Ammonia Leaching-extraction And Recovery Of Zinc From Blast Furnace Gas Ash

Blast Furnace dust is a by-product of ironmaking process.Its main components are iron and carbon.In addition,it contains a small amount of elements such as zinc,sodium and potassium.Among them,the harmful elements of zinc and the content of it need to be further reduced.In order to separate and recover of Zinc from blast furnace dust,It was selectively leached by ammonia-ammonium carbonate solution,and recovered by extraction and stripping.The Mextral54-100??-diketone,HA?and Lix84I?oxime,HNAPO?were used as extractant,and TRPO?phosphines?was used as co-extractant.Besides,the extraction mechanism of Zinc was studied by density functional theory?DFT?,based on quantum chemistry.The process of"ammonia-ammonium carbonate leaching-CO₂ enhanced extraction"of blast furnace dust was proposed.The main conclusion as follows:?1?The experimental results of recovering of zinc from blast furnace dust and resource utilization of dust was developed by ammonia-ammonium carbonate leaching show that the optimal reaction condition as follows:NH₃ concentration 2mol/L,?NH₄?₂CO₃ concentration 2mol/L,temperature 50?,liquid-to-solid 6:1,leaching time3h.Under the optimum conditions the leaching ratio of zinc and iron are 91%and1.15%,the content of zinc was decreased from 9.54%to 1.13%,the content of iron was concentrated from 35.9%to 47.6%,respectively.The XRD and SEM-EDS analysis of leaching residue showed that the oxides and sulfates of zinc in the raw material were dissolved and leached,the zinc-iron spinel was not leached and present together with the iron oxide in the residue.?2?The results showed that during the process of extracting zinc by HA and HNAPO,the O and C atoms on enol-form of HA,the C and N atoms on oxime,the O atom on phenol of HNAPO,which accounting for the highest contribution to the molecular frontier orbitals.FT-IR studies of extractant show that the stretching vibration peak of the C=C bond on the HA show red-shifted,the intensity of the distortion vibration peak of the C=N double bond on the oxime group changed,and the characteristic absorption peak of the phenolic hydroxyl group on the HNAPO disappeared after extraction reaction.Those results indicating that the enol form,oximido and phenolic hydroxyl group were the active centers during extraction process.After extracted zinc,Zn²⁺replaced enol-form hydrogen and with oxygen atom to form coordination bond,the C=O double bond stretched during zinc extraction process by HA.Besides,Zn²⁺replaced phenolic hydroxyl H atom and reacted with O and N atoms to form coordination bonds,the benzene and Zn?II?were on the same plane of zinc extracted HNAPO molecule.The?E(?E_LUMO–HOMO)and electronegativity of HA were lower than HNAPO.The chemical potential was higher than HNAPO,which indicated that the extraction capacity was in the order of HA>HNAPO.The experimental results were in good agreement with the theoretical prediction results.?3?Enhancing of CO₂ on the extracting of zinc from blast furnace dust ammonia leaching solution by HA,and tri-alkyl phosphine oxide?TRPO?diluted with kerosene.Results demonstrate that the extraction of zinc increases as the CO₂ pressure,HA and TRPO concentration increases in the organic phase.Zinc is effectively extracted from blast furnace dust ammonia leaching solution by 0.2MPa CO₂,1.2mol/L HA and0.2mol/L TRPO dissolved in kerosene at an initial pH of 8.0 and aqueous-to-organic phase ratio?A/O?of 2:1 using two countercurrent stages.The loaded organic phase that contained 5.28g/L Zn²⁺can be completely stripping by one-stage stripping with156.8g/L H₂SO₄ at phase flow ratio of A/O=1:1 to give a strip solution containing51.5g/L Zn²⁺.The extraction ratio of zinc can be promoted by CO₂ obviously,however,the excessive pressure of CO₂ could produce carbonate-precipitation.FT-IR studies verify that CO₂ could avoid the phenomenon of ammonia molecules co-extracted into HA and TRPO extraction system.Based on the experimental results,a flowsheet for the recovery of zinc from blast furnace dust ammonia leaching solution was developed and tested.The result showed that the zinc leaching rate about 91%,zinc extraction efficiency about 97%,respectively,and the concentration of Zinc was 51⁵8g/L in the stripping solution.