Study On Bleaching Test Of Beihai Kaolin Using Thiourea Dioxide

Beihai City in Guangxi Province is the main area to produce kaolin in our country, the Beihai kaolin belongs to not completely weathered granite residual ore deposit, has the crystal form to be good, the granularity to be thin,the whiteness to be higher and other characteristics, but the impurity iron element's existence in the undressed ore has affected the Beihai kaolin widespread application.At present, the whiteness before and after calcination of the purification Beihai kaolin's is between 80%-85%, not yet achievesⅠclass standards of quality raw materials in the paper industry and ceramic industry. This experiment,on the basis of research and analysis on the Beihai kaolin's mineral characteristics and existence's state of dyeing impurities,has carried out a large number of experimental investigation on the bleaching of Beihai Kaolin using thiourea dioxide, mainly used the method is: Using activatory dioxide thiourea in the role of a catalyst to blanch kaolin and the newborn liquid state dioxide thiourea to blanch kaolin, The results show that:(1) The Beihai kaolin's undressed ore,which main mineral composition is kaolinite, white mica and quartz,and furthermore,has a small amount of hematite, limonite,siderite and extremely small amount of diasporite.Iron is the main coloring elements in the Beihai kaolin,and a part exists by structural iron form ,others exist by the form of iron oxide minerals.They are the main target of edulcorating and whitening the Beihai kaolin.(2) Rare earth lanthanum was screened out,as a catalyst,can make bleach kaolin technology by thiourea dioxide to get rid of the dependence on high temperature and alkali conditions.When the pH value of slurry 9, the amount of thiourea dioxide 0.6%, reaction time 120min, and the amount of lanthanum is 0.2% catalyst (relative to the amount of thiourea dioxide),after bleaching,the Beihai kaolin's whiteness is increased from 82% to 90%. whiteness after calcination (1250℃)is increased from 84% to 92%,their iron oxide content is decreased from 1.17% to 0.78%.The natural whiteness has achieved levelⅠstandard kaolin raw material used in the papermaking industrial, the whiteness after calcination has achieved levelⅠstandard kaolin raw material used in the ceramic industry.(3) Best process that newly generated liquid thiourea dioxide bleachs the Beihai kaolin,is:ore slurry concentration is 20%,adjust the pH value of slurry to 4 with sulfuric acid,thiourea dosing quantity is 0.6 percent,oxyful dosing quantity is 0.55 percent,after reacting for 1 hour,adjust the pH value of slurry to 8,join 0.2% of lanthanum nitrate as catalyst,and continue reacting for 90 minutes ,after that it is over.It can make the whiteness of beihai kaolin in 89% above,and after calcined (1250℃) its whiteness reaches 91% or so,its iron oxide content declines to 0.85%,its whiteness in natural and after calcined both reached levelⅠstandard kaolin raw material used in the papermaking industrial and the ceramic industry.It approachs the same indicators of bleaching method in solid thiourea dioxide(4) Bleaching the Beihai kaolin with thiourea dioxide or newly generated liquid thiourea dioxide, the effect is better than the traditional sodium dithionite technology. Thiourea dioxide carries on the response mainly in weak alkaline condition,will not produce acidic waste water,and thiourea dioxide's decomposition products is urea which will not increase the COD and BOD values in water,is free from pollution to the environment.In short, it is a kind of new kaolin bleaching technology of green environmental protection.