Using the mixed fatty acids (MFA) produced by waste cooking oil as flotation collectors directly, the flotation effect is usually not satisfactory, especially at lower temperature, which may be due to the presence of large amounts of saturated fatty acids. In this study, waste cooking oil was separated into saturated fatty acids (SFA) and unsaturated fatty acids (UFA). The separation mechanism was studied by molecular simulation based on quantum and molecular mechanics. SFA and UFA were analyzed by iodine value, melting point measurement and Fourier transform infrared (FT-IR) spectroscopy to check the result of the separation. The micro-flotation and bench-scale flotation tests were performed to investigate the flotation differences between SFA and UFA. The results showed that the poor flotation performance of waste cooking oil was due to the large amount of SFA in presence. If the SFA was separated out, the TFe grade and recovery of the flotation concentrates would be increased by 4.09 and 2.70 percentage points, respectively and the SiO₂ grade would be 4.03 percentage points lower at the same time. This study would provide technical supports and theoretical guidance for the waste cooking oil application in the field of mineral processing.

To unveil the impact of each condition variable on the leaching efficiency index during the heap leaching process of rare earth ore and establish a prediction model for leaching conditions and efficiency, common parameters in the heap leaching process of rare earth ore were selected. In addition, the pilot-scale test data were collected over 50 days. Based on the collected data, the Ordinary Least Squares (OLS) linear regression method was used for fitting analysis to determine each variable’s influence on the change in leaching efficiency. The results indicated a linear relationship between the flow rate of the leaching solution and leaching efficiency. In contrast, no obvious linear relationship was observed between other condition variables and leaching efficiency. Spearman’s rank correlation coefficient was calculated to analyze the nonlinear correlation between the abovementioned variables and the leaching efficiency index. The correlation coefficients were found to be −0.78, 0.88, −0.93, −0.53, 0.71, and −0.93 for ammonium content in the leaching agent, pH of the leaching agent, rare earth content, ammonium content in the leaching solution, pH of the leaching solution, and the flow rate of the leaching solution, respectively. This suggests that the flow rate of the leaching solution, rare earth content, and pH of the leaching agent significantly influence leaching efficiency, thus affecting the rare earth leaching efficiency index. Based on the correlation analysis results of leaching conditions and efficiency, a dataset with limited data trained by the common Ordinary Least Squares model, linear regression model, random forest model, and support vector machine regression model was selected to develop a prediction model for the leaching process data. The results indicated that the random forest model had the lowest mean square error of 7.47 among the four models and the coefficient of determination closest to 1 (0.99). This model can effectively analyze and predict condition variables’ data and leaching efficiency index in the heap leaching process of rare earth ore, with a prediction accuracy exceeding 90%, thus providing intelligent guidance for the heap leaching process of rare earth ores.

Low flotation recovery, high pulp temperature, and large dosage of reagents are the typical disadvantages when using mixed fatty acids (MFA) prepared from hogwash oil for flotation directly. To determine the type of fatty acid that yields poor flotation performance, flotation performance and adsorption characteristics of saturated fatty acids (SFA) and unsaturated fatty acids (UFA) separated from the MFA were studied in our work. GC-MS, FT-IR, iodine value detection and melting point measurement showed that UFA contained –(CH=CH–CH₂)_n- groups and had much lower melting point. Quartz flotation tests were used to compare the flotation performance of UFA and SFA, which showed that UFA had excellent low-temperature floatability, and the flotation recovery of UFA was 35 percentage points higher than that of SFA at 20 °C and pH = 11.5. Zeta potential, FT-IR and XPS analysis indicated that UFA and SFA could adsorb onto the surface of activated quartz through chemisorption and hydrogen bonding. However, the adsorption of UFA was much stronger and more favorable; thus, the reason MFA have poor flotation performance was the presence of SFA.

The column leaching experiments, CT, numerical simulation and fractal theory were adopted to study the continuously weakening mechanism of the heap leaching velocity of weathered rare earth ores with the increase of ore burial depth. The variation characteristics of pore structure and the seepage law of solution in ore samples at different depths during leaching were explored, respectively. The results showed that the variation of characteristic parameters of the pore structure in the lower ore samples was the main reason for the decrease in the leaching velocity. For the lower ore samples after leaching, the number of pores with a pore volume of less than 0.01 mm³ and a pore radius of less than 0.8 mm increased, while pore connectivity, the fractal dimension of the pore shape, the ratio of pore length to width and pore throat length reduced. The solution paths of the upper and middle ore samples were concentrated while that of the lower samples were few, even interrupted. The pore pressure of the ore samples decreased after leaching, especially that of the lower ore samples. The research results are helpful to enrich the basic theory on the heap leaching of weathered rare earth ores.

Particle migration can affect the ore bodies stability of weathering crust elution-deposited rare earth ores during leaching. It may trigger geological disasters such as landslides. Therefore, direct shear tests, microstructure characterization tests, and numerical simulation tests were adopted. The mechanical behavior characteristics of ore samples with different burial depths were explored. Simultaneously, the evolution characteristics of their microstructure, mineral composition, and failure modes were also studied. The results showed that after leaching, the cohesion (c) initially rose and then dropped as the proportion of −0.075 mm particles increased. The internal friction angle (φ) initially dropped, then increased, and finally stabilized. When its proportion was greater than 20%, the c of the middle-upper part of the ore sample was greater than that of the upper part. Meanwhile, the φ was smaller than that of the upper part. Especially when its proportion was greater than 30%, the c increased gradually with depth. XRD analysis revealed that illite and kaolinite were the main mineral components for the fine particle migration. Simulation experiment results revealed that in ore samples with 10% fine particles, there was noticeable migration and deposition in the upper part. However, it was the least in the upper middle and lower parts. Contact number and coordination number sharply decreased with depth, then increased, and finally gradually reduced. As deposition increased, the shear zone tilt angle grew larger. More secondary shear zones formed. The cracks became more evenly distributed.