ENVIRONMENTALLY FRIENDLY TREATMENT METHOD OF REFINING MAGNESIUM SLAG

Abstract

A treatment method for a magnesium slag, comprises: Step a, producing magnesium particles and a crude solution of magnesium slag by digesting and sifting a magnesium slag; Step b, filtering the crude solution of magnesium slag sifted in Step a, so that mixed chlorides are obtained after a moisture in a filtrate is removed; Step c, obtaining a high purity magnesium oxide by dissolving a filter residue obtained in Step b via an ammonium sulfate method and a magnesium precipitation reaction as well as post-treatment. With the method, utilization of magnesium slag can reach up to more than 90% with a higher recycling rate, while the discharge of solid wastes can be reduced greatly which solid wastes are less contaminative to the environment, so that the contamination to the environment is greatly reduced and the required energy saving and emission reduction are also achieved.

Claims

1. An environmentally friendly treatment method for a refined magnesium slag, characterized in that it comprises the following steps: Step a, producing magnesium particles and a crude solution of magnesium slag by digesting and sifting a magnesium slag; Step b, filtering the crude solution of magnesium slag sifted in Step a, so that mixed chlorides are obtained after a moisture in a filtrate is removed; Step c, obtaining a magnesium oxide by dissolving a filter residue obtained in Step b via an ammonium sulfate method and a magnesium precipitation reaction as well as post-treatment; the magnesium oxide is a high purity magnesium oxide with a purity not less than 95%.

2. The environmentally friendly treatment method for a refined magnesium slag according to claim 1, characterized in that a solution of (NH.sub.4).sub.2SO.sub.4 is used in the ammonium sulfate method of Step c.

3. The environmentally friendly treatment method for a refined magnesium slag according to claim 1, characterized in that the post-treatment in Step c comprises, but not limited to, filtering and calcining solids obtained from the magnesium precipitation reaction.

4. The environmentally friendly treatment method for a refined magnesium slag according to claim 1, characterized in that Step a comprises the following steps: Step a1: the magnesium slag is pre-treated by crushing to a particle size of less than 2 meshes; Step a2: digesting the crushed magnesium slag; Step a3: sifting the digested magnesium slag solution to obtain a solid magnesium metal and the crude solution of magnesium slag.

5. The environmentally friendly treatment method for a refined magnesium slag according to claim 1, characterized in that Step b comprises the following steps: Step b1: filtering the sifted crude solution of magnesium slag; Step b2: evaporating a filtrate obtained from Step b1; Step b3: further concentrating the filtrate obtained from Step b2; Step b4: further filtering a concentrated solution obtained from Step b3, with the filtrate again going through Step b2 and processes thereafter, and the filter residue being remained for use; Step b5: drying the filter residue obtained from Step b4 to obtain solid mixed chlorides.

6. The environmentally friendly treatment method for a refined magnesium slag according to claim 1, characterized in that Step c comprises specifically the following steps: Step c1: dissolving the filter residue obtained from Step b1 by the ammonium sulfate method to obtain a magnesium ion solution; Step c2: filtering the solution obtained from Step c1; Step c3: processing the filtrate obtained from Step c2 in a magnesium precipitation reaction; Step c4: filtering a magnesium precipitation reaction solution obtained from Step c3; Step c5: cleaning the filter residue obtained from Step c4; Step c6: calcining the filter residue obtained from Step c5 to obtain the magnesium oxide.

7. The environmentally friendly treatment method for a refined magnesium slag according to claim 6, characterized in that Step c1 is specifically operated as dissolving the filter residue obtained by filtering in Step c1 via the solution of (NH.sub.4).sub.2SO.sub.4.

8. The environmentally friendly treatment method for a refined magnesium slag according to claim 7, characterized in that (NH.sub.4).sub.2SO.sub.4 has a concentration of 1.0 to 1.2 mol/L, and the filter residue dissolved in the solution of (NH.sub.4).sub.2SO.sub.4 amounts to 50 to 60 g/L.

9. The environmentally friendly treatment method for a refined magnesium slag according to claim 6, characterized in that the dissolving process in Step c1 further comprises heating the solution to boiling and staying for 5 to 10 minutes.

10. The environmentally friendly treatment method for a refined magnesium slag according to claim 6, characterized in that Step c3 is specifically operated as using ammonium hydroxide and ammoniurn bicarbonate as magnesium precipitator.

11. The environmentally friendly treatment method for a refined magnesium slag according to claim 10, characterized in that the ammonia has a concentration of 15 to 25%.

12. The environmentally friendly treatment method for a refined magnesium slag according to claim 10, characterized in that Mg.sup.2+, NH.sub.3.H.sub.2O and NH.sub.4HCO.sub.3 have a mole ratio of 1:1:(1-1.2).

13. The environmentally friendly treatment method for a refined magnesium slag according to claim 10, characterized in that a solid ammonium bicarbonate is added into the magnesium precipitation reaction solution; the ammonium bicarbonate is added into the reaction solution in a small amount but many times, with each adding amount of 2 to 5g/L.

14. The environmentally friendly treatment method for a refined magnesium slag according to claim 6, characterized in that an ammonia gas generated in Step c1 is collected as magnesium precipitator in Step c3.

15. The environmentally friendly treatment method for a refined magnesium slag according to claim 14, characterized in that the collected ammonia gas is dissolved in water, before being added into the reaction solution as magnesium precipitator in Step c3; or the ammonia gas is introduced into the reaction solution as magnesium precipitator in Step c3.

16. The environmentally friendly treatment method for a refined magnesium slag according to claim 14, characterized in that a steam in Step a and the ammonia gas are collected to form an ammonia as magnesium precipitator in Step c3.

17. The environmentally friendly treatment method for a refined magnesium slag according to claim 6, characterized in that Step c4 is specifically operated as filtering the reacted solution to collect the filtrate and filter residue respectively, after the magnesium precipitation reaction solution is fully reacted and precipitated.

18. The environmentally friendly treatment method for a refined magnesium slag according to claim 17, characterized in that the filtrate in Step c4 has a pH value of 4.5 to 6.0 by adjustment via H.sub.2SO.sub.4, and (NH.sub.4).sub.2SO.sub.4 is further added for bringing the NH.sub.4.sup.+ concentration in the filtrate up to 1.0-1.2 mol/L, so as to use the solution obtained thereby as a dissolution solution to the magnesium oxide in the magnesium slag in Step c1 using the ammonium sulfate method.

19. The environmentally friendly treatment method for a refined magnesium slag according to claim 6, characterized in that Step c5 is specifically operated as cleaning fully with pure water the filter residue obtained from Step c4 so as to bring an ion C1 concentration in the clean solution to less than 0.001 mol/L.

20. The environmentally friendly treatment method for a refined magnesium slag according to claim 19, characterized in that Step c6 is specifically operated as calcining the cleaned precipitants after preliminary drying; the calcining process has a temperature of between 800 to 900 C. and a duration of between 1.5 to 2 hours.

Description

DESCRIPTION OF DRAWINGS

[0055] FIG. 1 is a schematic flow chart of a treatment method for a magnesium slag according to this invention.

SPECIFIC EMBODIMENTS

[0056] A detailed and complete description of this invention will be given below, with reference to some embodiments thereof.

Embodiment 1

[0057] In this embodiment, a magnesium slag generated as casted scraps of refined magnesium and magnesium alloy by Hunan s.r.m Technology Co., Ltd. as raw materials in a recycling method of this invention, wherein the magnesium slag has a lower content of magnesium particles. The specific procedure is shown in FIG. 1 and particularly comprises:

[0058] (1) crushing: a refined magnesium slag with a particle diameter of 1.0 to 5.0 mm is crushed by means of a crusher with a sifter aperture size of 3 meshes;

[0059] (2) digesting (curing): the crushed magnesium slag is digested via water, with a mass ratio of the magnesium slag to water during digestion of 1:3 and a digestion time of 2 hours;

[0060] (3) sifting: a vibrosieve with 16 meshes is used to screen the above mixed solution to separate magnesium particles therefrom;

[0061] (4) filtering: the mixed solution after separating magnesium particles is filtered using a filter press with a filter cloth of 500 meshes;

[0062] (5) removing moisture from a filtrate: a crystallizer and supporting filtering device and drying device are used to conduct processes such as evaporating, concentrating, filtering or drying with respect the filtrate generated by filtering so as to obtain mixed chlorides;

[0063] (6) dissolving via ammonium sulfate method: a filter residue generated by filtering in Step (4) is dissolved in ammonium sulfate solution, with a concentration of (NH4).sub.2SO.sub.4 of 1.2 mol/L and a amount of dissolved filter residue in the (NH4).sub.2SO.sub.4 solution of 60 g/L. An electrical heating tube is used during dissolution for heating the solution to boiling and staying for 5 min, wherein an ammonia gas generated in the reaction process is introduced into pure water to form the ammonium hydroxide for further magnesium precipitation reaction;

[0064] (7) filtering: the above mentioned solution is filtered by means of a filter press with a filter cloth of 500 meshes, wherein the filter residue generated by filtering can be used as roadbed filler in road construction or discarded;

[0065] (8) magnesium precipitation reaction: ammonium hydroxide and ammonium bicarbonate can be used as magnesium precipitator, wherein the ammonium hydroxide has a concentration of 20% and can be obtained by mixing a concentrated ammonium hydroxide with the ammonium hydroxide generated in Step (6) in a certain ratio, while the ammonium bicarbonate is added in a solid form with each adding amount of 2 to 5 g/L, up to a predetermined amount, so as to ensure that Mg.sup.2+, NH.sub.3.H.sub.2O and NH.sub.4HCO.sub.3 have a mole ratio of 1:1:1;

[0066] (9) filtering: the above mentioned solution is filtered by means of a filter press with a filter cloth of 500 meshes, and the generated filtrate has a pH value of about 5.0 by adjustment via H.sub.2SO.sub.4, wherein (NH.sub.4).sub.2SO.sub.4 is added to bring the NH.sup.4+ concentration in the solution to 1.2 mol/L, which solution can be circulated for dissolving the magnesium oxide in the magnesium slag in Step (6) via ammonium sulfate method;

[0067] (10) cleaning: the precipitants generated by filtering are cleaned with pure water, so that the concentration of Cl.sup. contained in the clean solution is less than 0.001 mol/L;

[0068] (11) calcining: the cleaned precipitants are calcined at a temperature of 810 C., with a calcining duration of 2.0, so as to obtain the magnesium oxide.

[0069] 100 Kg of refined magnesium slags are recycled by the above mentioned method, with 5.2 Kg of recycled magnesium particles, 40.2 Kg of mixed chlorides, 42.8 Kg of magnesium oxides and 7.4 Kg of filter residues in Step (7) being obtained, wherein a recycling rate or utilization of the magnesium slag is 88.2% and a purity of the magnesium oxide reaches up to 98.6%, thereby meeting the requirement of high purity magnesium oxide.

Embodiment 2

[0070] This embodiment is differentiated from Embodiment 1 only in that a magnesium slag generated as waste die-casted parts of refined magnesium and magnesium alloy by Hunan s.r.m Technology Co., Ltd. is used as the magnesium slag, wherein magnesium metal particles in said magnesium slag have a diameter of 1.0 to 7.0 mm, and further, the refined magnesium slag is crushed by means of a crusher with a sifter aperture size of 2 meshed in Step (1).

[0071] 100 Kg of refined magnesium slags are recycled, with 7.6 Kg of recycled magnesium particles, 45.1 Kg of mixed chlorides, 36.4 Kg of magnesium oxides and 9.2 Kg of filter residues in Step (6) being obtained, wherein a recycling rate or utilization of the magnesium slag is 89.1% and a purity of the magnesium oxide reaches up to 98.1%, thereby meeting the requirement of high purity magnesium oxide.

Embodiment 3

[0072] This embodiment is differentiated from Embodiment 1 only in that the (NH.sub.4).sub.2SO.sub.4 solution used in Step (6) via the ammonium sulfate method is generated by adjusting the pH value of the filtrate obtained in Step (9) in Embodiment 2 using H.sub.2SO.sub.4 and adding (NH.sub.4).sub.2SO.sub.4, wherein the solution has a pH value of 5.0 and a NH.sub.4.sup.+ concentration of 1.2 mol/L. The filter residue dissolved in the (NH.sub.4).sub.2SO.sub.4 solution amounts to 60 g/L.

[0073] 100 Kg of refined magnesium slags are recycled by the above mentioned method, with 7.8 Kg of recycled magnesium particles, 44.9 Kg of mixed chlorides, 37.0 Kg of magnesium oxides and 9.4 Kg of filter residues in Step (6) being obtained, wherein a recycling rate or utilization of the magnesium slag is 89.7% and a purity of the magnesium oxide reaches up to 98.2%, thereby meeting the requirement of high purity magnesium oxide.

Embodiment 4

[0074] This embodiment is differentiated from Embodiment 1 only in that: Step (2) digesting (curing): the crushed magnesium slag is digested via water, with a mass ratio of the magnesium slag to water during digestion of 1:2 and a digestion time of 2 hours;

[0075] Step (3) sifting: the above mentioned mixed solution is sifted by means of a vibrosieve having 10 meshes to separate magnesium particles therefrom;

[0076] Step (6) dissolving via the ammonium sulfate method: (NH.sub.4).sub.2SO.sub.4 has a concentration of 1.0 mol/L, and the filter residue dissolved in the (NH.sub.4).sub.2SO.sub.4 solution amounts to 50 g/L. An electrical heating tube is used in the dissolving process for heating the solution to boiling and staying for 10 min;

[0077] Step (8) the magnesium precipitation reaction: the ammonium hydroxide has a concentration of 15%, and Mg.sup.2+, NH.sub.3.H.sub.2O and NH.sub.4HCO.sub.3 have a mole ratio of 1:1:2;

[0078] Step (9) filtering: the pH value of the filtrate is adjusted to about 6.0 using H.sub.2SO.sub.4, and (NH.sub.4).sub.2SO.sub.4 is added to bring the NH.sup.4+ concentration in the solution to 1.0 mol/L;

[0079] Step (11) calcining: the cleaned precipitants is calcined at a temperature of 900 C. with a calcining time of 1.5 hours, so as to obtain the magnesium oxide.

[0080] 100 Kg of refined magnesium slags are recycled, with 4.0 Kg of recycled magnesium particles, 41.0 Kg of mixed chlorides, 43.5 Kg of magnesium oxides and 7.6 Kg of filter residues in Step (6) being obtained, wherein a recycling rate or utilization of the magnesium slag is 88.5% and a purity of the magnesium oxide reaches up to 98.3%, thereby meeting the requirement of high purity magnesium oxide.

Embodiment 5

[0081] This embodiment is differentiated from Embodiment 1 only in that:

[0082] Step (3) sifting: the above mentioned mixed solution is sifted by means of a vibrosieve having 20 meshes to separate magnesium particles therefrom;

[0083] Step (6) dissolving via the ammonium sulfate method: (NH.sub.4).sub.2SO.sub.4 has a concentration of 1.1 mol/L, and the filter residue dissolved in the (NH.sub.4).sub.2SO.sub.4 solution amounts to 55 g/L. An electrical heating tube is used in the dissolving process for heating the solution to boiling and staying for 8 min;

[0084] Step (8) the magnesium precipitation reaction: the ammonium hydroxide has a concentration of 25%;

[0085] Step (9) filtering: the pH value of the filtrate is adjusted to about 4.5 using H.sub.2SO.sub.4, and (NH.sub.4).sub.2SO.sub.4 is added to bring the NH.sup.4+ concentration in the solution to 1.1 mol/L;

[0086] Step (11) calcining: the cleaned precipitants is calcined at a temperature of 800 C. with a calcining time of 2.0 hours, so as to obtain the magnesium oxide.

[0087] 100 Kg of refined magnesium slags are recycled, with 5.9 Kg of recycled magnesium particles, 40.9 Kg of mixed chlorides, 41.5 Kg of magnesium oxides and 7.3 Kg of filter residues in Step (6) being obtained, wherein a recycling rate or utilization of the magnesium slag is 88.3% and a purity of the magnesium oxide reaches up to 98.5%, thereby meeting the requirement of high purity magnesium oxide.

[0088] Finally, it is to be noted here that all the above embodiments are only provided for further detailed description of the technical solution according to this invention, without being interpreted as limiting to the protection scope of this invention, so that all the non-essential changes and modifications a skilled person in the art can make to the above disclosure of this invention shall fall within the protection scope of this invention.