Comparative Assessment of Regional Volcanic By-products and Olivine for Enhanced Weathering in Mediterranean Alkaline Soils

Enhanced Weathering (EW) is gaining traction as a carbon dioxide removal (CDR)
technology, yet its viable large-scale deployment requires balancing carbon sequestration
efficiency with agronomic, environmental, and economic costs and benefits. In this
study, we present the setup and preliminary insights from a mesocosm experiment
carried out at the University of Palermo (Italy), designed to compare the performance of
regional volcanic by-products against a commercial olivine benchmark. We utilized 32
outdoor mesocosms (0.27 square meters each) arranged in a randomized block design,
applying silicate amendments at a rate of 50 t/ha.
The experiment compares three silicate materials with distinct physical and mineralogical
properties: (i) basaltic mine waste from local quarrying (Dv50 of 38.7 microns), (ii) volcanic
ash from Mt. Etna—a sandy, highly porous material rich in amorphous silica with a low bulk
density—and (iii) commercial olivine (Dv50 of 30.2 microns). These materials are applied to
both bare soil and soil vegetated with a mix of local forage legumes, allowing us to assess
the role of plant roots in driving the dynamics of weathering rates and the fate of weathering
products.
We quantify the CDR potential by monitoring alkalinity, Dissolved Inorganic Carbon (DIC),
and major cations (Mg2+, Ca2+, K+, Na+) in drainage waters. Crucially, we also analyze
the soil profile to monitor the precipitation of pedogenic carbonates and changes in
exchangeable major cation pools to assess the long-term effects of the silicate
amendments.
Simultaneously, we monitor the biomass growth to identify potential fertilization benefits.
We also assess the potential trade-offs of trace element release, specifically focusing on
the high Nickel (Ni) content inherent in olivine compared to the volcanic waste streams.
Data collected will be used to calibrate the Soil Model for Enhanced Weathering (SMEW),
bridging the gap between mesocosm-scale observations and numerical simulation to
refine dissolution factors for the seasonally dry, alkaline soil conditions typical of the
Mediterranean.
Using regional volcanic waste streams can provide a cost-effective and agronomically
viable alternative to commercial minerals, delivering competitive CDR rates while
supporting a circular economy and reducing the carbon footprint of mineral sourcing,
grinding, and transport.