Preparation and mechanical properties of polypropylene fiber reinforced calcined kaolin-fly ash based geopolymer

To improve the environmental benefits and solve the problems of large shrinkage and high brittleness, the partial replacement of calcined kaolin by fly ash as a raw material for geopolymer synthesis and the influences of polypropylene (PP) fiber on the mechanical properties and volume stability were investigated. The results show that compressive strength of the geopolymer containing 33.3%(mass fraction) fly ash by steam curing at 80 ℃ for 6 d is improved by 35.5%. The 3-day compressive strength, flexural strength and impacting energy of geopolymers containing 0.05%PP fiber increase by 67.8%, 36.1% and 6.25%, while the shrinkage and modulus of compressibility decrease by 38.6% and 31.3%, respectively. The results of scanning electron microscopy (SEM) and the appearances of crack growths confirm that PP fiber can offer a bridging effect over the harmful pores and defects and change the expanding ways of cracks, resulting in a great improvement of strength and toughness.

Characterization of Calcined Kaolin/TiO_2 Composite Particle Material Prepared by Mechano-Chemical Method

Calcined kaolin/TiO2 composite particle material （CK/TCPM） was prepared with TiO2 coating on the surfaces of calcined kaolin particles by the mechano-chemical method. X-ray diffraction （XRD） and scanning electron microscope （SEM） were used to investigate the microstructures and morphologies, respectively. The mechanism of the mechano-chemical reaction between calcined kaolin and TiO2 was studied by infrared spectra （IR）. The results show that TiO2 coats evenly on the surfaces of calcined kaolin particles by Si-O-Ti and Al-O-Ti bonds on their interfaces. The hiding power and whiteness of CK/TCPM are 17.12 g/m^2 and 95.7%, respectively, presenting its similarity to TiO2 in pigment properties.

APPLICATIONS OF FLOCCULANT IN BLEACHING AND WASHING OF KAOLIN

The difficulties of washing during the dressing of kaolin ore have been analyzed, the multistep intermittent washing model has been deduced, and effective methods for dealing with the difficulties were put forward. Experimental results show that the bleaching and washing process was enhanced, the washing time was shortened and the consumption of water was reduced by means of adding flocculant.

IMPROVEMENT OF BLEACHING OF KAOLIN USING CHELATING AGENTS

Bleaching of the kaolin ore from Shaziling Kaolin Mine in Jiangxi Province of China was studied with the aim of enhancing the quality and value of the ore to meet the requirements from the ceramics manufacturers. Factors affecting the reductive bleaching of kaolin ore with sodium dithionite as the bleaching agent were studied and optimized to increase the whiteness of the kaolin ore from 38. 5% to about 65%. However, it was found that in the conventional bleaching process, a washing step to remove the ferrous ions from the bleached kaolin suspension was indispensable, which made the process complicated and restricted the capacity of the production. In addition, the whiteness of the bleached kaolin products was unstable. To solve the above problems, a new technique with the application of chelating agents in the bleaching process was developed to remove ferrous ions and get rid of the washing step. The bleaching process of kaolin was simplified. The whiteness of the bleached kaolin products was stabilized as well as increased to about 70%. The mechanism of the bleaching process and the action of the chelating agents were discussed.

Coating mechanism of nano-TiO_2 films on the surface of ultra-fine calcined coal kaolin particles

A new type of mineral composite was made by calcined coal kaolin.The interaction mechanism of an inorganic modification reagent TiOSO4 with the surface of ultra-fine calcined coal kaolin particles（substrate） was studied by X-ray photoelectron spectroscopy.The results show that chemisorption exists in the phase boundary between the modification agent and the substrate surface,while physical adsorption occurs on the modification layers of hydrate titanium dioxide.The interaction force was calculated and analyzed according to DLVO theory between ultra-fine calcined coal kaolin particles and hydrate titanium dioxide nano-particles in the modification system.It is shown that the both electrostatic force and van der Waals force are attractive,and the coacervation between ultra-fine calcined coal kaolin particles and hydrate titanium dioxide nano-particles leads to the coating of hydrate titanium dioxide on the surface of ultra-fine calcined coal kaolin particles.

STUDY ON ENHANCING THE WHITENESS OF CALCINED KAOLIN BY USING ADDITIVE

To meet some special requirements such as paper filler,ceramic titanium white and synthetic 4A zeolite, the raising whiteness of calcined kaolin has become more and more important. The calcined experiments were carried out with and without additive to increase the whiteness of calcined kaolin. Results show that additive of chloride (A) or oxides can obviously increase the whiteness of calcined kaolin. Meantime,the mechanisms of enhancing the whiteness of calcined kaolin were discussed.

Study of Surface Modification Mechanism of Calcined Kaolin by MAS NMR

The 29 Si and 27 Al in modified and unmodified calcined kaolin were researched and compared by using MAS NMR. The result shows that the chemical shift of -106×10 -6 of 29 Si almost keeps unchanged after being modified, but 27 Al changes obviously. The chemical shift of 5.44×10 -6 and 65.69×10 -6 of 27 Al are separately shifted to 3.8×10 -6 -4.4×10 -6 and 54.6×10 -6 -59.9×10 -6 after being modified. And the chemical modification of kaolin is completed by linking with Al on the surface of it.

Influence of acid leaching and calcination on iron removal of coal kaolin

Calcination and acid leaching of coal kaolin were studied to determine an effective and economical preparation method of calcined kaolin. Thermogravimetric-differential thermal analysis （TG-DTA） and X-ray diffraction （XRD） demonstrated that 900＆#176;C was the suitable temperature for the calcination. Leaching tests showed that hydrochloric acid was more effective for iron dissolution from raw coal kaolin （RCK）, whereas oxalic acid was more effective on iron dissolution from calcined coal kaolin （CCK）. The iron dissolution from CCK was 28.78wt%, which is far less effective than the 54.86wt% of RCK under their respective optimal conditions. Through analysis by using M？ssbauer spectroscopy, it is detected that nearly all of the structural ferrous ions in RCK were removed by hydrochloric acid. However, iron sites in CCK changed slightly by oxalic acid leaching because nearly all ferrous ions were transformed into ferric species after firing at 900＆#176;C. It can be concluded that it is difficult to remove the structural ferric ions and ferric oxides evolved from the structural ferrous ions. Thus, iron removal by acids should be conducted prior to calcination.

Dry Separation of Iron Minerals from Low-Grade Coal-series Kaolin

Dry separation of iron mineral from low-grade coal-series kaolin in Hubei Province of China was investigated. The structure and chemical composition of the kaolin ore were determined by X-ray diffraction(XRD) and X-ray Fluorescence(XRF) analyses. The narrow particle size range classification, dry magnetic separation and calcination were carried out to evaluate the particle size distribution, and the relation between the content of iron and the whiteness. Experimental results revealed that the highest content of iron(3.70%) in kaolin ore was in the particle size range from 60 to 74 μm, and pyrite was the main occurrence of iron in the kaolin ore. Dry magnetic separation showed that the removal rate of iron in kaolin ore could be increased obviously after calcination, and the rate of iron removal was 60% in the particle size range from 60 to 74 μm. As pyrite can be transformed into hematite through calcination, thermodynamic studies and XRD analysis showed that the maximum content of hematite was obtained at 900 ℃, which would be more beneficial to magnetic separation.

Influence of Replacement Level of Coal-series Kaolin on Hydration of Ordinary Portland Cement by X-ray Diffraction/Rietveld Method

The influence of replacement level of calcined coal-series kaolin(CCK) on hydration of ordinary Portland cement(OPC) was studied by X-ray diffraction(XRD)/Rietveld method. X-ray diffraction/Rietveld method was used to quantify the crystalline phase composition of the hydrated samples. Additionally, the morphology of hydrated samples was observed by scanning electron microscopy(SEM). The results showed that, calcium hydroxide(CH), ettringite(AFt) and amorphous phase content in hydrated samples decreased as the replacement level of CCK increased, while AFm and str?tlingite increased, which was caused by the combination of dilute, physical and pozzolanic effects. The hydration of anhydrous cement phases was accelerated by physical effect but hindered by the retardation effect of CCK. The role of each effects was discussed in detail to analyze the mechanism of OPC hydration with CCK addition. The SEM images showed that the shortening of AFt at 1 day and the denser texture at 28 days was observed with CCK addition, which was caused by the physical and pozzolanic effects, respectively.

Alumina Recovery from Kaolin with Mineral Impurities

The alumina recovery from low grade kaolin （K-JS） treated through thermal and mechanical methods was investigated. High grade kaolin （K-SX） was used as comparison. The optimum calcination temperatures for K-JS and K-SX were both 600 ℃, which resulted in 89.34wt% of alumina extraction from K-JS and 83.37wt% from K-SX. With the increase in calcination temperature, the chemical reactivity of calcined K-JS and K-SX to acid decreased. Mechanical treatment was much more effective in increasing the alumina extraction from activated kaolin. Around 99wt% of alumina was extracted from K-JS ground for 10 hours and 95wt% of alumina was extracted from K-SX ground for 20 hours. The IR results showed that the substitute of A1 for Si occurred in calcined K-SX, however, the impurities in K-JS decreased this substitute. More alumina could be extracted from low grade kaolin than that from high grade kaolin under identical thermal or mechanical conditions.

Production of γ-Al₂O₃from Kaolin

The paper reports a process for synthesis of γ-alumina from kaolin. Kaolin was transformed to meta-kaolin by calcination at 800oC for 2h. γ-alumina powder was synthesized through extracting alumina from meta- kaolin via H2SO4 and meta-kaolin reactions and consequently precipitation in ethanol, which led to form the aluminum sulfate. The precipitated aluminum sulfate was dried and calcined at 900 oC for 2h, which resulted the formation of γ-alumina. The structure of γ-alumina was confirmed by XRD and FTIR and the mean particles size of γ-alumina was determined by SEM to be 0.5 - 0.9 μm. The study revealed the kaolin could be promising material for preparation of γ-alumina.

SYNTHESES OF 4A ZEOLITE IN DETERGENTS WITH KAOLIN

The main technical conditions for synthesizing 4A zeolite with kaolin were determined. The whiteness and calcium ion exchange capacity (CIEC) of the product were increased by calcining and screening the colouring ions, and the high quality 4A zeolite was synthesized successfully. Moreover, the formation mechanism of zeolite also discussed.

高吸油量煅烧高岭土的制备与性能表征

通过插层剂二甲基亚砜、接枝剂甲醇和剥离试剂十六烷基三甲基溴化铵协同超声震荡辅助作用,将层状煤系高岭土剥离为超细片状煤系高岭土。通过X射线衍射(XRD)、傅里叶红外(FT-IR)、N_(2)吸附-脱附及扫描电镜(SEM)与能谱分析(EDS)等技术手段对煤系高岭土进行表征。结果表明,其层间距由层状煤系高岭土的0.708 nm扩大到片状煤系高岭土的1.12 nm,内部孔隙增加,形成了裂隙形状的介孔且孔径分布均匀。煅烧高岭土较煤系高岭土的吸油性能大幅提升,其吸油量从60~73 g/100 g煤系高岭土增至70~79 g/100 g煅烧高岭土。整个制备工艺流程中无引入强酸强碱等腐蚀性物质,提供了一种环境友好型煅烧高岭土制备技术。

基于高岭土增韧环氧树脂水泥基材料的多强度组合指标配比优化法

煅烧高岭土能有效改善环氧树脂水泥基材料的力学性能,实验表明:煅烧高岭土可大大提高环氧树脂水泥基材料的3 d早期抗折、抗压强度,当高岭土掺量为30%时,改性环氧树脂水泥基材料的抗折及抗压强度分别提高了134.28%、106.25%;当高岭土掺量小于30%时,改性环氧树脂水泥基材料具有二次抗折强度,且抗折强度残余率大于50%。根据不同高岭土掺量对改性环氧树脂水泥基材料抗压强度、抗折强度、二次抗折强度的影响规律,提出了适用于不同结构工程受力特点的多强度组合指标配比优化法,获得了考虑二次抗拉强度影响的不同最大拉应力和最大压应力组合条件下最优的高岭土配比,为实际不同结构体不同部位不同受力特征的高岭土改性环氧树脂水泥基材料制备提供了理论依据。

煅烧高岭土对沥青老化性能影响的试验研究

为改善沥青路面路用性能,延长使用寿命,研究煅烧高岭土(CK)改性沥青的抗老化性能。通过旋转薄膜烘箱(RTFOT)、压力老化容器(PAV)、动态剪切流变仪(DSR)和傅里叶红外光谱(FT-IR)分析CK对沥青老化性能的影响以及沥青老化前后的化学官能团变化。结果表明:随着CK掺量的增加,沥青软化点和粘度逐渐升高,针入度和延度有所降低,同时CK使沥青具有较高的复剪切模量,当CK掺量为15%时,抗车辙性能最优;CK显著降低了基质沥青软化点指数(SPI)、粘度指数(VAI)和复剪切模量指数(CMAI),大幅提高了针入度保留率(PRR)和相位角指数(PAI);FT-IR试验表明,CK抑制了基质沥青热氧老化时羰基指数(I_(C=O))和亚砜基指数(I_(S=O))的产生,从而有效地改善了沥青的抗老化性能。

不连沟煤矿煤矸石中分选高岭岩试验研究

为了实现煤矸石的多用途资源化利用,以不连沟煤矿煤矸石为研究对象,在分析煤矸石的理化特性,确定高岭岩在煤矸石中赋存状态的基础上,探讨了煤矸石分选高岭岩的理论与方法,并研究了不同煅烧温度、煅烧时间对高岭岩煅烧高岭土白度的影响。试验结果表明:通过基于图像识别和物质识别的智能干选及风力分选技术,可以从煤矸石中有效分选出高岭岩,高岭岩煅烧高岭土过程中,在煅烧温度为1 000℃、煅烧时间3 h的条件下,高岭土产品的白度可达84%,可满足二级白度高岭土的工业应用要求。

煅烧高岭土/Sb_(2)O_(3)协效阻燃LDPE电缆护套研究

采用煅烧高岭土部分替代Sb_(2)O_(3)制备LDPE阻燃电缆护套材料,考察煅烧高岭土与卤锑阻燃剂对LDPE的协效阻燃作用,结果表明:煅烧高岭土部分替代Sb_(2)O_(3)对LDPE阻燃材料维卡软化点温度的影响不大;用20%(质量分数)煅烧高岭土替代氧化锑时,LDPE阻燃材料的起始分解温度提高,点燃自熄时间较短,具有较佳的耐热性,能够与卤锑阻燃剂起到阻燃协效作用,并能降低材料成本。

Box-Behnken模型优化煤系高岭土增白实验研究及表征

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3.0 h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(calcined kaoline,CK);响应面回归模型的相关系数R^(2)=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、Na_(2)S_(2)O_(4)用量、矿浆pH值及反应温度;在矿浆pH值为3.6、Na_(2)S_(2)O_(4)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Fe_(2)O_(3)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/T 14563-2020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3.0 h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。

某砂质高岭土增白试验研究

为了合理高效开发云南某高岭土矿资源,基于矿石性质分析,分别采用连二亚硫酸钠和二氧化硫脲2种还原剂开展增白试验研究。针对粒度-0.020 mm的高岭土样品,确定二氧化硫脲漂白适宜的工艺条件为矿浆浓度20%、二氧化硫脲用量2.0%、矿浆pH值13、草酸用量5%、反应温度30℃、反应时间20 min。在此条件下,高岭土中Fe_(2)O_(3)含量从0.95%降低至0.70%,除铁率达26.32%,自然白度由65.0%提高至83.5%。与连二亚硫酸钠相比,除铁率提高了11.58个百分点,自然白度提高了9.1个百分点。二氧化硫脲在加热或被碱催化时产生强还原性的次硫酸,次硫酸将高岭土中不溶性铁还原为可溶性亚铁后除去,进而提升砂质高岭土的白度。相较于二亚硫酸钠,二氧化硫脲除铁效果好、化学性质稳定且环境污染小,可用于同类型高岭石的除铁增白。