Study On Rare Earth Leaching Of Bastnaesite Mediated By Acidithiobacillus Ferrooxidans

Bastnasite（REFCO₃）is a typical rare earth fluorine carbonate mineral and an important source of rare earth minerals.Currently,these valuable rare earths are mainly obtained from bastnasite by high temperature roasting followed by acid leaching,however,this method has major problems such as high consumption of acid and other chemical materials,high costs and easy pollution of the surrounding environment.Biological hydrometallurgical technology has outstanding characteristics such as being economical,green and environmentally friendly.Acidithiobacillus ferrooxidans（abbreviated as A.ferrooxidans）is a typical acidophilic bacterium that produces acid continuously from simple inorganic substances and has been used industrially in various fields such as bioleaching of copper.Therefore,this study proposes to use the acid and Fe³⁺generated during the oxidation of pyrite by A.ferrooxidans to leach rare earths from cerium fluorocarbon ores and focuses on the factors influencing the dissolution of cerium fluorocarbon ores mediated by A.ferrooxidans;the dissolution effect at the interface between A.ferrooxidans and cerium fluorocarbon ores;the main secondary minerals in the leaching system and the absorption of rare earths.The main secondary minerals in the leaching system and their adsorption to rare earths were investigated.The main conclusions drawn from carrying out the above aspects of the study are as follows:（1）In a certain range,appropriate to reduce the particle size of bastnasite can significantly accelerate the dissolution of cerium fluorocarbon ore and rare earths dissolution rate,such as the particle size down to about 0.075 mm（200 mesh）,leaching rate significantly increased,about 0.15 mm（100 mesh）cerium fluorocarbon ore particle size of 3 times.（2）The addition of F^-ligands(Fe³⁺and Al³⁺)to the leach solution both helped to promote the dissolution of bastnaesite,and because the stability constant of Al³⁺complexing with F^-to form[Al F₆]^3-was greater than that of Fe³⁺complexing with F^-to form[Fe F₅]^2-,the promotion effect of Al³⁺was better than that of Fe³⁺at the same molar concentration of the two.（3）After roasting at high temperatures（500°C and 600°C）,bastnaesite was converted to rare earth oxides,and the leaching of rare earths from bastnaesite was significantly enhanced under acidic conditions（p H<3）,with Ce and La leaching rates greater than 65%,much higher than those in the unroasted bastnaesite system（less than 3%）.（4）In both contact and non-contact experiments,the growth of A.ferrooxidans,the chemical variables of the leaching solution and the leaching effect of rare earths were not significantly different in the two experimental systems,indicating that there was no significant physical leaching effect of A.ferrooxidans at the bastnaesite interface.（5）In the rare earth adsorption experiments,neither the A.ferrooxidans fungus nor the secondary minerals showed any significant adsorption effect on the rare earths in solution,indicating that the rare earths existed mainly in ionic form in the leachate.In summary,A.ferrooxidans was used to leach the roasted bastnaesite in a two-step process to obtain good leaching results for the rare earths.Without the addition of strong acids and other chemical materials,the vast majority of the rare earths in bastnaesite have been dissolved in about 5 days of leaching.Roasting has a large effect on the dissolution of bastnaesite and the leaching of rare earths,e.g.when the roasting temperature is increased to 600°C,where both La and Ce leaching rates reach 80%.