Search Results (6)

The efficacy of spray dry systems compared to wet flue gas desulphurisation (FGD) units depends on applying a highly reactive scrubbing reagent. This study assessed sodium-based compounds derived from natural sources and waste by-products as potential agents for treating sulphur dioxide (SO₂). Sodium carbonate (Na₂CO₃) and sodium bicarbonate (NaHCO₃) were acquired from mineral deposits, whereas the black ash waste (Na₂CO₃·NaHCO₃) was obtained from the pulp and paper sector. The sorbents introduced in slurry form were subject to SO₂ absorption conditions in a lab-scale spray dryer, including an inlet gas phase temperature of 120–180 °C, flue gas flow rate of 21–34 m³/h, and sodium to sulphur normalised stoichiometric ratio (Na:S) of 0.25–1. The comparative performance was evaluated using the metric of %SO₂ ($\%{\eta }_{DeS{O}_X}$) removal efficiency. The results showed that NaHCO₃ had the highest overall result, with a removal efficiency of 62% at saturation. Black ash was the second best-performing reagent, with a 56% removal efficiency, while Na₂CO₃ had the lowest efficiency (53%). The maximum degree of SO₂ reduction achieved using NaHCO₃ under specific operating parameters was at an NSR of 0.875 (69%), a reaction temperature of 120 °C (73%), and a gas inlet flow rate of 34 m³/h. In conclusion, the sodium reagents produced significant SO₂ neutralisation, exceeding 50% in their unprocessed state, which is within acceptable limits in small- to medium-sized coal-fired power plants considering retrofitting pollution control systems. Full article

It is thought that geopolymers are easy to carbonate, especially when they are cured in ambient temperatures. Matrix gel’s composition and microstructure, and new products of geopolymers (GPs) after carbonation were investigated in this study on the basis of XRD and SEM-EDS measurements and ternary diagram analysis, which were prepared from low-lime fly ash (FA) and ground granulated blast-furnace slag (GGBS) alone or a blend, as a precursor. The specimens were hardened in a 20 °C environment with alkali activator solution (S/N = 1.1 in mole), followed by storage under sealing or accelerated carbonation. XRD patterns show that carbonation products were nahcolite for the sole FA-based GP and calcite for the GPs using GGBS alone or as a blend. The SEM images of carbonated samples show that there were cube-shaped calcite and small calcite particles in the GGBS-based GP, but hail-like particles in the FA/GGBS blend-based GP. The hail-like particles were complexes of calcite and C-A-S-H gels determined by ternary diagram analysis, and were found to plug the top of the pores of the spongy C-A-S-H gels. We also confirmed that combined ternary diagram analysis of S-(C + M + N)-A and A-(C + M)-N are very effective in determining the gel type of a geopolymer, as well as the products and compositional changes after carbonation, in which oxide components of gels are determined by SEM-EDS. In the former diagram, C-A-S-H gels were plotted linearly along the (C + M + N)-albite (Ab) join, while N-A-S-H gels showed a scattered distribution. In the latter diagram, the plots for N-A-S-H and C-A-S-H gels are distributed in different zones. N = Na₂O, C = CaO, M = MgO, A = Al₂O₃, S = SiO₂, H = H₂O. Full article

The present work investigates the production of sodium bicarbonate in combination with the co-utilization of saline brine and carbon capture, utilization, and sequestration (CCUS). The use of ammonia in the traditional Solvay process could be eliminated by using a modified Solvay process. This study compared the modification with the addition of three buffering additives: Ca(OH)₂, KOH, and NH₄HCO₃. The effectiveness of these processes, using two qualities of saline brine (desalination and aquifer), is compared based on the purity of the produced NaHCO₃. It was found that the use of Ca(OH)₂ did not produce high-purity NaHCO₃, while NH₄HCO₃ and KOH performed better. Desalination brine utilization with NH₄HCO₃ resulted in the production of high-purity NaHCO₃, while the second most suitable method involved the use of KOH, and the main co-product formed was Na₂CO₃. Geochemical modeling is performed in order to have insights into the carbonation (in the reactor) and precipitation (in the oven) behavior of the reactions. It predicted the precipitation of mineral phases well, though kinetics might hinder some saturated solids to dissolve first. The present study shows that accurate characterization is critical to accurately assess the success of modified Solvay processes. The use of QXRD and SEM analyses, complemented with geochemical modeling, helped to better understand the processes and the formation of NaHCO₃. Further investigations on diverse brines could provide for their better utilization by the geological carbon sequestration and water desalination industries that produce them. Full article

Many industrial processes make use of sodium because sodium is the fifth most abundant metal and the seventh most abundant element on Earth. Consequently, there are many sodium-containing industrial wastes that could potentially be used for carbon capture, paving the way towards a circular and biobased economy. For example, a common industrial chemical is NaOH, which is found in black liquor, a by-product of the paper and pulp industry. Nonetheless, the literature available on CO₂ absorption capacity of aqueous NaOH is scarce for making a fair comparison with sodium-containing waste. Therefore, to fill this gap and set the foundation for future research on carbon capture, the CO₂ absorption capacity of NaOH solutions in a concentration range of 1–8 w/w% was evaluated, a wider range compared with currently available data. The data set presented here enables evaluating the performance of sodium-based wastes, which are complex mixtures and might contain other compounds that enhance or worsen their carbon capture capacity. We designed a customized reactor using a 3D-printer to facilitate in-line measurements and proper mixing between phases without the energy of stirring. The mixing performance was confirmed by computational fluid dynamics simulations. The CO₂ absorption capacity was measured via weight analysis and the progress of carbonation using a pH meter and an FTIR probe in-line. At 5 w/w% NaOH and higher, the reaction resulted in precipitation. The solids were analyzed with X-ray diffraction and scanning electron microscope, and nahcolite and natrite were identified. With our setup, we achieved absorption capacities in the range of 9.5 to 78.9 g CO₂/L for 1 w/w% and 8 w/w% of NaOH, respectively. The results are in fair agreement with previously reported literature, suggesting that non-forced mixing reactors function for carbon capture without the need of stirring equipment and a possible lower energy consumption. Full article

The article presents the studies on understanding the chemical evolution of Maloye Yarovoe lake that is located in the semi-arid landscape of and represent the most widespread chemical type of saline lake (Cl-Na) on the territory of Kulunda steppe (south of Western Siberia). The lake has gone through several changes in its state which are well represented in its sediments: section 1 (4.52–4.97 m) represents the subbase; section 2 (3.0–4.57 m) corresponds to a “shallow lake” stage and contains two sublayers; section 3 (0–2.25 m) illustrates an increase in erosion of the shoreline and corresponds to a “deep lake” stage. The extrapolation of radiocarbon dates suggests that the most significant changes in the state of the lake occurred at about 6.5–7.1 ka BP (transition from a small lake to a large one with intensified coastal erosion) and at about 5.69 and 3.5 ka BP (increase in the organic component). The results of sequential extraction of elements correspond to chemical changes occurred in a certain time of the lake state by changing in their distribution level and fraction type along the core. The results of lake water evaporation and organic matter degradation modelling performed in Phreeqc for oxic and anoxic condition showed the following stages of chemical divides could be expected in case of further lakes desiccation: Halite—Epsomite—Bischofite/Carnalite with possibility of Nahcolite precipitation in carbonate enriched periods (summer and autumn periods of organic matter degradation). Water–rock interaction processes in combination with biogeochemical reactions affect drastically not only the migration features of elements in water and sediments, but also the type of mineral crystallization in lake sediments. Full article

The Vuoriyarvi Devonian alkaline–ultramafic complex (northwest Russia) contains magnesiocarbonatites with rare earth mineralization localized in the Petyayan-Vara area. High concentrations of rare earth elements are found in two types of these rocks: (a) ancylite-dominant magnesiocarbonatites with ancylite–baryte–strontianite–calcite–quartz (±late Ca–Fe–Mg carbonates) ore assemblage, i.e., “ancylite ores”; (b) breccias of magnesiocarbonatites with a quartz–bastnäsite matrix (±late Ca–Fe–Mg carbonates), i.e., “bastnäsite ores.” We studied fluid inclusions in quartz and late-stage Ca–Fe–Mg carbonates from these ore assemblages. Fluid inclusion data show that ore-related mineralization was formed in several stages. We propose the following TX evolution scheme for ore-related processes: (1) the formation of ancylite ores began under the influence of highly concentrated (>50 wt.%) sulphate fluids (with thenardite and anhydrite predominant in the daughter phases of inclusions) at a temperature above300–350 °C; (2) the completion of the formation of ancylite ores and their auto-metasomatic alteration occurred under the influence of concentrated (40–45 wt.%) carbonate fluids (shortite and synchysite–Ce in fluid inclusions) at a temperature above 250–275 °C; (3) bastnäsite ores deposited from low-concentrated (20–30 wt.%) hydrocarbonate–chloride fluids (halite, nahcolite, and/or gaylussite in fluid inclusions) at a temperature of 190–250 °C or higher. Later hydrothermal mineralization was related to the low-concentration hydrocarbonate–chloride fluids (<15 wt.% NaCl-equ.) at 150–200 °C. The presented data show the specific features of the mineral and fluid evolution of ore-related late-stage hydrothermal rare earth element (REE) mineralization of the Vuoriyarvi alkaline–ultramafic complex. Full article