The invention discloses a production method of heavy soda ash. The production method comprises the following steps: adding light soda ash and a 
sodium carbonate saturated solution into a hydration crystallizer; introducing 
crystal mush into a thickener to adjust the 
solid-to-
liquid ratio after the reaction, separating the 
crystal mush in the thickener in a centrifugal 
machine, and introducing thesupernatant of the thickener into a 
mother liquor barrel; separating, washing with washing water, removing salt and impurities on the surface of 
crystal mush, and feeding centrifugate into the motherliquor 
barrel; treating the centrifuged 
solid to obtain a heavy soda ash product; evaporating the 20-50% 
mother liquor until the common saturation point of 
sodium carbonate and 
sodium chloride is reached to separate out 
sodium carbonate monohydrate crystals, mixing the 
sodium carbonate monohydrate crystals and steam condensate, recycling the mixture into a hydration crystallizer, and feeding the residual sodium 
chloride and 
sodium carbonate co-saturated solution into a combined-soda 
system vacuum salt making device; enabling 50-80% 
mother liquor to enter a clarification device, adding 
sodium sulfide, removing iron impurities, and enabling clarified liquor to enter a hydration crystallizer to continue to prepare heavy soda ash. According to the method, sodium 
chloride and iron impurities inthe 
sodium bicarbonate mother liquor in the current 
sodium bicarbonate production process can be removed, 
discharge of the 
sodium bicarbonate mother liquor is reduced, and the quality of the sodium 
bicarbonate product is improved.