Meaning and current condition of steel slag recycling
Current condition of steel slag recycling in China
Traditional dry processing technology
At present most of the domestic steel plants employ a simple crushing magnetic separation technology for slag recycling, the equipments used mainly include1 to 2 jaw crushers or 1 cone crusher + several units of belt type dry iron removers or 1 to 2 magnetic separators. The disadvantages are: too many processes; slag and iron separation is not complete; recovery of low grade iron particles to 5mm (TFe content of about 40%) which is not conducive to steel metallurgy; tailing particles are larger than 1mm with high iron content (about 5%), resulting in a lot of waste of resources and economic inefficiency.
Effects of low-grade steel slag for steelmaking as follows:
Slag and other harmful elements parathion return to molten steel and continuously enriched, which affects steel quality due to impurities, resulting in increase in the amount of slag, serious spatter and because the weight of liquid metal can not be accurately determined, the control accuracy over chemical composition of the molten steel is affected during smelting process technology. During pouring, short-foot waste is likely to appear due to lack of liquid steel weight. The main component of SiO2 slag will reduce alkalinity and change the composition of slag, which is harmful to improve the life of the lining and dephosphorization. This technology is generally used by more steel plants.
Dry + wet mill election
This method needs high investment and large area of land, and is not suitable for large pieces of steel slag recycling. For large pieces of steel slag recycling, it should comply with other crude election method with tailing mud to be concentrated, precipitated, dewatered and dried before use, in this way it not only pollutes the environment but also increases land occupation and investment, which means economic inefficiency.
Fatal flaw:
Due to high tailing sludge recycling costs, currently natural precipitation sludge recycling and mechanical methods are widely used. Natural sedimentation method requires construction of large-scale sedimentation tank system, settling for a long time, the effect is poor; mechanical methods uses inclined plate settler and a filter and matching tank, pump, pipe network system to process technology the tailings slurry, Maanshan Iron & Steel Plant uses this method. Either way substantially increases in investment and operating costs. Water content of tailing slag is high after dehydration and its activity loses after finely ground washing, and can not be used for slag powder production, basically loses value. And washed selected particles of iron easily get rusted, with main component of Fe (OH) 2, which will increase the hydrogen content of steel in the decomposition furnace, affecting the quality of steel. Tailing sludge sedimentation pond system takes up a lot of land, and because the tailing mud has no use value, this will occupy a lot of land and pollute the environment. A lot of domestic steel plants use this process technology, Maanshan Iron and Steel Plant is just one of them.
How to dispose steel slag with simple but effective technology and produce high quality slag steel, iron power and recyclable tailing slag is the key technology for more added value of steel slag.