Sewage treatment of lead-zinc smelting flue gas acid purification process

Using a unique treatment process of waste acid, the acid waste water to the decontamination of arsenic, pumps and other toxic, harmful heavy metal ions after partially qualified dilute acid plant can be used to point back; the other dilute acid neutralized After treatment and further arsenic removal treatment, it is sent to the whole plant wastewater treatment system for deep treatment, and then pumped to the high tank for production and reuse. The relevant national quality standards stipulate As <0.3% in raw materials, but the lead content in some domestic mines has higher arsenic content. The consequences are difficult to bring environmental governance lead zinc smelting enterprises so that some enterprises atmospheric emissions and wastewater discharge exceeded.

Chenzhou City Jingui Silver Industry Co., Ltd. is a production and operation of electrolytic lead, silver high, high purity bismuth, high purity silver nitrate-based high-tech enterprises, is an important base for production and export of silver in China. The company adopts advanced production technology and advanced equipment to eliminate backward and polluting production lines and focus on the implementation of lead, zinc and silver projects. The first phase of the lead, zinc and silver project and the 100,000 tons/year one-step lead-smelting project are based on the feasibility report of 100,000 tons/year lead smelting and one-step lead-smelting prepared by Hunan International Consulting Co., Ltd., using internationally advanced lead smelting. Process - a one-step lead-smelting process for oxygen bottom blowing, to build a 100,000 tons/year lead smelting production line. The product scale of the project is 100,000 tons of lead and 80,000 tons of sulfuric acid, while recovering gold, silver, zinc, copper and antimony. , tin , antimony and other valuable metals. The total investment of the project is 480 million yuan, covering an area of ​​more than 300 acres. The project is located in the non-ferrous metal industrial park of Cangzhou City. After the project is completed and put into production, the annual sales revenue will be 2.5 billion yuan, the profit and tax will be 250 million yuan, and more than 800 new jobs will be created. The annual savings of coal and water will be 30%, and waste water, waste gas and waste residue will be reduced by 20%. The project also listed the “Double Hundred” project in Hunan Province and the provincial key projects, and is also a key construction project in Cangzhou City.

In order to solve the heavy metal pollution caused by lead and zinc smelting, the company and Hunan Xiangniu Environmental Protection Industrial Co., Ltd. jointly developed a new process of acid treatment: using an organic sulfur desulfurization-neutralization-oxidation-combination membrane separation process to build a processing capacity. 550m3/d, remove toxic and harmful heavy metal ions such as arsenic and pumps in dirty acid wastewater. The sulphur acid treated by this project is derived from the sulphuric acid produced by the lead-zinc smelting flue gas purification process. The main pollutants are pH, As, Hg, Pb, Zn, Cu, Cd, F, etc. The first type of pollutants have high concentration and are highly difficult to treat. The project is based on saving investment, saving land occupation and reducing operating costs. When designing the project, the self-flow arrangement is adopted as much as possible to reduce the number of upgrades, saving energy consumption and simplifying operation management. Ensure that the engineering system design complies with environmental protection related technologies and legal norms and requirements, and removes toxic and harmful heavy metal ions such as arsenic and mercury in the waste water wastewater to ensure the stability of the effluent water quality after treatment, and can reduce emissions: arsenic 1.5 tons/year. Lead 4.5 tons / year.

I. Construction Scale According to the requirements of the construction unit Cangzhou Jingui Yinye Co., Ltd., the scale of design and treatment of the sewage treatment of this project is: Q=100～300m3/d; intermittent treatment according to 40m3 per treatment. The maximum treatment capacity of sulphuric acid is: 200m3/d. The design processing scale is: Q=5～20m3/h.

Second, the emission law and the flue gas purification process to the lead and zinc smelting enterprises are continuous production processes, and the pollution of acid and acid is intermittent. Therefore, the sewage treatment facility is designed to operate intermittently. After the process is used to remove toxic and harmful heavy metal ions such as arsenic and pump in the sewage acid wastewater, part of the qualified dilute acid (about 10-15 m3, concentration is about 5%) can be reused for the flue gas acidification point (for dilution) The acid is formulated into 93% dilute acid to absorb SO3 gas in the flue gas); after the other part of the dilute acid is neutralized and further dearsenized, the pump is pumped to the whole plant wastewater treatment system for deep treatment, reuse or compliance.

Third, the raw water quality

The process refers to the following parameters (see Table 1). Table 1 Lead concentrate composition and soil acid concentration

Fourth, the processing standard

After removing most of the toxic and harmful heavy metal ions and arsenic in the sulphuric acid, the dilute acid (concentration is about 5%) can be reused in the flue gas sulphuric acid point (the SO3 gas in the dilute acid absorption flue gas is prepared). ); after the other part of the dilute acid is neutralized and biologically purified, it is all used for washing; the most of the As, Hg, Pb, Cd, etc. are removed from the sulphuric acid, and the standard of dilute acid can be achieved. Smoke makes acid. Sewage acid is treated by vulcanization + neutralization method and then treated into acid waste water treatment station. The removal rate of pollutants by vulcanization + neutralization treatment process is: copper 88%, lead 88.6%, zinc 98%, cadmium 90%, arsenic 96%, Mercury is 60% and fluorine is 65%. Therefore, the concentration of pollutants entering the acid sewage station is shown in Table 2. Table 2 Concentration of pollutants entering the acid sewage station

V. Sewage treatment process description and reaction mechanism of each step

The smelting acid generated by the smelting furnace flue gas acid purification washing is transported by the construction unit to the septic acid storage collection tank, and is lifted to the sulphurization reaction tank by the septic acid transfer pump. Then, the configured organic sulfur solution is introduced into the vulcanization reaction tank from the organic sulfur storage tank through the dosing pump, and is vulcanized with harmful metal ions such as Cu, Pb, Zn, Cd in the dirty acid waste water to form a water-insoluble solution. The metal sulfide precipitates; at the same time, the arsenic in the dirty acid wastewater (the arsenic in the acid is mainly in the form of trivalent arsenic, that is, AsO+ ions) undergoes a sulfurization reaction to form a precipitate of arsenic sulfide which is hardly soluble in water. In the sulphurization reaction tank, the oxidation/reduction potential is controlled by the PH/ORP instrument within a certain range, and the dosing amount is controlled by this, and under this control condition, the arsenic removal rate can reach 90% to 95%. The reaction mechanism of the process is: 3Na2S+S2O3+3H2O=As2S3↓+6NaOH Cue2+S2-=CUS↓ Pb2++S2-=PbS↓ Zn2++S2-=ZnS↓ Cd2++S2-=CdS↓ Hg2++ S2-=HgS↓

The effluent from the sulphurization reaction tank flows from the clarification tank to the slag and water. The harmful metal sulfides and arsenic sulfide deposited on the lower part of the thickener are dehydrated by the sludge bottom pump pump to the diaphragm press automatic type box filter press, and the metal sulfide and arsenic sulfide slag are reused as products. Utilization; the filtrate and the supernatant of the clarifier are self-flowing to the dilute acid pool. Most of the dilute acid in the dilute acid pool is upgraded by the construction unit to the flue gas production point. The remaining portion of the dilute acid in the dilute acid tank is pumped to a neutralization tank. The powdered lime is formulated into a lime emulsion in a lime preparation tank, and flows to the lime dosing tank through a feed pump, and then enters a neutralization tank through a dosing pump to carry out a neutralization reaction to neutralize the strong acid in the contaminated acid. In the reaction, the pH value is detected online, and the pH value is strictly controlled to control the dosage of the limestone emulsion. The reaction mechanism of the process is as follows: Ca(OH)2+H2SO4=CaSO4↓+H2O The effluent from the neutralization tank is dewatered by the sludge pump to the gypsum filter press, and the dry gypsum residue is recycled; the filtrate flows to the intermediate pool.

The intermediate pool effluent is lifted by a self-priming pump to the second section of the neutralization tank. The powdered lime is formulated into a lime emulsion in the lime preparation tank, and flows to the lime dosing tank through the self-flowing, and then enters the second neutralization tank through the dosing pump to carry out the neutralization reaction, thereby increasing the pH value of the wastewater and reacting with the trivalent arsenic in the wastewater. , forming a poorly soluble calcium meta-arsenite [Ca(ASO2)2] or a basic salt of calcium arsenite [Ca(OH)AsO2]. When the lime is excessive, calcium pyroar arsenate (Ca2As2O5) is formed. The pH value is strictly controlled to control the dosage of the lime emulsion. Solid form ferrous sulfate Ferrous sulfate salts formulated as formulated groove ferrous sulfate solution, ferrous sulfate by gravity to the dosing tank, and then adding arsenic removal groove by the pump into the oxidation, while, PAM PAM prepared solution tank It is pumped into the human oxidizing and arsenic removal tank, and when it is filled with compressed air, it flocculates with arsenic and further reacts to form more insoluble salts such as iron pyroar arsenate, thereby achieving the purpose of removing arsenic from wastewater. . The reaction mechanism is as follows: Ca(OH)2+H2SO4=CaSO4↓+H2O+CO2↑ 2Ca(OH)2+As2O3=Ca2As2O5↓+2H2O Ca(OH)2+Fe2+→Fe(OH)2↓+Ca2+ 3Ca( OH)2+2Fe3+-2Fe(OH)3↓+3Ca2+ AS2O3+2Fe(OH)2→Fe2As2O5↓+2H2O H3AsO4+Fe(OH)3→FeAsO4↓+3H2O H3AsO3+Fe(OH)3→FeAsO3↓+3H2O Ca2++2F→CaF2↓ The salt of pentavalent arsenic is less soluble than the salt of trivalent arsenic, and the solubility of iron salt of arsenic is also small.

For example, arsenic in wastewater is mainly trivalent. In order to reduce the treatment cost and simplify the treatment process, adding compressed air to oxygen in the arsenic removal tank and oxidizing trivalent arsenic to pentavalent arsenic can improve the treatment effect.

Sewage acid wastewater treatment process diagram

The effluent from the iron salt oxidizing and de-arsenic tank is pumped to the biological purification filter press for dewatering, and the filter residue is recycled; the filtrate flows to the outlet tank. The effluent from the water outlet is upgraded by the construction unit to the production water point of the whole plant. Through the implementation of this treatment process, zero emissions of lead and zinc smelting of sulphuric acid and wastewater can be achieved.

field fence

Pasture Fence,Galvanized Fencing,Animal Fencing,field fence

anping yaqi wire mesh co.,ltd , https://www.yaqisteelwire.com