Elsevier

Minerals Engineering

Volume 113, November 2017, Pages 1-7
Minerals Engineering

The effect of sodium alginate on the flotation separation of scheelite from calcite and fluorite

https://doi.org/10.1016/j.mineng.2017.07.016Get rights and content

Highlights

Abstract

In this paper, the effect of sodium alginate on the flotation separation of scheelite from calcite and fluorite using sodium oleate as collector was investigated. Flotation results showed that sodium alginate could selectively depress the flotation of calcite and fluorite in pH range of 7–12 when it was added before sodium oleate. The selective depressant effect of sodium alginate was studied using zeta potential measurements, contact angle measurements and FTIR. The zeta potential measurements results showed that sodium alginate exhibited little influence on the surface charge of scheelite but had remarkable effect on that of calcite and fluorite. The results of contact angle measurements indicated that sodium alginate could produce selective, non-recoverable decrease in surface hydrophobicity of calcite and fluorite. The FTIR studies demonstrated the chemical absorption of sodium alginate on calcite and fluorite surface and no form of adsorption on scheelite surface.

Introduction

Scheelite (CaWO4) is a typical tungstate mineral and usually co-exists with other calcium-containing minerals, such as calcite (CaCO3) and fluorite (CaF2) in scheelite deposits. By now, flotation is the most commonly used technique to separate scheelite from calcite and fluorite (Hu et al., 2012). However, due to the same Ca2+ species on the cleavage (Pradip et al., 2002), the calcium minerals exhibit similar surface reactivity to traditional collectors such as fatty acids and their derivatives in flotation practice. It has been widely recognized that fatty acid collectors can collect these calcium minerals by forming calcium dicarboxylates on the mineral surface through chemisorption between Ca2+ and carboxyl (single bondCOOsingle bond) (Atademir et al., 1981, Rao et al., 1990, Rao and Forssberg, 1991, Ozcan and Bulutcu, 1993, Zhang and Song, 2003). Therefore, it is almost impossible to separate scheelite from calcite and fluorite using traditional fatty acid collector if no depressant is used.

Depressants in scheelite flotation, which are used for decreasing the flotability of calcite and fluorite, mainly include some inorganic salts and organic colloid. Sodium silicate and its solution with inorganic salt ions as well as organic colloid, are often applied in scheelite flotation to depress calcite and fluorite (Hanumantha Rao et al., 1989, Irannajad et al., 2009). But the sodium silicate-based depressants have also been proven to be able to adsorb on scheelite surface (Bo et al., 2015) thus showing inevitable influence on scheelite flotation (Kazmi et al., 2011, Liu et al., 2016). Phosphates, such as sodium phosphate (Na3PO4), sodium pyrophosphate (Na4P2O7) and sodium hexametaphosphate ((NaPO3)6) are also common depressants in scheelite flotation (Yongxin and Changgen, 1983). However, it is hard to find a proper phosphate to depress calcite and fluorite at the same time (Changgen and Yongxin, 1983). Other depressants such as quebracho, dextrin, and starch are also demonstrated to have limited selectivity in ore flotation (Castro and Hoces, 1993, Hiçyìlmaz et al., 1993, Liu et al., 2016, Ozcan et al., 1994). The efficient separation of scheelite from calcite and fluorite remains a problem.

Sodium alginate is a kind of natural polysaccharides. It can dissolve in aqueous solution and become hydrophilic colloid. Owing to its stable properties, unique pH sensitivity and biocompatibility, sodium alginate is usually used as food thickeners, emulsifiers, stabilizers, and controlled release agents of drugs (Pawar and Edgar, 2012). As there are chelating groups such as hydroxy (HOsingle bond) and carboxyl (single bondCOOsingle bond) in its molecule, sodium alginate has the potential for chelating calcium minerals and then making their surface hydrophilic in solutions. However, there are little published papers referring to utilizing its chelating capability in flotation field, especially in the separation of scheelite from calcite and fluorite.

In this paper, sodium alginate (NaAl) was introduced as a flotation modifier to selectively separate scheelite from calcite and fluorite using sodium oleate (NaOl) as collector. Micro-flotation tests on single mineral and mixed minerals were conducted to show the selective depressant effect of NaAl on calcite and fluorite. Zeta potential measurements, contact angle measurements and FTIR studies on minerals with and without treatment of NaAl and NaOl were performed to define the depressant effect mechanism.

Section snippets

Mineral samples and reagents

The samples of scheelite, calcite and fluorite were all obtained from Xintianling mine, Hunan, China. Hand-selected crystals of these minerals were crushed to −1 mm by a laboratory roll crusher. The crushed products were then ground in a ceramic ball mill and dry-sieved to obtain the −74 + 38 μm-size fractions for micro-flotation tests. A portion of −38 μm-size fraction particles was further ground to −2 μm for zeta potential measurements and FTIR studies. The purities of these samples were 97.25%

Micro-flotation test results

Single mineral flotation tests were conducted using NaOl as collector and NaAl as depressant. The effects of reagent dosage and pulp pH on the flotation recoveries of scheelite, calcite and fluorite were studied and the results are shown in Fig. 3, Fig. 4, Fig. 5. The standard deviation of the plotted mean recovery values is shown as the error bars in the figures.

Fig. 3 shows the effect of NaOl dosage on the flotation behavior of scheelite, calcite and fluorite approximately at pH 7. The

Conclusions

Sodium alginate exhibits selective depressant effect on calcite and fluorite in scheelite flotation. Using sodium alginate as depressant and sodium oleate as collector can realize the preferential flotation separation of scheelite from calcite and fluorite in pH range of 7–12. Through analyzing the zeta potential, contact angle and IR spectrum, it is concluded that sodium alginate chemically adsorbs on the surface of calcite and fluorite and hinders the adsorption of sodium oleate. Sodium

Acknowledgements

This work was supported by the Major State Basic Research Development Program of China (973program) (2014CB643402).

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