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

• Published in: International journal of minerals, metallurgy and materials metallurgy and materials, 2014-04, Vol.21 (4), p.317-325
• Main Authors: Zhu, Pei-wang, Zeng, Wei-qiang, Xu, Xiu-lin, Cheng, Le-ming, Jiang, Xiao, Shi, Zheng-lun
• Format: Article
• Language: English
• Subjects: Acid leaching; Calcination; Ceramics; Characterization and Evaluation of Materials; Chemistry and Materials Science; Coal; Composites; Corrosion and Coatings; Differential thermal analysis; Dissolution; Economic analysis; Ferric ions; Ferrous ions; Glass; Hydrochloric acid; Hydrochloric acid leaching; Ions; Iron; Kaolin; Leaching; Materials Science; Metallic Materials; Mossbauer spectroscopy; Natural Materials; Oxalic acid; Roasting; Surfaces and Interfaces; TG-DTA; Thermal analysis; Thin Films; Tribology; X-ray diffraction; X-射线衍射; 三价铁离子; 焙烧; 煅烧高岭土; 煤系高岭土; 酸浸取; 除铁
• ISSN: 1674-4799; 1869-103X
• DOI: 10.1007/s12613-014-0911-z

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.