A continuous process for manufacture of magnesite and silica from olivine, CO2 and H2O

Abstract

Abstract Mineral carbonation is based on the reaction of CO2 with metal oxide bearing materials to form solid carbonates. Further technology development and cost reduction are however needed for an industrial realisation of mineral carbonation. Added value products are clearly one factor, which may change the cost estimates. Separation of reaction products and sufficient product quality must be demonstrated. A concept of using CO2 and water for reaction with olivine in a continuous process with separation of reaction products has been investigated. The reaction products, magnesite and silica, are of potential commercial interest. The process consists of three steps: (1) dissolution of olivine; (2) precipitation of magnesite and (3) precipitation of silica. Separation and precipitation of the reaction products do not require chemical additives, such as acids or bases, and there will thus be few requirements of chemical reclamation. A semi-continuous set of laboratory-scale experiments including process steps 1 and 2 have been carried out. Experimental conditions were in the range 100–150 bar and 130–250 ∘C. Process step 3 has been tested separately, using process water from step 2. The results show a congruent dissolution of olivine with reaction rates comparable to known kinetic models in the lower end of the temperature range. Precipitation of magnesite and silica has different dependence on pH and temperature, and detailed reaction mechanisms are addressed through the experiments. Magnesite precipitation takes place at high temperature (180–250 ∘C). A magnesite with very low iron-content can be precipitated as the only product in the second reaction step.