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+, and Cl−, , and . 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 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 , and the leaching efficiency of rare earth were 83.21, 81.52, and 80.12% at the optimal leaching concentration, respectively. The 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 . Combined with the effect on the rare earth leaching process, anions and cations were considered separately, and and Cl− were selected; the relationship between the rare earth leaching efficiency and zeta potential conforms to the follow equations: :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 and Cl− and the swelling ratios were 1.874 and 2.015%, respectively.
Highlights
Weathered crust elution-deposited rare earth ore is of extremely high economic and strategic value, it is a special rare earth resource in the world (Simandl, 2014; Zhang B. et al, 2018; Zou et al, 2020)
In the study of the influence of anion and cation on weathered crust elution-deposited rare earth ore, it was found that the order of the rare earth leaching ability in three valence cations of NH4+ > K+ > Na+, Mg2+ > Ca2+, Al3+ > Fe3+ and the NH4+ were the most affected electrolyte cations on rare earth leaching efficiency; rare earth leaching efficiency was 86.93% at the optimal leaching concentration
In the study of zeta potential on clay mineral surface, it was found that NH4+ had the greatest effect on zeta potential in the influence of different cations on zeta potential of weathered crust elution-deposited rare earth ore, and the zeta potential was −18.1 mV at the optimal leaching concentration
Summary
Weathered crust elution-deposited rare earth ore is of extremely high economic and strategic value, it is a special rare earth resource in the world (Simandl, 2014; Zhang B. et al, 2018; Zou et al, 2020). The rare earth elements mainly existed in the ionic or hydrated ionic state on the surface of the clay minerals (Huang et al, 2005). Due to this special property, the essential process during leaching is an ion exchange reaction between the surface of clay minerals of absorbed rare earth ions and cations in lixiviant. The leaching process causes the swelling of clay minerals, which has a certain influence on the safety of mine production and the low efficiency of the leaching agents, resulting in high consumption of electrolyte solution in actual industrial production
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