Study On Synthesis Of Basicmagnesium Carbonate From Brineand Salt Separation Of Motherliquor

The mother liquor after seawater evaporation and salt production is called brine.Brine contains a large amount of inorganic salts such as sodium,magnesium and potassium.It is a valuable resource treasure,but the further separation and use of salt in brine is difficult.China's annual production of brine is 20 million cubic meters,but when the utilization rate of brine is less than 20%.Most of the brine after sun-salt is discharged into the sea,causing seawater pollution.Therefore,the efficient and comprehensive utilization of brine resources has always been a subject worthy of discussion and research.The process of preparing basic magnesium carbonate by reacting brine as a raw material,and then separating the remaining salts.The research on the preparation of basic magnesium carbonate by reacting brine with sodium carbonate and sodium carbonate and sodium hydroxide was carried out.The effects of raw material ratio,reaction time and reaction temperature on the conversion of magnesium ions in brine were investigated.XRD and SEM structural morphologies were characterized by basic magnesium carbonate crystal products.The suitable conditions for synthesizing basic magnesium carbonate from the mixture of sodium carbonate and sodium hydroxide are as follows:Mg²⁺:CO₃^2-:OH^-is5:4.8:2,the reaction temperature is 60?,and the reaction time is 2.5 h.The magnesium ion conversion rate is 100%,the carbonate ion conversion rate is 91%,and the bicarbonate ion is not present in the solution,and the obtained basic magnesium carbonate is a spherical product having a diameter of 10?30?m.The evaporation law of the mother liquor at 25?after magnesium removal was studied.The evaporation process was divided into 5 stages according to the difference of evaporation precipitates,and the theoretical analysis of evaporation and salt formation of each ion was carried out.Based on the Pitzer model,combined with the ionic strength function,the activity of each ion is expressed.The reliable thermodynamic data is used to study the solubility data of the metastable phase diagram K⁺,Na⁺//Cl^-,SO4^2-,CO₃^2--H₂O quintuple system at 25?.The regression calculation shows that the experimental values are close to the calculated values and accord with the salt precipitation law of the metastable phase diagram K⁺,Na⁺//Cl^-,SO4^2-,CO₃^2--H₂O quintuple system at 25?.Two methods were designed to separate the remaining mother liquor after the preparation of basic magnesium carbonate by brine.The first one is direct evaporation separation method:evaporation begins to precipitate pure sodium chloride solid,and precipitates a mixture of sodium chloride and sodium sulfate over time.According to the phase diagram of Na Cl-Na₂SO₄-H₂O system,the separation of sodium chloride and sodium sulfate is realized,and the content of the mixture which continues to evaporate is less,so the recycling process is designed to realize the recycling of the mother liquor.The second,indirect phase diagram separation method:after the remaining mother liquor is precipitated by calcium chloride,a small amount of carbonate is converted into the stable phase diagram of K⁺,Na⁺//Cl^-,SO₄^2--H₂O quaternary system at 0?and 25?,which can be realized according to the phase diagram of the system.Partial sodium chloride and sodium sulfate were separated.After separation,the mother liquor was added with cesium chloride to precipitate a small amount of sulfate.After separation of sodium chloride and potassium chloride according to the stable phase diagram of KCl-Na Cl-H₂O ternary system at 25?and 100?,the brine was obtained according to the above method.Comprehensive development and utilization.