A continuous process for manufacture of magnesite and silica from olivine, CO2 and H2O (original) (raw)

Carbon Dioxide Sequestration by Aqueous Mineral Carbonation of Magnesium Silicate Minerals

Greenhouse Gas Control Technologies - 6th International Conference, 2003

The dramatic increase in atmospheric carbon dioxide since the Industrial Revolution has caused concerns about global warming. Fossil-fuel-fired power plants contribute approximately one third of the total human-caused emissions of carbon dioxide. Increased efficiency of these power plants will have a large impact on carbon dioxide emissions, but additional measures will be needed to slow or stop the projected increase in the concentration of atmospheric carbon dioxide. By accelerating the naturally occurring carbonation of magnesium silicate minerals it is possible to sequester carbon dioxide in the geologically stable mineral magnesite (MgCO 3). The carbonation of two classes of magnesium silicate minerals, olivine (Mg 2 SiO 4) and serpentine (Mg 3 Si 2 O 5 (OH) 4), was investigated in an aqueous process. The slow natural geologic process that converts both of these minerals to magnesite can be accelerated by increasing the surface area, increasing the activity of carbon dioxide in the solution, introducing imperfections into the crystal lattice by high-energy attrition grinding, and in the case of serpentine, by thermally activating the mineral by removing the chemically bound water. The effect of temperature is complex because it affects both the solubility of carbon dioxide and the rate of mineral dissolution in opposing fashions. Thus an optimum temperature for carbonation of olivine is approximately 185 o C and 155 o C for serpentine. This paper will elucidate the interaction of these variables and use kinetic studies to propose a process for the sequestration of the carbon dioxide.

CO2 sequestration by carbonation of olivine: a new process for optimal separation of the solids produced

Green Processing and Synthesis, 2019

CO 2 sequestration by reaction with abundant, reactive minerals such as olivine has often been considered. The most straightforward, direct process consists in performing the reaction at high temperature and CO 2 pressure, in view to producing silica, magnesium and iron carbonates and recovering the traces of nickel and chromite contained in the feedstock mineral. Most of direct processes were found to have an overall cost far larger than the CO 2 removal tax, because of incomplete carbonation and insufficient properties of the reaction products. Similar conclusions could be drawn in a previous investigation with a tubular autoclave. An indirect process has been designed for high conversion of olivine and the production of separate, profitable products e.g. silica, carbonates, nickel salts, so that the overall process could be economically viable: the various steps of the process are described in the paper. Olivine particles (120 µm) can be converted at 81% with a low excess of acid within 3 h at 95°C. The silica quantitatively recovered exhibits a BET area over 400 m 2 g-1 , allowing valuable applications to be considered. Besides, the low contents of nickel cations could be separated from the magnesium-rich solution by ion exchange with a very high selectivity.

Process optimization for mineral carbonation in aqueous phase

International Journal of Mineral Processing, 2014

Carbon dioxide sequestration by a pH-swing carbonation process was considered in this work. A multi-step aqueous process is described for the fractional precipitation of magnesium carbonate and other minerals in an aqueous system at room temperature and atmospheric pressure. With the aim to achieve higher purity and deliver more valuable mineral products, the process was split into four steps. The first step consists of Mg leaching from the magnesium silicate in a stirred vessel using 1 M HCl at 80 °C, followed by a three step precipitation in reactors in sequence to remove Fe(OH) 3 , then Fe(OH) 2 and other divalent ions, and finally MgCO 3 nucleation and growth. Hydrated magnesium carbonate [MgCO 3 ·3H 2 O, nesquehonite] crystals were confirmed using X-ray diffraction (XRD) as final products. The optimal pH of precipitation reactors based on the maximum solid purity and production were determined by carrying out detailed mass balance. The maximum productivity and highest purity for nesquehonite was found to be dependent on pH values for the two last steps. The results also demonstrated that the process is optimized at pH 9 and 10 for the second and third step of precipitation respectively. The highest carbonation efficiency expressed as the conversion of Mg ions to magnesium carbonate, reached 82.5wt %. The maximum magnesium content in the final product was 99.21 wt % of MgO when the second precipitation reactor pH was equal to 9. This experimental study demonstrates that carbon dioxide sequestration requires at least 3.74 times the weight of ore to provide the Mg for mineral production. This confirms the possibility to use this process route for CO 2 mitigation.

Mineral Carbonation for Carbon Sequestration with Industrial Waste

Energy Procedia, 2013

The increasing factitious carbon dioxide emission, mainly caused by fossil fuel combustion, has led to concerns about global warming. Reduction of carbon dioxide by mineral carbonation has been proposed as one of the most promising options. There are many effective starting materials and reaction routes for mineral carbonation. Recently, many studies have focused on the aqueous reaction of carbon dioxide with the alkaline earth minerals such as serpentine, olivine and wollastonite. However, these minerals need a lot of energy consumption and worry about environmental issues associated with mining operation. Therefore, use of industrial waste instead of natural mineral as starting material has been proposed. The overall goal of this study was to develop a process to use industrial wastes such as waste cement powder and blast furnace slag. It was found that the industrial wastes were more reactive than natural minerals so that they could be reacted under mild conditions. Various experiments were performed to find efficient reactions routes to enhance carbonation process, minimizing energy consumption and costs.

Mechanical activation of ultramafic mine waste materials for enhanced mineral carbonation

2017

The potential success of integrating mineral carbonation, as a pathway to CO2 sequestration, in mining projects, is dependent on the mineralogical composition and characteristics of its waste rock and tailings. Ultramafic rocks have proven the best potential substrate for mineral carbonation and their ability to alter and to convert CO2 into its carbonate mineral form is dependent on the original mineralogy and particle surface area. CO2 conversion kinetics is complex and with the application of appropriate comminution technologies, its efficiency can be enhanced. The objective of this research is to evaluate mechanical activation to enhance the carbonation storage capacity of mine waste material. Three approaches were taken in this research. The first approach was to characterize the microstructure of the mechanically-activated mineral olivine, a predominant mineral constituent of ultramafic rocks, using X-ray diffraction patterns and line profile analysis methods with full pattern fitting method. The second approach was to compare the structural and chemical changes of mine waste with pure olivine, both of which were activated by various mechanical forces under both wet or dry conditions and subsequently carbonated in a direct aqueous carbonation process. Regardless of milling conditions, forsterite (Mg2SiO4), the olivine mineral variety in the mine waste, was found to be the main mineral being mechanically-activated and carbonated. It was determined that lizardite (Mg3(Si2O5)(OH)4), a hydrated magnesium silicate also common in ultramafic hosted mineral deposits, acted as catalyzer assisting forsterite reaching high levels of activation. This condition generated a greater CO2 conversion to carbonate than that of pure olivine with the equal specific milling energy input. The stirred mill proved to be the most efficient form of mechanical activation visa -vis the direct aqueous carbonation process, followed by the planetary mill and the vibratory mill. The third approach analyzes the feasibility of mechanical activation in an integrated mineral carbonation process in a nickel mine considering iii the life cycle of the process. The minimum operating cost for 60% CO2 sequestration efficiency was 105-107 $/t CO2 avoided. At this point, the Turnagain project can potentially sequester 238 Mt/y CO2 using its waste during the 28-year life of mine. iv Preface This thesis is composed of a series of papers that have either been published in peerreviewed scholarly journals or have been submitted for review and subsequent publication. The following is a statement of contributions made to the jointly authored paper contained in this thesis: 1. Li, J and Hitch, M., 2017. A review of mechanical activation of magnesium silicates for mineral carbonation. Submitted to a journal for publication, Li wrote the entire paper. Hitch provided proofreading. This paper forms chapter 2 of this thesis. 2. Li, J and Hitch, M., 2016. Characterization of the microstructure of mechanically-activated olivine using X-ray diffraction pattern analysis. Minerals Engineering. 86: 24-33. Li is responsible conducting all experiments and data analysis, and writing the manuscript. Hitch provided proofreading. This paper forms chapter 3 of this thesis.

Continuing Studies on Direct Aqueous Mineral Carbonation of CO� Sequestration

2002

Direct aqueous mineral carbonation has been investigated as a process to convert gaseous CO 2 into a geologically stable, solid final form. The process utilizes a solution of sodium bicarbonate (NaHCO 3), sodium chloride (NaCl), and water, mixed with a mineral reactant, such as olivine (Mg 2 SiO 4) or serpentine [Mg 3 Si 2 O 5 (OH) 4 ]. Carbon dioxide is dissolved into this slurry, by diffusion through the surface and gas dispersion within the aqueous phase. The process includes dissolution of the mineral and precipitation of the magnesium carbonate mineral magnesite (MgCO 3) in a single unit operation. Activation of the silicate minerals has been achieved by thermal and mechanical means, resulting in up to 80% stoichiometric conversion of the silicate to the carbonate within 30 minutes. Heat treatment of the serpentine, or attrition grinding of the olivine and/or serpentine, appear to activate the minerals by the generation of a non-crystalline phase. Successful conversion to the carbonate has been demonstrated at ambient temperature and relatively low (10 atm) partial pressure of CO 2 (P CO2). However, optimum results have been achieved using the bicarbonate-bearing solution, and high P CO2. Specific conditions include: 185°C; P CO2 =150 atm; 30% solids. Studies suggest that the mineral dissolution rate is not solely surface controlled, while the carbonate precipitation rate is primarily dependent on the bicarbonate concentration of the slurry. Current and future activities include further examination of the reaction pathways and pretreatment options, the development of a continuous flow reactor, and an evaluation of the economic feasibility of the process.

Mg-Silicate Carbonation Based on an HCl- and NH3-Recyclable Process: Effect of Carbonation Temperature

Chemical Engineering & Technology, 2012

A new indirect mineral carbonation process is studied which could mitigate anthropogenic CO 2 emissions. In this process, magnesium silicate is dissolved in HCl and the resulting MgCl 2 solution is subsequently reacted with CO 2 in NH 3 . HCl and NH 3 are recovered from NH 4 Cl in a two-step thermal decomposition. Carbonation is investigated from 30°C to 180°C at 4 MPa CO 2 pressure and Mg-carbonate morphology transformations with increasing temperature are identified. Nesquehonite (MgCO 3 · 3H 2 O) is obtained below 70°C, hydromagnesite (Mg 5 (CO 3 ) 4 (OH) 2 · 4H 2 O) is formed at 100°C, and further temperature increase to 180°C leads to magnesite (MgCO 3 ) precipitation. Nesquehonite and magnesite can fix more CO 2 per mole Mg than hydromagnesite.

Silicate Production and Availability for Mineral Carbonation

Environmental Science & Technology, 2011

Atmospheric carbon dioxide sequestered as carbonates through the accelerated weathering of silicate minerals is proposed as a climate change mitigation technology with the potential to capture billions of tonnes of carbon per year. Although these materials can be mined expressly for carbonation, they are also produced by human activities (cement, iron and steel making, coal combustion etc.). Despite their potential, there is poor global accounting of silicates produced in this way. This paper presents production estimates (by proxy) of various silicate materials including aggregate and mine waste, cement kiln dust, construction and demolition waste, iron and steel slag and fuel ash. Approximately 7-17 billion tonnes are produced globally each year with an approximate annual sequestration potential of 190-332 million tonnes C. These estimates provide justification for additional research to accurately quantify the contemporary production of silicate minerals and to determine the location and carbon capture potential of historic material accumulations.

Mechanism of formation of engineered magnesite: A useful mineral to mitigate CO2 industrial emissions

Journal of CO2 Utilization, 2019

Magnesium carbonate production at the industrial scale is a realistic option to reduce the industrial emissions of CO2. Ultrabasic rocks and/or alkaline mine waste provide magnesium sources and are widely available in the Earth's crust. Here, we investigated the aqueous carbonation of magnesium hydroxide under moderate temperature (25-90°C) and pressure (initial pressure of CO2=50 bar) using NaOH as the CO2 sequestering agent. From time-resolved Raman measurements, we demonstrate that the aqueous carbonation of magnesium hydroxide can be an effective engineered method to trap CO2 into a solid material and produce large amounts of magnesite MgCO3 (6 kg/m 3 h), or hydromagnesite Mg5(CO3)4(OH)2.4H2O (120 kg/m 3 h) at 90°C or nesquehonite MgCO3.3H2O (40 kg/m 3 h) at 25°C. Higher production rates were measured for nesquehonite (at 25°C) and hydromagnesite (at 60 and 90°C). However, only the magnesite produced at 90°C ensures a permanent CO2 storage because this mineral is the most stable Mg carbonate under Earth surface conditions, and it could be co-used as construction material in roadbeds, bricks with fireretarding property and granular fill. The use of specific organic additives can reduce the reaction temperature to precipitate magnesite. For example, ferric EDTA (ethylenediaminetetraacetic acid) reduces the temperature from 90 to 60°C. However, more time is required to complete magnesite precipitation reaction at this lower temperature (15h at 90°C and 7 days at 60°C). These results suggests that functionalized organic groups can reduce the energetic barriers during mineral nucleation.