Fayalite Research Articles

Effects of pressure on the chemical looping combustion of coal with CuFe2O4 combined oxygen carrier

Chemical looping combustion (CLC) has fast developed as an attractive technology for clean utilization of coal as well as inherent CO2 separation at the low energy penalty. Increase of the system pressure has been acknowledged as one of the effective measures in CLC for sufficient conversion of coal along with affiliated benefits for CO2 sequestration, but the complex consequences as incurred should be well considered. In this research, reaction of a typical Chinese bituminous coal of high sulfur content (designated as LZ) with CuFe2O4 combined oxygen carrier (OC) within 0.1–3.0 MPa in the CO2 atmosphere was systematically investigated, with focus on the effect of the system pressure to the conversion of LZ coal, transfer of the oxygen involved in CuFe2O4, sulfur evolution and redistribution. Sequential reactions of CuFe2O4 with the volatiles emitted from pyrolysis of LZ coal and further reaction with the released gasification products and residual char were accomplished, which was beneficial to overcome the mass transfer limitation of the reducing gases evolved from LZ coal to OC under the pressurized conditions and alleviate the inhibition effect resulting from accumulation of the transferred reactive gases around the surroundings of OC. And thus, under the pressurized conditions, improved conversion of LZ coal was reached by oxidization of more intractable C-C/C-H groups to oxygen bound carbon groups. Meanwhile, deep reduction of the added CuFe2O4 occurred with deficient Fe3O4 at the lower valence being formed, which would interact with the silicon minerals present in LZ coal to form various iron silicates. Furthermore, sulfur evolution from coal was found to directionally interact with the reduced CuFe2O4 to mainly form solid Cu2S due to their high combination potential. And deeper reduction of Cu2S was instigated especially at 3.0 MPa with Cu1.8S formed, and the total solid sulfur fraction was increased with the elevated system pressure. Overall, comprehensive information on the interaction of coal of high sulfur content with CuFe2O4 under the extended pressurized conditions around 0.1–3.0 MPa was provided, which would be meaningful for the realistic pressurized CLC in the future.

High-pressure crystal structure and equation of state of ferromagnesian jeffbenite: implications for stability in the transition zone and uppermost lower mantle

Jeffbenite, ideally Mg3Al2Si3O12, has been identified as inclusions in super-deep diamonds originating from depths that exceed 300 km. Although Mg-end member jeffbenite has limited stability at upper-mantle conditions, iron-bearing jeffbenite may have broader P–T stability that extends to the transition zone or uppermost lower mantle, incorporating significant amounts of ferric iron. Using synchrotron-based, single-crystal X-ray diffraction (XRD) and synchrotron Mössbauer spectroscopy (SMS) at pressures up to 29 GPa, we report the crystal structure, compressibility, and likely spin transition of iron in ferromagnesian jeffbenite (Mg2.32Al0.03Fe2+1.28Fe3+1.77Si2.85O12). High-pressure structure refinements reveal that Fe3+ substitution for Si in the T2 site, which shares edges with the M2 octahedron, likely stabilizes jeffbenite at high pressure, because it increases the cation-to-cation distance between these sites. Although ferromagnesian jeffbenite does not undergo a structural phase transition below 30 GPa, SMS hyperfine parameters suggest the onset of an electronic spin transition of iron from high-spin (HS) to low-spin (LS) at around 22 GPa, which may increase its stability at high pressures. Pressure–volume data were fit to a third order Birch–Murnaghan equation of state, resulting in V0 = 816.54(9), KT0 = 181.54(1.39), and $${K}_{T0}^{\prime}$$ = 2.76(14). These equation of state parameters are applicable to evaluating the encapsulation pressures of super-deep diamonds. The density and bulk modulus of ferromagnesian jeffbenite are similar to or higher than pyrope–almandine, pyrope–majorite, and skiagite–majorite solid solution garnets, further suggesting that jeffbenite may be an important ferric–iron silicate in the deeper parts of the mantle transition zone and uppermost lower mantle. However, future studies on the influence of temperature and oxidation state on the stability and equations of state of iron-bearing jeffbennite are still needed to determine what role, if any, jeffbenite plays in transition-zone mineralogy.

Determination of phase relations of the olivine\u2013ahrensite transition in the Mg2SiO4\u2013Fe2SiO4 system at 1740\xa0K using modern multi-anvil techniques

The phase relations of iron-rich olivine and its high-pressure polymorphs are important for planetary science and meteoritics because these minerals are the main constituents of terrestrial mantles and meteorites. The olivine–ahrensite binary loop was previously determined by thermochemical calculations in combination with high-pressure experiments; however, the transition pressures contained significant uncertainties. Here we determined the binary loop of the olivine–ahrensite transition in the (Mg,Fe)2SiO4 system at 1740 K in the pressure range of 7.5–11.2 GPa using a multi-anvil apparatus with the pressure determined using in situ X-ray diffraction, compositional analysis of quenched run products, and thermochemical calculation. Based on the determined binary loop, a user-friendly software was developed to calculate pressure from the coexisting olivine and ahrensite compositions. The software is used to estimate the shock conditions of several L6-type chondrites. The obtained olivine–ahrensite phase relations can also be applied for precise in-house multi-anvil pressure calibration at high temperatures.

Handling trace elements in WEEE recycling through copper smelting-an experimental and thermodynamic study

Recycling of waste electrical and electronic equipment (WEEE) is attracting increasing attention, due to the presence of valuable metals and the risk of environmental emissions associated with WEEE disposal. In this study, the distributions of trace elements (Ag, Ni, Co, and Sn) between copper alloy and magnetite/wüstite-saturated iron silicate slags were investigated at 1200–1300 °C and PO2 of 10-10-10-6.5 atm, simulating the conditions of WEEE reprocessing through secondary copper smelting and converting. The high-temperature isothermal equilibration experiments were conducted in synthesized magnetite/wüstite crucibles under controlled CO-CO2 atmospheres followed by quenching in an ice-water mixture. The phase compositions and concentrations of the trace elements in copper alloy, magnetite/wüstite, and slag were determined by Electron Probe X-ray Microanalysis and Laser Ablation-High-Resolution Inductively Coupled Plasma-Mass Spectrometry. The distribution coefficients of all investigated trace elements between copper alloy and slag increased with decreasing oxygen partial pressure and increasing temperature. Ag distributed strongly into the copper alloy at all conditions, whereas Co mainly deported into the slag phase. Ni and Sn were concentrated in the alloy at lower PO2 and in the slag at higher PO2. Varying concentrations of Ni, Co, and Sn were also dissolved into the solid magnetite/wüstite phase.

Synthesis, impedance analysis and Na-ion kinetic studies of combustion derived orthorhombic Nano-Na2FeSiO4 for Na-ion batteries cathode

In this study, we report the synthesis of sodium iron silicate (Na2FeSiO4) as a cathode material for Na-ion batteries for the first time using fast and highly scalable urea combustion technique. In the present work, different combustion reactions using various fuels are carried out. The fuel of urea provides enough energy/flame temperature to the reaction to achieve orthorhombic phase of Na2FeSiO4 (NFS) with C2221 space group. Further, the amounts of sodium precursors and urea are optimized by performing the different combustion reactions at a fixed stoichiometric ratio (Sr) of 0.23. The structure, microstructural and elemental analysis are studied by XRD, FESEM, XPS, FTIR and BET characterizations. The electrochemical performance of NFS is studied in the different voltage windows, where NFS cathode exhibits high irreversible capacity loss during initial cycle in the voltage window of 1.5–4.5 V. Results show that growth of the SEI layer is upper cut-off voltage dependent. For instance, nano-NFS cathode shows almost negligible capacity loss during first cycle as the upper cut-off voltage decreases to 4.3 V. EIS studies show the continuous increase of interfacial resistance during first charge/discharge process probably due to concentration polarisation at solid/liquid interface suggesting the sluggish kinetics of Na+ ions at the electrode/electrolyte interface. Furthermore, ex-situ XRD and FTIR techniques are used to understand the interfacial resistance growth mechanism. The Na-ion diffusion coefficient calculation also compliments the impedance data and indicate the sluggish Na-ion movement in pristine NFS. The results do indicate that pure NFS, due to poor kinetics of Na-ion despite its nanophase and mesoporous nature, is not found suitable as high performing cathode material.

Characterization of Supplementary Cementitious Materials and Fibers to Be Implemented in High Temperature Concretes for Thermal Energy Storage (TES) Application

Six supplementary cementitious materials (SCMs) were identified to be incorporated in concrete exposed to high-temperature cycling conditions within the thermal energy storage literature. The selected SCMs are bauxite, chamotte, ground granulated blast furnace slag, iron silicate, silica fume, and steel slag. A microstructural characterization was carried out through an optical microscope, X-ray diffraction analysis, and FT-IR. Also, a pozzolanic test was performed to study the reaction of SCMs silico-aluminous components. The formation of calcium silica hydrate was observed in all SCMs pozzolanic test. Steel slag, iron silicate, and ground granulated blast furnace slag required further milling to enhance cement reaction. Moreover, the tensile strength of three fibers (polypropylene, steel, and glass fibers) was tested after exposure to an alkalinity environment at ambient temperature during one and three months. Results show an alkaline environment entails a tensile strength decrease in polypropylene and steel fibers, leading to corrosion in the later ones.

A new material for combustion exhaust aftertreatment at low temperature

Materials which catalyse the reduction of gas phase nitrogen oxides (NOx), from combustion devices such as diesel engines, are needed to meet emissions regulations and improve air quality. Here we use flow tube and diesel engine laboratory systems to investigate an iron silicate material (LowCat) which catalyses CO oxidation and NOx reduction simultaneously and is effective at low temperatures. LowCat’s potential for emissions mitigation was assessed by combining quantitative kinetics with an understanding of its mechanism of action. Annealing LowCat transforms a goethite component to hematite, increasing its catalytic activity. A surface bound O intermediate, critical to the binding of NH3 reductant, forms from and facilitates reduction of NO2 at room temperature. This intermediate can also be formed from reduction of O2 by NO above 450 K. This mechanistic understanding allowed a quantitative assessment of LowCat’s performance. The catalyst shows significant activity under conditions relevant to automotive and other diesel combustion systems and has the particular advantage of reducing NO2 to N2 at temperatures below 150 °C. LowCat represents an exciting opportunity to create Selective Catalytic Reduction (SCR) exhaust aftertreatment systems with superior low temperature performance, which is needed for low load operation of diesel-powered vehicles and low temperature combustion devices that are often important contributors to urban air quality.

Rheology of amorphous olivine thin films characterized by nanoindentation

The rheological properties of amorphous olivine thin films deposited by pulsed laser deposition have been studied based on ambient temperature nanoindentation under constant strain-rate as well as relaxation conditions. The amorphous olivine films exhibit a viscoelastic-viscoplastic behavior with a significant rate dependency. The strain-rate sensitivity m is equal to ∼0.05 which is very high for silicates, indicating a complex out-of-equilibrium structure. The minimum apparent activation volume determined from nanoindentation experiments corresponds to Mg and Fe atomic metallic sites in the (Mg,Fe)2SiO4 crystalline lattice. The ambient temperature creep behavior of the amorphous olivine films differs very much from the one of single crystal olivine. This behavior directly connects to the recent demonstration of the activation of grain boundary sliding in polycrystalline olivine following grain boundary amorphization under high-stress.

EFFECT OF Ca2+ AND Mg2+ IONS ON THE REVERSE CATIONIC FLOTATION OF ITABIRITIC IRON ORE

In this work the effect of the Ca 2+ and Mg 2+ ions, added as salts of chlorine, on the reverse cationic flotation at pH 10.5 of an itabiritic iron ore sample was evaluated. In general, it was observed that the total ion concentrations higher than 83 mg/L in aqueous solution increased the Fe recovery and SiO 2 content in obtained concentrates compared in absence of them. The opposite occurred with Fe content. This effect is due to the electrostatic attraction between the positive species from these ions hydrolysis in aqueous solution and the negative surface of quartz, which avoided the adsorption of the ions aminium, whose main adsorption mechanism is by electrostatic attraction of them with the mineral negative surface. However the use of ethylenediaminetetraacetic acid - EDTA after the ore conditioning with Ca 2+ and Mg 2+ ions, into adequate proportions of EDTA to total ions, produced concentrates with similar contents of Fe and SiO 2 with the concentrates of this sample in absence of ions once they were complexed by EDTA and is no longer adsorbed on negative quartz surface.

Influences of thermal treatment temperature on microstructures and properties of glass-ceramics from gold tailings

Use CaO-Al2O3-SiO2 glass-ceramics from gold tailings in Hanyin as main raw materials, which were prepared by a melting method. In this paper, the effects of nucleation temperature and crystallization temperature on microstructures and properties of the glass-ceramic specimens were investigated. The thermal property of the glass-ceramics was discussed by differential scanning calorimetry (DSC), and microstructure was characterized by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Methods of a 4-point bending strength test, DIL-402C dilatometer and Archimedes method were used to determine the bending strength, thermal expanding coefficient and density of glass-ceramics. The experiment results indicated that the optimal properties of glass-ceramics were obtained by nucleation at 800 °C for 2 h, and then crystalling at 950 °C for 3 h. XRD analyses demonstrated that the main phase of gold tailings glass-ceramics was augite and diopside (CaMgSi2O6), and the minor phase was potassium iron silicate (KFeSi2O6). The bending strength, density and thermal expanding coefficient of the glass-ceramics were 128 MPa, 2.840 g/cm3 and 7.85 × 10−6/°C, respectively.

Effect of basicity on the reduction swelling behavior and mechanism of limestone fluxed iron ore pellets

Limestone fluxed iron ore pellets are reduced in CO-rich atmosphere generally accompanied by swelling behavior. If the reduction swelling index (RSI) exceeds the normal range (≥20%), it will seriously hinder the stable and anterograde production of iron making. To better guide the industrial production, the effect of binary basicity (CaO/SiO2) on the reduction swelling behavior and mechanism of limestone fluxed iron ore pellets was investigated. Meanwhile, X-ray diffraction technique was used to analyze the phase transformation in pellets with different basicity during the reduction process, and the microstructures of different substances were examined by SEM-EDS. The above researches confirmed that the crystal volume expansion caused by crystal structure transformation during hematite (α-Fe2O3) reduced to maghemite (γ-Fe2O3) was the fundamental reason for the swelling of limestone fluxed pellets. Low basicity (0.4–0.8) amplified the volume expansion produced in this process, while high basicity (1.0–1.2) reversed it. This inconsistency stemmed from the difference in the composition of binding phase. Compared with calcium iron silicate in low basicity pellets, complex calcium ferrite (SFCA) as the binding phase of high basicity pellets had excellent reducibility, which promoted uniform reduction rate of high basicity pellets. The increased of SFCA content i reduced the quantities of hematite and effectively inhibited swelling of pellets. From this investigation, increasing the basicity above 1.0 to promote the formation of SFCA was an effective way for decreasing the reduction swelling index of limestone fluxed pellets.

Triple-layer ITO/BiVO4/Fe2TiO5 heterojunction photoanode coated with iron silicate for highly efficient solar water splitting

Solar water splitting as a promising way to convert solar energy into hydrogen energy has been largely limited by the low efficiency of photoanodes in photoelectrochemical water oxidation. In this work, through deliberately employing a indium tin oxide (ITO) underlayer as an electron transport layer (ETL) and a Fe2TiO5 overlayer as a hole transport layer (HTL), a novel triple-layer ITO/BiVO4/Fe2TiO5 heterojunction photoanode was prepared by solution-processed sequential deposition. Owing to the unique ETL/BiVO4/HTL heterojunction structure, the photocurrent density at 1.23 VRHE was significantly increased from 1.70 mA/cm2 for the pristine BiVO4 photoanode to 4.60 mA/cm2 for the ITO/BiVO4/Fe2TiO5 photoanode. After iron silicate (Fe-Sil) was deposited as a new and efficient cocatalyst, the resultant quaternary ITO/BiVO4/Fe2TiO5/Fe-Sil photoanode achieved an extremely high photocurrent density of 6.19 mA/cm2 and an ABPE value as high as 2.55%, indicating an outstanding performance toward solar water oxidation. The high performance of the quaternary ITO/BiVO4/Fe2TiO5/Fe-Sil photoanode may be attributed to the desired ETL/BiVO4/HTL heterojunction structure in combination with the utilization of the Fe-Sil as an efficient oxygen evolution cocatalyst.

Settling of Copper Phases in Lime Modified Iron Silicate Slag

Copper in discarded slag decreases the profits and copper recovery during the pyrometallurgical extraction processes. The copper losses to slag can be reduced by using a settling furnace, in which mechanically entrained copper droplets separate from the slag under the action of gravity. The settling rate of entrained droplets can be increased by modifying the slag composition and, thus, the slag properties, which are known to influence the settling rate. The knowledge of industrial CaO slag modification in a reduced iron silicate slag with a Fe/SiO2 ratio close to unity is limited. An industrial trial was thus conducted in an electric settling furnace, where the slag had been pretreated in a fuming furnace, to investigate the effect of CaO slag modification on the final slag copper content. Slag samples were collected from the ingoing and outgoing slag and from within the furnace of batches modified with CaO up to about 16 wt %. The trial was evaluated by comparing the final slag copper content and the copper recovery in the settling furnace. The results indicate that the settling becomes more efficient with the CaO modification as the final slag copper content decreased with increasing CaO content.

Behavior of light elements in iron-silicate-water-sulfur system during early Earth\u2019s evolution

Hydrogen (H) is considered to be one of the candidates for light elements in the Earth’s core, but the amount and timing of delivery have been unknown. We investigated the effects of sulfur (S), another candidate element in the core, on deuteration of iron (Fe) in iron–silicate–water system up to 6–12 GPa, ~ 1200 K using in situ neutron diffraction measurements. The sample initially contained saturated water (D2O) as Mg(OD)2 in the ideal composition (Fe–MgSiO3–D2O) of the primitive Earth. In the existence of water and sulfur, phase transitions of Fe, dehydration of Mg(OD)2, and formation of iron sulfide (FeS) and silicates occurred with increasing temperature. The deuterium (D) solubility (x) in iron deuterides (FeDx) increased with temperature and pressure, resulting in a maximum of x = 0.33(4) for the hydrous sample without S at 11.2 GPa and 1067 K. FeS was hardly deuterated until Fe deuteration had completed. The lower D concentrations in the S-containing system do not exceed the miscibility gap (x < ~ 0.4). Both H and S can be incorporated into solid Fe and other light elements could have dissolved into molten iron hydride and/or FeS during the later process of Earth’s evolution.

Influence of Process Parameters on Copper Content in Reduced Iron Silicate Slag in a Settling Furnace

During the pyrometallurgical extraction of copper, a significant fraction of this metal is lost with discard slag, which decreases profits and overall copper recovery. These copper losses can be reduced by using a settling furnace, in which suspended droplets containing copper separate from slag under the influence of gravity. An industrial trial was conducted in a settling furnace to increase the knowledge of the effect of temperature and settling time on the copper content of slag, and thus enhance the settling process to increase copper recovery. Slag samples were collected from four sample points: the ingoing and outgoing slag stream, within the furnace during settling, and the granulated slag. The chemical composition of the slag samples was analyzed and compared between batches with different temperatures and settling times. The appearance of copper and its associated phases were analyzed using a scanning electron microscope with an energy-dispersive X-ray spectroscopy detector (SEM-EDS). The results indicated that the outgoing slag copper content increased with an increase in temperature, and it was also concluded to be influenced by the attachment of copper to spinels and gas bubbles. The results indicate that regulating the settling furnace temperature to a lower interval could increase copper recovery.

Separation and stabilization of arsenic in copper smelting wastewater by zinc slag

Copper smelting wastewater shows strong acidity, has a high arsenic concentration and has many types of heavy metals, which not only restricts the sustainable development of copper smelting enterprises but also poses a danger to the ecological environment. Here, we propose a new process for treating copper smelting wastewater with zinc slag. We studied both the solid-liquid chemical reaction process as well as the mechanism by which zinc slag removes arsenic in copper smelting wastewater in a water bath at 85 °C under atmospheric pressure. Specifically, 5 g of zinc slag reacted with copper smelting wastewater with an initial arsenic concentration of 6000 mg/L for 4 h resulted in an arsenic removal rate of 99.65%, and the leaching concentration of arsenic in the toxicity characteristic leaching procedure experiment was only 0.52 mg/L. Zinc slag is dissolved in Copper smelting wastewater to release iron ions and silicate. The solid-liquid reaction of the two is accompanied by coprecipitation of iron arsenate and the in-situ covering of silica gel, resulting in a core-shell precipitate with iron arsenate as the core and silica gel as the shell. The colloidal chemistry of silica gel and cations and its chemical stability can effectively prevent the dissolution of arsenic ions and significantly improve the stability of iron arsenate. Zinc slag, a dual functional material for removing arsenic and fixing arsenic, shows extraordinary potential for the removal and fixation of arsenic in copper smelting wastewater. This approach could further improve wastewater treatment in the non-ferrous smelting industry.

COMBINED EFFECT OF PYROMETALLURGICAL AND HYDROMETALLURGICAL PROCESSES ON QUARTZ ORE PURIFICATION

Recent advances in high-tech applications have highlighted the growing demand on highly pure silicates like quartz. Therefore, purification of quartz ore was determined as the subject of this study performed by pyrometallurgical followed by hydrometallurgical processes. In this research, the effect of thermal treatment (TT) followed by oxalic acid (OA) bleaching of quartz was examined to have a better understanding on the relationship between Fe remaining in concentrate and colour response. The level of TT temperature was found to have a significant effect on the purification of quartz by OA. The maximum Fe rejection rate was observed to occur both for non-treated and TT quartz up to 250°C. TT between 400°C and 900°C showed poor purification performance: decreasing L* value, and increasing a* and b* values. It is important to note that further increase in TT temperature to 1100°C resulted in the poorest bleaching: Fe rejection rate decreased, but colour response improved providing the highest L* value and the lowest a* and b* values. This finding was explained by the formation of dissolution resistant iron silicates. Moreover, the rate of Fe removal from quartz ore and differences observed in its colour response by OA bleaching were explained by changes in crystalline structure and formation of microcracks.

Аеродинамічне розділення залізорудних окатишів по крупності

The studies on reheating of fired pellets of a suitable fraction used in the bottom and side beds have been analyzed. It has been shown that due to the loss of the crystallization of the glass iron silicate bond, the strength of the pellets decreases at their reduction and their destruction in the metallurgical unit increases, thus leading to a deterioration in its performance. It has been concluded that for the bed, it is necessary to purposefully separate the fraction of the pellets of the required size that does not fall into the finished product. The ways of organizing air classification of fired pellets in open warehouses of finished products have been studied and the possibility of its organization has been considered. The particle trajectories and the factors influencing this process have been analyzed. It has been shown that an important characteristic of the particles dispersion is the influence of the ratio of the coefficient of viscous resistance to the flight of a particle in the air to the mass of a particle, as a result of which an initially flat flow for the particles of different sizes will disintegrate into a fan. This fan of the particles scattering at a certain height can be used to sort them by size class. The conditions have been determined under which the dispersion of the fan of the particles in the horizontal plane will be maximum. Equations have been proposed to describe the law of motion of particles before hitting the jet and after having been blown off by the jet. Mechanisms have been developed for selecting design conditions under which the horizontal distances between the particles of different sizes (the difference of the corresponding coordinates) at the set horizon will be maximum and sufficient for sorting the particles by their size. The visualization of the process of the particle scattering in the MathCAD software environment has been performed, which makes it possible for the technologist to set the initial conditions he needs and to obtain clearly presented final results of the motion of a fan of the particles of different sizes that are clear to him

Direct measurement of fungal contribution to silicate weathering rates in soil

AbstractChemical weathering produces solutes that control groundwater chemistry and supply ecosystems with essential nutrients. Although microbial activity influences silicate weathering rates and associated nutrient fluxes, its relative contribution to silicate weathering in natural settings remains largely unknown. We provide the first quantitative estimates of in situ silicate weathering rates that account for microbially induced dissolution and identify microbial actors associated with weathering. Nanoscale topography measurements showed that fungi colonizing olivine [(Mg,Fe)2SiO4] samples in a Mg-deficient forest soil accounted for up to 16% of the weathering flux after 9 mo of incubation. A local increase in olivine weathering rate was measured and attributed to fungal hyphae of Verticillium sp. Altogether, this approach provides quantitative parameters of bioweathering (i.e., rates and actors) and opens new avenues to improve elemental budgets in natural settings.

Atomic-scale mixing between MgO and H2O in the deep interiors of water-rich planets

Water-rich planets exist in our Solar System (Uranus and Neptune) and are found to be common in the extrasolar systems (some of the sub-Neptunes). In conventional models of these planets a thick water-rich layer is underlain by a separate rocky interior. Here we report experimental results on two rock-forming minerals, olivine ((Mg,Fe)2SiO4) and ferropericlase ((Mg,Fe)O), in water at the pressure and temperature conditions expected for the water-rich planets. Our data indicate a selective leaching of MgO, which peaks between 20 and 40 GPa and above 1,500 K. For water-rich planets with 1–6 Earth masses (>50 wt% H2O), the chemical reaction at the deep water–rock interface would lead to high concentrations of MgO in the H2O layer. For Uranus and Neptune, the top ~3% of the H2O layer would have a large storage capacity for MgO. If an early dynamic process enables the rock–H2O reaction, the topmost H2O layer may be rich in MgO, possibly affecting the thermal history of the planet.