Creating soil from steel slag

Our forest cover is depleting with every passing day due to urbanisation and rapid industrial growth.

To rebuild it, we need lots of fertile soil. Unfortunately, natural soil takes millions of years to form, as soil-making is mainly a function of time, temperature, and pressure.

In such a scenario, could we replace natural soil with artificial soil that is economical and environmentally safe?

This is precisely what Shashibhushan Biliangadi, a researcher with the IITB-Monash Research Academy, is working on for his PhD project titled, ‘Soon artificial soils to replace natural soils for vegetation’.

Says Shashibhushan, “Millions of tonnes of solid waste are generated every year. For instance, approximately 150-200 kg of steel slag is generated for every ton of steel produced. Steel slag constitutes nutrients which are essential for vegetation. However, the slag usually ends up in landfills or dumping sites due to lack of recycling technologies. Our research, therefore, aims to invent a proper soil mix using steel slag for the establishment of vegetation.”

The biggest challenge he faces is that steel slag is extremely alkaline in nature (pH>10). “Steel slag comprises 30-40% lime,” explains Shashibhushan, “which is adsorbed on to macro- and micro-pores. No plants and soil friendly micro-organisms would grow at this pH, except alkalinity tolerant/resistant plant species.”

Interestingly, steel slag is already being used as fertiliser to increase the pH (potential of hydrogen) of acidic soils and to supply nutrients like calcium, magnesium, and iron. Yet this alone with compost would not support vegetation due to the high level of alkalinity.

Says Shashibhushan, “Soil formation is not an easy task. Nature takes care of many things which humans cannot replicate. The material we are trying to convert as soil is not hazardous. But because it is alkaline, it induces extra stress on plants. An interesting thing we observed during our experiment was that mushroom colonies sprouted in certain artificial soil mixes. This gave us hope that slag can be converted to soil. Unfortunately, the colonies diminished within a week of germination, so we are now trying to ascertain why they are not growing to the full.”

The IITB-Monash Research Academy is a collaboration between India and Australia that endeavours to strengthen scientific relationships between the two countries. Graduate research scholars like Shashibhushan study for a dually-badged PhD from both IIT Bombay and Monash University, spending time at both institutions to enrich their research experience.

Fig 2: Biological growth in one of the artificial soil mixes

Says Prof Murali Sastry, CEO of the Academy, “Mining and metallurgical companies are facing a huge problem while disposing solid wastes like slag, tailings, over-burdens, etc. Dumping / stockpiling these materials not only consumes land mass but also could pollute nearby water sources, ground water, soil and air. It would be wonderful if they could be converted into synthetic soil that can be used in place of natural top-soil to replenish and revegetate degraded lands, landfills, abandoned mine sites and metal-contaminated sites.”