Reducing loss of soda in red mud in process of Bayer digestion

In the process of alumina production by Bayer process,the loss of soda is mainly caused by the formation of sodium hydrate alumino-silicate.Based on the thermodynamic analysis of the reaction law between sodium hydrate alumino-silicate and hydrogarnet,it is found that hydrogarnet with more amount of SiO_2(x>1) can not be decomposed by caustic solution easily,while hydrogarnet with x<0.5 can be decomposed into sodium hydrate alumino-silicate,and sodium hydrate alumino-silicate can also be transformed into hydrogarnet with the addition of CaO.But in sodium carbonate solution,any form of hydrogarnet can be decomposed into sodium hydrate alumino-silicate.Experimental results show that bauxite in different areas has little influence on the loss of soda,while more concentration of Na_2CO_3 or lower concentration of Na_2O in spent solution,or worse quality of limes will enhance N/S in red mud,and cause more loss of soda.Therefore,decreasing the concentration of Na_2CO_3 or obtaining better quality of limes will reduce N/S.