Lead/Zinc Sulfide Mineral
Differential Flotation

The differential flotation of polymetallic lead-zinc ores is based on the fact that the zinc mineral is theoretically hydrophilic (water repelling) and will not float without activation. In most instances the lead minerals are floated as a concentrate and the zinc minerals are discharged from the flotation circuit as a tailings product. When the zinc minerals have been separated from the lead minerals they can be activated using copper sulfate to be separated from the waste minerals by flotation methods.

Each of the flotation circuits may have three sections; roughers flotation cells, cleaner flotation cells and cleaner scavengers cells.  Slurry first passes through the lead rougher where, aided by the addition of specific reagents, the lead content is separated from the rest of the slurry or tailings. The lead concentrate is then “cleaned” in two additional stages of flotation to obtain a concentrate containing 64% lead.

The tailings from the lead flotation cells pass into the zinc flotation line where different reagents are added to convert the zinc mineral surface chemistry and allow the particles to adhere to flotation bubbles.  After the rougher concentration step, the zinc concentrates are reground in a small ball mill to clean their surfaces for additional chemical activation. The zinc concentrates are also cleaned in subsequent flotation stages to arrive at a final concentrate containing 55% zinc.

After flotation, the zinc concentrate may undergo an acid leach quality control process, which helps to reduce magnesium levels in the concentrate if required.

This description of the differential froth flotation process sounds relatively straight forward and simple but depending upon the mineralogy of the ore being processed may be chemically quite complex. Chemicals called xanthates are used to condition the mineral particle surfaces so that they will adhere to floating bubbles introduced into the flotation cell. If the elasticity of the bubbles is too low they may burst and release the mineral particles back into the flotation cell. Sometimes the zinc minerals float with the lead minerals making a very dirty lead concentrate. Therefore, it is important to understand the mineralogy of the orebody and do extensive bench scale and pilot plant testing prior to designing and building a beneficiation plant that may cost hundreds of millions of dollars.