Experimental Study Of Technology On Bleaching Kaolin With Thiourea Dioxide Strengthened By Mechanical Activation

As a new reducing agent,thiourea dioxide(TD)has an advantage of strong reducibility,stockpile security,less dosage and pollution-free,which makes it widely used in dyeing,paper making and other industries.TD was also used in reducing bleaching kaolin field.But,due to the possession of TD deco mposing into sulfoxylate and show its reducibility only happened in the environment of strongly alkaline(pH>10)heating(>70?),the application of TD is greatly limited.To reduce the dependence of TD releasing reducibility on heating and strongly alkaline and further promote the application of TD in kaolin industry,ball mill,which is widely used in ceramic industry,was introduced to mechanically activate kaolin,which can make TD show a higher reducibility when it is in the environment of normal temperature(25?~40?)and weak base(pH?8).Specific results are as follows:(1)Experiment of bleaching Xingzi kaolin with TD strengthened by mechanical activation was done,using single factor experiments to analyze how activation time,TD dosage,planetary ball mill speed,slurry density and feeding methods influence kaolin whiteness and iron content.When the reaction conditions are as follows: planetary ball mill speed 400r/min,ratio of water and material 1:2,TD dosage 0.8% of kaolin dry material,reduction reaction time 2h,the effect is most obvious.Under these conditions,the whiteness of Xingzi kaolin can be improved from 68.02% to around 77%.Compared to kaolin samples bleached by 1.4% sodium hydrosulfite,whose whiteness is 71.78%,and samples bleached by TD with the same dosage but in 25 ? and 85 ? environment of traditional stirred bleaching,whose whiteness are respectively 71.98% and 74.63%,TD strengthened by mechanical activation bleaching method has obvious advantages.(2)Using optimum conditions of TD bleaching strengthened by mechanical activation method to bleach high whiteness Yunnan kaolin and coloring substance more complicated Zhanjiang kaolin,the effect is also obvious.The whiteness of Yunnan kaolin can be improved from 84.83 to 88.83%,the whiteness of Zhanjiang kaolin can be improved from 61.71 to 72.68.(3)Do controlled trials of milling the three kinds of kaolin.It was showed that there is only some improvement of the whiteness of the three samples,but it's not obvious.It means that the reduce of fineness after milling doesn't make significantly improve of the whiteness.The obvious effect of bleaching kaolin with TD strengthened by mechanical activation is the result of TD bleaching promoted by mechanical activation.(4)By testing and analyzing the samples before and after bleaching with TD strengthened by mechanical activation,it can be showed that: after mechanical activation,original compact lamellar structure of Xingzi kaolin is opened,releasing iron oxide adsorbed between layers,which makes it more efficiently reduced by TD.After mechanical activation,dehydroxylation shappened to kaolin ite,some of the structure water lost,tetrahedral ordering and bridge between the tetrahedral and octahedral is destroyed.(5)Expanded laboratory test: do pilot test of bleaching kaolin with TD strengthened by mechanical activation with commercially available Xingzi kaolin,using a 200 kg large ball mill.Test showed that: a better bleaching and iron removal effect of kaolin can be reached by raising the pH to 13 and setting the activation time to 14 h.