The flotation separation of parisite from calcium-bearing gangue minerals, such as fluorite and calcite, poses a significant challenge in the rare earth ore production process. In this study, an eco-friendly and highly selective depressant polyaspartic acid (PASP) was adopted in the flotation separation of parisite from calcite and fluorite, and its depression mechanism was investigated through various surface analysis and testing methods, including zeta potential tests, contact angle measurements, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The flotation test results indicated that PASP significantly inhibited the flotation of fluorite and calcite, with negligible effect on parisite when using octyl hydroxamic acid (OHA) as a collector at weak alkaline pH. The artificial mixed mineral flotation proved that PASP could achieve effective flotation separation of parisite from calcite and fluorite. Zeta potential tests and FTIR analyses demonstrated that the adsorption of PASP prevented OHA adsorption on calcite and fluorite surfaces, with minimal impact on OHA adsorption on parisite surface. XPS analyses confirmed that PASP was mainly chemisorbed on the surfaces of calcite and fluorite through the chelation reaction between polar groups (–NH– and –COO − ) of PASP with the Ca 2+ on these surfaces. AFM clearly showed the agglomerative adsorption of PASP on the surfaces of fluorite and calcite. Thus, PASP could be an efficient depressant for calcite and fluorite in parisite flotation, providing novel insights into addressing rare earth ore flotation challenges.
Hydrolytic polymaleic acid (HPMA) was used as a highly selective depressant instead of water glass to achieve the flotation separation of parisite from calcite and fluorite. The inhibitory effect and mechanism of HPMA on fluorite and calcite was investigated using micro-flotation, zeta potential, contact angle measurements, adsorption measurements, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and quantum chemical calculations. The results from single and artificially mixed minerals showed that parisite could be successfully separated from calcite and fluorite by using HPMA as a depressant. Further analysis revealed that HPMA chemically adsorbed onto the Ca 2+ active sites of calcite and fluorite, forming a hydrophilic compound, Ca(COOR), which prevented the octyl hydroxamic acid (OHA) collector adsorbing on their surfaces. In contrast, HPMA only weakly physically adsorbed onto the surface of parisite, allowing it to maintain good floatability after conditioning with HPMA. Therefore, HPMA has a potential as an inhibitor for effectively separating parisite from fluorite and calcite in rare earth ore flotation process.
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