阅读说明：本技术 一种混凝-化学沉淀处理复合重金属废水的方法 (Method for treating composite heavy metal wastewater by coagulation-chemical precipitation ) 是由 袁蓉芳 周北海 许丹丹 邱丽佳 于 2019-10-23 设计创作，主要内容包括：本发明涉及废水处理领域,提供了一种混凝-化学沉淀处理复合重金属废水的方法,包括以下步骤：(1)检测废水中重金属种类和浓度；(2)向废水中投加FeSO<Sub>4</Sub>,将Cr(Ⅵ)还原为Cr(Ⅲ)；(3)调节pH值至最佳范围；(4)投加PFS进行第一阶段混凝-化学沉淀反应；(5)向上清液中投加Na<Sub>2</Sub>S,与Hg反应生成HgS沉淀；(6)再次调节pH值至最佳范围；(7)再次投加PFS,进行第二阶段混凝-化学沉淀反应。本发明的优点是：采用分段投加方式,使不同重金属在最佳pH条件下进行去除,处理效果好,水中多种重金属能同时达标,并且操作简便、成本低,无二次污染问题。(The invention relates to the field of wastewater treatment, and provides a method for treating composite heavy metal wastewater by coagulation-chemical precipitation, which comprises the following steps: (1) detecting the types and the concentrations of heavy metals in the wastewater; (2) FeSO is added into the waste water 4 Reducing Cr (VI) into Cr (III); (3) adjusting the pH value to an optimal range; (4) PFS is added to carry out a first-stage coagulation-chemical precipitation reaction; (5) adding Na into the supernatant 2 S, reacting with Hg to generate HgS precipitate; (6) adjusting pH again to the maximumThe optimal range; (7) and adding PFS again to carry out second-stage coagulation-chemical precipitation reaction. The invention has the advantages that: the method has the advantages that different heavy metals are removed under the condition of optimal pH by adopting a segmented feeding mode, the treatment effect is good, multiple heavy metals in water can reach the standard simultaneously, the operation is simple and convenient, the cost is low, and the problem of secondary pollution is avoided.)

1. The method for treating the composite heavy metal wastewater by coagulation-chemical precipitation is characterized by comprising the following steps of:

(1) detecting the types and the concentrations of heavy metals in the composite heavy metal wastewater;

(2) FeSO is added into the waste water₄Reducing Cr (VI) into Cr (III);

(3) detecting the pH value of the wastewater, and adding inorganic acid or alkali to adjust the pH value to an optimal range;

(4) a coagulant PFS is added into the wastewater to carry out a first-stage coagulation-chemical precipitation reaction for removing heavy metals of Pb, Cu, Zn and Cr (VI) in the water, and the discharged sediments after precipitation are treated safely to a certain extent;

(5) adding Na into the supernatant after precipitation₂S, reacting with Hg in water to generate HgS precipitate;

(6) adding inorganic base into the wastewater, and adjusting the pH value to be in an optimal range;

(7) and (3) adding a coagulant PFS into the wastewater to perform a second-stage coagulation-chemical precipitation reaction for removing heavy metals Cd and Hg in the wastewater, performing certain safe treatment on the precipitated sediments, and enabling the supernate to meet the heavy metal discharge standard and be discharged up to the standard.

2. The method for treating the composite heavy metal wastewater by coagulation-chemical precipitation as claimed in claim 1, wherein the method comprises the following steps: in the step (1), the heavy metals are typically Pb, Cu, Zn, Cd, Hg and Cr (VI), and are common heavy metal types in industrial wastewater.

3. The method for treating the composite heavy metal wastewater by coagulation-chemical precipitation as claimed in claim 1, wherein the method comprises the following steps: in step (2), according to FeSO₄FeSO is added according to the mass ratio of 14:1 to Cr (VI)₄。

4. The method for treating the composite heavy metal wastewater by coagulation-chemical precipitation as claimed in claim 1, wherein the method comprises the following steps: in step (3), the pH is adjusted to 7. The specific reasons are as follows: the optimal pH value range for removing the heavy metals by the coagulation-chemical precipitation method is obtained through experimental research and is as follows: the optimal pH value ranges of Pb and Cu are both 6-7, the optimal pH value ranges of Zn and Cr (VI) are both 7-8, the optimal pH value range of Cd is 9-10, and the optimal pH value of Hg is 9. Therefore, the pH value is adjusted to 7 in the step, and the heavy metals of Pb, Cu, Zn and Cr (VI) in the wastewater are removed.

5. The method for treating the composite heavy metal wastewater by coagulation-chemical precipitation as claimed in claim 1, wherein the method comprises the following steps: in step (4), the reason for selecting the coagulant PFS is: the PFS is the best coagulant category through the experimental research of heavy metal coagulation-chemical precipitation treatment. The concentration of PFS added in the technical scheme is determined by the concentration of heavy metal, and the PFS adding amount formula in the first stage is as follows:

ρ(PFS)＝(0.3±0.05)×ρ(Pb)+(0.12±0.02)×ρ(Cu)+(1±0.02)×ρ(Zn)+(0.8±0.15)×ρ(Cr)

wherein the unit of the concentration ρ is mg/L.

The stirring speed after the coagulant PFS is added is 200-300 r/min, the coagulation time is 20-30 min, and the precipitation time is 30-40 min.

6. The method for treating the composite heavy metal wastewater by coagulation-chemical precipitation as claimed in claim 1, wherein the method comprises the following steps: in step (5), according to Na₂Adding Na with the mass ratio of S to Hg of 16:5₂S。

7. The method for treating the composite heavy metal wastewater by coagulation-chemical precipitation as claimed in claim 1, wherein the method comprises the following steps: in the step (6), the pH value is adjusted to 9, and the optimal pH value for removing Cd and Hg heavy metals by a coagulation-chemical precipitation method is obtained.

8. The method for treating the composite heavy metal wastewater by coagulation-chemical precipitation as claimed in claim 1, wherein the method comprises the following steps: in the step (7), the adding amount of the PFS is still determined by the concentration of the heavy metal, and the adding amount of the PFS in the second stage is represented by the following formula:

ρ(PFS)＝(6±1)ρ(Cd)+(44±7)ρ(Hg)

wherein the unit of the concentration ρ is mg/L.

The stirring speed and the coagulation time after the coagulant PFS is added are basically consistent with the settling time and the step (4).

Technical Field

The invention relates to the field of wastewater treatment, in particular to a method for treating composite heavy metal wastewater by coagulation-chemical precipitation.

Background

In recent years, with the rapid development of the industry in China, the heavy metal wastewater generated in the production process of the industries such as metal smelting, machining, chemical treatment, mining and the like is increasing day by day, and in most cases, the wastewater contains a plurality of heavy metals such as Pb, Cu, Zn, Cd, Hg, Cr (VI) and the like, namely the composite heavy metal wastewater. If the composite heavy metal wastewater is directly discharged into a water environment without being treated, the composite heavy metal wastewater not only can directly harm animals and plants in the water, but also can cause great adverse effects on human health and even the whole ecological system. Therefore, the purification treatment of the composite heavy metal wastewater is needed to reduce the concentration of various heavy metals to below the limit value regulated by the national Integrated wastewater discharge Standard (GB 8978-1996).

Common methods for treating the composite heavy metal wastewater include a physical chemical method and a biological method, wherein the biological method is to remove heavy metals by using microorganisms or metabolites generated by the microorganisms, and the method has a long strain screening period and is still in an exploration stage. Therefore, at present, the physical and chemical method is mainly adopted to treat the composite heavy metal wastewater. For example, the invention patent with the publication number of CN109569530A proposes a composite adsorbent for adsorbing heavy metal lead in wastewater, which removes lead ions in water by an adsorbent formed by combining modified calcium alginate, activated carbon, diatomite, beer yeast paste and chitosan. Although the adsorption method has a good effect of removing heavy metals, the cost of the adsorbent is high, and additional treatment is required after adsorption saturation. The invention patent with publication number CN103936105A proposes an electrochemical method for treating industrial wastewater, which takes magnesium or magnesium alloy As an anode, generates high-activity magnesium hydroxide under the electrochemical action, and can simultaneously adsorb and remove heavy metals such As Zn, Cd, Cu, As and the like in the wastewater. Although the magnesium anode electrochemical device has the advantages of difficult passivation of polar plates and less waste residue, the electrochemical method has large power consumption and higher cost, and the power generation of China mainly depends on a thermal power generation mode of a large amount of coal and other fossil fuels, so certain environmental pollution can not be caused in the power generation process. Therefore, the problem to be solved at present is to find a method for treating composite heavy metal wastewater, which can remove a plurality of heavy metals simultaneously, and has low cost and good effect.

Disclosure of Invention

In view of the above, the present invention aims to provide a coagulation-chemical precipitation method for treating wastewater containing complex heavy metals. The method can effectively remove various heavy metals in the wastewater at the same time, and has the advantages of simple operation, low cost and no secondary pollution.

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

a method for treating composite heavy metal wastewater by coagulation-chemical precipitation comprises the following specific steps:

(1) detecting the types and the concentrations of heavy metals in the composite heavy metal wastewater;

(2) FeSO is added into the waste water₄Reducing Cr (VI) into Cr (III);

(3) detecting the pH value of the wastewater, and adding inorganic acid or alkali to adjust the pH value to an optimal range;

(4) a coagulant PFS is added into the wastewater to carry out a first-stage coagulation-chemical precipitation reaction for removing heavy metals of Pb, Cu, Zn and Cr (VI) in the water, and the discharged sediments after precipitation are treated safely to a certain extent;

(5) adding Na into the supernatant after precipitation₂S, reacting with Hg in water to generate HgS precipitate;

(6) adding inorganic base into the wastewater, and adjusting the pH value to be in an optimal range;

(7) and (3) adding a coagulant PFS into the wastewater to perform a second-stage coagulation-chemical precipitation reaction for removing heavy metals Cd and Hg in the wastewater, performing certain safe treatment on the precipitated sediments, and enabling the supernate to meet the heavy metal discharge standard and be discharged up to the standard.

As a further improvement of the invention, in the step (1), the heavy metals are mainly represented by Pb, Cu, Zn, Cd, Hg and Cr (VI), and are the heavy metal types commonly found in industrial wastewater.

As a self-service hairIn a further development, in step (2), according to FeSO₄FeSO is added according to the mass ratio of 14:1 to Cr (VI)₄。

As a further improvement of the invention, in the step (3), the pH value is adjusted to 7. The specific reasons are as follows: the optimal pH value range for removing the heavy metals by the coagulation-chemical precipitation method is obtained through experimental research and is as follows: the optimal pH value ranges of Pb and Cu are both 6-7, the optimal pH value ranges of Zn and Cr (VI) are both 7-8, the optimal pH value range of Cd is 9-10, and the optimal pH value of Hg is 9. Therefore, the pH value is adjusted to 7 in the step, and the heavy metals of Pb, Cu, Zn and Cr (VI) in the wastewater are removed.

As a further improvement of the present invention, in the step (4), the reason why the coagulant PFS is selected is that: the PFS is the best coagulant category through the experimental research of heavy metal coagulation-chemical precipitation treatment. The concentration of PFS added in the technical scheme is determined by the concentration of heavy metal, and the PFS adding amount formula in the first stage is as follows:

ρ(PFS)＝(0.3±0.05)×ρ(Pb)+(0.12±0.02)×ρ(Cu)+(1±0.02)×ρ(Zn)+(0.8±0.15)×ρ(Cr)

wherein the unit of the concentration ρ is mg/L.

As a further improvement of the invention, in the step (4), the stirring speed after the coagulant PFS is added is 200-300 r/min, the coagulation time is 20-30 min, and the precipitation time is 30-40 min.

As a further improvement of the invention, in the step (5), according to Na₂Adding Na according to the mass ratio of S to Hg of 16:5₂S。

As a further improvement of the invention, in the step (6), the pH value is adjusted to 9, which is the optimal pH value for removing Cd and Hg heavy metals by a coagulation-chemical precipitation method.

As a further improvement of the invention, in the step (7), the adding amount of PFS is still determined by the concentration of heavy metal, and the adding amount of PFS in the second stage is represented by the formula:

ρ(PFS)＝(6±1)ρ(Cd)+(44±7)ρ(Hg)

wherein the unit of the concentration ρ is mg/L.

As a further improvement of the invention, the stirring speed and the coagulation time in the step (7) are basically consistent with the precipitation time and the step (4).

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

1. the invention selects the coagulant with optimal effect, determines the optimal coagulant adding amount according to the heavy metal concentration, not only can achieve better heavy metal removal effect, but also can reduce the medicament dosage and save the operation cost.

2. The invention provides a coagulant adding formula, can quickly obtain the required coagulant amount according to different heavy metal types and concentrations of a water body, is suitable for treating various heavy metal polluted wastewater, and has certain guiding significance for regulating and controlling operation of a water plant.

3. The invention adopts a way of adding coagulant by stages, and removes different heavy metals under the condition of optimal pH by adjusting the pH value of the water body at different stages, thereby improving the treatment rate and enhancing the treatment effect.

4. The invention can remove a plurality of heavy metals simultaneously, and the effluent completely meets the limit requirements of the national Integrated wastewater discharge Standard (GB 8978-1996).

5. The method has the advantages of simple and convenient operation, low cost, no secondary pollution problem and easy engineering application.

Drawings

FIG. 1 is a flow chart of a coagulation-chemical precipitation method for treating composite heavy metal wastewater.

Detailed Description

In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to specific embodiments.