Silicates, flotation

This was shown, for example, by electrokinetic measurements of Kavanagh and Quirk177) in the system Fe203-illite at pH 2.5. Electrophoretic and cation-exchange data indicated that the net charge of clay surface became strongly positive at low pH values as a result of adsorption of polycations Fe3+. Further examples of metal ion hydrolysis in oxide and silicate flotation systems were published by Fuerstenau178) and Stumm et al.62). 

M. C. Fuerstenau, The Role of Mreel Ion Hydrolysis in Oxide and Silicate Flotation Systems. 

Manser, R. M. (1975). Handbook of Silicate Flotation , 196 pp. Warren Spring Lab., Stevenage, England. 

Table XI-1 (from Ref. 166) lists the potential-determining ion and its concentration giving zero charge on the mineral. There is a large family of minerals for which hydrogen (or hydroxide) ion is potential determining—oxides, silicates, phosphates, carbonates, and so on. For these, adsorption of surfactant ions is highly pH-dependent. An example is shown in Fig. XI-14. This type of behavior has important applications in flotation and is discussed further in Section XIII-4.

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. 

A simple two-mineral separation, say of galena (specific gravity 7.5) from a siliceous gangue (specific gravity 2.65) can be taken as a good example to illustrate the process. The flotation operation comprises the following successive steps. 

The attachment of minerals to the bubbles, which is the heart of the flotation process, occurs. Once this occurs, gravity completes the separation readily. In the present example, galena attaches itself to the bubbles and thereby its effective density is drastically reduced. This causes galena to buoy up in spite of the fact that it is, in reality, much heavier than the siliceous gangue. 

Abdel-Khalek, N. A. Evaluation of flotation strategies for sedimentary phosphates with siliceous and carbonates gangues. Miner. Eng. 2000, 13, 789-793. 

Some porphyry copper ores contain naturally floatable gangue minerals, such as chlorites and aluminosilicates, as well as preactivated quartz. Sodium silicate, carboxy methyl-cellulose and dextrins are common depressants used to control gangue flotation. 

The modifier used in the flotation of these ores included a mixture of sodium silicate and Calgon. Good selectivity was also achieved using boiled starch. 

Carboxilic acid flotation of malachite has been commercially used for over 70 years. This collector is prepared by heating a mixture of hydrolysed palm oil (or oleic acid) and fuel oil in a 3 1 ratio. This mixture is manly used for recovery of malachite from siliceous ores. The use of carboxylic acid for malachite flotation from carbonaceous ores resulted in both reduced concentrate grade and recovery. 

Type of gangue minerals - some ore types contain silicate gangue free of slimes, which are the most amenable to flotation. Ores with dolomitic gangue can be beneficiated... 

In a large number of oxide flotation plants, sodium silicate (Na2Si03) is used as a gangue depressant. In the past two decades, a new line of depressants has been developed and introduced into a number of operating plants. Some of these depressants include (a) a mixture of sodium phosphate and lignin sulphonate (i.e. depressant 3XD), (b) a mixture of a low-molecular-weight acrylic acid and sodium silicate (depressant 2D) and (c) hydrosol based on the reaction of sodium silicate with alumina sulphate (depressant SD). These depressants were extensively examined on copper oxide ores from the Nchanga mine in Zambia. 

Effect of degree of fatty acid mixture dispersion on Cu/Co flotation from siliceous Kolwezi open pit ore - laboratory-locked cycle tests... 

One of the main problems associated with beneficiation of the Kolwezi siliceous ore is the production of malachite and pseudomalachte slimes that have a relatively low flotation rate. Most of the copper losses occurring in the plant are in the -15 pm fraction. Experimental testwork conducted with a different palm oil emulsifier indicated that copper recovery from the fine fraction can be significantly improved with the use of petroleum sulphonate (Petrosol 845) as the emulsifier [21] for palm oil. Significant improvement in copper recovery was realized in the fine fractions with the use of palm oil emulsified with Petrosol 845. 

The flowsheet used to treat dolomitic oxide copper ores is somewhat different from that used in the beneficiation of siliceous oxide copper ores. This is due to the fact that dolomitic ore usually contains elevated amounts of slimes, in which case a split circuit flowsheet has been adopted in a number of operations. The typical flowsheet used for treatment of dolomitic ores is shown in Figure 19.8. Usually, the scavenger tailings are deslimed and the sand fraction is retreated in a scalp copper flotation stage. When the ore is deslimed before flotation, a large amount of fine copper is lost in the slime fraction. 

In the case of carbonatite ores, a beneficiation process involves preflotation followed by reactivation and flotation of pyrochlore. In the case of pegmatitic ores that contain silicates, biotite, albite and limonite, as the gangue minerals, direct flotation of pyrochlore can be achieved with a variety of different collectors. 

A number of studies have been conducted [1,2] in which different fatty acid modifications were examined. High selectivity and high calcite-dolomite recoveries were obtained with emulsified fatty acid with soda ash and sodium silicate. Table 22.2 shows the results from calcite/dolomite flotation using different fatty acid type collectors and various modifications. 

Sodium silicate has a strong depressing effect on pyrochlore, and it is sometimes used during calcite flotation. Sodium silicate hydrosol is prepared by reacting ferric chloride and silicate, followed by acidification of the mixture, which has a positive effect on selectivity. The addition of small quantities of hydrosol (100 g/t) resulted in significant improvement in concentrate grade. 

The apatite barite bulk flotation was accomplished with a mixture of tall oil fatty acid and sulphonate (Aero 827) at an alkaline pH. Sodium silicate and caustic tapioca starch were used for pyrochlore depression during the bulk apatite barite flotation stage. 

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. 

A large portion of monazite production comes from mineral sand deposits. In the beneficiation of monazite from mineral sand deposits that contain garnet, ilmenite, shell and silicates, the physical concentration and combination of physical preconcentration-flotation is used. Several reagent schemes using flotation were developed throughout various studies [8-10] and some have been confirmed in continuous pilot plants. 

India has very large deposits of monazite on the coastal shores of Kerala and Chennai. A typical mineral composition of this type of deposit is 60% ilmenite, 1.2% rutile, 5% zircon, 6.4% garnet, 4% silinanite, 16% quartz, 2.5-5% monazite and 1-7% shell. Research work involved different anionic collectors and pH during monazite flotation, along with the level of sodium silicate used as depressant. 

Experimental work conducted at different levels of sodium silicate (Table 24.9) indicates that sodium silicate is an excellent depressant for titanium, zircon and other gangue minerals while the monazite flotation is not affected. 

Effect of sodium silicate on monazite flotation from Kerala and Chennai beach sand (India)... 

The type of gangue depressant and modifier used during ilmenite flotation depends on the type of gangue present in the ore. Sodium silicate is commonly used as a gangue depressant. In a recent study [4], it was demonstrated that the effectiveness of silicates as depressants improved significantly with the use of acidified silicate. Figure 25.4 shows the effect of acidified silicate on the ilmenite grade-recovery relationship. 

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