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The production process of iron and steel industry includes mining, sintering, ironmaking, steelmaking (continuous casting) and steel rolling.
1. Iron ore mining wastewater
There are four kinds of iron-making ores: hematite, magnetite, limonite and siderite. Select low-grade iron ore (wet screening, gravity separation, magnetic separation and flotation) to obtain high-grade iron ore. Mineral processing mainly produces wastewater and waste residue pollution. Because sulfur and iron can produce sulfate, it is acidic wastewater, and it contains high concentration of suspended solids, various metal ions, mineral processing reagents and so on. Concentrator needs a lot of water, so we should advocate multi-purpose of one water to improve the reuse rate of wastewater treatment; Recovering useful metals from wastewater; Reduce wastewater discharge.
2. Sintering plant wastewater
The sintering low-processing technology is divided into two steps: mixing mineral powder, fuel and solvent into balls and sintering them into blocks. Sintering wastewater mainly comes from wet dust removal and drainage, washing ground water and equipment cooling water drainage. Dust removal water and washing water have high suspended matter content and can be recycled after purification; The temperature of cooling water is high, so it should be recycled.
3. Ironmaking plant wastewater
Ironmaking is a production process in which iron ore, solvent and coke are put into a blast furnace in a certain proportion, melted into pig iron, and slag and blast furnace gas are produced at the same time.
The wastewater produced is mainly blast furnace gas washing water and slag washing wastewater. The wastewater is characterized by high water temperature and high concentration of suspended solids, which can be as high as1000-3000mg/L. ..
4. Steelmaking wastewater
When steelmaking, more carbon elements and impurities such as silicon, manganese, sulfur and forest should be removed from iron, and alloy elements such as nickel, tin, copper, chromium and molybdenum should be added. At present, steelmaking is mainly divided into converter steelmaking (mainly pure oxygen top-blown converter steelmaking) and electric furnace steelmaking (smelting special steel). Steelmaking includes the production process of continuous casting machine, in which molten steel is poured into crystallizer, cooled and shaped with water, and rolled into ingots with a certain length.
Steelmaking wastewater is divided into:
Indirect cooling water for equipment. High water temperature, no pollution;
Direct cooling wastewater of equipment and products. It contains a large amount of iron oxide and a small amount of grease, which can be recycled after treatment;
Dust removal wastewater, slag washing wastewater.
Steel-making wastewater can be recycled after removing suspended solids and cooling, and most steel mills have implemented water recycling.
5. Waste water from rolling mills
Ingots are rolled into plates, pipes, dies and wires. Steel rolling is divided into hot rolling and cold rolling. Hot rolling is to add hot rolling to make products; Cold rolling is rolling at room temperature. In the production process of hot-rolled and cold-rolled products, a large amount of direct cooling water is needed to clean steel and equipment.
Hot rolling wastewater contains a lot of iron oxide and oil, with high water temperature and large water quantity. After cooling, degreasing, filtering and precipitation, it can be recycled.
The main pollutants in cold rolling wastewater are oil (including emulsion), acid and alkali, and chromium ions, which should be treated separately and recycled.
6. Grade of wastewater from iron and steel industry
(Waste water unit ton/ton product, other units kilogram/ton product)
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