Evaluation Of Ion-adsorption Rare Earths Leaching Characterization And The Selection Of Leaching Reagents

It is necessary to optimize the green and high efficiency leaching process of ion-adsorption rare earth（IARE）based on the characterization of minerals and reagents and the requirement of leaching efficiency（LE）and environmental protection（EP）.Therefore,it is great theoretical significance and practical application value to establish a set of simple methods to evaluate the LE and environmental impact of leaching reagent and correlation with minerals for the scientific development of IARE resources.In this study,the effect of leaching agents and their concentrations as well as the minerals on rare earth concentration,p H,conductivity and Zeta potential of clay minerals was investigated by a continuous equilibrium titration leaching method using an electroacoustic Zeta potential meter.Therefore,the influence of mineral particle size,sampling dosage,electrolyte concentration and analysis method of rare earth content on the determination results and error range were determined.Combing the relationship of these parameters with pollutants concentration and turbidity of water leaching solution of tailings with different electrolytes,a system method has been established for obtaining parameters above and the abrasion p H and exchange p H of minerals,determining the dependence of LE on reagents and their concentration,evaluating the pollutants emission and soil erosion risk of tailings,selecting leaching reagents and their optimal concentration range.This method can completely replace the previous methods of column drenching and equilibrium leaching due to its less agent consumption,less time,has less error and more information.With the method above,the influence of reagents and their concentrations on the LE of IARE,Zeta potential of clay minerals,the p H and conductivity of suspension solution of two typical mineral samples during the equilibrium leaching process by continuous titration of electrolyte solutions,such as the sulfate,nitrate and chloride of aluminum,magnesium,zinc,calcium,potassium,sodium and ammonium were investigated,and the Zeta potential,p H,conductivity,the concentrations of sulfate or chloride,the turbidity of equilibrium solution of tailings in water were determined.The results show that for each electrolyte,the LE of IARE increases with the increase of electrolyte concentration,however,the required concentration range and the increase range are different.Among the tested cations,aluminum has the highest LE and the fastest rate with increasing concentration.In nitrate medium,the LE,Zeta potential and p H all changed in the order of aluminum,calcium,magnesium,zinc,potassium,ammonium and sodium,which accords with the hydration theory.Similar order is observed for chloride and sulfate medium.but for the order of p H in chloride,calcium and magnesium move forward.More importance,the order of LE in sulfate medium,mono valence ions ammonium and potassium exceeds the bivalent cation.Compared with nitrate electrolyte and chloride electrolyte,the Zeta potentials of clay minerals in sulfate electrolyte are more negative and the LE of IARE is higher.This fact is related to the adsorption of sulfate into the stern layer of the double electric layer on the surface of clay particles,so that the trivalent rare earth ions can be more easily leached due to the formation of low valence rare earth sulfate cation.However,the enhancement of the interaction between bivalent cation and sulfate group in buck solution will reduce the LE of IARE,resulting in a reversal phenomenon between mono valence of K⁺,NH₄⁺and two valence of Mg²⁺,Zn^2+.The large negative value of Zeta potential of clay minerals increases because the high valence of anions are adsorbed into the stern layer or mono valence of cations are mainly distributed in the diffusion layer.High valence of ions are more likely to enter the stern layer and show stronger LE of IARE and high stability of tailings.There is a linear relation between Zeta potential and the LE of IARE,and its slope value and the linear range are related to the type of both electrolyte and mineral,which can be used to evaluate the leaching capacity of each reagent for IARE.The p H value of leachate decreases with the increase of concentration of electrolytes,and is related to the electrolyte type and concentration.Therefore,the exchange capability of electrolyte for hydrogen ion can be evaluated by the dependence of p H on the electrolyte type and their concentration.Furthermore,the relationship of LE of IARE with the acidity of minerals can be discussed by comparing with its abrasive p H.After leaching with electrolyte solutions,Zeta potential,p H,turbidity and pollutant ion escape ability of tailings all change in the order of aluminum,calcium,magnesium and zinc,potassium,ammonium and sodium.However,according to this order,Zeta potential decreases,while p H,turbidity and pollutant ion escape ability increase.With the increase of leaching times,the concentration of anions of electrolytes and the conductivity of solution decreased,however,the p H of suspension increases gradually.The Zeta potential of clay minerals in tailings increases first and then decreases for aluminum salts,decreases first and then increases for ammonium,potassium and sodium salts.little change was observed for calcium,magnesium and zinc salts.After three times of water immersion,the turbidity of solution is mainly determined by the valence state of cations.Large turbidity is observed for mono valence cations,no or less turbidity for aluminum ions and bivalent cation,which are determined by their Zeta potentials.So,selecting electrolytes of high valence cations can greatly improve the LE of IARE and reduce the soil erosion and pollutant emission from the tailings.