Microstructural characterization of high-performance steel fiber reinforced geopolymer concrete

Due to growing environmental and economic concerns associated with conventional building materials, research interest gravitates towards the development of novel environmentally friendly materials as alternatives to conventional Portland cement concrete. Geopolymer concrete is a class of novel advanced and sustainable structural materials that hold promise for the future of infrastructure. Its synthesis comprises industrial by-products (fly ash and slag among others) in the role of binder and thus reduces the demand in Portland cement leading to a significant carbon footprint reduction. In the present study a High-Performance Fiber Reinforced Geopolymer Concrete (HPFRGC) is synthesized from first principles and is subsequently characterized, with particular emphasis on its microstructural and mineralogical properties. The study explores the linkage between the microstructure and mineralogy of the precursors, and the properties of the final product. Both fresh and hardened HPFRGC are studied. Experimental results illustrate the correlation between microstructure, mineralogy and final mechanical properties can be used as an indicator of suitability of industrial by-products for geopolymer precursors. The effect of these choices on stability and physical properties of the material is also explored in the study

Characterization of hard scale formed in the kraft mill green liquor processing equipment

Scaling, the formation of hard deposits, in green liquor handling systems is a persistent problem in many kraft pulp mills. Scaling is commonly believed to be a result of pirssonite (Na 2 CO 3 ·CaCO 3 ·2H 2 O) formation when the green liquor total titrateable alkali (TTA) is high. In this study, we characterized 12 scale samples obtained from 10 kraft pulp mills using various analytical methods, including TGA/DSC (thermogravimetric analysis/ differential scanning calorimetry), XRF (X-ray fluorescence spectrometry), XRD (X-ray diffraction spectrometry), SEM (scanning electron microscopy), and EMPA (electron microprobe analyzer). The analysis identified only four of these samples as pirssonite; the remaining consisted mostly of calcite (CaCO 3 ). The reason for the predominant presence of calcite in the majority of the scale samples is not known. It may be a result of selective dissolution of sodium carbonate (Na 2 CO 3 ) from the pirssonite scale during the time when the green liquor total TTA was low, leaving the insoluble CaCO 3 behind.This work was conducted as part of the research program on Increasing Energy and Chemical Recovery Efficiency in the Kraft Process. The program is jointly supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and a consortium of the following companies: An - dritz, Babcock & Wilcox, Boise, Carter Holt Harvey, Celulose Nipo-Brasileira, Clyde-Bergemann, DMI Peace River Pulp, Fab - ria, International Paper, Irving Pulp & Paper, Metso Power, MeadWestvaco, StoraEnso Research, and Tembec

Effects of chloride, potassium, and sulfate on the causticizing reaction in the kraft recovery process

We studied the effects of chloride (Cl), potassium ( k), and sulfate (S o 4 ) on the equilibrium of the causticizing reaction over a wide range of causticizing conditions, using oli , an advanced thermodynamic program for equilibrium calculations in aqueous solutions of ionic salts. Cl, k, and S o 4 were shown to have little or no effect on the causticizing equilibrium. Under a given causticizing condition, coastal mills, due to their much higher naCl concentration, are predicted to have a causticizing efficiency 1%–2% lower than that of inland mills.This work was part of the research program on Increasing Energy and Chemical Recovery Efficiency in the Kraft Pro - cess. The program is jointly supported by the Natural Scienc - es and Engineering Research Council of Canada (NSERC) and a consortium of the following companies: Abitibi-Bowater, Alstom Power, Andritz, Aracruz Celulose, Babcock & Wilcox, Boise, Celulose Nipo-Brasileira, Carter Holt Harvey, Clyde- Bergemann, Diamond Power International, Domtar, DMI Peace River Pulp, Georgia Pacific, International Paper, Irving Pulp & Paper, Metso Power, MeadWestvaco, Stora Enso Re - search, Tembec, and Votorantim Celulose e Papel

Ferric Sulfate Leaching of Pyrrhotite Tailings between 30 to 55 °C

Mine tailings present major environmental issues in the mining industry. However due to the depletion of high-grade sulfide ores for metal recovery, tailings could also be a potential resource for certain valuable metals. The present study investigates the potential to recover nickel from pyrrhotite tailings. Leaching tests were performed in acidic ferric sulfate media with 0.14 wt % solids to keep the ferric concentration essentially constant. The temperature was varied between 30 and 55 °C, and the ferric concentration was in a range 0.02–0.3 M. The results showed that both temperature and ferric sulfate concentration had significant effects on the nickel extraction kinetics. The shrinking core model (SCM) was applied to the nickel extraction data. The rate controlling step was found to be product layer diffusion. The Arrhenius plot yielded an activation energy of Ea = 62.12 kJ/mol based on apparent reaction rates obtained by the SCM. The reaction order with respect to ferric ion was found to be 1 at the high concentration range. SEM images of partially leached tailings confirmed the presence of elemental sulfur around the pyrrhotite particles, which was responsible for the observed non-linear leaching kinetics (diffusion control)

Ferric Sulfate Leaching of Pyrrhotite Tailings between 30 to 55 °C

Mine tailings present major environmental issues in the mining industry. However due to the depletion of high-grade sulfide ores for metal recovery, tailings could also be a potential resource for certain valuable metals. The present study investigates the potential to recover nickel from pyrrhotite tailings. Leaching tests were performed in acidic ferric sulfate media with 0.14 wt % solids to keep the ferric concentration essentially constant. The temperature was varied between 30 and 55 °C, and the ferric concentration was in a range 0.02–0.3 M. The results showed that both temperature and ferric sulfate concentration had significant effects on the nickel extraction kinetics. The shrinking core model (SCM) was applied to the nickel extraction data. The rate controlling step was found to be product layer diffusion. The Arrhenius plot yielded an activation energy of Ea = 62.12 kJ/mol based on apparent reaction rates obtained by the SCM. The reaction order with respect to ferric ion was found to be 1 at the high concentration range. SEM images of partially leached tailings confirmed the presence of elemental sulfur around the pyrrhotite particles, which was responsible for the observed non-linear leaching kinetics (diffusion control)