Investigations on mineralogical characteristics of rare earth minerals in Bayan Obo tailings during the roasting process

This paper focused on the investigation of the mineralogical characteristics of rare earth minerals from Bayan Obo tailings during the roasting process in the presence of coal,Ca（OH）_2 and NaOH.Roasting experiments and leaching experiments were carried out to study the decomposition of rare earth minerals.The results indicated that bastnaesite and monazite could be completely decomposed at 650 ℃ and the leaching ratio of rare earths could reach 89.78%.The reaction mechanisms of bastnaesite and monazite at 650 ℃were analyzed.For bastnaesite,both the outer layer decomposition and inner core decomposition occurred simultaneously during the roasting.However,monazite was decomposed in a spatial sequence starting from the outer layer and proceeding to the inner core.

Separation of Sc_(2)O_(3) from Bayan Obo tailings through an innovative roasting method

Sc_(2)O_(3)was successfully extracted and separated from Bayan Obo tailings by a CaCl_(2)-reductive carbon powder-combinative roasting method.The optimum pro-cess condition was obtained through adjusting specific ef-fect factors.It is found that Sc_(2)O_(3)with the ratio of 87.51%is leached out under roasting temperature of 800℃for 2 h through adding 73%CaCl_(2),and 20%reductive carbon powder with liquid to solid ratio of 3.Moreover,the specific reaction mechanism during roasting process was investi-gated by thermogravimetric–differential scanning calorimetry(TG-DSC)and X-ray diffraction(XRD)tech-niques.The results show that the main phases(SiO_(2),CaF_(2) and NaFeSi_(2)O_(6))as well as important phases(LiScSi_(2)O_(6),REFCO_(3)and REPO_(4))would turn into new phases(CaFe-SiO_(4),Fe,Ca_(3)(PO_(4))_(2),NaCl,RE_(2)O_(3)and Sc_(2)O_(3))after com-plicated reactions,which effectively break up the original mineral compositions and activate the existing state of containing scandium matter,consequently facilitating the subsequent hydrochloric acid leaching process.

Process and property optimization of ceramsite preparation by Bayan Obo tailings and blast furnace slag

The ceramsite was prepared by using Bayan Obo tailings and blast furnace slag of Baotou Steel as the main raw materials and coal gangue as pore-forming agent,and the process system and the performance of ceramsite were optimized.The phase transformation rules of the ceramsite prepared by multi-source solid waste in sintering method were clarified.The influence of sintering process parameters on ceramsite performance and the purification effect of ceramsite on ammonia nitrogen wastewater were revealed.The results show that the reasonable proportion of raw materials for preparing ceramsite is 60%tailings,35%blast furnace slag and 5%coal gangue.The reasonable preparation process of ceramsite is preheating at 350℃ for 12 min,increasing the temperature to 750℃ and holding for 60 min,then increasing the temperature to 1130℃ and roasting for 20 min.The cooling method is to cool down with the furnace.The prepared ceramsite has compressive strength of 1.89 MPa,porosity of 51.31%,water absorption of 31.42%,and bulk density of 1.94 g/cm^(3).When the ceramsite is used to treat ammonia nitrogen wastewater,the removal rate of ammonia nitrogen is 47.33%.

Iron recovery and rare earths enrichment from Bayan Obo tailings using Coal-Ca(OH)2-NaOH roasting followed by magnetic separation

The recovery of iron and enrichment of rare earths from Bayan Obo railings were investigated using Coal Ca（OH） 2 NaOH roasting followed by magnetic separation. The influences of roasting temperature, roasting time, coal content, milling time, Ca（OH）2 dosage and NaOH dosage on the iron and rare earths recovery were explored. The results showed that the magnetic concentrate containing 70.01 wt. % Fe with the iron recovery of 94.34G and the tailings of magnetic separation containing 11.46 wt. % rare earth oxides （REO） with the REO recovery of 98. 19% were obtained under the optimum conditions （i. e. , roasting temperature of 650℃, roasting time of 60 min, coal content of 2.0%, milling time of 5 min, and NaOH dosage of 2.0%）. The Ca（OH）2 dosage had no effect on the separation of iron and rare earths. According to the mineralogical and morphologic analysis, the iron and rare earths of Bayan Obo tailings could be utilized in subsequent ironmaking process and hydrometallurgy process.

Effect of bastnaesite as reductant on hematite reduction during in-situ suspension magnetization roasting of refractory iron ore under neutral atmosphere

The iron tailings of Bayan Obo mines are solid waste,which occupies land area and also causes environmental pollution;however,this waste can be recycled.In this study,based on the characteristics of iron minerals and fluorocarbonate contained in Bayan Obo iron tailings,clean magnetization roasting of iron minerals by bastnaesite from iron tailings during in-situ suspension magnetization roasting in a neutral atmosphere was explored.The results show that for iron tailings with a mass of 12 g,a N_(2) gas flow rate of 600 mL/min,and roasting for 5 min at 800℃,iron concentrate with a 60.44%iron grade at an iron recovery of 76.04%could be obtained.X-ray diffraction analysis showed that the weak magnetic hematite was reduced to strong magnetic magnetite in the neutral atmosphere,without additional reductant.The kinetics of the magnetization roasting of mineral mixtures(bastnaesite and hematite)in a neutral atmosphere showed that the optimal reaction mechanism function was the three-dimensional diffusion model with activation energy of 161.8838 kJ·mol^(-1);this indicates that the reaction was a heterogeneous,diffusion-controlled solid-state reaction.