Organic-Inorganic Salts Enhanced Leaching Ion Adsorption Rare Earth In Stepwise

Efficient leaching and green production are the key contents in the development of ion-adsorption type rare earth ore.Among them,the basic content of a new leaching technology is to select the appropriate leaching agent and determine the required concentration range and leaching steps.Therefore,many studies have been performed on the enhancement of leaching process using inorganic salt electrolyte and organic acids or salts.Although organic acid salts can promote the leaching of ion-adsorption type rare earth ore,the coordination adsorption of organic acid anion on the surface of clay minerals can lead to an increase in the absolute value of Zeta potential of clay minerals,which make it difficult to form effective percolation in ion-adsorption type rare earth ore,its practical application is still difficult.In this paper,a staged leaching method is promoted,which use organic acid salt to leach rare earths,and inorganic salts to callback the Zeta potential of ion-adsorption type of rare earths ore.This method can also improve the recovery rate of rare earths,reduce water and soil loss form tailings and ensure the quality of leaching water above drain standards.Therefore,in the staged column leaching process,a small amount of organic salts were used firstly,and then the inorganic salt to leach the ion-absorption type of rare earth.The concentration of rare earth and impurities,such as aluminum,uranium and thorium in the leaching solution as well as the Zeta potential of tailings were monitored to study the influence of process conditions,for instance the type and the used amount of leaching agents,to the leaching efficiency in the staged leaching method.It indicates that among the organic acid salt leaching agents in the first stage,sodium citrate has the best effect due to its coordination with rare earth and its strong adsorption on the surface of clay minerals.Moreover,sodium citrate has a strong leaching ability for aluminum ions,uranium and thorium,and its leaching amount is related to the mineral source.In the second stage,the focus was on studying the effect of staged leaching of calcium chloride,magnesium chloride,ammonium sulfate,aluminum chloride,as well as aluminum sulfate and sodium citrate.It has been proven that the rare earth leaching efficiency can all exceed 100%,and the difference is not significant;However,the absolute value of Zeta potential of clay minerals in tailings decreases,and the difference is obvious.Therefore,the selection of inorganic salts in the second stage is mainly based on their cost and environmental protection effects,with the goal of stabilizing tailings,reducing landslide risk,and eliminating pollutant release.When the coordination ability of inorganic salt cations with citric acid is strong,the rare earth leaching rate will be reduced due to competition with rare earth coordination,especially during aluminum salt leaching.Before aluminum sulfate leaching,a small section of weakly coordinated sodium chloride leaching needs to be added to eliminate the impact.The leaching conditions for samples of Dingnan ore and Fujian ore by sodium citrate and calcium chloride in different stages were systematically studied.The optimum conditions were determined as follows: the mass concentration of sodium citrate in the first stage was 4%,and the ratio of ore weight to feed was 0.3.The concentration of calcium chloride in the second stage was 0.032mol/L and 0.128 mol/L,and the ratio of ore weight to feed was 0.3 and 0.7,respectively.Kinetics of ion-adsorbed rare earth minerals extracted by calcium chloride or sodium citrate and calcium chloride in staged process under different leaching concentration,clay mineral particle sizes and column ratio are also studied.The leaching of rare earth ions are accorded with the dynamic process under the control of internal diffusion model in our experiments.The increase of leaching agent concentration,the decrease of mineral particle size and the decrease of column ratio are conducive to the increase of rare earth leaching rate.The effect of initial water content and leaching method on the leaching effect of sodium citrate and calcium chloride in different stages shows that with the increase of water content,the outflow peak of rare earth gradually moves backward,but the peak value changes little.Compared with column leaching,rapid leaching driven by pressure difference has the greatest influence on the Dingnan sample.The first-stage leaching rate of rare earth decreases obviously,while the rare earth is mainly concentrated in the second-stage leaching,but it has little influence on the total leaching efficiency.The new leaching method proposed in this study can not only promote the advance leaching of rare earth,increase the peak concentration,facilitate subsequent enrichment and recovery,save costs,but also stabilize tailings and eliminate environmental impacts.In addition,the citrate ions remaining in tailings can provide organic carbon sources for the restoration of tailings.