Enhanced Rock Weathering

Enhanced Rock Weathering (ERW) is one of the most promising carbon dioxide removal (CDR) technologies that has been developed to mitigate the damages of anthropogenic climate change. ERW is the spreading of finely ground silicate rock in agricultural settings as a replacement for lime, which increases soil alkalinity and forms secondary carbonate minerals (eg. calcite) that trap CO2. While ERW has been shown to be an effective method of drawing down CO2, some challenges with this method remain. One issue is the emissions associated with mining and pulverizing silicate rock amendments specifically for ERW. As such, the use of mine wastes has been suggested as a means of reducing the embedded carbon emissions of ERW. Here we assess carbon drawdown of two different mine residues (kimberlite and serpentinite) and three commonly used agricultural amendments for ERW (basalt, metabasalt, wollastonite). Our growth chamber experiments used pea plants grown in soil amended with each of the five rock types at four spreading rates: 0.1, 0.5, 1.0, and 5.0 kg/m2. This trial ran for three months, with leachates being collected every two weeks, and following the completion of the trial, the leachates were analyzed for alkalinity (aka. dissolved carbonate) to determine the rate of carbon drawdown. Another issue that was addressed through this trial is the lack of knowledge surrounding the effects of silicate rock amendment on soil, plant, and water contamination. As such, the collected leachates were also analyzed for metal contamination. Overall, it was found that carbon capture did occur during these trials, with a statistically significant increase in alkalinity being seen for each rock type (P<0.01). Further, while elevated nickel was seen in some leachates, all leachates analyzed had a nickel concentration below the legal limit (P<0.001).