Paragenetic Association and Synergistic Separation of Li-ga-ree Multielements In High-alumina Coal and Coal Ash

Author:Shao Pei

Supervisor:wang wen feng


Degree Year:2019





With the depletion of traditional rare metal deposits,coal-bearing associated metal deposits have attracted much attention.In recent years,technological research on extracting rare earth elements from coal and coal ash has been strengthened in the United States.The rare metal minerals associated in high-alumina coal are expected to become an important source of rare elements,but it is not clear to paragenetic association and synergistic separation of Li-Ga-REE multi-element.Aiming at this scientific problem,the Permo-Carboniferous coal seam in Datong coalfield and fly ash from coal-fired power plants were selected as the research object.By means of orthogonal experiment,XRD,XRF,SEM,ICP-MS and NMR were used to study the symbiotic combination characteristics of Li-Ga-REE in high-alumina coal and coal ash and their synergistic separation technology.The following results have been achieved.(1)The paragenetic association characteristics of Al-Li-Ga-REE multi-elements in Permo-Carboniferous coal in Datong coalfield are clarified.The content of Al2O3 in coal ash ranges from 10.77%to 71.37%,with an average of 38.88%.High-alumina coal is mainly distributed in Tongxin and Tashan coal mines in the northeast of the coalfield and Zhifengshan coal mine in the southeast of the coalfield.Li,Ga and REE are relatively enriched in the northern and eastern of the coalfield.Li,Ga and REE mainly occur in clay minerals,and boehmite and phosphate are also important carriers of Ga and REE,respectively.(2)The enrichment mechanism of paragenetic association of Al-Li-Ga-REE multi-element in coal is revealed.Al,Li,Ga and REE are mainly transported from the source area to the accumulation center of coal-forming peat marshes,often enriched in the marsh deposits of delta plain.Sedimentary parent rock is granite in Yinshan mountain and bauxite strata of Benxi Formation.From bottom to top,the sediments of No.3,5 and 8 coal seams are gradually weakened by the influence of seawater,and the contents of Li,Ga and REE are gradually increased.The short-term transgression causes enrichment of HREE at the bottom of No.5 coal seam.(3)The mineralogical and elemental geochemical characteristics of high-alumina coal ash are illuminated.The main minerals in high-alumina coal ash include mullite,corundum,quartz and hematite,and the glass phase exists in Q4(0Al)structure of silica-oxygen tetrahedron.The contents of Zn,Bi,Pb,Cu,U,Be,Li,Tl,In,Ta,Cs,Th and LREE increase with the fineness of fly ash,while the contents of Cd,Ni,Mo,Cr,Co,Rb,Ga,Sc,Sr,Y and HREE decrease and then increase with the fineness of fly ash.These elements mainly occur in glass phase,and mullite is an important carrier of Al and part of Ga.(4)The synergistic separation technology of Li-Ga-REE in high-alumina coal ash was obtained.It was found that the optimum ratio of sintering additives was 0.45g of Na2CO3 and 1.46g of CaCO3 per gram of fly ash(FNC).The leaching rates of Li and Ga in FNC tended to be stable in 4 days,and their leaching rates were 95.75%and87.60%respectively.The residual coefficients of REE in the residue were 95.78%.Ammonia water adjusting acidity and alkalinity can be used to separate Li and Ga from leaching solution and REE from residue.When pH=6,Ga3+in leaching solution precipitates completely in the form of Ga(OH)3,while REE3+in hydrochloric acid solution precipitates in the form of REE(OH)3 at pH=11.5.(5)The influence mechanism of leaching Li,Ga and REE from high-alumina fly ash by oxalic acid was explored.The results of orthogonal experiments indicate that the effects of sintering additives,oxalic acid concentration and leaching time on the leaching efficiency of Li,Ga and REE decrease in turn.The bridge oxygen bond in Si-O(Al-O)polymer structure in fly ash was destroyed in the roasting process of sintering additives,which greatly accelerates the leaching rate of rare elements.The leaching rate of Li and Ga in FNC increased with the increase of oxalic acid concentration and leaching time.(6)The law of material change and element migration in the process of synergistic separation was revealed.New substances NaAlO2 and Ca2SiO4 were generated in the roasting process of sintering additives Na2CO3 and CaCO3,which releases Li,Ga and REE from fly ash.Al,Li and Ga are dissolved in leaching solution in the form of cation,and REE is combined with oxalic acid to form oxalate precipitation.Be,Cr,Mn,Co,Cu,Zn,Mo,Nb,Ba,Tl and U are easily leached by oxalic acid,while Sc,Ni,Rb,Sr,Cd,In,Cs,W,Pb,Bi,Th and Ta are enriched in the residue.There are 126 figures,16 tables,6 schedules and 223 references in this paper.