CN108975469B

CN108975469B - Method for removing phosphate radicals and sulfate radicals in iron phosphate wastewater step by step

Info

Publication number: CN108975469B
Application number: CN201710413371.6A
Authority: CN
Inventors: 刘晨明; 李雅; 曹宏斌
Original assignee: Institute of Process Engineering of CAS
Current assignee: Institute of Process Engineering of CAS
Priority date: 2017-06-05
Filing date: 2017-06-05
Publication date: 2020-07-07
Anticipated expiration: 2037-06-05
Also published as: CN108975469A

Abstract

The invention relates to a method for removing phosphate radicals and sulfate radicals in iron phosphate wastewater step by step, which comprises the following steps: (1) adding alkali liquor into the iron phosphate wastewater to adjust the pH value to 4-11; (2) adding ferric sulfate to perform precipitation reaction; (3) adding alkali liquor again to adjust the pH value to 3-9; (4) adding a flocculating agent, stirring, standing, and performing solid-liquid separation to obtain a filtrate and a solid containing ferric phosphate; (5) adding calcium hydroxide into the filtrate obtained in the step (4), carrying out precipitation reaction, and carrying out solid-liquid separation to obtain filtrate and a solid containing calcium sulfate; wherein the alkali liquor comprises any one or a combination of at least two of sodium hydroxide, potassium hydroxide or ammonia water. The removal of phosphate radicals and sulfate radicals is realized, calcium sulfate is obtained by recovery, and the resource degree is higher than that of the prior art. The phosphate radical content of the final effluent is below 0.5g/L, and the sulfate radical content is below 1.5 g/L.

Description

Method for removing phosphate radicals and sulfate radicals in iron phosphate wastewater step by step

Technical Field

The invention relates to the field of industrial wastewater treatment, in particular to a method for removing phosphate radicals and sulfate radicals in iron phosphate wastewater step by step.

Background

In the production process of the iron phosphate, a large amount of comprehensive wastewater containing high-concentration phosphate radicals, sulfate radicals and ammonia nitrogen is generated. The pollutant in the iron phosphate wastewater is expressed as NH according to ions₄ ⁺(ammonium ion), SO₄ ^2-(sulfate ion), PO₄ ^3-(phosphate ion). If the treatment does not reach the standard, the phosphate radical and ammonia nitrogen in the wastewater can cause serious pollution to the environment. And high-concentration ions in the wastewater are not recycled, so that resource waste is caused. The traditional lime adding method is used for synchronously removing phosphate radicals and sulfate radicals in wastewater, a large amount of mixed sludge is generated, the mixed sludge cannot be treated and recovered, and resource waste and secondary pollution are caused.

In order to remove and recover phosphate and sulfate respectively, if sulfate is removed first and then phosphate is removed, ions capable of precipitating with sulfate are mainly calcium ions and barium ions, but calcium ions and barium ions can also precipitate with phosphate simultaneously. If phosphate radical is removed first and then sulfate radical is removed, the type and proportion of the alkali liquor added for adjusting the pH value during phosphate radical removal can affect the subsequent removal of sulfate radical and the purity of the recovered calcium sulfate. At present, no report is found on a method for respectively removing sulfate and phosphate.

Disclosure of Invention

In view of the problems in the prior art, the invention aims to provide a method for removing phosphate radicals and sulfate radicals in iron phosphate wastewater step by step, and aims to solve the problem that the phosphate radicals and the sulfate radicals cannot be removed and recovered step by step in the iron phosphate wastewater treatment process.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides a method for removing phosphate radicals and sulfate radicals in iron phosphate wastewater step by step, which comprises the following steps:

(1) adding alkali liquor into the iron phosphate wastewater to adjust the pH value to 4-11, such as 4, 5, 6, 7, 8, 9, 10 or 11;

(2) adding ferric sulfate to perform precipitation reaction;

(3) adding alkali liquor again to adjust the pH value to 3-9, such as 3, 4, 5, 6, 7, 8 or 9; after ferric sulfate is added in the step (2), because ferric sulfate belongs to strong acid and weak base salt, the pH value of wastewater can be reduced, and the reaction environment is influenced, so that alkaline liquor is added to adjust the pH value, on one hand, complete precipitation is facilitated, on the other hand, when the addition of ferric sulfate cannot enable phosphate radical to be fully precipitated, the generated precipitate and the added alkaline liquor can form hydroxyl complex colloid without filtration within the range of pH value of 3-9, and the phosphate radical is further adsorbed and removed.

(4) Adding a flocculating agent, stirring, standing, and performing solid-liquid separation to obtain a filtrate and a solid containing ferric phosphate; the flocculant is added to accelerate the coagulation of the precipitated particles, form larger-particle precipitates and enable solid and liquid to be separated more easily;

(5) adding calcium hydroxide into the filtrate obtained in the step (4), carrying out precipitation reaction, and carrying out solid-liquid separation to obtain filtrate and a solid containing calcium sulfate;

wherein the alkali liquor comprises any one or a combination of at least two of sodium hydroxide, potassium hydroxide or ammonia water, wherein the typical but non-limiting combination is as follows: a combination of sodium hydroxide and ammonia, a combination of potassium hydroxide and ammonia, and a combination of sodium hydroxide and potassium hydroxide. The alkali liquor of the invention does not influence the subsequent separation of sulfate radicals, and overcomes the technical problem that the addition of some alkali liquor is not beneficial to the subsequent removal of sulfate radicals in the prior art.

The method comprises the steps of adding a certain amount of ferric sulfate solid into ferric phosphate wastewater containing phosphate radicals, sulfate radicals and ammonia nitrogen, enabling the ferric phosphate solid to fully react with the phosphate radicals in the water to generate ferric phosphate precipitates, and recovering the precipitates. And adding lime into the residual sulfate radicals in the wastewater to generate calcium sulfate, and recovering and removing the calcium sulfate.

The lye of the present invention preferably comprises a combination of at least two of sodium hydroxide, potassium hydroxide and aqueous ammonia.

Preferably, the alkali liquor is selected from any one of sodium hydroxide and ammonia water mixed according to a volume ratio of (0.1-3): 1, potassium hydroxide and ammonia water mixed according to a volume ratio of (0.1-3): 1, sodium hydroxide and potassium hydroxide mixed according to a volume ratio of (0.1-3): 1 or sodium hydroxide, potassium hydroxide and ammonia water mixed according to a volume ratio of (0.1-2): 1.

For example, the volume ratio of sodium hydroxide to ammonia is 0.1:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, or 3:1, etc. The volume ratio of the potassium hydroxide to the ammonia water is 0.1:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1 or 3:1, and the like. The volume ratio of sodium hydroxide to potassium hydroxide is 0.1:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1 or 3:1, etc. The volume ratio of the sodium hydroxide to the potassium hydroxide to the ammonia water is 0.1:0.5:1, 0.5:2:1, 1:0.1:1, 1.5:2:1 or 2:1:1, and the like.

The pH value in the step (1) is preferably 5-10.

The mass of the added ferric sulfate in the step (2) of the invention is preferably determined by calculation according to the molar ratio of iron to phosphate radical of (0.5-2): 1, such as 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.8:1 or 2: 1.

Preferably, the mass of the added ferric sulfate in the step (2) is determined by calculating according to the molar ratio of iron to phosphate radical of (0.8-1.2): 1, so that the phosphate radical is separated thoroughly while iron ions are not remained as much as possible.

In the invention, the precipitate generated in the step (2) does not need to be filtered before the step (4), and the precipitate is left in the system to have a certain adsorption effect on phosphate radicals. The precipitation reaction of adding iron and phosphate radical is cooperated with the adsorption action, so that the separation of the phosphate radical can be ensured, the residual amount of ferric sulfate can be controlled in a small range, and the interference to the subsequent sulfate radical recovery step is reduced.

Preferably, the precipitation reaction in step (2) is stirred.

Preferably, the precipitation reaction time in step (2) is 30min to 2h, such as 30min, 45min, 1h, 1.2h, 1.5h or 2h, etc., preferably 30min to 1 h.

Preferably, the form of adding ferric sulfate in step (2) comprises an aqueous solution of ferric sulfate and/or ferric sulfate solids.

Preferably, the precipitation reaction in step (2) is followed by filtration.

The pH value in the step (3) of the invention is preferably 3-8, and more preferably 3.5-6.5.

The flocculant of step (4) of the present invention preferably comprises any one or a combination of at least two of PAM, PAC, PAS, PFC or PFS, wherein a typical but non-limiting combination is: a combination of PAM and PAC, a combination of PAC and PAS, a combination of PFC and PFS, a combination of PAM and PFC. Any one or a combination of at least two of PAM, PAC or PFS is preferred.

Preferably, the form of adding the flocculant in step (4) comprises an aqueous flocculant solution.

Preferably, the mass concentration of the flocculant in the flocculant aqueous solution is 0.5-5 wt%, such as 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 3 wt%, 4 wt% or 5 wt%, etc., preferably 0.5-2%.

Preferably, the ratio of the volume of the added flocculant aqueous solution in the step (4) to the volume of the treated wastewater is 1 (500-2000), such as 1:500, 1:600, 1:800, 1:1000, 1:1200, 1:1300, 1:1500, 1:1800 or 1:2000, etc., preferably 1 (500-1500).

Preferably, the stirring time in the step (4) is 2-10 min, such as 2min, 5min, 8min or 10min, and preferably 2-8 min.

Preferably, the standing time in the step (4) is 5-30 min, such as 5min, 10min, 15min, 20min, 25min or 30min, and preferably 10-30 min.

Preferably, the solid-liquid separation in step (4) comprises filtration.

The mass of the calcium hydroxide added in the step (5) of the present invention is determined according to the molar ratio of calcium to sulfate radical (1-2: 1), for example, 1:1, 1.2:1, 1.5:1, 1.8:1 or 2: 1.

Preferably, the mass of the added calcium hydroxide in the step (5) is determined according to the molar ratio of calcium to sulfate radical of (1.5-2): 1.

Preferably, the precipitation reaction in step (5) is stirred.

Preferably, the precipitation reaction time in step (5) is 20min to 2h, such as 20min, 25min, 30min, 45min, 1h, 1.5h or 2h, etc., preferably 20min to 1 h.

Preferably, the solid-liquid separation in step (5) comprises filtration.

Step (5) of the present invention preferably further comprises:

(6) and (5) adding carbonate into the filtrate obtained in the step (5), carrying out precipitation reaction, and carrying out solid-liquid separation to obtain a filtrate and a solid containing calcium carbonate. Excess calcium was removed.

Preferably, the carbonate salt in step (6) comprises any one of sodium carbonate, potassium carbonate, sodium bicarbonate or potassium bicarbonate or a combination of at least two thereof, wherein a typical but non-limiting combination is: a combination of sodium carbonate and potassium carbonate, a combination of potassium carbonate and potassium bicarbonate, a combination lamp of sodium bicarbonate and potassium carbonate, preferably sodium carbonate and/or potassium carbonate.

Preferably, the mass of the carbonate added in the step (6) is determined according to the molar ratio of calcium to carbonate being (1-3): 1, such as 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.5:1 or 3:1, etc.

Preferably, the mass of the added carbonate in the step (6) is determined according to the molar ratio of calcium to carbonate being (1-2): 1.

Preferably, the precipitation reaction in step (6) is stirred.

Preferably, the precipitation reaction time in the step (6) is 10min to 1h, such as 10min, 20min, 30min, 45min, 50min or 1h, etc., preferably 20 to 40 min.

Preferably, the solid-liquid separation in step (6) comprises filtration.

The step (6) of the present invention preferably further comprises:

(7) and (4) recovering ammonia nitrogen in the filtrate obtained in the step (6).

Preferably, the means of recovery comprises gas stripping rectification. No further adjustment of the pH is required.

As a preferred technical scheme of the invention, the method for removing the phosphate radical and the sulfate radical in the iron phosphate wastewater step by step comprises the following steps:

(1) adding alkali liquor into the iron phosphate wastewater to adjust the pH value to 4-11,

(2) adding ferric sulfate, stirring and carrying out precipitation reaction for 30 min-2 h; the mass of the added ferric sulfate is determined by calculating according to the molar ratio of iron to phosphate radical (0.5-2): 1;

(3) adding alkali liquor again to adjust the pH value to 3-9;

(4) adding a flocculant solution, wherein the mass concentration of the flocculant in the flocculant solution is 0.5-5 wt%, the volume ratio of the flocculant solution to the ferric phosphate wastewater is 1 (500-2000), stirring for 2-10 min, standing for 5-30 min, and filtering to obtain a filtrate and a solid containing ferric phosphate;

(5) adding calcium hydroxide into the filtrate obtained in the step (4), wherein the mass of the added calcium hydroxide is determined according to the molar ratio of calcium to sulfate radical (1-3) to 1; stirring, precipitating and reacting for 20 min-2 h, and filtering to obtain filtrate and solid containing calcium sulfate;

(6) adding carbonate into the filtrate obtained in the step (5), wherein the mass of the added carbonate is determined according to the molar ratio of calcium to carbonate (1-3) to 1; stirring, precipitating and reacting for 20 min-2 h, and filtering to obtain filtrate and solid containing calcium carbonate;

(7) gas stripping rectification is carried out on the filtrate obtained in the step (6) to recover ammonia nitrogen in the filtrate;

wherein the alkali liquor comprises one or at least two of sodium hydroxide, potassium hydroxide or ammonia water in a certain proportion.

Compared with the prior art, the invention has at least the following beneficial effects:

(1) traditional one-time precipitation is easy to occur, and the technical content required for separately recovering two mixed high-valence anions is high. The invention overcomes the technical problem that the prior precipitation technology can not remove and recover phosphate radical and sulfate radical step by step, the precipitation reaction of the phosphate radical and ferric sulfate requires proper pH value, the pH value of the reaction of the phosphate radical and ferric sulfate mastered by the invention can ensure that the phosphate radical can be precipitated to the maximum extent, and the purity of subsequent calcium sulfate recovery is ensured.

(2) The subsequent removal of sulfate radicals is not influenced while the pH value of the alkali liquor is adjusted, the technical problem that the addition of certain alkali liquor is not beneficial to the subsequent removal of the sulfate radicals is solved, and the respective removal of the phosphate radicals and the sulfate radicals is realized. The invention does not produce mixed sludge, the obtained ferric phosphate and calcium sulfate can be recovered, and the resource degree is higher than that of the prior art.

(3) The phosphate radical content of the final effluent is below 0.5g/L, and the sulfate radical content is below 1.5 g/L.

Drawings

FIG. 1 is a schematic flow diagram of a step-by-step removal method of phosphate radicals and sulfate radicals in iron phosphate wastewater.

Detailed Description

The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.

Example 1

Removing phosphate radicals and sulfate radicals in the iron phosphate wastewater step by step, which comprises the following specific steps:

1) taking iron phosphate production wastewater, testing the concentration of phosphate radical and sulfate radical in the wastewater, and adding alkali liquor to adjust the pH of the wastewater to 6-9;

2) adding ferric sulfate solid according to the concentration of the tested phosphate radical, wherein the mole number of iron ions is 0.5 times of that of the phosphate radical ions, and stirring for reaction for 30 min;

3) adding alkali liquor again to adjust pH to 3-3.5, and stirring for 2 min;

4) adding 5% PFC, wherein the volume ratio of PFC to the ferric phosphate wastewater is 1:2000, stirring and reacting for 10min, precipitating and standing for 30min, filtering to obtain a solid containing ferric phosphate and a filtrate, and analyzing the sulfate radical concentration and the phosphate radical concentration in the filtrate;

5) measuring the sulfate radical concentration in the filtrate obtained in the step 4), adding calcium hydroxide solid according to the molar ratio of calcium to sulfate radical of 1:1, stirring and reacting for 20min, standing and filtering to obtain calcium sulfate solid and filtrate, recovering the solid, and analyzing the filtrate for residual calcium concentration, sulfate radical concentration and phosphate radical concentration. And carrying out next treatment.

6) Adding sodium carbonate according to the molar ratio of carbonate to calcium of 1:1 of the concentration of calcium in the step 5), stirring for reacting for 20min, standing and filtering to obtain calcium carbonate solid and filtrate;

7) and (3) recovering ammonia nitrogen in the filtrate obtained in the step 6) through steam stripping rectification.

The alkali liquor is sodium hydroxide and ammonia water mixed according to the volume ratio of 0.1: 2.

The final water entry and exit indices are shown in table 1.

TABLE 1

Index (I)	Inflow water	Discharging water
			pH	1.13	12.58
Phosphate radical (mg/L)	17000	500 (step 4) discharging water, wherein,final water not detected)
			Sulfate radical (mg/L)	70000	1500
Ca(mg/L)	985	228
			Ammonia nitrogen (mg/L)	5400	<15

Example 2

The method for removing phosphate radicals and sulfate radicals in iron phosphate wastewater step by step comprises the following specific steps:

2) adding ferric sulfate solid according to the concentration of the tested phosphate radical, wherein the mole number of iron ions is 2 times of that of the phosphate radical ions, and stirring for reaction for 2 hours;

3) adding alkali liquor again to adjust pH to 7-8, and stirring for 2 min;

4) adding 3% PAS, stirring and reacting for 2min, wherein the volume ratio of the PAS to the iron phosphate wastewater is 1:500, precipitating and standing for 5min, filtering to obtain a solid containing iron phosphate and a filtrate, and analyzing the sulfate radical concentration and the phosphate radical concentration in the filtrate;

5) measuring the sulfate radical concentration in the filtrate obtained in the step 4), adding calcium hydroxide solid according to the molar ratio of calcium to sulfate radical of 1.2:1, stirring for reacting for 20min, standing and filtering to obtain calcium sulfate solid and filtrate, recovering the solid, and analyzing the residual calcium concentration, sulfate radical concentration and phosphate radical concentration in the filtrate. And carrying out next treatment.

6) Adding sodium carbonate according to the molar ratio of carbonate to calcium of 3:1 of the concentration of calcium in the step 5), stirring for reacting for 20min, standing and filtering to obtain calcium carbonate solid and filtrate;

The alkali liquor is sodium hydroxide and ammonia water mixed according to the volume ratio of 0.1: 1.

The final water entry and exit indices are shown in table 2.

TABLE 2

Index (I)	Inflow water	Discharging water
			pH	1.13	12.58
Phosphate radical (mg/L)	17000	200 (step 4) final effluent not detected)
			Sulfate radical (mg/L)	70000	1300
Ca(mg/L)	985	16
			Ammonia nitrogen (mg/L)	5400	<15

Example 3

2) adding ferric sulfate solid according to the concentration of the tested phosphate radical, wherein the mole number of iron ions is 1.2 times of that of the phosphate radical ions, and stirring for reaction for 30 min;

3) adding alkali liquor again to adjust pH to 3.5-4.5, stirring for 2 min;

4) adding 0.5% PFS, stirring and reacting for 5min, wherein the volume ratio of the PFS to the ferric phosphate wastewater is 1:1500, precipitating and standing for 30min, filtering to obtain a solid containing ferric phosphate and a filtrate, and analyzing the sulfate concentration and the phosphate concentration in the filtrate;

6) Adding sodium carbonate according to the molar ratio of carbonate to calcium of 2:1 of the concentration of calcium in the step 5), stirring for reacting for 20min, standing and filtering to obtain calcium carbonate solid and filtrate;

7) and 6) carrying out steam stripping rectification on the filtrate obtained in the step 6) to recover ammonia nitrogen in the filtrate.

The alkali liquor is potassium hydroxide and ammonia water mixed according to the volume ratio of 3: 1.

The final water entry and exit indices are shown in table 3.

TABLE 3

Index (I)	Inflow water	Discharging water
			pH	1.13	12.58
Phosphate radical (mg/L)	17000	500 (step 4) Water out, Final Water out not detected)
			Sulfate radical (mg/L)	70000	1200
Ca(mg/L)	985	20
			Ammonia nitrogen (mg/L)	5400	<15

Example 4

2) adding ferric sulfate solid according to the concentration of the tested phosphate radical, wherein the mole number of iron ions is 1.5 times of that of the phosphate radical ions, and stirring for reaction for 1 h;

3) adding alkali liquor again to adjust pH to 5-7, and stirring for 2 min;

4) adding 2% PAC, stirring and reacting for 5min, wherein the volume ratio of the PAC to the ferric phosphate wastewater is 1:1000, precipitating and standing for 20min, filtering to obtain a solid containing ferric phosphate and a filtrate, and analyzing the sulfate radical concentration and the phosphate radical concentration in the filtrate;

5) measuring the sulfate radical concentration in the filtrate obtained in the step 4), adding calcium hydroxide solid according to the molar ratio of calcium to sulfate radical of 2:1, stirring and reacting for 20min, standing and filtering to obtain calcium sulfate solid and filtrate, recovering the solid, and analyzing the filtrate for residual calcium concentration, sulfate radical concentration and phosphate radical concentration. And carrying out next treatment.

6) Adding sodium carbonate according to the molar ratio of carbonate to calcium of 1.3:1 of the concentration of calcium in the step 5), stirring for reacting for 20min, standing and filtering to obtain calcium carbonate solid and filtrate;

The alkali liquor is sodium hydroxide and ammonia water mixed according to the volume ratio of 2: 1.

The final water entry and exit indices are shown in table 4.

TABLE 4

Index (I)	Inflow water	Discharging water
			pH	1.13	12.58
Phosphate radical (mg/L)	17000	200 (step 4) discharging water, final discharging water is not detected)
			Sulfate radical (mg/L)	70000	800
Ca(mg/L)	985	100
			Ammonia nitrogen (mg/L)	5400	<15

Example 5

2) adding ferric sulfate solid according to the concentration of the tested phosphate radical, wherein the mole number of iron ions is 1 time of that of the phosphate radical ions, and stirring for reacting for 45 min;

3) adding alkali liquor into the reaction solution again to adjust the pH to 4-5, and stirring for 2 min;

4) adding 1% PAM, stirring and reacting for 7min, wherein the volume ratio of the PAM to the ferric phosphate wastewater is 1:800, precipitating and standing for 25min, filtering to obtain a solid containing ferric phosphate and a filtrate, and analyzing the sulfate radical concentration and the phosphate radical concentration in the filtrate;

5) measuring the sulfate radical concentration in the filtrate obtained in the step 4), adding calcium hydroxide solid according to the molar ratio of calcium to sulfate radical of 1.8:1, stirring for reacting for 20min, standing and filtering to obtain calcium sulfate solid and filtrate, recovering the solid, and analyzing the residual calcium concentration, sulfate radical concentration and phosphate radical concentration in the filtrate. And carrying out next treatment.

6) Adding sodium carbonate according to the molar ratio of carbonate to calcium of 1.8:1 of the concentration of calcium in the step 5), stirring for reacting for 20min, standing and filtering to obtain calcium carbonate solid and filtrate;

The alkali liquor is sodium hydroxide, potassium hydroxide and ammonia water which are mixed according to the volume ratio of 1:0.3: 1.

The final water entry and exit indices are shown in table 5.

TABLE 5

Index (I)	Inflow water	Discharging water
			pH	1.13	12.58
Phosphate radical (mg/L)	17000	200 (step 4) discharging water, final discharging water is not detected)
			Sulfate radical (mg/L)	70000	1000
Ca(mg/L)	985	30
			Ammonia nitrogen (mg/L)	5400	<15

Comparative example 1

The difference from example 5 is that: the alkali liquor is replaced by sodium hydroxide.

The final water entry and exit indices are shown in table 6.

Comparative example 2

The difference from example 5 is that: the pH value range regulated in the step 2) is 9.5-11.

The final water entry and exit indices are shown in table 7.

Comparative example 3

The only difference from example 5 is that: and (3) adding a filtering step after the step 2), separating ferric sulfate precipitate from the reaction liquid, and further processing the filtrate in the step 3).

The final water entry and exit indices are shown in Table 8.

TABLE 6

Index (I)	Inflow water	Discharging water
			pH	1.13	12.58
Phosphate radical (mg/L)	17000	320 (step 4) discharging water, final discharging water is not detected)
			Sulfate radical (mg/L)	70000	2000
Ca(mg/L)	985	30
			Ammonia nitrogen (mg/L)	5400	<15

TABLE 7

Index (I)	Inflow water	Discharging water
			pH	1.13	12.58
Phosphate radical (mg/L)	17000	700 (step 4) Water out, Final Water out not detected)
			Sulfate radical (mg/L)	70000	25000
Ca(mg/L)	985	30
			Ammonia nitrogen (mg/L)	5400	<15

TABLE 8

Index (I)	Inflow water	Discharging water
			pH	1.13	12.58
Phosphate radical (mg/L)	17000	1000 (step 4) discharging water, final discharging water not detected)
			Sulfate radical (mg/L)	70000	1000
Ca(mg/L)	985	30
			Ammonia nitrogen (mg/L)	5400	<15

Comparing the results of example 5 with those of comparative examples 1-2, it can be seen that the adjustment of the pH in the present invention is critical for the first step of phosphate removal, and that a pH outside the scope of the invention results in a very incomplete separation of phosphate and a reduced recovery of sulfate; and the pH and the composite alkali liquor have a synergistic effect, the effect of the combination of the pH and the composite alkali liquor is obviously better than the separation effect of a single alkali liquor, and the results of the comparative example 5 and the comparative example 3 show that the addition of ferric sulfate according to the metering ratio can not completely precipitate phosphate radicals, under the condition, the further removal of the phosphate radicals is more facilitated without filtering, and the influence of the residual iron of excessive ferric sulfate on the recovery quality of the sulfate radicals is also avoided, so that the synergistic effect between the non-filtering and the addition of the ferric sulfate is embodied.

The applicant states that the present invention is illustrated by the above examples to show the detailed process equipment and process flow of the present invention, but the present invention is not limited to the above detailed process equipment and process flow, i.e. it does not mean that the present invention must rely on the above detailed process equipment and process flow to be implemented. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims

1. A step-by-step removal method of phosphate radicals and sulfate radicals in iron phosphate wastewater is characterized by comprising the following steps:

(1) adding alkali liquor into the iron phosphate wastewater to adjust the pH value to 4-11;

(2) adding ferric sulfate to perform precipitation reaction;

(3) adding alkali liquor again to adjust the pH value to 3-9;

(4) adding a flocculating agent, stirring, standing, and performing solid-liquid separation to obtain a filtrate and a solid containing ferric phosphate;

wherein the alkali liquor comprises any one or a combination of at least two of sodium hydroxide, potassium hydroxide or ammonia water.

2. The method of claim 1, wherein the lye comprises a combination of at least two of sodium hydroxide, potassium hydroxide and aqueous ammonia.

3. The method according to claim 2, wherein the alkali solution is selected from any one of sodium hydroxide and ammonia water mixed according to a volume ratio of (0.1-3): 1, potassium hydroxide and ammonia water mixed according to a volume ratio of (0.1-3): 1, sodium hydroxide and potassium hydroxide mixed according to a volume ratio of (0.1-3): 1 or sodium hydroxide, potassium hydroxide and ammonia water mixed according to a volume ratio of (0.1-2): 1.

4. The method of claim 1 or 2, wherein the pH in step (1) is 5 to 10.

5. The method of claim 1 or 2, wherein the mass of the added ferric sulfate in the step (2) is determined by calculating the molar ratio of the iron to the phosphate to be (0.5-2): 1.

6. The method of claim 5, wherein the mass of the added ferric sulfate in the step (2) is determined by calculating the molar ratio of the iron to the phosphate to be (0.8-1.2): 1.

7. The method of claim 1 or 2, wherein the precipitation reaction of step (2) is stirred.

8. The method of claim 1 or 2, wherein the precipitation reaction time in step (2) is 30min to 2 h.

9. The method of claim 8, wherein the precipitation reaction time in step (2) is 30min to 1 h.

10. The method of claim 1 or 2, wherein the form of added iron sulfate in step (2) comprises an aqueous solution of iron sulfate and/or iron sulfate solids.

11. The method of claim 1 or 2, wherein the precipitation reaction in step (2) is followed by filtration.

12. The method of claim 1 or 2, wherein the pH in step (3) is 3 to 8.

13. The method of claim 12, wherein the pH of step (3) is 3.5 to 6.5.

14. The method of claim 1 or 2, wherein the flocculant of step (4) comprises any one of PAM, PAC, PAS, PFC or PFS or a combination of at least two thereof.

15. The method of claim 14, wherein the flocculant of step (4) comprises any one of PAM, PAC or PFS or a combination of at least two.

16. The method of claim 1 or claim 2, wherein the form of adding the flocculent in step (4) comprises an aqueous flocculent solution.

17. The method of claim 16, wherein the mass concentration of the flocculant in the aqueous flocculant solution is 0.5 to 5 wt%.

18. The method of claim 17, wherein the mass concentration of the flocculant in the aqueous flocculant solution is 0.5 to 2 wt%.

19. The method according to claim 1 or 2, wherein the volume ratio of the flocculant adding water solution in the step (4) to the ferric phosphate wastewater is 1 (500-2000).

20. The method according to claim 19, wherein the ratio of the volume of the flocculant aqueous solution added in the step (4) to the volume of the ferric phosphate wastewater is 1 (500-1500).

21. The method of claim 1 or 2, wherein the stirring time in step (4) is 2-10 min.

22. The method of claim 1 or 2, wherein the stirring time in step (4) is 2-8 min.

23. The method of claim 1 or 2, wherein the standing time in the step (4) is 5 to 30 min.

24. The method of claim 23, wherein the standing time in the step (4) is 10-30 min.

25. The method of claim 1 or 2, wherein the solid-liquid separation of step (4) comprises filtration.

26. The method according to claim 1 or 2, wherein the mass of the calcium hydroxide added in the step (5) is determined according to the molar ratio of calcium to sulfate being (1-3): 1.

27. The method according to claim 26, wherein the mass of the calcium hydroxide added in the step (5) is determined according to the molar ratio of calcium to sulfate being (1.5-2): 1.

28. The method of claim 1 or 2, wherein the precipitation reaction of step (5) is stirred.

29. The method of claim 1 or 2, wherein the precipitation reaction time in step (5) is 20min to 2 h.

30. The method of claim 29, wherein the precipitation reaction of step (5) is carried out for a period of time ranging from 20min to 1 h.

31. The method of claim 1 or 2, wherein the solid-liquid separation of step (5) comprises filtration.

32. The method of claim 1 or 2, wherein step (5) is further followed by:

(6) and (5) adding carbonate into the filtrate obtained in the step (5), carrying out precipitation reaction, and carrying out solid-liquid separation to obtain a filtrate and a solid containing calcium carbonate.

33. The method of claim 32, wherein the carbonate salt of step (6) comprises any one of sodium carbonate, potassium carbonate, sodium bicarbonate, or potassium bicarbonate, or a combination of at least two thereof.

34. The method of claim 33, wherein the carbonate salt of step (6) is sodium carbonate and/or potassium carbonate.

35. The method according to claim 32, wherein the mass of the carbonate added in step (6) is determined according to the molar ratio of calcium to carbonate being (1-3): 1.

36. The method according to claim 35, wherein the mass of the added carbonate in the step (6) is determined according to the molar ratio of calcium to carbonate being (1-2): 1.

37. The method of claim 32, wherein the precipitation reaction of step (6) is stirred.

38. The method of claim 32, wherein the precipitation reaction of step (6) is carried out for a time period of 10min to 1 h.

39. The method of claim 38, wherein the precipitation reaction of step (6) is carried out for a period of 20min to 40 min.

40. The method of claim 32, wherein the solid-liquid separation of step (6) comprises filtration.

41. The method of claim 32, wherein step (6) is further followed by:

42. The method of claim 41, wherein the means for recovering comprises gas stripping rectification.

43. The method of claim 1, comprising the steps of:

(3) adding alkali liquor again to adjust the pH value to 3-9;

(4) adding a flocculant solution, wherein the mass concentration of the flocculant in the flocculant solution is 0.5-5 wt%, and the volume ratio of the flocculant solution to the ferric phosphate wastewater is 1 (500-2000); stirring for 2-10 min, standing for 5-30 min, and filtering to obtain filtrate and solid containing iron phosphate;

(6) adding carbonate into the filtrate obtained in the step (5), wherein the mass of the added carbonate is determined according to the molar ratio of calcium to carbonate (1-3) to 1; stirring, precipitating and reacting for 10 min-1 h, and filtering to obtain filtrate and solid containing calcium carbonate;