Selective flotation separation of spodumene from feldspar using sodium alginate as an organic depressant

Sodium alginate (SA) was investigated for use as a depressant in the spodumene–feldspar system. In this flotation system, the SA is added before the cation collector, dodecylamine (DDA). The effects of SA on mineral floatability were systematically investigated by flotation experiments, X-ray photoelectron spectroscopy (XPS), Fourier transform IR spectroscopy (FTIR), zeta potential measurements, and speciation analysis. Single-mineral flotation results showed that using 30 mg/L SA allowed the separation of spodumene from feldspar at pH 6, although there was a strong pH dependence. Zeta potential measurements and FTIR analysis showed that SA and DDA can adsorb onto both minerals. XPS analysis revealed the adsorption mechanism: the strong affinity of SA for the mineral surface arose from the complexation of SA and Al sites. Analysis of the surface and solution chemistry revealed that SA chelated Al 3+ or its hydroxides and hindered the subsequent adsorption of DDA, resulting in a hydrophilic feldspar surface. In addition, there were more aluminium hydroxides and unsaturated O atoms on the spodumene surface than on that of feldspar, and these provided available sites for the adsorption of DDA to form a stable reticular structure with SA, thus improving the floatability of the spodumene at certain pH values. Lastly, a model for SA and DDA adsorption at the water–solid interface is proposed.