Preparation Of Magnesium Carbonate Hydrates From Magnesium Chloride Mineralization Of Carbon Dioxide

To slow down the ecological environment problem caused by greenhouse effect,governments are developing a variety of technologies to fix and utilize carbon dioxide.For the technology of carbon dioxide mineralization,it is very important to choose a kind of mineralized raw material which is cheap and abundant.However,it is calculated that more than 20 million tons of bischoffite?MgCl₂·6H₂O?are discarded every year in Qinghai province.This is not only a serious waste of magnesium resources,but also can affect the ecological balance of salt lake.Therefore,the preparation of magnesium carbonate hydrates by carbon dioxide mineralization with MgCl₂ can reduce the emission of carbon dioxide and utilize the wasted magnesium resources,realizing a win-win style of environment and economy.Based on mineralization of carbon dioxide by magnesium chloride in salt lake,this article studies the precipitation of nesquehonite and hydromagnesite in MgCl₂-?NH₄?₂CO₃ and MgCl₂-NH3·H₂O-CO₂ systems.The main contents are as follows.?1?Magnesium carbonate hydrates was prepared with precipitation method by reaction of MgCl₂ with?NH₄?₂CO₃.Effects of reaction temperatures?10?90??,initial concentrations(0.5 mol·L^-1,2 mol·L^-1)and titration speeds?33.3 mL·min-1,2.5 mL·min-1,0.83 mL·min-1?on the composition and morphology of magnesium carbonate hydrates were investigated.At the temperature of 20?50?,the rod-like nesquehonite are obtained.While the temperature is up to 80?90?,the products are hydromagnesite of flower-like.The initial concentration and titration speed also have certain effects on the morphology of nesquehonite and hydromagnesite.?2?Nesquehonite was prepared with precipitation method by reaction of MgCl₂,CO₂ and NH3·H₂O.Effects of numerous factors such as reaction temperature?20?50??,NH3·H₂O concentration(1?5 mol·L^-1),ethanol amount?0-60%?and so on were investigated.At the temperature of 20?,the product is magnesium hydroxide of amorphous.With the temperature of 30?50?,the product is nesquehonite of rod-like.To a certain extent,adding ethanol solvent can promote precipitation and crystallization reaction.But with excessive ethanol added,phase transformation would occur:nesquehonite transforming into hydromagnesite.Under the optimum parameters,the ratio of fixed carbon and MgCl₂ utilization can reach 95.87%and 98.78%.And the products are the rod-like crystals of uniform size,smooth surface.Also,the purity of products is above 98%.?3?Hydromagnesite was prepared with precipitation method by reaction of MgCl₂,CO₂ and NH3·H₂O.Effects of numerous factors such as reaction temperature?60?90??,NH3·H₂O concentration(1?5 mol·L^-1),ethanol solvents?0-60%?and so on were investigated.When the temperature is from 80 to 90?,the product is hydromagnesite of perfect crystallinity,and it is approximately spherical particle with the flower-like structure.To a certain extent,adding ethanol solvent can promote the precipitation.At the same time,phase transformation would not occur and the morphology is similar to the product without addition of ethanol.Under the optimum parameters,the ratio of fixed carbon and MgCl₂ utilization can reach 95.87%and 98.78%.And the products are the flower-like structure.Also,the purity of products is above 98%.