Phosphate By-product Silica Gel Preparation Of Sodium Metasilicate Pentahydrate Technical Studies

Large amounts of by-product silica gel and fluorosilicic acid are discharged every year in the phosphate fertilizer industry. Plenty of silica gel containing fluorine is produced when producing fluoride salt or hydrofluoric acid from fluorosilicic acid. At present, these silica gel containing fluorine was stored in phosphor-gypsum yard directly and its recovery and utilization ratio is almost zero.The main purpose of this subject was to produce sodium metasilicate pentahydrate from phosphate fertilizer by-product silica gel containing fluorine through solution crystallization method of the recycling used mother liquor. In the thesis, the technical process was determined by means of studying the crystallization theory and doing trial test.Based on condition experiments and orthogonal tests, the suitable controllingconditions were established:①sodium hydroxide concentration was 40%～50%;②ingredient ratio was 1.9～2.1;③reaction temperature was approximately 91℃;④reaction time was 1.0-1.5 hours;⑤crystal concentration was 36%～42%;⑥quantity of the crystal seed was 0.75%～2.0%;⑦crystallization time was 3-5 hours.The innovations in the paper are as following:①the technical process was simplified by combining the reaction and condense process steps;②adding some ethylenediaminetetraacetic acid disodium salt in the crystallization process was beneficial for improving the anti-caking characteristics of the products;③dealing with the recycling utilized mother liquor using settlement method was simply and effective and the product quality can reach the excellent standard of HG/T 2568-94 type-I requirements.The first productivity of the products was about 83% and its total yield can reach 97.32% and 94.78% when SiO2 and Na2O were recycled from the mother liquor respectively.