Flotation separation of limonite from quartz with sodium oleate: effects of limonite dissolution and addition of sodium hexametaphosphate

The utilisation of limonite ore is potentially important to China as the high quality iron resource, such as magnetite and hematite of high grade, are rapidly depleting, but many detrimental impurities, such quartz and calcite etc, are difficult to upgrade to make suitable concentrates for the blast furnace. The flotation behaviour of limonite, quartz and their mixture by using sodium oleate as collector were studied systematically in this paper. Single-mineral flotation tests showed that the flotation recovery of limonite was much higher than that of quartz in a broad range of pH. However, flotation tests for the mixture of limonite and quartz showed rather poor mineral separation efficiency with the flotation recovery of both minerals being high in froth products. The flotation separation efficiency of limonite from quartz was substantially improved by adding sodium hexametaphosphate (SHMP) as a depressant for quartz flotation. To elucidate these phenomena, the solution species calculation of limonite dissolution and the measurements of iron ions content were carried out. It was found that iron ions or its species released into the pulp from the dissolving of limonite could effectively activate the flotation of quartz but have little influence on the flotation of limonite. In the presence of SHMP, iron ions or its species lost their activating power on quartz flotation which caused by the chemical reaction between SHMP and iron ions or its species, and then removed iron ions or its species from quartz surface into the solution.