Effect of pCO2 on direct flue gas mineral carbonation at pilot scale.

Concerns about global warming phenomena induced the development of research about the control of anthropogenic greenhouse gases emissions. The current work studies on the scaling up of aqueous mineral carbonation route to reduce the CO2 emissions at the chimney of industrial emitters. The reactivity of serpentinite in a stirred tank reactor was studied for several partial pressures of CO2 (pCO2) (0.4, 0.7, 1.3 and 1.6 bar). Prior to carbonation, the feedstock was finely grinded and dehydroxyled at 650 °C by a thermal treatment. The major content of magnetite was removed (7.5 wt% · total weight-1). Experiments were carried out under batch mode at room temperature using real cement plant flue gas (14-18 vol% CO2) and open pit drainage water. The effect of the raw water and the pCO2 on the carbonation efficiency was measured. First, the main results showed a positive effect of the quarry water as a slight enhancement of the Mg leaching in comparison with distilled water. Secondly, a pCO2 of 1.3 bar was the optimal working pressure which provided the highest efficiency of the carbonation reaction (0.8 gCO2 · g residue-1). Precipitation rates of dissolved CO2 ranged from 7% to 33%. Pure precipitate was obtained and essentially composed of Nesquehonite. At a pCO2 of 1.3 bar, additional physical retreatment of the solid material after being contacted with 6 batches of gas enhanced considerably mineral carbonation efficiency (0.17 gCO2 · g residue-1.).

CO2 sequestration using waste concrete and anorthosite tailings by direct mineral carbonation in gas-solid-liquid and gas-solid routes.

Mineral carbonation (MC) represents a promising alternative for sequestering CO2. In this work, the CO2 sequestration capacity of the available calcium-bearing materials waste concrete and anorthosite tailings is assessed in gas-solid-liquid and gas-solid routes using 18.2% flue CO2 gas. The objective is to screen for a better potential residue and phase route and as the ultimate purpose to develop a cost-effective process. The results indicate the possibility of removing 66% from inlet CO2 using waste concrete for the aqueous route. However, the results that were obtained with the carbonation of anorthosite were less significant, with 34% as the maximal percentage of CO2 removal. The difference in terms of reactivity could be explained by the accessibility to calcium. In fact, anorthosite presents a framework structure wherein the calcium is trapped, which could slow the calcium dissolution into the aqueous phase compared to the concrete sample, where calcium can more easily leach. In the other part of the study concerning gas-solid carbonation, the results of CO2 removal did not exceed 15%, which is not economically interesting for scaling up the process. The results obtained with waste concrete samples in aqueous phase are interesting. In fact, 34.6% of the introduced CO2 is converted into carbonate after 15 min of contact with the gas without chemical additives and at a relatively low gas pressure. Research on the optimization of the aqueous process using waste concrete should be performed to enhance the reaction rate and to develop a cost-effective process.

Reaction mechanism for the aqueous-phase mineral carbonation of heat-activated serpentine at low temperatures and pressures in flue gas conditions.

Mineral carbonation is known as one of the safest ways to sequester CO2. Nevertheless, the slow kinetics and low carbonation rates constitute a major barrier for any possible industrial application. To date, no studies have focused on reacting serpentinite with a relatively low partial pressure of CO2 (pCO2) close to flue gas conditions. In this work, finely ground and heat-treated serpentinite [Mg3Si2O5(OH)4] extracted from mining residues was reacted with a 18.2 vol % CO2 gas stream at moderate global pressures to investigate the effect on CO2 solubility and Mg leaching. Serpentinite dissolution rates were also measured to define the rate-limiting step. Successive batches of gas were contacted with the same serpentinite to identify surface-limiting factors using scanning electron microscopy (SEM) analysis. Investigation of the serpentinite carbonation reaction mechanisms under conditions close to a direct flue gas treatment showed that increased dissolution rates could be achieved relative to prior work, with an average Mg dissolution rate of 3.55 × 10(-11) mol cm(-2) s(-1). This study provides another perspective of the feasibility of applying a mineral carbonation process to reduce industrial greenhouse gas (GHG) emissions from large emission sources.

Carbon dioxide sequestration by mineral carbonation via iron complexation using bipyridine chelating ligands.

An innovative mineral carbonation method was developed to synthesize iron(II) carbonate (FeCO3) by cation complexation using 2,2'-bipyridine as ligand. First, complexes of iron(II) and different ligands were theoretically analyzed and discounted in terms of their temperature and pH-dependent stabilities, iron-ligand interactions, possible by-products and difficulty of analysis, choosing 2,2'-bipyridine as the most suitable ligand. Then, the Job plot was used to verify the complex formula. The stability of [Fe(bipy)3]2+ at pH 1-12 was further monitored for 7 days using UV-Vis and IR spectroscopy. Good stability was observed between pH 3 and 8, decreasing within pH 9-12 where the carbonation reaction occurs. Finally, the reaction between Na2CO3 and [Fe(bipy)3]2+ was performed at 21, 60, and 80 °C and pH 9-12. The total inorganic carbon measured after 2 h shows that the best carbonate conversion (50%) occurred at 80 °C and pH 11, being the most suitable conditions for carbon sequestration. SEM-EDS and XRD were used to examine the effect of synthesis parameters on the morphology and composition of FeCO3. The FeCO3 particle size increased from 10 µm at 21 °C to 26 and 170 µm at 60 and 80 °C respectively with no pH dependence. In addition, EDS analysis supported the carbonate identity, whose amorphous nature was confirmed by XRD. These results would help prevent the iron hydroxide precipitation problem during mineral carbonation using iron-rich silicates. These results are promising for its application as a carbon sequestration method with a CO2 uptake of around 50% obtaining Fe-rich carbonate.

CO2 sequestration by mineral carbonation of steel slags under ambient temperature: parameters influence, and optimization.

This work focuses on the influence of different parameters on the efficiency of steel slag carbonation in slurry phase under ambient temperature. In the first part, a response surface methodology was used to identify the effect and the interactions of the gas pressure, liquid/solid (L/S) ratio, gas/liquid ratio (G/L), and reaction time on the CO2 removed/sample and to optimize the parameters. In the second part, the parameters' effect on the dissolution of CO2 and its conversion into carbonates were studied more in detail. The results show that the pressure and the G/L ratio have a positive effect on both the dissolution and the conversion of CO2. These results have been correlated with the higher CO2 mass introduced in the reactor. On the other hand, an important effect of the L/S ratio on the overall CO2 removal and more specifically on the carbonate precipitation has been identified. The best results were obtained L/S ratios of 4:1 and 10:1 with respectively 0.046 and 0.052 gCO2 carbonated/g sample. These yields were achieved after 10 min reaction, at ambient temperature, and 10.68 bar of total gas pressure following direct gas treatment.

Direct gas-solid carbonation of serpentinite residues in the absence and presence of water vapor: a feasibility study for carbon dioxide sequestration.

Mineral carbonation of serpentinite mining residue offers an environmentally secure and permanent storage of carbon dioxide. The strategy of using readily available mining residue for the direct treatment of flue gas could improve the energy demand and economics of CO2 sequestration by avoiding the mineral extraction and separate CO2 capture steps. The present is a laboratory scale study to assess the possibility of CO2 fixation in serpentinite mining residues via direct gas-solid reaction. The degree of carbonation is measured both in the absence and presence of water vapor in a batch reactor. The gas used is a simulated gas mixture reproducing an average cement flue gas CO2 composition of 18 vol.% CO2. The reaction parameters considered are temperature, total gas pressure, time, and concentration of water vapor. In the absence of water vapor, the gas-solid carbonation of serpentinite mining residues is negligible, but the residues removed CO2 from the feed gas possibly due to reversible adsorption. The presence of small amount of water vapor enhances the gas-solid carbonation, but the measured rates are too low for practical application. The maximum CO2 fixation obtained is 0.07 g CO2 when reacting 1 g of residue at 200 °C and 25 barg (pCO2 ≈ 4.7) in a gas mixture containing 18 vol.% CO2 and 10 vol.% water vapor in 1 h. The fixation is likely surface limited and restricted due to poor gas-solid interaction. It was identified that both the relative humidity and carbon dioxide-water vapor ratio have a role in CO2 fixation regardless of the percentage of water vapor.