Geochemistry of high-pH waters from serpentinites of the Gruppo di Voltri (Genova, Italy) and reaction path modeling of CO 2 sequestration in serpentinite aquifers

Abstract

The large number of geochemical data gathered on the Gruppo di Voltri springs confirm that progressive interaction of meteoric waters with ultramafic rocks variably affected by serpentinization leads initially to the formation of Mg–HCO 3 waters when the system is open to CO 2, and Na–HCO 3 and Ca–OH type water upon further interaction with the rock, under highly reducing closed-system conditions with respect to CO 2. As indicated by 3H data, these high-pH waters have had long residence times underground in deep aquifers hosted by serpentinitic rocks. These waters are the only available evidence of the presence of such deep aquifers. High-pressure injection of CO 2 into these deep aquifers was simulated by reaction path modeling. Results indicate that this is a feasible methodology to reduce the inputs of anthropogenic CO 2 into the atmosphere. Serpentinitic rocks have a high capacity for CO 2 sequestration, mainly through formation of carbonate minerals. Dissolution of serpentinitic rocks and precipitation of magnesite and silica minerals occurs naturally in areas of high terrestrial CO 2 fluxes such as in southern Tuscany, corroborating the feasibility of this methodology of CO 2 sequestration. However, this process causes a progressive decrease in the porosity of the aquifer, at least under closed-system conditions. These side effects must be carefully evaluated by means of further laboratory tests and field activities.