Effects of Ion Characteristics on the Leaching of Weathered Crust Elution-Deposited Rare Earth Ore

Abstract

To reveal the ion-exchange mechanism in the leaching process of weathered crust elution-deposited rare earth ores with different leaching agents, the effects of a variety of cations and anions at different concentrations on the leaching process were investigated, including Al3+, Fe3+, Ca2+, Mg2+, Na+, K+, NH4+ and Cl−, NO3-, and SO42-. Meanwhile, the relationships between different concentrations of cations and anions and leaching efficiency were investigated, as was the relationship between different concentrations of cations and anions and zeta potential. The effect of different ions on the swelling of clay minerals during leaching process was also investigated. The results shown that NH4+ was the most affected electrolyte cation in terms of rare earth leaching efficiency during the leaching process of weathered crust elution-deposited rare earth ore among three different cationic valence states, and the leaching efficiency was 86.93% at the optimal leaching concentration. The influence of the three anions on the leaching efficiency of rare earth was NO3->Cl->SO42-, and the leaching efficiency of rare earth were 83.21, 81.52, and 80.12% at the optimal leaching concentration, respectively. The NH4+ had the greatest effect on the zeta potential of weathered crust elution-deposited rare earth ore, and the zeta potential was −18.1 mV at the optimal leaching concentration. Additionally, the order of the effect of three anions on zeta potential was SO42->NO3->Cl-. Combined with the effect on the rare earth leaching process, anions and cations were considered separately, and NH4+ and Cl− were selected; the relationship between the rare earth leaching efficiency and zeta potential conforms to the follow equations: NH4+:Y = −0.48X2 – 13.51X – 1.58, R2 = 0.98133 and Cl−:Y= −1.22X2 – 17.64X + 23.29, R2 = 0.99010. It was also found in the swelling experiment of the weathered crust elution-deposited rare earth ore that the swelling ratio of clay minerals was the lowest when the cation and anion were NH4+ and Cl− and the swelling ratios were 1.874 and 2.015%, respectively.

Development Review on Leaching Technology and Leaching Agents of Weathered Crust Elution-Deposited Rare Earth Ores

“…The rare earth of weathered crust elution-deposited rare earth ores are adsorbed on clay minerals in the form of hydrated ions or hydroxyl hydrated ions [5], and can only be recovered and enriched by ion exchange. China has successively developed three generations of leaching technologies.…”

Effects of Ammonium Salts on Rare Earth Leaching Process of Weathered Crust Elution-Deposited Rare Earth Ores

“…The weathered crust elution-deposited rare earth ores are formed by the chemical weathering of various bedrocks [4,5] and are widely distributed in warm and moist regions, predominantly in southern China [6][7][8]. Rare earth elements mainly exist in the ionic or hydration ionic state on the surface of the clay minerals [9][10][11]. It is difficult to recover this type of rare earth ore using conventional beneficiation methods, and rare earth is normally recovered using an ion exchange method, and by adding electrolyte solution [12,13].…”

Rare Earth Occurrence States of Weathered Crust Elution-Deposited Rare Earth Ores in Southern Yunnan

“…Weathered crust elution-deposited rare earth ores are rich in medium and heavy rare earth elements; thus, they have high economic value and are strategic mineral resources in China [1][2][3]. This mineral was firstly discovered in the Jiangxi province of China, and is mainly located in the Jiangxi, Fujian, Hunan, Guangdong, Guangxi and Zhejiang provinces [4,5]. In recent years, large medium-heavy rare earth deposits have been discovered in southern Yunnan [6], with the characteristics of high altitude, diverse metallogenic models, large differences in the rare earth element content distribution, and a diverse and complex terrain.…”