Combining waste rock and beneficial microbes to enhance soil for carbon capture

Project duration: July 2023–June 2026

Project lead

Team

Bobby Pejcic, Renee Birchall, Anicia Henne, Diogenes Antille, Jonathan Anderson, Maja Arsic and Cathryn O’Sullivan.

Opportunity

It’s been suggested that enhanced rock weathering (ERW) can play an important role in removing carbon dioxide (CO₂) from the atmosphere and improving soil fertility but, at present, it’s a slow, expensive and inefficient process. When rock dust is applied to soils natural weathering processes result in CO₂ from the air being captured and stored in the soil as mineral carbonates. The rate of rock weathering is a critical factor in making ERW a viable option for carbon sequestration in agricultural soils but a more innovative and radical approach is needed to improve performance. This requires the development of alternative materials and methods for ERW.

Recent studies and modelling have shown that the application of finely crushed magnesium (Mg)- or calcium (Ca)-rich rock to soils can enhance CO₂ sequestration. Likewise, agricultural studies have shown rock dusts can increase soil fertility and plant performance by improving mineral availability and changing the physicochemical properties of soils.  

Soil microbes play a critical role in controlling the rates of rock weathering in natural systems but there’s been very limited exploration in combining rock dusts with microbial additions and organic inputs to enhance natural soil processes that accelerate rock weathering. Considering global croplands cover around 12 million km², there is significant potential for CO₂ capture and storage, and for improving soil health and yield. Moreover, enhanced rock weathering enables farmers to participate in carbon farming without the need to use productive land for tree planting.

This is an emerging science area, and one with great potential across a number of sectors. What’s needed to drive ERW forward, beyond the current theoretical realm towards widespread use in carbon negative agricultural systems, is a fundamental understanding of the role of chemical and microbial processes in determining the rate of ERW in agricultural soils and how to accelerate it.

Goal

Our aim is to develop a new ERW material that facilitates CO₂ uptake and mineralisation. By combining rock dusts with microbial additions and organic inputs we can enhance the natural soil processes to accelerate rock weathering. Optimising all three of these factors may result in rates of mineral solubilisation that are orders of magnitude above those achieved when rock dust is applied alone.

We’ll use rock dust from mine or quarry waste that’s free from contaminants and rich in Mg and Ca, which have a naturally high capacity for CO₂ absorption, together with microbial and fungal communities that are capable of increasing the rate of weathering of the target rock material. We will also add organic inputs to provide habitat and a source of bioavailable nutrients to drive microbial activity. Various combinations of these will be tested to assess the impact on rock weathering rates, CO₂ absorption, and soil properties. Once the desirable combinations have been identified, they’ll be engineered (blended or combined in specific ratios, granulated or pelletised) to create products that are easy to apply.

The resulting bioactive organo-mineral soil material would be a circular product that will sequester carbon over a very extensive area, while also boosting soil fertility and crop performance. And it can help develop a new future for the mineral resource sector by enabling geomaterials to be used for applications relevant to CO₂ capture and sequestration. 

Barriers

There are numerous challenges with sequestration timescales and the varying environments of Australia’s agricultural landscape, logistics, the emissions cost of producing and transporting rock dust, the current economic cost of rocks specifically for carbon capture and storage (~$300–350 per metric ton), and application issues such as rate and method.

Our novel approach addresses all these challenges and will enable us to create a product that is energy-efficient in production and transport, can significantly accelerate weathering, and be applied easily and at lower rates. 

References

Beerling et al. (2020). Potential for large-scale CO₂ removal via enhanced rock weathering with croplands. https://www.nature.com/articles/s41586-020-2448-9

Snæbjörnsdóttir et al. (2020). Carbon dioxide storage through mineral carbonation.
https://www.nature.com/articles/s43017-019-0011-8