Can chemistry help maintain carbonates in solution so they do not immediately precipitate on surfaces, which slow or stop subsequent carbonation reactions?
Biological processes might be used to accelerate the weathering process. This acceleration might, for example, be implemented in large leaching piles such as those used for biologically mediated extraction of copper from ores. Microbes may be able to enhance the physical weathering of magnesium (Mg)- and calcium (Ca)-containing silicate minerals, as well as to enhance the liberation of the metal ions from their mineral form. Strong acids could be used to achieve this same goal, but in this case large amounts of acid would be required to liberate significant quantities of the metal ions, energy would need to be added to recover the acid, and the carbonation reaction would no longer be spontaneous.
Microbiological systems may be able to circumvent these limitations by selectively producing acid in quantities large enough only to break up the minerals while providing an important mechanism to enhance metal extraction. In this context, biological processes would not leach the bulk of the alkaline source rock but would be used to mechanically decompose rock particles, increasing surface area and thereby increasing the rate at which subsequent processing could dissolve rock and make carbonates.
Biological systems can play an important role in significantly enhancing the natural rate of weathering, which occurs on extremely long time scales (approximately 105 to 106 years). They could speed up these processes by breaking up mineral particles and increasing the reactive surface area. This is possible if the microbes or bacteria act very specifically (for example, producing acid) in key locations to help break apart the mineral structure. These bacteria could further speed the process by increasing the liberation of metal ions from the silicate minerals. Producing a carbonate mineral could be achieved by then combining these systems with some form of CO2 (such as aqueous, supercritical, or gaseous).
A key consideration with respect to the use of biological systems to enhance the rate of weathering is the potential leverage available to the microbes. Because of the large quantities of silicate minerals necessary to sequester industrially interesting quantities of CO2, it is crucial that each microbe be able to help liberate several orders of magnitude more metal ions than the amount of acid produced.
The aim of research will be to identify the role that bacteria and microbes can play in enhancing the weathering process of serpentine (or similar) minerals to extract suitable metal ions (Mg2+, Ca2+) to neutralize carbonic acid. It will be necessary to understand the scale, biochemistry, and kinetics of each of these processes and reactions.
Following are some specific questions that need to be addressed:
Can biological systems extract energy from the overall exothermic and spontaneous carbonation reaction? Are other energy sources and nutrients required for the microbes?