Active CaCO3 Research Articles

Promotion of active H-assisted CaCO3 conversion for integrated CO2 capture and methanation

Carbonate hydrogenation is a new path for the conversion of metal carbonate with potentially lower energy consumption and CO2 emissions comparing to the traditional thermal decomposition, and the integrated CO2 capture and utilization (ICCU) represents its latest development. However, the slow hydrogenation rate of carbonate at low temperatures is one key scientific challenge for applications. Herein, we report an acidity regulation approach to prepare ZrO2-doped Ni/CaO dual-function material with good CO2 capacity, fast and highly selective conversion below 600 °C for integrated CO2 capture and utilization by methanation (ICCU-methanation). Experiments and DFT calculations show that the introduction of ZrO2 as acid sites effectively strengthens *H adsorption and reduces the formation barrier of intermediate *COOH during carbonate hydrogenation. Thus, Ni10(ZrO2)10CaO80 exhibits a CH4 STY of 14.1 mmol∙min−1∙gNi−1 at 550 °C, 6 times higher than the reference DFM. Furthermore, the presence of O2 in flue gas is observed to have no effect on ICCU-methanation, but steam could delay the in-situ methanation. Long-term cyclic test shows that the optimal Ni10(ZrO2)5CaO85 has a stable CO2 capacity of 7.5 mmol ∙gDFM−1, 98 % CO2 conversion and 95.5 % CH4 selectivity under flue gas containing both steam and O2 at 600 °C, suggesting a good potential to be applied in ICCU-methanation.

Real-time application and modelling of the NOx-sorption reaction on a particulate calcium carbonate surface-flow filter exposed to combustion exhaust.

Of major interest, especially in city environments, and increasingly inside vehicles or industrial plants, is the drive to reduce human exposure to nitrogen oxides (NOx). This trend has drawn increasing attention to filtration, which has developed remarkably owing to the capabilities of recently developed mathematical models and novel filter concepts. This paper reports on the study of the kinetic modelling of adsorption of nitrogen dioxide (NO2), collected from the tailpipe of a diesel engine, reacting to calcium nitrate salt (Ca(NO3)2) on a surface flow filter consisting of a coating of fine ground limestone or marble (CaCO3) in combination with micro-nanofibrillated cellulose (MNFC) acting as binder and humectant applied onto a multiply recycled newsprint substrate. The coating and substrate are both porous, but on different pore size scales, with the coating having significantly lower permeability. To maximise gas-coating contact, therefore, the coating deposition is pixelated, achieved by pin coating. An axially dispersed gaseous plug flow model (dispersion model) was used to simulate the transport within the coating pore network structure, following earlier flow modelling studies, and a kinetic reaction model was used to examine NO2 to NO3- conversion in correlation with experimental results. Modelling results indicate a 60.38% conversion of exposed NO2 gas to Ca(NO3)2 under the specific conditions applied, with an absolute relative error between the predicted and experimentally estimated value being 0.81%. The model additionally enabled a prediction of effects of changing parameters over a limited perturbation range, thus assisting in predicting filter element consumption, with attention given to the active component CaCO3 surface as a function of particle size in relation to the gas contact exchange, promoting the reaction over time. It is intended that the Ca(NO3)2 formed from the reaction can go on to be used as a value-added fertiliser, thus contributing to circular economy.

Effect of thermal-oxidative and mechanical degradation of recycled LDPE on foaming

In this study, we investigated the effect of recycling process on the molecular structure, viscoelasticity and foaming behavior of low density polyethylene (LDPE). A series of LDPE samples with different recycling process was prepared by multiple extrusion using a twin-screw extruder. The molecular weight distribution (MWD) was characterized by gel permeation chromatography (GPC). Wider MWD indicated the generation of higher molecular weight products. Small-amplitude oscillation rheology showed reduced loss factors, indicating that the chain entanglement was more difficult to relax. Moreover, nonlinear viscoelasticity was investigated using elongational rheology and molecular stress function (MSF) model. The results showed a steeper strain hardening exhibited in recycled LDPE. The correlated parameter β in the MSF model indicated that the recycling did not significantly change the branches regularity in LDPE, while the increasing [Formula: see text], the other correlated parameter, indicated that the chain entanglement was enhanced, which was corresponded to the improvement of high molecular weight component. The foaming results revealed that the recycled LDPE had finer cellular structure and higher nucleation density. Moreover, despite adding PP and active CaCO3 to simulate the impurities, the foamability loss of these mixed samples was well restricted and still valuable. Recycled LDPE is instead better than its corresponding virgin one in foaming performance, exhibiting the application potential for further developments.

Chiroptically Active Multi-Modal Calcium Carbonate-Based Nanocomposites.

The development of multimodal nano- and micro-structures has become an increasingly popular area of research in recent years. In particular, the combination of two or more desirable properties within a single structure opens multiple opportunities from biomedicine, sensing, and catalysis, to a variety of optical applications. Here, for the first time, we report the synthesis and characterization of multimodal chiroptically active CaCO3 nanocomposites. These composites have been prepared by a modified microemulsion method in the presence of an amino acid (cysteine). Following this, additional modalities have been introduced by loading the composites with luminescent nanoparticles or doping with Eu3+ ions. The luminescent composites have been produced by the incorporation of CuInZnS/ZnS or CdSe@ZnS/ZnS core/shell quantum dots, or via doping with trivalent europium. In this manner, we have produced chiroptically active composites with orange, green, and red luminescence. Overall, this work demonstrates the unique advantage and potential of our approach and new class of chiroptically active CaCO3 nanocomposites, which display tunable functionality to specific requirements via the incorporation of desired ions, nanoparticles, and chirality of the structure.

FTIR and XRD Characterization of the Cements Available in Commercial Market of Nepal

In the engineering material characterizations and analytical domains where the specific physicochemical properties of the materials are probed through various sophisticated instrumental tools and techniques, the XRD and FTIR spectroscopy stand as the standalone applications as the former discloses the crystallographic structure, crystallite/grain sizes, and the chemical compositions of the specific materials nondestructively while the latter reveals details about the IR active vibrations modes of each covalent bond of their chemical constituents. In the present studies, we employ both of these techniques, and characterize the specifically selected variable manufactured ready-to-use dry OPC type cements available in the commercial markets of Nepal. The former technique derived the specific 2\(\theta\) value deterministic for identifying the closely packed interatomic layers with the significant levels of CaCO3, Ca(OH)2, and arsenic As5+ based AsO43- unit bearing crystalline phases in each samples. The calculated crystallite sizes of them are found as equal as that reported for the calcite based OPC cements, and are directly adopted to depict their utmost intermixing propensities with the carbon dust and hence, act as the most potential evidence of unlocking the possibility of inventing cement-carbon composites based supercapacitors and conductive devices, and of speculating their distinguishable hydration rates and setting times. And, the latter technique produced intense IR active bands in the designated wave number regions are used to confirm their silicate (SiO42-) tetrahedra, amorphous CaCO3 phases & the CO32-unit holding chemical constituents, 2CaO.SiO2 and 3CaO.SiO2 type chemical compounds explicitly. The presence of diffused type IR bands specific to the Al2O3 based chemical compounds signified that all of them contains significant levels of the alumina based hardening elements, but the complete absence of the peak typical to the Mg-O signified that none of them contains magnesia. The similar analyses of the IR bands further reveal that none of them possesses heavy and active type CaCO3, but have trace amounts of the AsO43- based chemical compounds as predicted by the XRD. The intensive peak area and the depth intensity studies of the designated IR bands speculate the dissimilar quantitative proportions and percentage compositions of these chemical constituents in them. The authors believe that the general results presented herewith illuminate the fundamental chemical constituents to be incorporated compulsorily into the OPC type cements so that they function normally and exhibit good cementitious abilities.

Formation processes of paper-thin raft and coated bubble: Calcium carbonate deposition at gas–water interface

Travertines are hot spring carbonate deposits that exhibit characteristic fabrics, including a paper-thin raft and a coated bubble formed by the calcification of water and bubble surfaces, respectively. A previous study interpreted that compared with the water surface, the bubble surface displays more active CO2 degassing and resultant active CaCO3 precipitation. However, considering the CO2 partial pressure and the volumes of atmosphere and bubbles, it is possible that more active CO2 degassing occurs on the water surface. In addition, the surfaces of water and bubbles at the travertine-depositing sites are negatively charged, but it is still unclear whether the CaCO3 nucleation on these surfaces occurs via amorphous precursors, like the CaCO3 nucleation on negatively charged organic matter. This study provides a solution to these uncertainties by examining the aragonitic travertines formed in the Nagayu area of Japan. Through field observations, two types of paper-thin rafts were recognized: one with a smooth surface and formed in approximately 1 h, and the other with a rough surface and formed in approximately 3 h. In addition, the bubbles generated on the microbial mat during the daytime were covered with white minerals within an hour, and with ivory-colored minerals over 8 h after sunset, forming firm coated bubbles. Microelectrode measurements revealed that the active CO2 degassing on the water surface significantly increased the CaCO3 saturation state to cause active CaCO3 precipitation. In contrast, less active CO2 degassing on the bubble surface did not increase the saturation state, and moderate CaCO3 precipitation occurred due to the moderately high saturation state of the hot spring water. Various microscopic observations revealed that the smooth-surfaced paper-thin raft comprises a micritic layer of approximately 10–20 μm, which represents tightly arranged submicron-sized granular aragonite. At the lower surface of this layer, hemispherical aragonite partially grew toward the hot spring water. In addition, the rough-surfaced paper-thin raft and coated bubble comprise bundled and acicular aragonites arranged along the surfaces of water and bubble, from which hemispherical aragonite grew toward the hot spring water. Neither the paper-thin raft nor the coated bubble contains primary amorphous CaCO3. These results suggest that the smooth-surfaced paper-thin raft is formed by active CaCO3 nucleation on the water surface and subsequent crystal growth, and that the water surface is unfavorable for preserving the amorphous precursors potentially involved in the nucleation. The rough-surfaced paper-thin raft and the coated bubble could have been formed by the attachment of externally formed acicular aragonite to the water/bubble surface and subsequent crystal growth. The revealed formation processes of the paper-thin raft and coated bubble provide valuable information for interpreting their formation mechanism in other travertine deposits, including those in the geological past.

Hierarchical pore carbon-calcium nanocages for highly effective removal of ammonium-nitrogen and phosphorus

Reconstructing industrial waste slags as adsorbents to purify ammonium‐nitrogen and phosphorus wastewater is a promising method. However, owing to the tight structure, most slags only have a few exposed strong metal adsorption sites for limited treatment. Thus in this paper, paper mill sludge rich in both CaCO3 and organic carbon was selected to construct a highly-active multi-porous carbon‑calcium nanocages adsorbent (Ca-pPSC750). Activation test reflected that KOH intervention not only made sludge organic matter into multistage-pore carbon, but also facilitated the uniform distribution of active CaCO3 nanoparticles. Adsorption results showed that the maximum removal capacity of Ca-pPSC750 for NH4+-N and PO43−-P was up to 248.9 and 104.1 mg g−1, more than 10 times that of the same kind of adsorbents. The whole adsorption process is not limited by the initial pH and coexisting ions of water. This work not only experimentally verifies the existence of a slightly-alkaline microenvironment on the surface of hierarchical pore carbon‑calcium nanocages adsorbents for the first time, but also eliminates the pH limitation of the adsorption reaction for pollutant remediation, thereby expanding the applicability of papermaking sludge adsorption technology. It provides a solution for the efficient purification of high concentration NH4+-N and PO43−P wastewater.

Hierarchically doping calcium carbonate pellets for directly solar-driven high-temperature thermochemical energy storage

Ca-based thermochemical energy storage (TCES) system is one of the most promising energy storage techniques for the next generation concentrated solar power systems (CSP). However, it still suffers from low optical absorption, poor cycle stability, and limited energy storage density. Here, a hierarchically doping strategy is proposed to overcome above challenges and achieve high-performance energy storage under direct solar irradiation. Hierarchically doped calcium carbonate pellets, which are suitable for scalable applications, are successfully fabricated with Al-doped internal cores and Mn-rich external shells. The average solar absorptance achieves 87.15% with a 7.4% increase compared with traditionally homogeneous doping approaches. The energy storage density is still as high as 1143 kJ/kg after 20 cycles, which is enhanced by 16.6% over homogeneous counterparts. The underlying mechanism is that hierarchically doping increases contents of active CaCO3 inside pellets and absorption-enhanced substances on the outer surface simultaneously. This work presents a novel approach for the design of high-performance pellets for achieving scalable and efficient thermochemical energy storage under direct solar irradiation.

A simple method to determine the reactivity of calcium carbonate in soils

AbstractDetermination of soil carbonate is important for numerous chemical and physical soil processes in arid and semi‐arid zones. Here, we modify a conventional method to more easily determine active CaCO3 (ACC) fraction in soils. Unlike the conventional method where the oxalate used up after reaction with carbonate is determined by titration with KMnO4, the proposed method uses the difference between total carbonate analyzed before and after reaction with oxalate to determine ACC. The method compared well to the conventional approach; the procedure was faster, did not require KMnO4, and appeared to be unaffected by exchangeable Ca. The proposed method is well‐suited for samples across a wide range of total carbonate.

Improvement of degraded agricultural soil in an arid zone following short- and long-term treated municipal wastewater application: A case study of Gabes perimeter, Tunisia

This work aimed to study the short, medium, and long-term influences of treated wastewater (WWTP) as a soil irrigation technique on physical, chemical, and microbiological properties. Sampled soil plots were irrigated with WWTP for 1, 7, and 15 years. Rain-fed regime soil has been used as a control. This study was conducted in El Hamma of Gabes (southeast of Tunisia), an arid zone, during the dry season. Three soil profiles at 0–20, 20–40, and 40–60 cm were sampled. Physical and chemical analyzes, including pH, electrical conductivity, total organic carbon, total nitrogen, cation exchange capacity, and active and total CaCO3 were evaluated. Soil microbial biomass C and N were performed according to the fumigation extraction method. Soil microbial contamination was assessed by enumerating total, Fecal Coliforms, E. coli, and Fecal Streptococci with the most probable number (MPN) method and plate medium count. Bacterial and fungal enumeration were evaluated by the plate count agar method. In addition, the DGGE molecular analysis was also assessed in the different soil samples. The obtained physical and chemical evaluation proved that the WWTP irrigation practice improves soil fertility. Microbial biomass C and N increased by increasing the time of WWTP irrigation. In addition, the sanitary quality of the soil is affected by the increase of pathogens. We have observed an increase in microbial biomass as demonstrated by an increase in heterotrophic bacteria and filamentous fungi in the soil irrigated with WWTP compared to the control. Long-term WWTP irrigation has increased the activities of the soil microorganisms and then soil fertility. Meanwhile, the same pathogens and bacteria could pose a serious threat to sanitary soil quality and a limiting factor for the use of WWTP in agriculture areas without tertiary treatment.

Short-term land degradation driven by livestock grazing does not affect soil properties in semiarid steppe rangelands

The soil–vegetation relationships are reciprocal and fundamental for terrestrial ecosystem integrity. However, the long-term degradation of vegetation cover alters edaphic conditions, which can lead to degradation of habitats, and obstructs proper ecosystem functioning. This study aimed to assess the effects of the degradation of perennial steppe vegetation due to overgrazing (i.e., continuous and free grazing) on the physicochemical characteristics and soil fertility in the steppe rangelands of Halfa (Macrochloa tenacissima syn. Stipa tenacissima) of semi-arid areas in Algeria. The edaphic parameters of the superficial horizons of degraded steppes and other undegraded steppes were compared in order to suggest adequate strategies for rangeland management and remedy the degradation of vegetation and thereby ensure the sustainability of these agro-pastoral systems. The soil, collected from the surface horizons (A1 and A2) of pedological profiles, was analyzed according to standard methods of soil physicochemical analyses to determine the particle size fractions (clay, silt, and sands), pH, electrical conductivity (EC), total and active CaCO3, organic matter (SOM), organic carbon, total nitrogen, and the C:N ratio. The distribution and variation of soil parameters between horizons and the two types of steppes were examined using generalized linear mixed models and redundancy analysis. Findings of this study revealed that the degradation of steppe vegetation cover by short-term overgrazing did not cause a significant variability in soil physicochemical parameters between degraded and undegraded steppes and the horizons A1 and A2. The sites studied have clayey–silty textures in non-degraded steppes and coarse textures dominated by sands in degraded steppes. The edaphic environment of the Halfa grass steppes was characterized by a calcareous substratum with high carbonate content (total CaCO3 = 36.8–41%, active CaCO3 = 17.5–18.5%), with an alkaline pH (8.09–8.19) and EC averaging 0.99 ± 1.24 dS/m. Soils had low SOM contents (1.42–2.93%), organic carbon (0.82–1.64%), and nitrogen (0.1–0.15%). The strong positive correlations recorded between the fine-size fractions, SOM, total CaCO3, nitrogen, and EC indicated good soil structural stability in undegraded steppes, while the negative correlations between these same variables with sand and pH substantiate the structural degradation of the soil. The negative correlation between C:N ratio and SOM indicated that the rate of SOM mineralization was rapid in semiarid steppes, with a higher fertility state in the undegraded steppe. Our findings suggest and urge to implement a restoration plan against the degradation of semi-arid Halfa steppes in order to avoid the irreversible state of soil and habitat destruction in the future because even the degradation of rangeland plant cover due to livestock overgrazing—in the short term—has not affected the edaphic characteristics of steppe rangelands.

Soil fertility indicators and soil stoichiometry in semi-arid steppe rangelands

Soil fertility depends on vegetation cover, climatic conditions and soil-specific edaphic factors that regulate transformation processes of plant residues and organic matter. Soil physicochemical characteristics in drylands negatively affect evolutionary process of soil materials resulting in fertility loss. This study investigated the variability of soil physicochemical parameters and fertility estimates in three types of semi-arid steppe rangelands of North Africa, viz. Stipa tenacissima, Artemisia herba-alba and Atriplex halimus. The effect of soil parameters on the evolution of soil fertility was appraised using soil organic carbon (SOC), available phosphorus (AP) and C:P ratio as fertility indicators. In two semi-arid regions with haplic calcisols, soil was sampled in six replicates at each steppe rangeland and a control (bare soil). Using standard protocols, each sample was analyzed to determine pH, electrical conductivity (EC), SOC, AP, C:P ratio, total and active CaCO3. All the soil physicochemical parameters tested, except total CaCO3, showed positive increases in A. halimus and S. tenacissima steppe rangelands. The variation of pH and EC values among rangelands was significant, with A. halimus rangelands had significantly the highest scores and A. herba-alba rangelands the lowest scores. The redundancy analysis showed that the edaphic factors triggering significant increases in scores of soil fertility indicators, when compared to the control, were active CaCO3, EC and pH. These physicochemical parameters positively determined the accumulation of AP and SOC, especially in A. halimus rangelands. The high values of stochiometric C:P ratio were associated to soil characteristics of S. tenacissima and A. herba-alba rangelands. Our findings suggest that soil physicochemical parameters of semi-arid steppe rangelands - compared to bare soil - influenced the evolution of soil fertility and stoichiometric C:P ratio. The type of steppe vegetation differently affects the physicochemistry and stoichiometry of the soil.

Recycling of Spent Pot Lining First Cut from Aluminum Smelters by Utilizing the Two-Step Decomposition Characteristics of Dolomite.

Spent Pot Lining First Cut (shortened to SPL-1cut) is a solid waste discharged from a primary aluminum electrolytic production process. SPL-1cut is classified as hazardous waste in China because it contains large amounts of soluble sodium fluoride and a tiny amount of cyanide. Most of SPL-1cut is carbon—about 65%—and its calorific value is 22.587 MJ∙kg−1. There is a high level of sodium fluoride in SPL-1cut—about 15%—and sodium fluoride is randomly distributed in the carbon granule. The recycling of SPL-1cut using dolomite as a reactant, based on the characteristics of the two-step decomposition of dolomite at a high temperature, is discussed. The recycling of SPL-1cut was performed under the following heating conditions: the heating temperature was 850 °C, the holding time was 120 min, and 40% of the dolomite was added to the SPL-1cut. It was found that the cyanides are completely oxidized and decomposed, and dolomite is decomposed into MgO and active CaCO3. At the same time, NaF reacts with active CaCO3 and converts into CaF2. The results provide references for using SPL-1cut as an alternative fuel in the dolomite calcination process of the Pidgeon Process.

Effects of Temporal Variation in Long-Term Cultivation on Organic Carbon Sequestration in Calcareous Soils: Nile Delta, Egypt

Soil carbon sequestration is a riskier long-term strategy for climate mitigation than direct emissions reduction, but it plays a main role in closing carbon emission gaps. Effects of long-term cultivation on soil carbon sequestration were studied at the western edge of the Nile Delta near Alexandria, Egypt. Seven agricultural fields of different ages (0–50 years in use) were selected and compared with the surrounding desert (virgin soil) and desert shrub-land. Samples were taken at three horizons, 0–30, 30–60, and 60–90 cm, and tested for differences in physical and chemical properties. The results of long-term cultivation reveal that the European Commission (EC) value was 11.77 dS/m in virgin soil, while the EC values decreased to 5.82, 4.23, 3.74, 2.40, and 2.26 dS/m after 5, 10, 20, 30, and 50 years of cultivation, respectively. The calcareous rock fraction smaller than 50 μm in size revealed another phenomenon, where active calcium carbonate content increased with cultivation practices from 1.15% (virgin soil) to 5.42%, 6.47%, 8.38%, and 10.13% after 5, 10, 20, and 30 years of cultivation, respectively, while shrub-land also showed a low amount of active CaCO3 with 1.38%. In fifty years of cultivation, soil bulk density decreased significantly from 1.67 to 1.11 g/cm3, and it decreased to 1.65, 1.44, 1.40, and 1.25 g/cm3 after 5, 10, 20, and 30 years, respectively. These results reveal that the increase in soil carbon stock in the upper 90 cm amounted to 41.02 t C/ha after five years of cultivation, compared to virgin soil with 13.47 t C/ha. Soil carbon levels increased steeply during the five years of cultivation, with an average rate of 8.20 t C/ha per year in the upper 90 cm. After the first five years of cultivation, the carbon sequestration rate slowed, reaching 4.68, 3.77, 2.58, and 1.93 t C/ha per year after 10, 20, 30, and 50 years, respectively, resulting in sequestration-potential values of 46.78, 75.63, 77.43, and 96.45 t C/ha. These results indicate that potential soil carbon sequestration resembles a logarithmic curve until the equilibrium state between carbon application and decomposition by microorganisms is reached.

Safe utilization of chromium-bearing vanadate residue by recovery of vanadium and chromium based on calcium circulation

A safe, economical treatment of hazardous chromium-bearing vanadate residue (CVR) will significantly benefit the clean production of chromate-bearing salts. This study investigated recovery of sodium vanadate and sodium chromate from CVR in sodium bicarbonate solution. Results indicate that the stability of calcium vanadate and calcium chromate depends on pH and [HCO3–]. CaV2O6·4H2O transforms into CaV2O6·4H2O, CaV2O6·2H2O, CaV2O6, Ca2V2O7·2H2O, and Ca5(VO4)3(OH) when pH increases from 7.51 to 12.32. Increasing pH and reducing CVR dosage improve the vanadate extraction rate, and high V2O5 and Na2Cr2O7·2H2O extraction rates are achieved in dilute NaHCO3 solution. Moreover, addition of NaOH positively contributes to the recovery of vanadate and chromate from CVR. Over 95% V2O5 and Na2Cr2O7·2H2O in CVR can be extracted from 60 g/L NaHCO3 and 30 g/L NaOH solutions at 90 °C for 2 h. In order to reduce the hazardous residue containing chromate after recovery of CVR, calcium circulation is presented. Results show that more than 60% lime can be saved with fresh residue addition to remove vanadate from sodium chromate solution due to the active CaCO3. Moreover, no lime is required in removal of vanadate when the roasting residue is added. Therefore, a novel process is developed for utilization of CVR.

Response of a spring-fed fen ecosystem in Central Eastern Europe (NW Romania) to climate changes during the last 4000 years: A high resolution multi-proxy reconstruction

We document the long-term development of a spring-fed fen assessing its sensivity to climate changes over the last ca. 4000 years. Our investigation is based on high-resolution, continuous plant macrofossil remains and mollusc records, complemented by pollen, geochemical analysis and radiocarbon dating of Valea Morii, located in the Feleac Hills (Transylvanian Depression) in NW Romania, Central Eastern Europe. Based on our palaeocological data we have distinguished three stages of wet habitat conditions: two stages between 4000 and 2450 cal yr BP and one in the last 800 cal yr BP, and one dry stage between ca. 2450 and 800 cal yr BP. These local habitat conditions appear to reasonably reflect regional climate characteristics. High-resolution analysis of two replicated cores documented a mostly comparable pattern of local plant and mollusc succession, and stable isotope values from ca. 500 cal yr BP. The appearance of C. mariscus during the last two centuries may be related to increased wetness and associated active CaCO3 precipitation, which allowed this plant to colonise the spring-fed fen studied. However, it can be not excluded that the occurrence and spread of a Cladium mariscus population at this site during the last two centuries might have been partly favoured by the warming of the climate after the Little Ice Age. The potential of carbonate oxygen stable isotope values as an indicator of major trends in climatic change, both temperature and humidity, in mountain spring-fed fen deposits is shown. Carbon isotopes in the carbonates were found to be useful in reconstruction of changes in vegetation, soil development and the dissolution of bedrock carbonates, primarily as a reaction to changes in climate humidity.

Calcium carbonate deposition drives nutrient cycling in a calcareous headwater stream

AbstractCalcium carbonate (CaCO3) deposition is common in aquatic ecosystems and may reduce phosphorus availability via coprecipitation of phosphate, an impact with broad implications for ecosystem processes. To determine if CaCO3 deposition in streams increases phosphorus (P) retention in minerals while reducing P availability to organisms, we studied paired streams (with and without active CaCO3 deposition) subjected to experimental shading and monitored changes in ecosystem attributes (e.g., periphyton biomass content, nutrient spiraling, periphyton nutrient limitation, and leaf litter decomposition). Shading reduced rates of CaCO3 deposition by over 50%, suggesting that a substantial proportion of CaCO3 deposition is supported by photosynthetically induced changes in alkalinity. Shading‐induced reductions in CaCO3 deposition led to increases in epilithon biomass P content (P < 0.05) and periphyton growth (F2,12 = 5.79, P < 0.05). Reductions in CaCO3 deposition also relieved P limitation of periphyton growth (F3,16 = 59.32, P < 0.001), extended P uptake lengths at least an order of magnitude, and reduced both P mass transfer velocity and areal uptake rates by over 80% (F2,3 = 22.62, P < 0.05 and F2,3 = 13.19, P < 0.05, respectively). Finally, while shading caused reductions in leaf litter decomposition in the non‐CaCO3 depositing stream (F5,7 = 22.45, P < 0.001), shading had no effect on leaf litter decomposition in the stream with active CaCO3 deposition. These results indicate that CaCO3 deposition can regulate P bioavailability and retention in streams and may drive streams to be P limited, as has been suggested in lake and wetland ecosystems.

Condition Monitoring of Limestone and Soft Sensing Model of SO2 Emissions in a Circulating Fluidized Bed Boiler

Soft sensing models of the desulfurization process are developed in a circulating fluidized bed (CFB) boiler that can capture sulfur dioxide (SO2) with the limestone sorbent in the furnace. First, calcining utilization of CaCO3 and sulfating utilization of CaO are proposed by mechanism analysis of the theoretical air and flue gas, and the online prediction method is achieved by using an adaptive-tree-structure-based fuzzy inference system (ATSFIS). Second, condition monitoring models of active CaCO3, active CaO, and soft sensing model of SO2 emissions are studied by using the experimental data of a CFB boiler in China, which can monitor the storage and condition of the limestone in the furnace and predict SO2 emissions. Finally, a nonlinear proportional–integral–derivative (PID) control system based on the above models is designed to control the feed rate of limestone for the reduction of SO2 emissions. The simulation results show that the soft sensing models are consistent with the mechanism test results...

English

Mycorrhizal fungi are an essential component to consider for better management of soil fertility, particularly in degraded rangelands of drylands. The present article presents a field survey of colonization and intensity of arbuscular mycorrhizal fungi (AMF) on prickly pear (Opuntia ficus-indica) roots from young (5 years old) and old (more than 20 years) plantations. The results observed were explained by seasonality and edaphic factors. Prickly pear roots showed a mycorrhizal frequency (F%) up to 100% of colonization and a mycorrhizal intensity (M%) that may exceed 70%. According to ANOVAs, both F% and M% varied significantly between Prickly pear plantation ages, but only M% between seasons. The Generalized linear model showed that edaphic factors have no effect on the variation of F%. However the statistical model showed that M% were significantly influenced by active CaCO3, organic matter, carbon, nitrogen, phosphorus contents and C/N. Our findings highlight the importance of mycorrhization in rehabilitation programs of degraded rangelands by prickly pear plantations in semiarid and arid lands, particularly during early plant ages and under environmental abiotic stresses such as climate and soil type.

Prospects of damaged calcareous spring systems in temperate Europe: Can we restore travertine-marl deposition?

Calcareous mires are peat forming systems fed by calcareous groundwater that regularly deposit travertine (CaCO3) on the soil surface or in small pools that are present in such mires. At present almost all calcareous mires in Poland are degraded, most often by land use, which has led to disturbances in local hydrological systems. An experiment was set up in a degraded spring mire in western Poland to test if travertine deposition could be restored. Trees were removed to increase surface water temperatures, and a system of open water pools was constructed to measure CaCO3 deposition in the surface water. We also studied three references systems with active CaCO3 deposition in Poland and in Latvia. The pools in the restoration site in Poland showed very little CaCO3 deposition (less than 0.2 μg · cm−2 · d−1), while the Polish reference site had significantly higher, but still modest, rates of CaCO3 deposition (ca 0.8 μg · cm−2 · d−1). At the reference sites in Latvia, we measured considerable CaCO3 deposition (up to 8 μg · cm−2 · d−1). Five years after the restoration measures in the Polish restoration site had been carried out, the vegetation showed little resemblance to the vegetation in spring systems with active calcite deposition in Poland and Latvia. Water analyses showed that the water in our restoration project was not supersaturated by calcite and had very low CO2 concentrations compared to the reference areas. The CO2 concentrations in the pool seemed a good predictor for CaCO3 deposition, better than Ca2+ concentrations. Changes in ground water flows in the source area could have been responsible for the loss of supersaturated groundwater at our restoration site. Our study showed that efforts to restore former calcareous mires can be frustrated when groundwater flow paths have been altered.