INVESTIGATION OF THE EFFECT OF HYDROLYSIS LIGNIN ADDITIVES ON THE PELLETIZABILITY OF FINE-GRAINED MAGNETITE CONCENTRATES

A. V. VITYUGIN, V. M. VITYUGIN

(Presented by the scientific seminar of the Department of General Chemical Technology)

Iron-ore pellets are the most promising ore raw material for ferrous metallurgy. At present, ore-preparation practice has mastered two types of this product: fluxed and non-fluxed pellets. Recently, much attention has been devoted to mastering the technology for producing partially reduced iron-bearing pellets.

Magnetite concentrates of deep beneficiation do not lend themselves to independent pelletizing because of their elevated moisture content and low plasticity. As a moisture-absorbing plasticizer, bentonite additives in amounts of 0.5–1.5% are usually used. However, an excessive increase in the bentonite addition leads to a substantial decrease in iron content and a reduction in pellet strength.

In light of the foregoing, the use of hydrolysis lignin appears very promising, since it is distinguished by a favorable combination of such properties as high moisture-absorbing capacity, plasticity, and reducing ability. The economic advisability of replacing bentonite with hydrolysis lignin is based on the fact that lignin is a practically unused, large-tonnage waste product of the hydrolysis industry. In addition, unlike ballast bentonite, lignin additions should ultimately lead to an increase in the iron content in fired pellets.

Below are presented the results of an experimental study of the effect of hydrolysis lignin additions from the Krasnoyarsk Biochemical Plant on the pelletizability of magnetite concentrate from the Sokolovsko-Sarbai Mining and Beneficiation Combine (SSGOK).

The lignin was preliminarily dried and ground to a particle size of less than 0.1 mm. In the experiments, lignin was used in an air-dry state (moisture content 4.7%). The water-physical properties of the materials and mixtures studied are given in Table 1.

To determine the pelletizability and the optimum moisture content for pelletizing of the materials studied, equations 1 and 2 were taken as the basis:

$$ K = \frac{W_{\text{m.m.v.}}}{W_{\text{m.k.v.}} - W_{\text{m.m.v.}}}, \tag{1} $$

$$ W^{p}_{\text{o.p.t.}} = \frac{W_{\text{m.m.v.}}}{K}, \tag{2} $$

where \(K\) is the pelletizability coefficient;
\(W_{\mathrm{m.m.c.}}\) is the maximum molecular moisture capacity, %;
\(W_{\mathrm{m.c.c.}}\) is the maximum capillary moisture capacity, %;
\(W_{\mathrm{o.p.p.}}^{p}\) is the optimum moisture content of the mixture before pelletizing, %.

Direct use of equations (1 and 2) for mixtures containing lignin is impossible, since the latter is characterized by increased microporosity (pore size \(30\text{–}200\,\text{\AA}\)) and swelling. The water of the micropores

Table 1

Water-physical properties of the investigated materials

belongs to hidden capillary water. Calculations showed that, in the lignin samples studied, the amount of micropore water averages 84%. This amount of hidden capillary water \((W_{\mathrm{m.c.c.}}^{\mathrm{hidden}})\) must be subtracted from the experimental value \((W_{\mathrm{m.c.c.}})\) in order to obtain the value of the effective capillary moisture capacity. Taking the above into account, the calculation formula for determining the pelletizability coefficient of a mixture containing lignin \((K^{1})\) is expressed as

\[ K^{1}=\frac{W_{\mathrm{m.m.c.}}}{W_{\mathrm{m.c.c.}}-W_{\mathrm{m.c.c.}}^{\mathrm{hidden}}\cdot x-W_{\mathrm{m.m.c.}}}, \tag{3} \]

where \(W_{\mathrm{m.c.c.}}^{\mathrm{hidden}}\) is the moisture of lignin micropores, %,
\(x\) is the fraction of lignin in the mixture, unit fractions.

Accordingly, the optimum moisture content of the mixture for pelletizing was calculated from the equation

\[ W_{\mathrm{o.p.p.}}^{p}=\frac{W_{\mathrm{m.m.c.}}}{K^{1}}. \tag{4} \]

The dependences of the calculated values \((K^{1},\ W_{\mathrm{o.p.p.}}^{p})\) and the experimental values \((W_{\mathrm{m.m.c.}}^{p})\) on the lignin content in the mixture with SSGOK concentrate are shown in Fig. 1.

As was to be expected, the introduction of lignin into the mixture directly proportionally increases the value of the maximum molecular moisture capacity (straight line “a”). The change in the pelletizability coefficient of the mixture within the range of lignin additions up to 10% has a curvilinear dependence, since the value \((W_{\mathrm{m.c.c.}})\) is not additive. The dependence of \(W_{\mathrm{o.p.p.}}^{p}\) on the amount of bentonite additions has an analogous character.

To verify the established calculated relationships, pelletizing experiments were carried out on several mixtures in a disc pelletizer 1 m in diameter, with a rim height of 0.1 m, a disc inclination angle of 45°, and a peripheral speed of 0.8 m/s. The good agreement between the calculated and actual moisture contents of the mixtures before pelletizing confirms the validity of the calcula-

... of the dependence of the pelletizability coefficient on the lignin addition. Thus, for example, the calculated value \(W_{p/\mathrm{opt.}}\) for mixtures with 1% and 5% lignin was 8.5% and 11.2%, while the actual values were, respectively, 8.6% and 11.3%.

Visual observations showed a very high rate of pelletizing of concentrate mixtures with lignin.

Fig. 1. Effect of lignin additions on the pelletizability of SSGOK magnetite concentrate (curve “v”), on the maximum molecular moisture capacity of the mixture (curve “a”), and on the optimum moisture content for pelletizing the mixture (curve “b”)

Thus, the preliminary investigations convincingly show the rationality of using hydrolysis lignin in the production of iron-ore pellets. In the near future it is planned to carry out pilot-plant testing of lignin additions in producing fluxed pellets at the SSGOK pilot plant.

REFERENCES

1. V. M. Vityugin, A. S. Bogma. Evaluation of the pelletizability of fine-grained materials. Izv. VUZov, “Ferrous Metallurgy,” No. 4, 1969.

2. V. M. Vityugin, A. S. Bogma, P. N. Dokuchaev. Calculation of the optimum moisture content of dispersed materials before granulation. Izv. VUZov, “Ferrous Metallurgy,” No. 8, 1969.