Study On The Seawater Softening Process With CO₂ Captured And Mineralization

Seawater contains Ca²⁺and Mg²⁺ions that caused scaling,which hinders normal operation during industrial production,increases energy consumption,and affects production efficiency.The technology of seawater softening with CO₂ captured and mineralization achieves the coupling of carbon sequestration and decalcification.On the one hand,this technology can reduce the concentration of Ca²⁺in seawater and the total hardness of seawater,which is beneficial to further desalination and resource extraction.On the other hand,it absorbs CO₂ during the process so that it can reduces the greenhouse gases in the atmosphere and the exhaust in the air,which effectively solves the environmental problems.This research designes a series of experiments to explore the effect of different process conditions on the decalcification process by analyzing the changes of Ca²⁺,Mg²⁺concentration,alkalinity,pH values in the liquid phase and the transformation of solid-phase sediments.The decalcification rate,product purity and economics are the inspection indexes to select the optimal process conditions.The experimental results show that when MgO is used as an alkali source,the Ca²⁺ion concentration in the initial stage decreases rapidly with the CO₂ inserting,the solid phase composition is MgO,Mg（OH）₂ without CaCO₃,and while the CO₂continuous insert,the change of Ca²⁺ion concentration is becoming stable and the MgO and Mg（OH）₂ disappeared in the solid phase compositions.The formation of solid salt is a crystallized process.The crystallization kinetics of calcium carbonate have been studied under different process conditions.The nucleation and growth rates were calculated,which compared with theoretical value using software to fit the kinetic equations.According to the parameters of the fitting equation,the crystallization kinetics of calcium carbonate was further analyzed and discussed.As a result,it was found that crystal growth of calcium carbonate does not conform to the L law.Different process conditions have different effects on nucleation and growth activation energy.The decalcified solution contains a large amount of magnesium ions.The crystallization kinetics of magnesium was also studied in this paper.Summarizing the previous research work,it was found that when the alkalinity source n（OH^-）/n(Mg²⁺)was added in the range of 0.5 to 1.7,the precipitated solid phase was magnesium trihydrate.By changing the amount of alkali source added,the temperature,and the stirring rate,the crystallization kinetics of magnesium carbonate was investigated.The nucleation and growth rates were calculated,which compared with theoretical value using software to fit the kinetic equations.According to the parameters of the fitting equation,the crystallization kinetics of magnesium carbonate was further analyzed and discussed.