CN86107432A - Used for aluminium electrolysis lithium salts-magnesium salts-rare earth compound composite additive and adding technology thereof - Google Patents

Abstract

The present invention is to provide the LMR composite additive and the technology thereof of producing aluminium-based rare-earth alloy.This additive is made up of lithium, magnesium, three kinds of compounds of rare earth.Key of the present invention is to select suitable electrolyte ingredient, and electrolytic process parameter and technical qualification, the most important thing is to control LiF in the ionogen, MgF ₂, REO content.When adopting electrolysis production aluminium-based rare-earth alloy of the present invention, can improve current efficiency 1-3%, save direct current consumption 300～500 degree/tons, reduction anode carbon and fluoride salt consumption, minimizing HF quantity discharged.LMR is a kind of perfect additive of Aluminium Electrolysis.

Description

Used for aluminium electrolysis lithium salts-magnesium salts-rare earth compound composite additive and adding technology thereof

The present invention relates to electrolysis of aluminum metallurgy and use additive, particularly relate to aluminium reduction process direct production rare earth aluminium alloy additive therefor.

In the electrolytic aluminium refining technological process, often in ionogen, add LiF, Li ₂CO ₃, CaF ₂, MgF ₂And so on additive, with the physicochemical property of improving the ionogen fused salt and the technico-economical comparison of electrolysis production.For direct production contains the aluminium and the master alloy thereof of rare earth element, can in electrolyzer, add such as RE ₂O ₃, REOCl, RE ₂(CO ₃) ₃Deng mixed rare earth compound.

Learn that according to disclosed document the past, mostly above-mentioned additive was to be used with single or two kinds of blended modes in Aluminium Electrolysis.Because the character and the effect of various additives are not quite similar, so the additive and the adding technology thereof of single in the past or two components all have its limitation and weak point technically and economically.LiF, CaF are added in for example independent or mixing ₂, MgF ₂Or Li ₂CO ₃, can only improve the technico-economical comparison of electrolyte property and electrolytic process, but can not change the performance of aluminium.Otherwise, add RE merely ₂(CO ₃) ₃Deng rare earth compound, can only produce the aluminium that contains rare earth element and the quality of reinforced aluminum, and can not have a significant effect improving the electrolysis tech economic target.In addition, also there are some other shortcomings in single composition additive, costs an arm and a leg as lithium-containing compound, if consumption is big, then uneconomical.The magnesium-containing compound poor electric conductivity, and easily separate out magnesium addition and pollute the aluminium quality.If ionogen middle-weight rare earths compounds content is too high, will produce bearth precipitation, cause certain difficulty and RE utilization ratio low or the like to operation.

Task of the present invention is to propose a kind of additive and adding technology thereof with comprehensive effectiveness, with the obvious various performances of improving aluminum electrolyzation technology economic target and reinforced aluminum.

This composite additive mainly is made up of the compound of lithium, magnesium and rare earth, therefore abbreviates the LMR composite additive again as.Adopt LMR composite additive of the present invention and adding technology thereof, can reach and both produce the aluminium that contains rare earth, can improve the dual purpose of electrolysis production main economic and technical indices simultaneously again.It has concentrated three kinds to add composition advantage separately, and its each self-applying is brought into play, and can make up for each other's deficiencies and learn from each other again, and the effect that complements each other is arranged, thereby, can obtain comprehensive technical economic benefit and social benefit for Aluminium Electrolysis.

When adopting the inventive method production to contain the application rare earth aluminium of 0.1～0.5%RE, current efficiency can improve 1.5～3.0%.1 ton of aluminium of every production can be saved direct current consumption 300～600 degree, reduces HF gas emissions 20～30%.Also have some other advantage,, prolong bath life, current strengthening or the like as reducing anode carbon consumption and fluoride salt consumption.Adopt method of the present invention, the most outstanding advantage is not need to change original cell construction and any utility appliance of addition.Present method is not subjected to the restriction of electrolysis grooved kind and capacity.

The action principle of LMR composite additive is clear and easy to understand, and Technology is simple, easily operation.

With Li ₂CO ₃-MgF ₂-RE ₂(CO ₃) ₃Be that additive is an example, RE in electrolyzer ₂(CO ₃) ₃And Li ₂CO ₃Following reaction takes place:

Enter REO, MgF in the ionogen ₂, LiF, every increase by 1% weight can reduce Na respectively ₃AlF ₆Liquidus temperature be 3 ℃, 5 ℃ and 8 ℃.Statistical law shows that 10 ℃ of the every reductions of electrolysis temperature then may improve current efficiency 1.0～1.5%.In general, the LMR composite additive can reduce by 10～30 ℃ of electrolysis temperatures.Therefore, the LMR additive comes down to a kind of additive of realizing low-temperature electrolytic.Carrying out low-temperature electrolytic is a kind of trend of aluminum electrolyzation technology development.Its advantage is an Increasing Production and Energy Saving, alleviates the anodic oxidation scaling loss, reduces fluorochemical volatile quantity and trough heat lost by radiation.LiF and MgF ₂All can increase phase interface tension force between ionogen and aluminium liquid, thereby, the dissolving and the secondary reaction loss of aluminium reduced.Especially MgF ₂, it is suppressing to have special-effect in the metal mist generation.Even under constant temperature, MgF ₂The effect that improves current efficiency is also arranged.Though MgF ₂Electroconductibility own is relatively poor, but since the variation of its surface tension effects, MgF ₂The effect that the carbon slag improves electrolyte conductivity of getting rid of is arranged.LiF electric conductivity height in addition, LiF and MgF ₂The acting in conjunction meeting obviously reduces electrolytic resistance.Electrolyte voltage is fallen reduce 50～150 millivolts.

Calculate by Faraday's law of electrolysis, have following relationship: W=2980V between electrolytic power consumption W and current efficiency η and the average cell voltage V ^-1 _ηDegree/ton aluminium

Thus formula as can be known, power consumption will be along with the decline of the raising of current efficiency and bath voltage and is reduced.One of theoretical basis foundation that the present invention that Here it is is energy-conservation.

Add LiF and MgF ₂Except the Increasing Production and Energy Saving effect is arranged, electrolytic process also had many other benefits.Li ⁺Compare Na ⁺A little less than carbon cathode soaked into corrosive power, the swelling internal stress of generation was little, therefore can delay bottom carbon cathode breakage.In addition, Mg ²⁺Compare Na ⁺More near negative electrode, it can form electrochemical barrier and suppress Na ⁺Discharge is separated out, and separates out with electric current and wastes thereby reduced deleterious Na.MgF ₂As a kind of mineralizer, also can quicken γ-Al ₂O ₃To α-Al ₂O ₃Transform, help electrolyzer to form hard stove nation and stablize regular burner hearth, can prevent sidepiece electric leakage and protection sidepiece carbon lining.Contain LiF and MgF ₂Electrolyte crust loosely easily smash, can reduce labor intensity and mechanical load.

The purpose of being furnished with a small amount of rare earth compound in the LMR composite additive is to separate out the RE element.Only contain the rare earth aluminium of 0.1～0.5%RE, all be greatly improved at aspect of performances such as mechanics, electricity, processing, intensity and acid-alkali-corrosive-resistings than commercial-purity aluminium.This is because RE has the effect of degassing and purifying, crystal grain thinning and reinforced aluminum matrix quality in aluminium.The atomic radius 1.74～2.04 of RE

, than the atomic radius 1.43 of aluminium Greatly.So RE is easy to fill up aluminium grain cenotype surface imperfection place, hinders crystal grain and continue to grow up.Therefore, RE has crystal grain thinning and metamorphism to aluminium.RE than aluminium to H ₂, O ₂, N ₂, elements such as S, F, Fe, Si, Mn avidity big, can and discharge with impurity chemical combination.RE and Si, Fe impurity form intermetallic compound and shift to crystal boundary, make the specific conductivity of aluminium improve about 3%.Rare earth aluminium intensity height, acid-alkali-corrosive-resisting increases several times than fine aluminium.In a word, rare earth element is a kind of reinforcer that strengthens the aluminium performance.Rare earth compound in the ionogen can be transformed into RE through electrochemistry and two kinds of reaction paths of metallothermic reduction.Be under the electrolysis state of negative electrode with aluminium liquid, because the reduction of RE activity in Al, REO and Al ₂O ₃Decomposition voltage be tending towards equal.Therefore, two kinds of ions of RE and Al may mix electrolysis and common-battery is separated out.And be dissolved in RE complex ion in the ionogen, under electrolysis temperature, also can be come out by Li, Al metal replacement.New life goes back ortho states RE alloying reaction is taken place for rapid and Al, makes the even Mass of RE in aluminium liquid.Adopt the present invention to produce rare earth aluminium and the method for oozing is compared, both do not had the RE segregation phenomena, save the remelting energy and RE consumption again with remelting.

Using the essence of LMR additive, is to add lithium, magnesium, rare earth compound simultaneously in aluminium cell, makes ionogen convert Na to ₃AlF ₆-MgF ₂-LiF-RE ₂O ₃-Al ₂O ₃The polybasic molten salt system carries out aluminium and rare earth mixing electrolysis and coelectrodeposition.The control additive capacity makes and contains LiF=2.0～3.5%, MgF in the ionogen composition ₂=2.0～4.0%, REO=0.1～2.0%, CaF ₂＜4%, NaF and AlF ₃Molecular ratio be between 2.6～2.9.The ratio and the quantity of LMR composite additive each component are decided by electrolytical concrete composition.Three kinds of compositions can add respectively in the LMR composite additive, also can choose two kinds wantonly and mix interpolation, but preferably three kinds of compositions add together.Seek out best effect, must make LiF, MgF in the ionogen ₂, REO concentration reaches the scope of above-mentioned requirements.So the proportioning of additive and consumption are crucial.No matter adopting which kind of addition means, all is to spare no effort to and to add as less at every turn.About this point, use the initial stage particularly important for additive.LiF and MgF ₂Change in concentration is comparatively suitable to improve 0.3～0.5% weekly.Generally be to add Li man-hour adding ₂CO ₃And MgF ₂, add RE after going out aluminium ₂(CO ₃) ₃These additives will be sprinkling upon on the electrolyte shell surface of newly forming equably, cover the Al of last 5～10 cm thicks then ₂O ₃Insulation material.Additive should replace on former and later two big machined surfaces of electrolyzer by turns and add, and both ends of the surface and place, corner do not add.Suitable electrolysis temperature is 935～955 ℃, about 15 ℃ of the overheated temperature difference, and the anode and cathode distance is 3.5～4.5 centimetres.Require to adopt the low aluminium levels operation of polyelectrolyte.Concrete technical qualification essential factor electrolyzer practical situation and deciding.Though the LMR additive is applicable to various Al ₂O ₃, but use processable or sandy alumina optimum.Use contains lithium type aluminum oxide, can reduce the lithium salts unit consumption.Preferably use bulk or particulate state Li ₂CO ₃Remove Li ₂CO ₃, MgF ₂And RE ₂(CO ₃) ₃Outside, can also be with the various oxide compounds, fluorochemical, muriate and the carbonate that contain Li, Mg, RE.

Be an application example of the present invention below:

In design current intensity is on the slotting soberberg anode formula aluminium cell of side of 60 kilo-amperes, has used the LMR composite additive.Strength of current is increased to 61.4 kilo-amperes, anodic current density be 0.86 the peace/centimetre ²LiF is 3.12% in the ionogen, MgF ₂Be 2.16%, RE ₂O ₃Be 0.127%, CaF ₂Be 1.88%, molecular ratio is 2.7～2.9.20 centimetres of electrolyte levels.27 centimetres of aluminium levels, 943 ℃ of electrolysis temperatures.Through annual product, current efficiency reaches 90%, and direct current consumption is 14065 degree/tons, and RE content is 0.1～0.3% in the aluminium.Compare with the conventional aluminium electrolyzer, use after the LMR additive, current efficiency improves 2%, and power consumption reduces by 460 degree/tons, and anode mix is saved 5 kilograms/ton, 1 kilogram/ton of aluminium carbonate unit consumption, and the rare earth casting yield reaches 92%.REO concentration reaches at 1% o'clock in ionogen, produces the rare earth aluminium mother alloy that contains rare earth 3%.When REO concentration reaches 2%, obtain containing 8%RE in the rare earth aluminium mother alloy.

Claims (4)

1, a kind of used for aluminium electrolysis composite additive that constitutes by lithium salts, magnesium salts and mixed rare earth compound three components (being called for short the LMR composite additive).When it is characterized in that aluminium cell uses composite additive, determine addition, make LiF, MgF according to ionogen composition in the groove ₂, the concentration of REO in ionogen is controlled at LiF: 2.0～3.5%, MgF ₂: 2.0～4.0%, REO: in 0.1～2.0% scope.

2,, it is characterized in that wherein lithium salts, magnesium salts and mixed rare earth compound is with Li as claim 1, described LMR composite additive ₂CO ₃, MgF ₂And RE ₂(CO ₃) ₃For good.In addition, also can replace Li with the oxide compound that contains lithium, magnesium, rare earth, fluorochemical, muriate or its carbonate ₂CO ₃, MgF ₂And RE ₂(CO ₃) ₃

3, as the adding technology of claim 1 or 2, described LMR composite additive, it is characterized in that:

1. remove LiF:2.0～3.5% in the control ionogen, MgF ₂: 2.0～4.0%, outside REO:0.1～2.0%, also should control the CaF in the ionogen ₂＜4%, NaF and AlF ₃Molecular ratio between 2.6～2.9.

2. three of the LMR composite additive kinds of components can add respectively, also can be any two kinds of combinations or three kinds of components add simultaneously.

3. addition means is to add less and to spare no effort to good at every turn.Beginning to adjust composition period, with control LiF and MgF ₂Concentration raises and 0.3～0.5% to be advisable weekly, after treating respectively to add composition and reaching specified requirement concentration, press the addition that analytical data is controlled lithium, magnesium salts again, keep the ionogen ingredient stability in claimed range of the present invention.And the interpolation speed of rare earth compound is analyzed content by RE in the aluminium at any time and is decided.Adjust the RE content in the LMR composite additive, can produce content of rare earth and be 0.1～10% rare earth aluminium and mother alloy thereof.

4. the anode and cathode distance is 3.5～4.5 centimetres.

5. electrolysis temperature keeps about 15 ℃ superheating temperature at 935～955 ℃.

6. adopt polyelectrolyte level and low aluminium levels operation favourable, shell face aluminum oxide insulation material layer thickness is 5～10 centimetres.

7. be interrupted or add continuously Al ₂O ₃All can, but adopt point type or medium spacing blanking better.

4,, it is characterized in that being suitable for various aluminum oxide as the adding technology of claim 3, described LMR composite additive.The most handy Al that contains lithium ₂O ₃, or processable Al ₂O ₃Or sand shape Al ₂O ₃