Hydroxamate collectors

Chrysocolla (CuOxSi02 Cu= 10-36%, SG — 2-2.4) is the most studied mineral of all the oxide minerals. Extensive laboratory studies have been conducted by numerous researchers [9-11]. The laboratory research work indicates that chrysocolla can be floated using the sulphidization method, as shown in Figure 19.4, or by hydroxamate collectors. However, none of these processes have been applied at an industrial scale. 

The Ta/Nb flotation was accomplished using collector RS702. This collector is composed of amine acetate, phosphoric acid esters and hydroxamate. Collector RS702 is a powerful collector, capable of floating a variety of niobium minerals that are contained in the flotation feed. Metallurgical results obtained from a continuous locked-cycle test are shown in Table 23.14. 

Limited research studies [6] show that the minerals from the yttrium groups can be recovered using alkyl hydroxamate collectors which form complex reactions with REO. 

Froth flotation has proven to be an efficient method of removing titaniferous impurities (mainly iron-rich anatase) from kaolin clays. Fatty acid reagent, primarily tall oil, is used extensively in the reverse flotation of these impurities. This flotation collector typically requires divalent cations (usually Ca +) to activate the coloured impurities and enhance collector adsorption. This is not very selective since the tall oil can also absorb on the kaolinite particles. Alkyl hydroxamate collectors are relatively new in the kaolin industry but provide significant advantages. Hydroxamates do not require activators, substantially increase the removal of colored impurities and are very selective. 

R.H. Yoon and J. Yordan, Beneficiation of Kaolin Clay by Froth Flotation Using Hydroxamate Collectors , Minerals Engineering, 1992,5(3-5), pp. 457-467. 

Figure 19.2 Effect of pH on malachite recovery using hydroxamic acid as collector.

There are only a few collectors suitable for tin flotation that have been introduced into operating plants in the 1970s, but today they have been replaced (i.e. arsonic acid, phospho-nic acid) due to toxicity and high prices. Other collectors that have been extensively studied include oleic acid, sodium oleate, alkyl phosphoric acid and hydroxamates [2—4],... 

Hydroxamic acid used as a collector has shown to give better selectivity than fatty acid. However, it has yet to be tested in an operating plant. 

In this study, the flotation performance of a series of newly developed hy-droxamate-based collectors was evaluated on different crude clays from Georgia, USA. These new collectors provide improved selectivity over the standard tall oil chemistry and the commercial hydroxamate reagent. Aero Promoter 6493 (AP 6493). The modified hydroxamates have the advantages of higher activity, easier... 

The newly developed modified alkyl hydroxamate reagents (from Cytec Industries) tested in this study include S-8704, S-8704D, S-8705, S-8706, S-8706D and S-8765, while the reference collectors used were Aero Promoter 6493 (also from Cytec) and tall oil. The crude clays were dispersed using sodium silicate while soda ash was used to adjust the pH. The frother used in the flotation tests was Aerofroth 70. 

The so-called chelating collectors, such as hydroxamic acids, continue to be studied by flotation specialists. The flotation selectivity of minerals partly soluble in the flotation pulp has been studied, at bench scale, in [159]. It has been shown that optimum results are achieved, when the mineral to be floated is the most soluble in the system and the chelate formed with the cation on the surface is most stable. 

For example, as shown in Figure 10.36 (15), no adsorption of myristate (an anionic surfactant) occurs below the isoelectric point (pH 7.0) of chromite (even though the surfaces are oppositely charged), while essentially complete flotation is achieved at about pH 9.0 (when the surfactant and surface are similarly charged). The lack of flotation below the lEP was attributed to the limited solubility of myristic acid under these conditions. A similar behaviour has been observed for the flotation of haematite with myristate. Chemisorption of another anionic collector, octyl hydroxamate, has also been observed on haematite at pH 9.0 (15). 

IM octyl hydroxamate. Cupric octyl hydroxam-ate has major bands at 925, 1095, 1380, 1450, and 1535 cm while bands at 1380, 1450 and 1535 cm are observed on chrysocolla after it has been treated with the collector, hence indicating the formation of cupric octyl hydroxamate at the surface during the adsorption process. This surface reaction is evident from the fact that chrysocolla changes colour from its natural blue-green to a vivid green colour upon adsorption of the collector. 

Fatty acids and soaps dominate the nonsulflde flotation. These collectors also tend to be nonse-lective because almost all minerals can be floated. The use of appropriate activators or depressants alleviates the problem to some extent. The lack of selectivity is often related to the tendency of fatty acids to form a precipitated phase with dissolved multivalent ions. The more tolerant ether carboxylic acids have been tested in some cases. Amines are used invariably for silicate minerals. Other collectors such as sulfates, sulfonates, phosphonic acids, hydroxamates, and some amphoteric surfactants have gained little importance. 

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