Technical Research On Preparation Of Toothpaste Grade Strontium Chloride

With the rapid development of people's living standards in recent years,the toothpaste at present can't satisfy people's needs for its single function.Because of antiallergic property,strontium chloride is used as a toothpaste additive.However,the application of strontium chloride in toothpaste has not been industrialized by the limitation of technology and engineering technology.Strontium chloride is produced by the method of strontium hydroxide and magnesium chloride,which has the advantages of easy access to raw materials,easy cleaning,simple process and low cost.It has great development potential in the production of high purity strontium chloride in toothpaste.Our major works mainly studied the preparation of strontium hydroxide by industrial strontium calcining,compared the method of magnesium chloride and hydrochloric acid for preparation of toothpaste grade strontium chloride,then studied the SrCl₂?6H₂O crystallization process,and used the pilot experiment by magnesium chloride method.Strontium hydroxide was prepared by calcining.In this experiment,we studied the relationship of sagger of different materials,thickness of material layer and calcination method with calcination time.Then,the products calcined were immersed in water to study the influence of the mass ratio of SrO and H₂O,the recrystallization number and the cycle number of mother liquid for the purity of strontium hydroxide.Finally,the prepared strontium hydroxide was characterized.The results show that the calcining effect is best for corundum sagger with strontium carbonate owing to the lesser adhesion,and the best condition of material thickness is 5 cm,which is calcined at 1250?temperatures for 2 h.Compared with the method of muffle furnace,the microwave is shorter and the activity of preparing strontium oxide is higher to calcinate strontium carbonate of the same mass at the same temperature.Then the effects of solid-liquid ratio,the number of mother liquid cycles and the number of recrystallization on the purity of strontium hydroxide were studied.The results show that the best solid-liquid ratio of 1:8,recrystallization and mother liquor circulation can prepare strontium hydroxide with purity greater than 99%.The toothpaste grade strontium chloride was prepared by the method of strontium hydroxide and magnesium chloride.In the experiment,the strontium hydroxide and magnesium chloride with a recrystallization were used as raw materials.We removed the SO₄^2-in magnesium chloride solution,and then studied the effects of reaction temperature,magnesium chloride concentration and Mg?OH?₂washing on the purity and yield of strontium chloride.When the molar ratio of SrCl₂to SO₄^2-is 30:1,the SO₄^2-can be effectively removed.When the reaction temperature is greater than 90?,MgCl₂ solution with saturated solution,distilled water washing of Mg?OH?₂,we can not only obtain the toothpaste grade SrCl₂?6H₂O,but also improve the yield of strontium.In the experiment of preparing toothpaste standard strontium chloride by strontium hydroxide and hydrochloric acid,the reaction of strontium hydroxide and hydrochloric acid with different purity was studied.The standard strontium chloride for toothpaste can be obtained by the reaction of primary recrystallization hydroxide and hydrochloric acid.However,compared with magnesium chloride method,the purity of strontium chloride prepared by hydrochloric acid method is low and the content of impurities is high.The crystallization process of strontium chloride solution was studied to explore the effects of initial supersaturation,cooling rate,agitation rate,crystallization time and ultrasound on the morphology of SrCl₂?6H₂O crystal.The crystal size of SrCl₂?6H₂O is distribution uniformity with the condition of supersaturation of 0.25,cooling rate 10?/h,the stirring speed 400 rpm,crystal time 1 h.In this condition,the average length L of SrCl₂?6H₂O crystal obtained is 700-800?m,and the average width W is 45-65?m.Strontium chloride crystals prepared by ultrasonic method become coarse and short,and the average length and average width of strontium chloride crystals increase with the increase of the time interval of ultrasound.Therefore,the ultrasonic method is beneficial to obtain the short and thick SrCl₂?6H₂O crystal.Magnesium chloride method was used as the best method to prepare toothpaste grade strontium chloride.In the pilot experiment,the concentration of pH,Mg²⁺and Sr²⁺of the reaction solution were optimized,when the reaction temperature is greater than 90?,the reaction completed in about 30 min.The content of strontium chloride in filtrate could be improved by the number of filtration.The content of strontium in Mg?OH?₂ filter can be reduced in the initial stage of cycle washing,and then decreased to 5.28%after 1 h.The method of evaporation has great influence on the purity of strontium chloride.The direct evaporation crystallization results in low purity strontium chloride and high impurity content,which does not meet the standard of toothpaste.Compared with direct evaporation crystallization,cooling crystallization makes the content of product impurities decrease,and the strontium chloride content is up to 99%,which is consistent with the toothpaste grade.