CN108059223B

CN108059223B - Method for removing silicon from negative-hardness wastewater

Info

Publication number: CN108059223B
Application number: CN201711402136.5A
Authority: CN
Inventors: 王晓阳; 盛雪芹; 杨权; 陈立辉; 谢晓朋; 郝翰
Original assignee: Beijing Hanqi Environment Technology Co ltd
Current assignee: Beijing Hanqi Environmental Technology Co.,Ltd.
Priority date: 2017-12-22
Filing date: 2017-12-22
Publication date: 2020-10-02
Anticipated expiration: 2037-12-22
Also published as: CN108059223A

Abstract

The invention discloses a method for removing silicon from negative hardness wastewater, which can effectively remove silicon in the negative hardness wastewater, and the silicon removal is completed by adding lime, calcium chloride or calcium sulfate, a coagulant and a flocculating agent to act on a high-efficiency sedimentation tank process in a synergistic manner. The method improves the problems of large lime adding amount and low silicon removal efficiency in the conventional silicon removal process for treating negative hardness wastewater by using lime, and realizes the efficient utilization of lime. The method has the characteristics of low silicon content in effluent, low drug consumption, wide silicon removal content range, high solid content of sludge and small occupied area.

Description

Method for removing silicon from negative-hardness wastewater

Technical Field

The invention relates to the field of water treatment, in particular to a method for removing silicon from negative-hardness wastewater.

Background

Silicon compounds in industrial waters can pose varying levels of harm to the production process. Silicon compounds of the industrial boiler make-up water, geothermal water and cooling water are easy to form silica scale, and the formed silica scale is compact and hard and is difficult to clean by a common method, so that the heat transfer efficiency and the safe operation of equipment are seriously influenced; in water for the electronic industry, silicon dioxide can cause great harm to semiconductor production on the surface of monocrystalline silicon, and the quality of electronic tubes and solid circuits is reduced; in the water for papermaking industry, the paper becomes brittle due to the over-high content of silicon dioxide; in the water for rayon industry, the high content of silicic acid will affect the fiber strength and the viscosity of viscose; in hydrometallurgical waters, emulsification occurs with silicic acid contents above a certain range, which affects production. For this reason, silicon removal is a significant consideration in various feedwater treatment systems. Effective reinjection water after the industrial wastewater is qualified in treatment and standard discharge water after the industrial wastewater is qualified in treatment need to be subjected to desiliconization. When the method is used for advanced treatment of sewage, such as ultrafiltration and reverse osmosis membrane treatment, if the silicon content is too high, formed silica scale can block the membrane, so that the membrane treatment effect is poor, and even the membrane can fail.

At present, the wide technologies for treating silicon compounds in industrial sewage worldwide mainly include a coagulation desilication technology, an electrocoagulation desilication technology, an ion exchange desilication technology, an air flotation desilication technology and an ultrafiltration desilication technology. As a non-advanced treatment silicon removal method, the most widely applied technology is mainly a coagulation silicon removal technology, and the concrete method comprises the following steps: 1. firstly, preparing a silicon removing agent, a coagulant and a flocculating agent; 2. Adjusting the pH value of the treated sewage, and controlling the dosage and time; 3. adding a prepared silicon removing agent, a coagulant and a flocculating agent into the treated sewage, wherein the agents react chemically in the sewage to generate precipitates, and the precipitates form the coagulation of silicon compounds; 4. standing and settling the formed flocs in a clarification tank; 5. the supernatant after sedimentation is treated water, and the lower layer is treated waste liquid. The method for removing silicon by lime coagulating sedimentation is a silicon removal method with low cost and wide application, but has the defects of low lime utilization rate, large dosage, difficult removal of silicon compounds in effluent to a lower level and difficult realization of sewage with high effluent requirement due to the characteristics of lime. Particularly, when the silicon in the negative hardness water is treated, the effect of removing the silicon by adding the pure lime is poor, and the expected effect cannot be achieved at all.

Disclosure of Invention

The invention mainly aims to disclose a method for removing silicon from negative-hardness wastewater, which can effectively remove the content of silicon compounds in the negative-hardness wastewater, and the silicon removal is completed by adding lime, calcium chloride or calcium sulfate, a coagulant and a flocculating agent to act on a high-efficiency sedimentation tank process in a synergistic manner.

The invention combines the high-efficiency sedimentation tank process to remove the silicon compounds in the negative hardness wastewater, and the specific steps are as follows:

(1) adding lime solution into the reaction tank through automatic dosing equipment to adjust the pH value to 9-11 and providing enough Ca by using calcium chloride or calcium sulfate solution²⁺；

(2) Adding an aluminum salt coagulant into a coagulation tank, and generating insoluble complex compounds and complex alum floc through the actions of compressing double electronic layers, adsorbing electrical neutralization, bridging adsorption, rolling sweep adsorption and the like;

(3) adding a polyacrylamide flocculant into the flocculation tank to ensure that the alum flocs are aggregated to form dense and large alum flocs for rapid precipitation;

in the high-efficiency sedimentation tank process, after lime, calcium chloride or calcium sulfate is added into the wastewater, the wastewater is quickly stirred for 10-20 min;

in the high-efficiency sedimentation tank process, after an aluminum salt coagulant is added into the wastewater, the wastewater is quickly stirred for 3-5 min;

in the high-efficiency sedimentation tank process, after a flocculating agent is added into the wastewater, the wastewater is stirred at a slow speed for 10-15 min;

in the high-efficiency sedimentation tank process, a sludge return pipe is arranged at the bottom of the high-efficiency sedimentation tank, and part of sludge is returned to a flocculation area, wherein the return rate is 4-8%.

Compared with the existing method for treating negative hardness water by lime, the method for removing silicon from negative hardness wastewater mainly has the following advantages: (1) removing silicon in the negative hardness wastewater by the synergistic effect of lime, calcium chloride or calcium sulfate; (2) the process parameters are optimized by combining with the high-efficiency sedimentation tank process; (3) the efficient sedimentation tank is provided with the sludge return pipe, so that sludge return is realized, the sludge concentration is increased, the utilization rate of lime, calcium chloride or calcium sulfate is improved, the lime adding amount is reduced, the sludge discharge amount is reduced, the cost is saved, a carrier is provided for sedimentation, the sedimentation of silicon is accelerated, and the silicon removal rate is increased. (4) The range of the silicon content is wide, and the treatment effect can reach 15mg/L (by SiO)₂Meter) below.

Drawings

FIG. 1 is a sectional view of a high efficiency settling tank for the process of the present invention

In the figure, A is a lime, calcium chloride or calcium sulfate adding area, B is a coagulation area, C is a flocculation area, and D is a precipitation-concentration area

1. A water inlet pipe; 2. lime, calcium chloride or calcium sulfate feeding pipes; 3. a lime, calcium chloride or calcium sulfate mixer; 4. a coagulant adding pipe; 5. a coagulation stirrer; 6. a flocculating agent feeding ring; 7. a flocculation stirrer; an inclined tube settling zone; 9. a bottom pipe; 10. a sludge return line; 11. a mud collection hopper; 12. a water collection tank; 13. a concentration mud scraper; 14. a water outlet pipe; 15. a draft tube; 16. and pushing the flow wall.

Detailed Description

The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

The device shown in figure 1 adopts a process of a high-efficiency sedimentation tank, and the process is divided into four parts: the lime, calcium chloride or calcium sulfate feeding area A, the coagulation area B, the flocculation area C and the precipitation-concentration area D are communicated with one another. The silicon-containing wastewater firstly enters a lime, calcium chloride or calcium sulfate adding area A through a water inlet pipe 1, lime, calcium chloride or calcium sulfate solution with the concentration of 5-10% is added into the lime, calcium chloride or calcium sulfate adding area A through an automatic medicine adding device and an adding pipe 2, the adding amount is automatically adjusted according to the water inflow, the lime, calcium chloride or calcium sulfate solution is rapidly stirred for 10-20min through a lime, calcium chloride or calcium sulfate stirrer 3, and enough Ca in the wastewater is obtained²⁺With CO in the waste water₃ ^2-Formation of CaCO₃Precipitation with SiO in the wastewater₃ ^2-CaSiO also forms a peptized state₃Precipitation, CaCO₃The precipitate is attached to CaSiO in a peptized state₃Precipitating more easily, adding 10% of coagulant polyaluminium chloride through a coagulant adding pipe 4, and rapidly stirring for 3-5min by a coagulation stirrer 5 to obtain Ca in the wastewater² ⁺、 SiO₃ ^2-With Al³⁺Further, a hardly soluble alum blossom complex is formed. Sewage enters the bottom of a flocculation area C through a bottom pipeline 9 of a coagulation area B, the bottom pipeline 9 is communicated with a guide cylinder 15 of the flocculation area D, wastewater enters the guide cylinder 15 of the flocculation area C to form an internal circulation inside the guide cylinder 15, a flocculating agent polyacrylamide solution is added through a flocculating agent adding pipe 8 and fully mixed with the wastewater from top to bottom, after the wastewater is stirred for 10-15min at a low speed by a flocculation stirrer 9, the formed complex compounds and complex alum flocs are rapidly aggregated and enlarged, the complex compounds and the complex alum flocs enter a precipitation-sludge concentration area D through a flow pushing wall 16 by utilizing the flow speed of the water, the precipitation-sludge concentration area D is provided with a concentration mud scraper 13 and a sludge return pipeline 10, 4-8% of sludge flows back to the bottom of the flocculation area C through the sludge return pipeline 10 to ensure that the sludge flows back to theThe sludge concentration in the draft tube 15 has increased the collision probability between alum blossom, is favorable to the formation of big alum blossom in the waste water, improves the medicament utilization ratio moreover, reduces medicament dosage, and concentrated mud scraper 13 will deposit the sludge concentration at the bottom of the pool and scrape to the mud collection fill 11 in, and the clear water is discharged through outlet pipe 14 after collecting through water catch bowl 12.

Example 1

1740mg/L of total Silicon (SiO) in the water coming from waste water of oil field₂Metering), passing through a lime and calcium chloride adding area A, adding lime in an amount of 2.1g/L and calcium chloride in an amount of 3.1g/L, and rapidly stirring and reacting for 20min in the area A; PAC is added into the coagulation zone B to be 100mg/L, and the rapid stirring time in the zone B is 3 min; adding PAM into the flocculation zone C to be 1.0mg/L, and stirring at a low speed in the zone D for 12 min; in the sedimentation-concentration zone D, the mud and the water are quickly separated, clear water flows upwards, the clear water is separated through an inclined pipe and enters a water collecting tank, the mud sinks downwards, the mud is concentrated and then discharged through a concentration mud scraper, and 4% of the mud flows back to the flocculation zone C; the final effluent quality contains 11.9mg/L of total silicon, and the silicon removal rate reaches 99.3 percent.

Example 2

The water content of the gasified sewage water is 98mg/L (SiO)₂Metering), passing through a lime and calcium chloride adding area A, adding lime in an amount of 0.26g/L and calcium chloride in an amount of 0.5g/L, and stirring and reacting for 18min in the area A; PAC is added into the coagulation zone B to be 100mg/L, and the rapid stirring time in the zone B is 3 min; adding PAM into the flocculation zone C to be 0.5mg/L, and stirring at a low speed in the zone D for 12 min; in the sedimentation-concentration zone D, the mud and the water are quickly separated, clear water flows upwards, the clear water is separated through an inclined pipe and enters a water collecting tank, the mud sinks downwards, the mud is concentrated and then discharged through a concentration mud scraper, and 6% of the mud flows back to the flocculation zone C; the final effluent quality contains 12.5mg/L of total silicon, and the silicon removal rate reaches 87.2 percent.

Example 3

The reuse water of a water plant contains 200mg/L of total Silicon (SiO)₂Metering), passing through a lime and calcium chloride adding area A, adding 1.2g/L lime and 2.1g/L calcium chloride, and stirring and reacting for 20min in the area A; PAC is added into the coagulation zone B to be 100mg/L, and the rapid stirring time in the zone B is 3 min; adding PAM into the flocculation zone C to be 1.0mg/L, and stirring at a low speed in the zone D for 12 min; in the precipitation-concentrationIn the region D, the sludge and the water are quickly separated, clear water flows upwards, enters a water collecting tank through the separation of an inclined pipe, the sludge sinks downwards, is concentrated and then discharged outside through a concentration mud scraper, and 6 percent of sludge flows back to the flocculation region C; the final effluent quality contains 13.9mg/L of total silicon, and the silicon removal rate reaches 93.1 percent.

Although the invention has been described in detail with respect to the general description and the specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method for removing silicon from negative hardness wastewater can effectively remove silicon in the negative hardness wastewater, and is characterized in that the silicon removal is completed by adding lime, calcium chloride or calcium sulfate, a coagulant and a flocculant into a high-efficiency sedimentation tank and performing synergistic interaction, wherein the high-efficiency sedimentation tank comprises a lime, calcium chloride or calcium sulfate adding area, a coagulation area, a flocculation area and a sedimentation-concentration area; the specific method comprises the following steps:

(1) adding lime solution into a lime, calcium chloride or calcium sulfate adding area through automatic dosing equipment to adjust p H value to 9-11, and providing enough Ca through the calcium chloride or calcium sulfate solution²⁺Rapidly stirring for 10-20 min;

(2) adding an aluminum salt coagulant into the coagulation area, and rapidly stirring for 3-5min to complete hydrolysis and polycondensation reaction of sewage, so that a colloid dispersion system is destabilized and condensed to generate an insoluble complex compound and complex alum blossom;

(3) adding a polyacrylamide flocculant into the flocculation area, and slowly stirring for 10-15min to make insoluble complex compounds, complex alum floc and flocculant collide with each other and aggregate to form larger compact alum floc, thereby accelerating precipitation;

(4) a sludge return pipeline is arranged at the bottom of the sedimentation-concentration zone to return partial sludge to the flocculation zone, and the reflux ratio is 4-8%; ca in the negative hardness wastewater²⁺、Mg²⁺The content is low.