Study On The Role Of Key Microbial Metabolites In Indirect Bioleaching Of Weathered Crust Elution-deposited Rare Earth Ore

Weathered crust elution-deposited rare earth ore(also known as ion adsorption rare earth ore,or ionic rare earth ore)is a strategic key mineral resource and a specific mineral species for conservation mining in China.The traditional ammonium sulphate leaching method,which was once commonly used in industry,has gradually been restricted due to environmental requirements.This poses a serious challenge to the rare earth industry.It is urgent need to develop clean and efficient new technologies.Bioleaching is particularly suitable for the treatment of low-grade complex mineral resources due to its advantages in terms of low carbon,green and low cost,and has important potential for the clean and efficient extraction of weathered crust elutiondeposited rare earth ore.Rare earth bioleaching mainly uses biofilm action(direct action principle)and chemical bonding/complexation of metabolites(indirect action principle)to extract valuable elements from minerals.Due to weathered crust elutiondeposited rare earth ore in-situ leaching is mainly used in industry,conventional bioleaching methods are difficult to apply.The use of bioleaching based on the indirect action/non-contact principle is the inevitable choice.That is,leaching mainly using microbial metabolites.Therefore,citric acid/citrate and gluconic acid/gluconate based microbial metabolites are used as leaching agents to construct a non-contact bioleaching system in this paper,and then carry out research on leaching behaviour,permeability and morphological transformation of rare earth elements.The results of the mineralogical analysis showed that the main phases of the weathered crust elution-deposited rare earth ore included quartz,feldspar,mica,kaolinite and eclogite,etc.The main chemical components were aluminosilicate and compounds containing iron,potassium,sodium,magnesium and titanium.The rare earth elements were mainly present in the ionic phase with a grade of 0.0726 ‰;some of the Al was present in the form of hydrated ions or hydroxyl hydrated ions,which are easily leached by cation exchange.Microbial metabolites(citrate and gluconate)prepared by biofermentation-separation and purification were used as leaching agents to construct a weathered crust elution-deposited rare earth ore non-contact bioleaching system,followed by a study of leaching behaviour and permeability.The results showed that the selected microbial metabolite leaching agent could effectively leach rare earth elements from weathered crust elution-deposited rare earth ore,with the ability to leach rare earth elements ranked from strong to weak: citrate > gluconate > ammonium sulphate.At the cation concentration of 15 m M and the liquid-solid ratio of 6:1,the leaching efficiency of rare earth elements in the citrate leaching system reached over 99%.Within a range of leaching agent concentration,p H and mineral particle size,increasing leaching agent concentration,decreasing p H and increasing mineral particle size all contribute to enhancing solution permeability during leaching process.The leaching agent seepage rates in the range of 5～50 m M leaching agent concentration are in descending order:ammonium sulphate ≈ gluconate > citrate.Zeta potential analysis showed that the amount of negative charge on the mineral surface decreased with increasing leaching agent concentration and decreasing p H,the less negative charge on the mineral surface,the thinner the double electric layer,resulting in the increase in the leaching agent seepage rate.Surface tension analysis showed that leaching agent type,concentration and p H did not have a significant effect on the surface tension of the solution and had a limited effect on permeability.Based on rare earth complex titration experiments and leach solution characterization,the chemical forms,migration and transformation mechanisms of rare earth elements during weathered crust elution-deposited rare earth ore leaching process were investigated.During weathered crust elution-deposited rare earth ore leaching process,rare earth ions form a variety of complex complexes with citrate,thus transferring rare earth elements from the mineral surface to the leaching solution.The type,chemical form and molecular structure of the complexes are determined by the concentration of rare earth elements and citrate,the p H of the solution and other factors.This study helps to reveal the bioleaching mechanism of weathered crust elutiondeposited rare earth ore,provide a theoretical basis for the regulation and enhancement of the non-contact bioleaching process,and help to establish a new theory and method for weathered crust elution-deposited rare earth ore clean and efficient extraction.