ZHAND MAI (CN)
SEETHARAMAN SESHADRI (SE)
| JPS62278120A | 1987-12-03 |
LI, P.: "Leaching Process Investigation of Secondary Aluminum Dross: The Effect of C02 on Leaching Process of Salt Cake from Aluminum Remelting Process", METALLURGICAL AND MATERIALS TRANSACTIONS B, vol. 43, no. 5, October 2012 (2012-10-01), pages 1220 - 1230, XP035112278
MIYAMOTO, Y.: "Ecomaterials synthesis and recycling by nitriding combustion", CURRENT OPINION IN SOLID STATE AND MATERIALS SCIENCE, vol. 7, no. 3, June 2003 (2003-06-01), pages 241 - 245, XP055163244
See also references of EP 2855720A4
PENG LI ET AL.: "METALLURGICAL AND MATERIALS TRANSACTIONS B", vol. 43, 17 May 2012, SPRINGERVERLAG, article "Leaching Process Investigation of Secondary Aluminum Dross: The Effect of CO on Leaching Process of Salt Cake from Aluminum Remelting Process", pages: 1220 - 1230
| CLAIMS 1. Method of recovering values from aluminum dross comprising the steps of: al) dissolving the aluminum dross in water thereby forming a salt solution, H3 containing gas, and solid residues; bl) separating the H3 containing gas; and cl) reacting the H3 containing gas with C02 in C02 containing water saturated to at least 20 % of maximum C02 saturation to form ammonium carbonate and/or ammonium bicarbonate. 2. Method according to claim 1 wherein the method additionally comprises one ore more of the following steps: dl) separating solid residues from the salt solution; el) evaporating water from the salt solution and reclaiming the salt components, and; fl) forming aluminum oxynitride from the solid residues such as silicon aluminum oxynitride ands/or magnesium silicon aluminum oxynitride. 3. Method according to claim 1 or 2 wherein in step cl) the C02 containing water is saturated to at least 40 % of maximum C02 saturation, preferably at least 60%, more preferably at least 80%, most preferably fully saturated. 4. Method according to any one of the preceding claims, wherein in step cl) C02 is bubbled through the water to maintain sufficient levels of C02 saturation. Method according to any one of the preceding claims, wherein the dross contains at least one nitrogen containing component, in particular A1N. 6. Method according to any one of the preceding claims, wherein the temperature in step al) when dissolving the dross in water is held above 80 °C, preferably the water is boiling. 7. Method according to any one of the preceding claims, wherein the in step cl) the mole ratio between C02/NH3 is controlled to be > 0.53, preferably >0.6. 8. Method according to any one of the preceding claims, wherein the in step cl) the temperature of the C02 containing water is held in the range of 10-50 °C, preferably in the range of 15-30 °C. 9. Method according to any one of the preceding claims, wherein in step al) the solid-liquid ratio is in the range of 1 :4 to 1 : 100, preferably in the range of 1 : 10 to 1 :30. 10. Method of recovering values from aluminum dross comprising the steps of: a2) dissolving the aluminum dross in C02 containing water saturated to at least 20 % of maximum C02 saturation, thereby forming a salt solution, and solid residues; and b2) separating the solid residues from the salt solution. 11. Method according to claim 10, wherein the method additionally comprises one ore more of the following steps: c2) evaporating water from the salt solution and reclaiming the salt components; d2) forming aluminum oxynitride from the solid residues. 12. Method according to claim 10 or 11 wherein the aluminum oxynitride is silicon aluminum oxynitride or magnesium silicon aluminum oxynitride. 13. Method according to any one of claims 10 -12, wherein the C02 containing water saturated to at least 40 % of maximum C02 saturation, preferably at least 60%, more preferably at least 80%, most preferably fully saturated. 14. Method according to any one of claims 10-13, wherein the C02 is bubbled through the water to maintain sufficient levels of C02 saturation. 15. Method according to any one of claims 10 -14, wherein in step a2) the temperature of the C02 containing water is held in the range of 10-80 °C, preferably in the range of 15-50 °C. 16. Method according to any one of claims 10 -16, wherein in step a2) the solid- liquid ratio is in the range of 1 :4 to 1 : 100, preferably in the range of 1 : 10 to 1 :30. |
TECHNICAL FIELD
The invention relates to a method of recovering values from aluminum dross. BACKGROUND
Aluminum dross is a by-product from aluminum smelting. If the aluminum content in the dross is sufficiently high the dross can be melted to recover metallic aluminum. The residue from remelting the dross is sometime called a salt cake. In the present application the term aluminum dross also includes salt cakes from aluminum dross. The common ingredients of aluminum dross are NaCl , KC1, A1 2 0 3 , A1N, MgO, Si0 2 and entrapped metallic aluminum, which could be as high as 5 wt % or more. The dross contains some water-soluble compounds, which react with water or environmental humidity and release chlorides and/or generate toxic gases in particular NH 3 . Depositing the dross or using them as landfill can therefore have a negative environmental impact. Aluminum and other metals present in the dross may also leach to the environment.
OBJECT OF THE INVENTION
It is an object of the invention to reduce environmental impact from aluminum dross.
Another object of the invention is to recover values from aluminum dross.
DESCRIPTION OF THE INVENTION
At least one of the objects is at least to some extent solved by the method as defined in the claims.
According to one embodiment of the invention the method comprises the steps of: al) dissolving the aluminum dross in water thereby forming a salt solution, NH 3 containing gas, and solid residues;
bl) separating the NH 3 containing gas; and
cl) reacting the NH 3 containing gas with C0 2 in C0 2 containing water saturated to at least 20 % of maximum C0 2 saturation to form ammonium carbonate and/or ammonium bicarbonate.
By reacting the NH 3 containing gas in C0 2 containing water ammonium carbonate and/or ammonium bicarbonate is formed. The resulting aqueous solution will contain almost entirely the ammonium carbonates/bicarbonates, free of salt, and can be used as a fertilizer. Alternately, water can be evaporated to produce solid ammonium carbonate. However, it is preferred to maintain it as liquid fertilizers since, as known in the art, liquid fertilizers have several advantages over solid fertilizers.
The remaining salt solution including solid residues is less harmful to the environment than the original aluminum dross, and can be further treated to further reduce its environmental impact as well as to recover additional values therefrom. Furthermore, the method can be used to capture C0 2 gas to reduce emissions of C0 2 to air from a C0 2 emitting source.
Preferably the method additionally includes the step:
dl) separating solid residues from the salt solution;
Thereby solid residues from the dross such as e.g. oxides of Al, Mg, Si and metallic aluminum can be handled separately. For instance the residues can be used to produce ceramic materials, preferably alumnium oxynitrides such as SiAlON, MgSiAlON. Nitrogen can be reinstated by heat treating the residues in a nitrogen atmosphere. The residues may also be reused as slag formers in melting metallurgy.
Preferably the method additionally includes the step:
el) Evaporating water from the salt solution and reclaiming the salt components.
Water is preferably evaporated after removing solid residues. After evaporation, salt components such as NaCl and KCl remain. Smaller amounts (typically less than 10 % by weight) of CaF 2 may also be present depending on the composition of the dross. The recovered salt components can, for instance, be reused in aluminum smelting process
Preferably in step cl) the C0 2 containing water is saturated to at least 40 % of maximum C0 2 saturation, preferably at least 60%, more preferably at least 80%, most preferably fully saturated. Higher saturation of C0 2 facilitates the formation of ammonium carbonate and/or ammonium bicarbonate.
Preferably in step cl) the C0 2 is bubbled through the water to maintain sufficient levels of C0 2 saturation. Thereby the desired state facilitating formation of ammonium carbonate and/or ammonium bicarbonate is maintained.
The dross and contains nitrogen containing components, in particular A1N. A1N reacts with water through hydrolysis forming NH 4+ /NH 3 .The dross may additionally contain components such as NaCl, KCl, Al, A1 2 0 3 , Si0 2 , Si, CaF 2 , MgO, Fe 2 0 3 , CaO. Typically A1 2 0 3 is around 30-60 wt%, A1N 5-15 wt%, NaCl+KCl 20-50 wt%, MgO < 10 wt%, Si+Si0 2 < 10 wt%, Fe 2 0 3 < 5 wt%, Al < 10 wt%, CaO < 5 wt%. The dross may contain traces of A1P, AI4C3 and CaF 2 . If A1P is present PH 3 gas may also evaporate and producing phosphate when reacting with H 2 0 and H 3 that will add value to the fertilizer.
The temperature, when dissolving the dross in water is held above 80 °C, preferably the water is boiling. Increasing temperatures facilitates the releasing of ammonia gas to gas phase. In C0 2 -free boiling water ammonia gas will be released to gas phase almost completely. The ammonia gas is accompanied by steam emission as well.
Preferably in step al) the solution is stirred during dissolving. Preferably the duration of the dissolving step al) is in the range of 0.5-10 hours, preferably 1-4 hours.
Preferably in step cl) the mole ratio between C0 2 /NH 3 is controlled to be > 0.53, preferably >0.6. Thereby formation of ammonium bicarbonate is facilitated.
Preferably in step cl) the temperature of the C0 2 containing water is held in the range of 10- 50 °C, preferably in the range of 15-30° C.
The water in step al) may be deionized.
Preferably, in step al) the solid-liquid ratio is in the range of 1 :4 to 1 : 100, preferably in the range of 1 : 10 to 1 :30.
Of course, the aluminum dross may be crushed and/or milled and/or ground before being dissolved in step al).
According to another embodiment of the invention the method comprises the steps of: a2) dissolving the aluminum dross in C0 2 containing water saturated to at least 20 % of maximum C0 2 saturation, thereby forming a salt solution, and solid residues; and b2) separating the solid residues from the salt solution. The C0 2 saturation prevents hydrolysis of A1N and thereby formation of H 3 gas.
Additionally small amount of H 3 produced can be effectively absorbed by the formation of H 4 HC0 3 species in the aqueous salt solution. Dissolving in C0 2 - saturated water enables the selective dissolution removal of the chlorides by forming a salt solution without affecting A1N, which will remain in the solid residue. In other words, this is an alternative way of using C0 2 -containing water to reduce the environmental impacts of aluminum dross and recover values therefrom. Both methods address the issue of H 3 . The solid residues may include oxides of Al, Mg, Si, A1N and metallic aluminum. The residues can be used to produce ceramic materials, preferably alumnium oxynitrides such as SiAlON, MgSiAlON, or they may also be reused as slag formers and/or as alloying additives in melting metallurgy.
Preferably the method additionally comprises the step:
c2) evaporating water from the salt solution and reclaiming the salt components;
Water is preferably evaporated after removing solid residues. After evaporating salt components such as NaCl and KC1 remain. Smaller amounts (typically less than 10 % by weight) of CaF 2 may also be present depending on the composition of the dross. The recovered salt components can for instance be reused in aluminum smelting process Preferably the method additionally comprises the step:
d2) forming aluminum oxynitride from the solid residues, in particular silicon aluminum oxynitride or magnesium silicon aluminum oxynitride.
Preferably in step a2), the C0 2 containing water saturated to at least 40 % of maximum C0 2 saturation, preferably at least 60%, more preferably at least 80%, most preferably fully saturated. Higher C0 2 saturation is better for preventing AIN to react with water as well as for capturing any formed NH 3 .
Preferably in step a2), the C0 2 is bubbled through the water to maintain sufficient levels of C0 2 saturation. Thereby the C0 2 saturation can be maintained at desired levels.
Preferably, in step a2) the solid-liquid ratio is in the range of 1 :4 to 1 : 100, preferably in the range of 1 : 10 to 1 :30.
Preferably in step a2) the temperature of the C0 2 containing water is held in the range of 10-80 °C, preferably in the range of 15-50 °C.
Preferably in step a2) the solution is stirred during dissolving.
Preferably the duration of the dissolving step a2) is in the range of 0.5-10 hours, preferably 1-4 hours.
Of course, the aluminum dross may be crushed and/or milled and/or ground before being dissolved in step a2).
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