RU2343215C1 - Recovery technique of gallium from alkaline solutions by means of cementation by aluminum gallium - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: recovery technique of gallium from alkaline solutions by means of cementation by aluminum gallium with release of hydrogen includes periodical feed of gallium by feeding of granulated aluminium. Process is implemented at renovation of air-gas mixture above surface of solution by means of ventilation with constant air intake and measurement of hydrogen concentration in air-gas mixture above surface of solution. Feeding of aluminium in gallium is implemented at achieving of hydrogen concentration less than prescribed value.

EFFECT: improving of controllability and reliability growth of the control for cementation process.

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Description

The invention relates to a method for extracting gallium from alkaline solutions by gallam aluminum cementation.

A known method for the extraction of gallium from aluminate solutions by cementation of aluminum gallama (Gusarova TD, Shalavina EL, Ponomarev VD On electrode potentials in the gallium-aluminum system. In the book: Extraction of gallium, vanadium, scandium from alumina products production .-- Alma-Ata, Science of the Academy of Sciences of the Kazakh SSR, 1967, p.25). The process is monitored by changing the potential in the solution-gallam system. A metal electrode for contact with gallam, a silver chloride or calomel reference electrode, and a potentiometer are introduced into the control and measurement circuit.

The disadvantage of this method is the frequent failures of the circuit, explained by the imperfection of the design of electrolytic keys (bridges), in which contact with the solution is often disturbed, the reference electrodes are short-lived, and the complexity of the entire circuit.

Closest to the claimed technical solution (prototype) is a method of extracting gallium from a solution of sodium aluminate by cementing with aluminum gallama with controlled introduction of aluminum into the cementing alloy by measuring electrode potential (A.S. USSR No. 1648253, class C22B 58/00, publ. 07.05 .91). Each successive portion of granular aluminum is introduced after the device registers a potential value of -1.92-1.95 V with respect to the saturated calomel electrode. The potential variation curves depending on the concentration of aluminum in the gallam, which varies with time, incompletely and indirectly reflect the course of the process, since they are a logarithmic function of the concentration of aluminum in gallam. In particular, in case of an overdose of aluminum or overheating of the solution under conditions of rapid hydrogen evolution, the prototype, due to its operating principle, gives a false executive signal to the automatic loading system, which leads to repeated overdosing of aluminum into gallam and creates an emergency. In addition, the disadvantage of this method is the frequent failures of the measuring system, and the associated serious technological violations, due to imperfections in the contact of the reference electrode with an alkaline solution under industrial conditions, as well as the need for constant maintenance of electrolytic keys. Due to the narrow specificity of the gallium cementation process by gallam of aluminum, the industry does not produce control and measuring devices ready for operation in this area. Therefore, in practice, it is necessary to adapt available equipment, for example, sets of instruments for measuring pH, with significant alterations in schemes, settings and installation location. In gallium metallurgy, such adapted systems for measuring the potential of gallams give systematic failures, but have been used for many years, since they have not been a fundamental replacement to them so far.

The objective of the invention is to improve the controllability and reliability of control over the process of cementation of gallium by gallam of aluminum from alkaline solutions, which eliminates technological violations of the process.

The technical result is achieved by the fact that in the method of extracting gallium from alkaline solutions by cementing with aluminum gallam with hydrogen evolution, including periodic feeding of gallam with granulated aluminum, cementation is carried out by updating the gas-air mixture above the solution surface by ventilation with a constant flow of air and measuring the concentration of hydrogen in the gas-air mixture above the surface of the solution, and the supply of aluminum to the gallam is carried out when the hydrogen concentration is below a predetermined value Acquisitions.

The essence of the method is as follows.

When gallium is cemented by gallam of aluminum from alkaline solutions, in addition to the target process of gallium reduction, a competing hydrogen evolution inevitable in this electrochemical system occurs:

2Al + Na ₂ O + 3H ₂ O = 2NaAlO ₂ + 3H ₂ .

In the extreme case, when 1 g of aluminum is dissolved, 1.24 L of hydrogen is released. Bubbles of gas pass through the solution and rise to its surface, where hydrogen is mixed with atmospheric air.

Hardware design of the cementation process in practice always includes an exhaust ventilation system. However, the inflow (suction) of air to the surface of the solution is not regulated and is determined in each case by the total cross-section of the technological holes and leaky joints in the lid of the cementing apparatus. If the amount of suction in the apparatus is adjusted, for example, using a special damper and the air flow is strictly constant, then during the consumption of one portion of granulated aluminum, the hydrogen concentration above the solution surface will change according to the same law as the interfacial exchange rate on the gallam surface. This allows you to more accurately and correctly determine the time of the next load of the cementing agent in comparison with the prototype.

Figure 1 schematically presents one of the possible structural options for the implementation of the proposed method.

Figure 2 explains the principle of controlling the cementation process by the time-varying concentration of hydrogen in the gas-air mixture above the surface of the solution

In the apparatus having a housing 1 provided with a lid 2, there is a gallium-containing alkaline solution 3 and gallam 4. Using a dispenser 5, granular aluminum is introduced portionwise into the apparatus to feed gallam 4. As a result, parallel electrochemical reactions of aluminum displacement from solution 3 of gallium and hydrogen take place, that is, the cementation process. Reduced gallium is attached to gallam 4, and released into the hydrogen goes to the surface of the solution 3 and mixes with the air entering through the valve 6. The size of the opening of the valve 6 and the degree of its opening are chosen so that the hydrogen concentration above the surface of the solution 3 does not exceed a safe level. The resulting air-gas mixture is removed through the exhaust duct 7, where a sensor 8 is installed, which responds to the value of the concentration of hydrogen in the gas mixture. Data from the sensor 8 is transmitted to the analyzer 9, which in turn automatically controls the aluminum dispenser 5. Thus, in this implementation of the method, the hydrogen analyzer 9 performs the function of a control and measuring and control device.

As a portion of aluminum is consumed, the concentration of hydrogen in the gas-air mixture above the solution surface increases, passes through a maximum, and begins to decrease. When the hydrogen concentration is below a predetermined load level, a signal from dispenser 5 is received from analyzer 9, and the next portion of granules is fed into gallam 4. The process is repeated until the required extraction of gallium from the solution. After that, the aluminum dispenser 9 is turned off, and the aluminum contained in the gallam 4 completely passes into the solution, and the concentration of hydrogen above the surface of the solution 3 tends to zero. The change in the hydrogen content recorded by the sensor 8 and the gas analyzer 9, with a portion of the supply of aluminum to gallam 4 is shown schematically in figure 2.

To exclude the formation of an explosive mixture above the surface of solution 3 (under the cover 2 of the apparatus), the air intake must be adjusted using the damper 6 so that the hydrogen concentration does not exceed 4 vol.%. As already noted, a simple stoichiometric calculation shows that when 1 g of aluminum is dissolved, up to 1.24 L of hydrogen is released. On the other hand, industrial practice shows that one portion of granular aluminum is consumed in an average of 20 minutes. Therefore, for the safety of the process for each gram of aluminum, an air flow of at least 0.09 m ³ / h is required. Taking into account 1.1 ÷ 10-fold excess of this value in order to guarantee the exclusion of conditions for the formation of an explosive mixture, the calculated formula for determining air leakage through the shutter 6 for existing industrial gallium cementing machines can be represented as:

Q≥K · m,

where Q is the air flow, m ³ / h,

K = 0.1 ÷ 0.9 - coefficient,

m is the mass of a portion of aluminum for each recharge of gallam, g.

Example

Gallium was cemented by gallam of aluminum from a production solution of the following composition, g / l: Na ₂ O _t 194.7; Na ₂ O _ku 132.3; Al ₂ O ₃ 42.9; Ga 0.33 in a laboratory electrochemical cell with a volume of 0.8 l, equipped with a lid with holes, placed in a laboratory box with a hood. In one of the openings of the cell lid above the solution surface, an AVP-01G hydrogen gas analyzer sensor, commercially available, was fixed. Aluminum was introduced into gallam in portions of 1 g. Upon dissolution of the first portion of aluminum, it was found that the maximum hydrogen concentration in this case was 0.82 vol.%. Further, the level of gallam recharge with aluminum was set at 0.4 vol.%. A total of 8 servings of aluminum were loaded. The average dissolution time of one portion was 18 minutes, and the degree of gallium recovery was 84.8%. Recording the hydrogen concentration during the experiment, made through the interface of the gas analyzer, is completely similar to the graph shown in figure 2, which obviously allows you to effectively control the cementation process.

Further, the method was tested on an enlarged laboratory scale for a month. The granulated aluminum dispenser was also controlled by the signal of the AVP-01G hydrogen gas analyzer. Installation and configuration of instrumentation did not require any alterations.

There were no failures in the aluminum dispenser control system and related technological violations of the cementation process during the entire test period.

For comparison, it should be noted that in factory practice, systems with gallam potential measurement give failures on average 2 times a day.

Thus, the invention provides improved controllability and increased reliability of control over the process of cementation of gallium by gallam of aluminum from alkaline solutions.

Claims (1)

A method of extracting gallium from alkaline solutions by gallam aluminum cementation with hydrogen evolution, including periodic gallam replenishment by feeding granular aluminum, characterized in that the carburizing is carried out by updating the gas-air mixture above the solution surface by ventilation with a constant flow of air and measuring the concentration of hydrogen in the gas-air mixture above the solution surface and the supply of aluminum to the gallam is carried out when the hydrogen concentration is below a predetermined value.

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