Effect of Ca/Mg molar ratio on the calcium-based sorbents

Steelmaking industry faces urgent demands for both steel slag utilization and CO_(2)abatement.Ca and Mg of steel slag can be extracted by acid solution and used to prepare sorbents for CO_(2)capture.In this work,the calcium-based sorbents were prepared from stainless steel slag leachate by co-precipitation,and the initial CO_(2)chemisorption capacity of the calcium-based sorbent prepared from steel slag with the Ca and Mg molar ratio of 3.64:1 was 0.40 g/g.Moreover,the effect of Ca/Mg molar ratio on the morphology,structure,and CO_(2)chemisorption capacity of the calcium-based sorbents were investigated.The results show that the optimal Ca/Mg molar ratio of sorbent for CO_(2)capture was4.2:1,and the skeleton support effect of MgO in calcium-based sorbents was determined.Meanwhile,the chemisorption kinetics of the sorbents was studied using the Avrami-Erofeev model.There were two processes of CO_(2)chemisorption,and the activation energy of the first stage(reaction control)was found to be lower than that of the second stage(diffusion control).

Sulfuric acid leaching kinetics of South African chromite

The sulfuric acid leaching kinetics of South African chromite was investigated. The negative influence of a solid product layer constituted of a silicon-rich phase and chromium-rich sulfate was eliminated by crushing the chromite and by selecting proper leaching con- ditions. The dimensionless change in specific surface area and the conversion rate of the chromite were observed to exhibit a proportional re- lationship. A modified shrinking particle model was developed to account for the change in reactive surface area, and the model was fitted to experimental data. The resulting model was observed to describe experimental findings very well. Kinetics analysis revealed that the leach- ing process is controlled by a chemical reaction under the employed experimental conditions and the activation energy of the reaction is 48 kJ.mol-1.

Carbonation of calcium-containing mineral and industrial by-products

The use of carbon dioxide(CO_(2))and calciumcontaining by-products from industrial activities is receiving increasing interest as a route to valuable carbonate materials while reducing CO_(2) emissions and saving natural resources.In this work,wet-chemical experimental data was assessed,which involved the carbonation of three types of materials in aqueous solutions,namely,1)wollastonite,a calcium silicate mineral,2)steelmaking slag,a by-product of steel production,and 3)paper bottom ash(PBA)from waste paper incineration.Aims were to achieve either a high carbonation degree and/or a pure carbonate product with potential commercial value.Producing a pure precipitated calcium carbonate(PCC)material that may find use in paper industry products puts strong requirements on purity and brightness.The parameters investigated were particle size,CO_(2)pressure,temperature,solid/liquid ratio,and the use of additives that affect the solubilities of CO_(2)and/or calcium carbonate.Temperatures and pressures were varied up to 180℃and 4 MPa.Data obtained with the wollastinite mineral allowed for a comparison between natural resources and the industrial by-product materials,the latter typically being more reactive.With respect to temperature and pressure trends reported by others were largely confirmed,with temperatures above 150℃introducing thermodynamic limitations depending on CO_(2)pressure.The influence of additives showed some promise,although costs may make recycling and reuse of additives a necessity for a largescale process.When using steelmaking slag,magnetic separation may remove some iron-containing material from the process(although this is far from perfect),while the addition of bicarbonate supported the removal of phosphorous,aside from improving calcium extraction.The experiments with paper bottom ash(PBA)gave new data,showing that its reactivity resembles that of steelmaking slag,while its composition results in relatively pure carbonate product.Also,with PBA no additives were needed to achieve this.

A stepwise process for carbon dioxide sequestration using magnesium silicates

This work involves the production of magnesium in the form of Mg(OH)_(2)from serpentinite rock(nickel mine tailing)material followed by conversion into MgCO_(3)using a pressurised fluidised bed(PFB)reactor operating at 400℃-600℃and pressures up to 2.85 MPa.Our approach is rooted in the thermodynamic fact that the reaction between Mg(OH)_(2)and gaseous CO_(2)forming MgCO_(3)and water releases significant amounts of heat.The main problem is,however,the chemical kinetics;the reaction is slow and has to be accelerated in order to be used in an economically viable process for large-scale(~1 Mt/a)CO_(2)sequestration.We have constructed a labscale PFB reactor test-setup for optimising the carbonation reaction.At high enough temperatures and conversion levels the reaction should provide the heat for the proceeding Mg(OH)_(2)production step,making the overall process energy neutral.So far we have been able to achieve a conversion degree of 26%at 500℃and 2.85 MPa after 30 min(particle size 125-212μm).In this paper the test facility and our latest results and progress on CO_(2)mineral carbonation are summarised.Also,the possible integration of the iron as a feedstock for iron and steel production will be briefly addressed.An interesting side-effect of this carbon dioxide capture and storage(CCS)route is that significant amounts of iron are obtained from the serpentinite rock material.This is released during the Mg(OH)_(2)production and can be of great interest to the iron-and steel producing sector,which at the same time is Finland’s largest CO_(2)producer.