Low Loss On Ignition Research Articles

A Holocene lacustrine record of variations in chemical weathering intensity in the Mu Us Desert, China

The Mu Us Desert is an ideal location to study environmental changes during the Late Quaternary, because of its unique characteristics. The Abaoyan (ABY) profile, a typical aeolian-lacustrine profile located at the eastern edge of the desert, was investigated in this study. A basic chronological framework was established based on a combination of radiocarbon dating by accelerator mass spectrometry and in situ sedimentary phase identification. Furthermore, changes in regional chemical weathering intensity since the Holocene were evaluated through comprehensive analysis of the collected samples in terms of grain size, loss on ignition (LOI), chromaticity, geochemical element contents, and soil micromorphology. The results showed that the ABY profile was under the influence of primary and moderate chemical weathering. Regional paleoclimatic environmental changes could be divided into four stages. During Stage I (before 12.6 ka BP; pre-Holocene), the ABY profile was dominated by aeolian sand, showing a coarse average grain size, low LOI, and high chromaticity values, which may have indicated a dry and cold period. During Stage II (12.6–10.3 ka BP; early Holocene), the ABY profile was dominated by lacustrine sediments, indicating a shallow lake water environment with strong chemical weathering and a warm and humid climate. During Stage III (10.3–4.2 ka BP), the profile was dominated by sandy peat deposits with a relatively large proportion of clay particles suggesting that the intensity of chemical weathering was relatively strong in the region during this period and the climate was mainly warm and humid. During Stage IV (after 4.2 ka BP), the sediment was dominated by aeolian sand and secondary loess, the chromaticity increased, the LOI reduced, and the regional chemical weathering intensity was weaker. The change in chemical weathering intensity in this region was inferred to be a positive response to the Holocene East Asian monsoon circulation.

Incorporation of high loss-on-ignition fly ash into high-strength mortar: Influence on short-term engineering properties

The re-utilization of fly ash (FA), a primary by-product of thermal power plants, in producing various types of sustainable construction materials has been studied by many researchers. The quality of FA varies depending on either the characteristics of coal or the combustion techniques. Most previous studies used FA with a low loss-on-ignition (LOI), while the use of FA with a high LOI in the production of construction materials is still limited. Finding ways to reusing of locally available FA in sustainable construction materials is crucial. Therefore, this study aims to investigate the effect of high LOI FA content on the short-term engineering properties of high-strength mortars (as a modified concept of reactive powder concrete) in terms of workability, fresh unit weight, compressive and flexural strengths, drying shrinkage, and thermal conductivity. The mortar mixtures were designed with a constant water-to-binder ratio of 0.24 and the 0–60% high LOI FA was used to replace cement (step increment of 15% by weight). Test results found that the substitution of cement with high LOI FA significantly affected the engineering properties of high-strength mortars. Increasing the high LOI FA content improved the workability while reducing fresh unit weight, mechanical strength, drying shrinkage, and thermal conductivity of high-strength mortars. Although the short-term properties of mortars were negatively affected by the incorporation of high LOI FA, the mortar samples containing 60% high LOI FA registered relatively high 28-day compressive and flexural strengths of about 34 and 6 MPa, respectively. In another aspect, using high LOI FA in the production of construction materials is beneficial in reducing the use of cement as well as limiting environmental pollution due to the disposal of this FA type, contributing to a greener environment toward a sustainable development goal.

Holocene hydroclimate changes revealed by multiple proxies from an alpine lake in the central Tianshan Mountains, Northwest China

Alpine wetland ecosystems are of importance in water conservation and animal husbandry in the arid central Asian. However, there is limited research on their formation and relationship with climate. In this study, we evaluated the long-term interactions of vegetation, hydrology, and climate based on multiple proxies (lithology, grain size, loss-on-ignition (LOI) at 550 °C, and pollen) obtained from a sediment core (BY10A) from Lake Swan, an alpine lake in the central Tianshan Mountains of northwest China (2541 m a.s.l.). Our records show that Holocene sediment facies change considerably within core BY10A, with the succession from bottom to top comprising fluvial, peat, and lake sediments. The fluvial deposits were characterized by coarser sediment, which was probably reworked from extensive sand dunes developed over the basin during the early Holocene (12.0–7.5 cal kyr BP). Regional biological productivity was low at this time as indicated by the low LOI value, and the remains of vegetation was degraded under the dry climate. A warm and wet climate prevailed from 7.5 to 2.0 cal kyr BP, resulting in the establishment of peat. The ability of the peat surface to efficiently trap fine particles was enhanced when regional sand dune bodies (coarser part) became largely stabilized by vegetation growth in response to increases in moisture availability. After 2.0 cal kyr BP, a rise in water level, leading to the formation of Lake Swan, indicated a further shift to a wetter climate. During this interval, there was an increasing influence of lacustrine settling and/or wave action on the grain size distribution and the pollen assemblage. This study indicates a stepwise wetting trend from the early to late Holocene. Findings show that changes in moisture, regulated by the prevailing westerlies, exerted a significant influence on the evolution of vegetation communities and lake level in our study area.

Sintering properties of olivine and its utilization potential as a refractory raw material: Mineralogical and microstructural investigations

In this study, an olivine sample obtained as final tailing from a chromite enrichment plant was examined for its sintering properties and utilization potential as a refractory raw material. For this purpose, cylindrical specimens were first prepared and then sintered at the temperatures of 1300, 1400, 1450 and 1500 °C for 2 h in a laboratory furnace. Quality of the products was evaluated in terms of some physical and mechanical refractory specifications such as bulk density, water absorption, porosity, shrinkage and cold crushing strength. Furthermore, phase developments and microstructural changes due to the sintering were determined in detail with X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, respectively. According to the experimental results, with increasing temperature, the bulk density and shrinkage values increased while the porosity and water absorption values decreased. Specifically, the bulk density and shrinkage values varied in the ranges of 2.33–2.60 g/cm3 and 1–5%, respectively. The porosity values of 24.10 and 15.68% were obtained after sintering at 1300 and 1500 °C, respectively. The cold crushing strengths slowly increased from 46.90 to 55.86 MPa after sintering between 1300 and 1450 °C. A sudden rise to 93.44 MPa was then observed at 1500 °C. Accordingly, the thermo-optical analysis indicates that the olivine exhibited a sintering point of 1478 °C and no softening up to 1500 °C. However, the formation of undesirable low-melting enstatite was detected by the XRD and SEM analysis which also specified the increasing amorphous phase and crystallizations of forsterite and spinels with rising temperature. Overall results have shown that the olivine sample used has a promising potential as a refractory raw material mainly due to its high MgO content, low loss on ignition (LOI) value and appropriate particle size.

Terrestrial mollusk records in the loess sequences from eastern Central Asia since the last deglaciation and their paleoenvironmental significance

A variety of proxies has been studied to document paleoclimatic changes in arid Central Asia (ACA). However, biological archives, which can be directly related to climatic conditions, are still scarce in this region. Here we report records of the total count fossils (TCF) of terrestrial mollusks, organic carbon isotopes (δ13Corg) and loss on ignition (LOI), since the last deglaciation in the Talede and XRBLK loess sections in Xinjiang, eastern Central Asia. Prior to the Holocene, the records show rare fossils with relatively low LOI and more positive δ13Corg, indicating low biomass/organic carbon content under dry conditions which were unfavorable for the survival of snails. In contrast, TCF increased abruptly at the beginning of Holocene, coincident with a prominent increase in LOI and a marked negative shift in δ13Corg. Furthermore, TCF increased gradually to its maximum and δ13Corg became progressively negative with constant high LOI from the early to late Holocene. The variations imply a trend towards wetter environment, with optimal moisture (precipitation/relative humidity) conditions occurring in the late Holocene. Overall, this Holocene moisture evolution history could be attributed to the variations of Westerlies strength modulated by the latitudinal temperature gradient and the insolation-related evaporation should also be concerned.

Properties of Alkali Activated Lightweight Aggregate Generated from Sidoarjo Volcanic Mud (Lusi), Fly Ash, and Municipal Solid Waste Incineration Bottom Ash.

Production of artificial lightweight aggregate (LWA) from industrial by-products or abundant volcanic mud is a promising solution to prevent damaging the environment due to the mining of natural aggregate. However, improvements are still needed in order to control the high water absorption of LWA and strength reduction in resulting concrete or mortar. Hence in this research, fly ash, municipal solid waste incineration bottom ash (MSWI BA), and Sidoarjo volcanic mud (Lusi) were employed as a precursor and activated using NaOH 6 M and Na2SiO3 in producing LWA. The influence of the type of the precursors on the physical properties of resulting LWA was investigated. The effect of replacing natural fine aggregate with the resulting LWA on the compressive strength and volume density of mortar was also determined. Finer particles, a high amount of amorphous phase, and low loss on ignition (LOI) of the raw material improved the properties of resulting LWA. Mortar compressive strength was decreased by 6% when replacing 16% by volume of natural fine aggregate with fly ash based LWA. Compared to the expanded clay LWA, the properties of alternative LWAs in this study were slightly, but not significantly, inferior. Alternative LWA becomes attractive when considering that expanded clay LWA requires more energy during the sintering process.

Application of compound reagent H511 in the flotation removal of unburned carbon from fly ash

This article aims to study the effect of flotation reagent H511 on the removal of unburned carbon (UC) from fly ash. The gas chromatography/mass spectrometry revealed that the main components in H511 were cyclohexanol, d-limonene, longifolene, and 2-cyclohexylidene-cyclohexanone. It is found that the H511 could reacted with the UC surface through zeta potential tests. The induction time indicated that the H511 had a greater positive effect on the adhesion between UC particles and the bubble than diesel. The froth property test indicated that the flotation pulp treated by the H511 had great froth stability due to the effect of cyclohexanol in H511. The flotation showed that the carbon removal rate of H511 was approximately 60 % higher than that of the diesel/sec-octyl alcohol. Fly ash particles with loss on ignition less than 8% can be obtained by H511. This study have great influence for removing UC from raw fly ash and obtaining high-quality, low loss on ignition (LOI) fly ash resources.

Petrogenesis of mafic dykes from the western Bastar craton of Central India and their relation to outgrowth of Columbia supercontinent

We report mineral compositions and bulk rock geochemistry of mafic dykes intruded in the western part of Bastar craton, comprising of Archaean Amgaon Group and Proterozoic Dongargarh Supergroup of rocks. Field relations show two distinct trends of these dykes which are almost perpendicular to each other but having similar mineralogical and geochemical characteristics. Dykes are mostly composed of pyroxenes, plagioclase and subordinate amount of amphiboles and Fe-Ti oxides (magnetite and ilmenite). These hypersthene normative basaltic dykes show tholeiitic trend and are characterised by narrow compositional variations of MgO (6.06–7.08 wt%), FeOt (15.06–17.78 wt%), TiO2 (1.18–2.24 wt%), Al2O3 (11.96–15.54 wt%) and low Mg# [atomic Mg/(Mg + Fe2+) × 100] values in the range of 37–48. Low loss on ignition (LOI) values <2 wt% and significant trends of trace elements (Nb, La, Th, Sr) with Zr indicate insignificant effects of post magmatic processes in these dykes. Smooth correlations between major oxides and MgO, among trace element ratios (Ce/La, Th/Yb, Nb/Yb) and negative Nb-Ta anomalies without positive Zr and Hf anomalies negate the crustal contamination effects. The correlations of compatible (e.g. Cr, Ni) and incompatible (e.g. Ba, Rb) elements show involvement of both fractional crystallisation and partial melting processes in their formation. Flat heavy rare earth element (HREE) pattern with low (Tb/Yb)n values reveal their genesis from a mantle source without involvement of garnet and geochemical models suggested in the present study indicate melting from spinel lherzolite mantle source. Strong geochemical similarities of present dykes with those of earlier reported Lakhna (1.46 Ga) and Bandimal (1.42 Ga) dykes of northern Bastar craton suggest a widespread mafic magmatic event across the Bastar craton during 1.42–1.46 Ga. Present dykes therefore represent a subduction related outgrowth of Columbia supercontinent due to the accretion of continental margins.

Experimental Investigation of the Decarburization Behavior of Medical Waste Incinerator Fly Ash (MWIFA)

The objective of the research was to compare the flotation performance of medical waste incinerator fly ash (MWIFA) by considering two methods: the cyclonic-static micro-bubble flotation column (FCSMC) method and conventional flotation cell (CFC) method. The results indicated that for FSCMC, the optimum parameters were kerosene = 3.5 g/kg·ash, methyl isobutyl carbinol (MIBC) = 0.2 g/kg·ash, Tween 80 = 7.5% of kerosene concentration, slurry concentration = 100 g/L, and pump speed = 380 r/min. The optimized conditions resulted in a higher dioxin removal efficiency (90.98%), carbon removal efficiency (91.88%) and lower loss on ignition (LOI) (4.96%). The data obtained from the CFC under different optimum operating conditions were 88.65%, 90.63% and 5.68%, respectively. FSCMC was proven to be more efficient for the flotation of MWIFA than CFC.

Structure formation of aerated concrete containing waste coal combustion products generated in the thermal vortex power units

The results of fly ash research, generated in the process of waste coal combustion in the thermal vortex power units and used as an aggregate in aerated concrete, are provided. It is established that fly ash can be used in the production of cement or concrete with low loss on ignition (LOI). The permitted value of LOI in fly ash, affecting the structure formation and operational properties of aerated concrete, are defined. During non-autoclaved hardening of aerated concrete with fly ash aggregate and LOI not higher than 2%, the formation of acicular crystals of ettringite, reinforcing interporous partitions, takes place.

Hydrologic changes in Colorado during the mid-Holocene and Younger Dryas

The stratigraphy of Upper Big Creek Lake (UBC), an overflowing lake in northern Colorado, indicates that the lake responded to a series of hydroclimatic changes over the past ~13,000years. Modern sediments in eight comparator lakes from across Wyoming and Colorado facilitate the stratigraphic interpretation by showing that littoral sediments have exponentially higher sand content, lower loss-on-ignition (LOI), and lower net accumulation rates than off-shore sediments. Sand layers in two near-shore cores from UBC share the characteristics of the modern littoral sediments (>80% sand, <5% LOI, and <10cm/ka accumulation rates), and indicate that UBC was >1.9m below its outlet from 12,500 to 11,300 and from 7500 to 2100calyr BP. Ground-penetrating radar (GPR) profiles consistent with the low-water episodes show correlative sand layers and submerged wave-cut scarps around the lake margin. The stratigraphic features correlate with those formed in the comparator lakes during extensive droughts at >11,300, 6900–6000, and 4800–3400calyr BP as well as a series of north-south anti-phased droughts between 5800 and 1200calyr BP. Lake closure at UBC amplified the local changes, and demonstrates that climate changes can increase the extent of intermittent streamflow in the Rocky Mountains relative to today.

Simple Mechanical Beneficiation Method of Coarse Fly Ash with High LOI for Making HVFA Mortar

This study focusses on the effect of milling of fly ash obtained from four different sources on the properties of high volume fly ash (HVFA) mortar. Two fly ash samples with low loss-on-ignition (LOI) were taken from a coal-fired power plant, while the other two with high LOIs were obtained from a textile factory and from a paper mill, respectively. Milling was performed using a rod mill at a certain period of time. The workability of HVFA mortar with constant water to cementitious ratio was controlled by adjusting the superplasticizer content. The results show that the specific gravity of fly ash increases after milling. Utilizing milled fly ash ends up with significant strength increase of HVFA mortar, especially those utilizing high LOI fly ash. This shows that milling is an excellent fly ash beneficiation technique, especially on the one with high LOI value.

Holocene paleohydrology of Quistococha Lake (Peru) in the upper Amazon Basin: Influence on carbon accumulation

In order to study the impact of hydrological changes of the Amazon River on sedimentation process and organic matter (OM) accumulation, in an Amazonian floodplain lake during the Holocene, three sediment cores were collected from Quistococha Lake, Peru. The cores were dated with 14C accelerator mass spectrometry (AMS), radiographed, and described. Bulk density, granulometry, loss on ignition (LOI), total organic carbon (TOC) and total nitrogen (TN) contents were measured, and stable isotopic composition of TOC (δ13C) and TN (δ15N) and carbon accumulation rates were determined. Two distinctive sedimentary depositional phases were identified based on the lithology, granulometry and the geochemical characteristics of sedimentary OM. Between about 6100 and 4900calyears BP, the lake was under strong influence of the Amazon River. The river induced highest sedimentation rates (mean 0.5cmyr−1), a predominant deposition of relatively coarse particles (coarse silt), low LOI (1%), low contents of organic carbon (0.5%), low C/N ratios (~10), relatively low δ13C values (−26.0‰), very laminated sediments and high carbon accumulation rates between 14 and 29gCm−2yr−1. A gap in the record between about 4900 and 2600calyears BP corresponds to a sedimentation hiatus during the dry mid Holocene. This gap is probably due to an avulsion of the main stem that induced significant changes in the lacustrine sedimentation. After 2600calyears BP, sedimentation resumed but now the lake was isolated far from the Amazon influence. The resumption of sedimentation corresponds to wetter conditions during the late Holocene and an increase in water levels. The lake was now characterized by very low sedimentation rates (0.02cmyr−1), fine organic-rich sediments with high LOI (between 20 and 80%), TOC (between 10 and 40% of TOC), high C/N ratio (20), and lower δ13C and δ15N indicating a predominant deposition of C3-plant derived OM. Carbon accumulation in this sedimentary depositional phase was about 8gCm−2yr−1. These results, combined with those of studies from other isolated lakes (Cordeiro et al., 1997, 2008; Turcq et al., 2002) and from other floodplain lakes (Moreira et al., 2012; Moreira et al., 2013), point out that floodplain lakes with strong influences from the Amazon River act as important carbon sinks in the Amazon Basin despite their low carbon concentrations.

Distribution and speciation of phosphorus in sediments of Dongping Lake, North China

Dongping Lake is an important regulator for the Eastern Route of South-to-North Water Diversion Project in China, and the water quality assurance of it is of great importance. To investigate the distribution characteristics and burial process of phosphorus (P) in Dongping Lake as well as their relationship with regional economic development and human activities, 33 spatially distributed surface sediment samples and one lake sediment core were extracted from Dongping Lake. A harmonized procedure for the P forms in freshwater sediments developed by the European Programme, Standards, Measurements, and Testing was used in this paper. The results show that NaOH–P (P bound to Al, Fe, Mn oxides or hydroxides), HCl–P (Ca-bound P), inorganic phosphorus (IP), organic phosphorus (OP), and total phosphorus (TP) in the surface sediments show a strong spatial variability. The highest NaOH–P and OP concentrations were observed in the eastern and south-eastern region of the lake and decreased gradually away from the mouth area of Dawen River. We deduced that anthropogenic input via the Dawen River is the main contributor. The higher concentration of HCl–P occurred in the north-west region of the lake and increased in a gradient away from the mouth area of Dawen River, and this pattern of distribution could be related to grain-size effects and higher transport energies close to riverine inlets. Pollution reflected by phosphorus in the core sediments of Dongping Lake is well consistent with the economic development history of Dongping County. From the beginning of the 20th century to the middle 1970s, the concentrations of each P speciation did not vary largely and runoff of the Yellow River mainly contributed to the P accumulation in the sediment, which might reflect the background values of them in the lake in pre-industrial period. The stable Mz (mean grain size), low loss-on-ignition (LOI), and high sedimentary flux also support this. The rapid increase of NaOH–P and OP at 10–0 cm (especially 5–0 cm) indicates the enhancing anthropogenic eutrophication since the middle 1970s. The LOI peak period and a coarsening of particle size also support this interpretation. However, the decreasing of TP and HCl–P was attributed to the change in sediment supply. As due to construction of dams around the lake, runoff of the Dawen River mainly contributed to the P accumulation in the sediment during this period.

Application of Taguchi Method of Experimental Design for Chemical Process Optimisation: A Case Study

This case study is one of the distinctive researches which highlight the factor ratings and process optimisation through Taguchi design. This research has been conducted with a special reference to chemical plants in India. The objective of the present study was to establish optimal setting of four factors, viz., ( i) temperature (°C), ( ii) percentage of chemical (Borex), ( iii) pH and ( iv) time (Hrs). The present study was conducted to ensure optimisation of two response variables which were ( i) Loss-on-Ignition (LoI) (lower the better) and ( ii) chemical Borate content (higher the better). The unique 10 step methodology was adopted for arriving at optimal setting of four factors. Validation of optimal settings has been done by comparing actual values (means and signal to noise [S/N] ratios) for optimal setting with predicted values (means and S/N ratios). The results show that the Taguchi parameter design improves the response variables ( i) LoI (lower is better) and ( ii) chemical Borate content (higher is better), as the Taguchi L9 experiment resulted in lower LoI (less than 15 per cent) and high Borate percentage of chemical (greater than 45 per cent). The optimisation of response variables has ensured breakthrough improvement in the manufacturing process of Zinc Borate. The result underlines effectiveness of Taguchi optimisation technique.

Simulation studies on direct ash recycling and reburning technology in a tangentially fired 500 MW pulverized coal boiler

For thermal power generation companies, the use of refined ash (defined as having a loss on ignition (LOI) of less than 6%) has not only made it suitable to produce lightweight aggregate, but has also introduced significant cost benefits through recycling. However, the ash having a high unburned carbon content (greater than 6%) cannot be recycled and still must be disposed of underground and by landfill. In this paper, an ash recycling and reburning technology was examined to improve ash usage in 500MW pulverized coal (PC) boiler and simulation was performed to find the optimal conditions of ash supplying position and its amount that would not affect the boiler condition. Kinetic parameters for the reaction rate of ash were derived from a drop tube furnace (DTF) and adopted to accurately describe the characteristics of high LOI ash. In addition, the simulation results were then validated through real scale tests. Based on the simulation results, this paper suggest that the optimal supply condition for ash reburning is D burner sight window and 4ton/h (with 0.01% of total air) in terms of combustion stability and burnout because the upper burner location has more sufficient oxidizer in the particle pathway as well as maximized mixing effect between coal and oxidizer. The real scale tests evidently represent that ash reburning can be method to make low LOI ash.

Strength and heat evolution of concretes containing bagasse ash from thermal power plants in sugar industry

Two different sources of bagasse ash with low and high loss on ignition (LOI) were used in this experiment. Ordinary Portland cement was replaced by bagasse ash at the levels of 20%, 30%, and 40% by weight of binder. The effects of LOI, fineness, and cement replacement of bagasse ash on the compressive strength of concrete were investigated. Additionally, the heat evolution of concrete mixed with ground bagasse ash with low LOI was also measured. The results revealed that the compressive strength of concrete containing unground bagasse ash was much lower than that of control concrete (CON). Concrete mixed with low LOI ground bagasse ash had a slightly higher compressive strength than the mixture with high LOI ground bagasse ash. The replacement of cement by ground bagasse ash with low and high LOI at 30% and 20% by weight of binder, respectively, result in a compressive strength at 28days as high as that of CON concrete. Finally, the temperature of bagasse ash concretes could be reduced by 13–37% relative to CON concrete, depending on the level of cement replacement by ground bagasse ash with low LOI.

Coupling between the Changes in CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; Concentration and Sediment Biogeochemistry in Mudflat of Salinas de San Pedro, California, USA

We investigated the effects of elevated carbon dioxide (CO2) on biogeochemistry of marsh sediment including speciation of selected heavy metals in Salinas de San Pedro mudflat in California. The Salinas de San Pedro mudflat has higher carbon (C) content than the vast majority of fully-vegetated salt marshes even with the higher tidal action in the mudflat. Sources for CO2 were identified as atmospheric CO2 as well as due to local fault degassing process. We measured carbon dioxide, methane, total organic carbon, dissolved oxygen, salinity, and heavy metal concentration in various salt marsh locations. Overall, our results showed that CO2 concentration ranging from 418.7 to 436.9 (ppm), which are slightly different in various chambers but are in good agreement with some heavy metal concentrations values in mudflat at or around the same location. The selected metal concentration values (ppm) ranging from 0.003 - 0.011 (As); 0.001 - 0.005 (Cd); 0.04 - 0.02 (Cr); 0.13 - 0.38 (Cu); 0.11 - 0.38 (Pb); 0.0009 - 0.020 (Se); and 0.188 - 0.321 (Zn). The low dissolved oxygen (ppm) in the pore water sediment indicated suboxic environment. Additionally, CO2 (ppm) and loss on ignition (LOI) (%) correlated inversely; the higher CO2 content, the lower was the LOI (%); that is to say the excess CO2 causes higher rates of decomposition and therefore it leads to lower LOI (%) on the mudflat surface. It appears that the elevated CO2 makes changes in salt marsh pore water chemistry for instance the free ionic metal (Cu 2+ , Pb 2+ , etc.) speciation is one of the most reactive form because simply assimilated by the non-decayed or alive organisms in sediment of salt marsh and/or in water. This means that CO2 not only is a sign of improvement in plant productivity, but also activates microbial decomposition through increases in dissolved organic carbon availability. CO2 also increases acidification processes such as anaerobic degradation of microorganism and oxidation of reduced components. The heavy metal concentrations in sediment samples were slightly higher in suboxic layer, yet it appears that salt marsh sediments in Salinas de San Pedro act like a sink for nutrient and carbon by maximizing carbon sequestration.

Thermochemical Pretreatments for Agricultural Residue Ash Production for Concrete

Agricultural residue ash is known to be a very reactive source of supplementary cementitious material (SCM) for use in concrete. The influence of thermochemical pretreatments on the reactivity of agricultural residue ash (ARA) was studied for its use as an SCM. It was shown that pretreatments are effective in the partial removal of alkali metals and other impurities out of both wheat straw and rice straw, leading to ARA with lower loss on ignition (LOI), higher internal surface area, and higher amorphous silica content than unpretreated ARA. It was shown that the alkali content correlated with the LOI and amorphous silica content of the ash. When used at a cement replacement rate of 20% by mass, pretreated ARA accelerated the hydration of cement paste samples, whereas unpretreated ARA retarded the cement hydration. Pretreatments were found to increase ARA reactivity, as measured by calcium hydroxide content reduction with time. ARA increased the compressive strength of mortar samples by 25% when used as 20% replacement of cement in the samples. The calcium hydroxide content of paste samples and mortar compressive strength was found to correlate to the amorphous silica content of the ash.

Leaching Behavior of Hazardous Heavy Metals from Lime Fly Ash Cements

AbstractThe heavy metals leaching potential of lime fly ash cements was evaluated for one low loss on ignition (LLOI) and one high loss on ignition ash (HLOI). Three different test methods were used: (1) a standard shaken (stirred) extraction test, (2) a modified shaken extraction test, and (3) a modified EP-TOX test. Testing was conducted on the as-receive ashes and lime fly ash samples cured for 0, 7, 28, and 84 days at 40°C. The results show that such curing time sequences can be used to study the rate of sequestration by the hydration product relative to the rate of leaching from the ash. X-ray diffraction (XRD) was used to characterize the reaction products of cured lime fly ash cements and isothermal calorimetry to study the rates of hydration at 25 and 40°C. The leaching tests results indicate that leachability of some heavy metals is greatly dependent on leachant pH and likewise, the test method used. Furthermore, formation of hydration products throughout the leaching does appear to partially seq...