Development Of Preparation Process Of Soda Ash From Industrial Waste Salt

This paper studied a preparation process by metathesis reaction in an aqueous solution for soda ash and by-product of ammonium chloride from raw materials of industrial waste sodium chloride and ammonium bicarbonate. The preparation of soda ash was the first unit of the process and recycling the by-product of ammonium chloride from the mother liquor in the first unit was the second unit of the process. The optimal experimental condition of the first unit was determined by orthogonal experiments of testing the effects of temperature, reaction time and reactants ratio on the yield of intermediate product of sodium bicarbonate by single metathesis reaction. Afterwards, the influence of salting-out agents on recycling the sodium bicarbonate from the mother liquor and the condition of preparing by-product of ammonium chloride in the second unit by concentration and crystallization method were investigated. Thereafter, material balance of preparation process of sodium carbonate and ammonium chloride for annual treatment of 73,000 tons of industrial waste salts was calculated and the key types of equipments were determined.The scope of experimental condition of the first unit was determined by the quaternary perspective system phase diagram of water and salts firstly, and the effects of temperature and reaction time on the yield of intermediate product of sodium bicarbonate were studied. We discovered that the yield of sodium bicarbonate would increase with appropriate increasing temperature and reaction time. In the meanwhile, adjuisting reactants ratio in an appropriate range would improve the yield as well. Orthogonal experiment results showed that the optimal condition was 35℃ of reaction temperature,1.05 of ratio of waste salt and ammonium bicarbonate and 120 min of reaction time. With the optimal condition, the yield of intermediate product of sodium bicarbonate by single reaction reached a peak value of 75%. The intermediate product was calcined at 400℃ afterwards for the product of soda ash which was in line with national standards.On the basis of anti-solvent principles, three kinds of organic salting-out agents were tested in treatment of mother liquor for increasing the yield of the intermediate product of sodium bicarbonate. The results showed that agent C was discovered to increase the yield of sodium bicarbonate in single reaction for nearly 10 percentages when the amount of agent C was 1.5 times by molar mass of waste salt.In the second unit, two kinds of acids were used to recycle the by-product from the clarified mother liquor after salting out. The experiment confirmed the concentrated hydrochloric acid was the better acid for yielding ammonium chloride as high as 86.42% and the product was detected for the nitrogen content which was in line with national standards.The process simulation software Aspen was used to calculate the material balance of preparation process of sodium carbonate and ammonium chloride for annual treatment of 73,000 tons of waste sodium chloride. The graphs of PFD and PID were drawn and the key types of equipments were preliminary determined.