Process for the separation of insoluble materials in the production of soda ash

In a process for the production of soda ash from trona by the normal monohydrate process including the steps of calcining said trona to form a mixture of sodium carbonate and insoluble impurities, forming an initial aqueous solution of said carbonate containing a slurry of said impurities, separating said impurities from said sodium carbonate solution to form a purified solution, crystallizing sodium carbonate monohydrate from said purified solution and drying such crystals to form soda ash, the improvement comprising subjecting said initial solution to a first hydrocyclone separation step to provide a first overflow containing dissolved sodium carbonate and relatively fine insoluble impurities and a first underflow containing dissolved sodium carbonate and relatively coarse insoluble impurities, subjecting said first overflow successively to thickening, filtration, color removal, filtration, crystallization and drying steps to provide a soda ash product, and adding said first underflow to an aqueous medium to form a second slurry and then subjecting said second slurry to a second hydrocyclone separation step to provide a second overflow and a second underflow, recycling said second overflow to said initial aqueous solution, and subjecting said second underflow to a screening step to provide a screen oversize fraction which is discarded and a screen undersize which is recycled to said initial aqueous solution.