Upgrading process of copper smelting acid-making wastewater treatment system

Copper acid wastewater quality

The acid wastewater of the copper system consists of three parts: 530,000 tons of sulfuric acid, 300,000 tons of sulfuric acid and a sodium sulfite system. The water quality of its acid wastewater is shown in Table 1.

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In vivo concentration process of acidic wastewater

2.1 Process flow

The 300,000t acid production system, the 530,000t acid production system, and the sodium sulfite purification system are scattered and constructed, with large acid water treatment capacity and low acidity (2%~5%). In vivo concentration according to the existing equipment and facilities, after being dedusted by a suspension filter, the bottom discharge liquid enters the sludge tank, and the supernatant liquid enters the clear liquid tank.

In order to prevent the sludge tank from escaping due to the large instantaneous bottom displacement of the system, the sludge tank is connected to the overflow pipeline to the clear liquid tank.

The bottom effluent and the supernatant can be pumped to the filter press respectively for pressure filtration to ensure the continuous and stable operation of the system.

After the system is pressure filtered, the waste residue is transported to the hazardous waste storage yard, and the filtrate with an acidity of about 15% after concentration in the body enters the filtrate tank, part of which is pumped to purification and reuse, and part of which is discharged into the underground pipeline for raw acid water to enter the vulcanization process. The reduction concentration process is shown in Figure 1.

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2.2 Device configuration

The main equipment configuration of acid wastewater concentration in vivo is shown in Table 2. The principle of configuration is to use the original flue and acid wastewater transportation pipeline.

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(1) 300,000 t sulfuric acid system, equipped with corresponding transfer pumps for the existing tanks and installed a 100m2 filter press and supporting facilities in the new steel structure color board room on the north side of the existing steel platform.

(2) 530,000 t sulfuric acid system, equipped with a corresponding conveying pump for the existing slag tank, and installed a 100m2 filter press and supporting facilities in the newly built steel structure color board room in the open space on the east side of the electric mist removal.

(3) For the sodium sulfite system, add two slag tank transfer pumps, use the existing steel platform on the south side of the system to install two 80m2 filter presses and supporting facilities and seal them with a color board room, and consider the problem of acid water reuse in the design.

2.3 Layout

The quality improvement and weight reduction concentration unit is the acid wastewater reduction and concentration unit in each acid production system of the chemical plant. It is constructed in multiple workshops. After pressure filtration and adiabatic evaporation of the copper system acid wastewater, most of the acid waste is reused for the fumes of the acid production system. Air purification.

The 530,000 t sulfuric acid upgrading and weight reduction equipment is arranged in the open air on the east side of the electric demister; the 300,000 t sulfuric acid upgrading and weight reduction equipment is arranged in the open air on the north side of the existing filter press system; the sodium sulfite system is arranged on the east side of the existing large purification system On the arsenic removal frame, a new filter press room was built, and the lifting pump was arranged under the original platform.

Upgrading of the acid wastewater treatment system

The upgrading and reconstruction project of the acid wastewater treatment system adopts the internal concentration and lime iron salt method, and the treatment capacity is 1500m3/d. This project includes a vulcanization section, gypsum neutralization section, deep defluorination, and advanced treatment.

3.1 Process flow and equipment configuration

All equipment for the lime-iron-salt method is newly built. The main equipment configuration is shown in Table 3, and the process flow is shown in Figure 2.

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3.1.1 Vulcanization unit

The acid wastewater uses the original 5000m3 acid pool to lift the pump station to equalize the pH, flow, and water quality of the wastewater, and mix the prepared sodium sulfide solution with a concentration of 10% and the acidity of 2% to 5% discharged from the copper smelting flue gas acid production system. The acid wastewater containing nickel, copper, and metalloids is pumped into the sulfidation reactor.

Adding sodium sulfide to the vulcanization reactor makes the heavy metal ions react with sulfide ions to form insoluble metal sulfide precipitation, whose solubility product is smaller than the corresponding metal hydroxide, and is easier to dehydrate, thereby removing part of the nickel and copper in the acid water. , lead and other heavy metals and arsenic.

Then it enters the thickener for solid-liquid separation, and the clarified liquid on the upper part of the thickener is discharged from the annular chute at the top to the first-stage thickener supernatant storage tank to provide stable flow control for subsequent reaction facilities. The hydrogen sulfide gas generated in the reaction process is treated with dilute acid + liquid alkali absorption, and the absorption liquid is fed into the sulfurization reactor for reuse. The supernatant of the thickener and the filtrate of the filter press enter the neutralization reaction process.

3.1.2 Neutralization unit

The supernatant from the vulcanization unit enters a first-stage neutralization reactor and CaO is added to adjust the pH to about 3.5.

The reaction liquid enters the first-stage thickener for neutralization, and the bottom sludge from the thickener enters the first-stage sedimentation tank for neutralization. After the first stage of the filter press, the bottom sludge is sent to the waste disposal center.

The supernatant and the pressure filtrate enter the second-stage neutralization reactor, and the pH is adjusted to about 9. The neutralization liquid enters the second-stage neutralization thickener, and the bottom sludge of the thickener enters the second-stage neutralization sludge tank. After being filtered by the second-stage neutralization filter press, it is sent to the waste residue disposal center. Carry out a deep defluorination process.

3.1.3 Deep defluorination unit

After two stages of neutralization, the acid wastewater has a fluoride ion concentration of about 30 to 50 mg/L, which cannot meet the discharge requirements and requires further advanced treatment to reach below 5 mg/L.

Therefore, the neutralized wastewater needs to enter the deep defluorination reactor, and aluminum salt, calcium chloride, flocculant and fluoride removal agent are added to the reactor to cause a flocculation reaction with the fluorine in the wastewater.

After fully reacted, it is deposited in the thickener in the deep defluorination section, and the bottom sludge of the thickener enters the sludge tank. After being filtered by the pump and the filter press, the pressure filtrate and clear liquid enter the advanced treatment unit, and the pressure filter residue is sent to waste. Yi Disposal Center.

3.1.4 Deep processing unit

The advanced treatment unit uses hydroxy iron to carry out advanced treatment of low-concentration heavy metals. Iron-based chemicals are used as treatment agents to remove heavy metals to improve wastewater treatment conditions and the environment.

The iron-based agent used is an active agent with a unique double-layer structure of hydroxyl and anion layers, with a specific surface area and interface reactivity more than 10,000 times larger than traditional materials, and has a special net-capture function for heavy metal ions in wastewater.

Through the special structure of the iron-based agent, it can reduce, adsorb and complex, ion exchange, encapsulate and co-precipitate and replace the metals in the wastewater, and can simultaneously reduce and adsorb various heavy metals so that the heavy metals can be separated from the water and the wastewater can meet the standard. emission.

The advanced treatment unit consists of a first-level reaction treatment tank and a first-level high-density sedimentation tank. The supernatant from the lime neutralization section enters the aeration tank, and the effluent flows into the primary reaction treatment tank by gravity. The active iron-based chemical is added to the primary reaction treatment tank to remove heavy metals, arsenic, etc. remaining in the wastewater after pretreatment. pollutants. After the wastewater is fully reacted, gravity flows into the high-density clarifier for solid-liquid separation, and the sludge is pumped to the original reaction tank by a pump.

3.2 Layout

The general principles of the layout of the sewage treatment plant are: in line with the technological process, smooth and continuous, adaptable to production flexibility, and reasonably reserved for development; the layout is compact and reasonable, saving construction land, the foundation is placed in the original soil layer, and the earthwork excavation is minimized. , backfill and outbound transportation to ensure safe operation and save infrastructure investment; according to the site topographic characteristics, taking into account the engineering geological characteristics, the layout is adapted to local conditions.

On the premise of realizing self-flow after one lift, the vertical layout should minimize the lifting height, reduce the power consumption of lifting, and reduce the operating cost; pay attention to the orientation, meet the ventilation and lighting, and strive for the best layout design.

The newly built lime iron salt processing unit is located in the northeast corner of the dressing and smelting chemical plant, covering an area of about 8000m2. The east side is adjacent to the raw material pretreatment workshop of the copper factory, the north side is the idle area outside the fence, the west side is the hardened wastewater pit, and the south side is the acid water emergency water treatment station. There is no residential area outside the project boundary, and there is an open reserved site within the factory boundary.

Transformation effect

The acid wastewater treatment system adopts the in vivo concentration and lime iron salt method to upgrade and transform. After a series of process treatments, the effluent quality reaches the GB25467-2010 standard. The specific indicators are shown in Table 4. The project was completed in December 2017. During the same period, the copper plant took over the commissioning and operation for two months, and has now been officially put into production.

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