Xanthate as collector

Flotation of pyrite using either ethyl xanthate or potassium butyl xanthate as collector. Glycol frother is also usually employed in this separation. 

General mechanism of galena flotation using xanthate as collector is attributed to the formation of lead xanthate on the mineral surface ... 

Fig. 5.3. Structure of minerophilic group of xanthate as collector for sulfides.

Activators are chemicals that permit or reinforce the adsorption of collectors onto particles, usually by complexing with the collector, or bridging between the collector and the solid. For example, sphalerite (ZnS) can only be floated using ethyl xanthate as collector if the particles are first treated with copper sulfate. The copper species adsorbs first and acts as a bridge to the xanthate, allowing it to function as a collector for the sphalerite. 

The collecting capability of isobutyl xanthate is equal to or higher than that of n-butyl xanthate. Two examples for the flotation of copper ore using butyl xanthates as collectors can be seen as follows ... 

With sodium ethyl xanthate as collector, the frothing capabilities of various synthesized dodecyl phenyl polypropylene ether alcohol frothers from dode-cylphenol and epoxy ethane in the flotation of lead zinc ore of Australia Broken Hill are listed in Table 3.2. As shown in Table 3.2, the frothing capability of dodecyl phenyl polypropylene ether alcohol is as same as that of eucalyptus oil. 

Alkali metal xanthates are prepared in high yield from reaction of amyl alcohols with alkah metal hydroxide and carbon disulfide (39—42). The xanthates are useful as collectors in the flotation of minerals and have minor uses in vulcani2ation of mbber and as herbicides (39,41). 

Table 8 summarizes domestic consumption by use for amyl alcohols. About 55% of the total 1-pentanol and 2-methyl-1-butanol production is used for zinc diamyldithiophosphate lubrication oil additives (150) as important corrosion inhibitors and antiwear additives. Amyl xanthate salts are useful as frothers in the flotation of metal ores because of their low water solubiUty and miscibility with phenoHcs and natural oils. Potassium amyl xanthate, a collector in flotation of copper, lead, and zinc ores, is no longer produced in the United States, but imports from Germany and Yugoslavia were 910 —1100 t in 1989 (150). 

Xanthate compounds are widely used as collectors in flotation. Their function is to render the mineral surface hydrophobic and thus facilitate bubble attachment. The adsorption of xanthates onto sulfide minerals occurs via an electrochemical mechanism involving the reduction of oxygen and the anodic adsorption of xanthate. 

The primary collector used in PGM flotation is xanthate. As a choice of secondary collectors, dithiophosphates and mercaptans are used in some operating plants. 

In recent studies, a new line of PGM collectors had been developed [13] known as the PM series. These collectors are an ester-modified mixture of xanthate + mercaptan. The reaction product forms an oily greenish-coloured liquid. The results obtained using the PM series of collectors are shown in Table 18.5. High PGM recovery was obtained using a combination of sodium amyl xanthate plus collector PM301. 

Flotation of the lead oxide minerals is a difficult problem not least because there are no known direct acting collectors. Normally, during oxide lead flotation, a sulphidization method is used with xanthate as a collector. In the majority of cases, the ore is pretreated using a desliming process, especially if the ore contains clay and Fe-hydroxides. Another method includes the preconcentration using heavy liquid. 

In plant practice, lead oxide minerals are recovered using a sulphidization method with xanthate as the primary collector and mercaptans as the secondary collector. 

Suitable collectors can render hydrophilic minerals such as silicas or hydroxides hydrophobic. An ideal collector is a substance that attaches with the help of a functional group to the solid (mineral) surface often by ligand exchange or electrostatic interaction, and exposes hydrophobic groups toward the water. Thus, amphi-patic substances (see Chapter 4.5), such as alkyl compounds with C to C18 chains are widely used with carboxylates, or amine polar heads. Surfactants that form hemicelles on the surface are also suitable. For sulfide minerals mercaptanes, monothiocarbonates and dithiophosphates are used as collectors. Xanthates or their oxidation products, dixanthogen (R - O - C - S -)2 are used as collectors for... 

The one hundred year history of froth flotation may be classified into three periods. The earliest stage is from the end of the 19 century to the early 20 century, i.e. surface flotation or bulk oil flotation. The natural hydrophobic sulphide minerals can be collected by the addition of oil. Froth flotation came into practice in 1909 with the use of pine oil, mechanical flotation machine in 1912, and xanthate and aerofloat as collectors in 1924—1925 (Gaudin, 1932 Sutherland and Wark, 1955). 

In the 2nd period ranging from the 1930s to the 1950s, basic research on flotation was conducted widely in order to understand the principles of the flotation process. Taggart and co-workers (1930, 1945) proposed a chemical reaction hypothesis, based on which the flotation of sulphide minerals was explained by the solubility product of the metal-collector salts involved. It was plausible at that time that the floatability of copper, lead, and zinc sulphide minerals using xanthate as a collector decreased in the order of increase of the solubility product of their metal xanthate (Karkovsky, 1957). Sutherland and Wark (1955) paid attention to the fact that this model was not always consistent with the established values of the solubility products of the species involved. They believed that the interaction of thio-collectors with sulphides should be considered as adsorption and proposed a mechanism of competitive adsorption between xanthate and hydroxide ions, which explained the Barsky empirical relationship between the upper pH limit of flotation and collector concentration. Gaudin (1957) concurred with Wark s explanation of this phenomenon. Du Rietz... 

The influence of pulp potential on the flotation of marmatite at different pH is given in Fig. 4.20 using ethyl xanthate as a collector. In acidic pH media, marmatite exhibits a wide floatable potential range and the upper potential limit of flotation... 

Figure 4.20 Flotation recovery of marmatite as a function of pulp potential with ethyl xanthate as a collector at different pH (KEX 10" mol/L)...

Figure 4.22(b) shows that no anodic oxidation peaks occurred at lower potential region in alkaline media for marmatite electrode in xanthate and dithiocarbamate solution indicates no formation of collector species on marmatite. When the potential increases to higher potential region, the occurrence of anodic oxidation peak may be due to the self-oxidation of marmatite. It accounts for no flotation of marmatite in alkaline media either using xanthate or dithiocarbamate as collectors. 

The influence of potential on the floatability of pyrite with butyl xanthate as a collector has been determined and the result is given in Fig. 4.23. It follows that flotation begins at 0.1 V for an initial KBX concentration of 10 mol/L. The flotation potential ranges from 0.10 V to +0.31 V. 

The effect of DMPS on the flotation recovery of pyrrhotite and marmatite in the presence and absence of CUSO4 with butyl xanthate is shown in Fig. 5.16. It follows that the flotation of pyrrhotite and marmatite is greatly affected by DMPS addition. In the absence of cupric ion the recovery of pyrrhotite hardly exceeded 40%. At pH = 2, the recovery of marmatite is more than 90%, but the recovery sharply decreases to below 20% with pH increasing. These results show that pyrrhotite and marmatite can not be separated in the absence of cupric ion with DMPS as depressant and xanthate as a collector. In the presence of cupric ions, marmatite flotation improves under wide pH condition. The flotation of pyrrhotite is activated only aroimd pH = 2. The results demonstrate that flotation separation of copper-activated marmatite from pyrrhotite is possible in the presence of butyl xanthate and DMPS. 

At pH = 6, the flotation recovery of marmatite, arsenopyrite and pyrrhotite as a function of depressant dosage GX2 is given in Fig. 5.22. With the increase of GX2 dosage, the flotation recovery of these three minerals decreases. However, marmatite remains with reasonably high flotation recovery of above 70%, and arsenopyrite and pyrrhotite exhibit poor flotation with recovery of below 35% when the concentration of GX2 is above 120 mg/L. It indicates the possibility for flotation separation of marmatite from arsenopyrite and pyrrhotite by using 2,3-dihydroxyl propyl dithiocarbonic sodium as a depressant and butyl xanthate as a collector. 

The influence of pulp potential on the flotation of marmatite, arsenopyrite and pyrrhotite with 10 mol/L butyl xanthate as a collector in the presence of 150 mg/L 2,3-dihydroxyl propyl dithiocarbonic sodium (GX2) has been tested. Taking the flotation recovery to be 50% as a criterion, above which the mineral is considered to be floatable and otherwise not floatable, the upper and lower potential limits of the flotation of marmatite, arsenopyrite and pyrrhotite at different pH are presented in Fig. 5.25 and Table 5.1. It is evident that marmatite is floatable in some range of potential at various pH, whereas arsenopyrite and pyrrhotite are not floatable in the corresponding conditions. It suggests that the flotation separation of marmatite from arsenopyrite and pyrrhotite may be... 

Figure 5.25 The upper and lower potential limits of marmatite flotation with butyl xanthate as a collector in the presence of GX2...

Similarly, the influence of pulp potential on the flotation of marmatite, arsenopyrite and pyrrhotite with 10 mol/L butyl xanthate as a collector in the presence of 120mg/L (1-carbonic sodium-2-acetaic sodium) propanic sodium dithio carbonic sodium (TX4) has been tested. The results are given in Fig. 5.26 and Table 5.2. It can be seen from Fig. 5.26 that at pH=4.5 marmatite has wide floatable potential range from 0.3 V extended to above 0.7 V, at pH = 6.5 the floatable potential range is about 0.3-0.4 V, and at pH =9.2 marmatite is not floatable. Table 5.2 demonstrates that in these conditions, arsenopyrite and... 

Figure 5.34 Flotation recovery of arsenopyrite as a function of polyhydroxyl xanthate concentration with butyl xanthate as a collector...

Flotation recovery of sphalerite as a function of pH with butyl xanthate as a collector in the presence and absence of activator is presented in Fig. 6.1. Evidently, sphalerite exhibits good flotation in weak acidic media and the recovery decreases sharply with the increase of pH in the absence of activator. The flotation of sphalerite is activated in wide pH range in the presence of activators such as CUSO4 or Pb(N03)2. The recovery of sphalerite can be above 90% at pH < 12 using copper ion as an activator and at pH < 10 using lead ion as an activator. 

Figure 6.4 to Fig. 6.6 show the effect of pulp potential on the copper activation flotation of marmatite, arsenop5nrite and pyrrhotite in the presence of lO " mol/L Cu with 10" mol/L butyl xanthate as a collector. It is obvious that marmatite, arsenopyrite and pyrrhotite appear to have better flotation response at certain potential range at different pH conditions. 

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