| Global warming has been widely concerned by researchers all over the world.Mineralization and storage can transform the growing CO2 in the atmosphere into CaCO3 or MgCO3,and the technology of permanently,safely and stably fixing CO2 is promising.The reaction process may be referred to as a carbonation reaction,and the source of the reacted calcium or magnesium material is natural ore and alkaline solid waste materials.Wet direct carbonation is one of the accelerated carbonation technologies.This paper builds a gas-liquid-solid three-phase liquid phase carbonation reaction system.CaO,Ca(OH)2,MgO and Mg(OH)2 are the most effective active components of each calcium-magnesium material.In this paper,the reaction mechanism of four pure minerals and CO2 liquid phase carbonation is explored,and the liquid-solid ratio is explored.The mechanism of the influence of important operating parameters of pure mineral species,stirring speed,reaction temperature and aeration time on the reaction process and product,the dissolution of CO2 at the gas-liquid interface,the dissolution and transfer of alkaline minerals in solution and the precipitation process of carbonation products research.In the experiment,the pH,conductivity,total dissolved solids(TDS)and salinity(Salt)values were measured during the reaction,and the solid phase product was filtered,dried and subjected to thermogravimetric analysis after the reaction.The results show that each operating parameter affects the reaction rate and reaction product of liquid phase carbonation.The main conclusions are as follows:(1)The reaction rate of CaO and Ca(OH)2 is faster,the initial pH is above 12,the reaction rate of MgO and Mg(OH)2 is slower,and the initial pH is also lower.When the solid phase material is calcium hydroxide,the pH drops rapidly 30 minutes before the reaction,and the reaction rate is the fastest when the liquid-solid ratio is 40 mL/g.It indicates that the liquid-solid ratio is too high or too low,which is not conducive to the carbonation reaction.When the solid phase material is magnesium hydroxide,the change of liquid-solid ratio has little effect on the change of pH value;when CO2 is excessive,MgCO3 is more easily converted into Mg(HCO3)2,the liquid-solid ratio is different,Mg(OH)2 and CO2 The reaction produces different mineral phase products.Since the calcium-containing alkaline mineral phase reacts at a faster rate,calcium-rich minerals are preferred as a feedstock for the carbonation reaction.(2)Analysis of the thermogravimetric curve of calcium hydroxide shows that the highest conversion rate of carbonation is 98.63%when the liquid-solid ratio is 50 mL/g.When magnesium hydroxide is an alkaline mineral phase,the liquid-solid ratio has little effect on the rate of carbonation reaction.(3)The liquid phase carbonation conversion rate of Ca(OH)2 under the same conditions is higher than that of CaO which is the same as the calcium salt;the conversion rate of Mg(OH)2 is higher than that of MgO.The conversion rate at a stirring speed of 250 rpm was higher than the stirring speed of 50 rpm.The increase of the stirring speed is beneficial to promote the contact of the gas-liquid-solid three-phase.The entry of CO2 into the liquid phase is an important limiting factor.It is affected by the pH of the solution,the contact area of gas and liquid,and the gradient of CO2 concentration at the interface.Increasing the turbulent energy of the gas-liquid-solid three-phase increases the contact area of the gas-liquid two phases and promotes the absorption of CO2.The conversion at a reaction temperature of 45℃ is higher than the reaction temperature of 85℃.Prolonged ventilation time is beneficial for the wet direct carbonation reaction.The research in this paper provides basic data and theoretical guidance for process optimization and more complex alkaline mineral phase carbonation processes. |
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