CN87107133A - From the aluminium scrap slag, reclaim the flux of metal - Google Patents

Abstract

A flux for recovering metal from waste aluminum slag is especially suitable for recovering metal aluminum (aluminum alloy) from aluminum slag, and belongs to the technical field of metal treatment or recovery.

Aluminum is usually recovered from waste aluminum slag, the process is complicated, the conditions are poor, and the recovery rate is low. The flux of the present invention consists of NaNO ₃ , Na ₂ SiF ₆ and NaCl, KCl pre-melted mixture, etc. It can be used in various Recycling aluminum in different situations, the method is simple, the amount of use is small, and the recovery rate is high.

Description

Flux for recovering metals from scrap aluminum slag

The flux for recovering metal from waste aluminium slag is especially suitable for recovering metal aluminium (aluminium alloy) from waste aluminium slag, and belongs to the field of metal treating and recovering technology.

In the production process of smelting or remelting metal aluminum or aluminum alloy, from melting to ingot forming or casting parts including various smelting furnaces such as reverberatory furnaces, crucible furnaces and the like, a certain amount of scum-waste aluminum slag and casting waste are always generated in the furnaces, and are byproducts which are necessarily generated in any smelting process, but cannot be directly utilized and can only be treated as waste. Analysis has shown that this scrap, in particular the scrap aluminium slag, is a mixture mainly composed of metallic aluminium (alloy) and various oxides, nitrides, molten salt products, etc. According to the type of the furnace, actual operation conditions and different alloy grades, the amount of the generated aluminum scrap slag is different, the aluminum scrap slag generally accounts for about 2-8% of the weight of the ingredients, and the aluminum content in the slag and the waste can be from 30% to 90%. Typical slag composition is: 50-70% of metallic aluminum, 20-40% of oxide and nitride and 10-20% of other impurities.

The aluminum scrap slag and aluminum scrap contain a considerable amount of metallic aluminum (alloy), which is a substance with resource value, and the aluminum scrap slag and the aluminum scrap are reasonably recycled at present when the aluminum and aluminum alloy are increasingly widely used and the secondary aluminum industry is continuously developed, so that the aluminum scrap slag and the aluminum scrap have great economic value. However, particularly, the recovery of metallic aluminum from the aluminum scrap slag has certain difficulty, low recovery rate, high cost and poor conditions, so people do not wish to do the work.

The traditional method for recovering metallic aluminum from waste aluminum slag comprises the following steps: separating large metal fragments from the collected aluminum slag, smashing the residual slag blocks by a mechanical or manual method to form granules, sieving to remove ash powder, sending the sieved granules into a mill for further crushing until impurities except the metal particles are powdery, then sieving for the second time to remove fine-sieved dust and coarse-sieved large granules, and putting the sieved aluminum-containing metal granules with certain particle size (accounting for about 70% of the total weight) into a crucible furnace in batches for heating and remelting, separating out aluminum from the slag at the temperature of about 820 ℃, slightly stirring, scooping out the molten metal aluminum liquid into ingots for recycling, and skimming and cooling the scum on the upper part of the molten aluminum liquid, wherein the scum is still the slag with the metallic aluminum. The above operations can be repeated, and the recovery can be repeated. By adopting the method, because the metallic aluminum is wasted and consumed in the recovery process, only 40-50% of all aluminum in the slag can be recovered.

US4386956 "a process for recovering metal from aluminium dross" describes a method in which a wedge-shaped launder member is used to collect the dross, which is then pressurised in the launder to substantially extract the aluminium metal from the dross, which is then fed to a collection tank for recovery of the aluminium metal. The method is said to be capable of recovering 90-95% of metal aluminum from slag containing about 70% of aluminum, but the recovery cannot be realized in all disposable compression launder slag, and separation treatment and special melting treatment are also needed, and in addition, the recovery method is to collect and recover slag in the normal production process of a melting furnace or a holding furnace, which is easy to cause disorder of the production process.

In the patent document US4451287 "flux for recovering aluminum in reverberatory furnace" there is provided a solid granular flux consisting of a solid solution mixture of 40-60% KCl and 40-60% NaCl and more than 3% cryolite (Na)₃AlF₆) The method is used for recovering the metal aluminum from the molten pool dross of the reverberatory furnace, the ratio of the using amount of the fusing agent to the inert components in the molten pool is 0.3-0.4, and the direct action of the method is to improve the recovery amount of the metal. The flux is limited to directly recover the metal aluminum from the dross in the molten pool of the reverberatory furnace, and the use temperature is high, and the dosage of the flux is large.

The invention aims to invent a novel flux for recovering metal aluminum (aluminum alloy) from waste aluminum slag, and simultaneously invent a recovery process for recovering the metal aluminum by using the flux, so that the flux is less in use amount, simple in operation and high in recovery rate.

The flux of the present invention contains Na₂SiF₆(or Na)₃AlF₆) Premelted mixture of NaCl and KCl and main exothermic agent NaNO₃(or KNO)₃）。NaNO₃(or KNO)₃) Is thatThe main component of the flux plays a main heating role, and the flux is added into hot slag to instantly heat and increase the temperature of the slag, so that the slag in an unmelted state is quickly diluted, the slag and molten metal are well separated, the operation temperature in the recovery process is obviously reduced, and the component amount of the flux is 30-60% of the weight of the flux. Na (Na)₂SiF₆(or Na)₃AlF₆) For Al in slag₂O₃The aluminum alloy has partial absorption and dissolution effects, can destroy an oxide film on the surface of the aluminum beads, is beneficial to the collection of molten metal, and has the composition accounting for 15-30% of the weight of the flux. The premelting mixture of NaCl and KCl is a solid solution mixture consisting of NaCl and KCl with the same amount, can reduce the melting point of slag, prevent the thermal oxidation of metal aluminum and play a good role in protecting the reduction of the burning loss of the metal aluminum. Since the melting points of NaCl and KCl monomer compounds are 805 ℃ and 772 ℃ respectively, and the melting point of the equivalent solid solution mixture is about 652 ℃, NaCl and KCl are used in a eutectic solid solution state in order to lower the use temperature. The pre-melting mixture of NaCl and KCl is prepared through heating and melting NaCl 50% and KCl 50% in crucible furnace at 850 deg.c to dissolve them completely, casting in ingot mold, cooling, crushing manually or mechanically and sieving in 50-70 mesh sieve. The pre-melting mixture of NaCl and KCl is added into hot slag, the precipitated metal aluminum is in a spherulite state under the action of stirring, the molten salt is added more, the spherulites are added more, the addition amount of the spherulites is not excessive because the spherulites are not final products for recovery, and the weight of the composition of the spherulites in a flux is 10-40%.

In order to further improve the performance of the flux of the present invention, the following auxiliary components may be added to the flux to constitute a new flux, and these auxiliary components include the following 3:

(1) NaF (or Fe)₂O₃) And aluminum powder (or magnesium powder);

（2）CaCl₂(or CaF)₂）;

(3) Diatomaceous earth.

The auxiliary components can be added with the fusing agent respectively, or 2 or 3 of the fusing agents can be added simultaneously.

Adding NaF (or Fe)₂O₃) The aluminium powder (or magnesium powder) can obviously enhance the heating effect of the flux, and is mixed with NaNO₃Mixing, reacting at a lower temperature, emitting more heat, raising the temperature of the slag significantly, achieving the recovery of metallic aluminum at a lower temperature, and the content of the metallic aluminum in the flux is as follows: NaF (or Fe)₂O₃) 10-20% of aluminum powder (or magnesium powder) and 8-15% of aluminum powder (or magnesium powder). Adding CaF₂Or CaCl₂Can further reduce the melting point of NaCl and KCl pre-melting mixture, reduce the heat loss of metal aluminum, play a role in protection, and simultaneously CaF₂Can partially dissolve Al₂O₃Reducing the formation of spherulite phase, CaCl, of metallic aluminum₂Can prevent the flux from deliquescing in the process of storage and transportation, and the content of the flux is as follows: CaF₂1～5%，CaCl₂1 to 10 percent. In order to prevent the fluxing agent from being added into the hot slag to generate an over-violent effect, a proper amount of diatomite is added into the fluxing agent to play a certain protection effect, and the adding amount of the diatomite is 0-2%.

All the components of the flux are in industrial purity. When the flux is prepared, the components are weighed according to the required amount in percentage, are uniformly mixed by a manual or mechanical method, are placed in a drying oven at the temperature of 150-250 ℃ for heat preservation for 2-4 hours, the moisture is removed, and the flux is packaged by a plastic bag according to a certain amount (for example, 200 grams) for later use in order to prevent moisture deliquescence during transportation or storage.

When the new flux is used, the new flux is added into molten waste aluminum slag at a certain temperature, the temperature is obviously increased under the stirring effect, the precipitation of metal aluminum is accelerated, an oxidation film on the surface of an aluminum bead is damaged, molten metal is rapidly fused and converged, along with the continuation of heating, refining and stirring processes, the viscosity of the original black aluminum-containing slag in an unmelted state is obviously changed, aluminum liquid is precipitated from slag, the residual molten slag is changed into slag ash, the molten metal and the slag are quickly separated clearly, and at the moment, the molten metal is poured out, and the slag ash floating on the surface of the molten metal does not adhere to metal.

The basic method for recovering metallic aluminum from waste aluminum slag by using the flux is as follows: the temperature of the aluminum scrap slag reaches the flux recovery temperature, after the temperature is uniform, the flux is added into the slag, the adding amount is 1-2% of the weight of the slag, the slag is fully stirred for 5-8 minutes while stirring is carried out, and then a small amount of Na is added₂SiF₆(or Na)₃AlF₆) The weight of the aluminum slag is 0.2-1% of the weight of the aluminum slag, the stirring is continued for 2-4 minutes, at the moment, the slag and the (aluminum) liquid are clear and are completely separated, the slag skimming can be carried out, the metal aluminum liquid is collected, and the recovery process is completed.

It is necessary to bring the temperature of the aluminum scrap slag to the flux recovery temperature during recovery. Containing no NaF (or Fe)₂O₃) And a flux of aluminum powder (or magnesium powder), wherein the recovery temperature is 760-780 ℃, and the flux contains NaF (or Fe)₂O₃) And the recovery temperature of the flux with the aluminum powder (or magnesium powder) is 690-730 ℃. The flux recovery temperature means that the flux is added into the waste aluminum slag at the temperature, the flux can better separate aluminum and slag ash in the slag, the separation effect is fully carried out, the separation effect is not too strong, the separation effect of the flux is not good below the temperature, and the separation and recovery process can be well completed on the slag at the temperature higher than the temperature, but the oxidation and burning loss of the aluminum are easy to cause, the operation condition is deteriorated, the energy is wasted, and the recovery temperature of the flux is lower and better under the condition of ensuring the recovery effect or the recovery rate. In addition, after the flux is added, the flux and the slag must be stirred, and the flux and the slag can be fully mixed by stirring, mutually permeate, increase diffusion and better generate a series of physical and chemical actions, so that the aim of well separating the molten metal from the slag is fulfilled. The stirring can be performed manually or mechanically, and a special stirring mechanical device has better effect.

The addition amount of the flux can be determined according to different contents of metallic aluminum in the waste aluminum slag, the aluminum content of the slag is high, the lower limit of the addition amount of the flux is 1 percent, the aluminum content of the slag is low, and the upper limit of the addition amount of the flux is 2 percent. In addition, when the aluminum content in the slag is too low, for example, less than 30%, it is preferable to perform separation and screening to remove most of the slag ash and increase the aluminum content before recycling.

Different methods can be used for recovery depending on whether the aluminum scrap slag is cold or hot. The process for recovering aluminum from cold waste aluminum slag (cold recovery) comprises the following steps: the condensed aluminum scrap slag containing metallic aluminum (or aluminum alloy) is directly placed in a cold crucible furnace or a crucible furnace preheated to 150-300 ℃ for heating, the crucible furnace can be heated by any heat source, such as a coke furnace, a gas furnace, an oil furnace or an electric furnace, etc., the temperature of the slag reaches the recovery temperature of the flux, the flux is added (according to the basic method) and stirred, the slag and the (aluminum) liquid are separated, finally, the slag is removed, the aluminum liquid is collected, the recovery process is completed, and the process (thermal recovery) for recovering the aluminum from the hot aluminum scrap slag is as follows: a special crucible type recovery device is arranged near a large and medium aluminum processing melting furnace, under the condition that the recovery device is in a hot state, hot melting slag taken out of the melting furnace is rapidly transferred into the recovery device, a flux is added at a temperature not lower than the recovery temperature of the flux, the mixture is fully stirred to separate slag and liquid, and finally, the slag is taken off, aluminum liquid is collected, and the recovery process is completed. The two recycling operation processes can be repeatedly and continuously recycled, and are suitable for mass recycling production. The collected aluminum liquid can be cast into ingots or put back to the melting furnace for use.

For the intermittent aluminum melting process, the aluminum can be recovered from the slag by using the residual heat of the smelting furnace, and the process (the recovery method of the residual heat of the smelting furnace) comprises the following steps: leaving a small amount of metal aluminum liquid in a smelting furnace after the production process is finished, then adding cold or hot waste aluminum slag into the smelting furnace to ensure that the temperature of the slag reaches the flux recovery temperature, adding the flux and stirring after temperature equalization to separate the slag and the liquid, finally skimming the slag, collecting the aluminum liquid and finishing the recovery process. The amount of the residual aluminum liquid can be determined according to the size of the smelting furnace, and the depth of a molten pool of the residual aluminum liquid can be generally kept between 70 and 110 mm. The residual metallic aluminum liquid is necessary for the production process, and on the other hand, the residual metallic aluminum liquid can quickly heat the slag, more easily collect the aluminum separated from the slag and accelerate the recovery process. The aluminum ingot recovered in the way can be directly used for melting production as the original alloy.

Compared with the flux and the traditional recovery method provided in the patent literature, the new flux for recovering the metallic aluminum and the recovery process method thereof have the following advantages: (1) the method has the advantages that the recovery effect is good, the new flux has absorption and dissolution effects on alumina, can damage an oxidation film, avoids the occurrence of metal aluminum in a bead state, after slag is treated, metal liquid and slag are clearly separated, and the slag does not adhere to metals, (2) the recovery temperature is low, heat loss is low, the flux can be used for recovering aluminum at 690 ℃, the thermal state burning loss of aluminum is greatly reduced, the protection effect is good, (3) the consumption is low, the same amount of slag is treated, the consumption of the new flux is much less and only is 1-2% of the slag amount, and (4) the recovery rate is high, and can reach more than 85%, and is generally more than 90%. In addition, the new flux is used for recovering metals, the recovery method is simple, the recovery method can adapt to various different conditions, the recovery operation is carried out, particularly, cold-state waste aluminum slag is recovered, repeated crushing and sieving are not needed, the operation procedures and the cost are reduced, and the labor condition is improved.

Examples of different methods of recovery of the spent aluminium slag using the present fluxes of different composition are given below.

Example 1 Using a composition of 60% NaNO₃+20%Na₂SiF₆And (3) treating the slag of the cast aluminum alloy by using a flux of +20% (KCl + NaCl), wherein the content of metallic aluminum in the slag is 66.2%, and recovering by using a cold method, wherein the specific process and the result are as follows: adding 10 kg of molten slag (actually 6.62 kg of aluminum) into an SR-40 type resistance heating crucible furnace with the capacity of 40 kg, heating by power supply, detecting the temperature in the crucible by thermocouple control, stopping heating when the temperature reaches 770 ℃, preserving heat for a period of time, adding 100 g of flux (1 percent of the molten slag) after the temperature is uniform, stirring for 7 minutes, and then additionally adding Na₃SiF₆Stirring for 3 minutes by 50 g (0.5 percent of slag), completely separating slag and liquid, skimming the slag, casting molten metal aluminum into ingots, and actually measuring to obtain 6.1kg of metal aluminum, wherein the metal recovery rate is as follows:

the recovery rate (weight of aluminum recovered)/(weight of aluminum in the raw slag) × 100 ═ 6.1 (kg))/(6.62 (kg))/(100 ═ 92%

Example 2 use of a composition of 45% NaNO₃+25%Na₂SiF₆+30% (KCl + NaCl) flux, treating the casting crucible slag, with an initial aluminium content of 53.3% in the slag, recovered by cold process, the procedure and results of which are as follows: adding 5 kg of slag (actual aluminum is 2.66 kg) into an SR-40 type resistance crucible furnace, stopping heating when the temperature is heated to 760 ℃, adding 75 g of flux (1.5 percent of the slag) while stirring for 5 minutes after the temperature is uniform, and supplementing Na₃AlF₆Stirring for 3 minutes continuously for 25 g (0.5 percent of furnace slag), slagging off, casting the aluminum liquid into ingots, and actually measuring to obtain 2.35 kg of metal aluminum, wherein the calculated recovery rate is as follows:

2.35÷（5×53.3%）×100%＝88.3%

example 3 Using a composition of 60% NaNO₃+20%Na₂SiF₆+16%（KCl+NaCl）+1.8%CaCl₂+2%CaF₂+0.2% diatomite flux, treating the slag of common cast aluminum alloy smelting slag, the aluminum content in the slag is 66.5%, recovering by cold method, the concrete process and result are as follows: in an SR-40 type resistance heating crucible furnace with the capacity of 40 kg, when the furnace is preheated to 200 ℃, 10 kg of molten slag (about 6.65 kg of actual aluminum) is added into the furnace, the heating is continued, the temperature in the crucible is tested by a thermocouple, when the temperature reaches 770 ℃, the heating is stopped, the furnace is kept for a period of time, when the temperature is uniform, the furnace is stirred for 2 minutes, 100 g of flux (1 percent of the molten slag) is added in batches and stirred, after the flux is added, the furnace is stirred for 3 minutes, and then Na is added₂SiF₆20 g (0.2 percent of slag), stirring for 3 minutes, skimming, and casting molten metal aluminum into ingots. The obtained aluminum ingot weighs 6.1kg, and the recovery rate is actually as follows:

6.1/(10×0.665) ×100%＝92%

example 4 Using a composition of 30% NaNO₃+15%Na₂SiF₆+14%（KCl+NaCl）+20% NaF, 15% aluminum powder and 5% CaF₂And (3) treating common cast aluminum alloy smelting slag by using a diatomite fusing agent with 1 percent of aluminum content, wherein the aluminum content in the slag is 42 percent, and the smelting furnace waste heat is recycled, and the specific process and the result are as follows: after casting and smelting are finished in an SR-270 type resistance crucible furnace with the capacity of 270 kg, molten metal (about 10 kg) with the depth of about 100mm is left at the bottom of the crucible, the temperature is about 660-680 ℃, 25 kg of slag taken out in the process of smelting alloy in the furnace is directly placed into the crucible and pressed into molten aluminum, the crucible is heated, when the temperature rises to 700 ℃, heating is stopped, stirring is carried out for 3 minutes, 375 g of fusing agent (1.5 percent of the slag) is scattered for three times while stirring, after the fusing agent is added, stirring is continued for 2 minutes, and then 50 g of Na is additionally added₂SiF₆(0.2% of molten slag), stirring for 2 minutes, skimming, and casting the molten metal into ingots to obtain 19.5 kg of aluminum ingots, wherein the metal recovery rate is as follows:

the recovery rate (aluminum ingot weight-smelter residual aluminum liquid weight)/(metallic aluminum content in the raw slag) x 100 ═ 19.5-10)/(25 x 42%) × 100 ═ 90.5%

The components of the recovered alloy aluminum ingot meet the alloy standard, and the recovered alloy aluminum ingot can be directly used for casting alloy smelting.

In addition, the flux which meets the component range is used,

the actual recovery of slags of different origins and with different aluminium contents, the recovery results are as follows:

Claims (4)

1. A flux for recovering metallic aluminum from waste aluminum slag, comprising a pre-melted mixture of Na ₂ SiF ₆ (or Na ₃ AlF ₆ ), NaCl and KCl, characterized by: (1) The main exothermic agent is NaNO ₃ (or KNO ₃ ) (2) The weight percentage of each component in the flux is: NaNO ₃ (or KNO ₃ ) ″ 30～60% Na ₂ SiF ₆ (or Na ₃ AlF ₆ ) ″ 15～30% NaCl, KCl pre-melt mixture 10-40% 2. The flux according to claim 1, characterized in that it contains NaF (or Fe ₂ O ₃ ) and aluminum powder (or magnesium powder) as an enhanced heat generating agent, the contents of which are: NaF (or Fe ₂ O ₃ ) ″ 10～20% Aluminum powder (or magnesium powder) 8-15% 3. The flux according to claim 1 or 2, characterized in that it contains flux CaF ₂ or CaCl ₂ , the content of which is: CaF ₂ 1～5% CaCl ₂ 1～10% 4. A method for recovering metallic aluminum from waste aluminum slag using the flux of the present invention, wherein the waste aluminum slag reaches a recovery temperature, characterized in that: (1) When using a flux without NaF (or Fe ₂ O ₃ ) and aluminum powder (or magnesium powder), the recovery temperature is 760-780°C; when using a flux containing NaF (or Fe ₂ O ₃ ) and aluminum powder (or magnesium powder), the recovery temperature is 690-730°C. (2) Add flux to the waste aluminum slag in an amount of 1-2% of the weight of the waste aluminum slag and stir thoroughly for 5-8 minutes. Stir while adding. (3) Add 0.2-1% of the weight of the waste aluminum slag Na ₂ SiF ₆ (or Na ₃ AlF ₆ ) and continue stirring for 2-4 minutes. (4) Remove the slag on the surface and collect the aluminum liquid.