No abstract

Biomass and coal have different physicochemical properties and thermal behavior. During the co-combustion of coal-biomass mixtures, their thermal behavior varies according to the percentage of each fuel in the mixture. Thereby, this research aims to characterize the thermal behavior of mixtures of coal, sugarcane bagasse, and biomass sorghum bagasse as biomass in simulated combustion (O 2 /N 2) and oxy-fuel combustion (O 2 /CO 2) environments. Experiments have been performed in duplicate on a thermogravimetric analyzer at heating rate of 10 C/min. A uniform granulometry was considered for all materials (63 mm) in order to ensure a homogeneous mixture. Four biomass percentages in the mixture (10, 25, 50 and 75%) have been studied. Based on thermogravimetric (TG) and thermogravimetric (DTG) analyses, parameters such as combustion index, synergism, and activation energy have been determined, as well as the combustion environment influence on these parameters. The results indicate that, although sugarcane bagasse has the lowest activation energy, the thermal behavior of both types of biomass is similar. Thus, biomass sorghum bagasse can be used as an alternative biomass to supply the power required during sugarcane off-season. For both mixtures, optimal results were obtained at 25% of biomass. By analyzing the environment influence on combustion behavior, the results indicate that when N 2 is replaced with CO 2 , it is observed an increase in reaction reactivity, a higher oxidation rate of materials and an improvement in evaluated parameters.

This study investigated the leaching process in order to maximize Mg and Fe extraction and to produce amorphous silica (SiO 2 ) with high purity. For this, a mining waste identified as S-GO was employed; which is a serpentinite rock with high lizardite 1T and native brucite contents. A Taguchi Experiment Design was used in order to assess the parameters that influence the leaching process such as: granulometry, hydrochloric acid concentration (HCl), leaching temperature, and mass/volume ratio. Furthermore, thermogravimetric analysis (TGA) was done to understand the interrelation between the mineral structure and leaching performance. Results show that lizardite 1T-bearing serpentinite presents a low content of tetrahedral Al 3þ and high octahedral Fe 3þ contents on S-GO. Native brucite delayed the formation of a hydrated silica layer and improved dissolution of serpentines. For this, Mg and Fe extractions are efficient, reaching 88 ± 2% of Mg and Fe extracted during the first 30 min of reaction, under mild process conditions: stoichiometric mass/volume ratio, 1M HCl concentration, pressure of 1 bar, temperature of 100 C, and 300 mm particle size. On the other hand, an excess of acid improves Mg and Fe extraction by only 10 ± 5% for S-GO. Such characteristics reduce energetic penalties and costs involved on indirect mineral carbonation processes by the pH swing method.

pH-swing mineral carbonation is kinetically favorable and requires a short reaction time. It must also obtain a high extraction rate for reactive elements in the leaching process. The main purpose of this study is to investigate the behavior of different serpentinite rocks in the leaching processes; the reactivity of Brazilian serpentinite rocks (such as: S-GO and S-MG) is analyzed based on physicochemical properties in order to understand their relationship to leaching efficiency. Surface area-to-volume ratio (S BET /V p) and metals-to-silicon ratio (Σ(Mg, Ca)/Si) were used to measure reactivity. Leaching was carried out to determine Mg and Fe extraction. Reaction conditions for both serpentinite rocks were: 355-250 μm particle size, 4 M HCl concentration, 100°C, and 2 h of reaction time. Characterization results show that both serpentinite rocks (S-GO and S-MG) have high magnesium (Mg) content. S BET /V p was 36 for S-GO and 29 for S-MG, while Σ(Mg, Ca)/Si was 2.64 for S-GO and 1.20 for S-MG. These results suggest that S-GO is approximately 50% more reactive than S-MG, and that S-MG is limited by low accessible surface (S BET /V p) and the high mineralogical complexity (Σ(Mg, Ca)/Si). Leaching results confirmed the reactivity; Mg and Fe extraction from S-GO was 94 ± 1%. However, results for S-MG were 34% for Mg and 60% for Fe. In order to increase the reactivity of S-MG, particle size was reduced to 75-63 μm. Even though S-MG was mechanically activated, Mg and Fe extraction has not increased significantly.

In pH-swing mineral carbonation, several acid/base systems has been investigated. Currently the main acid/base systems employed are HCl/NaOH and NH 4 HSO 4 /NH 4 OH. However, the use of a HCl/NH 4 OH system was not yet elucidated. This study proposes to evaluate the feasibility of a pH-swing mineral carbonation based on HCl/ NH 4 OH system at atmospheric pressure and moderate temperatures using mining waste from asbestos production from Goiás State, Brazil (S-GO) for two conditions (i.e. stoichiometric conditions (T2E) and acid excess (T2)). Results indicated that the Fe 3+ content in S-GO acted as a catalyst, due to FeCl 3 hydrolysis in aqueous solutions. Thus, high Mg and Fe extraction efficiency (95 ± 2%), were achieved in the leaching stage for both conditions. The S 1 solid residue was mainly SiO 2 with 90 ± 1% purity content. In the purification stage 91.7 ± 1.9% of Fe t were removed, however, a loss of Mg of 13.6 ± 2.3% was also detected. On the carbonation stage, high purity hydromagnesite was formed in T2E; this stage had a 85% efficiency, thus, 36.7% of CO 2 was fixed. On T2, excess H 2 O and CO 2 promoted dypingite formation and reduced hydromagnesite formation. After carbonation, the formation of crystals was observed in the NH 4 Cl aqueous solution at 25°C, indicating NH 4 Cl supersaturation. The results of mass balance indicate that 4 ton of mineral waste will be employed for each ton of captured CO 2 , as well as 2.6 ton of HCl, and 4.5 ton of NH 4 OH. However, 1.7 ton of SiO 2 , 0.55 ton of iron oxides, and 2.7 ton of hydromagnesite could be produced.