RU2259411C2 - Method for oxidative alkali refining of lead - Google Patents

Abstract

FIELD: nonferrous metallurgy.

SUBSTANCE: invention is dealing with refining of black lead to remove antimony, arsenic, and tin impurities. For that end, impurities are oxidized by stirring lead-alkali melt and simultaneously feeding oxygen at controlled flow rate 7-10 L/min. Stirring of melt is performed with the aid of paddle agitator rotated at speed corresponding to Reynolds criterion value (5-7)·10³.

EFFECT: increased fullness of removal of impurities and accelerated refining process.

1 dwg, 1 tbl

Description

The invention relates to metallurgy of lead and can be used to clean crude lead from impurities of antimony, arsenic and tin.

A known method of oxidative refining of lead by supplying air to the surface of molten lead or by blowing the melt with air at a temperature of 750-800 ° C (Shivrin G.N. Metallurgy of lead and zinc. M .: Metallurgy, 1982, S. 124-127). The impurities present in the alloy (antimony, arsenic and tin) are oxidized directly with atmospheric oxygen to form antimony, arsenic and tin oxides, which interact with excess lead oxide to form stannates, arsenates, arsenites, antimonates and antimonites insoluble in lead. Impurities accumulate on the surface of lead in the form of slag. The content of impurities in the lead alloy can be reduced to hundredths of a percent. In this case, 4-5% of lead goes to slag and 1.5-2% is carried away with gases. The slag yield is 5-8% by weight of the alloy. Slags contain 75-80% of lead and 10-15% of the amount of antimony, tin and arsenic.

The disadvantages of the method include the transition to slag of a significant amount of lead; high temperatures and the associated high fuel consumption; significant losses of lead with exhaust gases; low degree of purification from impurities.

Closest to the claimed is a method of alkaline refining of lead ("Method for refining lead alloy from antimony when purging with air enriched with oxygen" DE 3332796, C1, C 22 B 13/06, 06/28/1984), the implementation of which is the mixing of lead melt and introduced caustic soda (NaOH), the supply of the air-oxygen mixture to the melts, the refining temperature of 630-650 ° C, while the oxygen consumption is a regulation factor that provides the specified temperature regime.

The disadvantages of the method include:

- a relatively high process temperature (630-650 ° C);

- unnormalized oxygen consumption, due to the need to maintain a given temperature, as well as mixing the melt, which will undoubtedly lead to reoxidation of lead, and as a result, a decrease in its extraction.

The objective of the invention is to provide deep purification of lead from antimony, arsenic and tin at a high speed of the process and the normalized flow of oxygen used as an oxidizing agent.

To achieve the specified technical result, the method of oxidative alkaline refining of lead involves the oxidation of impurities while mixing the lead and alkali melt with the introduction of oxygen, in which the lead and alkali melt are mixed with a paddle mixer at a rotation speed corresponding to the value of the Reynolds criterion (5 ÷ 7) · 10 ³ , and oxygen is bubbled through the melt at a flow rate of 7-10 l / min.

The method is implemented in a steel retort placed in a resistance shaft furnace. The retort is equipped with a paddle mixer and a steel tube immersed in molten lead, through which oxygen is fed into the actively mixed system (see drawing). The ratio of the mass of the alloy to the mass of alkali is (9-10): 1. The duration of phase mixing during oxygen bubbling is 7-10 minutes. This ensures the production of lead with the content of antimony, arsenic and tin at the level of 0.001% of each metal.

Due to the fact that the process of separating impurities from a lead alloy is heterogeneous, the most important factor in its depth is the creation of a developed phase contact surface. Intensive mixing of the melts using a paddle mixer provides effective dispersion of the interacting phases, the delivery of oxygen and alkali to the surface of the refined alloy. Oxygen sparged through the system is directly involved in the oxidation of impurities, and is also absorbed by molten alkali, while maintaining its oxidizing ability. The latter contributes to the efficient use of the gaseous reagent. In addition to the above, the standardization of oxygen consumption (7-10 l / min) eliminates the possibility of peroxidation of lead and reduce its extraction.

The method is as follows. The retort, installed in a resistance shaft furnace, has a feed opening through which molten or hard lead alloy and alkali NaOH are fed. After reaching the set temperature (4000 ° C), stirring is switched on and the oxygen reducer is opened, adjusting the gas flow using a rotameter (7-10 l / min). The weight ratio of lead alloy: alkali is maintained equal to (9-10): 1. Alkaline melt is used repeatedly. (Alkali consumption depends on the content of impurities in the refined alloy). The maximum antimony content in alkaline melt should not exceed 25-27%.

Mixing of the system lasts 7-10 minutes and depends on the initial content of impurities in the lead alloy. The end of the refining process is determined visually. The melt acquires a yellow-golden color, indicating the oxidation of lead. After disabling mixing, the contents of the retort are left to stand for 20-30 minutes. Through the valve in the bottom of the retort, the lead is poured into the molds. The melt remains in the retort for refining the next batch of lead or processing in order to separate antimony, tin and arsenic into independent products.

Refining according to the claimed method was carried out on the installation (see drawing), consisting of a steel cylindrical retort 1 with a diameter of 0.6 m and a height of 0.7 m, having a cover 2, in the center of which is a water-cooled bearing assembly 3, a shaft with a paddle mixer 4 ( the diameter of the stirrer is 0.2 m, the number of blades is 4). The rotation of the shaft was carried out from the electric motor 5 through a belt drive. The rotation speed of the mixer is 400 rpm, which for a given mixed medium provides a value of the Reynolds criterion of approximately (5 ÷ 7) · 10 ³ . In the cover 2 there is a loading hatch 6, and also a tube 7 with an inner diameter of 12 mm for supplying oxygen to the melt is installed, as well as a control mechanism for the shut-off device of the drain valve 8 located in the bottom of the retort 1. Retort 1 was installed in the shaft of the electric furnace 9. The set melt temperature 10 was supported by a thermocouple 11 and an automation unit 12.

The total volume of the retort is 0.2 m ³ . Refined metal and alkali of 500 and 50 kg were sequentially loaded into it, respectively. After heating the contents of the retort to 400 ° C, oxygen was supplied to the lead melt, the flow rate of which was 8 l / min and stirring was turned on.

The duration of mixing the first alloy is 7 minutes, the second 10 minutes. After mixing, the contents of the retort settled for 25 minutes, the drain valve was opened. Refined alloy was poured into molds.

The content of impurities in lead,%, is given in the table:

Lead Sb Sn As Alloy 1 Draft 0.24 0.27 0.14 Refined 0,0009 0,0007 0,0006 Alloy 11 Draft 3.45 0.06 0.01 Refined 0.0011 0,0005 0,0005

As follows from the table, when implementing the proposed method provides a deep extraction of antimony, tin and arsenic from lead alloy.

Claims (1)

The method of oxidative alkaline refining of lead, including the oxidation of impurities while mixing the lead melt and alkali with the introduction of oxygen, characterized in that the lead and alkali melt are mixed with a paddle mixer at a speed corresponding to the value of the Reynolds criterion (5-7) · 10 ³ and simultaneously through the melt oxygen is sparged at a rate of 7-10 l / min.