Research on Comprehensive Treatment Technology and Technology of Electroplating Wastewater

The treatment of electroplating wastewater has been paid more and more attention at home and abroad, and there are many researches on the treatment methods and processes of electroplating wastewater. In this paper, the treatment technology and process of electroplating industrial wastewater are discussed in detail, and the treatment effect is analyzed in detail. The results show that the treatment method is mature, the operation cost is low, and the effluent quality is up to standard, which can provide reference for the treatment of electroplating industrial wastewater. In order to eliminate or reduce its pollution to the environment, to achieve the purpose of protecting the environment and benefiting the people.

Key words: electroplating wastewater; treatment process; structure; operational benefit

Electroplating is a process that uses electrochemical methods to decorate, protect and obtain certain new properties of metal and non-metal surfaces. It is also one of the three major polluting industries in the world, and its wastewater discharge accounts for about industrial wastewater. 10% of total emissions, of which less than 50% of wastewater is effectively treated before discharge. The wastewater produced by it contains cyanide and heavy metal pollutants such as chromium, copper, zinc, cadmium and nickel. If it is improperly disposed, it will not only damage the ecological balance, but also endanger human health, so strengthen the integration of electroplating wastewater. Research on processing techniques and processes is especially necessary.

1 project overview

A certain hardware company is mainly engaged in the electroplating production of craft jewelry, which discharges a certain amount of electroplating production wastewater in the production process. The production wastewater mainly contains cyanide, gold, silver, chromium, acid and alkali and other strictly controlled pollutants.

According to the water quality of the old plant wastewater, the designed influent water quality meets the requirements of the new enterprise water pollutant discharge limit in the Electroplating Water Pollutant Emission Standard (DB44/1597-2015).

2 process

In the actual application process, because the traditional processing method is subject to various factors, it has its specific scope or limitation. The chemical precipitation method for treating electroplating wastewater has the advantages of simple process and wide processing objects. The chemical deepening method is a method of converting a heavy chemical substance in a dissolved state into a heavy metal chemical insoluble in water. The advantage of this process is that the precipitant lime, sodium carbonate, etc. are used, the source is wide, the price is low, and it is easy to manage, and the treated wastewater can reach the standard discharge.

The principle of redox treatment of electroplating wastewater is physical processes such as oxidation, reduction, acid-base neutralization and other chemical reactions and polymer flocculation. In the process of electroplating wastewater treatment, the toxic and harmful substances dissolved in the waste water can be oxidized or reduced in the redox reaction, thereby converting it into a non-toxic and harmless new substance.

According to the principle of classification and treatment, the cyanide-containing wastewater and the chromium-containing wastewater are separately pretreated, and the cyanide-containing wastewater and the chromium-containing wastewater are pretreated by alkaline chlorination and chemical reduction respectively, and the pretreated wastewater is discharged. The integrated wastewater regulating tank is mixed with the integrated wastewater, and the mixed wastewater is pumped to the pH adjusting tank, and the alkali solution is adjusted to pH=9.5, and then flows into the coagulation reaction tank for coagulation reaction. After the reaction is completed, it flows into the sedimentation tank for precipitation, and the effluent is filtered through a sand filter to adjust the pH and reach the standard discharge. The sedimented sludge is discharged to the sludge tank and dehydrated by a plate and frame filter press. The sludge is delivered to a qualified waste water treatment tank by a qualified hazardous waste company.

The chemical equation for the cyanogenation reaction of the two-stage alkaline chlorination method is as follows:

CN-+OCl-+H2O→CNCl+2OH-

CNCl+2OH-→CNO-+Cl-+H2O

2CNO-+4OH-+3Cl2→2CO2↑+N2↑+6Cl-+2H2O

The reducing agent reduces the hexavalent chromium to trivalent chromium under acidic conditions, and the reducing agent may be ferrous sulfate, sodium sulfite, sodium hydrogen sulfite or the like. The chemical equation for the hexavalent chromium reduction reaction is as follows:

2H2Cr2O7+6NaHSO3+3H2SO4→2Cr2(SO4)3+3Na2SO4+8H2O

H2Cr2O7+3Na2SO3+3H2SO4→Cr2(SO4)3+3Na2SO4+4H2O

Cr2O72-+6Fe2++14H+→2Cr3++6Fe3++7H2O

The main reaction chemical equation of the hydroxide precipitation method is as follows:

Cr3++3OH-→Cr(OH)3↓

Ni2++2OH-→Ni(OH)2↓

Cu2++2OH-→Cu(OH)2↓

Zn2++2OH-→Zn(OH)2↓

3 main structures

3.1 Cyanide-containing wastewater conditioning tank

It adopts underground reinforced concrete structure, epoxy resin anti-corrosion, internal size is 5m×2m×4m, volume is 40m3, residence time is 8h, air pipe on the bottom of the pool is regularly opened to prevent precipitation. Set 2 sets of corrosion-resistant self-priming pumps, which are automatically controlled according to the water level in the pool.

3.2 first stage cyanide pool

It adopts above-ground reinforced concrete structure, epoxy resin anti-corrosion, internal size is 1.5m×1.5m×1.6m, volume is 3m3, residence time is 0.6h, mechanical stirring device is adopted, and one set of pH and ORP automatic control dosing system is set. .

3.3 secondary cyanide pool

It adopts above-ground reinforced concrete structure, epoxy resin anti-corrosion, internal size is 1.5m×1.5m×1.6m, volume is 3m3, residence time is 0.6h, mechanical stirring device is adopted, and one set of pH and ORP automatic control dosing system is set. .

3.4 chromium-containing wastewater conditioning tank

It adopts underground reinforced concrete structure, epoxy resin anti-corrosion, internal size is 2.5m×2m×4m, volume is 20m3, residence time is 8h, air pipe on the bottom of the pool is regularly opened to prevent sedimentation. Set 2 sets of corrosion-resistant self-priming pumps, which are automatically controlled according to the water level in the pool.

3.5 restore pool

It adopts above-ground reinforced concrete structure, epoxy resin anticorrosion, internal size is 1.5m×1.5m×1.6m, volume is 3m3, residence time is 1h, mechanical stirring device is adopted, and one set of pH and ORP automatic control dosing system is set. The pH is controlled to 2 to 3 and the ORP value is 250 to 300 mV.

3.6 Integrated wastewater conditioning tank

It adopts underground reinforced concrete structure, epoxy resin anti-corrosion, internal size is 8m×5m×4m, volume is 160m3, residence time is 8h, air pipe on the bottom of the pool is regularly opened to prevent sedimentation. Set 2 sets of corrosion-resistant self-priming pumps, which are automatically controlled according to the water level in the pool.

3.7 pH adjustment pool

It adopts above-ground reinforced concrete structure, epoxy resin anti-corrosion, internal size is 1.8m×1.8m×2.0m, volume is 6m3, residence time is 0.3h, and a set of pH automatic control dosing system is adopted to control the pH value. It is 9.5 to 10.5.

3.8 coagulation reaction tank

It adopts above-ground reinforced concrete structure, epoxy resin anti-corrosion, internal size is 3m×1.8m×2.0m, inner division is 2 grids, respectively, fast mixing tank and slow mixing pool, volume is 10m3, residence time is 0.5h, mechanical agitation is adopted. Device.

3.9 inclined tube sedimentation tank

The inclined tube sedimentation tank adopts the upflow type anisotropic flow structure, the ground type reinforced concrete structure, the epoxy resin anticorrosion, the internal size is 8m×5m×4.5m, the hydraulic surface load is 0.6m3/m2 ̇h, and the inclined tube and tube are placed in the pool. The hole is 60 mm and the inclination is 60 degrees.

3.10 sand filter

The ground reinforced concrete structure is used, the epoxy resin is anticorrosive, the internal dimension is 3m×1.5m×3.0m, the design filter speed is 7m/h, the filter material is quartz sand, and the support layer is made of pebbles. The filter uses a perforated tube gas flushing system.

3.11 pH callback pool

It adopts the above-ground reinforced concrete structure, epoxy resin anticorrosion, internal size is 1.8m×1.5m×2.5m, volume is 6m3, residence time is 0.3h, and a set of pH automatic control dosing system is adopted.

3.12 sludge concentration tank

It adopts underground reinforced concrete structure, epoxy resin anti-corrosion, internal dimensions of 2.5m × 2m × 4m, volume of 20m3, using a fully automatic plate and frame filter press.

4 debugging and analysis

4.1 Pretreatment of cyanide-containing wastewater

After the cyanide-containing wastewater is upgraded to the first-stage cyanide-removing tank, the pH-controlled dosing system automatically adds lye to control the pH value between 11 and 11.5. The ORP-controlled dosing system automatically adds bleach to control the ORP value at 300-350 mV. After the effluent flows to the secondary cyanide tank, the pH control dosing system automatically adds the acid solution, and the pH value is controlled at 6.5-7. The ORP control dosing system automatically adds bleaching water to control the ORP value at 600-650 mV. The two-stage alkaline chlorination process is used, and the cyanide ions in the wastewater are oxidized to N2.

4.2 Pretreatment of chromium-containing wastewater

After the chromium-containing wastewater is lifted to the reduction tank, the pH control dosing system automatically adds the acid solution to control the pH value of 2 to 3. The ORP controlled dosing system automatically adds sodium sulfite solution to control the ORP value at 250-300 mV. The chemical reduction process is employed to reduce hexavalent chromium to trivalent chromium under acidic conditions.

4.3 Treatment of integrated wastewater

After the comprehensive wastewater is raised to the pH adjustment tank, the pH control dosing system automatically adds lye to control the pH value of 9-10, nickel, copper, zinc and trivalent chromium plasma and hydroxide hydroxide in the wastewater. Precipitation, then add PAC and PAM respectively through the fast mixing tank and the slow mixing tank to improve the effect of coagulation and sedimentation, and at the same time remove most of the organic pollutants and suspended pollutants. Finally, the wastewater is removed through the sand filter to remove fine and difficult. The precipitated suspension is discharged after the pH is adjusted to a pH of 7-8.

4.4 running effect

After a certain period of commissioning and operation, the system runs stably and the treatment effect is reliable. The effluent meets the emission limit requirements for new enterprise water pollutants in the Electroplating Water Pollutant Emission Standard (DB44/1597-2015).

5 investment and operating expenses

The total investment of the project is about 1.1 million yuan, and the treated water volume is 400t/d. The operating expenses mainly include: electricity, pharmacy, labor, etc., and the operating cost is about 1.9 yuan/m3.

Remarks: Pharmacy price NaOH is 2.5 yuan/kg, H2SO4 is 1 yuan/kg, NaOCl is 1 yuan/kg, NaHSO3 is 2 yuan/kg, PAC is 2 yuan/kg, PAM is 25 yuan/kg; comprehensive wastewater includes Pretreated cyanide-containing wastewater and chromium-containing wastewater.

Remarks: The electricity fee is 0.6 yuan / (kW ̇h); the labor cost is based on 2 people; the total operating cost is the sum of the previous 3 items.

6 summary

(1) There are many kinds of electroplating processes and complicated processes. The water quality of electroplating wastewater varies greatly among different enterprises, but the common feature is that they contain heavy metal ions, acids, alkalis and other pollutants. Electroplating wastewater should be collected and classified.

(2) The project comprehensively considers the properties of cyanide-containing, chromium-containing wastewater and comprehensive wastewater. The cyanide-containing wastewater and chromium-containing wastewater are separately collected and pretreated, and then combined with the integrated wastewater for treatment and discharge. The process adopts the traditional chemical method, the technology is mature, the operation is simple, the effect is stable and reliable, and it can withstand the impact of large water volume and high concentration load.

(3) In the design process, the above-ground and underground buildings are separately constructed to make the whole process more compact, convenient for construction and operation, and small in floor space. Maximize the use of mechanized and automated equipment to reduce labor intensity, improve wastewater treatment efficiency and stability of processing facilities.

(4) Electroplating enterprises should promote clean production, improve cleaning efficiency, and reduce the amount of wastewater generated. Conditional enterprises should be reused after wastewater treatment.