Alkali Loss Research Articles

Ultrasonic-induced crystallization for efficient extraction of hazardous sodium oxalate with ultra-low alkali loss in alumina industry: From laboratory-scale to continuous pilot-scale

Since sodium oxalate (Na2C2O4) in Bayer liquor seriously threatens the sustainable development of the alumina (Al2O3) industry, efficient extraction of Na2C2O4 and reduction of alkali loss have received widespread attention. A new process for extracting Na2C2O4 from mother aluminate liquor by ultrasonic-induced crystallization (UIC) is established at laboratory scale. Due to the controlled sound field and cavitation effect, compared with conventional crystallization (CC) process, the UIC process increases the Na2C2O4 extraction rate from 61 % to 70 %, and reduces the alkali loss rate from 41 % to 19 %. Numerical simulation and sonochemiluminescence confirm that the cavitation effect is mainly concentrated near the axis and at the tip of the titanium alloy horn, and the average life of the cavitation bubble is maintained at 0.9 ms. Density functional theory (DFT) calculations, crystal structure observations and simulations show that the UIC process successfully promotes the development of Na2C2O4 from long strips to lamellar forms, maintaining the safety of Al2O3 production. Additionally, UIC process operates stably on continuous pilot-scale (CPSC) system, with the Na2C2O4 extraction rate and TOC emission rate remaining at around 50 % and 85 % respectively. The UIC method for extracting Na2C2O4 is expected to generate annual profits of $ 267.3 million for China, while also providing support for the innovation and application of ultra-low alkali loss in Al2O3 industry.

Application of ultrasonic-enhanced active seed crystals in the removal of sodium oxalate from alumina refinery waste liquor

When organic matter, especially sodium oxalate (Na2C2O4), accumulates to a certain extent, it will seriously affect the alumina production process in the refinery and therefore urgently needs to be removed. This work attempts to illuminate the benefits of ultrasonic intensification of the crystallization process of Na2C2O4, taking the alumina refinery waste liquor, i.e., flat plate washing liquor, as a case study. The effects of different operating parameters (seed crystal addition amount, caustic soda concentration, reaction time, ultrasonic power) on the crystallization behavior and yield are discussed, and it is found that ultrasonic can increase the Na2C2O4 removal rate to 70.4%. The addition of ultrasonic promotes the morphological evolution of Na2C2O4 and is of great significance to the optimization of the components of the precipitated Na2C2O4. Specifically, the proportion of Na2C2O4 in the crystallized product reaches 64% with conventional conditions, while it reaches 77% with ultrasonic conditions. Therefore, ultrasonic can greatly reduce the alkali loss caused by the crystallization process of Na2C2O4 in flat plate washing liquor, which has great economic benefits.

H2O degassing triggered by alkali depletion in bimodal magma injection processes – a new experimental approach

Abstract. The injection of mafic magma into a hydrous felsic magma chamber is a potential trigger mechanism for bimodal explosive volcanism. As H2O is the most abundant volatile component in magmas, the interaction and the degassing behavior of mildly peralkaline hydrous rhyolitic melt in contact with hydrous basaltic melt were investigated by decompression experiments. Preparatory hydration experiments and bimodal magma decompression experiments, as well as reference experiments, were carried out in an internally heated argon pressure vessel. Pre-hydrated rhyolite and basalt cylinders were perfectly contacted together in a precious-metal capsule, heated to 1348 K at 210 MPa, and thermally equilibrated for 10 min. The initial sample properties were determined by a bimodal reference experiment, quenched immediately after equilibration. To simulate the magma ascent, three bimodal samples and a decompression experiment with two contacted rhyolite cylinders for testing the experimental setup were decompressed with 0.17 or 1.7 MPa s−1 to the final pressure of 100 MPa and then quenched. All decompression experiments resulted in vesiculated samples. The H2O vesicles observed in the decompressed sample of the monomodal rhyolite–rhyolite reference experiment are homogeneously distributed throughout the sample. The former interface between the contacted glass cylinders is invisible after decompression and quench. This reference experiment proves that the two-cylinder design does not influence the degassing behavior of the hydrous melt, e.g., an increased formation of vesicles at possible nucleation sites at the contact plane of the cylinders. The undecompressed bimodal rhyolite–basalt sample shows crystal-free rhyolitic glass, whereas 3 µm sized idiomorphic magnetite crystals coexist with glass in the basaltic part of the sample. Within the 10 min run time, a ∼ 300 µm wide hybrid composition zone developed between the hydrous rhyolitic and basaltic endmembers, caused by diffusion-induced mixing processes. Decompression and quenching of the bimodal melts resulted in vesiculated glass samples. A ∼ 100 µm wide zone of alkali-depleted rhyolitic glass as part of the ∼ 300–560 µm wide hybrid zone is covered with an enhanced number of H2O vesicles compared to the pristine rhyolitic and basaltic glass volumes. We suggest that this enhanced vesiculated zone forms by a rapid diffusional loss of alkalis from the mildly peralkaline rhyolitic melt into the basaltic melt of the sample. The reduced alkali concentration significantly reduces the H2O solubility of the rhyolitic melt. This process enhances the H2O supersaturation necessary for vesicle formation during decompression. In summary, the new findings imply that convective magma ascent driven by the injection of hot basaltic magma into a hydrous peralkaline rhyolitic melt reservoir leads to enhanced H2O vesicle formation near the melt interface and thus to efficient degassing. This in turn can accelerate buoyancy-driven magma ascent and mingling and mixing processes that induce further degassing and potentially trigger explosive volcanic eruptions.

Hydrothermal sulfate surges promote rare earth element transport and mineralization

Abstract The generation of sulfate-rich hydrothermal fluids is of great significance to investigate because it is closely associated with the formation of many important ore deposits, such as hydrothermal rare earth element (REE) deposits. However, the transport of REEs in sulfate-rich hydrothermal fluids is complicated by the retrograde solubility of common sulfate minerals depicted in current thermodynamic models. We present in situ and ex situ hydrothermal experimental evidence suggesting that the solubility of alkali sulfate changes from retrograde at low pressures to prograde at elevated pressures. Accordingly, we propose a sulfate surge temperature and pressure (T-P) window (250 °C, 90 MPa), above which the solubility of alkali sulfate increases significantly with increasing P and T. Although REE sulfates are weakly soluble in water, sulfate-rich hydrothermal fluids can transport high contents of REEs under the T-P conditions above the sulfate-surge window. Our results indicate that depressurization, cooling, and alkali loss are key factors controlling REE mineralization, which agrees well with geological observations.

Carbonation, Neutralization, and Reinforcement Corrosion for Concrete in Long-Term Atmospheric Exposures

This paper presents observations of carbonation and alkali loss for well-compacted reinforced concrete columns from the exterior and interior of a 60-y-old in-land building. Calcium carbonate formation was detected only in the outermost 10 mm to 15 mm. However, alkali loss and concrete pH reduction extended much further inward but reinforcement corrosion was not observed. Theoretical thermodynamic conditions dictate that corrosion initiation of reinforcement can result only from the long-term dissolution and loss by leaching of calcium hydroxide from the concrete matrix. These appear rate-limited by the barrier effect of carbonated concrete. These interpretations provide a new model for “carbonation” initiation of reinforcement corrosion. The results also show the potential for concretes to absorb atmospheric carbon dioxide (greenhouse gases) for an extended time without significant risk of reinforcement corrosion.

Mechanisms in Long-Term Marine Corrosion of Steel Reinforcement in Concretes

This paper is concerned with the mechanisms governing reinforcement corrosion in concretes in marine environments and how they influence the manner of local failure of the concrete. Despite the high pH of the concrete, air voids from inadequate concrete compaction can, under chloride conditions, produce localized pitting corrosion of adjacent steel bars. This may continue, under the hydrogen evolution cathodic reaction with the build-up of rusts causing localized concrete failure, followed by exposure of the steel to the environment, removal of the elevated concrete pH, and a subsequent much higher rate of corrosion. A completely separate deterioration process is the gradual dissolution and loss of concrete alkalis with time. This can lower the concrete pH sufficiently to permit general corrosion of steel to be thermodynamically feasible, it increases concrete permeability and it facilitates access to the environment to permit corrosion by oxygen reduction. The two processes produce different types of concrete failure. Examples drawn from actual reinforced concrete structures are given and the mechanisms explained, including the often-observed build-up of FeOOH-type rusts on the outside of magnetite rust layers well inside concretes. The implications that follow and research needs are discussed.

A Review on the Use of Chemicals as Steam Additives for Thermal Oil Recovery Applications

AbstractWe summarize the major recovery mechanisms of both steam-based recovery process and steam-chemical-based recovery process. Next, we review the previous lab-scale/field-scale studies examining the applications of surfactants, alkali, and novel chemicals in the steam-based oil recovery process. Among the different surfactants studied, alpha-olefin sulfonate (AOS) and linear toluene sulfonate are the recommended chemicals for their foam control/detergency effect. In particular, AOS was observed to perform especially well in residual oil saturation (ROS) reduction and sweep efficiency improvement when being co-injected with alkali. Application of organic alkali (alone or with a co-surfactant) has also drawn wide attention recently, but its efficacy in the field requires further investigation and the consumption of alkali by sands/clay is often an inevitable issue and, therefore, how to control the alkali loss requires further investigation. Novel chemical additives tested in the past five years include fatty acids (such as tail oil acid, TOA-Na+), biodiesel (o/w emulsion), along with other types of chemical additives including switchable hydrophilicity tertiary amines, chelating agents, deep eutectic solvents, graphite and SiO2 particles, ionic liquids, and urea. High thermal stability of some of the novel chemicals and their potential in increasing displacement efficiency and ROS reduction efficiency in the lab studies require further investigation for their optimized application in the field settings to minimize the use of steam while improving the recovery effectively.

Interlayer alkali ion governs robustness, reactivity, and dielectric properties of sintered lepidocrocite titanate

We investigate the structure across different length scales including the dielectric properties of Cs0.7Zn0.35Ti1.65O4, Rb0.75Zn0.375Ti1.625O4, and K0.8Zn0.4Ti1.6O4 sintered at TS ​= ​900–1100 ​°C, where the lepidocrocite-type crystal structure is preserved. The increasing interlayer distance in the Rb-/K-analog is explained by the alkali loss which reduces the electrostatic attraction between the sheets and the interlayer ion. Meanwhile, the interlayer contraction in the Cs-analog is rather unusual. The increasing (decreasing) interlayer distances correlate to upshift (downshift) of the Ti-O vibration in the Raman spectra. The three compositions show varied grain orientation depending on the interlayer ion and TS. The dielectric permittivity differs by one order of magnitude in the order Cs0.7Zn0.35Ti1.65O4 « Rb0.75Zn0.375Ti1.625O4 « K0.8Zn0.4Ti1.6O4, suggesting the interlayer ion as the dominating dipole. The influences of TS, pellet density (i.e., alkali loss), and grain size/morphology/orientation on the dielectric permittivity are discussed. The understanding of the response to a high temperature treatment would be beneficial not only to specimen fabrications for physical properties measurements, but also to applications where the thermal stability is of concern.

Approaches to improve alumina extraction based on the phase transformation mechanism of recovering alkali and extracting alumina by the calcification-carbonization method

Formation of the desilication product (DSP) in the Bayer process causes alkali and alumina loss in the red mud and serious environmental pollution. This paper elucidated the mechanism of the calcification-carbonization method for recovering alkali and extracting alumina in red mud through analyzing phase transformation and particle morphology evolution. Furthermore, approaches to improve alumina extraction throughout the process were proposed. The results showed that more than 93% alkali was recovered and alumina entering the calcified liquor increased as calcification temperature increased. Spherical-like aggregates of dense hydrogarnet were formed in the calcification process. The compact structure of hydrogarnet was destroyed by mechanical activation to enhance the carbonization decomposition ratio. The alumina extraction ratio increased from 32.9% to 43.1%, and fewer carbonization cycles were needed to reach the alumina extraction limit due to the mechanical activation of calcified slag. The increased temperature in the alumina leaching process impeded the alumina extraction and caused alkali loss.

Hybrid Atmosphere Processing of Lead-Free Piezoelectric Sodium Potassium Niobate-Based Ceramics

K0.5Na0.5NbO3-based ceramics, a promising group of lead-free piezoelectrics, are challenging to sinter dense while avoiding alkali evaporation. This work explores hybrid atmosphere processing, a new approach where reducing atmospheres is used during heating to avoid coarsening from alkali carbonates and hydroxides, and oxidizing atmospheres is used during sintering to avoid alkali evaporation. Discs of Li0.06(K0.52Na0.48)0.94Nb0.71Ta0.29O3 with 0.25 mol% Mn (KNNLTM) were sintered in air, N2, 9% H2 in N2, or 9% H2 in N2 during heating and air during sintering (hybrid atmosphere processing). The highest density was obtained by sintering in 9% H2 in N2, but resulted in high alkali loss and decomposition of the surface, followed by low piezoelectric response. However, with the hybrid H2/air processing it was possible to both avoid surface decomposition and leakage currently associated with alkali evaporation during sintering in H2, and to obtain a denser, more phase-pure and small-grained KNNLTM ceramic with a higher piezoelectric response than obtained by sintering in air or N2.

Mineralogical, chemical, and Sr-Nd isotopic effects of hydrothermal alteration of near-surface rhyolite in the Los Azufres geothermal field, Mexico

We present a combined mineralogical, chemical, and Sr-Nd isotopic study of hydrothermal alteration effects in near-surface Pleistocene rhyolite sampled at two distinct localities from the Los Azufres geothermal field (LAGF), Mexico. The alteration mineralogy of the near-surface rocks is dominated by silica polymorph minerals (cristobalite, tridymite, opal, and quartz), and kaolinite, showing an intense silicification in most altered samples. In some samples, alteration minerals berlinite, alunite, opal, and wollastonite, are also present. Sulfur (80–28, 300 μg/g) and LOI (1.36–12.18%) contents were used to indicate the intensity of alteration for the LAGF rock samples. The changes were considered as significant when they exceeded the analytical errors. Two main types of chemical and isotopic effects were documented: (1) small loss of both SiO2 and alkalis represented by one pair of samples, which did not show significant changes in the most major elements, REEs, Nb and Ta negative anomalies, nor in the normalized multiple-element LILE/REE, LILE/HFSE, and REE/HFSE ratio parameters, but indicated significant increase in Al, Fe, Ba, Ga, and Pb; and (2) significant gain of SiO2 accompanied by loss of alkalis for the rest of the rock samples collected from a different site showed significant decrease of most major elements, all REE concentrations and normalized multiple-element ratio parameters as well as changes in numerous trace element concentrations. During this alteration, the size of the Nb and Ta negative anomalies became smaller as a result of the alteration of the second type. Both types of alteration showed significant changes in 87Sr/86Sr, but generally not in 143Nd/144Nd, probably related to the involvement of highly heterogeneous crust in terms of 87Sr/86Sr.

Efflorescence and subflorescence induced microstructural and mechanical evolution in fly ash-based geopolymers

This paper reports the effects of efflorescence on the microstructural and mechanical properties of fly ash-based geopolymers. Geopolymer pastes manufactured by sodium hydroxide and sodium silicate activation of three Class F fly ashes exhibit varying efflorescence behaviour. The geopolymer derived from sodium silicate activation of fine fly ash, which has a compact microstructure, shows a relatively slow efflorescence rate and low efflorescence potential. The efflorescence occurring on the surface of the geopolymer specimens does not change their mineralogical characteristics. However, the compressive strength development and compressive modulus of geopolymers can be affected through processes related to the loss of alkalis, and also to subflorescence. The phenomenon of subflorescence can be regarded as an extended efflorescence taking place under the surface of the material, leading to crystallisation pressure, which may exceed the tensile strength of hardened binders and generate structural damage.

Weathering of the Madeira world-class Sn-Nb-Ta (Cryolite, REE, U, Th) deposit, Pitinga Mine (Amazon, Brazil)

The paper deals on the laterization of the Madeira deposit associated with the albite-enriched granite facies of the A-type Madeira granite (~1.82Ga). The Madeira deposit is located in the Amazon rain forest, where chemical weathering is intensive and lateritization is a major process of ore deposit formation. This deposit represents a particular case, where the parent rock is an ore deposit; thus primary mineralization and lateritic mineralization occur in the same profile. The parent rock has an unusual mineral association, which includes quartz, albite, k-feldspar, zircon, cryolite (Na3AlF6), fluorite, polylithionite, Zn-rich riebeckite, Zn-F-rich annite, thorite, cassiterite, pyrochlore, columbite, xenotime, gagarinite-(Y), fluocerite-(Ce), and genthelvite. An important feature of the rock is the F richness (2 to 6wt%) mainly in the form of cryolite or fluorspar in the matrix. We first investigated the micromorphological changes of these minerals throughout the soil profile and then focused the geochemical studies in selected profiles. The chemical data were converted into volumetric proportions to quantify the variations in element contents in samples with different degrees of lateritization, and we performed mass balance calculations with Al as the reference element. In this way, we obtain many new constraints on the processes that formed the weathering profile from the Madeira deposit. The parental rock was a clearly aluminous system with lower amounts of Fe. The total loss of alkalis and partial loss of SiO2 created kaolinitic clay minerals. The SiO2/Al2O3 molar ratio ≈2 was suitable for generating aluminous clay minerals with 1:1 structures, such as kaolinite. Greater losses of SiO2 occurred and gibbsite formed at the top of the weathering profiles. The leaching of alkaline elements led to relative enrichment in some economically important elements, such as Sn, Nb, and REEs, in the lateritic profiles. However, the distribution of some of the metals, such as Pb, Zn, and REEs, in the weathering profile is very unusual and may be explained by some special characteristics of the paragenesis and the richness of F in the solutions, which greatly influenced the weathering processes in two different ways. The intense corrosion of even very resistant minerals due to the presence of HF in the system and relative enrichment of HREE in the profile due to the formation of complexes with F− and the downward movement of these elements.

There Reduction of alkali loss in an ash leaching system

There are many points in a kraft mill where the alkaline compounds are purged from the process. Several effluents, solid waste, and air emissions contain alkali, which leads to the necessity of chemical makeups to maintain the liquor balance. The main loss of alkali at the Veracel mill is present in the wastewater from the recovery boiler; more precisely, it is from the ash leaching system, which represents 80% of the total losses. To minimize the alkaline losses while keeping the chloride level in the recovery cycle under control, a project was developed at Veracel. Key actions were taken by adjusting the control loops of the ash leaching system, mainly on the slurry density and purge control. These adjustments led to a decrease in alkali losses and to an increase of treated ash, and kept the chloride level of the recovery boiler dust at 2.6%.

Effect of co-precipitation and impregnation on K-decorated Fe2O3/Al2O3 oxygen carrier in Chemical Looping Combustion of bituminous coal

Chemical Looping Combustion (CLC) of coal is an innovative combustion technology for CO2 inherent capture, which uses oxygen carrier (OC) to transfer lattice oxygen to coal. However, coal gasification is the rate-limiting process for CLC of coal. Although carbon conversion and gasification rate are substantially improved with oxygen carriers in the presence of alkali additives, alkali loss in oxygen carrier is still a serious problem in the process of CLC of coal. The present work focuses on the OC–potassium interaction for two preparation methods of K-decorated OC. Different contents of catalyst (K2CO3) were added into the preparation of Fe-based oxygen carrier by both co-precipitation and impregnation. And the effect of K-decorated methods on oxygen carriers was investigated in a fluidized bed reactor. For co-precipitated oxygen carriers, CO2 gas yields (fCO2) were higher and CO gas yields (fCO) were lower than the ones for impregnated oxygen carriers. Total carbon conversions for co-precipitated oxygen carriers were also higher than those for impregnated oxygen carriers, and a shorter time of fast reaction stage always corresponded to co-precipitated oxygen carrier. 9 redox cycles were also conducted to investigate the stability of oxygen carrier reactivity and the potassium loss with cycle number. It was concluded that the reactivity of co-precipitated oxygen carriers was more stable during 9 redox cycles. Especially for K10-cp (oxygen carriers of 10% potassium content by co-precipitation), fCO2 increased slightly and fCO changed very little with cycle number. According to morphological features of oxygen carriers, co-precipitation was superior to impregnation in preventing oxygen carrier particle sintering. On the other hand, although potassium contents of all K-decorated oxygen carriers decreased with cycle number, the potassium loss for co-precipitated oxygen carriers was smaller. K10-cp performed the best characteristic in avoiding potassium loss: the potassium content decreased from 8.47% (fresh oxygen carrier) to 7.79% (after 9 cycles). X-ray diffractometer (XRD) analysis showed that the potassium ferrite, K2Fe22O34, was presented in K-decorated oxygen carriers. Based on the peak intensity ratio of IK2Fe22O34/IFe2O3, the higher the content of K2Fe22O34 in K-decorated Fe2O3/Al2O3 oxygen carrier was, the larger the conversion of CO to CO2 was, and the shorter the time of fast reaction stage was. Therefore, it was inferred that K2Fe22O34 acted as a support with catalytic effect. In addition, the content of K2Fe22O34 was higher in co-precipitated oxygen carriers than that in impregnation oxygen carriers. It can be used to explain that why a better reactivity was always found for co-precipitated oxygen carriers.

Contrasting mafic to felsic HP-HT granulites of the Blanský les Massif (Moldanubian Zone of southern Bohemia): complexity of mineral assemblages and metamorphic reactions

*Corr esponding author A detailed petrological and geochemical study of the Blanský les Granulite Massif (BLGM; Moldanubian Zone of the Bohemian Massif) provides evidence for processes and mineral assemblages previously unrecognized, or not fully appreciated, in the South Bohemian HP–HT Granulite Complex. It also underlines the “patchwork”-like nature of the BLGM, caused by distinct protolith compositions as well as the differences in occurrence, or preservation, of mineral assemblages, reaction textures, and/or variable changes in chemical compositions. Such a complexity reflects super position of several processes operating from the eclogite-facies metamorphic peak to the final emplacement, as well as variable resistance of individual rock types with distinct metamorphic fabrics. Even on a thin section scale, domains preserving evidence for early phases of eclogite-facies metamorphism, including original textural relations and largely intact HP–HT mineral assemblages, occur in close proximity to domains dominated by phases produced during later decompression. Consistent high-pressure estimates, 2.2–2.3 GPa (GASP), are newly obtained for S 1 /S 2 fabrics in the prevailing (type 1) felsic granulites, and correlate well with the recent finds of rare omphacite relics in the mafic granulites. It indicates that much of the HP history of the felsic and mafic rock types was shared and took place under eclogite-facies conditions. Three important metamorphic processes leading to chemical changes in felsic granulites are described. (1) The small bodies of Kfs-dominated hyperpotassic granulites with minor Grt (or, rarely, Di) are fairly common and provide direct evidence for operation of non-eutectic HP melting. These occurrences are accompanied by compositionally complementary residual (type 2) felsic granulites, rich in Qtz and Ky and partly depleted in alkalis with Zr. Owing to their Ca-poor composition, type 2 granulites were not involved in some of the decompression reactions, such as formation of plagioclase rims around kyanite and garnet breakdown, and thus their mineral assemblages remained effectively “frozen” during decompression. They further imply that the partial melting and genesis of the hyperpotassic melts took place under eclogite-facies conditions. (2) Another case of syn-metamorphic modification is represented by a local limited base-cation loss during superimposed amphibolite-facies de-alkalization, accompanying fluid flux along S 3 shear domains (formation of feldspar-free Qtz–Sill bands). (3) On a microscale, the retrogression reactions, often incomplete, were clearly associated with transfer of ions. The felsic Moldanubian HP–HT granulites were assumed by several authors to have undergone only limited modification during peak metamorphism, most notably loss of Cs, Th and U. Clearly, some of them may have suffered more significant changes, such as perceptible loss of alkalis or even relatively immobile elements (e.g., zirconium), compared to the likely primary protolith(s) composition.

Alkali ratio control for lead-free piezoelectric thin films utilizing elemental diffusivities in RF plasma

High performance piezoelectric thin films are generally lead-based, and find applications in sensing, actuation and transduction in the realms of biology, nanometrology, acoustics and energy harvesting. Potassium sodium niobate (KNN) is considered to be the most promising lead-free alternative, but it is hindered by the inability to control and attain perfect stoichiometry materials in the thin film form while using practical large area deposition techniques. In this work, we identify the contribution of the elemental diffusivities in the radio frequency (RF) plasma in determining the alkali loss in the KNN thin films. We have also examined the effect of the substrate temperature during the RF magnetron sputtering deposition on the crystal structure of the substrate and KNN thin films, as well as the effect of the post-annealing treatments. These results indicate the need for well-designed source materials and the potential to use the deposition partial pressure to alter the dopant concentrations.

Study on Alkaline Mass Transfer Regularity with Dissolution in Porous Media

Inducting dissolution speed constant and multistage reaction series to the alkaline solution transmission equation, this article established the alkaline solution transmission equation with multistage reaction dynamics in the porous media of stratum mineral and calculated one-dimensional alkaline solution concentration distribution. Experimental results verified the correctness of transmission equation, moreover, it further analyzed the alkaline solution regularity in the porous media. The model will be used to predict alkali loss, optimize alkaline solution concentration and slug size, thereby alkaline waterflooding or combination drive can obtain better displacement characteristics and improve the oil recovery.

High-Mg carbonatitic melts in diamonds, kimberlites and the sub-continental lithosphere

The trace elements of high-Mg carbonatitic high-density fluids (HDFs) trapped in six fibrous diamonds from Siberia exhibit patterns that are highly similar to those of Group I kimberlites, but are slightly more fractionated. The patterns of both are similar to the average pattern of post-Archaean xenoliths from the sub-continental lithospheric mantle (SCLM). The Siberian high-Mg carbonatitic HDFs are highly enriched in incompatible elements and have compositions comparable to those of high-Mg HDFs from Kankan, Guinea. However, in detail the latter show depletion of K, Rb, Cs, Nb and Ta and enrichment in Ba, Th, U and LREE relative to the Siberian HDFs. These differences correspond closely to those between the patterns of Group II and Group I kimberlites, respectively. Mixing, fractionation and melting were explored as possible scenarios to explain these similarities and to constrain the possible genetic relationships between HDFs, kimberlites and the SCLM. Addition of 2.5% of Group I kimberlitic magma or 0.5% of the Udachnaya high-Mg HDFs to a depleted peridotite closely reproduces the post-Archaean SCLM pattern. The formation of high-Mg HDFs through fractionation of kimberlitic magma calls for 80% crystallization of olivine, clinopyroxene, garnet, carbonate and ilmenite. However, mismatches in K, Rb, Y and Ho abundances, and absence of the postulated fractionating minerals as inclusions suggest other petrogenetic scenarios are more likely. High-Mg HDFs and kimberlites can be produced by melting of a common source. The pattern of the calculated source for Siberian HDF and Group I kimberlites resembles that of average post-Archean, rather than Archean, SCLM. Batch melting of such a source can produce high-Mg HDFs at 0.5% partial melting and Group I kimberlites at ~ 2%. Kankan HDFs and Group II kimberlites can be produced by 0.1 and 0.8% melting of average Archaean SCLM that carries phlogopite ± Fe–Ti oxides. The close correspondence between the trace-element composition of surface kimberlites and HDFs that were trapped at depth indicates that kimberlitic melts do not change their incompatible trace element contents much on their way to the surface (except for a possible loss of alkalis). The new data on the HDFs suggest a close genetic relation between high-Mg carbonatitic HDFs and kimberlites and reveals the similarity of the trace element of both to that of the post-Archaean SCLM. This similarity may reflect the interaction of such melts with the lithospheric keel, its melting to produce HDF and/or kimberlites or melting of deeper sources that led to formation of HDFs and kimberlite and to widespread metasomatism of the SCLM.

FROZEN DISEQUILIBRIUM IN THE FELDSPAR MINERALOGY OF THE KWANDONKAYA ANOROGENIC COMPLEX, NIGERIAN A-TYPE GRANITE PROVINCE

The alkali feldspars in members of the epizonal Kwandonkaya complex, one of the Younger Granite anorogenic plutons in north-central Nigeria, became frozen in a state of arrested reaction as the complex cooled. High sanidine solid-solution, the liquidus phase expected in porphyritic rocks in early ring-dykes and in cone sheets, has given way to exsolution-induced assemblages involving more ordered species, owing to interaction with an aqueous fluid as a necessary catalyst. The rocks now contain grains of orthoclase perthite, possibly zoned structurally, and structurally intermediate microcline; well-ordered microcline is rather sparse. The three intrusive centers, Buri, Jubga–Ziem and Panshanu, show a progression in terms of the time available for equilibration and the activity of H 2 O in the melt. The feldspars of this metaluminous complex define a transition from a hypersolvus to a subsolvus texture. We document clear signs of magma degassing in miarolitic pockets in an apical region at the Jubga–Ziem intrusive center. The peraluminous compositions that result, leading to unusual clay-mineral structures surrounding the insoluble accessory phases, are an expression of loss of alkalis due to degassing, and not an attribute of the felsic magma in this association. The prevalence of orthoclase and intermediate microcline in perthite at Kwandonkaya, either separately or coexisting, is considered representative of other centers of Mesozoic A-type granite and syenite emplacement in Nigeria.