How to avoid silica precipitation in sodium silicate

prabodhpai · Post by **prabodhpai** » Fri Nov 09, 2007 3:50 am

want to know how I could avoid precipitaiton of silica in manufacture of sodium silicate manufacture via hydrothermal route. Recently,I had made a batch trial of sodium silicate liquid of ratio Na₂o:Sio₂=1:2.50 30% solids. The size of the batch was 1000 kgs. The raw materials used were casutic soda flakes(99%) 110 kgs, rice husk ash (90%,black colour) 238 kgs and water 652 kgs. The same were charged into a reactor and heated with agitation till a pressure of 1 kg/cm2 was achieved. Later, the pressure rose to 2 kgs/cm2 and we began the filtration. The filtered sample was showing a ratio of 1:2.27,30 % solids. The total filtered silicate was weighed and we got 744 kgs of liquid silicate and 151 kgs of filter cake! We are confused how this can happen! Above all the total recovery is only 895 kgs as against 1000 kgs charged! Can someone please explain why this happened and how the precipitaion of silica could be avoided?