Kaolin has important applications in industries such as papermaking and ceramics. Flotation can remove impurities such as quartz, iron, and titanium from kaolin. Several flotation methods exist:
(1) Separation from gangue minerals such as quartz. Direct flotation is used, employing dodecylamine, triethanolamine, and pyridine as collectors for kaolin. Lignosulfonates are used to suppress silicate minerals such as quartz, and can also suppress iron minerals. The pH value is controlled at 3.0–3.1, and the pulp concentration is approximately 10%. The disadvantage of this method is that the foam is sticky and difficult to control; more effective dispersants should be sought.
(2) Removal of iron and titanium mineral impurities from kaolin. Reverse flotation is used, employing ammonium sulfate to suppress kaolin, and fatty acid (or petroleum sulfonate) collectors to collect iron (Fe₂O₃) and titanium (TiO) impurities. If the iron and titanium impurities are fine-grained, a carrier-based reverse flotation method can be used. The carrier can be calcite powder (CaCO₃, -320 mesh), which carries the fine iron and titanium impurities to the float. The frothy product is discarded, and the product in the tank is kaolin concentrate. The carrier can be reused 8-9 times. When appropriate, the frothy material is separated from the carrier and reused. Sometimes, it is discarded without separation if unnecessary. The pH value during flotation is 9.0.
(3) Removal of pyrite impurities. Sometimes iron impurities in kaolin exist in the form of pyrite. In this case, sodium hexametaphosphate is used as a dispersant, and xanthate is used to float away the pyrite.