Andalusite Flotation Separation Technology And Mechanistic Studies

Andalusite is an anhydrous aluminum-silicate mineral. Although it has the same chemical composition with kyanite and sillimanite, however, andalusite has totally different structures from those and thus it has different physical properties. Andalusite is good for silicon-aluminum metal and technical-ceramic as well as the best refractory. It is a non-metallic mineral being developed in our country, while flotation is one of the most commonly used beneficiation methods for fine-grained andalusite.Based on the differences in the crystal structure of the andalusite and its associated minerals (mainly quartz and biotite), this dissertation presents an attempt of a systematic study of the relationship among crystal structure, surface properties and flotation behavior of the andalusite and its associated minerals by various methods of analyzing crystal structure, quantum chemical calculating, measuring Zeta potential of the mineral surface, photoelectron spectroscopy, infrared spectroscopy, pharmaceutical absorption and flotation tests, aiming to make a comparative study on the flotation behavior of andalusite and its associated minerals in different types of flotation agents and interaction mechanism in the surface of andalusite and its associated minerals. The research contents and results of the tests are summarized as the following:1. There exist some differences on crystal structures and surface properties of andalusite and its associated mineralsAfter the mineral is broken, surface of andalusite differentiates from that of quartz's and biotite's because there are a relatively larger number of non-compensated aluminum ions on the crystal surface of andalusite, which makes it possible to use anionic-collector to float andalusite selectively.2. Adopting the anionic-collector flotation systemSDS tends to interact chemically with aluminum ions, which are controlled by electric charge, rather than silicon ions, and thus SDS is easier to be absorbed on the surface of andlusite rather than that of quartz and biotite.This dissertation describes a new technique on acid floatation of andalusite. In the test, petroleum sodium sulphonate is used as the collector and starch as the depressant. By means of the open floatation circuit consisting of 3-stages of rougher followed by 3-stages of cleaner with pH value between 3 and 4 of the acid pulp and a magnetic separation of flotation concentrate, a qualified andalusite concentrate with mass recovery of 56.53%, grade of A12O3 93.79%, grade of andalusite 93.79%, andalusite recovery 65.73%, is finally obtained.The results have shown that the mechanism of the depression of quartz and biotite by starch is deactivation with SDS as collector under acid condition. Starch may react with the activating metal ions in the aqueous environment to prevent the ions from adsorbing and thus activate quartz or biotite surfaces. It may also react with the metal ions adsorbed on quartz or biotite surfaces by either stripping them from the surfaces or forming hydrophilic compounds on the surface.3. Adopting the cationic-collector flotation systemIn the cationic-collector flotation system, different charging mechanism on the mineral surface is the primary factor to determine different floatability for andalusite and its associated minerals: quartz and biotite. By way of the inverse flotation consisting of 1-stages of rougher followed by 5-stages of scavenging in natural pH (around 7) of the slurry, an andalusite concentrate with mass recovery of 36.2%, grade of A12O3 48.33%, grade of andalusite 73.48% and andalusite recovery 61.50%, is finally obtained, when dodecylamine is used as the collector, Thus, this concentrate cannot meet the specifications of Level II.4. Investigations from interaction mechanism of collector and the mineral surfaceThis thesis studied in details the interaction mechanism of SDS with andalusite by means of quantum chemical calculation method. The following conclusions can be made: when dodecyl sulfonic acid ion is combined with Al atoms on the surface at different locations of andalusite, the total energy of the system is decreased, and dodecyl sulfonic acid ion in andalusite surface can produce chemical adsorption, so electrons are transferred from Al atom of andalusite (electron donors) to O atoms of SDS(acceptor). Adopting surface electrical measurement, flotation desorption test and IR means to studied the interaction mechanism of SDS with andalusite and associated minerals in detail, the conclusions were gained in the following:In the anionic-collector flotation system, sodium dodecyl sulfate is absorbed on the surface of the mineral in form of ionic bond interaction with pH value between 3 and 4. Therefore, there exists chemical absorption in which SDS ions are directly interacted with aluminum ions in form of ionic bond. On the other hand, sulfonate collector fixing on the surface of andalusite is a combination of physical and chemical absorption; Sulfonate being absorbed on the surface of quartz and biotite is a physical adsorption with the aid of Coulomb force and oxygen-based associating interaction. The low intensity of physical adsorption of the sulfonate-collectors on the surface of the andalusite's associated minerals determines the high efficiency of the cleaning operation.From quantum chemical calculation and the testing results of adsorption product, we can conclud that SDS is adsorbed on the surface of andalusite mainly in the form of dodecyl sulfonic acid ion under pH value between 3 ~ 4, and the interaction between dodecyl sulfonic acid ion with aluminum ion exists chemical adsorption directly. In addition, the surface adsorption point numbers determine the flotability.differences of the three minerals, such as andalusite, quartz and biotite.