Reducing soil acidity in abandoned mines

Materials World magazine
2 Jun 2017
Plots marked on the slope where biochar was applied. Photo: Andrew Harley

A charcoal-like substance is being used to reduce the acidity of soil in abandoned mines.

Mining of precious metals in the western United States has resulted in around 160,000 abandoned mines leaving a legacy of high-acidity soil.

Jim Ippolito, Associate Professor of soil science at Colorado State University, USA, aims to solve the issue of abandoned mines contaminating soil by using biochar – a charcoal-like substance that reduces soil acidity, made by burning plant material in a low-oxygen kiln.

Ippolito commented, ‘When you dig holes in the ground via mining and pull out rock that hasn’t seen the atmosphere in millions of years, the materials undergo a change […] These materials can start to acidify.’ The surfuric acid produced can react with surrounding rocks, releasing heavy metals, which are relatively harmless until they are absorbed by plants.

While it may at first seem counter-productive to burn plant matter to make biochar to stop plants being poisoned, Ippolito plans to use nuisance plants such as dead lodge pole pine trees, which have been killed by mountain pine beetles, in the kiln.

His team has tested the effectiveness of biochar on reducing soil acidity in Colorado and Idaho, with two different types of biochar reducing soil acidity.