Sodium carbonate manufacture via the Solvay ammonia-soda process Tamil revision mind map presented as a four-stage flow with two recycle loops: stage one ammoniation of brine with ammonia gas in a countercurrent tower, stage two carbonation where carbon dioxide is passed through to precipitate low-solubility sodium hydrogencarbonate, stage three thermal decomposition of the filtered sodium hydrogencarbonate to sodium carbonate releasing carbon dioxide that is recycled back to stage two, and stage four ammonia recovery from ammonium chloride using lime which regenerates ammonia gas recycled back to stage one, making the process economical since only brine, limestone and heat are consumed overall.