| Tailings are a typical bulk industrial solid waste generated during the beneficiation process,and remained a large amount of harmful substances such as heavy metals.How to effectively reduced heavy metals pollution and seek the optimal resource utilization was the focus of people's attention.In this study,the iron tailings were taken as the research object,using the leaching method to remove heavy metals in iron tailings,the removal rate of heavy metals in iron tailings with different leaching agents and leaching conditions was studied.Analyzed the change of heavy metals morphology in iron tailings before and after leaching,and the heavy metals in the leaching wastewater were recycled by chemical precipitation method.The iron tailings were mixed with alumina,silica,and calcium oxide,and a one-step sintering method was used to prepare glass-ceramics.The detection methods such as XRD,QXRD,SEM and EDS were used to analyzed the prepared samples,and the effect of microstructure and crystallinity on the mechanical and chemical properties of the sample was explored.The main results were as follows:?1?Pb,Cu,Cr reached the highest when the oxalic acid concentrations were 250,100,200 mmol/L,respectively,the removal rates were respectively 19.9%,43.9%and 4.2%.The removal effects of Zn and Ni were best when the concentrations of EDTA-2Na were 100 and200 mmol/L respectively,and the removal rates were 33.2%and 39.4%,respectively.During the oxalic acid leaching process,the removal rates of Cu and Pb gradually increased with the increase of shaking time,and the removal rates of Zn,Ni and Cr tended to be stable after 120min.EDTA-2Na had little effect on the removal rate of heavy metals with the extension of the shaking time,and it basically stabilized when the shaking time was 60 min.The morphology of heavy metals after oxalic acid leaching was analyzed,and it was found that the leaching can not only effectively remove the easily migrated forms of heavy metals,but also caused the migration and transformation between heavy metal forms.Correlation analysis found that the correlation coefficients of heavy metal leaching content and exchangeable state and carbonate binding state were 0.930 and 0.996,respectively.In the recovery experiment of heavy metals,when the p H was 4,the obtained precipitate was mainly iron hydroxide precipitate.When the p H was 6,the obtained precipitate was mainly the precipitate of Pb and Cu.When p H=7-8,mainly Zn hydroxide precipitate obtained.When the p H was 10,the resulting precipitate was mainly Mn precipitate and a small amount of Zn precipitate.The recovery rates of Pb,Zn,Cu,Mn and Fe could respectively reach 97.6%,99.5%,99.9%,99.7%and 100.0%when the p H was 10.?2?Under the heat treatment condition of 1450?for 2 h,the main crystalline phase of the samples obtained from the Al2O3:tailings and Al2O3:Si O2:tailings system was mullite?3Al2O3·2Si O2?,and the main crystalline phase in Al2O3:Si O2:Ca O:tailings system was anorthite?Ca Al2Si2O8?.The phase transformation of the samples sintered at 950-1450?was studied.It was found that at 950-1100?,the eutectic point between the raw materials was not reached due to the low temperature,and no crystal was formed by the reaction.Between 1100-1250?,the transformation of gehlenite to anorthite was observed.When the temperature was increased to 1250-1450?,all the crystalline phases in the sample were transformed to anorthite.Among Al2O3:tailings system,mullite had the largest content of 54.5%when Al2O3:tailings=2:3.In the Al2O3:Si O2:tailings system?Al2O3:Si O2:tailings=6:2:3?,the maximum content of mullite was 83.7%.In the Al2O3:Si O2:Ca O:tailings system,the content of anorthite reached its maximum?72.9%?when Al2O3:Si O2:Ca O:tailings=7:8:4:6.When the temperature increased from 1180?to 1450?,the anorthite content increased significantly from 4.1%to 67.9%.?3?When Al2O3:tailings was 2:14,the sample had the lowest water absorption rate?0.4%?,and the strongest acid and alkali resistance?99.97%and 99.99%?.When Al2O3:Si O2:tailings were reduced from 6:2:1 to 6:2:6,the water absorption rate was reduced from 31.4%to 0.7%,the acid and alkali resistance were respectively 99.84%and 99.97%when Al2O3:Si O2:tailings was 6:2:6.When the Al2O3:Si O2:Ca O:tailings decreased from7:8:4:2 to 7:8:4:6,the water absorption obviously decreased from 25.4%to 0.3%.The sample had the strongest acid and alkali resistance as Al2O3:Si O2:Ca O:tailings was 7:8:4:8,which were 98.44%and 99.97%,respectively.When the temperature was from 1250oC to 1450oC,the water absorption was reduced from 36.7%to 0.3%,the compressive strength of the samples increased from 203.6 MPa to 733.6 MPa,and the acid and alkali resistance were respectively 99.48%and 99.99%at 1450oC.The mechanical strength decreased as the porosity of the material increased,but in samples with higher crystallinity,the mechanical strength of the sample was toughened and strengthened due to the crack-crystal interaction.The glass-ceramic product obtained by mixing iron tailings with alumina,silicon oxide and calcium oxide after high temperature sintering by a 28-day toxic leaching test,the leaching concentrations of Pb,Zn and Cu in the leaching solution were 0.26,0.89 and 1.51 mg/L,respectively.The concentration of Cr and Ni was lower than the detection limit,which far below the limit specified by USA EPA. |
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