Fine-size separation of halloysite, kaolinite, and quartz minerals as binary systems using dispersion and sedimentation methods

Clay minerals are mainly composed of aluminum hydrosilicates. In some minerals, aluminum is completely or partially replaced by Fe or Mg. Alkaline minerals or alkali metals are present as major constituents of clay minerals. While some clay sources may contain a single clay mineral, they often contain different minerals such as quartz, calcite, feldspar, pyrite, etc. as impurities. They also contain organic matter and water-soluble salts. Halloysite is a clay mineral belonging to the kaolinite group and USA Environmental Protection Agency (EPA 4A) declared it as an innocuous/adaptable material to human health and the environment. Halloysite ore deposits are mainly found together with kaolinite and quartz minerals, but can also be found as a pure source. The degree of purity of halloysite ore determines the industrial area where it will be used and therefore its economic value. Since clay minerals are naturally composed of fine particles, it is necessary to disperse the clay particles in suspension to separate halloysite and kaolinite minerals. In addition, there are also fine-grained quartz minerals, and to recover pure halloysite minerals, it is necessary to determine their properties in the fine size fraction. In this study, the dispersion properties of halloysite, kaolinite, and quartz minerals in the presence of sodium silicate (SS), sodium tripolyphosphate (STPP), and sodium hexametaphosphate (SHMP) dispersants in fine-size fraction (-38 µm) were researched by particle size measurements and mineral separation properties were investigated by sedimentation experiments at different acidic, neutral, alkaline pH values. In dispersion experiments, the d90 values of halloysite, kaolinite, and quartz minerals were 74.0, 50.7, and 61.3 µm without any dispersant addition, and such values decreased to 54.7, 26.3, and 57.1 µm as SHMP increased to 10 kg/ton, respectively. d50 and d10 values showed a significant change for halloysite, while no important change was observed for kaolinite and halloysite. SHMP had the most effect on the particle size change in the dispersants especially on halloysite minerals. The least effect on particle size change was observed in the quartz sample with dispersant addition. The sedimentation experiments aimed to investigate the effects of pH on halloysite, kaolinite, and quartz recoveries in binary systems as settled products. Kaolinite settled more at acidic pH and halloysite at basic pH. There was no pH-dependent change in the settling behavior for halloysite and quartz. In the quartz-kaolinite system, quartz mineral settled more than kaolinite for all pH values. The settling experiments showed the importance of morphological differences between tubular halloysite and lamellar kaolinite minerals.