Nature's 'black gold' rush

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Estimated reading time ~ 8 mins

Up until 1709 the only way to produce iron was to smelt iron-ore with charcoal. Produced using a technique known as pyrolysis, wood is heated to a temperature of around 400 °C in the absence of oxygen to form charcoal.

As demand for iron soared, it was critical that enough charcoal was on hand to keep the furnaces stoked. Charcoal-based iron smelting had a serious cost however. Alongside the clearing of land for agriculture and timber, demand for charcoal from the ironmasters was one of the major causes of deforestation in Europe during the 17th Century.

Scarce supplies of wood and charcoal prompted the search for an alternative. It was Abraham Darby, a British ironmaster, who first demonstrated that iron could be produced in a furnace fired with metallurgical coal, or met coal for short. The discovery helped alleviate the pressure on Europe’s remaining forests, but so began the search for met coal to mine and exploit. Today, steel production accounts for ~7% of global greenhouse gas (GHG) emissions, of which met coal is a major contributor.

315 years later, demand for a product that is chemically very similar to charcoal is enjoying a renaissance as solutions that remove carbon from the atmosphere grow ever more important. Biochar, as its known, is also produced using pyrolysis, but can be made using a wider range of biomass feedstock, and crucially, it is heated to a much higher temperature (600-1000 °C).

While charcoal’s physical properties mean that it is useful for heating, biochar’s greater porosity and surface area means that it is ideal for carbon sequestration. Analysis also indicates that it will take at least 1,000 years to degrade, and realistically well beyond 10,000 years. To all intents and purposes, biochar is permanent given the timescales required to keep the rise in global temperatures below 1.5 °C. As well as its carbon removal properties, biochar also plays a role in improving soil health and increasing crop yields.

There’s a reason why it is called nature’s ‘black gold.’