The alkalinity of the sewage discharged from the magnetic separation plant is extremely high. If it is directly recirculated into the circulating water, the water quality will be deteriorated, resulting in serious pipe fouling. In order to return the external drainage to production, it is necessary to soften its water quality and reduce alkalinity. At the same time, it should make full use of the existing facilities of the enterprise to save investment. Taking the external sewage treatment project of Changgang Group's magnetic separation plant as an example, this paper expounds that the wastewater discharged from the magnetic separation plant should be properly treated under the condition of permitting conditions. The technology of multi-purpose and recycling should be adopted as much as possible to improve the repetition. Water use rate; the existing facilities of the enterprise should be utilized as much as possible, and the treatment plan should be determined according to local conditions.

I. Overview of production and drainage of magnetic separation plant

The Changgang Group Magnetic Separation Plant has the status quo of large water consumption per ton of steel and pollution surrounding environment. The production scale of the plant is 14,000 t/a, the new water consumption is 31.2 m ³ /h, the circulating water volume is 110 m ³ /h, and the circulation rate is 71.64%. The production operation system is intermittent operation, 2 shifts per day, 8 shifts per shift. Hours, total annual production for 8 months; external displacement is 50m ³ /h, 8.5h per day during production.

The circulating water used in the magnetic separation plant is mainly the water for washing the magnetic separator and the water for the filter cloth. The existing water system facilities are mainly one pump house, which is equipped with two sets of water pumps, which are respectively supplied with system circulating water and flushing filter cloth; the second sedimentation tank is divided into three compartments with a volume of 15×14×4(m), which doubles Pump suction basin; sludge treatment part mainly deals with magnetic separator washing water waste residue. The main facilities of the system are coarse particle separators (two units), sloping plate sedimentation tanks (two), belt filter presses (one unit), and two φ3×4 (m) dosing tanks. The overflow liquid of the inclined plate sedimentation tank flows into the secondary sedimentation tank (hereinafter referred to as the secondary sedimentation tank), and the pressure filtration water is discharged, mixed with the existing external drainage of the seamless plant, flows into the Qiyi irrigation area, and merges into the Weihe River. The drainage water is strongly alkaline. The new water is supplemented by the existing seamless plant storage tank, which is alkaline. The main process flow is shown below.

The results of the drainage sampling test and the water quality requirements of the circulating water in the plant are shown in the table below.

The main problems in the production of water in the magnetic separation plant are:

(1) The production water is recycled water, the pH value and alkalinity are much higher than the water quality requirements, which causes the water quality to deteriorate, resulting in serious pipe fouling, and the circulating water quality does not meet the reuse standard;

(2) The wastewater discharged from the plant contains residual flocculating agents, and the alkalinity is extremely high. The external discharge not only causes serious waste, but also may infiltrate into the underground or into the river body to cause serious pollution to the water source and the environment.

Second, the program design

At present, the magnetic separation plant has a complete sludge treatment facility. In order to solve the above problems, it adopts methods such as recycling waste water, reducing circulating water alkalinity and controlling pipeline fouling, so that the water system of the plant can operate safely and reasonably. . The specific measures are as follows:

The external drainage of the filter press is collected into the shallow groove of the ground and then discharged into the secondary settling tank. The original external drainage ditch will be abandoned, the DN200 plastic pipe will be pre-buried on the tank wall, and the overflow pipe of the inclined plate sedimentation tank will be connected, and then discharged into the second settling tank. The second settling tank is divided into three grids, and the circulating water is discharged into the first grid. After the secondary sedimentation overflows, it enters the third grid, and at the same time, the supplementary water is added, and then the pump is pressurized and recycled. In order to ensure that the water quality meets the production requirements, the water source of the supplementary water is changed from the original seamless plant's storage tank to the existing groundwater of the plant, and the flocculant, water quality stabilizer and scale inhibitor dispersant are added to the secondary settling tank. In order to reduce the circulating water alkalinity and control the fouling of the pipeline, an appropriate amount of sulfuric acid should also be added. Adding sulfuric acid to the first compartment of the secondary settling tank, the pH of the circulating water drops, but excessive addition of sulfuric acid will accelerate the corrosion of the equipment. Therefore, the regulating valve should be added at the outlet of the sulfuric acid tank (already) and in the secondary settling tank. A pH adjuster is installed at the end of the second cell, and a regulating valve installed at the outlet of the sulfuric acid tank is controlled by a pH adjuster transmitter to ensure that the pH of the third water in the pool is about 7.

The amount and concentration of the above agents should be entrusted to a professional manufacturer for water quality testing and analysis of scale components.

In order to better ensure the treatment effect, a magnetic cleaner is installed on the main pipe of the circulating water supply and the main pipe of the filter cloth flushing water supply.

After the external drainage of 50m ³ /h is recycled into the circulation system for unified treatment, the system can reduce the supplementary new water volume by 26.56m ³ /h, and the circulation rate can reach 95.8%, which meets the national standards of the corresponding industry; the circulating water quality meets the production requirements.

The newly added equipments are mainly three sets of dosing devices, which are respectively added with flocculant, water stabilizer and scale inhibitor and dispersant. Since the newly added medicine equipment has its own set of electric control box, the control motor power is 0.84kW/set. The electrical design task only provides low-voltage power supply (380V, 50Hz) for three (sets) dosing equipment, and corresponding work and protective grounding. As the project is retrofitted by the old factory, the power supply can be taken from the repair power switch box, and then connected to the supporting electric control box of the three sets of dosing devices.

Third, investment overview and benefit evaluation

The total investment of the project is 201,000 yuan. After the project is put into production, there is no need to increase the number of employees, and the labor cost increase is zero; the annual discharge of wastewater is 102,000 tons, and the annual increase of enterprise income is 17,700 yuan; the investment recovery period is 11.52 years, and the investment return rate is 8.7%, which has a good economy. Benefits and social benefits.

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