Calcium atoms are often replaced by rare earth elements (REEs) in the lattice of fluorapatite (Ca₁₀F₂(PO₄)₆), making the phosphate ore an important potential rare earth resource. In this paper, the electronic properties of REEs (La, Ce, Nd and Y) bearing fluorapatite crystals have been investigated by density functional theory. Results of calculation indicated that the existence of REEs increased the cell parameters of fluorapatite in varying degrees. The REEs substitution made the Fermi level of fluorapatite to move to higher energy levels, making it easier to accept electrons. Except for Y, all the other REEs (La, Ce and Nd) showed that the electronic state mainly exists in the valence band. The Fermi level of REEs were mainly contributed by La5d, Ce4f, Nd4f and Y4d, respectively. The Mulliken values of REE–F and REE–O bonds in REEs-bearing fluorapatites were larger than those of Ca–F and Ca–O bonds in the perfect crystal, and the values of Y–F and Y–O bonds were the largest. The results of interaction between fluorapatite and oleic acid by frontier molecular orbital analysis suggested that the substitution of REEs can improve the reactivity of fluorapatite with oleic acid.

In this study, the effects of four fine minerals, which were fine diaspore (FDIA), kaolinite, illite, and pyrophyllite (D₅₀ is about 4.55 μm, D₈₀ is about 10.78 μm), on the pulp rheology of the diaspore and pyrite mixed ores (D₅₀ is about 120.53 μm, D₈₀ is about 187.36 μm) and the recovery of pyrite were investigated through flotation tests, pulp rheology measurements, and sedimentation tests. It was found that fine minerals could change the pulp rheology and affect the pyrite recovery. The apparent viscosity of the mixed ores slurry increased with the addition of FDIA, kaolinite, and illite and the pyrite recovery decreased in varying degrees. When the addition was 15 wt.%, the recovery of pyrite decreased from 92.3% to 60.8%, 81.4%, and 84.7%, respectively. The addition of pyrophyllite had a significant deteriorating effect on flotation. When the addition of pyrophyllite was 5 wt.%, the pyrite recovery was reduced to 49.2%, and when the addition was further increased to 15 wt.%, the pyrite recovery reduced to 28.5%. However, the effect of pyrophyllite addition on the pulp rheology of the mixed ore was not remarkable. Pyrophyllite affected pyrite recovery not only by affecting the rheological behavior of the pulp, but also because pyrophyllite was adsorbed on the surface of pyrite and diaspore, producing hetero-aggregation, which made it difficult for the pyrite particles to collide with the bubbles effectively. This was the main reason for the reduction of pyrite recovery. Generally, the order in which the reduction of pyrite recovery was affected by the additions of fine minerals was pyrophyllite > FDIA > kaolinite > illite.

The mineralogical characteristics of a phosphate tailing were studied, and the occurrence state, mineral types, and embedded characteristics of phosphorus in the phosphate tailings were ascertained. The results show that the main minerals in the phosphate tailings are collophane. The main gangue minerals are quartz, dolomite, calcite, a small amount of potassium feldspar, plagioclase, chlorite, etc. Monazite was found in phosphate tailings. In addition, the coarse grain size of quartz and feldspar and fine embedded particle size of calcite and dolomite are also the main factors affecting the mineral processing of phosphate tailings. According to the analysis of mineralogical characteristics, the physical and chemical properties of phosphate tailings provided the basis for comprehensive utilization of phosphorus resources.

During the treatment of spent cathode carbon from electrolytic aluminum, a large amount of fluoride containing wastewater is generated. By adding different sodium source and aluminum source reagents, under the conditions of different addition order, pH, temperature and time, the effects of conventional static reaction, stirring reaction and ultrasonic assisted reaction on the crystallization properties of recovered cryolite were investigated. The results showed that under the optimum reaction conditions (sodium source: NaCl, aluminum source: AlCl₃, the molar ratio of AlCl₃ to NaCl is 1 : 3, addition order: first addition of AlCl₃ and then NaCl, pH is 8.57, time is 40 min, temperature at room temperature), the removal efficiency of fluoride ions was the highest when ultrasound assisted treatment was used. The cryolite products with ultrasound assisted crystallization and without ultrasound assisted crystallization were characterized using SEM and TEM. The results showed that the crystal particles obtained by ultrasound assisted crystallization were relatively concentrated, and the morphology was regular and the surface was smooth. Design Expert orthogonal software was used to design the response surface test, it was found that ultrasound time has the most significant impact on the content of recovered cryolite among single factors, and the interaction between ultrasound frequency and ultrasound power, ultrasound power and ultrasound time was highly significant among multiple factors.

Correction for ‘Study on ultrasonic leaching and recovery of fluoride from spent cathode carbon of aluminum electrolysis’ by Chenchen Wang et al., RSC Adv., 2023, 13, 16300–16310, https://doi.org/10.1039/D3RA02088F.