Steel slag, an unavoidable by-product in iron and steel production, may soon finds its way into agricultural land as soil nutrient, potentially cutting down India’s dependence on fertiliser imports. Now the third-largest steelmaker in the world, India produces over 12 million tonnes of slag each year, but less than 20% of that is used in the cement industry while the remaining keeps piling up at the steel mills, while countries like USA and Japan use slags extensively (more than 70% of the produce) in areas such as housing and road construction, land and mine filling. The steel ministry has requested the agriculture ministry to look into the scope of using these slags particularly in areas, mostly in the eastern part of the country, having acidic soils, where productivity is lower. Out of India’s 142 million hectare of arrable land, 49 million hectare is covered by acid soils. “The use of steel slag may be one of the most green solution which may avoid accumulation of large wastes in steel plants as well as help in treatment of soil for improving crop productivity at low cost,” the steel ministry said.
The integrated steel plants in the country generate large volumes of steel slag having more than 50% of free lime. Steel slag contains calcium, silicon, manganese, phosphate and iron. The use of steel slag as fertilisers and soil nutrients is gaining importance across the globe as it represents an eco-friendly application wherein advantages of chemical properties of steel-making slag can be utilised to promote the growth of plants and increase the yield of agricultural products, particularly in the areas where the soil is acidic. “Productivity of such soils are low mainly due to the fact that in areas of high rainfall, soils become acidic as a result of their reaction as soluble basic salts like calcium, manganese and potash, are leached away by drainage water and insoluble acidic residues impaired biological activity, low base saturation and other acidity-induced soil plant nutritional and fertility problems,” the steel ministry wrote.
Developed countries like Japan, USA have taken lead in making fertilisers as slag silicate fertiliser, by-produced lime fertiliser, slag phosphate fertiliser or iron matter of special fertiliser using steel-making slag. Though India’s fertilsier production has improved in recent times, it still depends on imports to bridge the demand-supply gap. India imported 5.5 million tonne urea, 4.4 million tonne DAP and 3.7 million tonnes of potash in 2016-17.