Controls on Cyclic Formation of Quaternary Early Diagenetic Dolomite

The origin of sedimentary dolomite and the factors that control its formation within the geological record remain speculative. In most models, dolomite formation is linked to evaporative conditions, high water temperature, increasing Mg/Ca ratio, increasing alkalinity, and high amounts of biomass. Here we challenge these archetypal views, by documenting a case example of Quaternary dolomite which formed in Lake Van at constantly low temperature (<4°C) and without direct control of the latter conditions. Dolomite occurs within highstand sediments related to suborbital climate variability (Dansgaard‐Oeschger cycles). We propose that dolomite precipitation is a product of a microbially influenced process, triggered by ecological stress, resulting from reventilation of the water‐sediment interface. Independently from the validity of this hypothesis, our results call for a reevaluation of the paleoenvironmental conditions often invoked for early diagenetic dolomite‐rich intervals within sedimentary sequences and for caution when interpreting time series of subrecent lacustrine carbonates

Ca-looping for postcombustion CO2 capture: A comparative analysis on the performances of dolomite and limestone

The low cost and wide availability of natural limestone (CaCO3) is at the basis of the industrial competitiveness of the Ca-looping (CaL) technology for postcombustion CO2 capture as already demonstrated by ~1Mwt scale pilot projects. A major focus of studies oriented towards further improving the efficiency of the CaL technology is how to prevent the gradual loss of capture capacity of limestone derived CaO as the number of carbonation/calcination cycles is increased. Natural dolomite (MgCa(CO3)2) has been proposed as an alternative sorbent precursor to limestone. Yet, carbonation of MgO is not thermodynamically favorable at CaL conditions, which may hinder the capture performance of dolomite. In the work described in this paper we carried out a thermogravimetric analysis on the multicyclic capture performance of natural dolomite under realistic regeneration conditions necessarily implying high calcination temperature, high CO2 concentration and fast transitions between the carbonation and calcination stages. Our study demonstrates that the sorbent derived from dolomite has a greater capture capacity as compared to limestone. SEM analysis shows that MgO grains in the decomposed dolomite are resistant to sintering under severe calcination conditions and segregate from CaO acting as a thermally stable support which mitigates the multicyclic loss of CaO conversion. Moreover, full decomposition of dolomite is achieved at significantly lower calcination temperatures as compared to limestone, which would help improving further the industrial competitiveness of the technology.Junta de Andalucía FQM-5735, TEP-7858, TEP-1900Ministerio de Economía y Competitividad FIS2011-25161, CTQ2011- 2762

Discriminating cool-water from warm-water carbonates and their diagenetic environments using element geochemistry: the Oligocene Tikorangi Formation (Taranaki Basin) and the dolomite effect

Fields portrayed within bivariate element plots have been used to distinguish between carbonates formed in warm- (tropical) water and cool- (temperate) water depositional settings. Here, element concentrations (Ca, Mg, Sr, Na, Fe, and Mn) have been determined for the carbonate fraction of bulk samples from the late Oligocene Tikorangi Formation, a subsurface, mixed dolomite-calcite, cool-water limestone sequence in Taranaki Basin, New Zealand. While the occurrence of dolomite is rare in New Zealand Cenozoic carbonates, and in cool-water carbonates more generally, the dolomite in the Tikorangi carbonates is shown to have a dramatic effect on the "traditional" positioning of cool-water limestone fields within bivariate element plots. Rare undolomitised, wholly calcitic carbonate samples in the Tikorangi Formation have the following average composition: Mg 2800 ppm; Ca 319 100 ppm; Na 800 ppm; Fe 6300 ppm; Sr 2400 ppm; and Mn 300 ppm. Tikorangi Formation dolomite-rich samples (>15% dolomite) have average values of: Mg 53 400 ppm; Ca 290 400 ppm; Na 4700 ppm; Fe 28 100 ppm; Sr 5400 ppm; and Mn 500 ppm. Element-element plots for dolomite-bearing samples show elevated Mg, Na, and Sr values compared with most other low-Mg calcite New Zealand Cenozoic limestones. The increased trace element contents are directly attributable to the trace element-enriched nature of the burial-derived dolomites, termed here the "dolomite effect". Fe levels in the Tikorangi Formation carbonates far exceed both modern and ancient cool-water and warm-water analogues, while Sr values are also higher than those in modern Tasmanian cool-water carbonates, and approach modern Bahaman warm-water carbonate values. Trace element data used in conjunction with more traditional petrographic data have aided in the diagenetic interpretation of the carbonate-dominated Tikorangi sequence. The geochemical results have been particularly useful for providing more definitive evidence for deep burial dolomitisation of the deposits under the influence of marine-modified pore fluids

Palaeoproterozoic magnesite: lithological and isotopic evidence for playa/sabkha environments

Magnesite forms a series of 1- to 15-m-thick beds within the approximate to2.0 Ga (Palaeoproterozoic) Tulomozerskaya Formation, NW Fennoscandian Shield, Russia. Drillcore material together with natural exposures reveal that the 680-m-thick formation is composed of a stromatolite-dolomite-'red bed' sequence formed in a complex combination of shallow-marine and non-marine, evaporitic environments. Dolomite-collapse breccia, stromatolitic and micritic dolostones and sparry allochemical dolostones are the principal rocks hosting the magnesite beds. All dolomite lithologies are marked by delta C-13 values from +7.1 parts per thousand to +11.6 parts per thousand (V-PDB) and delta O-18 ranging from 17.4 parts per thousand to 26.3 parts per thousand (V-SMOW). Magnesite occurs in different forms: finely laminated micritic; stromatolitic magnesite; and structureless micritic, crystalline and coarsely crystalline magnesite. All varieties exhibit anomalously high delta C-13 values ranging from +9.0 parts per thousand to +11.6 parts per thousand and delta O-18 values of 20.0-25.7 parts per thousand. Laminated and structureless micritic magnesite forms as a secondary phase replacing dolomite during early diagenesis, and replaced dolomite before the major phase of burial. Crystalline and coarsely crystalline magnesite replacing micritic magnesite formed late in the diagenetic/metamorphic history. Magnesite apparently precipitated from sea water-derived brine, diluted by meteoric fluids. Magnesitization was accomplished under evaporitic conditions (sabkha to playa lake environment) proposed to be similar to the Coorong or Lake Walyungup coastal playa magnesite. Magnesite and host dolostones formed in evaporative and partly restricted environments; consequently, extremely high delta C-13 values reflect a combined contribution from both global and local carbon reservoirs. A C- 13-rich global carbon reservoir (delta C-13 at around +5 parts per thousand) is related to the perturbation of the carbon cycle at 2.0 Ga, whereas the local enhancement in C-13 (up to +12 parts per thousand) is associated with evaporative and restricted environments with high bioproductivity

Carbonates in space - The challenge of low temperature data

Carbonates have repeatedly been discussed as possible carriers of stardust emission bands. However, the band assignments proposed so far were mainly based on room temperature powder transmission spectra of the respective minerals. Since very cold calcite grains have been claimed to be present in protostars and in Planetary Nebulae such as NGC 6302, the changes of their dielectric functions at low temperatures are relevant from an astronomical point of view. We have derived the IR optical constants of calcite and dolomite from reflectance spectra - measured at 300, 200, 100 and 10K - and calculated small particle spectra for different grain shapes, with the following results: i) The absorption efficiency factors both of calcite and dolomite are extremely dependent on the particle shapes. This is due to the high peak values of the optical constants of CaCO3 and CaMg[CO3]2. ii) The far infrared properties of calcite and dolomite depend also very significantly on the temperature. Below 200K, a pronounced sharpening and increase in the band strengths of the FIR resonances occurs. iii) In view of the intrinsic strength and sharpening of the 44 mum band of calcite at 200-100K, the absence of this band -- inferred from Infrared Space Observatory data -- in PNe requires dust temperatures below 45K. iv) Calcite grains at such low temperatures can account for the '92' mum band, while our data rule out dolomite as the carrier of the 60-65 mum band. The optical constants here presented are publicly available in the electronic database http://www.astro.uni-jena.de/Laboratory/OCDBComment: 20 pages, 10 figures, accepted by ApJ, corrected typo

Evidence of microbial activity from a shallow water whale fall (Voghera, northern Italy)

The fossil bones, associated carbonate cements and enclosing concretion of a Miocene mysticete from inner shelf deposits (Monte Vallassa Formation, northern Italy) were analyzed for evidence of microbial activity. Optical and scanning electron microscopy, Raman spectroscopy, and stable C and O isotope geochemistry were used for high spatial resolution microfacies and biosedimentological analyses. Whale cancellous bones were filled by different carbonate cements including microcrystalline dolomite, rhombohedral dolomite and sparry calcite. Biofabric and biominerals such as microbial peloids, clotted textures and pyrite framboids were associated with the dolomite cements. Dolomite inside cancellous bones and in the enclosing concretion showed similar isotopic values (avg δ 13C: -7.12‰; avg δ 18O: +3.81‰), depleted with respect to the (late) sparry calcite cement (avg δ 13C: -0.55‰; avg δ 18O: -0.98‰). Microcrystalline barite (BaSO 4) was observed on the external surface of the bones. In addition, two different types of microborings were recognized, distinguished by their size and morphology and were ascribed respectively to prokaryote and fungal trace makers. Our results testify for the development of a diverse microbial ecosystem during the decay of a shallow water whale carcass, which could be detected in the fossil record. However, none of the observed biosignatures (e.g., microbial peloids, clotted textures) can be used alone as a positive fossil evidence of the general development of a sulfophilic stage of whale fall ecological succession. The occurrence of the hard parts of chemosynthetic invertebrates associated with fossil whale bones is still the more convincing proof of the development of a sulfide-base chemoautotrophic ecosystem. © 2011 Elsevier B.V

Reactivity of dolomitizing fluids and Mg source evaluation of fault-controlled dolomitization at the Benicàssim outcrop analogue (Maestrat Basin, E Spain)

Peer reviewedPostprin

Acton mass flow system applied to PFBC feed

Dense phase pneumatic conveying and the Acton Mass Flow concept are defined with emphasis on the specific advantages to the coal and dolomite feed to the Pressurized Fluidized Bed Combustor. The transport and feed functions are explored with a comparison of designing the process for a combined function or for individual functions. The equipment required to accomplish these functions is described together with a typical example of sizing and air or gas requirements. A general outline of the control system required to obtain a uniform feed rate is provided. The condition of the coal and dolomite and conveying gas as required to obtain reliable transport and feed will be discussed

The role of limestone and dolomite tailings’ particle size in retention of heavy metals from liquid waste

Purpose. The study aims at investigating the role of particle size of mineral tailings derived from limestone, limestone marble, dolomite and dolomitic marble in heavy metal adsorption, in both batch and fixed bed conditions, so as to estimate whether grinding and/or sieving is necessary for their utilization. Methods. Fractions of different particle size have been studied. Adsorption has been examined in batch conditions from solutions of 5 mg/l Cd, 5 mg/l Pb, 100 mg/l Cu, 100 mg/l Zn, and their mixed solution simulating electroplating wastewater, and also in fixed bed conditions. Findings. Total Cd and Cu adsorption is achieved on all the mineral fractions, whereas Pb and Zn show a difference up to 20% depending on particle size. Referring to the mixed solution, Cd and Zn adsorption is lower, whereas no significant differences in Cu and Pb adsorption are observed. Adsorption capacity rises up to 0.03 mg/g Cd, 0.60 mg/g Cu, 0.03 mg/g Pb, 0.60 mg/g Zn. In fixed bed conditions, metal adsorption greater than 93% is achieved. Furthermore, leaching not exceeding 4% indicates a good metal retention. Finally, Taguchi method has proven that the particle size effect is not so strong compared to other parameters, including solution concentration and time. Originality. The particle size of mineral tailings has not yet been investigated as a parameter affecting heavy metal adsorption. Furthermore, heavy metal adsorption has been examined from separate metal solutions and not from a mixed one. The present study aims at contributing to these two research fields. Practical implications. Τhe differences in adsorption between mineral tailings’ fractions with different particle size are not as high as to make grinding of minerals necessary.Мета. Дослідження впливу розмірів частинок у хвостах збагачення вапняку, вапняного мармуру, доломіту та доломітового мармуру на процес адсорбції важких металів у нерухомому шарі для оцінки доцільності технології подрібнення й/або просіювання в подальшому використанні металів. Методика. Для виконання досліджень зразки вапняку та доломіту доставлені компанією, що займається виробництвом і продажем готових бетонів, а також кар’єрами у Греції. Хімічний і мінералогічний склад зразків був визначений рентгенівської флуоресценцією (XRF, ARL ADVANT XP), рентгенівської дифракцією (XRD, Siemens D-500) та атомно-абсорбційною спектрометрією (AAS, VARIAN AA240FS). Для дослідження механізму адсорбції були виміряні наступні параметри: рН відповідно до ISO 6588, пористість і питома площа поверхні за допомогою N2-адсорбції (NOVA-2200, версія 6.11) та катіонообмінна ємність (CEC) відповідно до EPA 9081 на основі змішування зразка з надлишком розчину ацетату натрію, в результаті якого потім визначались додані катіони натрію для матричних катіонів. Для сорбційних експериментів були використані окремі розчини, які містять 5 мг/л Cd, 5 мг/л Pb, 100 мг/л Cu, 100 мг/л Zn, отримані з аналітичних стандартних розчинів Fluka. Після сорбційних досліджень зібрані сорбенти були піддані дослідженням вилуговування. Результати. У процесі досліджень була досягнута повна адсорбція Cd і Cu з усіх мінеральних фракцій, проте до 20% адсорбції Pb і Zn визначалася розмірами частинок. Встановлено, що величина адсорбції Cd і Zn нижче у змішаному розчині, але при цьому даний показник для Cu і Pb залишається без змін. Поглинаюча здатність зростає до 0.03 мг/г Cd, 0.60 мг/г Cu, 0.03 мг/г Pb, 0.60 мг/г Zn. В умовах нерухомого шару досягається до 93% адсорбції металів. Більше того, витік, що не перевищує 4%, свідчить про ефективність вилучення металів. Доведено за методом Тагучі, що вплив розмірів частинок не є настільки значним, щоб не враховувати роль інших параметрів, таких як концентрація розчину і час. Вилуговування іонів металів (Cd, Cu, Pb, Zn), що зберігаються на всіх мінералах після адсорбції в періодичних умовах, не перевищує 4% та вказує на те, що вони досить зберігаються на поверхні мінералів. Це є важливим результатом для подальшого використання мінералів у якості субстратів на полігонах. Наукова новизна. Вперше розміри частинок у хвостах збагачення мінералів розглянуті як параметр, який впливає на процес адсорбції важких металів, при цьому даний процес вивчений також щодо окремих розчинів металів, а не тільки їх суміші. Практична значимість. Виявленні відмінності у показниках адсорбції для фракцій частинок різного розміру не такі значущі, щоб обумовлювати необхідність їх подрібнення в технологічному процесі.Цель. Исследование влияния размеров частиц в хвостах обогащения известняка, известкового мрамора, доломита и доломитового мрамора на процесс адсорбции тяжелых металлов в неподвижном слое для оценки целесообразности технологии измельчения и/или просеивания в дальнейшем использования металлов. Методика. Для выполнения исследований образцы известняка и доломита доставлены компанией, занимающейся производством и продажей готовых бетонов, а также карьерами в Греции. Химический и минералогический состав образцов был определен рентгеновской флуоресценцией (XRF, ARL ADVANT XP), рентгеновской дифракцией (XRD, Siemens D-500) и атомно-абсорбционной спектрометрией (AAS, VARIAN AA240FS). Для исследования механизма адсорбции были измерены следующие параметры: рН в соответствии с ISO 6588, пористость и удельная площадь поверхности с помощью N2-адсорбции (NOVA-2200, версия 6.11) и катионообменная емкость (CEC) в соответствии с EPA 9081 на основе смешивания образца с избытком раствора ацетата натрия, в результате которого затем определялись добавленные катионы натрия для матричных катионов. Для сорбционных экспериментов были использованы отдельные растворы, содержащие 5 мг/л Cd, 5 мг/л Pb, 100 мг/л Cu, 100 мг/л Zn, полученные из аналитических стандартных растворов Fluka. После сорбционных исследований собранные сорбенты были подвергнуты исследованиям выщелачивания. Результаты. В процессе исследований была достигнута полная адсорбция Cd и Cu из всех минеральных фракций, однако до 20% адсорбции Pb и Zn определялась размерами частиц. Установлено, что величина адсорбции Cd и Zn ниже в смешанном растворе, но при этом данный показатель для Cu и Pb остается без изменений. Поглощающая способность возрастает до 0.03 мг/г Cd, 0.60 мг/г Cu, 0.03 мг/г Pb, 0.60 мг/г Zn. В усло-виях неподвижного слоя достигается до 93% адсорбции металлов. Более того, утечка, не превышающая 4%, свидетельствует об эффективности извлечения металлов. Доказано по методу Тагучи, что влияние размеров частиц не является настолько значительным, чтобы не учитывать роль других параметров, таких как концентрация раствора и время. Выщелачивание ионов металлов (Cd, Cu, Pb, Zn), сохраняющихся на всех минералах после адсорбции в периодических условиях, не превышает 4% и указывает на то, что они достаточно сохраняются на поверхности минералов. Это является важным результатом для дальнейшего использования минералов в качестве субстратов на полигонах. Научная новизна. Впервые размеры частиц в хвостах обогащения минералов рассмотрены как параметр, оказывающий влияние на процесс адсорбции тяжелых металлов, при этом данный процесс изучен также в отношении отдельных растворов металлов, а не только их смеси. Практическая значимость. Выявленные различия в показателях адсорбции для фракций частиц различного размера не столь значимы, чтобы обусловливать необходимость их измельчения в технологическом процессе.The present study did not originate under any of project and no funding was raised for research. However, we would like to thank especially Professor Angeliki Moutsatsou and the personal of the Laboratory of Inorganic and Analytical Chemistry of the Chemical Engineering School in the National Technical University of Athens for their various support during the experimental work required for the successful realization of the present study