Extraction of selected rare earth elements from anthracite acid mine drainage using supercritical CO2 via coagulation and complexation

Rare earth elements(REEs)are valuable raw materials which are in great demand in modern high technology industries.Developing methods to produce/recover REEs from waste is significant to the national security of any developed country.This study was focused on investigating the use of supercritical CO2(sCO2)to extract REEs from anthracite acid mine drainage(AMD).Four different mine drainage water source locations at Blaschak Coal Corp.in Pennsylvania,USA were selected for sample collection.An extraction process was developed and demonstrated for two of those water sources containing the highest concentration of REEs.A method involving metal ion coagulation,their dissolution from the sludge into a concentrated aqueous HNO3 solution,complexation with organic ligands and sCO2 extraction was developed to recover REEs from AMD.Specifically,sodium aluminate(NaAlO2)was used as the coagulant to concentrate REEs from the AMD into a solid precipitate.Consequently,over 99%of the REEs in AMD is concentrated in the remaining sludge.During the coagulation process,the effects of pH and NaAlO2 concentration on REE precipitation were investigated.Fuming nitric acid(HNO3)was used to digest the pre-concentrated sludge and tributyl phosphate(TBP)was used to form REE/TBP/HNO3,a non-polar complex with selected REEs,specifically,cerium(Ce),lanthanum(La)and neodymium(Nd).HNO3 concentration and organic/aqueous phase ratio were considered as the variables to improve complexation efficiency.Dynamic extraction experiments using sCO2 and REE/TBP/HNO3 solutions were then conducted at optimal conditions of 60℃and 20 MPa.The overall REE extraction efficiencies are found to increase with the atomic number of the REE.As a result,the average overall REE extraction efficiencies of 41.8%,40.1%and 58.2%for Ce,La and Nd,respectively,are obtained.The potential improvements in the overall extraction efficiency are also discussed.

Separation and Identification of Flavonoids from Fistular Onion Stalk(Allium fisturosum L.var.Caespitosum Makio)

The chemical constituents of fistular onion stalk obtained by supercritical CO2 extraction were separated and purified by silica gel and sephadex LH-20 gel column chromatography and the preparative TLC method and four flavonoids were obtained. On the basis of the spectral data, they were structurally identified as （＋）-catechin, （-）-epieatechin, astragalin, and 3-O-β-D（2-O-β-D-glu- copyranosyl）-glucopyranosides of kaempferol.

Gas Chromatography–Mass Spectrometry for Quantitative and Qualitative Analysis of Essential Oil from Curcuma wenyujin Rhizomes

Objectives:A rapid and sensitive gas chromatography–mass spectrometry(GC–MS)method for quantitative and qualitative analysis of essential oil from Curcuma wenyujin rhizomes was established.Methods:The essential oil of C.wenyujin rhizomes was extracted by supercritical CO2 extraction(SFE).Six main bioactive compounds(eucalyptol,β-elemene,curzerene,germacrone,curdione,and curcumol)were analyzed in selected ion monitoring mode(SIM).Results:Curzerene is not originally present in C.wenyujin rhizomes,but is a product of the transformation of furanodiene at high temperature.The six target components demonstrated good linearity(R2>0.9979)over a relatively wide concentration range.The interday and intraday variations had relative standard deviation values less than 5%and the average recovery ranged from 96.95%to 100.04%.The limit of quantitation ranged from 0.032 to 0.235μg/mL.The developed method was successfully used to analyze the six compounds in 17 samples collected from different origins.Significant variation was observed for the concentrations of the six compounds.In addition,51 constituents were identified in C.wenyujin rhizome essential oil,consisting of 87.66%of the total essential oil,including curdione,curzerene,dehydrocurdione,germacrone,1,4-bis(2-benzimidazoyl)benzene,neocurdione,curcumenone,andβ-elemene.Conclusions:The proposed method will be useful in the quality control of C.wenyujin rhizome essential oil production.