Research Group on Adsorptive and Catalytic Process Engineering (ENGEPAC), Federal University of Santa Maria, Av. Roraima, 1000-7, 97105-900, Santa Maria, RS, Brazil; Department of Chemistry, Federal University of Santa Maria-UFSM, 1000 Roraima Avenue, 97105-900, Santa Maria, RS, Brazil.
Department of Civil and Environmental, Universidad de La Costa, CUC, Calle 58 # 55-66, Barranquilla, Atlántico, Colombia; Department of Sanitary and Environmental Engineering, Federal University of Santa Catarina, Florianópolis 88040-900, Santa Catarina, Brazil.
Chemosphere. 2022 Aug;301:134661. doi: 10.1016/j.chemosphere.2022.134661. Epub 2022 Apr 19.
High amounts of phosphogypsum (PG) are generated in the production of phosphoric acid. Previous literature demonstrates that obtaining rare earth elements (REE) from PG is a promising alternative to managing this waste. However, the reported leaching efficiencies are low in most cases, or drastic leaching conditions are required. Therefore, this work aimed to study the leaching conditions of REE from PG to obtain high leaching efficiency values. Initially, a 2 factorial experimental design investigated the factors that affect the conventional acid leaching of REE from PG (leaching acid (citric and sulfuric acid), solid/liquid ratio, acid concentration, and temperature). Better leaching efficiency values of the sum of all REE (62.0% and 89.7% for citric and sulfuric acid, respectively) were obtained using an acid concentration of 3 mol L, solid/liquid ratio of 1/20 g mL, and temperature of 80 °C. Subsequently, the experiments optimization, performed through a central composite rotational design, indicated that the maximum leaching efficiency was achieved using a sulfuric acid concentration of 2.9 mol L, solid/liquid ratio of 1.7/20 g mL, and 55 °C. Under these conditions, the leaching efficiency of the sum of all REE was 90.0%. Leaching kinetics results showed that the equilibrium was reached in about 20 min for most REE. The mechanism investigation suggested that surface chemical reaction and diffusion through the boundary layer controlled the leaching.
生产磷酸时会产生大量磷石膏 (PG)。先前的文献表明，从 PG 中提取稀土元素 (REE) 是一种处理这种废物的有前途的替代方法。然而，在大多数情况下，报道的浸出效率较低，或者需要苛刻的浸出条件。因此，这项工作旨在研究从 PG 中浸出 REE 的条件，以获得高浸出效率值。最初，采用 2 因子实验设计研究了影响 PG 中 REE 常规酸浸的因素（浸出酸（柠檬酸和硫酸）、固液比、酸浓度和温度）。使用 3 mol L 的酸浓度、1/20 g mL 的固液比和 80°C 的温度，获得了所有 REE 之和的更好浸出效率值（柠檬酸和硫酸分别为 62.0%和 89.7%）。随后，通过中心复合旋转设计进行的实验优化表明，在硫酸浓度为 2.9 mol L、固液比为 1.7/20 g mL 和 55°C 的条件下，可实现最大浸出效率。在此条件下，所有 REE 之和的浸出效率达到 90.0%。浸出动力学结果表明，大多数 REE 的平衡在 20 分钟左右达到。机理研究表明，表面化学反应和通过边界层的扩散控制浸出。
