Discrepant adsorption behavior of sodium alginate onto apatite and calcite surfaces: Implications for their selective flotation separation

The efficient flotation separation of apatite and calcite is an intricate problem due to their similar physicochemical properties. The selection and utilization of selective depressant is the key to address this obstacle. In this study, sodium alginate (NaAl) was introduced as a selective inhibitor in the flotation separation of apatite from calcite with sodium oleate (NaOL) as collector. The inhibitory performance of NaAl on these two minerals was investigated via flotation tests. The depressing mechanism of NaAl was studied through zeta potential analysis, adsorption capacity tests, Fourier transform infrared spectroscopy (FTIR) measurements and X-ray photoelectron spectroscopy (XPS) analysis. Flotation results indicated that NaAl demonstrated strong inhibitory impact on the calcite flotation, whereas it presented little influence on the apatite flotation in the pH range of 9–12. A concentrate with P 2 O 5 grade and recovery of 34.32% and 82.27% respectively was obtained in the bench-scale flotation experiment. Zeta potential analysis demonstrated that NaAl strongly affected the following NaOL adsorption onto the calcite surface, whereas it showed little influence on apatite. Adsorption test showed that NaAl absorbed on both these two mineral surfaces, whilst the adsorption amount on the calcite surface was significantly higher than that on the apatite surface. FTIR and XPS analyses further confirmed that NaAl adsorbed on the apatite surface through weak physical adsorption, while it chemically adhered on calcite in the form of calcium carboxyl which greatly prohibited the subsequent adhesion of NaOL on calcite. As a consequence, the calcite floatability was greatly depressed by NaAl and the selective flotation separation of apatite from calcite was realized.