Method of inhibiting degradation of extractant by anhydrous environment avoiding and metal stripping

Abstract

Provided is a method of inhibiting degradation of an extractant by an anhydrous environment avoiding and metal stripping, the method including the steps of: (a) stopping the addition of soda ash (Na.sub.2CO.sub.3) to an extracting reaction tank; (b) starting solution recirculation and stopping solvent recirculation of a settler; (c) supplying a solvent from a loaded organic tank to a scrubbing reaction tank, in which the scrubbing reaction tank, stripping reaction tank and extracting reaction tank are connected for circulation and operating stirrers of the scrubbing reaction tank, stripping reaction tank and extracting reaction tank; (d) supplying a sulfuric acid solution having a controlled concentration with a diluting solution to the stripping reaction tank; (e) transferring the solvents of the settler, the loaded organic tank and all the pipes to the scrubbing reaction tank; and (f) stopping the step (e) and initiating solvent recirculation.

Claims

1. A method of performing a solvent extraction and inhibiting degradation of an extractant by avoiding an anhydrous environment, the method comprising the steps of: (a) extracting cobalt and zinc from a leached solution by adding soda ash (Na.sub.2CO.sub.3) to an extracting reaction tank to provide a raffinate from which cobalt and zinc have been extracted and a residual solution including solvent and the cobalt and zinc extracted from the leached solution; (b) feeding the residual solution from the extracting reaction tank to a scrubbing reaction tank; (c) scrubbing manganese from the residual solution in the scrubbing reaction tank by supplying a solvent from a loaded organic tank to the scrubbing reaction tank to provide a scrubbed solvent; (d) feeding the scrubbed solvent to a stripping reaction tank; (e) stripping cobalt and zinc from the scrubbed solvent in the stripping reaction tank by adding a stripping solution to the stripping reaction tank; (f) recirculating solvent in a settler connected to the extracting reaction tank, the scrubbing reaction tank and the stripping reaction tank, wherein the scrubbing reaction tank, stripping reaction tank and extracting reaction tank are connected for circulation; (g) stopping addition of the soda ash (Na.sub.2CO.sub.3) to the extracting reaction tank; (h) starting recirculation of a solution of the settler and stopping solvent recirculation of the settler; (i) operating stirrers of the scrubbing reaction tank, stripping reaction tank and extracting reaction tank; (j) supplying a sulfuric acid solution with a diluting solution containing fresh water to the stripping reaction tank; (k) transferring the solvents of the settler, the loaded organic tank and pipes connecting the scrubbing reaction tank, stripping reaction tank and extracting reaction tank to the scrubbing reaction tank; and (l) stopping the step (k) and initiating solvent recirculation.

2. The method of claim 1, wherein the method further includes separating the raffinate and stripping solution into a separated solution and separated solvent in a coalescer, and treating a generated impurity in a crud treatment device, and the step (l) further includes recovering the solvent from the coalescer and crud treatment device.

3. The method of claim 1, wherein the flow rate of the supplied solvent in the step (c) is 400 m.sup.3/hr to 1,000 m.sup.3/hr.

4. The method of claim 1, wherein a concentration of sulfuric acid in the step (j) is 5 g/L to 50 g/L.

5. The method of claim 1, wherein a scrubbing feed solution having a sulfuric acid concentration of 2 g/L to 30 g/L and zinc concentration of 2 g/L to 20 g/L is supplied with the solvent to the scrubbing reaction tank in the step (k).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a simplified process diagram for Boleo cobalt/zinc solvent extraction (synergistic solvent extraction, DSX).

(2) FIG. 2 is a flowchart of inhibiting degradation of extractant according to an embodiment of the present invention.

(3) FIG. 3 is a graph illustrating extractant degradation rate depending on whether an anhydrous environment/normal environment according to an embodiment of the present invention.

(4) FIG. 4 is a graph illustrating the extractant degradation rate for steps of DSX according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(5) Hereinafter, exemplary embodiments of the present invention are described in detail with reference to the accompanying drawings, which are readily apparent to those skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the exemplary embodiments described herein.

(6) FIG. 2 is a flowchart of inhibiting degradation of extractant according to an embodiment of the present invention.

(7) Referring to FIG. 2, the method of inhibiting the degradation of extractants according to the present invention relates to the method including the steps of: (a) stopping the addition of soda ash (Na.sub.2CO.sub.3) to an extracting reaction tank; (b) starting solution recirculation and stopping solvent recirculation of a settler; (c) supplying a solvent from a loaded organic tank to a scrubbing reaction tank, in which the scrubbing reaction tank, stripping reaction tank and extracting reaction tank are connected for circulation and operating stirrers of the scrubbing reaction tank, stripping reaction tank and extracting reaction tank; (d) supplying a sulfuric acid solution having a controlled concentration with a diluting solution to the stripping reaction tank; (e) transferring the solvents of the settler, the loaded organic tank and all the pipes to the scrubbing reaction tank; and (f) stopping the step (e) and initiating solvent recirculation.

(8) Further, the method of inhibiting the degradation of extractants according to the present invention may further include (g) recovering the solvent from coalescer 40 and crud treatment device.

(9) In the step (a), for example, the diluent includes a kerosene series, and the extractant includes an oxime-based extractant and a neodecanoic acid-based extractant in the DSX solvent. When the DSX operation is shutdown, the addition of the soda ash (Na.sub.2CO.sub.3) into the extracting reaction tank 50 is stopped to adjust the pH of the extraction end, and the automatic pH adjustment device is stopped.

(10) In the step (b), the settler is connected to the extracting reaction tanks (E1 and E2) 50, the scrubbing reaction tanks (Sc1 and Sc2) 60 and the stripping reaction tanks (S1 and S2) 70. The solution of settler is recirculated, and the recirculation of the solvent is stopped while stopping the pH adjustment of the step (a).

(11) In the step (c), the scrubbing reaction tank, stripping reaction tank and extracting reaction tank are connected for circulation so that when the solvent is supplied from a loaded organic tank to scrubbing reaction tank, the solvent is sequentially circulated to the connected stripping reaction tank and extracting reaction tank. The stirrers of the scrubbing reaction tank, stripping reaction tank and extracting reaction tank are operated. The higher the flow rate of the feed solvent, the faster the removal of organic acids (e.g., 2-ethyl hexanoic acid) produced by degradation and impurities precipitated by the shutdown of the process. Thus, the solvent may be supplied at a flow rate of 400 m.sup.3/hr to 1,000 m.sup.3/hr, preferably 400 m.sup.3/hr to 800 m.sup.3/hr, and more preferably 500 m.sup.3/hr to 700 m.sup.3/hr.

(12) When the solvent is supplied, the stripping feed solution is supplied to the stripping reaction tank S2 in order to supply the stripping solution of the stripping reaction tank S1 to the surge tank. The stripping feed solution may be mixed with sulfuric acid. The mixture is diluted with a diluting solution containing fresh water and adjusted to a concentration of sulfuric acid of 5 g/L to 50 g/L, preferably 10 g/L to 30 g/L. In the step (d), the sulfuric acid solution having the concentration adjusted in the above step may be supplied to the stripping reaction tank S2, and then the stripping solution may be sent to the surge tank via the stripping reaction tank S1.

(13) In the step (e), the stripping feed solution is put into the stripping reaction tank S1, and then the solvent is continuously supplied to the scrubbing reaction tank Sc1 for stripping the DSX process solvent. The solvent supply pump is operated until all solvents in the settler, the loaded organic tank 20 and each connecting pipe are stripped, and the settler includes a settler connected to the extracting reaction tank (E1 and E2) 50 and the scrubbing reaction tanks (Sc1 and Sc2) 60.

(14) The stripping step is performed according to the following reaction formula, and the metal extracted in the solvent can be stripped.
R—Co(org)+H.sub.2SO.sub.4.fwdarw.R—H.sub.2(Org)+CoSO.sub.4  [Reaction formula 1]
R—Zn(org)+H.sub.2SO.sub.4.fwdarw.R—H.sub.2(Org)+ZnSO.sub.4  [Reaction formula 2]

(15) After the stripping step is carried out, all metals extracted in the solvent are stripped, and the mol total metal is lowered in the mol total metal/mol oxime, so that degradation of the extractant can be suppressed.

(16) If all metals are stripped from the solvent in the step (e), the scrubbing feed solution supplied to the scrubbing reaction tank S2 is stopped to supply in the step (f).

(17) In the step (e), the solvent of the loaded organic tank may be transferred to the scrubbing reaction tank Sc1 to be scrubbed, and the manganese (Mn) may be removed from the solvent through the scrubbing step. When the solvent is supplied from the loaded organic tank 20, the scrubbing solution is supplied to the scrubbing reaction tank Sc1. The scrubbing feed solution may be supplied by adjusting the concentration of sulfuric acid to 2 g/L to 30 g/L, preferably 5 g/L to 15 g/L with a sulfuric acid and a zinc solution. Further, the scrubbing feed solution may be supplied by adjusting a zinc concentration of 2 g/L to 20 g/L, preferably 2 g/L to 15 g/L.

(18) The scrubbing step is carried out according to the following reaction formula, and manganese (Mn), which is an impurity, can be removed.
R—Mn(org)+ZnSO.sub.4.fwdarw.R—Zn(Org)+MnSO.sub.4  [Reaction formula 3]

(19) After the scrubbing step, the solvent feed pump may be stopped in the step (f), and solvent recirculation may be started in all the settlers.

(20) The operation of all the stirrers can be maintained in the step (g) until all the steps are completed, and the operation is resumed so that the process of shutdown can be carried out.

(21) The step (g) is a step of rapidly recovering the solvent to the process in an anhydrous environment of the solvent which occurs according to the DSX process condition, separately from the shutdown. The solvent may be recovered from coalescer 40 or a crud treatment device in the step (g).

(22) The coalescer 40 is used for a step of recovering a trace amount of solvent contained in the solution before transferring the stripping solution to the surge tank and transferring the raffinate to the raffinate tank. The solvent is recovered to the holding tank through the coalescer 40. The holding tank is a place where the solution and solvent of several stages are gathered according to operation in the process. There is no stirrer, and the solution and solvent are recovered to the process according to on the level. In this regard, the solvent is not mixed with the solution but phase-separated and the degradation of the extractant occurs so that it is quickly recovered to the process.

(23) Further, in the step (f), the solvent collected with the crud for the crud treatment is collected in the crud collection tank during the treatment of the crud. After the treatment, the solvent is collected to the clean organic tank and recovered to the loaded organic tank.

(24) When collected in the tank, the solvent is in an anhydrous environment condition. To prevent this, the crud treatment process is improved so that the solvent is recovered to the process as soon as possible.

(25) The present invention can extend the lifetime of the extractant used in the DSX process by the method of inhibiting degradation of the extractant as described above.

(26) FIG. 3 is a graph illustrating an extractant degradation rate depending on whether an anhydrous environment/normal environment according to an embodiment of the present invention. The figure shows a similar tendency for about one week, but it can be seen that the difference between anhydrous environment and normal environment increases after 8 days.

(27) When the DSX solvent is exposed to an anhydrous environment, 2-ethyl hexanoic acid, which is a degradation product of the extractant, is not dissolved and not discharged in the solution unlike a normal operating environment and is eventually concentrated in the solvent. This accelerates the degradation of the extractant, and 2-ethyl hexanoic acid, which is a degradation product of the extractant, continues to be produced to accelerate the concentration and the degradation of the extractant.

(28) FIG. 4 is a graph illustrating the extractant degradation rate for steps of DSX according to an embodiment of the present invention.

(29) For the metal-concentrated solvent in the extracting step (EXT), the manganese-removed solvent in the scrubbing step (SCR) and the metal-stripped solvent in the stripping step (STR), the extracting step (EXT) containing a large amount of metal has the fastest in the degradation of the extractant, so that the metal is stripped through the same procedure as in the specification, and then the solvent is recirculated.