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Production of magnesium hydroxide from magnesium silicate for the purpose of CO2 mineralisation – Part 1: Application to Finnish serpentinite
Carbonation of abundantly available magnesium silicates such as serpentinites could be an attractive route to capture and store CO2. In this paper we describe a novel route to produce magnesium hydroxide, Mg(OH)2, from Finnish serpentinite. The resulting Mg(OH)2is much more reactive towards CO2than the parent serpentinite. The process route of producing Mg(OH)2as reported here involves a staged process of Mg extraction using a moderately high temperature solid/solid reaction of serpentinite and ammo- nium sulphate (AS) salt followed by precipitation of Mg(OH)2using aqueous ammonia. Tests at 400– 550 ?C showed promising results. An optimum range of reaction conditions for the extraction stage (Mg extraction) and precipitation stages (production of valuable products) of the process was also iden- tified. The valuable solid products refer to Fe-containing compound (dark brown solid, exhibiting the properties of FeOOH) and Mg(OH)2(white precipitate), both precipitated in an aqueous solution with 25% (v/v) ammonia at pH 8–9 and 11–12, respectively. In some cases all Mg extracted from serpentinite was converted to magnesium Mg(OH)2with very small volumes of ammonia solution added. Apart from the relatively cheap AS salt reagent, the prospect of recovery and use of by-products of the process: ammonia gas, FeOOH, and AS salt presents significant benefits.
Production of magnesium hydroxide from magnesium silicate for the purpose of CO2mineralization – Part 2: Mg extraction modeling and application to different Mg silicate rocks
Mineral carbonation of Mg silicates via a gas/solid carbonation of magnesium hydroxide, Mg(OH)2in a fluidized bed (FB) reactor process route is the most actively investigated route of carbon capture and stor- age by CO2mineralization (CCS) research in Finland. This paper reports Mg extraction behavior and pro- duction of magnesium hydroxide, Mg(OH)2from different Mg-silicate rocks from worldwide locations (Finland, Lithuania, Australia and Norway). Magnesium hydroxide, the reactive material for gas/solid mineralization of CO2can be produced from different Mg-silicate minerals via a staged solid/solid reac- tion with ammonium sulfate (AS) salt followed by precipitation in aqueous ammonia solution. A compar- ison is made for five different minerals. The kinetics of Mg extraction from Mg-silicate minerals and the possible effects of iron by-products on reactivity and kinetics were studied and modeled as well.
Dissolution of natural serpentinite in mineral and organic acids
Abundant resources of magnesium silicates make an interesting prospect for long-term storage of CO2by mineral carbonation. Several carbonation processes proposed in literature for CO2storage employ extraction of silicate minerals using a liquid solvent. In this study, the dissolution of natural serpentinite in respective solutions of acids, bases and ammonium salts has been investigated. Experiments performed at room temperature showed that H2SO4was most efficient at extracting magnesium from serpentinite, followed by HCl, HNO3, HCOOH and CH3COOH. Experiments for determining the dissolution kinetics was performed at temperatures of 30, 50 and 70 °C in 2 M solutions of H2SO4, HCl, and HNO3. At 70 °C temperatures all magnesium was extracted from serpentinite in each of the three acid solutions tested during 1–2 h. Also a large part of iron in serpentinite was extracted, while very little silicon dissolved (b4%). The dissolution rate seemed to be limited by product layer diffusion for serpentinite particles with a size distribution of 74–125 μm. The apparent activation energies were 68 kJ mol−1for dissolution in H2SO4, 70 kJ mol−1for dissolution in HCl, and 74 kJ mol−1for dissolution in HNO3.
ВЫСОКОМАГНЕЗИАЛЬНОЕ СЫРЬЕ КАРЕЛИИ И ПЕРСПЕКТИВЫ ЕГО ИСПОЛЬЗОВАНИЯ
В данной работе с учетом требований промыш- ленности к высокомагнезиальному сырью рассмат- риваются химический и минеральный составы высо- комагнезиальных пород различных месторождений и проявлений Карелии с целью выявления областей их практического применения. Используются данные собственных исследований и опубликованных мате- риалов по изучению высокомагнезиальных пород Карелии (Щипцов, 2005).
The mechanism of decomposition of serpentines from peridotites on heating
Serpentines from peridotites of San Jose and New Idria (California, USA) were previously heat treated ranging from 400 to 1,260 ?C, and then leached by using an original approach for acid processing of dehydrated serpentines. This approach is capable of releasing from the dehydrated serpentines ortho-[SiO4]4-, di-[Si2O7]6-, and other silicate anions, and moving them into solution in the form of soluble silicic acids. The discovery of these anions has led to the idea of the existence of differences in electronic configuration of Si–O bonds in siloxane bridges and different amount and allocation of ortho- [SiO4]4-and meta- [(SiO3)2-]nsilicate anions in serpen- tines silicate layers thus providing a new deeper insight into the mechanism of the temperature-induced decom- position of the serpentine silicate structure. It should be emphasized that in spite of a great number of studies devoted to the temperature-induced dehydroxylation and recrystallization processes of serpentine minerals, the mechanism of serpentine decomposition is still poorly understood because no one has studied particularities of the structural organization of silicate layers in serpentines. The effect of thermal treatment at different temperatures ranging from 400 to 1,260 ?C for 2 h on the above mentioned serpentinite samples was characterized by thermal analysis, X-ray diffraction, and chemical analysis. The observed evidence made possible a comprehensive modeling of the relevant dehydroxylation, high-tempera- ture crystallization, and recrystallization reactions. Com- plemented by chemical analysis data, the results obtained allows understanding the basic principles of the serpentine decomposition and crystallization processes, which govern the formation of stable high-temperature products like forsterite, enstatite, and protoenstatite, as well as the formation of different amount of silicic acids in solution via the new approach. These studies are of great interest and value to the pure and applied material sciences con- nected with serpentinites. Keywords Serpentine ? Dehydroxylation ? Decomposition ? Si–O(Si) bonds ? Silicate anions
Microstructure of calcined Mg-rich clay minerals of Egyptian serpentinites
The thermal behaviour of Mg-rich clay minerals in two serpentinites was studied by means of DSC-TG, XRD, IR and SEM. Experiments are carried out heating at temperatures in the 600- 1200 °C range for 2-4 hours. Analyses revealed that antigorite, talc and clinochlor are the main Mg-rich clay minerals. Dolomite and magnesite are accessory minerals. Chromite, magnetite and hematite are in small amounts. DSC-TG results of the antigorite - rich sample reveal that most of the loss of free water and water absorbed at surface (approx. 13%) occurs at approximately 750 °C. The decomposition into the high-temperature products forsterite + enstatite proceeds via an intermediate assemblage of forsterite and a talc-like phase, observed within a temperature interval of 100 ± 20 °C. The breakdown of antigorite and the talc-like phase is kinetically controlled by surface growth processes at the edges of grains. The decomposition of the talc-clinochlore-antigorite assemblage took place at higher temperature and produced enstatite and spinel. It is suggested that their formation dependents on how clinochlore dehydrates and on the talc trioctahedral arrangement, which provides rapid transformation into enstatite. The increase of the reaction rate with temperature is confirmed by XRD and IR data as well as by SEM. Results of this work, indicate that highly crystalline forsterite and enstatite form by dehydroxilation of Mg-rich minerals. riassunto. — Il comportamento termico di minerali argillosi ricchi di Mg presenti in due serpentiniti è stato analizzato tramite l’uso di apparecchiature quali DSC-TG, XRD, IR e SEM. Gli esperimenti sono stati condotti riscaldando il materiale a temperature comprese tra 600 e 1200 °C per intervalli di tempo variabili da 2 a 4 ore. Dalle analisi è emerso che i principali minerali ricchi di Mg sono antigorite, talco e clinocloro. Dolomite e magnesite figurano come accessori mentre cromite, magnetite ed ematite sono presenti in quantità modeste.