Experimental results here can give some new insights into the mechanism of selective recovery of scandium and sodium from high alkali Bayer red mud(RM) through sulfation-roasting-leaching process. Effects of roasting and leaching conditions including roasting time, roasting temperature, concentrated H_2SO_4 addition, leaching temperature, leaching time and liquid to RM solid ratio on the leaching rates of calcium, iron, aluminum, silicon, sodium, titanium, scandium and gallium were studied and analyzed, suggesting that roasting temperature and roasting time were the two primary constraints on selective recovery of Sc and Na. High leaching temperature also brought a negative effect on the iron leaching rate. Phase transitions and thermal behaviors of sulfated RM indicated that sodium had an inhibitory action on the liberation of SO_2 or SO_3 from metal sulfates, which should follow the decomposition order of TiOSO_4>Ga_2(SO_4)_3>Fe_2(SO_4)_3>NaFe(SO_4)_2>NaAl(SO_4)_2~Al_2(SO_4)_3>Na_3Sc(SO_4)_3>Na_2SO_4>CaSO_4. After water leaching, solid-liquid separation could be carried out extremely smoothly and >95 wt.% Na+, ~60 wt.% Sc in [Sc(H_2O)_x(SO_4)_n]^(3–2n)(x≤6) with impurities of 0 wt.% Fe^(3+), 0 wt.% Ti4+, 0 wt.% Ga^(3+), 7 wt.% Al^(3+), ~29 wt.% Ca^(2+) and ~3 wt.% Si^(4+) could be leached into leachant under the optimized roasting and leaching conditions. The alkali-free residue obtained could then be employed as iron-making or building materials.
Direct reduction of high-phosphorus oolitic hematite ore based on biomass pyrolysis gases(CO,H_2,and CH_4),tar,and char was conducted to investigate the effects of reduction temperature,iron ore-biomass mass ratio,and reduction time on the metallization rate.In addition,the effect of particle size on the dephosphorization and iron recovery rate was studied by magnetic separation.It was determined that the metallization rate of the hematite ore could reach 99.35% at iron ore-biomass mass ratio of 1∶0.6,reduction temperature of 1 100℃,and reduction time of 55 min.The metallization rate and the aggregation degree of iron particles increase with the increase of reduction temperature.The particle size of direct reduced iron(DRI) has a great influence on the quality of the iron concentrate during magnetic separation.The separation degree of slag and iron was improved by the addition of 15 mass% sodium carbonate.DRI with iron grade of 89.11%,iron recovery rate of 83.47%,and phosphorus content of 0.28% can be obtained when ore fines with particle size of-10 μm account for 78.15%.
Dong-bo HUANGYan-bing ZONGRu-fei WEIWei GAOXiao-ming LIU
Calcium silicate slag is the residue of process of pre-desilication alkali lime sintering applied in the high-alumina fly ash to extract the alumina.The quantitative phase analysis(QPA) of the calcium silicate slag has been performed by the Rietveld method based on the powder X-ray diffraction(XRD) with the aid of noncommercial software GSAS-EXPGUI.A known weight of crystalline internal standard(10% CaF_2) was added to the calcium silicate slag to calculate the fraction of amorphous phase and other crystalline phases on an absolute basis.Besides,the calcium silicate slag was characterized by X-ray fluorescence(XRF) and thermo gravimetric(TG) differential scanning calorimetry(DSC) to test the QPA results and investigate its other characters.Finally,the results show that the amorphous fraction is 17.5%(hereinafter,the percentages refer to the mass fraction),and the major crystalline phases detected in the calcium silicate slag consist of 23.5% Beta-Ca_2 SiO_4,10.0% bredigite,10.3% Ca_3Al_2O_6(C_3A) and 21.6% CaCO_3.
