CN112090018A

CN112090018A - Process for treating fly ash by using purified waste acid

Info

Publication number: CN112090018A
Application number: CN202010878032.7A
Authority: CN
Inventors: 张万柏; 沈莹; 赵宏飞; 曹向东; 杨晶; 秦二兰; 位百勇; 张大龙; 熊大伟; 黄岚; 马名烽
Original assignee: Bbmg Hongshulin Environmental Protection Technology Co ltd; BEIJING ECO-ISLAND SCIENCE AND TECHNOLOGY CO LTD; Bbmg Liushui Environmental Protection Technology Co ltd
Current assignee: BBMG HONGSHULIN ENVIRONMENTAL PROTECTION TECHNOLOGY Co.,Ltd.; BBMG LIUSHUI ENVIRONMENTAL PROTECTION TECHNOLOGY Co.,Ltd.; BEIJING ECO-ISLAND SCIENCE AND TECHNOLOGY Co.,Ltd.; BEIJING JINYU BEISHUI ENVIRONMENTAL PROTECTION TECHNOLOGY Co.,Ltd.
Priority date: 2020-08-27
Filing date: 2020-08-27
Publication date: 2020-12-18

Abstract

The invention relates to a process for treating fly ash by using purified waste acid. The method comprises the following steps: (1) mixing the fly ash with water, and uniformly stirring to obtain slurry; (2) adding the purified waste acid into the slurry obtained in the step (1) for full reaction to obtain a reaction solution; (3) and (3) filtering the reaction liquid obtained in the step (2) to obtain a filter cake and a filtrate. The purified waste acid is applied to a fly ash production line, the addition of acid is controlled, the pilot test effect is good, and multiple effects of absorbing the waste acid and improving heavy metals in the crystallized salt are achieved. The technical combination of waste acid and hazardous waste fly ash is realized, the comprehensive saving and recycling of resources are promoted, the environmental and safety problems caused by the stockpiling of high-concentration waste acid and fly ash are reduced, and the national policy guidance and social development requirements are completely met.

Description

Process for treating fly ash by using purified waste acid

Technical Field

The invention belongs to the field of environmental protection, and particularly relates to a process for treating fly ash by using purified waste acid.

Background

Sulfuric acid is the most active strong, binary inorganic acid and reacts with most metals. The high-concentration sulfuric acid has strong water absorption and can be used as dehydrating agent, carbonized wood, paper, cotton-linen fabric, biological skin and meat and other substances containing carbohydrate. When mixed with water, a large amount of heat energy is also released. It is strongly corrosive and oxidative. Sulfuric acid is one of important basic chemical raw materials, has wide application, can be used for manufacturing fertilizers, medicines, explosives, pigments, detergents, storage batteries and the like, and is also widely applied to industries of purifying petroleum, metal smelting, dyes and the like. Is commonly used as a chemical reagent and can be used as a dehydrating agent and a sulfonating agent in organic synthesis.

In the use process of some industries, sulfuric acid enters products after chemical reaction, or sulfate byproducts are formed, such as industries of chemical fertilizers, chemical fibers, feeds and the like; in other industries, sulfuric acid is used in drying, catalysis, alkylation, acid washing and other processes, and finally waste sulfuric acid containing impurities is produced and needs to be subjected to subsequent treatment.

In addition, fly ash generated by burning urban domestic garbage is enriched with some harmful heavy metals and is regarded as an important environmental pollutant. The traditional treatment methods mainly comprise safe landfill disposal, acid-base reagent leaching, chemical stabilization, melting treatment and the like, but all the methods cause damage to the environment.

Research in the present stage shows that the water washing fly ash can not remove insoluble chlorine (CaO. Al)₂O₃.CaCl2.10H₂O; AlOCl) to make the mixing proportion of the fly ash into the kiln lower. In recent years, research on acid-washing fly ash technology is carried out by a plurality of subject groups in China, wherein the subject group of Wang Hui group professor of Beijing university of science and technology analyzes the main chemical composition of the waste incineration fly ash, inspects the influence of the water washing process on the removal of main elements and heavy metals in the fly ash, the chemical composition change in the water washing process and the acid-washing effect of heavy metals in the fly ash, and evaluates the stability of acid-washing fly ash acid-washing residues. The results show that: when the L/S is 20, more than 60% of Cl, more than 47% of Na, K and Ca and more than 18% of Pb can be leached out in the water washing process. After washing, the contents of heavy metals Zn, Pb and Cu are respectively increased by 76.37%, 21.91% and 46.16%. Compared with the original ash, the leaching amount of Zn in the acid leaching process of the water washing fly ash is also greatly improved, and the leaching amount of Pb is slightly increased. When HCl concentration is high<At 1M (mol/L), the leaching of Pb and Zn increases rapidly with increasing HCl concentration, mainly because the exchangeable and carbonate bound states of heavy metals are sensitive to changes in ionic strength and pH in solution. Continuous extraction experiments on the washed fly ash acid leaching residues show that heavy metals mainly exist in a residual state, and the stability of the heavy metals is obviously improved.

However, the prior art does not have a technology for combining waste acid and fly ash, so further research is needed.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a process for treating fly ash by using purified waste acid. The process applies advanced diffusion dialysis membrane technology to effectively remove heavy metals in waste acid, and the waste acid pretreated by the method is applied to a fly ash production line, so that multiple effects of consuming the waste acid, saving alkali and improving the heavy metals in crystalline salt can be achieved, and the comprehensive utilization of waste-waste resources produced by using waste to prepare waste is realized.

The invention provides a process for treating fly ash by using purified waste acid, which comprises the following steps:

(1) mixing the fly ash with water, and uniformly stirring to obtain slurry;

(2) adding the purified waste acid into the slurry obtained in the step (1) for full reaction to obtain a reaction solution;

(3) and (3) filtering the reaction liquid obtained in the step (2) to obtain a filter cake and a filtrate.

Preferably, in the step (1), the weight ratio of the fly ash to the water is 1: 2.8-3.2.

Preferably, the rotating speed of the stirring in the step (1) is 100-120 r/min.

Preferably, in the step (1), the stirring time is 30-40 min.

Preferably, in the step (2), the waste acid is purified by using a diffusion dialysis membrane technology.

Preferably, the waste acid is waste sulfuric acid.

Preferably, the addition amount of the waste sulfuric acid accounts for 7-8 wt% of the weight of the fly ash.

Preferably, the adding flow rate of the waste sulfuric acid is 300-350L/h.

Preferably, in the step (3), the filtration is performed by suction filtration.

Preferably, the suction filtration time is 5-6 min.

The technical research process of the invention is obtained by scientific verification of 3 rounds of repeated experiments, and 3 experiments are sequentially marked as experiment I, experiment II and experiment III.

Experiment I was performed first, as follows:

mixing fly ash and water according to the weight ratio of 1:3 to obtain slurry a, setting 4 groups of experiments on the basis of the slurry a, and marking the experiments as I-0, I-60, I-70 and I-100, wherein 0ml of purified sulfuric acid, 60ml of purified sulfuric acid, 70ml of purified sulfuric acid and 100ml of purified sulfuric acid are respectively added into the slurry a to obtain corresponding reaction liquid. And then performing a correlation test.

The basic physicochemical data of the reaction solution are shown in Table 1.

TABLE 1 basic physicochemical data of the reaction solutions

Group of	Volume/ml	Mass/g	Ca/(mg/L)	Pb/(mg/L)	pH
						I-0	540	554	1.70×10⁴	59.8	12
I-60	320	334	1.66×10⁴	4.70	9
						I-70	370	370	1.46×10⁴	2.11	8
I-100	410	410	1.18×10⁴	1.33	8

The heavy metal content of the reaction solution is shown in table 2.

TABLE 2 heavy Metal content (mg/L)

The particle sizes of the reaction liquid and fly ash (unreacted raw fly ash) are shown in Table 3.

TABLE 3 particle size analysis (%)

Note: a indicates that the group was not subjected to the ultrasonic process; b indicates that the group was subjected to an ultrasonic process.

After the reaction of the reaction solution was completed, suction filtration was performed, and the obtained filter cake and fly ash (unreacted raw fly ash) were subjected to XRF analysis, respectively, and the results are shown in table 4.

TABLE 4 XRF analysis results (%)

Composition (I)	Fly ash	I-0	I-60	I-70	I-100
						SiO₂	8.96	10.31	9.57	9.53	9.31
Al₂O₃	3.77	3.87	3.72	3.67	3.56
						Fe₂O₃	1.47	1.99	1.69	1.69	1.59
CaO	37.56	52.40	54.38	55.56	60.12
						MgO	3.19	3.73	3.06	2.94	2.20
K₂O	5.07	1.20	1.60	1.51	1.16
						Na₂O	3.99	0.88	0.87	0.88	0.77
SO₃	5.54	6.26	9.30	10.16	11.72
						Cl^-	17.894	4.442	6.127	5.595	5.007

The XRD test patterns are respectively shown in figure 1 and figure 2.

The experimental phenomena during the execution of experiment I were: adding water into fly ash, dissolving, slowly adding sulfuric acid, making a moistening sound, placing a wet pH test paper over a beaker, making the test paper become orange red, and volatilizing acidic gas; the beaker is heated in the reaction process, and reaction heat is generated; after the acid is added dropwise, the solution becomes viscous; the suction filtration is difficult to change, and the grain composition is thinned.

For the volatilization of acid gas during the reaction, the subsequent pilot test is recommended to adopt plug-in addition of concentrated sulfuric acid to avoid the escape of the acid gas or adopt multi-point addition. In addition, according to the time of the first-stage water washing, the flow rate of dropwise adding sulfuric acid is adjusted so as to ensure that the sulfuric acid reacts fully as slowly as possible.

The experimental data are analyzed to obtain:

(1) compared with the filtrate generated by washing the fly ash with water, the volume of the acid washing fly ash is reduced by more than 200 milliliters, the alkalinity is weakened, the Pb content in heavy metal is obviously reduced, and the increase of the Cd content and other changes are not obvious.

(2) Compared with a filter cake of the water-washed fly ash, the particle size of slurry of the acid-washed fly ash is larger, and the content of most heavy metals (As, Cd, Cr, Cu, Fe, Hg, Ni, Pb, Zn, Ca and Mg) in total heavy metal analysis (XRF) is obviously reduced. The content of most heavy metals (As, Cd, Cr, Cu, Fe, Ni, Pb, Zn and Ca) in the heavy metal filtrate is obviously reduced.

(3) From the XRD patterns shown in fig. 1 and 2, it can be seen that: diffraction peaks of the acid-washed fly ash are obviously enhanced at the positions of 14 degrees and 26 degrees, wherein 14 degrees is CaSO₄.0.76H₂Characteristic diffraction peak of O, CaSO at 26 DEG₄Characteristic diffraction peaks. Indicating that there are a large amount of Ca ions and SO₄ ^2-The binding forms calcium sulfate precipitates that are trapped in the filter cake.

And combining the data of the experiment I, reducing the consumption of the waste sulfuric acid by the experiment II, and paying attention to the change of the Pb content in the filtrate and the influence of the added acid on the experiment suction filtration efficiency.

The procedure for experiment II is specifically as follows:

mixing fly ash and water according to the weight ratio of 1:3 to obtain slurry b, setting 6 groups of experiments on the basis of the slurry b, and marking as II-0, II-15, II-20, II-30, II-40 and II-50, wherein 0ml of purified sulfuric acid, 15ml of purified sulfuric acid, 20ml of purified sulfuric acid, 30ml of purified sulfuric acid, 40ml of purified sulfuric acid and 50ml of purified sulfuric acid are respectively added into the slurry b to obtain corresponding reaction liquid. And then performing a correlation test.

The heavy metal content of the reaction solution is shown in table 5.

TABLE 5 heavy Metal content (mg/L)

The basic physicochemical data of the reaction solution are shown in Table 6.

TABLE 6 basic physicochemical data of the reaction solutions

The experimental phenomena during the run of experiment II were: adding water into fly ash, dissolving, slowly adding sulfuric acid, making a moistening sound, placing a wet pH test paper over a beaker, making the test paper become orange red, and volatilizing acidic gas; the beaker is heated in the reaction process, and reaction heat is generated; after the acid is added dropwise, the solution becomes slightly viscous; the later stage of the filtration becomes slightly difficult.

The experimental data are analyzed to obtain:

(1) hardness dissolution: with the increase of the acid dosage, the dissolution of calcium hardness in the fly ash is gradually reduced, and calcium sulfate generated by the reaction is filtered and intercepted to a solid phase; as the amount of sulfuric acid was increased to 50ml, Mg was dissolved out.

(2) Typical heavy metal dissolution: along with the increase of the use amount of the sulfuric acid, the pH value of the fly ash filtrate gradually becomes smaller, and the Pb elution amount is obviously reduced; the Zn elution amount is firstly reduced and then increased, and the elution amount reaches 0.080mg/L at the minimum when 20ml of sulfuric acid is added. But Mg and Cd are gradually dissolved out with the increase of the dosage of the sulfuric acid.

(3) The volume of the filtrate was obtained: with the increase of the acid dosage, the loss rate of the filtrate is gradually increased within a certain suction filtration time of 6min, but the abnormal reduction occurs when 30ml of acid is added (the important point of the experiment is repeated). The same time (3min) was used for the three minutes before suction filtration with little change in the filtrate flow rate to give 350ml of filtrate.

Next, experiment III, which is a repetition experiment, was performed to mainly verify the repetition reliability of the experiment in which less than 30ml of waste sulfuric acid was added to the fly ash water wash (experiment was performed by replacing fly ash).

Also, in the foregoing manner, III-0, III-10, III-20, and III-30 are set to represent the water washing fly ash process, respectively, and the fly ash slurry takes up the waste sulfuric acid in an amount of 0ml, 10ml, 20ml, and 30 ml.

Experiments carried out by using fly ash different from the first two producing areas show that the experimental phenomenon does not have great change compared with the first two producing areas, the pH value is more than 9 when the acid adding amount is less than 30ml, heavy gold Mg is not dissolved out, and the contents of other heavy metals such as Ca, pb and the like also have a remarkable reduction trend. Specific experimental data are shown in tables 7 and 8.

TABLE 7 basic physicochemical data of the reaction solution

TABLE 8 heavy Metal content (mg/L) in the reaction solution

Heavy metal species	III-0	III-10	III-20	III-30
					As	Not detected out	Not detected out	Not detected out	Not detected out
Cd	Not detected out	Not detected out	Not detected out	0.220
					Cr	Not detected out	Not detected out	Not detected out	Not detected out
Hg	Not detected out	Not detected out	Not detected out	Not detected out
					Ni	Not detected out	Not detected out	Not detected out	Not detected out
Pb	9.72	6.72	3.20	2.79
					Zn	Not detected out	Not detected out	Not detected out	Not detected out
K	9.05×10³	9.83×10³	8.90×10³	8.28×10³
					Na	3.74×10⁴	2.78×10⁴	1.67×10⁴	1.34×10⁴
Ca	1.18×10⁴	1.14×10⁴	9.4×10³	8.9×10³
					Mg	Not detected out	Not detected out	Not detected out	Not detected out

The data and phenomena of experiment I, experiment II and experiment III are combined to obtain:

(1) hardness dissolution: along with the increase of the dosage of the sulfuric acid, the hardness dissolution of calcium in the fly ash is gradually reduced, and a calcium sulfate slightly soluble substance generated by the reaction is filtered and trapped in a solid-phase filter cake; this is demonstrated by XRD data (comparing XRD patterns of acid-washed fly ash and water-washed fly ash shows that diffraction peaks of acid-washed fly ash are obviously enhanced at 14 degree and 26 degree positions, wherein 14 degree is CaSO₄.0.76H₂Characteristic diffraction peak of O, 26 degrees CaSO₄Characteristic diffraction peaks); the pH of the filtrate becomes gradually smaller with the increase of the dosage of the sulfuric acid, and Mg can not be dissolved out when the dosage of the sulfuric acid is less than 40 ml.

(2) Typical metal dissolution: as the amount of sulfuric acid used increases, the amount of Pb in the solution decreases significantly; the dissolution of other heavy metals is required to be inhibited in process control, the pH is controlled to be more than 9, and multiple effects of absorbing waste acid, saving alkali and improving heavy metals in evaporation and crystallization salt can be realized.

(3) Acid addition process recommendations: for the volatilization of acid gas during reaction, the insertion-type addition of concentrated sulfuric acid is suggested to avoid the escape of the acid gas during pilot test, or multi-point addition is adopted; in addition, according to the time of the first-stage water washing, the flow rate of dropwise adding sulfuric acid is adjusted so as to ensure that the sulfuric acid fully reacts as slowly as possible.

(4) The dosage of sulfuric acid is as follows: considering the experimental data comprehensively, the overall operation of the fly ash system is not affected when adding the waste acid, the heat release is counteracted and the like, so that the pilot test experiment is recommended to be carried out according to the proportion of 7.5 percent of the waste acid in the total amount of the fly ash (namely, 30ml of sulfuric acid (30 percent) is added into 200g of the fly ash).

(5) Possible effects on the production process: the addition of acid may result in a fine particle size distribution, increasing the difficulty of solid-liquid separation.

And (4) conclusion: the results of repeated bench tests and analysis of experimental data can be obtained as follows: when the acid is added according to the proportion of 7.5 percent, the heavy metal Pb in the solution is obviously reduced, Ga has the tendency of reduction, and the multiple effects of absorbing waste acid, saving alkali and improving heavy metal in evaporation and crystallization salt can be achieved. Therefore, pilot experiments are feasible.

Pilot experiments were performed immediately thereafter. According to the analysis of the whole fly ash washing process and the water treatment process principle, the addition of waste acid in the first-stage washing tank does not have great influence on the prior process; the experimental data were considered together and pilot experiments were planned with an addition rate of 7.5%.

The experiments are divided into 5 groups and are named as E-0, E-260, E-280, E-300 and E-340 in sequence, and the adding amount of the waste sulfuric acid is respectively 0, 260L/h, 280L/h, 300L/h and 340L/h.

The basic physical and chemical properties of the respective reaction liquids obtained are shown in Table 9.

TABLE 9 basic physicochemical data of the reaction solutions

Numbering	Ca(mg/L)	Pb(mg/L)	S(mg/L)	pH
					E-0	4.28×10³	3.72	16.8	12
E-260	4.50×10³	3.40	16.1	12
					E-280	5.00×10³	3.69	14.3	12
E-300	2.90×10³	1.33	22.4	12
					E-340	5.90×10³	3.80	12.7	12

The contents of heavy metal elements in the reaction solution are shown in table 10.

TABLE 10 heavy Metal element content (mg/L)

The slag content and particle size distribution of some of the experimental groups are shown in Table 11.

TABLE 11 slag content and particle size distribution

The pilot experiment phenomenon is as follows: after the sulfuric acid is added, the temperature of the first-stage water washing tank and the first-stage filtrate tank is obviously increased. When the fly ash is thrown into the water washing tank, white slightly irritant alkaline gas escapes, and the gas escape time generally lasts about 30 s.

By analyzing the data, it can be obtained that:

(1) hardness dissolution: with the increase of the use amount of the sulfuric acid, the dissolution of calcium hardness in the fly ash slightly fluctuates, and when the acid addition amount reaches 300L/h, the dissolution of calcium is reduced by 30 percent; as the use amount of the sulfuric acid is increased, the pH value of the fly ash filtrate is basically unchanged, and Mg is not separated out.

(2) Typical heavy metal dissolution: the Pb elution amount fluctuates with the increase of the use amount of sulfuric acid, and when the acid addition amount reaches 300L/h, the elution of lead is reduced by 60 percent.

(3) Total sulfur dissolution: the total sulfur dissolution change fluctuates along with the addition of sulfuric acid, and the total sulfur content is reduced by 24 percent when the acid addition amount reaches 340L/h.

(4) Slag content: with the addition of sulfuric acid, the slag content in the filtrate is obviously reduced and is as low as less than 1%.

Effect evaluation of pilot test experiment: after adding sulfuric acid, white and slightly irritant alkaline gas escapes from the primary water washing tank and the primary filtrate tank, the gas escape time generally lasts about 10s, and the gas tends to disappear and rise (wherein the filtrate rises from 46 ℃ to 52 ℃); the gas collection system is fully capable of digesting this overflow gas each time fly ash is dosed in a water wash tank; adding waste sulfuric acid into a fly ash primary washing system at 300-350L/h, and stably controlling the pH value to be about 12; during pilot plant experiments, softened soda ash usage was saved by 8.0%.

The invention has the beneficial effects that:

the purified waste acid is applied to a fly ash production line, the addition of acid is controlled, the pilot test effect is good, and multiple effects of absorbing the waste acid and improving heavy metals in the crystallized salt are achieved. The technical combination of waste acid and hazardous waste fly ash is realized, the comprehensive saving and recycling of resources are promoted, the environmental and safety problems caused by the stockpiling of high-concentration waste acid and fly ash are reduced, and the national policy guidance and social development requirements are completely met.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is the XRD pattern of the filter cake in experiment I, experiment I-0.

FIG. 2 is an XRD pattern of the acid washed filter cake from experiment I.

Fig. 3 is a flow chart of a pilot test.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the examples given herein without any inventive step, are within the scope of the present invention.

Example 1

The embodiment provides a process for treating fly ash by using purified waste acid, which comprises the following steps:

(1) mixing fly ash and water according to the weight ratio of 1:2.8, stirring for 30min under the condition of 100r/min, and uniformly stirring to obtain slurry;

(2) purifying the waste sulfuric acid by adopting a diffusion dialysis membrane technology, adding the purified waste sulfuric acid into the slurry obtained in the step (1) at a flow rate of 300L/h, wherein the waste sulfuric acid accounts for 7 wt% of the weight of the fly ash, and fully reacting to obtain a reaction solution;

(3) and (3) carrying out suction filtration on the reaction liquid obtained in the step (2) for 5min to obtain a filter cake and filtrate.

Example 2

(1) mixing fly ash and water according to the weight ratio of 1:3.2, stirring for 40min under the condition of 120r/min, and uniformly stirring to obtain slurry;

(2) purifying the waste sulfuric acid by adopting a diffusion dialysis membrane technology, adding the purified waste sulfuric acid into the slurry obtained in the step (1) at a flow rate of 350L/h, wherein the waste sulfuric acid accounts for 8 wt% of the weight of the fly ash, and fully reacting to obtain a reaction solution;

(3) and (3) carrying out suction filtration on the reaction liquid obtained in the step (2) for 6min to obtain a filter cake and filtrate.

Example 3

(1) mixing fly ash and water according to the weight ratio of 1:3, stirring for 35min under the condition of 110r/min, and uniformly stirring to obtain slurry;

(2) purifying the waste sulfuric acid by adopting a diffusion dialysis membrane technology, adding the purified waste sulfuric acid into the slurry obtained in the step (1) at the flow rate of 325L/h, wherein the waste sulfuric acid accounts for 7.5 wt% of the weight of the fly ash, and fully reacting to obtain a reaction solution;

(3) and (3) carrying out suction filtration on the reaction liquid obtained in the step (2) for 5.5min to obtain a filter cake and filtrate.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims

1. A process for treating fly ash by using purified waste acid is characterized by comprising the following steps:

(1) mixing the fly ash with water, and uniformly stirring to obtain slurry;

2. The process for treating fly ash by using purified waste acid as claimed in claim 1, wherein in the step (1), the weight ratio of fly ash to water is 1: 2.8-3.2.

3. The process for treating fly ash by using purified waste acid as claimed in claim 1, wherein in the step (1), the rotation speed of the stirring is 100-120 r/min.

4. The process for treating fly ash with purified waste acid according to claim 1, wherein in the step (1), the stirring time is 30-40 min.

5. The process for treating fly ash with purified waste acid according to claim 1, wherein the purified waste acid is treated by diffusion dialysis membrane technology in step (2).

6. The process for treating fly ash with purified spent acid according to claim 5, wherein the spent acid is spent sulfuric acid.

7. The process for treating fly ash with purified waste acid according to claim 6, wherein the waste sulfuric acid is added in an amount of 7-8 wt.% based on the weight of the fly ash.

8. The process for treating fly ash with purified waste acid according to claim 6, wherein the addition flow rate of the waste sulfuric acid is 300-350L/h.

9. The process for treating fly ash with purified waste acid according to claim 1, wherein in the step (3), the filtration is performed by suction filtration.

10. The process for treating fly ash with purified waste acid according to claim 9, wherein the suction filtration time is 5-6 min.