CN114772799B

CN114772799B - Method for treating polluted acid wastewater containing mercury and thallium

Info

Publication number: CN114772799B
Application number: CN202210694750.8A
Authority: CN
Inventors: 乔继扬; 刘峰彪; 郑曦; 刘艳丽; 杨小明; 张凯; 王纪勇
Original assignee: BGRIMM Technology Group Co Ltd
Current assignee: BGRIMM Technology Group Co Ltd
Priority date: 2022-06-20
Filing date: 2022-06-20
Publication date: 2022-09-02
Anticipated expiration: 2042-06-20
Also published as: CN114772799A

Abstract

The application provides a method for treating polluted acid wastewater containing mercury and thallium, and relates to the field of wastewater treatment. The method for treating the polluted acid wastewater containing mercury and thallium comprises the following steps: mixing the mercury-and thallium-containing waste acid water with sodium sulfide, carrying out a first reaction, and then adding polyacrylamide to carry out first flocculation and precipitation to obtain a first supernatant and first bottom mud; mixing the first supernatant and the lime milk until the pH value of the system is 2-3, carrying out a second reaction, and then adding polyacrylamide for second flocculation and precipitation to obtain a second supernatant and second bottom mud; and mixing the second supernatant and the lime milk until the pH value of the system is 8-8.5, carrying out a third reaction, then adding sodium sulfide to carry out a fourth reaction, and then adding polyacrylamide to carry out a third flocculation precipitation, thereby obtaining a third supernatant and a third bottom mud. The method for treating the polluted acid wastewater containing mercury and thallium can effectively recover Hg, shorten the treatment process, reduce lime consumption and reduce the treatment cost and the hazardous waste amount.

Description

Method for treating polluted acid wastewater containing mercury and thallium

Technical Field

The application relates to the field of wastewater treatment, in particular to a method for treating mercury and thallium-containing waste acid wastewater.

Background

The waste acid wastewater generated by the lead-zinc smelting flue gas acid making process is not only the largest in amount, but also the most difficult to treat and recycle. Mainly contains various heavy metal ions such as mercury, thallium, lead, zinc, cadmium and the like, and has higher acidity. Has the characteristics of high pollutant concentration, complex components and different properties. It is often difficult to achieve the desired treatment effect with a single treatment process.

The prior waste acid treatment technologies mainly comprise a sulfuration-lime neutralization method, a lime-iron salt method, a lime neutralization method and the like. Vulcanization-lime neutralization: first, sulfuration is beneficial to recovery of valuable metals such as mercury, heavy metals such as cadmium and thallium cannot be removed under an acidic condition, most heavy metals can be removed through neutralization, but the pH value of hydroxide precipitates of the heavy metals such as cadmium and thallium is high, the pH value of effluent cannot meet the discharge requirement at the moment, acid needs to be regulated back, the treatment flow and the cost are increased, and the high pH value and excessive sodium sulfide addition can cause re-dissolution of mercury, so that the effluent cannot reach the standard. The lime-iron salt precipitation method is mainly used for removing arsenic and fluorine from acidic wastewater, but has large slag yield and poor mercury removal effect. Lime neutralization: the lime consumption is large, a high pH value is required, and the treatment effect is general. The hazardous waste amount is large.

Chinese patent CN104445733A discloses a process for removing thallium from lead-zinc smelting flue gas washing waste acid water, firstly homogenizing the waste acid water, adding a vulcanizing agent to carry out a sulfuration demercuration reaction to remove most mercury, then taking the supernatant after precipitation, adding a neutralizing agent to neutralize to a pH value of 9, then sequentially adding a sulfide and a flocculating agent, taking the supernatant after precipitation, adding acid and alkali to adjust to a pH value of 11, and then sequentially adding a sulfide and a flocculating agent, wherein the supernatant achieves a better treatment effect. But because the pH value is directly neutralized to 9 after the vulcanization, the generated neutralized slag contains a large amount of heavy metal precipitates, a large amount of hazardous waste is generated, and the hazardous waste treatment cost is increased. And finally, the pH is required to be adjusted back for discharging, so that the treatment flow and the cost are increased.

Chinese patent CN105948314A discloses a process for removing mercury in waste water of contaminated acid, potassium permanganate is added into the contaminated acid to react for 15-20 min, lime milk is added to react for 10min, the pH value is adjusted to 3-4, sodium sulfide is added to react for 30-40 min, a flocculating agent polyacrylamide is added to react for 5min and then filter pressing is carried out, the mercury content in filter residue is 0.264-20.33%, the filter residue is recovered, the mercury content in filtrate is less than 0.03 mg/L, and the filtrate is discharged. The method achieves the targets of mercury recovery and hazardous waste reduction, but the final mercury in the effluent is less than 0.03 mg/L, and can not meet the special emission standard in the emission standard of pollutants for the lead and zinc industry.

At present, most of treatment processes of waste acid in non-ferrous metal smelteries adopt a lime neutralization precipitation method and a vulcanization method, but in the waste acid containing multiple heavy metals such as mercury and thallium, thallium removal needs to ensure high pH and excessive addition of sodium sulfide, so that the mercury removal effect is unstable, and mercury re-dissolution is easily caused. And the excessive addition of lime and sodium sulfide not only causes the consumption of the medicament to be increased, but also has large hazardous waste generation amount.

Therefore, it is necessary to develop a waste acid and wastewater treatment process which can recover valuable heavy metals, reduce the amount of hazardous waste residues and stably meet the discharge standard.

Disclosure of Invention

The application aims to provide a method for treating mercury and thallium-containing waste acid wastewater so as to solve the problems.

In order to achieve the purpose, the following technical scheme is adopted in the application:

a method for treating mercury and thallium-containing polluted acid wastewater comprises the following steps:

mixing the mercury-and thallium-containing waste acid water with sodium sulfide, carrying out a first reaction, and then adding polyacrylamide to carry out first flocculation and precipitation to obtain a first supernatant and first bottom mud;

mixing the first supernatant and the lime milk until the pH value of the system is 2-3, carrying out a second reaction, and then adding polyacrylamide to carry out second flocculation precipitation to obtain a second supernatant and second bottom sludge;

and mixing the second supernatant and the lime milk until the pH value of the system is 8-8.5, carrying out a third reaction, then directly adding sodium sulfide to carry out a fourth reaction, and then adding polyacrylamide to carry out a third flocculation precipitation, thereby obtaining a third supernatant and a third bottom mud.

Preferably, before the first reaction, the adding amount of sodium sulfide is 3-5 times of the molar content of Hg in the mercury-thallium-containing polluted acid wastewater, and the OPR value of the first supernatant is controlled to be 339.8-344.9.

Preferably, the polyacrylamide is added in the form of a solution with a concentration of 0.05 to 0.1 wt.%.

Preferably, after the first reaction, adding 1-1.5 mL of polyacrylamide solution into each liter of the mercury and thallium-containing waste acid wastewater;

after the second reaction, adding 5-8 mL of polyacrylamide solution into each liter of the first supernatant;

and after the fourth reaction, adding 1-2 mL of polyacrylamide solution into each liter of the second supernatant.

Preferably, the time of the first reaction is 20-30 min, and the stirring speed is 200-250 rpm;

in the first flocculation precipitation process, stirring is firstly carried out for 2-5 min at the stirring speed of 100-150 rpm, and then standing is carried out for 1-2 h.

Preferably, the time of the second reaction is 30-60 min, and the stirring speed is 200-300 rpm;

in the second flocculation precipitation process, stirring is firstly carried out for 2-5 min at the stirring speed of 100-150 rpm, and then standing is carried out for 2 h.

Preferably, the third reaction time is 20-30 min, and the stirring speed is 200-300 rpm;

the fourth reaction time is 20-30 min, and the stirring speed is 200-300 rpm;

in the third flocculation precipitation process, stirring is firstly carried out for 2-5 min at the stirring speed of 100-150 rpm, and then standing is carried out for 1-2 h.

Preferably, after the third reaction, the addition amount of sodium sulfide is 0.12-0.18 g per liter of the second supernatant, and the OPR value of the second supernatant is controlled to be 59.6-95.

Preferably, after the fourth reaction, the mercury content is less than or equal to 0.01mg/L, and the thallium content is less than or equal to 0.005 mg/L.

Preferably, the first bottom sludge is recycled after being subjected to pressure filtration;

the second bottom sediment is returned to be mixed with the first supernatant and the lime cream for use, the reflux ratio is 2: 1-5: 1 (water inlet flow: bottom sediment reflux), and the rest is subjected to filter pressing and then is recycled;

and returning the third bottom sediment to be mixed with the second supernatant and the lime cream for use, wherein the reflux ratio is 2: 1-5: 1 (inflow rate: bottom sediment reflux), and performing filter pressing on the rest part to be used as hazardous waste.

Compared with the prior art, the beneficial effect of this application includes:

according to the method for treating the mercury-and thallium-containing waste acid water, most Hg is removed by directly vulcanizing the first reaction, and other heavy metals are hardly removed, so that the grade of Hg in the precipitate is high, mercury residues can be recovered, the adding amount of sodium sulfide is accurately controlled by controlling the ORP value of the reaction liquid to be 339.8-344.9, and the existing water quality fluctuation is responded; taking the supernatant after direct vulcanization in the second reaction, adding a mixture of lime milk and second reaction bottom mud, adjusting the pH to about 2-3 to obtain a large amount of neutralized gypsum residues, wherein the part of residues are general solid wastes and can be sold, and the economic value is favorably improved; the third reaction is to take the supernatant of the second stage, add the mixture of lime milk and third reaction bottom mud to adjust to the pH of 8-8.5, at this moment, can not reach the standard requirement of all heavy metals, according to the past process, need to carry on the flocculating settling to the supernatant again and then process, thus has lengthened the treatment process and can lead to the increase of floor area and cost; therefore, after the pH value is adjusted to 8-8.5, sodium sulfide is directly added into the reaction liquid, and the adding amount of the sodium sulfide is accurately controlled by controlling the ORP value of the reaction liquid to 59.6-95, so that mercury is less than 0.01mg/L and thallium is less than 0.005mg/L, and meanwhile, the pH is adjusted by adopting a mode of mixing lime milk and bottom mud, lime which is not completely reacted in the bottom mud is utilized, and the lime consumption can be reduced by 20%. The method can efficiently realize the resource recovery of mercury in the wastewater, the reduction of hazardous waste and the standard-reaching discharge of the wastewater.

Drawings

To more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments are briefly described below, and it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope of the present application.

FIG. 1 is a schematic flow chart of a method for treating mercury and thallium-containing contaminated acid wastewater provided by an example;

FIG. 2 is a graph showing the concentration change of each element in raw material contaminated acid sewage and after each stage of treatment.

Detailed Description

The terms as used herein:

"prepared from … …" is synonymous with "comprising". As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," "contains" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

The conjunction "consisting of … …" excludes any unspecified elements, steps or components. If used in a claim, the phrase is intended to claim as closed, meaning that it does not contain materials other than those described, except for the conventional impurities associated therewith. When the phrase "consisting of … …" appears in a clause of the subject matter of the claims rather than immediately after the subject matter, it defines only the elements described in the clause; other elements are not excluded from the claims as a whole.

When an amount, concentration, or other value or parameter is expressed as a range, preferred range, or as a range of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. For example, when the range "1 ~ 5" is disclosed, the ranges described should be construed to include the ranges "1 ~ 4", "1 ~ 3", "1 ~2 and 4~ 5", "1 ~3 and 5", and the like. When a range of values is described herein, unless otherwise stated, the range is intended to include the endpoints thereof and all integers and fractions within the range.

In these examples, the parts and percentages are by mass unless otherwise indicated.

"part by mass" means a basic unit of measure indicating a mass ratio of a plurality of components, and 1 part may represent any unit mass, for example, 1g or 2.689 g. If we say that the part by mass of the component A is a part by mass and the part by mass of the component B is B part by mass, the ratio of the part by mass of the component A to the part by mass of the component B is a: b. alternatively, the mass of the A component is aK and the mass of the B component is bK (K is an arbitrary number, and represents a multiple factor). It is not to be misunderstood that the sum of the parts by mass of all the components is not limited to the limit of 100 parts, unlike the parts by mass.

"and/or" is used to indicate that one or both of the illustrated conditions may occur, e.g., a and/or B includes (a and B) and (a or B).

mixing the first supernatant and the lime milk until the pH value of the system is 2-3 (any value between 2, 2.5, 3 or 2-3), carrying out a second reaction, and then adding polyacrylamide to carry out second flocculation precipitation to obtain a second supernatant and a second bottom mud;

and mixing the second supernatant and the lime milk until the pH value of the system is 8-8.5 (any value between 8, 8.1, 8.2, 8.3, 8.4, 8.5 or 8-8.5), performing a third reaction, then adding sodium sulfide for a fourth reaction, and then adding polyacrylamide for a third flocculation precipitation to obtain a third supernatant and a third bottom mud.

In an alternative embodiment, before the first reaction, the addition amount of sodium sulfide is 3 to 5 times (may be 3 times, 4 times, 5 times or any value between 3 and 5 times) of the molar content of Hg in the mercury and thallium-containing contaminated acid wastewater, and the OPR value of the first supernatant is controlled to be 339.8 to 344.9.

The adding amount of sodium sulfide is controlled by controlling the ORP value of the reaction liquid, so that 99 percent of Hg in the waste acid can be removed under the reaction condition in response to the existing water quality fluctuation.

In an alternative embodiment, the polyacrylamide is added in the form of a solution with a concentration of 0.05 to 0.1 wt.%.

Alternatively, the concentration of the polyacrylamide solution may be 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.1wt%, or any value between 0.05 and 0.1 wt%.

In an alternative embodiment, after the first reaction, 1 to 1.5mL (which may be any value of 1mL, 1.1mL, 1.2mL, 1.3mL, 1.4mL, 1.5mL, or 1 to 1.5 mL) of a polyacrylamide solution is added per liter of the mercury-and thallium-containing waste acid wastewater;

after the second reaction, adding 5-8 mL (any value of 5mL, 6mL, 7mL, 8mL or 5-8 mL) of polyacrylamide solution into each liter of the first supernatant;

after the fourth reaction, 1-2 mL (which may be any value of 1mL, 1.5mL, 2mL, or 1-2 mL) of polyacrylamide solution per liter of the second supernatant is added.

In an optional embodiment, the first reaction time is 20 to 30min (any value between 20min, 25 min, 30min or 20 to 30 min), the stirring speed is 200 to 250rpm (any value between 200rpm, 210 rpm, 220 rpm, 230 rpm, 240rpm, 250rpm or 200 to 250 rpm);

in the first flocculation precipitation process, stirring is firstly carried out for 2-5 min (any value of 2min, 3min, 4min, 5min or 2-5 min), the stirring speed is 100-150 rpm (any value of 100rpm, 110rpm, 120rpm, 130rpm, 140rpm, 150rpm or 100-150 rpm), and then standing is carried out for 1-2 h (any value of 1h, 1.5h, 2h or 1-2 h).

In an alternative embodiment, the second reaction time is 30-60 min (may be any value between 30min, 40min, 50min, 60min or 30-60 min), the stirring speed is 200-300 rpm (may be any value between 200rpm, 210 rpm, 220 rpm, 230 rpm, 240rpm, 250rpm, 260rpm, 270rpm, 280rpm, 290rpm, 300rpm or 200-300 rpm);

in the second flocculation precipitation process, the mixture is stirred for 2-5 min (any value of 2min, 3min, 4min, 5min or 2-5 min), the stirring speed is 100-150 rpm (any value of 100rpm, 110rpm, 120rpm, 130rpm, 140rpm, 150rpm or 100-150 rpm), and then the mixture is kept still for 1-2 h (any value of 1h, 1.5h, 2h or 1-2 h).

In an alternative embodiment, the third reaction time is 30 to 60min (may be any value between 30min, 40min, 50min, 60min or 30 to 60 min), the stirring speed is 200 to 300rpm (may be any value between 200rpm, 210 rpm, 220 rpm, 230 rpm, 240rpm, 250rpm, 260rpm, 270rpm, 280rpm, 290rpm, 300rpm or 200 to 300 rpm);

the fourth reaction time is 20-30 min (any value between 20min, 25 min, 30min or 20-30 min), the stirring speed is 200-300 rpm (any value between 200rpm, 210 rpm, 220 rpm, 230 rpm, 240rpm, 250rpm, 260rpm, 270rpm, 280rpm, 290rpm, 300rpm or 200-300 rpm);

in the third flocculation precipitation process, the mixture is stirred for 2-5 min (any value of 2min, 3min, 4min, 5min or 2-5 min), the stirring speed is 100-150 rpm (any value of 100rpm, 110rpm, 120rpm, 130rpm, 140rpm, 150rpm or 100-150 rpm), and then the mixture is kept still for 1-2 h (any value of 1h, 1.5h, 2h or 1-2 h).

In an optional embodiment, after the third reaction, the addition amount of sodium sulfide is 0.12-0.18 g per liter of the second supernatant, and since HgS is redissolved under alkaline conditions when the sodium sulfide is added excessively, the OPR value of the second supernatant needs to be controlled to be 59.6-95 to accurately control the addition amount of the sodium sulfide, and to also cope with the existing water quality fluctuation. Due to the fact that the precipitation pH of Tl and Cd is high, the Zn can be dissolved back under the high pH condition, and the residual HgS fine particles in the reaction system can be redissolved due to the increase of the pH. Therefore, in order to ensure the treatment effect, the solid-liquid separation is not carried out after the third reaction, but the fourth reaction is directly carried out, so that the treatment effect can be achieved and the treatment flow can be shortened under the condition that the pH is less than 9.

In an alternative embodiment, the mercury content is 0.01mg/L or less and the thallium content is 0.005mg/L or less after the fourth reaction.

In an alternative embodiment, the first bottom sludge is recovered after pressure filtration;

the second bottom sediment returns to be mixed with the first supernatant and the lime cream for use, the reflux ratio of the bottom sediment is 2: 1-5: 1 (the inflow rate: the reflux amount of the bottom sediment can be any value between 2:1, 3:1, 4: 1, 5:1 or 2: 1-5: 1), and the rest is subjected to filter pressing and then is used for recovery;

and returning the third bottom sediment to be mixed with the second supernatant and the lime cream for use, wherein the reflux ratio of the bottom sediment is 2: 1-5: 1 (the inflow rate: the reflux amount of the bottom sediment can be any value between 2:1, 3:1, 4: 1, 5:1 or 2: 1-5: 1), and the rest part is treated as hazardous waste after being subjected to filter pressing.

Because the mode of mixing and adding partial bottom mud reflux and lime cream is adopted, the lime which is not completely reacted in the bottom mud is reused, 20 percent of lime consumption can be saved, and the treatment cost and the hazardous waste amount are reduced.

Embodiments of the present application will be described in detail below with reference to specific examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present application and should not be construed as limiting the scope of the present application. The examples, in which specific conditions are not specified, were carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are conventional products which are not indicated by manufacturers and are commercially available.

Example 1

As shown in fig. 1, this embodiment provides a method for treating mercury-and thallium-containing waste acid wastewater, including the following steps:

first-stage treatment: sending waste acid wastewater (roasted waste acid) generated in the acid making process by using lead-zinc smelting flue gas into a waste acid adjusting storage tank, inputting the waste acid into a vulcanization reactor, adding sodium sulfide into the waste acid, wherein the adding amount is 3 times of the molar content of Hg in the waste acid, stirring and reacting for half an hour (the stirring speed is 200 rpm/min), the ORP value of a reaction liquid is 339.8, adding 0.05% of PAM solution, the adding amount is 1 mL/L, slowly stirring for 5 minutes (the stirring speed is 100 rpm/min), then automatically flowing into a vulcanizing sedimentation tank of a thickener, standing and settling to obtain a first supernatant and first bottom sludge, and recovering the first bottom sludge after being subjected to filter pressing by a filter press.

And (3) secondary treatment: taking the first supernatant, slowly adding 10% of lime milk and second bottom mud into a neutralization tank, adjusting the pH value to 2-3, stirring for reaction for half an hour (the stirring speed is 200 rpm/min), then adding 0.05% of PAM solution, enabling the adding amount to be 5 mL/L, slowly stirring for 5 minutes (the stirring speed is 100 rpm/min), enabling the mixture to automatically flow into a thickener neutralization sedimentation tank, standing and precipitating for 2 hours to obtain second supernatant and second bottom mud, partially refluxing the second bottom mud and mixing the second bottom mud with the lime milk, enabling the reflux ratio of the bottom mud to be 2:1 (water inlet flow rate: bottom mud reflux amount), and carrying out filter pressing and recycling on the rest part by a filter press.

And (3) third-stage treatment: and (3) taking the second supernatant, slowly adding a mixture of 10% lime milk and the bottom mud of the third-stage reaction, adjusting the pH to 8, stirring and reacting for half an hour (the stirring speed is 200 rpm/min), and then adding sodium sulfide, wherein the adding amount of the sodium sulfide is 0.12 g/L, and the ORP value of the reaction liquid is 59.6.

Stirring for reaction for half an hour (the stirring speed is 200 rpm/min), adding 0.05 percent of PAM solution, adding 2 mL/L, stirring slowly for 5 minutes (the stirring speed is 100 rpm/min), then automatically flowing to a thickener sedimentation tank, discharging supernatant, refluxing part of bottom mud and mixing with lime milk, wherein the reflux ratio of the bottom mud is 2:1 (water inlet flow: bottom mud reflux), and performing pressure filtration on the rest part of the bottom mud by a pressure filter to be treated as hazardous waste.

Example 2

The embodiment provides a method for treating polluted acid wastewater containing mercury and thallium, which comprises the following steps:

first-stage treatment: sending waste acid wastewater (roasted waste acid) generated in the acid making process by lead-zinc smelting flue gas into a waste acid adjusting storage tank, inputting the waste acid into a vulcanization reactor, adding sodium sulfide into the waste acid, wherein the adding amount is 4.1 times of the concentration of Hg in the waste acid, the ORP value of a reaction solution is 341.7, stirring and reacting for half an hour (the stirring speed is 200 rpm/min), adding 0.05% of PAM solution, the adding amount is 1.2 mL/L, slowly stirring for 5 minutes (the stirring speed is 100 rpm/min), then automatically flowing into a vulcanizing sedimentation tank of a thickener, standing and settling to obtain a first supernatant and first bottom sludge, and recovering the first bottom sludge after pressure filtration by a pressure filter.

And (3) secondary treatment: taking the first supernatant, slowly adding 10% of lime milk and second bottom mud into a neutralization tank, adjusting the pH value to 2-3, stirring for reaction for half an hour (the stirring speed is 200 rpm/min), then adding 0.05% of PAM solution, enabling the adding amount to be 6 mL/L, slowly stirring for 5 minutes (the stirring speed is 100 rpm/min), enabling the mixture to automatically flow into a thickener neutralization sedimentation tank, standing and precipitating for 2 hours to obtain second supernatant and second bottom mud, partially refluxing the second bottom mud and mixing the second bottom mud with the lime milk, enabling the reflux ratio of the bottom mud to be 3:1 (inflow rate: reflux amount of the bottom mud), and carrying out filter pressing and recycling on the rest part by a filter press.

And (3) third-stage treatment: and (3) taking the second supernatant, slowly adding a mixture of 10% of lime milk and the bottom mud of the third-stage reaction, adjusting the pH to 8, stirring and reacting for half an hour (the stirring speed is 200 rpm/min), then adding sodium sulfide, wherein the adding amount of the sodium sulfide is 0.15 g/L, the ORP value of the reaction liquid is 92.8, stirring and reacting for half an hour (the stirring speed is 200 rpm/min), then adding 0.05% of PAM solution, adding the PAM solution in an amount of 2 mL/L, slowly stirring for 5 minutes (the stirring speed is 100 rpm/min), then automatically flowing to a thickener sedimentation tank, discharging the supernatant, partially refluxing the bottom mud and mixing with the lime milk, wherein the ratio of the bottom mud to the bottom mud is 3:1 (water inflow rate: bottom mud reflux rate), and performing filter pressing on the rest part to be treated as dangerous waste.

Example 3

first-stage treatment: sending waste acid wastewater (roasted waste acid) generated in the acid making process by lead-zinc smelting flue gas into a waste acid adjusting storage tank, inputting the waste acid into a vulcanization reactor, adding sodium sulfide into the waste acid, wherein the adding amount is 5 times of the concentration of Hg in the waste acid, the ORP value of a reaction solution is 344.9, stirring and reacting for half an hour (the stirring speed is 200 rpm/min), adding 0.05% of PAM solution, the adding amount is 1.5 mL/L, slowly stirring for 5 minutes (the stirring speed is 100 rpm/min), then automatically flowing into a vulcanizing sedimentation tank of a thickener, standing and settling to obtain a first supernatant and first bottom sludge, and recovering the first bottom sludge after filter pressing by a filter press.

And (3) secondary treatment: taking the first supernatant, slowly adding 10% of lime milk and second bottom mud into a neutralization tank, adjusting the pH value to 2-3, stirring and reacting for half an hour (the stirring speed is 200 rpm/min), then adding 0.05% of PAM solution, adding 8 mL/L, slowly stirring for 5 minutes (the stirring speed is 100 rpm/min), automatically flowing into a neutralization and sedimentation tank of a thickener, standing and precipitating for 2 hours to obtain second supernatant and second bottom mud, partially refluxing the second bottom mud and mixing the second bottom mud with the lime milk, wherein the reflux ratio of the bottom mud is 5:1 (water inlet flow rate: bottom mud reflux), and filtering and recovering the rest of the second bottom mud by a filter press.

And (3) third-stage treatment: and (3) taking the second supernatant, slowly adding a mixture of 10% of lime milk and the bottom mud of the third-stage reaction, adjusting the pH to 8, stirring and reacting for half an hour (the stirring speed is 200 rpm/min), then adding sodium sulfide, wherein the adding amount of the sodium sulfide is 0.18 g/L, the ORP value of the reaction liquid is 95, stirring and reacting for half an hour (the stirring speed is 200 rpm/min), then adding 0.05% of PAM solution, adding the amount of the PAM solution into the solution at 2 mL/L, slowly stirring for 5 minutes (the stirring speed is 100 rpm/min), automatically flowing into a thickener precipitation tank, discharging the supernatant, partially refluxing the bottom mud and mixing the lime milk, wherein the reflux ratio of the bottom mud is 5:1 (water inlet flow rate: bottom mud reflux), and performing filter pressing on the residual part to be treated as dangerous waste.

FIG. 2 is a graph showing the concentration change of each element in raw material contaminated acid sewage and after each stage of treatment. As can be seen from FIG. 2, after the first-stage treatment, the Hg in the contaminated acid is reduced from 131.71 mg/L to 0.08 mg/L, most of the Hg is removed in the form of sulfide precipitation, the concentrations of other heavy metals are not changed at this time, the precipitate is filtered and naturally dried, the measured Hg content is 79.34%, and the mercury slag has recovery value; after the second-stage treatment, the concentration of the heavy metal in the waste acid is not obviously changed compared with that of the first-stage treatment. The main purpose of the reaction is to utilize lime to neutralize the acidity of waste acid, and the pH value is controlled between 2-3, so that a large amount of sludge is mainly CaSO ₄ It is a general solid waste and can be sold or transported out. The third stage is mainly used for removing residual heavy metal ions and ensuring that the emission standard is met, so that the heavy metal ions are neutralized to about pH8 to remove a large amount of Zn, the precipitation pH of Tl and Cd is high, the Zn is dissolved back under the high pH condition, and the residual HgS fine particles in the reaction system are dissolved again due to the increase of the pH. Therefore, in order to ensure the treatment effect, after the mixed solution is neutralized to the pH value of 8, sodium sulfide is directly added into the mixed solution for reaction, the ORP of the mixed solution is ensured to be 59.6-95, Hg is ensured to be less than 0.01mg/L, and Tl is ensured to be less than 0.005 mg/L.

Comparative example 1

Chinese patent CN104445733A discloses a process for removing thallium from lead-zinc smelting flue gas washing waste acid wastewater.

Firstly, homogenizing the waste water of the contaminated acid, adding a vulcanizing agent to carry out a vulcanization demercuration reaction to remove most of mercury, wherein the adding amount of the vulcanizing agent is 5-10 times of the calculated amount of a chemical reaction formula of the mercury content of the contaminated acid, so that the mercury content in the contaminated acid needs to be monitored in real time, which cannot be realized in the actual industrial production; the method controls the adding amount of the sodium sulfide in real time by controlling the ORP value 339.8-344.9 of the vulcanization reaction, and can cope with the existing water quality fluctuation.

Adding a neutralizing agent into the supernatant after precipitation to neutralize to a pH value of 9, and sequentially adding a sulfide and a flocculant, wherein the adding amount of the vulcanizing agent is 1-20 times of the thallium content of the contaminated acid, and thallium and other heavy metal ions are simultaneously precipitated and removed, so that the thallium content of the contaminated acid also needs to be monitored in real time, and all heavy metals in the contaminated acid are synchronously precipitated, so that the bottom sludge contains a large amount of heavy metals, and a large amount of hazardous waste is generated; according to the method, the supernatant after the vulcanization reaction is neutralized to the pH value of 2-3, almost no heavy metal is removed in the reaction, so that the generated sludge is common solid waste, and the generation amount of dangerous waste is reduced.

And finally, adding acid and alkali into the supernatant after precipitation to adjust the pH to 11, and then sequentially adding sulfide and a flocculating agent to obtain a better treatment effect on the supernatant. This results in high pH of the waste acid water from lead-zinc smelting, and the subsequent discharge needs to be adjusted back to meet the discharge requirement, resulting in increased flow path, and Zn (OH) ₂ And the re-dissolution of the HgS precipitate is not beneficial to the standard discharge. And this application neutralizes pH to 8 through throwing the neutralizing agent, and the add volume of rethread control vulcanization reaction's ORP value 59.6~95 comes real-time control sodium sulfide, accomplishes finally that all heavy metal is up to standard to discharge to need not the readjustment pH, shorten the processing procedure when accomplishing accurate automatic control, simultaneously, owing to adopt lime milk and the mode of bed mud mixture to adjust pH, utilized the lime of complete reaction in the bed mud, reducible 20% lime consumption.

Finally, it should be noted that: the above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present application.

Moreover, those skilled in the art will appreciate that while some embodiments herein include some features included in other embodiments, rather than other features, combinations of features of different embodiments are meant to be within the scope of the application and form different embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is only for enhancement of understanding of the general background of the application and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.

Claims

1. A method for treating mercury and thallium-containing polluted acid wastewater is characterized by comprising the following steps:

mixing the second supernatant and the lime milk until the pH value of the system is 8-8.5, performing a third reaction, then directly adding sodium sulfide to perform a fourth reaction, and then adding polyacrylamide to perform a third flocculation precipitation to obtain a third supernatant and a third bottom mud;

before the first reaction, the adding amount of sodium sulfide is 3-5 times of the molar content of Hg in the mercury and thallium-containing polluted acid wastewater, and the OPR value of a first supernatant is controlled to be 339.8-344.9; after the third reaction, the adding amount of sodium sulfide is 0.12-0.18 g per liter of the second supernatant, and the OPR value of the second supernatant is controlled to be 59.6-95.

2. The method for treating mercury and thallium-containing contaminated acid wastewater according to claim 1, wherein polyacrylamide is added in the form of a solution with a concentration of 0.05 to 0.1 wt%.

3. The method for treating mercury-and thallium-containing acidic wastewater according to claim 2, wherein after the first reaction, 1 to 1.5mL of polyacrylamide solution is added per liter of the mercury-and thallium-containing acidic wastewater;

after the second reaction is carried out, adding 5-8 mL of polyacrylamide solution into each liter of the first supernatant;

4. The method for treating mercury and thallium-containing contaminated acid wastewater according to claim 1, wherein the first reaction time is 20-30 min, and the stirring speed is 200-250 rpm;

5. The method for treating mercury and thallium-containing contaminated acid wastewater according to claim 1, wherein the second reaction time is 30-60 min, and the stirring speed is 200-300 rpm;

in the second flocculation precipitation process, stirring is firstly carried out for 2-5 min at the stirring speed of 100-150 rpm, and then standing is carried out for 1-2 h.

6. The method for treating mercury and thallium-containing contaminated acid wastewater according to claim 1, wherein the third reaction time is 20-30 min, and the stirring speed is 200-300 rpm;

the fourth reaction time is 20-30 min, and the stirring speed is 200-300 rpm;

7. The method for treating mercury-and thallium-containing waste acid water according to claim 1, wherein after the fourth reaction, the mercury content is 0.01mg/L or less, and the thallium content is 0.005mg/L or less.

8. The method for treating mercury and thallium-containing contaminated acid wastewater according to any one of claims 1 to 7, wherein the first bottom sludge is subjected to pressure filtration and then is recycled;

the second bottom mud returns to be mixed with the first supernatant and the lime milk for use, the reflux ratio is 2: 1-5: 1, and the rest is subjected to filter pressing and then is recycled;

and returning the third bottom sediment to be mixed with the second supernatant and the lime cream for use, wherein the reflux ratio is 2: 1-5: 1, and the rest is treated as hazardous waste after filter pressing.