Further, in step S100, the flocculants are PAC and PAM.
Further, the coagulation conditions were: the stirring speed is 50r/min, the adding amount of PAC and PAM is respectively 8 mg/L-15 mg/L and 0.5 mg/L-1.5 mg/L, and the hydraulic retention time is 30 min-60 min.
Further, the mass percent of PAC is 3 wt%; the mass percent of PAM is 2 wt%.
Further, in step S200,
the multi-medium filter removes suspended matters, colloids, bacteria, microorganisms and viruses with the particle size of more than 15 mu m in the wastewater;
the cartridge filter removes suspended matters and colloid with the particle size of more than 5 mu m in the wastewater;
the micro-filtration membrane component removes insoluble substances and suspended particles with the particle size of 0.1-15 mu m in the wastewater.
Further, the reduction pool comprises a primary reduction pool, a secondary reduction pool and a neutralization pool;
dilute sulfuric acid is added into the first-stage reduction tank and the second-stage reduction tank, the pH value is adjusted to 2-3, and then NaHSO is added3Solution reducing agent and Cr in concentrated water6+Fully reacting under the stirring condition, wherein the hydraulic retention time is HRT 120 min-180 min, and the reaction formula is as follows: cr (chromium) component2O7 2-+3HSO3-+5H+→2Cr3++3SO4 2-+4H2O;
The wastewater in the primary reduction pool enters a secondary reduction pool in a self-flowing mode;
controlling the oxidation-reduction potential ORP of the solution in the primary reduction pool to be 200 mV-230 mV, controlling the pH of the solution to be 2.5-3 and controlling the HRT to be 60 min-90 min;
controlling the oxidation-reduction potential ORP of the solution in the secondary reduction pool to be 160 mV-180 mV, controlling the pH of the solution to be 2-2.5 and controlling the HRT to be 60 min-90 min;
feeding the chromium-containing wastewater reduced by the secondary reduction tank into a neutralization tank, adjusting the pH value to 8-9, and adding Cr in the water3+Formation of Cr (OH)3A suspension having the formula: cr (chromium) component3++3OH-→Cr(OH)3↓。
Further, the mass concentration of the dilute sulfuric acid is 10-15%; NaHSO3The mass percentage of the solution is 30 wt% -35 wt%.
Further, step S300 is specifically as follows:
detoxicated Cr (OH)3The waste water enters a spray evaporation system, is sprayed into a drying tower by 5-50 mu m fog drops through an atomizing nozzle, and is in countercurrent contact with hot air in the drying tower to carry out heat transfer, and the water content of the fog drops in the tower is quickly transferredQuickly evaporated to dryness, containing Cr (OH)3Dense droplet crystallization to obtain Cr (OH)3And (5) crude product.
Further, the high-temperature flue gas waste heat of the calcining furnace returns to the spray evaporation system.
Compared with the traditional chromium-containing sewage treatment method, the method has the advantages of small occupied area and stable operation, realizes zero discharge of wastewater and recycling of chromium resources, and is embodied in the following aspects:
1) as the membrane method advanced treatment and recycling system is adopted, about 70 percent of wastewater is recycled for the system, thereby thoroughly solving the problems of large occupied area, much sludge and excessive hexavalent chromium of the traditional steel rolling chromium-containing wastewater and realizing zero discharge of the wastewater;
2) the method recovers Cr (OH) from about 30 percent of reverse osmosis concentrated water through a primary reduction pool, a secondary reduction pool, a neutralization pool and a spray evaporation system3Compared with a lime milk adding process, the lime-green solid mixture reduces more than 95% of dangerous sludge waste, and has remarkable environmental and economic benefits;
3) chromium in the chromium mud is recovered to obtain chromium green crude products with different purities, the chromium green crude products are used as main pigments of ceramic coatings, and the waste heat of high-temperature flue gas of a calcining furnace is returned to a spray evaporation system to realize waste heat utilization, so that the recovery and the waste heat utilization of the chromium are realized, and the chromium green spray evaporation system has better environmental protection benefit and economic benefit and saves more energy and reduces consumption;
4) compared with photocatalysis, ultraviolet catalysis and the like, the method has good hexavalent chromium reduction effect and high efficiency, is not influenced by factors such as external light source, power supply, catalyst loss, more side reaction and the like, and has the hexavalent chromium reduction rate (detoxification effect) of 100 percent;
5) and (3) pretreatment: the chromium wastewater is pretreated by adopting a multi-media filter, a cartridge filter and a microfiltration membrane component for suspended matters and colloidal substances contained in the chromium wastewater respectively, so that the service life of a reverse osmosis membrane component is prolonged, and transmembrane pressure difference is reduced; by pretreatment followed by treatment of CrO4 2-And Cr2O7 2-In the form of (A) is subjected to a reverse osmosis treatment based on CrO4 2-And Cr2O7 2-The ionic radius is far larger than that of Cr3+Radius of ionTherefore CrO4 2-And Cr2O7 2-Ions cannot pass through the reverse osmosis membrane, so that the quality of produced water is ensured;
6) the chromium concentration in the chromium wastewater passing through the reverse osmosis membrane module is high, the reaction rate is high, the efficiency is high, and the hexavalent chromium is completely reduced basically through the secondary reduction reaction and the ORP regulation.
Drawings
FIG. 1 is a flow chart of the zero discharge of chromium-containing wastewater and chromium recovery method in the steel industry.
Detailed Description
The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.
A zero discharge and chromium recovery method for chromium-containing wastewater in the steel industry comprises the following specific processes:
s100, sending chromium-containing wastewater generated in the steel rolling process into a wastewater adjusting tank for pretreatment, adding a flocculating agent into the wastewater adjusting tank for precipitation, and discharging sludge for sintering treatment;
s200, sequentially feeding supernatant wastewater in the wastewater adjusting tank into a multi-media filter and a security filter for filtration treatment, sequentially feeding the supernatant wastewater into a microfiltration membrane component for filtration and a reverse osmosis membrane component for desalination, recycling produced water desalted by the reverse osmosis membrane component into a circulating water system to replace fresh water or soft water, and feeding reverse osmosis concentrated water into a reduction tank for reduction and detoxification;
s300, detoxicated Cr (OH)3The suspension enters a spray evaporation system and is spray dried to generate Cr (OH)3A crude product;
s400, mixing Cr (OH)3And placing the crude product in a calcining furnace, and calcining at 1050-1150 ℃ to obtain the chromium green crude product.
The obtained chrome green crude product is used as a main pigment of ceramic paint, and the waste heat of the high-temperature flue gas of the calcining furnace returns to a spray evaporation system to realize waste heat utilization.
S100 specifically includes: flocculating agents added into the wastewater regulating tank are PAC (polyaluminium chloride) and PAM (polyacrylamide), the mass percent of PAC is 3 wt%, the mass percent of PAM is 2 wt%, and the coagulation conditions are as follows: the stirring speed is 50r/min, the adding amount of PAC and PAM is 8 mg/L-15 mg/L and 0.5 mg/L-1.5 mg/L respectively, the hydraulic retention time is 30 min-60 min, the aim is to remove suspended matters, colloids and the like in the chromium-containing wastewater, sludge in a wastewater adjusting tank is pumped to a sludge sedimentation tank through a sludge pump, and the sludge is dewatered and sintered after a certain amount of sludge is accumulated.
S200 specifically includes: sending the supernatant wastewater into a multi-media filter for filtering treatment, removing suspended matters, colloids, bacteria, microorganisms, viruses and the like with the particle size of more than 15 microns in the wastewater, reducing membrane biological pollution of a subsequent cartridge filter, and sending backwashing water of the multi-media filter to a wastewater adjusting tank;
after being filtered by a multi-medium filter, the supernatant wastewater enters a cartridge filter, the cartridge filter removes suspended matters and colloid with the particle size of more than 5 microns in the wastewater and reduces transmembrane pressure difference and membrane biological pollution of subsequent membrane modules, backwashing water of the cartridge filter is sent to a wastewater adjusting tank, and produced water is sent to a microfiltration membrane module;
the produced water flowing out of the cartridge filter enters a microfiltration membrane component for filtration, insoluble substances and suspended particles with the particle size of 0.1-15 μm are removed, the produced water is sent to a Reverse Osmosis (RO) membrane for desalination, and the backwashing water of the microfiltration membrane component returns to a wastewater adjusting tank;
the produced water (65-75% water content) after desalination by Reverse Osmosis (RO) membrane is reused in a circulating water system to replace new water or soft water, and reverse osmosis concentrated water containing a large amount of chromium salt, sulfate, chloride salt and the like is sent to a reduction tank for reduction and detoxification.
The reduction tank comprises a first-stage reduction tank, a second-stage reduction tank and a neutralization tank, reverse osmosis concentrated water is firstly sent into the first-stage reduction tank and then automatically flows into the second-stage reduction tank,
adding dilute sulfuric acid into the primary reduction tank, adjusting the pH value to 2-3, and adding NaHSO3Solution reducing agent and Cr in concentrated water6+Fully reacting under the stirring condition, wherein the hydraulic retention time is HRT 120 min-180 min, and the reaction formula is as follows: cr (chromium) component2O7 2-+3HSO3-+5H+→2Cr3++3SO4 2-+4H2O, the mass concentration of dilute sulphuric acid is 10-15 percent%,NaHSO3The mass percentage of the solution is 30-35 wt%;
adding dilute sulfuric acid into the secondary reduction tank, adjusting the pH value to 2-3, and adding NaHSO3Solution reducing agent and Cr in concentrated water6+Fully reacting under the stirring condition, wherein the hydraulic retention time is HRT 120 min-180 min, and the reaction formula is as follows: cr (chromium) component2O7 2-+3HSO3-+5H+→2Cr3++3SO4 2-+4H2O, the mass concentration of dilute sulphuric acid is 10 to 15 percent, and NaHSO3The mass percentage of the solution is 30-35 wt%;
controlling the oxidation-reduction potential ORP of the solution in the primary reduction pool to be 200 mV-230 mV, controlling the pH of the solution to be 2.5-3 and controlling the HRT to be 60 min-90 min;
controlling the oxidation-reduction potential ORP of the solution in the secondary reduction pool to be 160 mV-180 mV, controlling the pH of the solution to be 2-2.5 and controlling the HRT to be 60 min-90 min;
feeding the chromium-containing wastewater reduced by the secondary reduction tank into a neutralization tank, adjusting the pH value to 8-9, and adding Cr in the water3+Formation of Cr (OH)3A suspension having the formula: cr (chromium) component3++3OH-→Cr(OH)3↓。
S300 specifically includes: detoxicated Cr (OH)3The waste water enters a spray evaporation system, fog drops with the size of 5-50 mu m are sprayed into a drying tower through an atomizing nozzle, the drying tower is in countercurrent contact with hot air to carry out heat transfer, the water of the fog drops in the drying tower is quickly evaporated to dryness and contains Cr (OH)3Dense droplet crystallization to obtain Cr (OH)3The heat sources of the crude product and the spray evaporation system are from the high-temperature flue gas waste heat of a heating furnace/a heat treatment furnace in a steel rolling procedure and the flue gas waste heat of a calcining furnace, and the temperature is 300-400 ℃.
Example 1
Referring to a flow chart of a method for zero discharge of chromium-containing wastewater and chromium recovery in the steel industry shown in figure 1, the method is carried out according to the following flow:
adding PAC (polyaluminium chloride) and PAM (polyacrylamide) into the chromium-containing wastewater from the steel rolling process in a wastewater adjusting tank, wherein the mass percent of PAC is 3 wt%, the mass percent of PAM is 2 wt%, and the coagulation conditions are as follows: stirring at a speed of 50r/min, adding amounts of PAC and PAM of 8mg/L and 1.5mg/L respectively, and hydraulic retention time of 45min, wherein the aim is to remove suspended matters and colloid in wastewater, sludge in a wastewater adjusting tank is pumped to a sludge sedimentation tank through a sludge pump, and after a certain amount of sludge is accumulated, the sludge is dehydrated and sent to sintering treatment;
after passing through a wastewater adjusting tank, the chromium-containing wastewater is sent into a multi-media filter for pretreatment, suspended matters, colloids, turbidity, bacteria, microorganisms, viruses and the like which are more than 15 mu m in the wastewater are removed, membrane biological pollution of a subsequent cartridge filter is reduced, and backwashing water of the multi-media filter is sent into the wastewater adjusting tank;
the cartridge filter removes suspended matters and colloid with the particle size of more than 5 mu m in the wastewater and reduces transmembrane pressure difference and membrane biological pollution of subsequent membrane modules, backwashing water of the cartridge filter is sent to a wastewater adjusting tank, and produced water is sent to a microfiltration membrane module;
filtering the produced water in a microfiltration membrane component to remove insoluble substances and suspended particles with the particle size of 0.1-15 μm, desalting the produced water by a Reverse Osmosis (RO) membrane, and returning the backwashing water of the microfiltration membrane component to a wastewater-containing regulating reservoir;
the produced water (65-75% water content) after desalination by a Reverse Osmosis (RO) membrane is recycled to a circulating water system to replace new water or soft water, and reverse osmosis concentrated water containing a large amount of chromium salt is sent to a reduction tank for reduction and detoxification;
the reverse osmosis concentrated water is firstly sent into a first-stage reduction pool and then automatically flows into a second-stage reduction pool, the oxidation-reduction potential ORP of the solution of the first-stage reduction pool is controlled at 200mV, the pH value of the solution is 3, and the HRT is 90 min; controlling oxidation-reduction potential ORP in the secondary reduction pool at 180mV, controlling solution pH at 2 and HRT for 60min, feeding the chromium-containing wastewater reduced by the secondary reduction pool into a neutralization pool, adjusting pH to 8, and controlling Cr in the water3+Formation of Cr (OH)3The suspension is sent into a spray evaporation system for crystallization;
Cr(OH)3the suspension is sent to a spray evaporation system, is sprayed into a drying tower through an atomizing nozzle in the form of 5-50 micron fog drops, and is in countercurrent contact with hot air in the drying tower to transfer heat, and the water of the fog drops in the drying tower is evaporated to dryness rapidly and contains Cr (OH) due to small volume and large specific surface area of the fog drops3Dense droplet crystallization to obtain Cr (OH)3The heat source of the crude product and the spray evaporation system is from a heating furnace/heat of a steel rolling processTreating the high-temperature flue gas waste heat of the furnace and the flue gas waste heat of the calcining furnace at the temperature of 330 ℃;
spray drying produced Cr (OH)3Calcining the crude product in a calciner at 1050 ℃ to obtain a chromium green crude product which can be used as a main pigment of ceramic paint; the hot flue gas of the calcining furnace returns to a spray evaporation system for waste heat utilization.
Table 1 shows the raw water, product water physical property parameters and chromium green purity of the chromium wastewater in example 1:
TABLE 1
Example 2:
referring to a flow chart of a method for zero discharge of chromium-containing wastewater and chromium recovery in the steel industry shown in figure 1, the method is carried out according to the following flow:
adding PAC (polyaluminium chloride) and PAM (polyacrylamide) into the chromium-containing wastewater from the steel rolling process in a wastewater adjusting tank, wherein the mass percent of PAC is 3 wt%, the mass percent of PAM is 2 wt%, and the coagulation conditions are as follows: stirring at a speed of 50r/min, adding amounts of PAC and PAM of 12mg/L and 1mg/L respectively, and hydraulic retention time of 60min, wherein the aim is to remove suspended matters and colloids in wastewater, sludge in a wastewater adjusting tank is pumped to a sludge sedimentation tank through a sludge pump, and sludge is dewatered and conveyed to sintering treatment after a certain amount of sludge is accumulated;
after passing through a wastewater adjusting tank, the chromium-containing wastewater is sent into a multi-media filter for pretreatment, suspended matters, colloids, turbidity, bacteria, microorganisms, viruses and the like which are more than 15 mu m in the wastewater are removed, membrane biological pollution of a subsequent cartridge filter is reduced, and backwashing water of the multi-media filter is sent into the wastewater adjusting tank;
the cartridge filter removes suspended matters and colloid with the particle size of more than 5 mu m in the wastewater and reduces transmembrane pressure difference and membrane biological pollution of subsequent membrane modules, backwashing water of the cartridge filter is sent to a wastewater adjusting tank, and produced water is sent to a microfiltration membrane module;
filtering the produced water in a microfiltration membrane component to remove insoluble substances and suspended particles with the particle size of 0.1-15 μm, desalting the produced water by a Reverse Osmosis (RO) membrane, and returning the backwashing water of the microfiltration membrane component to a wastewater-containing regulating reservoir;
the produced water (65-75% water content) after desalination by a Reverse Osmosis (RO) membrane is recycled to a circulating water system to replace new water or soft water, and reverse osmosis concentrated water containing a large amount of chromium salt is sent to a reduction tank for reduction and detoxification;
the reverse osmosis concentrated water is firstly sent into a first-stage reduction pool and then automatically flows into a second-stage reduction pool, the oxidation-reduction potential ORP of the solution of the first-stage reduction pool is controlled at 215mV, the pH of the solution is 2.8, and the HRT is 80 min; controlling oxidation-reduction potential ORP in the secondary reduction pool at 170mV, controlling solution pH at 2.3 and HRT for 70min, feeding the chromium-containing wastewater reduced by the secondary reduction pool into a neutralization pool, adjusting pH to 8.5, and controlling Cr in water3+Formation of Cr (OH)3The suspension is sent into a spray evaporation system for crystallization;
Cr(OH)3the suspension is sent to a spray evaporation system, is sprayed into a drying tower through an atomizing nozzle in the form of 5-50 micron fog drops, and is in countercurrent contact with hot air in the drying tower to transfer heat, and the water of the fog drops in the drying tower is evaporated to dryness rapidly and contains Cr (OH) due to small volume and large specific surface area of the fog drops3Dense droplet crystallization to obtain Cr (OH)3Crude products, wherein the heat source of a spray evaporation system is from the high-temperature flue gas waste heat of a heating furnace/a heat treatment furnace in a steel rolling procedure and the flue gas waste heat of a calcining furnace, and the temperature is 330 ℃;
spray drying produced Cr (OH)3Calcining the crude product in a calcining furnace at 1100 ℃ to obtain a chromium green crude product which can be used as a main pigment of ceramic paint; the hot flue gas of the calcining furnace returns to a spray evaporation system for waste heat utilization.
Table 2 shows the raw water, product water physical property parameters and chromium green purity of the chromium wastewater in example 2:
TABLE 2
Example 3:
referring to a flow chart of a method for zero discharge of chromium-containing wastewater and chromium recovery in the steel industry shown in figure 1, the method is carried out according to the following flow:
adding PAC (polyaluminium chloride) and PAM (polyacrylamide) into the chromium-containing wastewater from the steel rolling process in a wastewater adjusting tank, wherein the mass percent of PAC is 3 wt%, the mass percent of PAM is 2 wt%, and the coagulation conditions are as follows: stirring at a speed of 50r/min, adding amounts of PAC and PAM of 15mg/L and 0.5mg/L respectively, and hydraulic retention time of 30min, wherein the aim is to remove suspended matters and colloid in wastewater, sludge in a wastewater adjusting tank is pumped to a sludge sedimentation tank through a sludge pump, and after a certain amount of sludge is accumulated, the sludge is dehydrated and sent to sintering treatment;
after passing through a wastewater adjusting tank, the chromium-containing wastewater is sent into a multi-media filter for pretreatment, suspended matters, colloids, turbidity, bacteria, microorganisms, viruses and the like which are more than 15 mu m in the wastewater are removed, membrane biological pollution of a subsequent cartridge filter is reduced, and backwashing water of the multi-media filter is sent into the wastewater adjusting tank;
the cartridge filter removes suspended matters and colloid with the particle size of more than 5 mu m in the wastewater and reduces transmembrane pressure difference and membrane biological pollution of subsequent membrane modules, backwashing water of the cartridge filter is sent to a wastewater adjusting tank, and produced water is sent to a microfiltration membrane module;
filtering the produced water in a microfiltration membrane component to remove insoluble substances and suspended particles with the particle size of 0.1-15 μm, desalting the produced water by a Reverse Osmosis (RO) membrane, and returning the backwashing water of the microfiltration membrane component to a wastewater-containing regulating reservoir;
the produced water (65-75% water content) after desalination by a Reverse Osmosis (RO) membrane is recycled to a circulating water system to replace new water or soft water, and reverse osmosis concentrated water containing a large amount of chromium salt is sent to a reduction tank for reduction and detoxification;
the reverse osmosis concentrated water is firstly sent into a first-stage reduction pool and then automatically flows into a second-stage reduction pool, the oxidation-reduction potential ORP of the solution of the first-stage reduction pool is controlled at 230mV, the pH value of the solution is 3, and the HRT is 90 min; controlling oxidation-reduction potential ORP in the secondary reduction pool at 180mV, controlling solution pH at 2 and HRT for 60min, feeding the chromium-containing wastewater reduced by the secondary reduction pool into a neutralization pool, adjusting pH to 9, and controlling Cr in the water3+Formation of Cr (OH)3The suspension is sent into a spray evaporation system for crystallization;
Cr(OH)3the suspension is sent to a spray evaporation system and sprayed into a drying tower through an atomizing nozzle in 5-50 micron fog dropsThe drying tower is in countercurrent contact with hot air for heat transfer, and the fog drops have small volume and large specific surface area, so that the water content of the fog drops in the tower is quickly evaporated to dryness and contains Cr (OH)3Dense droplet crystallization to obtain Cr (OH)3Crude products, wherein the heat source of a spray evaporation system is from the high-temperature flue gas waste heat of a heating furnace/a heat treatment furnace in a steel rolling procedure and the flue gas waste heat of a calcining furnace, and the temperature is 330 ℃;
spray drying produced Cr (OH)3Calcining the crude product in a calciner at 1150 ℃ to obtain a chromium green crude product which can be used as a main pigment of ceramic paint; the hot flue gas of the calcining furnace returns to a spray evaporation system for waste heat utilization.
Table 3 shows the raw water, product water physical property parameters and chromium green purity of the chromium wastewater in example 3:
TABLE 3
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims (9)

1. A zero discharge and chromium recovery method for chromium-containing wastewater in the steel industry is characterized by comprising the following steps:
s100, sending chromium-containing wastewater generated in the steel rolling process into a wastewater adjusting tank for pretreatment, adding a flocculating agent into the wastewater adjusting tank for precipitation, and discharging sludge for sintering treatment;
s200, sequentially feeding supernatant wastewater in the wastewater adjusting tank into a multi-media filter and a security filter for filtration treatment, sequentially feeding the supernatant wastewater into a microfiltration membrane component for filtration and a reverse osmosis membrane component for desalination, recycling produced water desalted by the reverse osmosis membrane component into a circulating water system to replace fresh water or soft water, and feeding reverse osmosis concentrated water into a reduction tank for reduction and detoxification;
s300, detoxicated Cr (OH)3The suspension enters a spray evaporation system and is sprayed and driedDrying to produce Cr (OH)3A crude product;
s400, mixing Cr (OH)3And placing the crude product in a calcining furnace, and calcining at 1050-1150 ℃ to obtain the chromium green crude product.
2. The method for zero discharge of chromium-containing wastewater and chromium recovery in the steel industry as claimed in claim 1, wherein in the step S100, the flocculating agent is PAC and PAM.
3. The method for zero discharge of chromium-containing wastewater and chromium recovery in the steel industry as claimed in claim 2, wherein the coagulation conditions are as follows: the stirring speed is 50r/min, the adding amount of PAC and PAM is respectively 8 mg/L-15 mg/L and 0.5 mg/L-1.5 mg/L, and the hydraulic retention time is 30 min-60 min.
4. The method for zero discharge of chromium-containing wastewater and chromium recovery in the steel industry as claimed in claim 3, wherein the PAC is 3 wt%; the mass percent of the PAM is 2 wt%.
5. The method for zero discharge of chromium-containing wastewater and recovery of chromium in steel industry as claimed in claim 1, wherein in step S200,
the multi-medium filter removes suspended matters, colloids, bacteria, microorganisms and viruses with the particle size of more than 15 mu m in the wastewater;
the cartridge filter removes suspended matters and colloid with the particle size of more than 5 mu m in the wastewater;
the micro-filtration membrane component removes insoluble substances and suspended particles with the particle size of 0.1-15 mu m in the wastewater.
6. The zero discharge and chromium recovery method for chromium-containing wastewater in the steel industry as claimed in claim 5, wherein the reduction tank comprises a primary reduction tank, a secondary reduction tank and a neutralization tank;
dilute sulfuric acid is added into the first-stage reduction tank and the second-stage reduction tank, the pH value is adjusted to 2-3, and then NaHSO is added3Solution reducing agent and Cr in concentrated water6+Stirring the mixtureFully reacting under the stirring condition, wherein the hydraulic retention time is HRT 120-180 min, and the reaction formula is as follows: cr (chromium) component2O7 2-+3HSO3-+5H+→2Cr3++3SO4 2-+4H2O;
The wastewater in the primary reduction pool enters a secondary reduction pool in a self-flowing mode;
controlling the oxidation-reduction potential ORP of the solution in the primary reduction pool to be 200 mV-230 mV, controlling the pH of the solution to be 2.5-3 and controlling the HRT to be 60 min-90 min;
controlling the oxidation-reduction potential ORP of the solution in the secondary reduction pool to be 160 mV-180 mV, controlling the pH of the solution to be 2-2.5 and controlling the HRT to be 60 min-90 min;
feeding the chromium-containing wastewater reduced by the secondary reduction tank into a neutralization tank, adjusting the pH value to 8-9, and adding Cr in the water3+Formation of Cr (OH)3A suspension having the formula: cr (chromium) component3++3OH-→Cr(OH)3↓。
7. The method for zero discharge of chromium-containing wastewater and chromium recovery in the steel industry as claimed in claim 6, wherein the mass concentration of the dilute sulfuric acid is 10% -15%; the NaHSO3The mass percentage of the solution is 30 wt% -35 wt%.
8. The method for zero discharge of chromium-containing wastewater and chromium recovery in the steel industry according to claim 1, wherein the step S300 is as follows:
detoxicated Cr (OH)3The waste water enters a spray evaporation system, fog drops with the size of 5-50 mu m are sprayed into a drying tower through an atomizing nozzle, the drying tower is in countercurrent contact with hot air to carry out heat transfer, the water of the fog drops in the drying tower is quickly evaporated to dryness and contains Cr (OH)3Dense droplet crystallization to obtain Cr (OH)3And (5) crude product.
9. The method for zero discharge of chromium-containing wastewater and chromium recovery in the steel industry as claimed in claim 1, wherein the high-temperature flue gas waste heat of the calciner is returned to the spray evaporation system.
CN202010617403.6A 2020-06-30 2020-06-30 Zero-discharge and chromium-recovery method for chromium-containing wastewater in steel industry Pending CN111747565A (en)

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