Method for treating mercury-containing wastewater generated in calcium carbide method polyvinyl chloride production process

Abstract

The invention relates to the technical field of industrial wastewater treatment, in particular to a method for treating mercury-containing wastewater generated in a calcium carbide method polyvinyl chloride production process, which comprises the following steps of: 1, adjusting the pH value of the mercury-containing wastewater to be neutral; 2, adding polyaluminum chloride and polyacrylamide, stirring, standing and precipitating to obtain primary supernate; step 3, siphoning the first-stage supernate into a mercury removal reaction precipitation area for chemical precipitation to obtain second-stage supernate; 4, siphoning the second-stage supernate into a flocculent precipitation area for flocculent precipitation to obtain third-stage supernate; and 5, siphoning the third-stage supernate into a clear water area for storage. According to the invention, polyaluminum chloride and polyacrylamide are added into the adjusting tank for pre-flocculation and precipitation, so that precipitation and separation of iron chips which are wrapped with mercury and are easy to precipitate and catalyst particles are promoted; and supernate obtained after precipitation is absorbed by adopting a siphonage method, so that the disturbance of the supernate to bottom precipitates in the absorption process is effectively reduced, and the mercury removal efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial wastewater treatment, and particularly relates to a treatment method of mercury-containing wastewater generated in a production process of polyvinyl chloride by calcium carbide method. BACKGROUND

[0002] Polyvinyl chloride (PVC) is a polymer formed by free radical polymerization of vinyl chloride monomer under the action of initiators such as peroxides and azo compounds, or under the action of light and heat. PVC usually appears as white or light yellow powder, and its relative density is 1.35-1.45. Due to the strong adjustability of mechanical properties, good electrical insulation, excellent acid and alkali resistance and solvent resistance, and outstanding flame retardance, PVC is widely used in the fields of building materials, packaging, electronics and electrical appliances, daily necessities and medical treatment, industry and special fields.

[0003] The production process of polyvinyl chloride mainly includes two core links of preparation of vinyl chloride monomer and polymerization of vinyl chloride monomer. At present, the industrialized preparation methods of vinyl chloride monomer mainly include calcium carbide method and ethylene method. In the calcium carbide method, coal is the core raw material, and the method has the advantages of low raw material cost and short production process. In the calcium carbide method, the synthesis reaction of vinyl chloride is usually carried out in the presence of a mercury chloride (HgCl2) / activated carbon catalyst. Mercury chloride can reduce the activation energy of the reaction and improve the selectivity of vinyl chloride. However, mercury chloride is easy to sublimate and soluble in water. In the synthesis and subsequent treatment process of vinyl chloride monomer, mercury can enter the washing water body to form mercury-containing wastewater.

[0004] The generation of mercury-containing wastewater is directly related to the use, processing and recovery of mercury (or mercury-containing compounds). In addition to the production process of polyvinyl chloride by calcium carbide method, the chlor-alkali industry, the electronic and lighting industry, the instrument and medical equipment manufacturing industry, the precious metal smelting and recycling industry, and the chemical synthesis and pharmaceutical industry will also produce mercury-containing wastewater. The existing technology generally dilutes the mercury-containing wastewater with high mercury content (more than 2 mg / L) to reduce the concentration of mercury, and then uses chemical precipitation and flocculation precipitation to remove mercury. The dissolved mercury and suspended mercury in the mercury-containing wastewater are removed in turn. Since the mercury-containing wastewater contains particles such as iron rust, broken catalyst (activated carbon) with small particle size, and part of the mercury exists in the form of organic mercury, which is not easy to precipitate, the above-mentioned methods for removing mercury not only consume a large amount of mercury removal reagents and dilution water, but also have the problem of low mercury removal efficiency. SUMMARY

[0005] In view of the problems of large consumption of mercury removal reagent and dilution water and low mercury removal efficiency in the existing treatment method of mercury-containing wastewater, the present application provides a treatment method of mercury-containing wastewater generated in a calcium carbide method PVC production process, in which polyaluminum chloride and polyacrylamide are added to a conditioning tank for pre-flocculation and precipitation, so as to promote the precipitation and separation of iron filings and catalyst particles which wrap and contain mercury.

[0006] The technical scheme of the present application is as follows: A treatment method of mercury-containing wastewater generated in a calcium carbide method PVC production process, comprising the following steps: Step one: adding acid or alkali to the mercury-containing wastewater in the conditioning tank to adjust the pH value of the mercury-containing wastewater to neutral; Step two: adding polyaluminum chloride and polyacrylamide to the conditioning tank, and then stirring, standing and precipitating to obtain primary supernatant and primary sludge; Step three: siphoning the primary supernatant into a mercury removal reaction precipitation zone of a chemical reaction unit for chemical precipitation to obtain secondary supernatant and secondary sludge; using a sludge pump to pump the primary sludge into a filter press for pressure filtration; Step four: siphoning the secondary supernatant into a flocculation precipitation zone of the chemical reaction unit for flocculation precipitation to obtain tertiary supernatant and tertiary sludge; using a sludge pump to pump the secondary sludge into the filter press for pressure filtration; Step five: siphoning the tertiary supernatant into a clean water zone of the chemical reaction unit for storage, and using a sludge pump to pump the tertiary sludge into the filter press for pressure filtration.

[0007] Further, in step one, the mercury content of the mercury-containing wastewater is 30-70 mg / L; in step three, the mercury content of the primary supernatant is ≤0.1 mg / L; in step five, the mercury content of the tertiary supernatant is ≤0.01 mg / L. The mercury-containing wastewater includes waste alkali, waste acid, catalyst extraction wastewater and converter leakage waste acid water.

[0008] Further, in step two, the addition amount of polyaluminum chloride is 0.5-0.6 kg / m 3 , and the addition amount of polyacrylamide is 0.06-0.07 kg / m 3The polyaluminum chloride hydrolysis generates positively charged hydrolysis products, which can react with the negatively charged particles in the mercury-containing wastewater to reduce the electrostatic repulsion between the particles, so that the particles are more likely to aggregate into larger flocs to accelerate the sedimentation. The linear structure of the polyacrylamide hydrolysis product can connect the larger particulate matter such as iron filings, rust, catalyst (such as activated carbon) particles containing mercury in the mercury-containing wastewater together through adsorption bridging to form larger flocs to accelerate the sedimentation. Under the combined action of the electro-neutralization reaction of the polyaluminum oxide and the adsorption bridging of the polyacrylamide, the various forms of mercury in the mercury-containing wastewater, especially the iron filings and catalyst particles containing mercury and easy to precipitate and other pollutants can form larger flocs, which are more likely to precipitate under the action of gravity, so that the various forms of mercury are brought to the bottom of the conditioning tank to realize the separation of the primary supernatant and the primary sludge.

[0009] Further, in step two, the stirring speed is 1300-1500 r / min, preferably 1400 r / min, and the standing and sedimentation time is 0.5-1 h.

[0010] Further, in step three, the primary supernatant is siphoned into the mercury removal reaction and precipitation area of the chemical reaction unit, and the composite mercury removal agent and sodium sulfide are added for chemical precipitation. After the addition of the composite mercury removal agent and sodium sulfide, the stirring is continued to reduce the mercury content. After uniform stirring, the standing and sedimentation is carried out for about 1 h to convert the ionic mercury into solid precipitate. The siphoning method can effectively move the liquid from one position to another position by using the pressure difference generated by the hydrostatic head. The present application uses the siphoning method to transfer the primary supernatant to the mercury removal reaction and precipitation area of the chemical reaction unit, which can extract the primary supernatant from the middle and upper part of the conditioning tank into the mercury removal reaction and precipitation area of the chemical reaction unit without disturbing the bottom layer of the precipitated sludge.

[0011] Further, the composite mercury removal agent includes sodium salt of ethylenediaminetetraacetic acid (EDTA), iron salt of ethylenediaminetetraacetic acid and calcium salt of ethylenediaminetetraacetic acid, and the addition amount of the composite mercury removal agent is 0.07-0.08 kg / m 3 The addition amount of sodium sulfide is 0.03-0.04 kg / m 3 .

[0012] Further, in step four, the secondary supernatant is siphoned into the flocculation and precipitation area of the chemical reaction unit, and the polyaluminum chloride and polyacrylamide are added for flocculation and precipitation. The solid precipitate generated by chemical precipitation is relatively small and easy to form a mercury complex with excess sodium sulfide suspended in the wastewater and difficult to quickly settle. Adding polyaluminum chloride and polyacrylamide to the flocculation and precipitation area of the chemical reaction unit is beneficial to promote the separation of the solid precipitate and the supernatant.

[0013] Further, the adding amount of polyaluminum chloride is 0.02-0.03 kg / m 3 , the adding amount of polyacrylamide is 0.0025-0.0035 kg / m 3 .

[0014] Further, it further comprises step six: sequentially performing sand filtration, carbon filtration and ion adsorption on the tertiary supernatant in the clear water zone to obtain the reclaimed water. The mercury content of the reclaimed water obtained after the sand filtration, carbon filtration and ion resin adsorption can reach below 0.003 mg / L.

[0015] Further, the treatment method of the mercury-containing wastewater is carried out in a mercury-containing wastewater treatment device, and the mercury-containing wastewater treatment device comprises a regulating tank, a liquid outlet of the regulating tank is communicated with a chemical reaction unit, the chemical reaction unit is communicated with an inlet of a sand filter tank, a liquid outlet of the sand filter tank is communicated with an inlet of a carbon filter tank, a liquid outlet of the carbon filter tank is communicated with an inlet of an ion adsorption tank, and a liquid outlet of the ion adsorption tank is communicated with an inlet of a reclaimed water tank. The chemical reaction unit comprises a mercury removal reaction precipitation zone, a flocculation precipitation zone and a clear water zone; a liquid outlet of the regulating tank is communicated with an inlet of the mercury removal reaction precipitation zone through a siphon pipe, a liquid outlet of the mercury removal reaction precipitation zone is communicated with an inlet of the flocculation precipitation zone through a siphon pipe, a liquid outlet of the flocculation precipitation zone is communicated with an inlet of the clear water zone through a siphon pipe, and a liquid outlet of the clear water zone is communicated with an inlet of the sand filter tank. A plurality of siphon pipes are arranged between the mercury removal reaction precipitation zone and the flocculation precipitation zone. A sludge pump is arranged on a blowdown pipe arranged at the bottom of the regulating tank, the mercury removal reaction precipitation zone and the flocculation precipitation zone.

[0016] The beneficial effects of the present application are as follows: The treatment method of the mercury-containing wastewater generated in the production process of the calcium carbide method polyvinyl chloride provided by the present application can pre-precipitate most of the precipitable mercury containing large-particle impurities by adding polyaluminum chloride and polyacrylamide into the regulating tank for pre-flocculation precipitation. The wastewater is treated in batches, the siphon method is combined with the chemical mercury removal and flocculation precipitation process, the sludge containing mercury is fully precipitated, the disturbance to the water is reduced, the supernatant is transferred to the next unit respectively until the ion adsorption unit, the mercury concentration in the supernatant can be greatly reduced, the mercury in the wastewater can prevent the pollution and impact of the mercury in the wastewater on the ion adsorption adsorption unit, and the consequence of the whole system paralysis can be avoided. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0018] Figure 1 is a process flow diagram of an embodiment of the present application.

[0019] In the figure, 1 is a regulating tank, 2 is a mercury removal reaction precipitation zone, 3 is a flocculation precipitation zone, 4 is a clear water zone, 5 is a sand filter tank, 6 is a carbon filter tank, 7 is an ion adsorption tank, 8 is a recycled water tank, 9 is a waste water tank, 10 is a filter press, 11 is a mercury-containing waste water source, and 12 is a recycled water pipeline. DETAILED DESCRIPTION

[0020] In order to make the person skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without creative labor should belong to the protection scope of the present application.

[0021] Embodiment 1 A treatment method of mercury-containing waste water generated in a calcium carbide method polyvinyl chloride production process, comprising the following steps: Step one: the total mercury content of the mercury-containing waste water in the middle and upper part of the regulating tank is 30.304 mg / L, and acid or alkali is added to the mercury-containing waste water in the regulating tank to adjust the pH value of the mercury-containing waste water to neutral. The mercury-containing waste water in the regulating tank is 50 m 3 The mercury-containing waste water includes waste alkali, waste acid, catalyst extraction waste water and converter leakage waste acid water. The mercury content of the waste alkali is about 1 mg / L, the VCM content is 0.5 mg / L, the sodium carbonate content is 8 wt%, the sodium hydroxide content is 5 wt%, and the sodium chloride content is 5 wt%. The mercury content of the waste acid is about 100-500 mg / L, the hydrochloric acid content is 21 wt%, and the VCM content is about 0.5 mg / L. The mercury content of the catalyst extraction waste water is about 1000 mg / L, the hydrochloric acid content is 1 wt%, the VCM content is about 0.5 mg / L, the mercury content of the converter leakage waste acid water is 500 mg / L, the hydrochloric acid content is 1 wt%, and the VCM is about 0.5 mg / L.

[0022] Step two: 25 kg of polyaluminum chloride and 3 kg of polyacrylamide are added to the regulating tank in sequence, and then stirring is performed at a stirring rate of 1400 r / min. The stirring motor model is YS7144, and the stirring motor power is 0.75 KW. After stirring, the slurry is left to stand for 1 h to obtain a first supernatant and a first sludge.

[0023] Step three: the total mercury content of the primary supernatant is 0.054 mg / L, the primary supernatant is siphoned into the mercury removal reaction precipitation area of the chemical reaction unit, and a composite mercury removal agent and sodium sulfide are added for continuous stirring, and after uniform stirring, the mixture is fully settled for about 1 h to obtain secondary supernatant and secondary sludge; the primary sludge is pumped into the filter press for pressure filtration. The composite mercury removal agent includes sodium salt of ethylenediaminetetraacetic acid (EDTA), iron salt of ethylenediaminetetraacetic acid, and calcium salt of ethylenediaminetetraacetic acid, and the addition amount of the composite mercury removal agent is 0.07-0.08 kg / m 3 , and the addition amount of sodium sulfide is 0.03-0.04 kg / m 3 .

[0024] Step four: the secondary supernatant is siphoned into the flocculation precipitation area of the chemical reaction unit, and polyaluminum chloride and polyacrylamide are added for flocculation precipitation to obtain tertiary supernatant and tertiary sludge; the secondary sludge is pumped into the filter press for pressure filtration. The addition amount of polyaluminum chloride is 0.02-0.03 kg / m 3 , and the addition amount of polyacrylamide is 0.0025-0.0035 kg / m 3 .

[0025] Step five: the mercury content of the tertiary supernatant is ≤0.01 mg / L. The tertiary supernatant is siphoned into the clean water area of the chemical reaction unit for storage, and the tertiary sludge is pumped into the filter press for pressure filtration.

[0026] Step six: the tertiary supernatant in the clean water area is sequentially subjected to sand filtration, carbon filtration, and ion adsorption to obtain recycled water, which is stored in a recycled water tank. The mercury content of the recycled water obtained after sand filtration, carbon filtration, and ion resin adsorption can be ≤0.003 mg / L.

[0027] The mercury-containing wastewater treatment method is carried out in a mercury-containing wastewater treatment device, which comprises a conditioning tank 1, the water inlet of the conditioning tank 1 is in communication with a mercury-containing wastewater source 11, the liquid outlet of the conditioning tank 1 is in communication with a chemical reaction unit, the chemical reaction unit is in communication with the inlet of a sand filter tank 5, the liquid outlet of the sand filter tank 5 is in communication with the inlet of a carbon filter tank 6, the liquid outlet of the carbon filter tank 6 is in communication with the inlet of an ion adsorption tank 7, the liquid outlet of the ion adsorption tank 7 is in communication with the inlet of a recycled water tank 8, the outlet of the recycled water tank 8 is in communication with a recycled water pipeline 12, the backwash water outlets of the sand filter tank 5, the carbon filter tank 6, and the ion adsorption tank 7 are all in communication with the inlet of a wastewater tank 9, and the liquid outlet of the wastewater tank 9 is in communication with the inlet of the conditioning tank 1.

[0028] The chemical reaction unit comprises a mercury removal reaction and precipitation area 2, a flocculation and precipitation area 3, and a clean water area 4; the liquid outlet of the adjusting tank 1 is connected to the inlet of the mercury removal reaction and precipitation area 2 through a siphon pipe, the liquid outlet of the mercury removal reaction and precipitation area 2 is connected to the inlet of the flocculation and precipitation area 3 through a siphon pipe, the liquid outlet of the flocculation and precipitation area 3 is connected to the inlet of the clean water area 4 through a siphon pipe, and the liquid outlet of the clean water area 4 is connected to the inlet of the sand filter tank 5. A plurality of siphon pipes are arranged between the mercury removal reaction and precipitation area 2 and the flocculation and precipitation area 3. The bottoms of the adjusting tank 1, the mercury removal reaction and precipitation area 2, and the flocculation and precipitation area 3 are connected to the filter press 10 through a blowdown pipe, and a sludge pump is arranged on the blowdown pipe.

[0029] Example 2 A treatment method of mercury-containing wastewater generated in a calcium carbide method PVC production process, comprising the following steps: Step one: the total mercury content of the mercury-containing wastewater in the middle and upper part of the adjusting tank is 30.304 mg / L, and an acid or a base is added to the mercury-containing wastewater in the adjusting tank to adjust the pH value of the mercury-containing wastewater to neutral. The mercury-containing wastewater in the adjusting tank is 50 m 3 The mercury-containing wastewater comprises waste alkali, waste acid, catalyst extraction wastewater, and converter leakage waste acid water, wherein the mercury content of the waste alkali is about 1 mg / L, the VCM content is 0.5 mg / L, the sodium carbonate content is 8 wt%, the sodium hydroxide content is 5 wt%, and the sodium chloride content is 5 wt%; the mercury content of the waste acid is about 100-500 mg / L, the hydrochloric acid content is 21 wt%, and the VCM content is about 0.5 mg / L; the mercury content of the catalyst extraction wastewater is about 1000 mg / L, the hydrochloric acid content is 1 wt%, the VCM content is about 0.5 mg / L, the mercury content of the converter leakage waste acid water is 500 mg / L, the hydrochloric acid content is 1 wt%, and the VCM is about 0.5 mg / L.

[0030] Step two: 25 kg of polyaluminum chloride and 3 kg of polyacrylamide are added to the adjusting tank in sequence, and then stirring is performed at a stirring rate of 1400 r / min, a stirring motor model of YS7144, and a stirring motor power of 0.75 KW. After stirring, the first supernatant and the first sludge are obtained after 1 h of standing and precipitation.

[0031] Step three: the total mercury content of the first supernatant is 0.054 mg / L, the first supernatant is siphoned into the mercury removal reaction and precipitation area of the chemical reaction unit, a composite mercury removal agent and sodium sulfide are added for continuous stirring, and after uniform stirring, standing and precipitation are performed for about 1 h to obtain the second supernatant and the second sludge; the first sludge is extracted into the filter press using a sludge pump for pressure filtration. The composite mercury removal agent comprises sodium salt of ethylenediaminetetraacetic acid (EDTA), iron salt of ethylenediaminetetraacetic acid, and calcium salt of ethylenediaminetetraacetic acid, and the addition amount of the composite mercury removal agent is 0.07-0.08 kg / m 3, the amount of sodium sulfide added is 0.03-0.04 kg / m 3 .

[0032] Step four: the secondary supernatant is siphoned into the flocculation precipitation area in the chemical reaction unit, polyaluminum chloride and polyacrylamide are added for flocculation precipitation, to obtain tertiary supernatant and tertiary sludge; the secondary sludge is pumped into the filter press by a sludge pump for pressure filtration. The amount of polyaluminum chloride added is 0.02-0.03 kg / m 3 , the amount of polyacrylamide added is 0.0025-0.0035 kg / m 3 .

[0033] Step five: the mercury content of the tertiary supernatant is detected to be ≤0.01 mg / L. The tertiary supernatant is siphoned into the clean water area in the chemical reaction unit for storage, and the tertiary sludge is pumped into the filter press by a sludge pump for pressure filtration.

[0034] Step six: the tertiary supernatant in the clean water area is sequentially subjected to sand filtration, carbon filtration and ion adsorption to obtain recycled water, which is stored in a recycled water tank. The mercury content of the recycled water obtained after sand filtration, carbon filtration and ion resin adsorption can be below 0.003 mg / L.

[0035] The treatment method of mercury-containing wastewater is carried out in a mercury-containing wastewater treatment device, which comprises a conditioning tank 1, the water inlet of the conditioning tank 1 is in communication with a mercury-containing wastewater source 11, the liquid outlet of the conditioning tank 1 is in communication with a chemical reaction unit, the chemical reaction unit is in communication with the inlet of a sand filter tank 5, the liquid outlet of the sand filter tank 5 is in communication with the inlet of a carbon filter tank 6, the liquid outlet of the carbon filter tank 6 is in communication with the inlet of an ion adsorption tank 7, the liquid outlet of the ion adsorption tank 7 is in communication with the inlet of a recycled water tank 8, the outlet of the recycled water tank 8 is in communication with a recycled water pipeline 12, the backwash water outlets of the sand filter tank 5, the carbon filter tank 6 and the ion adsorption tank 7 are all in communication with the inlet of a wastewater tank 9, and the liquid outlet of the wastewater tank 9 is in communication with the inlet of the conditioning tank 1.

[0036] The chemical reaction unit comprises a mercury removal reaction precipitation area 2, a flocculation precipitation area 3 and a clean water area 4; the liquid outlet of the conditioning tank 1 is in communication with the inlet of the mercury removal reaction precipitation area 2 through a siphon tube, the liquid outlet of the mercury removal reaction precipitation area 2 is in communication with the inlet of the flocculation precipitation area 3 through a siphon tube, the liquid outlet of the flocculation precipitation area 3 is in communication with the inlet of the clean water area 4 through a siphon tube, and the liquid outlet of the clean water area 4 is in communication with the inlet of the sand filter tank 5. A plurality of siphon tubes are arranged between the mercury removal reaction precipitation area 2 and the flocculation precipitation area 3. The bottoms of the conditioning tank 1, the mercury removal reaction precipitation area 2 and the flocculation precipitation area 3 are all in communication with a filter press 10 through a blowdown pipe, and a sludge pump is arranged on the blowdown pipe.

[0037] Example 3 A treatment method of mercury-containing wastewater generated in a calcium carbide method polyvinyl chloride production process, comprising the following steps: Step one: the total mercury content of the mercury-containing wastewater in the middle and upper part of the adjusting pool is 30.304 mg / L, and acid or alkali is added to the mercury-containing wastewater in the adjusting pool to adjust the pH value of the mercury-containing wastewater to neutral. The mercury-containing wastewater in the adjusting pool is 50 m 3 . The mercury-containing wastewater includes waste alkali, waste acid, catalyst extraction wastewater and converter leakage waste acid water, wherein the mercury content of the waste alkali is about 1 mg / L, the VCM content is 0.5 mg / L, the sodium carbonate content is 8 wt%, the sodium hydroxide content is 5 wt%, and the sodium chloride content is 5 wt%; the mercury content of the waste acid is about 100-500 mg / L, the hydrochloric acid content is 21 wt%, and the VCM content is about 0.5 mg / L; the mercury content of the catalyst extraction wastewater is about 1000 mg / L, the hydrochloric acid content is 1 wt%, the VCM content is about 0.5 mg / L, the mercury content of the converter leakage waste acid water is 500 mg / L, the hydrochloric acid content is 1 wt%, and the VCM is about 0.5 mg / L.

[0038] Step two: 25 kg of polyaluminum chloride and 3 kg of polyacrylamide are added to the adjusting pool in turn, and then stirring is performed, the stirring rate is 1400 r / min, the stirring motor model is YS7144, the stirring motor power is 0.75 KW, and after stirring, the supernatant and the first sludge are obtained after 1 h of standing and precipitation.

[0039] Step three: the total mercury content of the first supernatant is 0.054 mg / L, the first supernatant is siphoned into the mercury removal reaction and precipitation area of the chemical reaction unit, a composite mercury removal agent and sodium sulfide are added for continuous stirring, and after uniform stirring, standing and precipitation are performed for about 1 h, the second supernatant and the second sludge are obtained; the first sludge is pumped into the filter press using a sludge pump for pressure filtration. The composite mercury removal agent includes sodium salt of ethylenediaminetetraacetic acid (EDTA), iron salt of ethylenediaminetetraacetic acid and calcium salt of ethylenediaminetetraacetic acid, the addition amount of the composite mercury removal agent is 0.07-0.08 kg / m 3 , and the addition amount of sodium sulfide is 0.03-0.04 kg / m 3 .

[0040] Step four: the second supernatant is siphoned into the flocculation and precipitation area in the chemical reaction unit, polyaluminum chloride and polyacrylamide are added for flocculation and precipitation, the third supernatant and the third sludge are obtained; the second sludge is pumped into the filter press using a sludge pump for pressure filtration. The addition amount of polyaluminum chloride is 0.02-0.03 kg / m 3 , and the addition amount of polyacrylamide is 0.0025-0.0035 kg / m 3 .

[0041] Step five: mercury content of the supernatant of the third stage is less than or equal to 0.01 mg / L. The supernatant of the third stage is siphoned into the clean water area in the chemical reaction unit and stored, and the sludge pump is used to pump the sludge of the third stage into the filter press for pressure filtration.

[0042] Step six: the supernatant of the third stage in the clean water area is sequentially subjected to sand filtration, carbon filtration and ion adsorption to obtain the reclaimed water, which is stored in the reclaimed water tank. The mercury content of the reclaimed water obtained after sand filtration, carbon filtration and ion resin adsorption can be less than or equal to 0.003 mg / L.

[0043] The treatment method of mercury-containing wastewater is carried out in a mercury-containing wastewater treatment device. The mercury-containing wastewater treatment device comprises a conditioning tank 1, the water inlet of the conditioning tank 1 is in communication with a mercury-containing wastewater source 11, the liquid outlet of the conditioning tank 1 is in communication with a chemical reaction unit, the chemical reaction unit is in communication with the inlet of a sand filter tank 5, the liquid outlet of the sand filter tank 5 is in communication with the inlet of a carbon filter tank 6, the liquid outlet of the carbon filter tank 6 is in communication with the inlet of an ion adsorption tank 7, the liquid outlet of the ion adsorption tank 7 is in communication with the inlet of a reclaimed water tank 8, the outlet of the reclaimed water tank 8 is in communication with a reclaimed water pipeline 12, the backwash water outlets of the sand filter tank 5, the carbon filter tank 6 and the ion adsorption tank 7 are all in communication with the inlet of a wastewater tank 9, and the liquid outlet of the wastewater tank 9 is in communication with the inlet of the conditioning tank 1.

[0044] The chemical reaction unit comprises a mercury removal reaction precipitation area 2, a flocculation precipitation area 3 and a clean water area 4. The liquid outlet of the conditioning tank 1 is in communication with the inlet of the mercury removal reaction precipitation area 2 through a siphon tube, the liquid outlet of the mercury removal reaction precipitation area 2 is in communication with the inlet of the flocculation precipitation area 3 through a siphon tube, the liquid outlet of the flocculation precipitation area 3 is in communication with the inlet of the clean water area 4 through a siphon tube, and the liquid outlet of the clean water area 4 is in communication with the inlet of the sand filter tank 5. A plurality of siphon tubes are arranged between the mercury removal reaction precipitation area 2 and the flocculation precipitation area 3. The bottoms of the conditioning tank 1, the mercury removal reaction precipitation area 2 and the flocculation precipitation area 3 are all in communication with a filter press 10 through a blowdown pipe, and a sludge pump is arranged on the blowdown pipe.

[0045] Although the present application has been described in detail by referring to the preferred embodiments thereof, it is to be understood that the present application is not limited to them. Variations and modifications are possible in the embodiments of the present application without departing from the spirit and scope thereof. Any skilled person in the art can make equivalent modifications or substitutions without creative work, and all these modifications and substitutions should be encompassed in the scope of the present application.

Claims

1. A method for treating mercury-containing wastewater generated during the calcium carbide-based polyvinyl chloride production process, characterized in that, Includes the following steps: Step 1: Add acid or alkali to the mercury-containing wastewater in the equalization tank to adjust the pH value of the mercury-containing wastewater to neutral; Step 2: Add polyaluminum chloride and polyacrylamide to the equalization tank, then stir. After stirring, let it stand to settle and obtain primary supernatant and primary sludge. Step 3: Siphon the primary supernatant into the mercury removal reaction precipitation zone of the chemical reaction unit for chemical precipitation to obtain secondary supernatant and secondary sludge; The primary sludge is pumped into a filter press for filtration using a sludge pump. Step 4: Siphon the secondary supernatant into the flocculation and sedimentation zone in the chemical reaction unit for flocculation and sedimentation to obtain tertiary supernatant and tertiary sludge; The secondary sludge is pumped into the filter press for filtration using a sludge pump. Step 5: Siphon the tertiary supernatant into the clear water zone of the chemical reaction unit for storage, and use a sludge pump to pump the tertiary sludge into the filter press for filtration.

2. The processing method as described in claim 1, characterized in that, In step one, the mercury content of the mercury-containing wastewater is 30-70 mg / L; in step three, the mercury content of the primary supernatant is ≤0.1 mg / L; in step five, the mercury content of the tertiary supernatant is ≤0.01 mg / L.

3. The processing method as described in claim 1, characterized in that, In step two, the amount of polyaluminum chloride added is 0.5-0.6 kg / m³. 3 The amount of polyacrylamide added is 0.06-0.07 kg / m³. 3 .

4. The processing method as described in claim 1, characterized in that, In step two, the stirring speed is 1300-1500 r / min, and the settling time is 0.5-1 h.

5. The processing method as described in claim 1, characterized in that, In step three, the primary supernatant is siphoned into the mercury removal reaction precipitation zone of the chemical reaction unit, and a composite mercury removal agent and sodium sulfide are added for chemical precipitation.

6. The processing method as described in claim 5, characterized in that, The composite mercury removal agent is a complex containing calcium, sodium, and iron ions. The dosage of the composite mercury removal agent is 0.07-0.08 kg / m³. 3 The amount of sodium sulfide added is 0.03-0.04 kg / m³. 3 .

7. The processing method as described in claim 1, characterized in that, In step four, the secondary supernatant is siphoned into the flocculation and sedimentation zone of the chemical reaction unit, and polyaluminum chloride and polyacrylamide are added for flocculation and sedimentation.

8. The processing method as described in claim 7, characterized in that, The dosage of polyaluminum chloride is 0.02-0.03 kg / m³. 3 The amount of polyacrylamide added is 0.0025-0.0035 kg / m³. 3 .

9. The processing method as described in claim 1, characterized in that, It also includes step six: sequentially subjecting the three-stage supernatant in the clear water zone to sand filtration, carbon filtration, and ion adsorption to obtain recycled water.

10. The processing method as described in claim 9, characterized in that, The treatment method for mercury-containing wastewater is carried out in a mercury-containing wastewater treatment device, which includes an equalization tank. The liquid outlet of the equalization tank is connected to a chemical reaction unit. The chemical reaction unit is connected to the inlet of a sand filter tank. The liquid outlet of the sand filter tank is connected to the inlet of a carbon filter tank. The liquid outlet of the carbon filter tank is connected to the inlet of an ion adsorption tank. The liquid outlet of the ion adsorption tank is connected to the inlet of a recycled water tank. The chemical reaction unit includes a mercury removal reaction precipitation zone, a flocculation precipitation zone, and a clear water zone. The liquid outlet of the equalization tank is connected to the inlet of the mercury removal reaction precipitation zone via a siphon pipe, the liquid outlet of the mercury removal reaction precipitation zone is connected to the inlet of the flocculation precipitation zone via a siphon pipe, the liquid outlet of the flocculation precipitation zone is connected to the inlet of the clear water zone via a siphon pipe, and the liquid outlet of the clear water zone is connected to the inlet of the sand filter tank.

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