The Research On Preparation Of Precipitated Silica And Calcium Nitrate From The Yellow Phosphorus Slag

The yellow phosphorus slag is a kind of solid waste which is generated by usingelectric furnace to produce yellow phosphorus, its main ingredients is calcium silicate.In recent years, with the rapid development of phosphorus industry, production ofyellow phosphorus slag also show a trend of rapid growth, resulting in a large numberof yellow phosphorus slag piled up which occupy a large area of land resources. Also,the harmful ingredients of yellow phosphorus slag could be leached gradually withprecipitation, then immersing into the soil, causing contamination of soil and water.Currently, the application of yellow phosphorus slag is to produce cement, concrete orsilicon fertilizer, but low utilization and a small value. This research is to manufacturecrude precipitated silica firstly, in which yellow phosphorus slag is leached by nitricacid, then refining the crude precipitated silica to get high purity, high whiteness ofprecipitated silica, finally making a recycling of calcium nitrate from leachingsolution, so a new process of making use of yellow phosphorus slag is successfullydeveloped. The main results are as follows:(1) Crude precipitated silica was manufactured from yellow phosphorus slag bynitric acid leaching. By designing single factors tests and orthogonal tests, the impactof each factors towards precipitated silica’s whiteness were investigated, whichincluded the amount of nitric acid, the liquid-solid ratio, the granularity of yellowphosphorus slag, the stirring speed, the reaction time and the reaction temperature.The optimal conditions of the process were as follows: the amount of nitric acid was140%, the liquid-solid ratio was12.5:1, the granularity of yellow phosphorus slagwas150μm, the stirring speed was300r/min, the reaction time was110min, thereaction temperature was75℃. Under the optimal conditions to manufactureprecipitated silica, its whiteness was71.4%, its purity was96.2%. The size of eachfactors affecting the preparation of precipitated silica was as follows: the amount ofnitric acid> the granularity of yellow phosphorus slag> the reaction temperature> thereaction time> the liquid-solid ratio> the stirring speed. (2) Crude precipitated silica was refined by NaOH solution. By designingsingle factors tests and orthogonal tests, the impact of each factors towardsprecipitated silica’s yield were investigated, which included the concentration ofNaOH solution, the liquid-solid ratio, the reaction temperature, the reaction time, thestirring speed. The optimal conditions of the process were as follows: theconcentration of NaOH solution was12.5%, the liquid-solid ratio was12.5:1, thereaction temperature was85℃, the reaction time was60min, the stirring speed was300r/min. Under the optimal conditions to refine precipitated silica, its yield was80.3%, its whiteness was96.2%, its purity was99.3%. The SEM and FTIR analysisshowed the compound was amorphous hydrated silica. The size of each factorsaffecting the preparation of precipitated silica was as follows: the concentration ofNaOH solution>the reaction temperature> the stirring speed> the reaction time.(3) Calcium nitrate was recovered by using the method of crystalline from theleaching solution. The optimal conditions to manufacture calcium nitrate was got bysignal tests: the induced time was30min, the crystalline temperature was-8℃, theaging time was3h. Under the optimal conditions to get calcium nitrate, its yield was45.3%, its purity was99.94%which met the standards required by the industryHG3787-2005. The microscopy, TG and FTIR analysis showed the compound wasmonoclinic crystal, their diameter were almost equal, but the length were not equal,the result of TG analysis met the weightlessness of Ca(NO3)2·4H2O at hightemperatures.In this paper, the author adopted the method of combining acid leaching andalkali dissolving, successfully manufactured high purity, high whiteness ofprecipitated silica, and recovered the leaching solution, so improved thecomprehensive utilization of yellow phosphorus slag. This new process not onlyreaches the purpose of energy saving and environment protection, but also reducesthe cost of precipitated silica and calcium nitrate, therefore this process has a goodapplication and development prospect.