Retention Of Alkali Research Articles

Influence of mixing protocols on flow retention of one-part alkali activated slag systems

Poor workability and rapid flowability loss are among several challenges hindering the wider acceptance of alkali-activated slag (AAS) (i.e. shrinkage, efflorescence). Several attempts were made to solve this issue, focusing more on selected ingredients, proportions, type and dosage of admixtures, and addition sequence. This study shifted the focus to mixing protocol, highlighting its potential and effects on AAS flow retention considering mixing duration, sequence, and relaxation time. Various one-part AAS mixtures activated by 6 %, 8 %, and 10 % sodium metasilicate were tested. Mixing protocols were applied for 10–90 min, mixing with and without relaxation time. Mini-slump, flowability-loss rate, setting time, the heat of hydration, rheological properties, and compressive strength were evaluated. Changes in hydration products were also examined by XRD, FTIR and TGA. Pearson correlation coefficient and ANOVA were applied to identify the dominant factors. Results reveal the dependency of the optimum mixing protocol on the used activator dosage. A long mixing period with r intervals was more effective for high activator dosages due to the continuous breakdown of formed hydration products' links. Modifying the mixing protocol did not alter the amount of formed hydration products, regardless of the activator dosage. These findings pave the way to understanding the role played by the mixing protocol in mineral hydration for wider in-situ implementation of AAS and the flourishing potential of the ready-mix AAS market.

Quantifying metasomatic high-field-strength and rare-earth element transport from alkaline magmas

Abstract Alkaline igneous rocks host many global high-field-strength element (HFSE) and rare-earth element (REE) deposits. While HFSEs are commonly assumed to be immobile in hydrothermal systems, transport by late-stage hydrothermal fluids associated with alkaline magmas is reported. However, the magnitude of the flux and the conditions are poorly constrained and yet essential to understanding the formation of REE-HFSE ores. We examined the alteration of country rocks (“fenitization”) accompanying the emplacement of a syenite magma at Illerfissalik in Greenland, through analysis of changes in rock chemistry, mineralogy, and texture. Our novel geochemical maps show a 400-m-wide intrusion aureole, within which we observed typically tenfold increases in the concentrations of many elements, including HFSEs. Textures suggest both pervasive and structurally hosted fluid flow, with initial reaction occurring with the protolith's quartz cement, leading to increased permeability and enhancing chemical interaction with a mixed Ca-K-Na fenitizing fluid. We estimated the HFSE masses transferred from the syenite to the fenite by this fluid and found ~43 Mt of REEs were mobilized (~12% of the syenite-fenite system total rare-earth-oxide [TREO] budget), a mass comparable to the tonnages of some of the world's largest HFSE resources. We argue that fenite can yield crucial information about the tipping points in magma evolution because retention and/or loss of volatile-bonded alkali and HFSEs are key factors in the development of magmatic zirconosilicate-hosted HFSE ores (e.g., Kringlerne, at Ilímaussaq), or the formation of the syenite-hosted Nb-Ta-REE (Motzfeldt-type) roof-zone deposits.

Kinetics of the release of elemental precursors of syngas and syngas contaminants during devolatilization of switchgrass

In this study, the results from laboratory measurements of the devolatilization kinetics of switchgrass in a rapidly heated fixed bed reactor flushed with argon and operated at constant temperatures between 600 and 800°C was reported. Results indicate that switchgrass decomposes in two sequential stages during pyrolysis: stage I involves the evaporation and devolatilization of water and extractives and stage II involves that of hemicellulose, cellulose, and lignin. The estimated global activation energy for stage II increased from 52.80 to 59.39kJ/mol as the reactor temperature was increased from 600 to 800°C. The maximum conversion of carbon, hydrogen, oxygen, sulfur, and nitrogen ranged from 0.68 to 0.70, 0.90 to 0.95, 0.88 to 0.91, 0.70 to 0.80, and 0.55 to 0.66, respectively. The retention of alkali and alkaline earth metal (AAEM) species in the solid char after complete pyrolysis was significantly higher than in the original feed, indicating the importance of AAEM species in subsequent char processing.

Effects of gasification temperature and atmosphere on char structural evolution and AAEM retention during the gasification of Loy Yang brown coal

This study aims to investigate the influence of gasification temperature on the evolution of char structure and the retention of alkali and alkaline earth metallic (AAEM) species for a Victorian brown coal. The experiments were carried out at 800, 850 and 900°C in pure CO2, 15% H2O balanced with Ar and 15% H2O balanced with CO2 in a one-stage fluidised-bed/fixed-bed reactor. FT-Raman spectroscopy was used to characterise the structural features of the chars obtained at varying conversion levels during gasification. The concentrations of AAEM species in the chars left after gasification were quantified with inductively coupled plasma – optical emission spectroscopy. The specific char-O2 reactivity of the gasified char was measured in a thermogravimetric analyser. The results show that the CO2 and H2O partly compete for the active sites on the char. The increasing total Raman area caused by the formation of O-containing structures in char does not appear to be the only factor determining the char gasification rate in H2O-containing atmospheres. With increasing temperature, CO2 plays an increasingly more important role in the char evolution and subsequently influences the AAEM retention in char from the gas mixture. The gasification temperature does not change the individual reaction pathway for char-CO2 or char-H2O reaction within temperature range investigated.

Behavior of Alkali Metals and Ash in a Low-Temperature Circulating Fluidized Bed (LTCFB) Gasifier

A low-temperature circulating fluidized bed system (LTCFB) gasifier allows for pyrolysis and gasification to occur at low temperatures, thereby improving the retention of alkali and other inorganic elements within the system and minimizing the amount of ash species in the product gas. In addition, the low reactor temperature ensures that high-alkali biomass fuels can be used without risk of bed defluidization. This paper presents the first investigation of the fate of alkali metals and ash in low-temperature gasifiers. Measurements on bed material and product gas dust samples were made on a 100 kW and a 6 MW LTCFB gasifier. Of the total fuel ash entering the system, the largest fraction (40–50%) was retained in the secondary cyclone bottoms, while a lower amount (8–10%) was released as dust in the exit gas. Most of the alkali and alkaline earth metals were retained in the solid ash, along with Si and a minor fraction of Cl. Most Cl and S were released in gaseous form, with chlorine partly as methyl chlori...

Influences of heating rate during coal char preparation and AAEMs on volatile–char interaction with different sources of biomass volatile

Volatile–char interaction is important for the operation of co-gasification of coal and biomass. Biomass generally produces large amount of volatiles while char is mainly produced from coal. Hence, in this study, the interaction between coal char and volatiles from biomass samples (xylan, cellulose and rice straw) was examined using a rapid-heating thermobalance reactor. Three types of coal char, consisting of slow pyrolyzed-coal char (Ex-char), fast pyrolyzed-coal char (In-char), and acid washed-coal char (Ac-char), were employed to reveal influences of heating rate during char preparation and retention of alkali and alkaline earth metallic (AAEM) species on char surface. The steam gasification rates of all coal chars in both cases with and without volatile contacting were investigated from the gas evolution rate and remaining char analyses. The results indicate that the steam gasification rates of Ex-char and In-char were significantly diminished by the volatiles derived from all sources, especially rice straw. However, in the case of Ac-char, the reduction of steam gasification rate was less important. Moreover, the Ex-char exhibited the catalyst for the decomposition of biomass volatiles, resulting in the increase in gas production rate. Porous structure and the AAEM over char play crucial roles on the volatile–char interaction.

Ion chromatographic investigation of the ion-exchange properties of microdisperse sintered nanodiamonds

The possibility of using sintered diamonds as a stationary phase in ion chromatography has been evaluated. Bare sintered synthetic nanodiamonds demonstrated the properties of a weak cation-exchanger. The observed ion-exchange selectivity is similar to carboxylic type cation-exchangers. The regularities of retention of alkali, alkaline-earth and transition metal ions on a column packed with sintered nanodiamonds in dilute nitric acid were studied and the occurrence of chelating properties was noted. For the first time chromatographic separations of model mixtures of cations on diamonds have been obtained.

Non-trivial temperature effects on the cation exchange chromatography and chelation ion chromatography of metal ions.

The effect of column temperature upon the retention of metal ions on sulfonated and mono-, di-, and amino-carboxylated cation exchange columns has been investigated. The retention of alkali, alkaline earth and transition metal ions on each of the above types of cation exchanger was studied over the temperature range 19-65 degrees C. A major difference between the behaviour of mono- and divalent metal ions was shown on each of the above stationary phases, with the monovalent alkali metals exhibiting clearly exothermic behaviour (a decrease in retention with increased temperature) under acidic eluent conditions and an apparent relationship between retention factor and the magnitude of the temperature effect. The effect of temperature upon alkaline earth metal ions was less defined, although strongly endothermic behaviour (increase in retention with temperature) could be seen on all stationary phases through correct choice of eluent. The transition metal ions studied showed endothermic behaviour on all four stationary phases, with the sulfonated column unexpectedly showing the largest increases in retention. The above behaviour can be partially explained through the dominance of the type of solute-stationary phase interaction governing retention. In several of the above columns, both ion-exchange and surface complexation interactions can occur, with the effects of temperature indicating which process dominates under specific eluent conditions.

Retention of alkali, alkaline earth and transition metals on an itaconic acid cation-exchange column: Eluent pH, ionic strength and temperature effects upon selectivity

The unusual selectivity of a methylene succinic (itaconic) acid modified polymeric column was investigated for the separation of alkali, alkaline earth, transition and heavy metals employing non-chelating inorganic eluents. The retention of selected metal ions on the column was investigated with simple HNO 3 eluents and eluents prepared from KNO 3 and KCl salts of varying pH (adjusted using HNO 3). From these studies both the effect of eluent ionic strength and pH upon retention was evaluated for the itaconic acid stationary phase. The results obtained showed that despite slow exchange kinetics causing poor efficiencies, acceptable baseline separations of selected alkaline earth and transitions could be obtained under optimum conditions (the baseline separation of Mg(II), Ca(II), Mn(II), Cd(II), Zn(II) and Co(II) was possible using a 15 m M KNO 3–5 m M KCl eluent at pH 3.50 in under 25 min). The use of an simple ionic strength step gradient was shown that facilitated the addition of Pb(II) to the above group of metal ions. An investigation into the effect of temperature upon peak efficiency and retention showed increased column temperature could be used to improve the resolution of closely eluting metal ions such as Ca(II) and Sr(II) and Ca(II) and Mn(II).

Ion-exchange properties of hypercrosslinked polystyrene impregnated with methyl orange

A novel bipolar stationary phase (HCPS–MO) was prepared by impregnation of hypercrosslinked polystyrene (HCPS) with methyl orange (MO; 4-dimethylamino-4′-sulfoazobenzene) and its ion-exchange properties were studied. Simultaneous separation of cations and anions on HCPS–MO is possible, although it behaves preferentially as a cation-exchanger. Unusual selectivity of HCPS-MO for alkali and alkaline-earth metal cations: Na +<Li +∼K +<Rb +<NH 4 +<Cs + and Mg 2+<Sr 2+<Ca 2+<Ba 2+ was observed. The effect of temperature on retention of alkali and alkaline-earth metal cations was studied. Separation of Na +, K +, Rb +, NH 4 +, Cs +, Mg 2+ and Ca 2+ on HCPS–MO with diluted cerium(III) nitrate solution as an eluent in single run is presented.

Effect of temperature on retention of alkali and alkaline-earth metal ions on some aminocarboxylic acid functionalised silica based ion exchangers

The temperature effect on retention of alkali and alkaline-earth cations on three different carboxylic acid cation exchangers was investigated. The silica-bonded 2,6-diaminohexanoic (lysine), 2-aminoglutaric (glutamic acid) and iminodiacetic acids were used as cation exchangers and compared with bare silica. Perchloric acid was used as the eluent in all experiments. The dependence of retention (log k′) from reciprocal temperature (1/ T) is linear for all cations in the case of silica-bound lysine and glutamic acid. An abnormal parabolic dependence of log k′ vs. 1/ T was observed for iminodiacetic acid functionalized silica. The possible impact of complexation between functional groups of cation exchangers and retained cations and the effect of two carboxylic groups in a single ion-exchange site on retention are discussed. The calculated values of heats of adsorption are in the range 4–9 kJ/mol.

Liquid Chromatographic Retention of Alkali and Alkaline-Earth Metal Cations on Dynamically Coated Cryptand Stationary Phases

Liquid Chromatographic Retention of Alkali and Alkaline-Earth Metal Cations on Dynamically Coated Cryptand Stationary Phases

A STUDY OF THE SEVERAL FACTORS OF ACID EXCRETION IN NEPHRITIS

Recently acidosis in nephritis has attracted much attention among clinical investigators and many articles dealing with the subject have appeared. Considerable evidence has accumulated which leaves little doubt that in certain of the more severe types of chronic renal disease there occur mild grades of acidosis. The facts revealed in various researches which confirm the frequently observed clinical picture of acidosis in nephritis include lowered alveolar carbon dioxid tension, the decreased affinity of hemoglobin for oxygen, reduced alkalinity of the blood, increased intensity of urinary acidity (hydrogen ion concentration) and the retention of alkali by the body in cases in which the kidney is capable of the rapid elimination of an excess of alkali.¹ The purpose of the present communication is to present certain data on the acid excretion in nephritis which we have collected over a period of three years during our investigation of the process of acid