Fluorite, flotation

The ground ore was first subjected to barite flotation followed by fluorite flotation. By floating the barite and fluorite ahead of the bastnaesite, about 70% of the total weight was removed from bastnaesite flotation feed. The bastnaesite flotation feed was upgraded from 8.5% REO to about 30% REO. 

During fluorite flotation, Quebracho and lignin sulphonate mixture (MESB) was used with collector composed of a mixture of oleic acid and phosphoric ester. Collectors used for bastnaesite flotation included tall oil fatty acid modified with three ethylene tetra... 

The results obtained from the continuous locked-cycle tests are summarized in Table 24.8. The major contaminant of the bastnaesite concentrate was fluorite. Complete fluorite flotation was not possible without heavy losses of bastnaesite in the fluorite concentrate. 

The flotation of sulfidic, oxidic, and salt-type ores and, in special cases, silicate ores can be improved by the use of ether carboxylates as collectors [221,222]. In particular, the flotation of fluorite, barite, and scheelite is mentioned. Special synergistic combinations of ether carboxylates with fatty acids [223] and with vinyl- or alkylsulfonic acid polymer [224] are described. 

Floatability of bastnaesite found in barite-fluorite ores is extremely poor using either fatty acid flotation or sodium oleate. Research work conducted on an ore from Central Asia showed that the floatability of bastnaesite improved significantly after barite preflotation [5]. The flotation of bastnaesite from a carbonatite ore improved with the use of oleic acid modified with phosphate ester. The flotation of bastnaesite from deposits ofpegmatitic origin can be successfully accomplished with several types of collectors, including tall oil modified with secondary amine, and tall oil modified with petroleum sulphonate-encompassing group. 

A large portion of the REOs are produced from monazite- and bastnaesite-containing ores. In the majority of cases, bastnaesite and monazite ores are relatively complex and contain gangue minerals (calcite, barite, fluorite and apatite) with similar flotation properties as the monazite and bastnaesite. 

Because this ore was high in barite and fluorite, direct flotation of bastnaesite from the ore was not possible. It should be pointed out that fluorite has similar flotation properties as bastnaesite and depression of fluorite during bastnaesite flotation is difficult. 

The flowsheet that was developed for beneficiation of the Dong Pao ore involves sequential barite-fluorite-bastnaesite flotation. The flowsheet is presented in Figure 24.8. 

The reagent scheme developed during extensive laboratory testing is presented in Table 24.7. This reagent scheme is unique in such a way that the collector and number of depressants involved are composed of a number of chemicals that provide improved selectivity during sequential flotation of barite and fluorite from bastnaesite. 

For flotation of barite, sodium silicate was used as a depressant and barium chlorite as a barite activator. Barite collector SR82 was composed of petroleum sulphonate, sodium alkyl sulphate and succinamate mixture. The collector was selective towards both fluorite and bastnaesite. Over 96% of the barite was recovered in a relatively high-grade concentrate. 

Figure 3- Flotation recovery R (in %) of fluorite as dependent on the concentration c (in mol/L) of Na-do-decylbenzenesulfonate.

In laboratory tests of flotation, fluorite (CaF particles (range of particle diameters, 0.074-0.147 mm) with oleic acid as collector were aerated under three different conditions. These conditions and the percent CaF2 recovery after 10 min are as follows ... 

Although flotation was developed as a separation process for mineral processing and applies lo the sulfides of copper, lead, zinc, iron-molybdenum, cobalt, nickel, and arsenic and to nonsullides, such as phosphates, sodium chloride, potassium chloride, iron oxides, limestone, feldspar, fluorite, chromite, tungstates, silica, coal, and rhodochrosilc, flotation also applies to nonmineral separations. Flotation is used in the water disposal field, particularly in connection with petroleum waste water cleanup. 

In carrier flotation, small-sized (several pm diameter) particles become attached to the surfaces of larger particles (perhaps 50 pm diameter, the carrier particles) [630]. The carrier particles attach to the air bubbles and the combined aggregates of small desired particles, carrier particles, and air bubbles float to form the froth. An example is the use of limestone particles as carriers in the flotation removal of fine iron and titanium oxide mineral impurities from kaolinite clays [630]. The use of a fatty acid collector makes the impurity oxide particles hydrophobic these then aggregate on the carrier particles. In a sense, the opposite of carrier flotation is slime coating, in which the flotation of coarse particles is decreased or prevented by coating their surfaces with fine hydrophilic particles (slimes). An example is the slime coating of fine fluorite particles onto galena particles [630],... 

Fig. 1. A Principle of flotation in a mechanical-type cell. The rotor and stator (which is here omitted for simplicity) keep the mineral particles and air bubbles in dispersion for adhesion. B Formation of hydrophobic and hydrophilic adsorption layer on solid in quartz-fluorite system...

Wadsworth and coworkers (13, 14) have found considerable evidence for surface polarization in double-beam infrared spectroscopy. Not only do new differential peaks due to adsorption appear in the spectrograms but also the bands due entirely to the adsorbent are frequently appreciably shifted by adsorption. This occurred, for example, in calcium fluorite treated with oleic acid, in samples of bentonites taken from aqueous solutions of different pH, and in various minerals treated by flotation collectors. In fact, it is more the rule than the exception that the spectrograms of finely divided solids dispersed in the KI or KBr window exhibit distortion due to adsorption, whether adsorption occurs at the solid-aqueous solution or at the solid-vapor interface. For example, Eyring and Wadsworth (13) found that two (differential) peaks were produced by adsorption on willemite either from the vapor or aqueous solution of hexanethiol. These peaks were due to the influence of adsorption of the hexanethiol on the Si-O bands of the willemite and occurred at about 9.2 and 12.3 microns. 

The 0-pH diagram of Na2Si03 solution is shown in Fig. 2.2a (Fuerstenau et al., 1968). It can be seen that Si(OH)4 is predominant when pH is less than 9.4 whereas SiO(OH) is predominate when pH is greater than 9.4 and Si02(0H)2 is predominate when pH is above 12.6. Flotation of calcite and fluorite using sodium silicate as a depressant is shown... 

Fig. 2.4b shows the flotation of scheelite, fluorite and calcite using sodium oleate and trisodium phosphate. The flotation of fluorite and calcite can be depressed by sodium phosphate at pH < 9.5 and pH < 10.0, respectively, but not that of scheelite. Since the PZC of scheelite, fluorite and calcite are pH = 1.5, 9.5, and 10.0, respectively (Wang, 1983), anionic species H2POJ, HPO ", and PO " which are predominant, will not be adsorbed on the negatively charged surface of scheelite, and thus will have no depression effect at pH > 2.2 below pH 9.5, fluorite surface is positively charged and the anionic phosphate species can be adsorbed on fluorite, leading to its depression. A similar depression mechanism can be formulated for calcite at pH < 10.0. 

Fig. 2.9. Flotation recovery of the minerals using oleate as a function of pH 1—fluorite, 2—spodumene, 3—augite (Fuerstenau, 1977, 1980 Pugh and Stenius, 1985).

Competition of the dissolved mineral species with similarly charged collector species for adsorption sites can result in the depression of mineral flotation. For example, in the case of flotation of apatite and calcite with oleate as collector, the floatability is usually lower in saturated mineral supernatants than in pure water (Fig. 4.27). This is partly due to the competition by dissolved species such as PsO and CO which are present in saturated apatite and calcite supernatants (10 to 10 mol/1) in concentrations close to that of the anionic oleate ions. Similar effects are also observed in the case of flotation of fluorite with dodecyl amine (Fig. 4.28). Floatability of fluorite in its saturated solution is lower than that in water. The concentration of dissolved Ca species in the fluorite saturated solution is about 10 " mol/1 and only when the amine concentration is higher than 10 mol/1, the flotation obtained in it is similar to that obtained in water. 

As early as in the beginning of this century, chelating agents have been used as collectors in the flotation. For example, cupferron was used for flotation of oxidized copper minerals and 8-hydroxy quinoline for wolframite and lead-zinc minerals. Recently, chelating agents have been used as depressants by Schubert, Avotins and Nagaraj for the separation of fluorite from gangue minerals and molibdenite from copper sulfide minerals, respectively [3,13]. 

Tannins are mainly used as depressants for dolomite, calcite and silicate minerals in the flotation of scheelite, apatite, fluorite and copper sulfide. Like starch, tannins after modification by oxidation, sulfidization and aminization (tannin O, S and A, respectively) have been used as a depressant for hematite in the reverse flotation of quartz with oleic acid or dodecylamine as collectors [22]. Flotation results show quartz to be depressed by tannins in the order of tannin A > S at low concentrations of dodecylamine. When an anionic collector is used for the reverse flotation of Ca +-activated quartz with tannins as depressant for hematite, the order of depression is tannin A > O > S. 

Selective flotation of fluorite and barite is usually very difficult using water glass and tannic acid. However, good separation of these minerals has been achieved with the use of lignosulfonate [18]. Lignosulfonate can also selectively depress molybdenite and some rare earth metal minerals. In the reverse flotation of hematite and quartz, lignosulfonate has been used as a depressant of hematite. 

These are used to prevent flotation of one material while floating another. Lime and NaCN are examples. Both of these depress pyrite. Dichromate is a depressant for galena. HF is used to depress quartz in the flotation of feldspar with amine collectors. Sodium silicate is also a quartz depressant. Quebracho depresses calcite and dolomite in the flotation of fluorite with fatty acids. 

Most common is the theory of chemisorption of collectors at the surface of solid particles. However, it is, as a rule, at the same time noted that simultaneously concurrent processes take place, which are connected both with adsorption of surfactants at 1/g interfaces and with their interaction with ions in the flotation pulp. Thus, it is shown in [66] that saturated C 2—Cj4 fatty acids are selectively chemisorbed on calcium carbonate surfaces which provides them with an effective hydrophobisation. At the same time, C5—Cg acids are adsorbed mainly at 1/g interfaces which produces a substantial influence on the stability of the flotation foams. Free and Miller [67] have thoroughly investigated the behaviour of sodium oleate in the flotation of a calcium mineral, fluorite. It has been established that calcium dioleates are formed both in the bulk and at 1/s interfaces. In this case, an effective hydrophobisation of the surface of fluorite particles takes place both due to the interaction of oleate with calcium ions on the active sites and by adsorption of calcium dioleates formed in the solution. It has been once more confirmed [68] that classical collecting agents, xanthogenates, e.g. ethyl xanthogenate, form on the... 

Pugh, R.J., "The Role of the Solution Chemistry of Dodecylamine and Oleic Acid Collectors in the Flotation of Fluorite," Colloids and Surfaces, Vol. 18 pp. 19-41,1986. 

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