Preparation Of Amorphous Silica From Byproducts Of Zr-Containing Silica Residue And Alkali Wastewater Produced In Manufacturing Process Of ZrOCl₂

A large amount of Zr-containing silica residue with gel shape (mainly contains amorphous SiO2, ZrSiO4 and much hydrochloric acid solution) and alkali wastewater rich of Na2SiO3 is produced in industrial manufacturing process of ZrOCl2. Therefore, considerable economic value and remarkable environmental protection significance can be seen to recycle the SiO2 in them.Amorphous silica was prepared through Zr-containing silica residue and alkali wastewater from Henan Billions Chemicals Co., Ltd. by chemical precipitation method. The physical and chemical properties were characterized and its application technics in rubber products were studied. The forming mechnisim of amorphous silica was also researched.Amorphous silica was prepared by watering Zr-containing silica residue, alkali leaching and acid precipitating in sequence. Alkali leaching ratio of silica, purity and recycling percent of SiO2 were chosen as the indexes to optimize the alkali leaching and acid precipitating parameters. The optimized conditions were: purify Zr-containing silica residue by centrifuging and watering, alkali leaching temperature of 80°C, ratio of alkali volume to purified Zr-containing silica residue mass of 6:1, dosage of NaOH of 6.7 g per 100.0 g purified Zr-containing silica residue, and reaction time of 40 min. Acid precipitating temperature of 60°C, concentration and adding rate of sulfuric acid of 1.5 mol/L and 0.02 mL/s, reaction pH end-point of 4.0, and ageing time of 15 h. The silica content of amorphous silica prepared was 92.4%. The whitenesses and the mean particle size were 89.2% and about 8μm, respectively. The specific surface area was 531.9 m2/g, and the recycling percent of SiO2 was 92.8%. The quality of amorphous silica prepared by Zr-containing silica residue was a little inferior to the same type product in the market.Amorphous silica was also prepared by alkali wastewater. The optimized parameters were: adding rate and sulfuric acid concentration of 0.04 mL/s and 1.89 mol/L, reaction temperature of 80°C, reaction pH end-point of 8.0, and ageing time of 4 h. The silica content of amorphous silica prepared was 96.4%. The whiteness and mean particle size were 97.5% and about 0.15μm, respectively. The specific surface area was 310.0 m2/g, and and the recycling percent of SiO2 was 94.2%. The quality of amorphous silica prepared by alkali wastewater was much superior to the same type product in the market. The mechanism of preparing amorphous silica by Zr-containing silica residue was as follows: The ZrOCl2 in the purified Zr-containing silica residue transformed into NaCl and ZrO(OH)2 which was extremely good in suspension property and difficult to seperate out in alkali leaching process, and thus they entered into the acid precipitating process. Cl- and Zr4+ could react with hydrated silica to form aggregates, which affected the quality of amorphous silica prepared. Preparing process of amorphous silica by acid precipitating was very complicated, which was affected by supersaturation, temperature, time and pH value, etc.The amorphous silica prepared by Zr-containing silica residue and alkali wastewater and the same type product in the market were added into rubber according to the ingredient of nature rubber to prepare rubber clinker, respectively. The mechanical properties of rubber added amorphous silica were all reached requirements of related standard, and those added amorphous silica prepared by alkali wastewater were the best.