Mechanism of CeMgAl_(11)O_(19):Tb^(3+) alkaline fusion with sodium hydroxide

Comprehensive CeMgA111O19： Tb3＋ （CTMA） disintegration via alkaline fusion was discussed. The rare earth （RE） elements in CTMA were dissolved by HC1 completely after alkaline fusion. Relationships between the alkaline fusion temperature and various properties of the compounds were examined by various techniques to elu- cidate their roles in the expected CTMA disintegration. X-ray diffraction （XRD） analysis indicates the phase transformation sequence. A scientific hypothesis of crystal structure disintegration presents that sodium ions substitute for the europium and barium ions in the mirror plane and magnesium ions in the spinel block successively, resulting in that more oxygen vacancies and interstitial sodium ions appear. The unit cell [P63/mmc （194）] breaks from the mirror plane. Then it is decomposed into NaA102, and magnesium, cerium, and terbium ions combine with free OH- into MgO, Tb2O3 and CeO2; Tb2O3 and CeO2 change into Ceo.6Tbo.O2-x. In the end, the rare earth oxide is recycled easily by the acidolysis. The mechanism provides fundamental basis for recycling of REEs from waste phosphors.

Mechanism and kinetics of the BaMgAl_(10)O_(17):Eu^(2+) alkaline fusion reaction

Knowledge of the kinetics and mechanism of BaMgAl10017：Eu2＋ （BAM） fusion with sodium hydroxide will benefit recy- cling rare earth elements （REEs） from the waste phosphors. The reaction temperature range of 290-375 ~C and the reaction mecha- nism were determined using X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. Activation energy was determined by the four model-free methods, and calculated results showed that the Kissinger method value of 579.5 KJ/mol was close to the average value of the Kissinger-Akahira-Sunose （KAS） and the Flynn-Wall-Ozawa （FWO） methods of 563.5 kJ/mol. The calculated activation energy variation tendency versus conversion factor agreed with the proposed mechanism.

Mine tailings as a raw material in alkali activation: A review

The mining industry produces billions of tons of mine tailings annually.However,because of their lack of economic value,most of the tailings are discarded near the mining sites,typically under water.The primary environmental concerns of mine tailings are related to their heavy metal and sulfidic mineral content.Oxidation of sulfidic minerals can produce acid mine drainage that leaches heavy metals into the surrounding water.The management of tailing dams requires expensive construction and careful control,and there is the need for stable,sustainable,and economically viable management technologies.Alkali activation as a solidification/stabilization technology offers an attractive way to deal with mine tailings.Alkali activated materials are hardened,concrete-like structures that can be formed from raw materials that are rich in aluminum and silicon,which fortunately,are the main elements in mining residues.Furthermore,alkali activation can immobilize harmful heavy metals within the structure.This review describes the research on alkali activated mine tailings.The reactivity and chemistry of different minerals are discussed.Since many mine tailings are poorly reactive under alkaline conditions,different pretreatment methods and their effects on the mineralogy are reviewed.Possible applications for these materials are also discussed.