Effect of Humic Acids on the Flotation of Ilmenite and Zircon

EFFECT OF HUMIC ACIDS ON THE FLOTATION OF ILMENITE AND ZIRCON

S. A. BABENKO

(Presented by the scientific seminar of the departments of PMAKhP and OKhT)

The flotation properties of humic substances have been studied only slightly. In works dealing with this question, on the one hand [1, 2], it is categorically asserted that in the presence of humic substances the flotation process cannot take place, while on the other hand [3] only a decrease in the recovery of minerals into the concentrate is indicated when water containing humic substances is used in flotation. According to Sun Sh. Ch. [4], the presence in the pulp of humic substances in amounts up to 0.27 kg/t has no adverse effect on coal flotation. A successful attempt has been made to use humic substances (sodium humate) as a selective depressant in the flotation separation of an ilmenite–magnetite concentrate [5].

The contradictory assessment of the role of humic substances in the flotation process is apparently explained by the variability of their properties, arising from the variability of their composition. According to current views, humic substances include humic acids, fulvic acids, and humatomelanic acids. These substances, in variable amounts, may be introduced into the pulp with the water or with the solid phase, which, as was previously shown using the example of flotation of titanium–zirconium sands [6], is promoted by the alkaline medium of the pulp.

In the present work an attempt was made to study the effect of humic acids on the flotation of ilmenite and zircon. The indicated minerals were separated from a placer deposit by gravity and magnetic methods, carefully cleaned of clay films by scrubbing in a dense pulp and washing with distilled water. The minerals wetted in water were stored in vessels with tightly closing lids. Humic acids were isolated from peat according to the procedure adopted in soil science [7].

The collectors used were oleic acid, sodium alkyl sulfate, Petrov’s reagent, tall oil, Recycle, and ANP. The pH of the pulp was changed by adding hydrochloric acid.

Flotation tests remain, up to the present time, the only method that makes it possible to speak with certainty about the floatability of minerals. Therefore, the effect of humic acids on the flotation of ilmenite and zircon was studied by analyzing the final results of flotation tests carried out on pure minerals. The capacity of the flotation cell was 300 cm³, and the impeller rotation speed was 2100 rpm. The conditions of the flotation tests were as follows: solid-to-liquid ratio during flotation, 1:4; addition of humic substances, agitation for 2 min; addition of regulator, agitation for 5 min; addition—

collector addition, agitation 2 min; flotation time—3 min; deionized water, its temperature—20°C.

Humic acid affects the floatability of ilmenite and zircon with different collectors in different ways (Figs. 1 and 2).

Flotation of ilmenite with an oleic-acid emulsion, with the addition of humic acid at pH = 6.8, begins to be depressed only when the content of the latter in the pulp exceeds 56 mg/l. The flotation of zircon, however, is depressed at an insignificant consumption of humic acid—

Fig. 1. Effect of humic acid on the flotation of ilmenite: 1—oleic-acid emulsion (6.5 mg/l); 2—sodium alkyl sulfate (246 mg/l, pH = 4); 3—petrolatum (107 mg/l); 4—tall-oil emulsion (8.7 mg/l); 5—ANP (64 mg/l), pH = 5; 6—recycle (71.4 mg/l)

acid, and at 132 mg/l the recovery into the froth is only 7%, as against 46% without humic acid. Substitutes for oleic acid—oxidized petrolatum soap, oxidized recycle soap, and tall oil—with humic acid, at a content of the latter of 132 mg/l in the pulp, recover into the froth, respectively, 74%, 49%, and 60% of ilmenite, while without humic acid they recover 80%, 39%, and 70%; i.e., with petrolatum soap and tall oil there is some depression, whereas with recycle soap there is activation of ilmenite.

In flotation of zircon with the indicated substitutes for oleic acid in the presence of humic acid, a characteristic feature is substantial depression of zircon during flotation with tall oil (63% and 19%—respectively, the recovery into the zircon froth product without and with humic acid) and almost complete absence of any changes in the recovery of minerals into the froth during flotation with recycle (63%—recovery into the froth without humic acid and 60%—with humic acid).

Sodium alkyl sulfate, even when humic acid is present in the pulp in a small amount, sharply reduces the recovery into the froth of both ilmenite and zircon. At a humic-acid content in the pulp of 32 mg/l, the recovery into the concentrate of ilmenite and zircon was, respectively, 2% and 7%, as against 54% and 59% without humic acid.

A characteristic feature of most of the collectors used in the flotation of ilmenite with them in the presence of humic acid in small amounts (11–32 mg/l) is the presence of activation, increas-

increasing recovery into the froth by 7% for petroleum soap, by 10% for tall oil and oleic acid, and by 25% for Recycle soap.

As for the flotation of zircon in the presence of small amounts of humic acid, the activating effect appears only with tall oil (an increase of 5%).

Fig. 2. Effect of humic acid on the flotation of zircon: 1 — oleic acid emulsion (4.3 mg/l); 2 — sodium alkyl sulfate (54 mg/l), pH = 4; 3 — tall oil emulsion (6.5 mg/l); 4 — ANP (21.4 mg/l), pH = 5; 5 — Recycle (36 mg/l)

Humic acid present in the liquid phase of the pulp does not depress ilmenite and zircon if they are floated with ANP; on the contrary, the use of a cationic reagent in the presence of humic acid improves the floatability of these minerals, especially at low concentrations of it. Thus, the recovery into the froth of ilmenite and zircon without humic acid, using ANP, was 60% and 45%, respectively, whereas with humic acid (32 mg/l) the recovery increased to 89% for ilmenite and 76% for zircon.

These experiments were carried out under conditions excluding the influence of regulators on the behavior of humic acid in the flotation process, only for sodium alkyl sulfate and ANP, which are most active in an acid medium; the pH values were 4 and 5, respectively. Under these conditions, humic acids present in the flotation pulp cannot be classified as depressants, as had been assumed previously. As for sodium humate, even a small amount, 16 mg/l or more, suppresses the flotation of the indicated minerals with all anionic collectors.

The peculiarities of the flotation of ilmenite and zircon in the presence of humic acid with various collectors can be explained by the interaction of the minerals with humic acid. Because of its intense color, the latter is conveniently determined colorimetrically. The concentration of a humic acid solution is proportional to the intensity of its color. When humic acid is adsorbed by the surface of minerals, the concentration decreases; this was determined from the change in color intensity on a colorimeter. The experiments were carried out with mineral samples of 10 g; for each mineral sample, 10 ml of humic acid was used. The amount of humic acid adsorbed per 100 cm² of mineral surface was determined by calculation.

To determine the specific surface area of the minerals, 50 grains of ilmenite and zircon were measured under a microscope in two directions (eyepiece ×5, achromatic objective 13-89 A-30). The zircon grains are prismatic in shape, whereas the outlines of the ilmenite grains are completely irregular. On this basis, the surface of zircon grains was determined as the surface of a prism, and that of ilmenite as the surface of a sphere of equivalent diameter. To calculate the specific surface area, weighed portions of zircon and ilmenite were taken, and then the number of grains contained in these weighed portions was counted under a binocular microscope. The specific surface area calculated in this way was, for zircon, \(246 \text{ cm}^2/\text{g}\), and for ilmenite, \(288 \text{ cm}^2/\text{g}\).

The calculation given was checked against the determination of specific surface area by the permeability method [8]. The following data were obtained: zircon, \(256 \text{ cm}^2/\text{g}\); ilmenite, \(496 \text{ cm}^2/\text{g}\).

The specific surface area of zircon determined by the permeability method is very close in magnitude to the value obtained by calculation. The results in determining the specific surface area of ilmenite under the microscope and by the permeability method differ substantially from one another. This difference can be explained by the strongly developed microsurface of ilmenite grains, the calculation of which from microscopic measurements contains a considerable error toward lower values, since the surface of ilmenite was calculated as the surface of a sphere by equivalent diameter. In subsequent calculations the specific surface area of ilmenite obtained by the permeability method was used.

Fig. 3. Effect of pH on the adsorption of humic acid by ilmenite (upper curve) and zircon (lower curve). Concentration of humic acid, 0.021%. Interaction time, 5 min

The adsorption of humic acid by the minerals is decisively affected by the pH of the medium. At \(\text{pH} = 2.8\), adsorption of humic acid by ilmenite and zircon is maximal. As the pH of the medium increases from 2.8 to 3.0, adsorption decreases; in neutral and alkaline media, water molecules are adsorbed by the surface of the minerals (Fig. 3). Similar data were obtained earlier by Koganovskii [9].

The fact of adsorption of humic acid in an acidic medium explains the depression of minerals during their flotation with sodium alkyl sulfate and humic acid. Humic acid present in the liquid phase of the pulp in neutral and alkaline media promotes the attachment of hydrox-

strong ions on the surface of the minerals. It is known that an excess of alkali in the pulp causes depression of minerals by fixation of hydroxyl ions on their surface. In optimal amounts, hydroxyl ions activate the flotation of minerals. It is obvious that the maximum amount of hydroxyl ions fixed on the surface of minerals that still act as activators will depend on the flotation conditions, the type of collectors used, and the character of the mineral. With an increase in the pH of the medium, and also in the presence of sodium humate in the pulp, adsorption of hydroxyl ions by the minerals occurs. A slight increase in their hydration, especially if flotation proceeds in a neutral medium, promotes activation of the minerals owing to greater fixation of oleate ions. An increase in the concentration of sodium humate promotes an increase in the hydration of the particles, which leads to their depression.

Thus, the effect of humic acids on the flotation of ilmenite and zircon, which depends sharply on the amount of humic acids and the pH of the medium, is explained by the special features of their adsorption on the surface of the indicated minerals.

REFERENCES

1. F. G. Moses. Colloids and Flotation. Basic Principles of the Flotation Process. Collection of works by American authors edited by Prof. V. I. Trushchevich. Tsvetmetizdat, Moscow, 1932.

2. E. V. Mayer, G. Shranz. Flotation. Tsvetmetizdat, Moscow, 1933.

3. U. Runolinna. Flotation of ilmenite from titanomagnetite ore at the Otanmäki plant in Finland. In: Factories for the Beneficiation of Titanium Ores. Mekhanobr Transactions, issue 108, 1958.

4. Sh. Ch. Sun. Effect of coal oxidation on their flotation properties. In: Flotation of Useful Minerals. Gosgortekhizdat, 1962.

5. Yu. M. Chikin, B. V. Levinskii. Author’s certificate No. 160477 of January 18, 1963. “Byull. izobr.,” No. 4, 1964.

6. S. A. Babenko et al. Preparation for flotation of titanium-zirconium sands containing humic substances. Izvestiya VUZov, Gornyi Zhurnal, No. 11, 1962.

7. I. V. Tyurin. On a method of analysis for the comparative study of the composition of soil humus or humus. Transactions of the Soil Institute, Academy of Sciences of the USSR, vol. 38, 1951.

8. E. E. Serto, V. A. Bun’ko. Sampling, control, and automation of technological processes at beneficiation plants. Ugletekhizdat, 1957.

9. A. M. Koganovskii. Effect of electrolytes on micelle formation of humic and apocrenic acids and on their adsorption from aqueous solutions. Colloid Journal, vol. 24, 1962.