Mechanism And Experimental Study Of SHA/SLAS Synergistic Capture Of Bastnaesit

China possesses the world’s largest reserves of rare earth resources.However,as rare earth deposits continue to be exploited,the proportion of China’s reserves of rare earth resources in the world has been declining year by year.Furthermore,the easily beneficiated rare earth mineral resources are decreasing annually,and existing rare earth resources commonly suffer from severe weathering,complex mineral compositions,a high content of gangue minerals,complicated beneficiation processes,and low recovery for rare earth elements.Therefore,the efficient recovery and utilization of rare earth resources is crucial for ensuring the stability and sustainable development of China’s rare earth industry.The bastnaesite-type rare earth minerals are the most important for extracting rare earth elements and possess high industrial application value.Therefore,efficient recovery of these rare earth resources is a crucial component in the sustainable development strategy of the rare earth industry.In this thesis,bastnaesite was selected as the primary research subject,and a technical approach was proposed to synergistically collect bastnaesite using a combination collector of salicylhydroxamic acid（SHA）and sodium lauroyl sarcosinate（SLAS）.Firstly,the effects of collectors,depressants,and unavoidable ions on the flotation behavior of bastnaesite and gangue minerals have been determined through single mineral flotation tests.Secondly,the molecular structures and solution properties of salicylhydroxamic acid（SHA）and sodium lauroyl sarcosinate（SLAS）and the action mechanism of the combined SHA/SLAS collector on the surface of bastnaesite were analyzed by means of solution chemical analysis,surface tension test,Zeta potential test,FT-IR,XPS,To F-SIMS surface analysis and quantum chemical calculations.Finally,flotation tests were conducted on the rare earth ore from the No.1 deposit of Dalucao in Dechang,and the theoretical findings of this study were successfully applied to the flotation separation of actual bastnaesite ore.The outcomes of flotation tests conducted on single-minerals demonstrated that SLAS could effectively collect bastnaesite.Additionally,the combination collector of SHA/SLAS,when paired with the depressant of sodium silicate or citric acid at a slurry pH of 8,enabled the effective separation of bastnaesite from fluorite,barite,and calcite.In the SHA/SLAS flotation system,both Ca（Ⅱ）ions and Fe（Ⅲ）ions had depressant effects on bastnaesite,fluorite,barite and calcite under alkaline conditions,with Fe（Ⅲ）ions particularly exhibiting a significant depressant effect on barite.Additionally,Pb（II）ions at a concentration of 5.0×10^-5mol/L had an activating effect on the above four minerals within a pH range of 3 to 12.The surface adsorption characteristics revealed that SHA and SLAS primarily chemisorbed onto the bastnaesite surface in the form of salicylhydroxamic acid anions（SHA^-）and lauroylsarcosine anions（LAS^-）,with the optimal pH for adsorption between 8 to 9.SLAS exhibited high surface activity and could form intermolecular hydrogen bonds with SHA,and significantly reduced the surface tension of the SHA solution.Moreover,SLAS molecules have multilayer physical adsorption on the bastnaesite surface.The surface morphology of bastnaesite changed from smooth to rough after being treated with SHA/SLAS combination collector,forming a hydrophobic film consisting of numerous small particles on its surface.Additionally,the contact angle increased from 9.98^°to 51.36^°.The hydrophobic films may consist of Ce-SHA and Ce-LAS chelates,which were formed through the interaction between the hydroxamic group（-CONHOH）in the SHA molecule and the O atoms in the carboxyl（-COO^-）and amide groups（-CON）in the SLAS molecule with the Ce active site on the bastnaesite surface.The quantum chemical calculations showed that the adsorption of SHA^-,LAS^-,and SHA^-/LAS^-on Ce（OH）²⁺can occur spontaneously.The two O atoms in the hydroxamic acid group of SHA^-and the O atom in the amide group and the single bond O atom in the carboxyl group of LAS^-were all nucleophilic active sites for reactions,which undergo charge transfer with the active site Ce on the bastnaesite surface to form covalent bonds between Ce and O,forming a Ce-SHA five-membered or a Ce-LAS seven-membered cyclic chelate structure,respectively.The interaction between SHA^-/LAS^-and Ce active sites of Ce（OH）²⁺formed a five-membered chelating structure[SHA-Ce（OH）]⁺and a monodentate coordination structure[LAS-Ce（OH）]⁺,in which the synergistic effect of the benzene ring and long carbon chain hydrophobic groups enhanced the floatability of bastnaesite.The verified flotation test results of actual rare earth ore indicated that SHA/SLAS combined collector could effectively collect bastnaesite in a complex slurry system.The raw ore with a REO grade of 6.52%could be processed through the“one-stage rougher,three-stage scavenging,three-stage cleaning,and three-stage scavenger-cleaning”closed-circuit flotation process to obtain qualified rare earth concentrate with a REO grade of 51.07%and a recovery of 66.68%.In this thesis,the mechanisms of SHA and SLAS on bastnaesite and their synergistic collection effect were systematically investigated.Additionally,the theoretical model for the synergistic regulation of bastnaesite flotation by SHA/SLAS combined collector was initially constructed,providing a theoretical support and technical guidance for efficient recovery of bastnaesite.