以山西塔山煤系高岭土为原料,采用“先煅烧后漂白”工艺对其进行增白实验研究。通过单因素实验探究煅烧、化学漂白阶段的工艺参数,并对化学漂白阶段进行Box-Behnken响应面实验,优化制备工艺参数。采用XRD、SEM和FT-IR等手段对原料及实验各阶段产物进行表征,分析其理化性质以探究增白机理。实验结果表明:在煅烧温度为950℃、恒温时间为3.0h和NaCl质量分数为2%的煅烧条件下可获得白度为83.51%的样品(calcinedkaoline,CK);响应面回归模型的相关系数R2=0.9979,优化模型可信度较高;化学漂白实验对白度的影响有显著性关系的四因素为草酸用量、Na2S2O4用量、矿浆pH值及反应温度;在矿浆pH值为3.6、Na2S2O4质量分数为3.4%、草酸质量分数为3.9%和反应温度为38℃的响应面优化方案下对样品CK进行化学漂白,最终产品的Fe2O3质量分数由原先的1.93%降至0.28%,白度由5.72%升至90.09%,满足GB/T14563-2020优质高岭土白度要求。TG-DSC、XRD、SEM和FT-IR分析结果表明:原料的主要成分为高岭石,经950℃煅烧3.0h后其晶体结构发生变化,形成无定形且活性更高的偏高岭石,而未形成莫来石;化学还原漂白过程对偏高岭石内部结构影响甚微,即不会破坏偏高岭石的晶体结构。

Coal series kaolin from Shanxi Tashan was used as raw material, and the “cal-cination followed by bleaching” process was adopted for whitening experimental research. The process parameters of calcination and chemical bleaching stage were explored through single-fac-tor experiment. The Box-Behnken response surface experiment was carried out on the chemical bleaching stage to optimize the preparation process parameters. Techniques like XRD, SEM and FT-IR were used to characterize the raw materials and products at each experimental stage, and analyze their physicochemical properties to explore the whitening mechanism. The experimental results show that sample (calcined kaolin,CK) with calcination whiteness of 83.51% can be ob-tained at the condition of calcination temperature 950 ℃, holding time 3.0 h and NaCl mass ratio 2%. The correlation coefficient of the response surface regression model is R2=0.997 9, indica-ting a high confidence of the optimization model. The four factors that have a significant relation-ship on whiteness in chemical bleaching experiments are oxalic acid dosage, Na2S2O4 dosage, pH value of slurry and reaction temperature. Under the response surface optimization scheme with the slurry pH of 3.6, the mass ratio of Na2S2O4 is 3.4%, the mass ratio of oxalic acid is 3.9% and the reaction temperature is 38 ℃, the Fe2O3 content of the final product was reduced from 1.93% to 0.28%, and the whiteness increased from 5.72% to 90.09%, meeting the whiteness requirements of GB/T 14563-2020 high-quality kaolin. Analysis results from TG-DSC, XRD, SEM and FT-IR indicated that the main component of the raw material is kaolinite. After calcina-tion at 950 ℃ for 3.0 h, its crystal structure changed, forming amorphous and more active metakaolinite, without forming mullite. The chemical reduction bleaching process has little effect on the internal structure of metakaolinite, meaning that it does not destroy the crystal structure of metakaolinite.