Temperature, pressure, and duration impacts on the optimal stiffening of carbonates aged in diammonium phosphate solution

Diammonium phosphate (DAP) has been proven effective in improving the stiffness of weak or acid-damaged carbonates, thereby preserving hydraulic fracture conductivity. The reaction between DAP and calcite in chalk formations primarily produces hydroxyapatite (HAP), which is stiffer than calcite. However, the optimal reaction outcomes vary greatly with factors such as DAP concentration and reaction conditions. This study investigated the DAP-calcite reaction duration, pressure, and temperature effects on the stiffness magnitude of soft Austin chalk. Also, the catalyst effect and depth of HAP formation were examined. The study involved the assessment of stiffness non-destructively (impulse hammering), mineralogy (XRD, SEM), and elemental composition (XRF). The study tested 15 different DAP-chalk reaction variations, where the pressure, temperature, aging time and catalyst addition were modified in each case. The samples' elastic stiffness distributions were then collected and compared to the pre-reaction ones. The results showed that the elastic stiffness increased in all treated samples, with an 181% maximum increase achieved after 72 h at 6.9 MPa and 75 °C. However, the pressure effect was minor compared to the temperature. The SEM images revealed different HAP morphology corresponding to different treatment conditions. Although the treated samples showed an increased intensity of phosphorus throughout the entire sample, the near-surface zone (4-6 mm) was the most affected, as inferred from the XRF elemental analysis. The study's findings can help optimize hydraulic fracturing operations in weak carbonate reservoirs, improving production rates and overall well performance.

A Preliminary Step Towards a Physical Surrogate of the Human Calvarium to Model Fracture

A surrogate model of the human calvarium can be used to assess skull-fracture-related head injuries without continuously requiring post-mortem human skulls. Skull simulants developed in the literature often require sophisticated manufacturing procedures and/or materials not always practical when factoring in time or expense considerations. This study's objective was to fabricate three exploratory surrogate models (1. pure epoxy prototype, 2. epoxy-chalk mix prototype, and 3. epoxy-chalk three-layered prototype) of the calvarium to mimic the calvarium's mechanical response at fracture using readily available and cost-effective materials, specifically epoxy and chalk. The surrogates and calvaria were subject to quasi-static and dynamic impact 4-point bending and their mechanical responses were compared statistically. Under quasi-static loading, all three surrogates showed a considerable number of differences in mechanical response variables to calvaria that was deemed significant (p < 0.05). Under dynamic impact loading, there was no sufficient evidence to reject that the average mechanical response variables were equal between the epoxy-chalk three-layered prototype and calvaria (p > 0.05). This included force and bending moment at fracture, tensile strain at fracture, tensile and compressive stress at fracture, tensile modulus, and tensile strain rate. Overall, our study illustrates two main remarks: (1) the three exploratory surrogate models are potential candidates for mimicking the mechanical response of the calvarium at fracture during impact loading and (2) employing epoxy and chalk, which are readily available and cost-effective has the potential to mimic the mechanical response of calvaria in impact loading.

Electrokinetic behavior of artificial and natural calcites: A review of experimental measurements and surface complexation models

The surface charge of calcite in aqueous environments is essential to many industrial and environmental applications. Electrokinetic measurements are usually used to assess the calcite charging behavior and characterize its electrical double layer (EDL). Numerous surface complexation models (SCMs) have been proposed to interpret the effect of different surface interactions on the zeta potential. Because of their versatility, SCMs have also become important tools in reactive transport modeling. The research on enhanced oil recovery within the last decade has led to an increased number of publications reporting both zeta potential measurements and SCMs for calcite. Nonetheless, the measurements are often inconsistent and the reasons for choosing one model over another are unclear. In this work, we review the models proposed for calcite and address their main differences. We first collect a large number of published zeta potential measurements and then we fit a Diffuse Layer, Basic Stern, and Charge-Distribution Multi-Site Complexation models to a selected reliable dataset. For each model, we maintain a similar number of adjustable parameters. After optimizing the parameters of the models, we systematically compare their prediction capabilities against data obtained in monovalent and divalent electrolyte systems containing calcium, magnesium, sulfate, or carbonate. We show that, often, the discrepancies between the models and the experimental data can be explained by different levels of disequilibrium. Nonetheless, assumptions used in the development of the models may significantly reduce their extrapolability to variable chemical conditions. The poor agreement between the models tuned to electrokinetic data with surface charge measurements and dynamic retention from single-phase flowthrough tests show that zeta potential may not be the best type of data to characterize ion binding at the calcite surface. Including the effect of mineral impurities and temperature on the calcite surface speciation and electrokinetic behavior prevail as main challenges for reactive transport modeling.

Barite precipitation in porous media: Impact of pore structure and surface charge on ionic diffusion

Several scientific fields such as global carbon sequestration, deep geological radioactive waste disposal, and oil recovery/fracking encounter safety assessment issues originating from pore-scale processes such as mineral precipitation and dissolution. These processes occur in situations where the pore solution contains chemical complexity (such as pH, ionic strength, redox chemistry, etc.…) and the porous matrix contains physical complexity (such as pore size distribution, surface charge, surface roughness, etc.…). Thus, to comprehend the participation of each physicochemical phenomenon on governing mineral precipitation, it is essential to investigate the precipitation behavior of a given mineral in different confined volumes. In this study, a counter-diffusion approach was used to investigate barite precipitation in two porous materials: micritic chalk and compacted kaolinite. The two materials present similar water and anionic tracer diffusivities and total accessible porosities but distinct pore size distributions with pore throats of c.a. 660 nm in chalk versus c.a. 35 nm in kaolinite. X-ray tomography results obtained on the two materials showed a distinct distribution of barite precipitates: a 500 μm-thick homogeneous layer in chalk versus spherical clusters spread in a thickness of 2 mm in kaolinite. Mass balance calculations showed that barite precipitation led to a porosity decrease in the chalk reacted zone from 45% to 12% and in the kaolinite reacted zone from 36% to 34.5%. In contrast, water tracer diffusion experiments showed that diffusivity decreased by a factor of 28 in chalk and by a factor of 1000 in kaolinite. Such a discrepancy was attributed to the difference in the pore size distribution that would lead to the distinct barite precipitation patterns, capable of altering in a very different manner the connectivity within the reacted zone of the two selected porous media. Such local alterations in connectivity linked to pore volume reduction would also magnify surface charge effects on ionic transport, as indicated by chloride diffusion experiments and electrophoric tests using zeta potential measurements. Indeed, ³⁶Cl^- was strongly more hindered than water, when diffused in reacted materials, with a diffusivity decrease by a factor of 450 in chalk and a total restriction of ³⁶Cl^- in kaolinite. These experiments clearly provide an insight of how local pore structure properties combined with mineral reactivity could help in predicting the evolution of pore scale clogging and its impact on water and ionic diffusive transport.

Improving Head Rice Yield and Milling Quality: State-of-the-Art and Future Prospects

Increasing paddy yield in rice does not directly translate to enhancing food security because significant decrease in grain yield can happen during postharvest processing of the rice paddy. In parallel with enhancing paddy yield, improving the milling quality of rice is essential in ensuring food security by mitigating the impact of significant losses during the postharvest processing of rice grains. From an industrial standpoint, maximizing the milling recovery of whole grain polished rice is crucial in fetching higher revenues to rice farmers. Significant advances in rice postharvest processing technology have been achieved which are geared toward reducing the incidence of fissures and chalkiness to increase head rice yield (HRY) in rice. The genetic bases of kernel development and grain dimension are also characterized. In addition to these advancements, an integrated phenotyping suite to simultaneously characterize phenotypes related to milling quality will help in screening for breeding lines with high HRY. Toward this goal, modern imaging tools and computer algorithms are currently being developed for high-throughput characterization of rice milling quality. With the availability of more sophisticated, affordable, automated, and nondestructive phenotyping methods of milling quality, it is envisioned that significant improvement in HRY will be made possible to ensure rice food security in the future.

Quantitative non-destructive analysis of paper fillers using ATR-FT-IR spectroscopy with PLS method

A quantitative non-destructive express method of determining fillers -kaolin and chalk- in paper was created using attenuated total reflectance Fourier transform infrared (ATR-FT-IR) spectroscopy in the mid-IR and far-IR region (3800-245 cm^-1) combined with partial least squares (PLS) data analysis. Altogether, 30 two-component (cellulose pulp + kaolin and cellulose pulp + chalk) reference paper samples with known different filler concentrations and one reference paper sample without any fillers were prepared for calibration and validation. The reference values of filler concentrations in the prepared papers were determined by gravimetric analysis via dry ashing (for establishing accurate concentrations of fillers in paper) and ATR-FT-IR microspectroscopy (for evaluating homogeneity of the papers). Two-component (cellulose pulp + kaolin or cellulose pulp + chalk) PLS models were created with papers of different cellulose types and containing different amounts of fillers. The best model had root mean square errors of prediction (RMSEP) for determining the kaolin or chalk content in the two-component papers of 2.0 and 2.1 g/100 g, respectively. The performance indices were 90.4% and 92.9%, respectively. As a demonstration of practical applicability of the method, different papers from books, journals, etc. were analysed. It was concluded that the developed quantitative method is suitable for non-destructive express analysis of kaolin or chalk in paper. Graphical abstract.

Temporal variability of micro-organic contaminants in lowland chalk catchments: New insights into contaminant sources and hydrological processes

This paper explores the temporal variation of a broad suite of micro organic (MO) compounds within hydrologically linked compartments of a lowland Chalk catchment, the most important drinking water aquifer in the UK. It presents an assessment of results from relatively high frequency monitoring at a well-characterised site, including the type and concentrations of compounds detected and how they change under different hydrological conditions including exceptionally high groundwater levels and river flow conditions during 2014 and subsequent recovery. This study shows for the first time that within the Chalk groundwater there can be a greater diversity of the MOs compared to surface waters. Within the Chalk 26 different compounds were detected over the duration of the study compared to 17 in the surface water. Plasticisers (0.06-39μg/L) were found to dominate in the Chalk groundwater on 5 visits (38.4%) accounting for 14.5% of detections but contributing highest concentrations whilst other compounds dominated in the surface water. Trichloroethene and atrazine were among the most frequently detected compounds. The limit for the total pesticide concentration detected did not exceed EU/UK prescribed concentration values for drinking water. Emerging organic compounds such as caffeine, which currently do not have water quality limits, were also detected. The low numbers of compounds found within the hyporheic zone highlight the role of this transient interface in the attenuation and breakdown of the MOs, and provision of an important ecosystem service.

Sherborn's foraminiferal studies and their influence on the collections at the Natural History Museum, London

Sherborn's work on the Foraminifera clearly provided the initial spark to compile the major indexes for which he is famous. Contact and help from famous early micropalaeontologists such as T. Rupert Jones and Fortescue William Millett led Sherborn to produce his Bibliography of Foraminifera and subsequently a two-part Index of Foraminiferal Genera and Species. Edward Heron-Allen, whose mentor was Millett, was subsequently inspired by the bibliography to attempt to acquire every publication listed. This remarkable collection of literature was donated to the British Museum (Natural History) in 1926 along with the foraminiferal collections Heron-Allen had mainly purchased from early micropalaeontologists. This donation forms the backbone of the current NHM micropalaeontological collections. The NHM collections contain a relatively small amount of foraminiferal material published by Sherborn from the London Clay, Kimmeridge Clay and Speeton Clay. Another smaller collection reflects his longer-term interest in the British Chalk following regular fieldwork with A. W. Rowe. Other collections relating to Sherborn's early published work, particularly with T. R. Jones, are not present in the collections but these collections may have been sold or deposited elsewhere by his co-workers.

Designing climate-resilient rice with ideal grain quality suited for high-temperature stress

To ensure rice food security, the target outputs of future rice breeding programmes should focus on developing climate-resilient rice varieties with emphasis on increased head rice yield coupled with superior grain quality. This challenge is made greater by a world that is increasingly becoming warmer. Such environmental changes dramatically impact head rice and milling yield as well as increasing chalkiness because of impairment in starch accumulation and other storage biosynthetic pathways in the grain. This review highlights the knowledge gained through gene discovery via quantitative trait locus (QTL) cloning and structural-functional genomic strategies to reduce chalk, increase head rice yield, and develop stable lines with optimum grain quality in challenging environments. The newly discovered genes and the knowledge gained on the influence of specific alleles related to stability of grain quality attributes provide a robust platform for marker-assisted selection in breeding to design heat-tolerant rice varieties with superior grain quality. Using the chalkiness trait in rice as a case study, we demonstrate here that the emerging field of systems genetics can help fast-track the identification of novel alleles and gene targets that can be pyramided for the development of environmentally robust rice varieties that possess improved grain quality.

Nickel adsorption on chalk and calcite

Nickel uptake from solution by two types of chalk and calcite was investigated in batch sorption studies. The goal was to understand the difference in sorption behavior between synthetic and biogenic calcite. Experiments at atmospheric partial pressure of CO2, in solutions equilibrated with calcite and chalk and pH ranging from 7.7 to 8.8, explored the influence of initial concentration and the amount and type of sorbent on Ni uptake. Adsorption increases with increased surface area and pH. A surface complexation model describes the data well. Stability constants for the Ni surface complex are log KNi=-1.12 on calcite and log KNi=-0.43 and -0.50 on the two chalk samples. The study confirms that synthetic calcite and chalk both take up nickel, but Ni binds more strongly on the biogenic calcite than on inorganically precipitated, synthetic powder, because of the presence of trace amounts of polysaccharides and clay nanoparticles on the chalk surface.

Eating everything except food (PICA): A rare case report and review

PICA is an act or habit of eating non-food items such as stone, bricks, chalk, soap, paper, soil etc., It occurs in children who actually start seeing the world through the oral cavity. There are many theories behind it such as iron and zinc deficiency etc., We as dentists should be able to diagnose and treat such conditions, as they may cause ill-effects to the developing dentition. This case report attempt to highlights the importance of proper diagnosis and treatment of pica.