What is it about?
Global warming mitigation and energy transition require effective CO2 emission reduction and enhanced supply of critical metals. Carbon mineralization and concurrent critical metal recovery using a metal-complexing ligand offer a significant opportunity to simultaneously achieve both objectives for sustainable development. The utilization of ex-situ direct aqueous mineral carbonation can potentially make the CO2 mineralization process economically feasible owing to the value of nickel and cobalt recovered and comprehensive usage of mineral resources to sequester carbon and realize carbon credits. The success of high carbon mineralization efficiency and highly selective metal extraction in one step makes the accelerated mineral carbonation applicable. Nickel recovery from olivine silicate minerals can increase the global metal production and expand the reserves of explorable nickel resources.
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Why is it important?
This work forms the basis for an innovative and robust process that integrates CO2 mineralization and enhanced metal recovery from olivine. Nearly 90% nickel and cobalt extraction and mineral carbonation efficiency were simultaneously achieved in a highly selective single-step process. In this process, each t olivine can permanently stabilize 0.49 t CO2 gas as mineral carbonates and simultaneously 1.97 kg (4.35 lb) nickel and 0.05 kg (0.11 lb) cobalt were extracted. The extracted aqueous nickel- and cobalt- ligand complex in aqueous solution can be easily separated from the solid carbonates. The selective metal extraction and mineral carbonation can be conducted at various temperatures and kinetic control regimes. This innovation may have implications for the clean energy transition, enhanced CO2 storage and utilization, and enhanced supply of critical metals.
Perspectives
I hope this article can help us and industries gain confidence in achieving global warming mitigation. In the past, we always keep thinking of CO2 gas as waste. In fact, we can consider CO2 as a feed material to enhance the production of critical battery metals for clean energy transition. I strongly believe that CO2 emission reduction is not a burden for our society but actually a significant chance for evolution in technologies and sustainable developments.
Fei Wang
University of British Columbia
Read the Original
This page is a summary of: Carbon mineralization with concurrent critical metal recovery from olivine, Proceedings of the National Academy of Sciences, August 2022, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2203937119.
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Resources
Status of CO2 mineralization and its utilization prospects
Action is currently being taken globally to mitigate global warming. The objective of reducing CO2 emissions is not a burden for society but is a significant opportunity for evolution in various industries for the sustainable production of energy and the essential minerals, metals, and materials required for modern society. CO2 mineralization is one of the most promising methods to effectively reduce CO2 emissions via the formation of stable mineral carbonates. Accelerated mineral carbonation requires high capital costs for implementation. Accordingly, it has thus far not been economically feasible to carry out accelerated CO2 mineralization alone. Accelerated CO2 mineralization must be combined with other associated technologies to produce high-value products. The technical developments in enhanced metal recovery, nanomaterials, enhanced flotation, H2 production and applications in the cement industry may be suitable options. The utilization and generation of valuable byproducts may determine the economic feasibility of CO2 mineralization processes. The need for CO2 reduction and utilization can contribute to driving the development of many innovative and sustainable technologies for the future benefit of society. The implementation of carbon taxation may also significantly motivate the development of these technologies and their potential application
CO2 mineralization and concurrent utilization for nickel conversion from nickel silicates to nickel sulfides
Global warming due to increased greenhouse CO2 gas emissions and increasing nickel demand are two issues that are challenging the sustainable development of the modern world. These challenges can be met in one process whereby CO2 mineralization can be utilized for simultaneous mineral carbonation to stabilize CO2 gas and concurrent nickel sulfidization. The newly formed nickel sulfide may be recovered by conventional means to enhance industrial nickel supply. Mineral carbonation provides the pre-condition for nickel sulfidization to release nickel into aqueous solution from the crystal structure of olivine as a secondary nickel resource. The released nickel ions can be converted to nickel sulfide for further recovery while other bivalent metal ions such as Mg2+ can concurrently react with CO2 to form stable carbonates. The continuous supply of sulfide ions and CO2 is important to achieve selective nickel conversion and mineral carbonation. A mixed gas containing 5% H2S – 95% CO2 can accelerate mineral carbonation and form nickel sulfide.
Kinetics and mechanism of mineral carbonation of olivine for CO2 sequestration
Mineral carbonation (MC) is one of the most important methods to sequester CO2 due to the advantages of permanently storage and abundant mineral resources. This work was designed to investigate the MC chemistry and kinetics in order to further develop carbonation technology. The comprehensive effects of all factors on MC of olivine were investigated. The mechanism of the reaction has been elucidated and can vary under different conditions. With high addition of sodium salts and high CO2 partial pressure (PCO2), the rate of MC was controlled by chemical reaction between H+ and olivine no matter how the other variables were changed. The H+ concentration in the void between the well-crystallized carbonates formed by carbonation and the non-reacted olivine was believed to be the same as that in the aqueous bulk solution. The decrease in particle size, increase in temperature, HCO3− concentration and ionic strength in solution can dramatically enhance the carbonation. With little addition of sodium salts, the MC was controlled by diffusion through the Si-rich layer surrounding the olivine core. In contrast, with high addition of sodium salts but low PCO2, the MC was controlled by diffusion through the dense carbonate layer. The addition of sodium bicarbonate can dramatically increase the ionic strength and aid the dissolution of Si to temporarily aqueous H4SiO4 followed by decomposition to amorphous silica and consequently the removal of Si-rich layer. Under low PCO2, there was a limited supply of CO32− ions, which resulted in the formation of a dense and poorly porous carbonate layer between a layer of well-crystallized carbonates and non-reacted olivine.
Kinetic evaluation of mineral carbonation of natural silicate samples
Carbon sequestration by mineral carbonation of basic silicate minerals is an important technique for climate change mitigation, because of the formation of stable mineral carbonate products and the abundant resources of amenable minerals in nature. In practice, direct aqueous mineral carbonation may need to treat natural multiple-mineral mixtures including partially serpentinized ultramafic silicates, as potentially combined with mineral processing operations and enhanced metal recovery. This work investigated the kinetics of direct mineral carbonation of multiple-minerals natural silicate samples under conditions of 34.5 bar CO2 partial pressure, 175 ℃ and concentration of 1.5 m NaHCO3, with corresponding carbonation efficiency more than 85% in 3 h. It was found that the carbonation of a natural mixture of minerals was kinetically controlled by chemical reaction of the olivine dissolution under moderate CO2 partial pressure and aqueous ionic strength, regardless of olivine content and associated mineral compositions. It was important for kinetics analysis to calculate the effective mineral carbonation capacity based on the magnesium and iron contents in olivine. If the carbonation capacity was calculated based on the total content of magnesium, calcium and iron as is conventional, the mineral carbonation efficiency was proportional to the olivine content in natural silicate samples. The carbonation process of the natural mixtures could be completely attributed to the reaction of olivine while the other silicate minerals including serpentine and diopside, as well as iron sulfides and magnetite, did not significantly participate.
Utilization of Copper Nickel Sulfide Mine Tailings for CO2 Sequestration and Enhanced Nickel Sulfidization
Global warming mitigation strategies include reducing CO2 emissions and encouraging the use of battery-powered electrical vehicles. Nickel in olivine which is an important mineral of many nickel sulfide mines and suitable for permanent CO2 sequestration is regarded as non-recoverable and discarded in mine tailings as wastes. Enhancing nickel sulfide production from hitherto non-recoverable resources could help increase battery supply. This work shows that a copper nickel sulfide flotation mine tailing in Minnesota could be used for directly accelerated mineral carbonation and concurrent nickel sulfidization. In addition to converting magnesium and iron silicates to mineral carbonates for permanent CO2 storage, nickel in olivine is concurrently converted to nickel sulfide for potential recovery. The mineral carbonation of olivine is the dominant chemical reaction process and provides the precondition for nickel sulfidization. A pre-concentration step of olivine from tailings is recommended to enrich olivine and nickel contents for potential application.
Quantifying kinetics of mineralization of carbon dioxide by olivine under moderate conditions
Global warming mitigation is an urgent issue all over the world and the mineralization for CO2 sequestration is one of the best methods to permanently store CO2 gas. The current work has developed a quantified mineralization formula through the systematic investigation of the kinetics of mineralization of a dunite containing high-grade olivine under the chemical reaction control. The effect of the most important CO2 partial pressure, addition of sodium bicarbonate, specific surface area of the olivine, addition of sodium chloride and reaction temperature can be quantified to the 1.6th, 0.8th, 0.7th, 0.34th power and 47.97 kJ/mol activation energy respectively with a relative error less than ±5%. When there was high addition of sodium bicarbonate, the effect of sodium chloride was not significant. Once the addition of sodium bicarbonate and the CO2 partial pressure were high enough, the mineralization was always controlled by dissolution of olivine. The following quantified mineralization formula has been developed. α = (1 − (1 − k0 × [S]0.7 × [PCO2]1.6 × [NaHCO3]0.8 × e(−Ea×1000/RT) × t)3) × 100%, where is the correction factor, related to the mineralization capability of the material and others. The developed formula and the transformations can be applied to predict the mineralization efficiency, the necessary requirements of reaction time, required sodium bicarbonate and the relationship between the required specific surface area and CO2 partial pressure. It can be theoretically suitable for the materials where the majority are olivine and it is necessary to carry out several pre-tests to determine the value of the correction factor (k0).
Application and optimization of a quantified kinetic formula to mineral carbonation of natural silicate samples
Mineral carbonation for global warming mitigation has attracted worldwide attention. The combination of mineral processing for primary metal recovery and mineral carbonation for carbon sequestration is an emerging field of study with the potential to minimize capital costs. A quantified kinetic formula of mineral carbonation was tested for application to various natural silicate samples. Our research confirms the optimized kinetic formula can be successfully applied to predict mineral carbonation of various natural silicate samples within absolute 4% precision. The kinetic factor is exponentially dependent on the activation energy of carbonation of natural silicate samples. The application of the kinetic formula is restricted to a mineral carbonation process under chemical reaction control. The successful application is not affected by mineral compositions, olivine content, mineral carbonation capacity, specific surface area, particle size distribution, temperature, CO2 partial pressure or concentration of sodium bicarbonate in solution. This quantified kinetic formula can predict mineral carbonation efficiency for an integrated process of mineral processing and mineral carbonation.
The technology of CO2 sequestration by mineral carbonation: current status and future prospects
Mineral carbonation (MC) has been extensively researched all over the world since it was found as a naturally exothermic process to permanently sequester CO2. In order to accelerate the natural process, various methods for carbonation of Mg-/Ca-silicate minerals have been studied. It has been found that the MC efficiency will increase with an increase in CO2 pressure, retention time, temperature, mass ratio of Mg/Ca to Si in minerals, specific surface area, and the slurry concentration in a specific range, and with the introduction of NaCl and NaHCO3 or carbonic anhydrase. However, there is still no successful industrial application because of high economic costs and slow reaction rate. It is not economic to exploit Mg-/Ca-silicate minerals deposits or tailings to sequester CO2 by the MC due to the cost of grinding and heat pre-treatment. In some cases, the whole sequestration process may result in more CO2 emissions than the sequestered CO2 due to the requirements of energy inputs. The process, however, may be profitable as a whole (with carbon credits). It is suggested to combine the MC with valuable metals recovery from ore deposits in order to reduce the cost of the MC by cost sharing for mineral recovery.
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