Accelerated weathering of silicate rock dusts

Five commercial RDs were tested in four acid forest soils. First, RD dissolution was measured in batch renewal systems during one year at various starting pH (3.5-5.5) and constant temperatures (20-65°C). These showed that the ANCs of RDs exhibit a fast fraction (half-life <1 day) followed by a slower fraction. Second, pHstat tests performed between pH 3.5 and 4.5 revealed surface normalised dissolution rates that decreased factors 10-100 per unit pH increase, the range depending on the RD. The ranking of the observed surface area normalised dissolution confirmed that of literature-based values, weighed by the XRD derived mineralogical fractions. Third, lime-calibrated agitated soil-RD suspension tests were conducted during two months and yielded ANCs that were factor 2-5 times larger than in the batch renewal test because of buffering effects of soil particulates. Finally, an outdoor soil mesocosm on the four acid soils amended with RDs at 12 Mg/ha and 340 Mg/ha was established and soil pH was monitored during 2 years.