Selective flotation of quartz from feldspar using hydroxypropyl starch as depressant

Abstract

Feldspar and quartz are similar in composition and structure, and hence, they exhibit low flotation separation efficiency in acid or alkaline conditions and while using the traditional reagents scheme. In this study, hydroxypropyl starch (HPS) was introduced as a novel depressant in the flotation separation of quartz from feldspar. Magnesium chloride (MgCl2) was used as an activator and sodium oleate (NaOL) as a collector. The micro-flotation tests showed that the pulp pH had a decisive influence on the flotation separation of quartz from feldspar. At pH 10.50, quartz and feldspar could be partially separated without depressants. However, some amount of feldspar (10%-20%) remained afloat, resulting in a low quartz grade in the concentrate. The flotation of feldspar was selectively depressed using HPS as depressant, leading to a much higher separation efficiency, and the selectivity index increased from 4.57 to 7.52. The high selective performance of HPS depressant was also confirmed via the bench-scale flotation tests, and the yield of the feldspar products increased from 22.70% to 30.20%, while the grade of K2O + Na2O increased from 13.73% to 14.35%. The inhibitory mechanisms of feldspar and quartz were analyzed through Raman and X-ray photoelectron spectroscopy. These results indicated that HPS leaned towards complex formations with Al-sites on the surface of feldspar, thereby reducing the adsorption of NaOL and inhibiting the flotation of feldspar. Therefore, HPS could be used as a feldspar depressant in flotation separation quartz from feldspar.