The Research On Whiteness Of Diatomite

The application of diatomite is very extensive because of many excellent characters,such as high specific surface area,strong adsorptive and chemical stability.As diatomite industry started late,backward in R&D and production technology,the utilization of diatomite resource is low value-added.As high grade diatomite is not very much In China,each year our country have to import a large number of diatomite filter aids and functional filler with high valued-added from abroad,we are faced with the contradiction between shortage of high grade diatomite resource and the growing needs for high-end diatomite products.Therefore,R&D of low grade diatomite has huge market demand,good application prospect,high economic and social benefit.The whiteness of diatomite is an important index effecting the value in many fields.In this paper,the white diatomite from Jinlin Changbai as raw experimental material,the physical and chemical properties are analyzed in detail.We selected the appropriate flux calcination process,researched the species and dosage of fluxing agent,ways of mixing,the calcination temperature,the heating rate,the cooling method for the influence of whiteness,preliminary explored and validated the mechanism of flux calcination diatomite.The main conclusions are as follows:(1)The main mineral composition of diatomite from Changbai is amorphous silica opal and some quartz,cristobalite.The surface morphology of diatom is disc-type with the diameter of several microns to dozens of microns.There are a small amount of debris scattered around the disc and surface,arranged holes with nanometers to dozens of nanometers.The colour of diatomite from Changbai is light grey,the colour is beige after calcination without other treatments.With the increase of calcination temperature,the colour becomes red.Calcination would change the specific surface area and porous structure to a certain extent.The higher the calcination temperature,the more serious the microstructure is destroyed,the more serious molten agglomeration is.(2)The result of fluxing agent shows that:the dry mixing fluxing agent and diatomite to enhance the whiteness is more significant.Na is the most effective element to improve the whiteness of diatomite.The additions of NaCl or Na₂CO₃ both can improve the whiteness of diatomite markedly,the effect of KCl or MgCl₂ for whiteness is limited.The flux whiteness of diatomite increased from 46%to 88%with the dosage of Na 2.33%of NaCl.Increasing the dosage of fluxing agent is beneficial to improve the flux whiteness of diatomite,however,when cations of fluxing agent is too high,the flux whiteness of diatomite will decrease slightly.Calcination temperature,the heating rate,the cooling method all can play a role to the flux whiteness of diatomite.(3)The cations of fluxing agent(such as Na⁺)hindered the formation of ?-Fe₂O₃,making iron element is stable in some form(entering to the structure of quartz to replace silicon,entering to the octahedral site of diatomite,dispering into as small as nanometer particles or single atom)without colour.The role of sodium element is to stabilize the iron atom in structure and to balance valence bond in the valence state.